opportunities for research via nees and anss · 1geotechnical engineer, brigham young university,...

III: Opportunities for Research via NEES and ANSS • Ground motion, pore water pressure and SFSI monitoring at NEES permanently

instrumented field sites, by T. L. Youd, J. H. Steidl, and R. L. Nigbor.

• Field testing capabilities of the nees@UCLA equipment site for soil-structure interaction applications, by Jonathan P. Stewart, Daniel H. Whang and John W. Wallace.

• A brief overview of the NEESGrid simulation platform OpenSees: application to the soil–foundation–structure interaction problems, by Boris Jeremić.

• Large-displacement facility for testing of highly ductile lifeline systems, by Scott L. Jones, Keith E. Kesner, Thomas D. O’Rourke, Harry E. Stewart, Tarek Abdoun, and Michael J. O’Rourke.

• The promise of NEES research, by Steven McCabe (NSF).

• Opportunities for soil-structure interaction research via ANSS, by Mehmet Çelebi and Janise Rodgers.

Ground Motion, Pore Water Pressure and SFSI Monitoring at NEES Permanently Instrumented Field Sites

T. L. Youd1, J. H. Steidl2, and R. L. Nigbor3

1Geotechnical Engineer, Brigham Young University, USA 2Seismologist, University of California at Santa Barbara, USA 3Structural Engineer, University of Southern California, USA

Abstract---As part of the George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES), two permanently instrumented field sites for monitoring ground motion, pore water pressure generation, ground deformation, and soil-foundation-structure interaction (SFSI), were added to the NEES equipment portfolio. The sites are the Wildlife Liquefaction Array (WLA) and the Garner Valley Downhole Array (GVDA); both are located in highly seismic areas of the southern California; both have histories of monitored earthquake responses; both are underlain by liquefiable layers; and both have been well characterized. To engender ground deformation, the WLA site is adjacent to a 3-m high bank of the Alamo River. A reconfigurable, steel-framed structure has been constructed at the GVDA site and instrumented with sensors in the structure, foundation, and underlying soil. These field sites will monitor responses generated by earthquakes and by active experiments using shakers. These sites will provide beds for testing of new in-situ characterization techniques and for development of new sensor technologies. Telepresence and teleparticipation capabilities will provide opportunities for collaborative research and educational interaction. The continuous streaming of data to the NEES data repository, ANSS, and local networks will provide ready access to the collected data.

Keywords---Earthquakes, structures, found-ations, interaction, instrumentation, liquefaction

INTRODUCTION Records from field sites during actual earthquake shaking provide essential information for development and validation of analytical and empirical models of ground response, pore water pressure generation, ground deformation and soil-foundation-structure interaction (SFSI). The purpose of this project is to provide such data by instrument ing two field sites, the Wildlife liquefaction array (WLA) and the Garner Valley downhole array (GVDA). Both sites are located in highly seismic areas of southern California

Fig. 1: Map of southern California showing locations of WLA and GVDA and epicenters of earthquakes with magnitudes greater than 4.5 between 1932 and 1997. (Fig. 1). Each site is equipped with surface and downhole accelerometers, pore pressure transducers, and inclinometers to monitor ground response and ground deformation during earthquake shaking. In addition, GVDA will be equipped with a single-degree-of-freedom structure to monitor SFSI response. When completed, the sites will become part of the George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES).

The WLA and GVDA sites can also be artificially excited with shakers either on the ground or on the SFSI structure. Demonstration projects at GVDA using shakers are being developed in cooperation with NEES projects at the University of Texas and the University of California at Los Angeles. These demonstration projects, scheduled for August 2004, will test the response of the instrumentation and demonstrate the capability of the electronic systems to stream data in real time to the NEES-grid network.

Fig. 2: Area surrounding WLA site showing localities where liquefaction effects have occurred during earthquakes in the past 75 years

Fig.3: 1950 Sand boil deposit near house about 1.5 km northwest of WLA site

WILDLIFE LIQUEFACTION ARRAY WLA is located on the west bank of the

Alamo River 13 km due north of Brawley, California and 160 km due east of San Diego. The site is located in the Imperial Wildlife Area, a California State game refuge. This area has been frequently shaken by earthquakes with six events in the past 75 years generating liquefaction effects within 10 km of the WLA site (Fig. 2). Fig. 3 is a photograph of one of those effects, a sand boil that erupted during an earthquake in 1950 at a locality about 1.5 km northwest of WLA. Based on this history, there is high expectation that additional liquefaction-producing earthquakes will shake the WLA site during the 10-year operational phase (2004-2014) of the NEES program.

Because sand boils erupted pervasively in the floodplain of the Alamo River during the 1981 Westmorland earthquake, an instrumented site was established at that locality in 1882 by the US Geological Survey (USGS), with T.L. Youd as project leader. That site, noted as the “Existing USGS Station” on Fig. 4, was equipped with

Fig. 4: Aerial view of WLS showing localities of old and new sites

Fig. 5: Plan and cross sectional views of instrumentation placed at Wildlife site in 1982 (Bennett et al., 1984) surface and downhole force-balance accelerometers (FBA) and six electrically transduced piezometers. The downhole FBA was placed at a depth of 7 m, immediately below the liquefiable layer, and five of the six piezometers were placed within the liquefiable layer. Fig. 5(a) is a plan view of the 1982 instrumentation and Fig. 5(b) is a cross section showing the soil stratigraphy and the positions of the six piezometers and the FBA (Bennett et al, 1984). In November of 1987 WLA was struck by two earthquakes, the Elmore Ranch event (M = 6.2) at 5:54 pm PST November 23 and the Superstition Hills event (M = 6.6) 11 hours later at 5:15 am PST November 24. Ground motions and pore water pressures were recorded during

the Elmore Ranch event, but the pore pressures did not rise significantly. During the Superstition Hills event, however, pore pressures rose to a pore pressure ratio of 100 % and numerous sand boils erupted within and near the instrumented site (Holzer et al., 1989; Youd and Holzer, 1994). Lateral spread displacements as great as 300 mm were also measured during the Superstition hills event (Dobry et al., 1992). Many researchers have used the data collected from the 1987 earthquakes to analyze the response of the site and to develop or verify models for predicting ground response and ground deformation. Since 1987, the piezometers installed in 1982 have failed and the site has been disturbed by additional investigations. Because of the deterioration of the 1982 site, we proposed and developed a new NEES equipment site to reestablish WLA , but at a locality 65 m down river (northward) from the 1982 USGS site. The localities of both the old and new sites are marked on Fig. 4, and a scaled map of the sites is reproduced in Fig. 6. Also noted on the map are localities of 24 CPT soundings we installed in April 2003 to define the sediment stratigraphy beneath the new site. Fig. 7 is a stratigraphic cross section beneath line A-A’ developed from the CPT data. Fig. 7 also indicates the position of the free face at the river bank. Fig. 8 is a view of the steep river bank and the USGS CPT rig working at the site.

To test the liquefaction susceptibility of sediments in the granular layer beneath WLA, we applied the CPT procedure for evaluating liquefaction resistance published by Youd et al. (2001) to the data collected from CPT 35 for a magnitude 6.5 earthquake and peak ground acceleration (Amax) levels ranging from 0.2 g to 0.4 g. The results of that analysis, noted on Fig. 9, indicate that for a peak acceleration of 0.3 g to 0.4 g, a likely occurrence, much of the granular layer would liquefy. With the nearness of the incised river, liquefaction to this extent would likely lead to ground deformation and lateral spread toward the river.

Fig. 10 shows the approximate locations of instruments placed at the site. The purposes of the downhole and horizontal FBA arrays are to monitor ground response during future earthquakes. The piezometers are to monitor pore water pressure changes generated in response to ground shaking and ground deformation. The piezometers are field-proven ParoScientific devices that were carefully saturated prior to installation. The positioning

Fig. 6: Map of 1982 and new WLA site with localities of CPT soundings

Fig. 7: Cross section A-A’ at WLA showing continuity of granular layer between 2.4 m and 7.0 m depth and intersection of those layer with the 3-m deep Alamo river channel

Fig. 8: Steep bank of Alamo River with USGS CPT rig conducting a sounding at WLA site casings are flexible pipes that were surveyed with a positioning sensor after installation and will be resurveyed after significant earthquakes. The intent of these casings is to detect the depths and amounts of ground deformation after an earthquake, including the thickness and nature of the failure zone.

A Kinemetrics /BRTT Antelope data acquisition system, installed in a small instrumentation structure erected at the site, records data from all of the instruments. The recorded data is streamed from the site by radio link in near real-time to the NEES grid data

Fig. 9: Liquefaction resistance of sediments penetrated by CPT 35 at WLA for a magnitude 6.5 earthquake and various level of PGA

Fig. 10: Map showing approximate locations of FBA’s, piezometers, inclinometer casings installed at WLA archive, making the data available to interested individuals shortly after future earthquakes.

GARNER VALLEY DOWNHOLE ARRAY

The Garner Valley Downhole Array (GVDA) is located in southern California at a latitude of 33o 40.127’ north, and a longitude of 116o 40.427’ west. The instrument site is located in a narrow valley within the Peninsular Ranges Batholith east of Hemet and southwest of Palm Springs, California. The valley is 4 km wide at its widest and about 10 km long. The valley trends northwest-southeast parallel to the major faults of southern California. The valley floor is at an elevation of 1310 m and the surrounding mountains reach heights slightly greater than 3,000 m.

Fig. 11: Topographic map of GVDA showing boundaries of site, instrument locations, and CPT soundings

Fig. 11 is a topographic map of GVDA showing the boundaries of the site, installed instruments, and CPT soundings placed as part of the NEES project.

GVDA is in a seismically active region and lies only 7 km from the main trace of the San Jacinto fault and 35 km from the San Andreas fault (Fig. 12). Historically, the San Jacinto is the most active strike-slip fault system in southern California. A fault slip rate of 10 mm/yr and an absence of large earthquakes since at least 1890 lead to a relatively high probability for magnitude 6.0 or larger earthquake on the San Jacinto fault near the site in the near future. The USGS/Caltech southern California seismic network (SCSN) of high-gain velocity transducers and the UC San Diego ten-station array of velocity transducers in the Anza region provide excellent coverage of local and regional seismicity (Steidl et al., 1998).

The near-surface stratigraphy beneath the site consists of 18-25 m of lake-bed alluvium overlying weathered granite to a depth of 88 m. Sediments in the upper 18-25 m consist of alternating layers of sand, silty sand, clayey sand, and silty gravel. The alluvium gradually transitions into decomposed granite in the depth interval between 18 m to 25m. The decomposed granite classifies as gravely sand (Steidl et al., 1998). The ground water levels beneath the site ranges from near surface in wet seasons to several meters depth during dry seasons.

Fig 12: Map showing location of GVDA (diamond), nearby faults (lines) and epicenters of recently recorded earthquakes (circles) (after Steidl et al., 1998)

Geotechnical properties of the site have been

defined with samples from SPT borings and data from CPT soundings. Grain size and other index tests have bee conducted on the retrieved split-spoon samples. SPT have been conducted to a depth of 30 m and CPT to a depth of 18 m as part of the NEES and previous investigations. Fig. 13 is cross section of sediment layers to a depth of 18 m compiled from CPT data. To test liquefaction susceptibility of granular layers beneath GVDA, we applied the standard CPT procedure for evaluating liquefaction resistance as published by Youd et al. (2001). Results from this analysis using data from CPT 1, a magnitude 7.0 earthquake and PGA levels ranging from 0.2 g to 0.4 g are plotted on Fig. 14. For a peak acceleration of 0.3 g to 0.4 g, a likely occurrence in the next 10 years, liquefaction would likely occur beneath the site.

Compression and shear wave velocities were measured to depths as great as 500 m using downhole and suspension logging techniques. Gamma radiation and electrical resistivity logs have also been compiled from geophysical tests in open boreholes. Logs of some of these measurements are plotted on Fig. 15.

Fig. 13: Cross section of sediments beneath GVDA interpreted from CPT data

Fig. 14: Liquefaction susceptibility of sediments beneath GVDA calculated from CPT 1 data

At GVDA, seismic motions are monitored by

arrays of five surface and six downhole FBA’s. The map position of the various FBA’s is noted on Fig. 16. Fig.17 is a cross section of the site with plotted depths of the downhole FBA’s. All of the FBA’s noted on Fig. 16 were placed prior to the NEES project, except for the FBA at 150 m, with support from previous projects and supporting agencies.

In addition to the FBA arrays noted above, a remote station has been set on a bedrock outcrop 3 km east of the main site. This station contains an FBA set into the rock surface and a second FBA set at a depth of 30 m. Data from this remote site is telemetered back to the main station via a radio link.

Fig. 15: Compression-wave (a) and shear-wave (ß) velocities and other geophysical measures beneath GVDA site (after Steidl et al., 1998))

Fig. 16: Horizontal distribution of FBA’s and relative location of liquefaction array at GVDA (after Steidl et al., 1998)

Two piezometers have been set at GVDA within the deeper crystalline bedrock in sealed off fracture zones at depths of 335 m and 419 m. These piezometers monitor the ambient hydrostatic pressure in the bedrock and dynamic pore pressures generated by seismic waves.

Pore-pressure response within the alluvial sand and decomposed granite layers are monitored by an array of seven piezometers set at depths between 3 m to 13 m (Fig. 18). These piezometers are set in gravel packs placed at the bottoms of uncased boreholes. Bentonite chips were placed above the gravel packs to seal the boreholes. These piezometers are ParoScientific and PSA models that were set in February 2000 to replace a previous set of piezometers that had failed. The piezometers set in 2000 have functioned without further failures.

Fig. 17: Cross section of GVDA site with depths of installed FBA’s (after Steidl et al., 1998)

An additional piezometer was set at a depth of 6.5 m in an open slotted casing to monitor depths and fluctuations of the shallow ground water table. As with the WLA site, data from GVDA will be streamed between the site, the southern California HP WREN system, and the NEES grid via radio links.

GVDA TEST STRUCTURE

A major addition to the GVDA site for the NEES project was the construction of a test structure for monitoring of soil-foundation-structure-interaction (SFSI) during earthquake shaking. This structure can also be excited by shakers mounted on the structure or nearby on the ground surface. The general purpose for the SFSI test structure is to provide a medium-scale reconfigurable steel-frame structure founded on a rigid, massive concrete slab on grade. The superstructure is of a size appropriate for testing on a large NEES shake table. Provisions are made for mounting shakers on the roof for active experiments to complement the primary purpose of passive response to earthquake monitoring.

The design criteria for the GVDA SFSI Test Structure are defined as follows:

Fig. 18: Cross section of GVDA site showing depths of electrically transduced piezometers

Fig. 19: GVDA site with superimposed approximate drawing of the test structure. • The structure is founded on a simple spread

footing at grade. • The foundation bearing pressure is 33-48

kPa footing to insure high stresses. • Approximately 50% of the mass is in the

foundation to insure significant SFSI. • The superstructure size is appropriate for

mounting on NEES shake tables (4 m x 4 m, 50 ton maxima).

• The steel frame is reconfigurable to allow flexibility.

• The bracing system is adjustable to allow adjustment of stiffness and damping.

• A strong RC rigid roof slab was placed to provide additional mass and a platform for shaker mounting.

• The 7-10 Hz fixed-base natural frequency of superstructure can be adjusted from approximately 5 to 15 Hz with adjustments to stiffness and mass.

• The stiffness of the foundation soils changes with ground water level. These soils are softer during wet seasons with high water table and stiffer during dry seasons with a deeper water table.

• Instruments in the foundation soils include accelerometers, stress cells, piezometers, and displacement transducers.

• Instruments in the structure include accelerometers, strain gages, and load cells.

• Cased holes were installed on each side of the structure for cross-hole seismic velocity tests before, during and after experiments.

• The structure is covered with architectural cladding attached with flexible connections.

From preliminary analyses of the stiffness of the structure relative to the site, we calculate a dimensionless site parameter, s, equal to 1.6 as illustrated in Fig. 20. For this calculation, the frequency ratio, W/Ws, was set at 0.7, which yielded an approximately 30 % reduction in the frequency of the soil-foundation-structure system compared to the stricture on a rigid fixed base. In this calculation, W is the natural frequency of whole system, Ws is the natural frequency of the structure on a rigid base, s is a dimensionless parameter hWs/Cs, where Cs the shear wave velocity of the soil.

A web-based simulation tool is being developed to assist the design of SFSI experiments at GVDA. The primary purpose of the simulation tool is to provide users with a simple JAVA-based interface to perform finite element analyses of the SFSI structure. The simulation tool will be a web-based application with the finite element analyses performed on the server side by implementing the JAVA SERVLET technology. The results will be displayed for the remote user via a TCP/IP protocol through a web browser. This simulation tool eventually will be used to verify the structural configurations and the shaker parameters for experiments to be conducted at this NEES-sponsored test facility.

0

0.2

0.4

0.6

0.8

1

1.2

0.01 0.1 1 10

S

(W/W

s)2

Fig. 20: Property of equivalent one degree of freedom system of v = 0.33, Cs = 150 m/sec and h = 4 m

SUMMARY

The purpose of NEES is to provide a national, networked, simulation resource that includes geographically-distributed, shared-use, next -generation experimental research Equipment Sites built and operated to advance earthquake engineering research and education through collaborative and integrated experimentation, theory, data archiving, and model-based simulation. The goal is to accelerate progress in earthquake engineering research and to improve the seismic design and performance of civil and mechanical infrastructure systems through the integration of people, ideas, and tools in a collaboratory environment. Open access to and use of NEES research facilities and data by all elements of the earthquake engineering community, including researchers, educators, students, practitioners, and IT experts, is a key element of this goal (http://www.NEES.org/NCI/purpose.html).

The WLA and GVDA instrumented sites are key elements in the NEES system to meet this purpose and goal. These field sites will provide data from monitored responses generated by earthquakes and by active experiments using shakers. These sites will also provide beds for testing of new in-situ characterization techniques and for development of new sensor technologies. The telepresence and teleparticipation capabilities of the sites will provide opportunities for collaborative research and educational interaction. The continuous streaming of data to the NEES data repository, ANSS, and local networks will provide ready access to the collected data.

REFERENCES

Bennett, M.J., McLaughlin, P.V., Sarmiento,

John, and Youd, T.L. , 1984, Geotechnical investigation of liquefaction sites, Imperial Valley, California: U.S. Geological Survey Open File Report, 84-252, 103 p.

Dobry, R., Baziar, M.H., O'Rourke, T.D., Roth, B.L., and Youd, T.L., Liquefaction and ground failure in the Imperial Valley, southern California during the 1979, 1981, and 1987 earthquakes: in Case Studies of Liquefaction and Lifeline Performance During Past Earthquakes: National Center for Earthquake Engineering Research Technical Report NCEER-92-0002, v. 2, p. 4-1 to 4-85.

Holzer, T.L., Youd, T.L., and Hanks, T.C., 1989, Dynamics of liquefaction during the Superstition Hills Earthquake (M = 6.5) of November 24, 1987: Science, April 7, 1989, v. 244, p. 56-59.

Steidl, J.H., Archuleta, R.G., Tumarkin, A.g., and Bonilla, L.F., 1998, Observations and modeling of ground motion and pore pressure at the Garner Valley, California, test site: Proceedings, 2nd Int. Symposium on the Effects of Surface Geology on Seismic Motion, Yokohama, Japan, A.A. Balkema, Rotterdam, p. 225-232.

Wolf, J.P. Foundation Vibration Analysis Using Simple Physical Models, Prentice-Hall, 1994

Youd, T.L. and Holzer, T.L., 1994, Piezometer performance at the Wildlife liquefaction site: Journal of Geotechnical Engineering, ASCE, v. 120, no. 6, p. 975-995.

Youd, T.L., Idriss, I.M. Andrus, R.D. Arango, I., Castro, G., Christian, J.T., Dobry, R., Liam Finn, W.D.L., Harder, L.F., Jr., Hynes, M.E., Ishihara, K., Koester, J.P., Liao, S.S.C., Marcuson, W.F., III, Martin, G.R., Mitchell, J.K., Moriwaki, Y., Power, M.S., Robertson, P.K., Seed, R.B., Stokoe, K.H., II, 2001, Liquefaction resistance of soils: summary report from the 1996 NCEER and 1998 NCEER/NSF Workshops on Evaluation of Liquefaction Resistance of Soils, Journal of Geotechnical and Geoenvironmental Engineering, ASCE, v. 127, No. 10, p 817-833.

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Field Testing Capabilities of the nees@UCLA Equipment Site for Soil-Structure Interaction Applications

Jonathan P. Stewart,a) Daniel H. Whang,b) and John W. Wallacea)

The nees@UCLA field testing has equipment for field testing and monitoring

of structural and geotechnical performance. The equipment includes shakers for

exciting structural and/or foundation systems, numerous sensors for monitoring

accelerations and deformations within the excited structure (e.g., accelerometers,

displacement transducers, strain gauges), and real time data acquisition and

dissemination capabilities. A key application area for this equipment is testing of

soil-foundation-structure systems. Such testing can, for example, be used to

evaluate the stiffness and damping associated with foundation-soil interaction.

Existing test data for such phenomena is limited, hence there is a significant need

for this type of research. The results would enable the verification and calibration

of computational and design models used in practice.

INTRODUCTION

The U.S. National Science Foundation is developing the George E. Brown, Jr. Network

for Earthquake Engineering Simulation (NEES) Program with the goal of transforming the

nation’s ability to carry out earthquake engineering research. In particular, NEES seeks to

shift the emphasis from current reliance on physical testing to integrated experimentation,

computation, theory, databases and model-based simulation. To support this goal, 15

different advanced testing facilities, termed Equipment Sites, are being developed that will be

geographically distributed across the United States. The Equipment Sites will consist of (a)

structural laboratories, (b) shaking tables, (c) geotechnical centrifuges, (d) mobile and

permanent field testing facilities and (e) a tsunami wave basin.

a) Associate Professor, Civil and Environmental Engineering Dept., University of California, Los Angeles b) Assistant Researcher, Civil and Environmental Engineering Dept., University of California, Los Angeles

Proceedings Third UJNR Workshop on Soil-Structure Interaction, March 29-30, 2004, Menlo Park, California, USA.

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One such Equipment Site with a focus on field testing and monitoring of structural

performance has been developed at the University of California, Los Angeles (nees@UCLA).

The nees@UCLA equipment site provides state-of-the-art equipment for forced vibration

testing and seismic monitoring of full-scale structural and geotechnical systems. The

equipment portfolio includes shakers for exciting structural systems, numerous sensors for

monitoring accelerations and deformations within the excited structure (e.g., accelerometers

and strain gauges), and real-time data acquisition and dissemination capabilities.

The major equipment components of the site are illustrated in Figure 1 and include the

following:

A. Eccentric mass shakers that can apply harmonic excitation across a wide frequency

range in one or two horizontal directions. These shakers can induce weak to strong

forced vibration of structures. For small structures, excitation into the nonlinear range

is possible when the shakers are operated near their maximum force capacity. The

shakers can be operated in a wired or wireless mode.

B. Linear inertial shaker that can apply broadband excitation at low force levels. This

shaker can be programmed to approximately reproduce the seismic structural

response that would have occurred for any specified base-level acceleration time

history (assuming the properties of the structure are known). The shaker can be

controlled in a wired or wireless mode.

C. Above-ground sensors that can be installed at the ground surface or on building,

bridge, or geo-structures to record acceleration or deformation responses.

Accelerations are recorded with uni-directional or triaxial accelerometers.

Deformations (i.e., relative displacements between two points) are recorded with

LVDTs or using fiber-optic sensors.

D. Retrievable subsurface accelerometers (RSAs) that can be deployed below-ground

to record ground vibrations in three directions. The sensors and their housing are

specially designed to be retrievable upon the completion of testing.

E. Wireless field data acquisition system that efficiently transmits data in wireless

mode from the tested structure to the high performance mobile network (see

following item).

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F. High performance mobile network that (a) receives and locally stores data at a

mobile command center deployed near the test site; (b) transmits selected data in near

real time via satellite to the UCLA global backbone; and (c) broadcasts data via the

NEESpop server into the NEESgrid for teleobservation of experiments.

As shown in Fig. 1, a typical application of the equipment would have shakers installed

on or within a structure, a dense array of sensors throughout the structure and RSAs deployed

below the ground surface. Data from the building sensors and RSAs are transmitted wireless

via field data loggers to the mobile command center where all data are locally stored.

Selected data channels and video streams could be transmitted via satellite to the UCLA

global backbone for subsequent dissemination via NEESpop for teleobservation of the

experiment.

Fig. 1. Schematic illustration of deployed equipment from the nees@UCLA Site

One point that should be emphasized is that the nees@UCLA equipment can be utilized

with several types of vibration sources. Obviously, the eccentric mass shakers and linear

inertial shaker are two such types, but the equipment is also ideally suited for seismic

monitoring of structural or geo-systems (i.e., aftershock or microtremor sources).

We anticipate several general categories of application for the nees@UCLA equipment

site, including (1) building or bridge structural response/performance studies; (2) seismic

health monitoring and sensor network studies; (3) response/performance studies for geo-

structures and soil deposits; and (4) soil-structure interaction (SSI) studies. The remainder of

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this paper briefly describes opportunities for SSI research with the nees@UCLA equipment

portfolio.

SOIL-STRUCTURE INTERACTION RESEARCH OPPORTUNTIES

PREVIOUS TESTING

A principal goal of soil-structure interaction testing is often the evaluation of effective

stiffness and damping associated with foundation-soil interaction, which is often quantified

by so-called foundation impedance functions. Table 1 presents a summary of forced vibration

tests that have been performed in the field with the objective of identifying foundation

impedance functions. It should be noted that laboratory-scale studies of SSI for shallow

foundations have also been performed (e.g., Gajan et al., 2004). Such tests can also provide

valuable insight, but the limited scale of the models precludes the tests from properly

capturing important SSI phenomena such as radiation damping.

Table 1. Summary of forced vibration tests used to infer impedance functions

Foundation Dimensions

Embed. (m) f1 (Hz)1 Vs (m/s) Source Freq (Hz)

Impedance obtained

Freq range (Hz) Reference

3m×3m 0-1.5 17.5 305 Vibrator on ground

7-70 1.3 (e=1.5); 1.5 (e = 0)

k u , c u , k θ , c θ

modal freq. only

Lin and Jennings, 1984

25m×25m 4-5.5 NS: 2.16; EW: 1.26

300 Vibrator on roof

NS: 0.8-2.5; EW: 0.8-1.75

NS:1.06; EW:1.1

k u , c u , k θ , c θ

NS:0.8-2.5; EW:0.8-1.75

Luco et al., 1988; Wong et al., 1988

1.3m×1.3m;1.2m×1.1m

0 n/a 120; 75 Vibrator on fndn.

10-60 n/a k u , c u , k θ , c θ

0-60 Crouse et al., 1990

d=10.8m 5.2 9.37 300 Vibrator on

roof/fndn

2-20 2 k u , c u , k θ , c θ , k u θ ,

c u θ , k v , c v

5-14 DeBarros and Luco, 1995

1 Fundamental mode, fixed-base frequency

ResultsExcitation

f~/f

Testing by Lin and Jennings (1984) was performed on a small model structure and

provided spring and dashpot coefficients near the fundamental-mode system frequency. The

results were used to evaluate the effect of foundation embedment on the impedance

functions. Comparisons to impedance function models for unembedded foundations were

favorable, but a bias was noted for embedded foundations.

Testing by Luco et al. (1988) was performed on a full-scale structure (i.e., the 9-story

Millikan Library on the Caltech campus). The results were used to evaluate whether simple

impedance function models could reproduce the observed foundation impedance functions.

Example results are shown in Figure 2 for normalized translation and rocking impedance

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functions. The “rigid” and “flexible” experimental results relate to the use of different sensors

installed on the foundation for system identification. Normalized results are plotted in Figure

2 against the predictions of the Apsel and Luco (1987) theoretical impedance function model.

There are no significant differences between the results for the “flexible” and “rigid”

foundation assumptions. The results for rocking (left frame) compare favorably to the

predictions from theory, while the results for translation (right frame) do not.

Testing by Crouse et al. (1990) was performed on foundation pads for typical

accelerograph installations. Tested foundations were ~ 1.2m square concrete pads with and

without corner piers. Adjustments to the site shear wave velocity were needed to match the

observed impedance functions.

Fig. 2. Comparison of theoretical and experimental estimates of impedance functions for Millikan library building, NS direction (after Wong et al., 1988)

Testing by deBarros and Luco (1995) was performed on the one-quarter scale reinforced

concrete Hualien, Taiwan containment model. The model structure is of a similar design to

the well-known Lotung, Taiwan containment model, but is sited on foundation soils with

considerably larger shear stiffness than those at Lotung (Vs ≈ 300 m/s at Hualien vs. ≈ 100-

150 m/s at Lotung). As with the Millikan library, results compared to theory more favorably

for rocking than for horizontal translations. Data interpretation was complicated by

differences in the results for perpendicular horizontal directions, which was attributed to

laterally heterogeneous soil properties.

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Attempts to evaluate impedance from seismic data have been made by Moslem and

Trifunac (1986) and Kim (2001). The results for rocking stiffness were meaningful only near

the first-mode frequency. The identification exercises were not particularly successful for

translational stiffness nor for damping in either translation or rocking due to noise effects and

potential synchronization problems in the data acquisition systems (i.e., small time lags can

produce significant errors in measured damping). An interesting finding from the Moslem

and Trifunac (1986) work was that the rocking stiffness during earthquake shaking was

reduced from that during forced vibration testing, which was attributed to soil nonlinearity.

OPPORTUNITIES FOR FUTURE FOUNDATION TESTING

Several pertinent observations can be made from the testing/analysis in the literature.

First, investigators often found that linking the site shear wave velocity profile to the velocity

that provides the best match to the field data to be non-trivial. This highlights both the

difficulty of fitting simplified theoretical models to field measurements and the consequent

need for an inventory of test data to guide parameter selection. Second, the results from the

Millikan library highlight the importance of soil nonlinearity on foundation-soil stiffness.

Unfortunately, these test data were not sufficient to define the soil strain field beneath the

foundation, which is needed to enable rational predictions of nonlinear soil properties within

this domain. Third, the available data generally does not address, or provides very limited

coverage, of a number of significant issues including: (1) localized foundation settlement

induced by cyclic loading, which has been widely observed following earthquakes (e.g., see

Bray and Stewart, 2000); and (2) foundation-soil damping associated with soil hysteresis or

radiation effects.

The nees@UCLA equipment is ideally suited for meeting these research needs. Whether

employed on existing structures or specially constructed model structures in the field, the

equipment could be used to:

1. Dynamically excite the structure with eccentric mass shakers or the linear inertial

shaker, thus creating base shear forces and moments, which would lead to relative

foundation/free-field displacements and rocking;

2. Record foundation and ground vibrations with accelerometers, displacement

transducers, and/or strain gauges, which quantify foundation vibrations and potential

foundation deformations.

7

3. Record subsurface accelerations with RSAs, thus enabling recordings of the wave

field emanating from the foundation and the inference of subsurface shear strains.

4. Transmit the data wireless to the mobile command center, where it can be locally

stored and viewed, and also sent via satellite to the UCLA global backbone for

dissemination over the internet.

Accordingly, foundation vibration testing is expected to be a major application of the

nees@UCLA equipment site once it becomes operational in October 2004.

CONCLUSIONS

The development of the NSF-funded nees@UCLA Equipment Site is approaching

completion, and will provide a valuable shared-use resource for field testing and monitoring

of structural and geotechnical performance. The nees@UCLA equipment portfolio includes

shakers for exciting structural systems, numerous sensors for monitoring accelerations and

deformations within the excited structure (e.g., accelerometers and strain gauges), and real-

time data acquisition and dissemination capabilities. The full nees@UCLA site goes “on

line” for public use October 1, 2004. The site provides equipment that is ideally suited to

soil-structure interaction testing and research.

ACKNOWLEDGEMENTS

This research was funded by the National Science Foundation under Cooperative

Agreement No.CMS-0086596, and is gratefully acknowledged.

REFERENCES

Apsel, R.J. and Luco, J.E., 1987. Impedance functions for foundations embedded in a layered

medium: an integral equation approach, J. Earthquake Engrg. Struct. Dynamics 15, 213-231.

Bray, J.D. and Stewart, J.P., coordinators, 2000. Chapter 8: Damage patterns and foundation

performance in Adapazari. Kocaeli, Turkey Earthquake of August 17, 1999 Reconnaissance

Report, T.L. Youd, J.P. Bardet, and J.D. Bray, eds., Earthquake Spectra 16, Supplement A, 163-

189.

Gajan, S. Phalen, J.D., Kutter, B.L., Hutchinson, T.C., and Martin, G.R., 2004. Centrifuge modeling

of nonlinear cyclic load-deformation behavior of shallow foundations, Proc. 11th Int. Conf. Soil

8

Dyn. Earthquake Engrg. & 3rd Int. Conf. Earthquake Geotech. Engrg., Berkeley, CA, Vol. 2, 742-

749.

Crouse, C.B., Hushmand, B., Luco, J.E., and Wong, H.L., 1990. Foundation impedance functions:

Theory versus Experiment, J. Geotech. Engrg. 116, 432-449.

de Barros, F.C.P. and Luco, J.E., 1995. Identification of foundation impedance functions and soil

properties from vibration tests of the Hualien containment model, J. Soil Dyn. Earthquake Eng.

14, 229-248.

Kim, S., 2001. Calibration of simple models for seismic soil structure interaction from field

performance data, Ph.D. Dissertation, Univ. of Calif., Los Angeles.

Lin, A.N. and Jennings, P.C., 1984. Effect of embedment on foundation-soil impedances, J. Engrg.

Mech.. 110, 1060-1075.

Luco, J.E., Trifunac, M.D., and Wong, H.L., 1988. Isolation of soil-structure interaction effects by

full-scale forced vibration tests, J. Earthquake Engrg. Struct. Dynamics 16, 1-21.

Moslem, K. and Trifunac, M.D., 1986. Effects of soil-structure interaction on the response of building

during the strong earthquake ground motion, Rpt. No. 86-04, Univ. of Southern California, Dept.

of Civil Engrg.

Wong, H.L., Trifunac, M.D., and Luco, J.E., 1988. A comparison of soil-structure interaction

calculations with results of full-scale forced vibration tests, Soil Dyn. & Earthquake Engrg. 7, 22-

31.

Proceedings Third UJNR Workshop on Soil–Structure Interaction, March 29–30, 2004, Menlo Park, California, USA.

A Brief Overview of the

NEESgrid Simulation Platform OpenSees:

Application to the

Soil–Foundation–Structure Interaction Problems

Boris Jeremic 1

Presented here is an overview of our recent work in the area of soil–structure interac-

tion. The overview is centered around NEESgrid simulation platform OpenSees. In partic-

ular described are simulation tools available for soil–foundation–structure (SFS) interaction

analysis. Illustration of available tools is described through examples related to the widely

accepted idea (or ideal) that the SFS interaction is beneficial to the behavior of the structural

system under earthquake loading. The beneficial role of SFS interaction has been essentially

turned into dogma for many structural engineers. For Example the NEHRP-94 seismic code

states that: ”These [seismic] forces therefore can be evaluated conservatively without the

adjustments recommended in Sec. 2.5 [i.e. for SFS interaction effects]”. Even though de-

sign spectra are derived on a conservative basis, and the above statement may hold for a

large class of structures, there are case histories that show that the perceived role of SFS

interaction is an over–simplification and may lead to unsafe design.

OpenSees: the NEESgrid Simulation Platform

Motivation

There exists a need of the structural/geotechnical engineers for a set of simulation tools tobe used in assessing future performance of infrastructure (bridges, buildings, port structures,dams...). The tools need to be hierarchical in nature, from very simplistic ones, usually usedin initial phases of the design, to very sophisticated ones that are used to assess performance

1Department of Civil and Environmental Engineering, University of California, One Shields Ave., Davis, CA 95616, Email:[email protected].

1


of structures during extreme loads. This set of hierarchical models will exist concurrently withthe physical system they represent. Moreover, available models (of different sophistication) willprovide designers, owners and operators with the capability to assess future performance. Thisseems to be very important as it will empower designers, owners and operators to make educateddecisions on the current state or future performance of structures. The hierarchical set of modelsshould be able to foretell the state of the structure (deformations, safety, limit loads...) for bothservice and extreme loads. In addition to that, the observed performance can (and should) beused to update and validate models through simulations. This additional benefit of being ableto validate models goes along well with a much wider goal of verification and validation of thedeveloped simulations tools (c.f. [8] and [9]).

In this paper, a brief overview of some of the tools available in the OpenSees NEESgrid com-putational platform is presented. The described tools are mostly developed and implemented bythe UC Davis Computational Geomechanics group. The descriptions are fairly brief in natureand references to relevant published work are provided for the more interested readers. Inter-ested readers are also welcome to visit the author’s web site which features links to relatedprojects and publications (http://sokocalo.engr.ucdavis.edu/˜ jeremic/)

Template Elasto–Plasticity

The standard incremental theory of elasto–plasticity was used to develop and implement a tem-plate constitutive driver. The separation of elastic models, yield function, plastic flow direc-tions and evolution laws (hardening and/or softening) was achieved using the object orientedparadigm. The implementation into OpenSees finite element platform allows use of existingand development of new elasto–plastic material models by simply combining yield functions,plastic flow directions (or plastic potential functions) and evolution laws into a working elastic–plastic models. Examples of such combinations (and more details on the approach) are given ina recent paper [6].

The next few examples show various capabilities (from very simplistic to sophisticated ones)of the approach. One of the simplest models to be tried first is obtained by combining Drucker–Prager yield surface, Drucker–Prager flow directions and the perfectly plastic hardening rule.Figures 1 shows results from a monotonic triaxial loading on one such sample. As expected theload displacement response is bilinear. The volumetric response is at first compressive (withinthe elastic limits) and then becomes dilative when the material becomes elastic–plastic.

Figure 2 shows results for cyclic triaxial loading of a normally consolidated sand specimenusing the Manzari and Dafalias ([7]) elastic–plastic material model. The load displacementcurve shows near saturation after few cycles while the volumetric response is compressive.

2

http://sokocalo.engr.ucdavis.edu/~jeremic/


0 2 4 6 8 100

5

10

15

20

25

30

35

40

εa (%)

q (k

Pa)

0 2 4 6 8 10−7

−6

−5

−4

−3

−2

−1

0

1

εa (%)

ε v (%

)

Figure 1: Monotonic triaxial loading on a soil sample modeled using Drucker-Prager yield surface,

Drucker-Prager flow direction, perfectly plastic hardening rule.

−0.15 −0.1 −0.05 0 0.05 0.1 0.15−20

−10

0

10

20

30

εa (%)

q (k

Pa)

−0.1 −0.05 0 0.05 0.1 0.15−0.5

0

0.5

1

1.5

2

2.5

3

εa (%)

ε v (%

)

Figure 2: Cyclic triaxial loading results for normally consolidated soil sample modeled using Drucker-

Prager yield surface, Manzari-Dafalias flow direction, bounding surface hardening rule.

Full Coupling of Solid and Fluid

The full coupling of solid and fluid in computational geomechanics is a necessary part of thecomputational formulation if one expects to obtain realistic results. This is particularly impor-tant for problems involving soil structure interaction, where a stiff structure interacts with softsoil (that might become even softer after the buildup of pore pressure and the reduction of ef-fective stresses). A formulation originally proposed in [16] is used as a basis. Few changesand improvements are described in some more details in [5]. It proves beneficial to treat theproblem using mixed unknown field consisting of uLj → solid displacements pL → fluid pres-sures ULj → fluid displacements. After finite element discretization of the governing equations,one obtains the following system of equations that needs to be solved using some time stepping

3


scheme:

(Ms)KijL 0 0

0 0 0

0 0 (Mf )KijL

¨uLj

¨pL

¨ULj

+

(C1)KijL 0 −(C2)KijL

0 0 0

−(C2)LjiK 0 (C3)KijL

˙uLj

˙pL

˙ULj

+

(KEP )KijL −(G1)KiL 0

−(G1)LjK −(P )KL −(G2)LjK

0 −(G2)KiL 0

uLj

pL

ULj

=

(fs)Ki

0

(ff )Ki

It is interesting to note that damping terms for this coupled system are only present if thesubtensor (C1)KijL = (C2)KijL = (C3)KijL are present, and that is the case only if the fluiddisplaces relative to the solid, as shown in the equation below:

(C1)KijL = (C2)KijL = (C3)KijL =

∫

Ω

Nu,UK n2k−1ij N

u,UL dΩ

The consequence is that the basic energy dissipating mechanism in geomaterials are stemmingfrom either (a) inelastic deformation or (b) from coupling of the fluid (can also be air) and thesolid matrix.

Simulation of coupled problems, like wave propagation in fully saturated soils, are challeng-ing, yet of great practical significance. For example, Figure 3 shows results of viscous couplingfor a vertically propagating wave in fully saturated porous medium (saturated soil) for differentvalues of permeability. It is obvious that the permeability will greatly affect the response (givenin terms of soil displacements, pore fluid pressures and fluid displacements).

Single Pile in Layered Soils

Numerical modeling of behavior or piles in layered soils has not received much attention dueto the large computational and modeling efforts required. The problem is quite interesting andof great practical importance as soils are mostly layered, particularly close to bodies of water,where piles are used. As an example, figure 4 shows moment, shear force and pressure (c.f[12, 14]). Pressure here relates to the integral of all the forces acting on a pile, and it hasdimension force per length. In particular, the first set of figures, shows results for a pile with asand layer sandwiched between two soft clay layers, while the other set of figures shows resultsfor a pile in layers of sand–clay–sand. The effects of soft layers (clay) on stiff layers (sand) areobvious.

Pile Group Simulations

In addition to modeling of single piles, pile groups pose some significant simulations challenges.Both the computational and modeling aspects need to be tackled, but the benefit of simulation

4


0 0.05 0.1 0.15 0.2 0.25 0.3−4

−3

−2

−1

0

1

2x 10

−3

Sol

id D

ispl

acem

ent (

m)

Top node2m from top4m from top6m from top

0 0.05 0.1 0.15 0.2 0.25 0.3−0.5

0

0.5

1

Por

e pr

essu

re (

kPa)

0 0.05 0.1 0.15 0.2 0.25 0.3−4

−3

−2

−1

0

1

2x 10

−3

Time (sec)

Flu

id D

ispl

acem

ent (

m)

0 0.05 0.1 0.15 0.2 0.25 0.3−4

−3

−2

−1

0

1

2x 10

−3

Sol

id D

ispl

acem

ent (

m)

Top node2m from top4m from top6m from top

0 0.05 0.1 0.15 0.2 0.25 0.3−0.5

0

0.5

1

Por

e pr

essu

re (

kPa)

0 0.05 0.1 0.15 0.2 0.25 0.3−4

−3

−2

−1

0

1

2x 10

−3

Time (sec)

Flu

id D

ispl

acem

ent (

m)

Figure 3: Viscous coupling for a vertically propagating wave in two soils with different permeability,

left soil has k = 10−3m/s while the one of the right has k = 10

−5m/s.

−1000 0 1000 2000−10

−8

−6

−4

−2

0

2

SOFT CLAY

Cu = 21.7 kPa

−1.718

SAND

φ = 37.1o

−3.436

SOFT CLAY

Cu = 21.7 kPa

Bending Moment (kN.m)

Dep

th (

m)

−400 −200 0 200 400 600−10

−8

−6

−4

−2

0

2

Shear Force (kN)0 200 400

−10

−8

−6

−4

−2

0

2

Lateral Resistance (kN/m)−1000 0 1000 2000

−10

−8

−6

−4

−2

0

2

SAND

φ = 37.1o

−1.718

SOFT CLAY

Cu = 21.7 kPa

−3.436

SAND

φ = 37.1o

Bending Moment (kN.m)

Dep

th (

m)

−400 −200 0 200 400 600−10

−8

−6

−4

−2

0

2

Shear Force (kN)−100 0 100 200 300

−10

−8

−6

−4

−2

0

2

Lateral Resistance (kN/m)

Figure 4: Moment, shear force and pressure for a single pile in layered soils, left figures, clay–sand–clay

layers, right figures, sand–clay–sand layers.

results to practical problems can be significant. For example, Figure 5 shows the numericallygenerated interaction P-Y curves for piles in a 4x3 pile group (c.f [13]). It is obvious from thispicture that one cannot simply scale back the single pile load deformation response to analyzepile groups.

5


Figure 5: Load displacement interaction diagrams for piles in a pile group.

Dynamic SFS Interaction Modeling

One of the basis for seismic analysis of soil–foundation–structure (SFS) system is appropriateformulation and implementation. The finite size of finite element models introduces many prob-lems, including the input of seismic motions, trapping of wave energy in the finite size model tolist just a few. The recently developed Domain Reduction Method (DRM) for elastic problems[2, 15] is used and adapted for SFS interaction problems. One of the best features of the DRMis that in addition to being applicable to elastic problems, close inspection of the formulationshows that it can be applied to inelastic problems as well. Formulation and implementation de-tails are given in [4]. Figure 6 shows the application of the DRM to SFS problems. The seismicwave field (free field) obtained using some of the available methods, including closed form so-lutions (Green’s functions or large scale geophysical simulations), are used to provide input forthe DRM. The input requires displacements and accelerations on a single layer of elements thatcompletely encompasses the inelastic domain with the SFS system. The effective forces that areused to load the system are then

Peffi

Peffb

P effe

=

0

−MΩ+

be u0e − KΩ+

be u0e

MΩ+

eb u0b + KΩ+

eb u0b

Seismic amplification of local, soft soil sites has been reported many times, yet robust andaccurate 3D simulation techniques have not been fully developed to help analyze SFS interactionproblems. For example, Figure 7, obtained by using our DRM implementation in OpenSees,

6


Fault

Plastic (Soil) "Bowls"

Figure 6: Seismic SFS interaction using large scale geophysical wave propagation and the DRM (soil

islands) to assess the behavior of a bridge during an earthquake.

shows vertical wave propagation through stiff (dense sand) and soft (soft clay) soils subject to thesame earthquake. The result shows that the soft soil site has an increase in surface deformationof 3.5 times than that one of the stiff site.

0 5 10 15 20 25 30 35 40

0.0000−38.0

0.0077−30.0

0.0783−28.0

0.0791−20.0

0.0844−16.0

0.0878−12.0

0.1248 −8.0

0.1800 −4.0

0.1946 0.0

Time (s)

Dis

plac

emen

t (m

)

Z(m) Max

0 5 10 15 20 25 30 35 40

0.0000−38.0

0.0224−30.0

0.0879−28.0

0.1102−20.0

0.1161−16.0

0.1227−12.0

0.3961 −8.0

0.6258 −4.0

0.6928 0.0

Time (s)

Dis

plac

emen

t (m

)

Z(m) Max

Figure 7: Seismic wave propagation resulting from the same earthquake acting on a stiff and soft soil

site.

SFS Case Study

A simple case study was performed in order to investigate SFS interaction effects during earth-quakes (eg. Jeremic et al. [3]). A simplified SFS model, using soil springs was used to illustratebeneficial and detrimental effects of SFS interaction on performance of the structure. The pro-totype structure is a typical bent of the I–880 highway structure in Oakland, CA. The modelconsists of inelastic fiber column–beams to represent the bridge piers where much of the in-elastic behavior is expected to occur, elastic column–beams to represent the deck and equivalentzero-length foundation springs to represent the soil-foundation system. Figure 8 shows the framemodels, one without and one with the SFS interaction. Foundation springs were obtained from

7


∆∆F F

x

z

x

z

yy

Figure 8: Two frame models for the Bent #16,fully £xed and the model with soil springs.

a detailed 3D finite element model of the pile group foundation system using elastic soil prop-erties. It is noted that the inelastic analysis of soil–foundation system was also performed fora limited number of load cases and it was shown that, at least for small deformations expectedhere, the response can be very well approximated with elastic soil behavior. The foundationsystem consists of a 5 × 5 pile groups connected with a massive pile cap. The piles are madeof reinforced concrete and reside in a steel shell with a diameter of 0.6m. The schematic figureof the pile cap, the piles and the finite element mesh for the soil–foundation system is show inFigure 9.

a)

7.2

0.6 1.5 1.5 1.5 1.5 0.6

7.2

21.2

1.5

0.60.60.60.60.6 b)

Figure 9: (a) Schematics of the pile cap and the piles. (b) Finite element mesh for soil foundation system.

A uniform hazard spectra for SD (soil) site conditions was derived for a site in Oaklandwhich represents an event with a 10 % probability of exceedance in 50 years. The hazard isdominated by earthquakes on the Hayward fault which is located about 7 km east of the I–880 site. The ground motion model of Abrahamson and Silva [1] was used in generating thespectra (Somerville and Collins [10]). The spectra contains rupture directivity effects whichwere represented in the probabilistic hazard analysis using the empirical model proposed bySomerville et al. [11]. The spectra were generated for both fault-parallel (FP) and fault-normal(FN) directions. Three time histories were selected: two from the modified suite of Loma Prieta

8


motions (recorded at Gilroy and Corralitos) and one from Kobe. Detailed description of groundmotion generation is given by Jeremic et al. [3]

The main feature in evaluation of the two bent models is in different behavior of the samebent for chosen input motions. Presented here are result from two Loma Prieta motions (Corral-itos and Gilroy). The effects of SFS interaction are considered to be beneficial to the structureunder the following conditions:

• There are no significant permanent deformations in the structure resulting from yieldingof the pier, or

• The energy dissipation (hysteretic loops) of the system with SFS interaction is smallerthan that with fixed foundation, leading to the conclusion that there is less damage to thestructure.

If any of the above criteria is not fulfilled, it is assumed that SFS interaction is detrimentalto the structure behavior. Presented here are two examples of bent behavior, one representingbeneficial effects and one for detrimental effects of SFS interaction. Figure 10 shows behaviorof the bent subjected to the scaled Corralitos record. This record was scaled to match the hazardspectra at a period of 0.77 sec. As is evident from the spectra shown in Figure 10, the demandsimposed by the earthquake are more significant in the short period range, hence the fixed basemodel experiences higher demands than the model with SFS interaction. Both SFS and non SFSinteraction results show small permanent deformation (of the order of one to two centimeters).However, the hysteretic loops of the model considering SFS interaction effects are much smallerthen those of the non SFS interaction model thus suggesting much smaller levels of damage forthe SFS interaction model. The results in Figure 11, on the other hand, clearly indicate that

a)

Spring ModelFixed Model

0.5

0.4

0.3

0.2

0.1

0

−0.1

−0.2

−0.30 5 10 15 20 25 30 35 40

Time (Sec)

Hor

izan

tal D

ispl

acem

ent (

m)

b)−0.3 −0.2 −0.1 0 0.1 0.2 0.3 0.4 0.5

Displacement (m)

Fixed ModelSpring model

x 1066

4

2

0

−2

−4

−6

−8

Shea

r Fo

rce

(N)

Figure 10: LP–Corralitos Record : a) displacement time history for fixed and spring supported models,

b) horizontal displacement vs shear force for fixed and SFS interaction models.

the SFS interaction model subjected to scaled Gilroy earthquake is dissipating more energy and

9


also being subjected to larger deformations than the non–SFS interaction model. The spectraldemands are initially higher in the short period range for this record, however, it is likely thatthe fixed base model moves into a region of slightly lower demands (just beyond 0.5 seconds)since the degree of inelasticity is not severe. The shift in the period from 1.24 seconds of theSFS interaction model takes it into a region of increased demand thus causing higher drifts.

a)

Hor

izan

tal D

ispl

acem

ent (

m)

0.3

0.2

0.1

0

−0.1

−0.2

−0.30 5 10 15 20 25 30

Time (Sec)35 40 45 50

Spring ModelFixed Model

b)

She

ar F

orce

(N

)

x 10

−0.3 −0.2 −0.1 0 0.1 0.2 0.3Displacement (m)

Fixed ModelSpring model

6

4

2

0

−2

−4

−6

−8

6

Figure 11: LP–Gilroy Record: a) displacement time history for fixed and SFS interaction models, b)

horizontal displacement vs shear force for £xed and SFS interaction models.

Summary

The NEESgrid computational simulation platform OpenSees is a very versatile simulation tool.The selected examples, developed mostly within the computational geomechanics group at UCDshow part of this versatility. In addition to that, OpenSees features a number of other models,elements, solutions procedures, making it one of the most useful simulations tools (platforms)available today.

Acknowledgment

This work was supported in part by a number of grants. We list them bellow. Earthquake En-gineering Research Centers Program of the National Science Foundation under Award NumberEEC-9701568 (cognizant program director Dr. Joy Pauschke); Civil and Mechanical Systemprogram, Directorate of Engineering of the National Science Foundation, under Award NSF-CMS-0337811 (cognizant program director Dr. Steve McCabe) and NSF–CMS–0324661 (cog-nizant program director Dr. Richard Fragaszy); California Environmental Protection Agencyunder Award Cal–EPA 02-002-96V (cognizant program director Ms. Stacey Patenaude).

10


The author also wishes to acknowledge colleagues and current and former students who havecontributed to the described work: Professors Sashi Kunnath, Gregory Fenves, Zhaohui Yangand Feng Xiong, Dr. Frank McKenna, and students Xiaoyan Wu, Ritu Jain, James Putnam, QingLiu, Jinxiu Liao, Kallol Sett, Zhao Cheng, Matthias Preisig, Guanzhou Jie, Vlado Vukadin andIan Tucker.

References

[1] N. A. Abrahamson and W. J. Silva. Empirical response spectral attenuation relations forshallow crustal earthqaueks. Seismological Research Letters, 68:94–127, 1997.

[2] Jacobo Bielak, Kostas Loukakis, Yoshaiki Hisada, and Chaiki Yoshimura. Domain re-duction method for three–dimensional earthquake modeling in localized regions. part I:Theory. Bulletin of the Seismological Society of America, 93(2):817–824, 2003.

[3] Boris Jeremic, Sashi Kunnath, and Feng Xiong. Influence of soil–structure interaction onseismic response of bridges. International Journal for Engineering Structures, 26(3):391–402, February 2003.

[4] Boris Jeremic and Jinxiu Liao. Domain reduction method for soil-foundation-structure in-teraction analysis. Technical Report UCD-CGM 01-2004, University of California, Davis,January 2004.

[5] Boris Jeremic and Qing Liu. Fully coupled, solid–fluid formulation and implementation.Technical Report UCD-CGM 02-2004, University of California, Davis, March 2004.

[6] Boris Jeremic and Zhaohui Yang. Template elastic–plastic computations in geomechan-ics. International Journal for Numerical and Analytical Methods in Geomechanics,26(14):1407–1427, 2002.

[7] M. T. Manzari and Y. F. Dafalias. A critical state two–surface plasticity model for sands.Geotechnique, 47(2):255–272, 1997.

[8] William L. Oberkampf, Timothy G. Trucano, and Charles Hirsch. Verification, validationand predictive capability in computational engineering and physics. In Proceedings of

the Foundations for Verif ication and Validation on the 21st Century Workshop, pages 1–74, Laurel, Maryland, October 22-23 2002. Johns Hopkins University / Applied PhysicsLaboratory.

[9] Patrick J. Roache. Verif ication and Validation in Computational Science and Engineering.hermosa publishers, 1998. ISBN 0-913478-08-3.

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[10] Paul Somerville and Nancy Collins. Ground motions time histories for the I-880 bridge,Oakland. Report to peer methodology testbeds projects, URS Corporation, 2002.

[11] P.G. Somerville, N.F. Smith, R.W Graves, and N.A. Abrahamson. Modification of em-pirical strong ground motion attenuations to include the amplitude and duration effects ofrupture directivity. Seismological Research Letters, 68:199–222, 1997.

[12] Zhaohui Yang and Boris Jeremic. Numerical analysis of pile behaviour under lateral loadsin layered elastic-plastic soils. International Journal for Numerical and Analytical Meth-

ods in Geomechanics, 26(14):1385–1406, 2002.

[13] Zhaohui Yang and Boris Jeremic. Numerical study of the effective stiffness for pilegroups. International Journal for Numerical and Analytical Methods in Geomechanics,27(15):1255–1276, Dec 2003.

[14] Zhaohui Yang and Boris Jeremic. Soil layering effects on lateral pile behavior. In print in

ASCE Journal of Geotechnical and Geoenvironmental Engineering, July 2004.

[15] Chaiki Yoshimura, Jacobo Bielak, and Yoshaiki Hisada. Domain reduction method forthree–dimensional earthquake modeling in localized regions. part II: Verification and ex-amples. Bulletin of the Seismological Society of America, 93(2):825–840, 2003.

[16] O. C. Zienkiewicz and T. Shiomi. Dynamic behaviour of saturated porous media; the gen-eralized Biot formulation and its numerical solution. International Journal for Numerical

Methods in Engineering, 8:71–96, 1984.

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1

Large-displacement Facility for Testing Highly Ductile Lifeline Systems

Scott L. Jones,a) Keith E. Kesner,a) Thomas D. O’Rourke,a) Harry E. Stewart,a) Tarek Abdoun,b) and Michael J. O’Rourke b)

Innovative testing facilities are being constructed at Cornell University and

Rensselaer Polytechnic Institute (RPI) as part of Phase 2 of the George E. Brown,

Jr. Network for Earthquake Engineering Simulation (NEES) of the National

Science Foundation. The project will develop advanced simulation and

experimental evaluation of key lifeline components under earthquake conditions.

This paper describes the experimental facilities, as well as the problems of soil-

structure interaction and above-ground structural response that can be addressed

through physical simulation with the facilities. Issues associated with rate of

ground rupture, angle of intersection between buried lifeline and ground

displacement planes, and size of the facility also are treated. The paper explores

the use of full- and near-full-scale simulations at Cornell combined with

centrifuge experiments at RPI to cover a broad range of sizes, geometries, and

time rate effects on the performance of lifelines in the field.

INTRODUCTION

Lifeline systems are essential for civil infrastructure because they deliver the resources

and services needed to sustain a modern community. Lifelines are often grouped into six

principal systems: electric power, gas and liquid fuels, telecommunications, transportation,

wastewater facilities, and water supply. When an earthquake strikes, life and property are

threatened in the short term when functional water supply, transportation systems, electric

power, and telecommunications either fail or lose their capabilities during emergency

operations. In the long term, earthquake recovery is prolonged, especially when significant

construction is required to rehabilitate damaged facilities.

a) School of Civil and Environmental Engineering, 220 Hollister Hall, Cornell University, Ithaca, NY 14853 b) Department of Civil and Environmental Engineering, JEC 4049, Rensselaer Polytechnic Institute, Troy, NY 12180

Proceedings Third UJNR Workshop on Soil-Structure Interaction, March 29-30, 2004, Menlo Park, California, USA.

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There is a compelling need in the George E. Brown Jr. Network for Earthquake

Engineering Simulation (NEES) for experimental and testing facilities to evaluate lifeline

earthquake behavior. Not only are experimental facilities required for investigating the

aboveground response of structures, such as viaducts and bridges, but equipment is needed to

investigate the soil-structure interaction of underground lifeline components. In congested

urban and suburban environments, large portions of lifeline systems are buried or constructed

underground. Understanding how ground deformation affects buried lifelines, therefore, is a

critical aspect of earthquake engineering, which needs to be addressed in NEES by advanced

laboratory experiments and computational modeling.

The remainder of this paper describes the experimental facilities at Cornell University

that were developed specifically for the NEES project and some examples of research

projects that might be undertaken at the Cornell NEES facility.

EXPERIMENTAL FACILITIES

The NEES equipment will be housed primarily in the George Winter Civil Infrastructure

Laboratory at Cornell University, with complementary equipment being housed in the

Centrifuge Facility at Rensselaer Polytechnic Institute (RPI). Figure 1 provides an expanded

view of the existing Winter Lab highbay within which elements of the NEES equipment

system are shown along with some possible experimental layouts. The strong walls are

modular and can be assembled for a maximum 17-m length for the low wall and 7.2-m height

for the high wall. There will be two 0.91-m actuators and one 0.63-m actuator. Soil will be

stored in special bins recessed into the walls to conserve space. Room is available for

supplemental soil storage in the high bay should a future experiment require additional

volumes of soil. A portable conveyor system provides rapid movement and placement of

soil. Nominal soil test boxes are shown. The dimensions of the boxes need to be chosen

according to the purpose and type of experiment. Room is available for boxes as long as

20m. A nominal bending test on pressurized pipe is also shown. The vertical reaction frames

shown in Figure 1 are not a part of the NEES equipment but may be provided depending on

availability of funds as the project draws to a close. The remainder of this section provides a

summary of the NEES equipment and its performance specifications (Tables 1-5).

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Figure 1. Perspective View of George Winter Infrastructure Laboratory Highbay with NEES Equipment in Place.

LARGE-DISPLACEMENT ACTUATORS AND SERVO-HYDRAULICS

Servo-hydraulic actuators and ancillary hydraulic equipment are necessary to support

large-displacement physical testing for lifeline systems. Recent testing at Cornell in

collaboration with Tokyo Gas has involved the largest laboratory tests ever performed of

pipeline response to permanent ground deformation to improve design and siting procedures

for steel pipelines with elbows (Yoshizaki et al. 2003). The motions imposed on the test

system were on the order of a meter so that full soil-structure interaction could be mobilized.

Multiple actuators with one-way strokes on the order of 2m will provide unique testing

equipment that can be used on a very wide range of buried and above-ground lifeline

systems. These actuators and supporting hydraulic equipment will provide state-of-the-art

systems not available at other experimental locations.

In addition to the ability to test large-scale structures, material tests can be performed

using hydraulic wedge grips. The grips can be used for testing of materials ranging from

brittle matrix composites to geo-textiles to ductile steel coupons. Up to a 220 kN tensile

Soil Test Boxes

High ModularReaction Wall

Low Modular Reaction Wall

Soil Storage Bins

Actuators

Pipe Bending Test

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Table 1. Servo-Hydraulics Performance Specifications

Large-Displacement Actuators and

Servo-Hydraulics

Performance Specification

Linear Hydraulic Actuators

Two actuators with load capacities of 295 kN tension, 498 kN compression, strokes of +/- 0.91 meters. One actuator with load capacity of 445 kN tension, 649 kN compression, stroke of +/- 0.63 m.

Hydraulic Power Supplies

Servovalves, manifolds, and pump with flow rates and capacities for large actuator movements and simultaneous use of multiple actuators.

Electronic Controls Independent control of either load or displacement on multiple actuators in simultaneous use.

Hydraulic Wedge Grips

Apply up to 220 kN tension to gripped material while ensuring a true alignment of axial force; grips should not slip in the direction of loading.

force can be applied to gripped material while ensuring true alignment of the tensile force.

Installation of the grips in a 900 kN four post (approximately 1.5 m high) test frame ( +/- 75

mm displacement) will allow for testing of large-scale tensile specimens to high strain levels.

The hydraulic grips are an essential component in the development of new materials for

lifelines.

DATA ACQUISITION AND SENSORS

Upgraded high-speed data acquisition systems will be assembled using a variety of

components. Two Pentium 4 computers will be interfaced with high-speed multiplexers,

signal conditioners, and data converter boards. The data acquisition systems will be

interfaced with the servo-hydraulic system controls and connected to the Internet. The main

sensors consist of an advanced fiber-optic signal conditioning unit and large-stroke

displacement transducers. The fiber optic instrumentation consists of a high-resolution, high-

precision system. This is a high-speed sensor conditioner that can adapt to slow or fast

testing (sampling rates up to 1000Hz). All data acquisition systems will be capable of multi-

channel measurements of temperature, pressure, force, displacement, or strain using a

common sensor-conditioning unit with interchangeable sensors. Magneto-strictive

displacement measuring devices with 2-m ranges also will be used. These devices are a

necessary measuring tool for large-displacement soil-foundation-structure interaction (SFSI)

testing.

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Table 2. Data Acquisition Performance Specifications

Data Acquisition Systems


Computers High-speed, large storage capacity, Internet connectivity A/D boards. Multiplexers

16-bit resolution, expandable for 128 to 256 data channels

Signal Conditioning Stable power supply; low noise; independent variable gain; capable of using a wide variety of transducers

Sensors Large displacement (up to 2 m), precision and accuracy, compatibility with signal conditioning and other control systems, fiber-optic system capable of measuring strains up to 5000 to 10000 microstrain, laser extensometers for large displacement measurements.

MODULAR REACTION WALLS

Experiments on lifelines can be performed in numerous ways using a segmentally

precast, post-tensioned concrete strong wall/floor assembly. The baseline assembly would be

made up of a long, low segmental box girder along the existing lab floor with modular high

walls perpendicular to each other and forming a corner on one end (see Figure 5). The low

box segments would form a maximum length of 17 m off of which the soil box experiments

Table 3. Modular Reaction Wall Performance Specifications

Modular Reaction Walls


Low strong wall/box Must resist lateral loads of 675 kN locally and 1350 kN overall anywhere along the height; must resist local vertical loads of 900 kN; must be match-cast, precast so as to be easily post-tensioned to form a long, low wall and be stackable for storage; each segment must weigh less than 89 kN to use existing overhead crane; must be hollow to allow for access from within; must be able to post-tension to both high walls.

High strong walls Must resist lateral loads of 900 kN at a height of 5m from a fixed base; must resist vertical tensile/compressive loads of 1800 kN; must be able to post-tension to the low strong wall/box in two directions; must be able to post-tension to perpendicular high strong wall to facilitate lateral loading in two directions.

Floor anchor system

The combination of existing 900 kN floor anchors and 14 supplemental 670 kN floor anchors can be used to anchor reaction frames, test specimens and strong wall components to the existing structure.

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Figure 2. Plan View of Modular Strong Wall System for Large-displacement Lifeline Experiments

on buried lifelines will react. Simple extension of the low strong wall to include two narrow

high walls at one end broadens the possibilities of shared use of the proposed NEES site. The

top surface of the low wall will be used for a variety of above-ground lifeline testing

including highway component and system testing as well as structural pipe testing prior to the

soil-structure interaction tests. On this surface, vertical loads can be applied to bridge

girders, substructure components and bridge connections. In the raised wall portion of the

assembly these components and systems can be tested with lateral loads in two directions.

Vertical loads can be supported off of the low wall acting as a strong floor or off of the high

walls through an attached load frame. Experiments on the top surface of the low wall can

take place without interfering with the floor space where the soil box experiments would be

set up. In addition, when the floor space is not being used for soil box experiments, various

structural configurations can be tested under lateral loads laying flat. A limited version of

this arrangement was recently used in the Winter Lab for the research on unbonded post-

tensioned concrete columns. Finally, the low wall could be built in two parts with portions of

the high walls stacked on the inside of the openings to form abutments. These two abutments

could then be used as reaction walls to conduct soil-structure interaction experiments in an

axial configuration. To join the reaction wall components to the existing floor a combination

of existing 900 kN floor anchors and 14 supplemental 670 kN anchors are used. The 14

supplemental anchors were specifically added to anchor reaction wall components. Eight of

High Strong Wall Units Low Strong

Wall Units

Existing 900 kN Floor Anchors

Supplemental 670 kN Floor Anchors

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Table 4. Soil Storage Performance Specifications

Soil-Storage Performance Specification Soil Bins On-site storage of on the order of 50 to 55 m3 of soil used in

large-scale movable split soil boxes. The bins are loaded through the open top and unloaded using sliding gates at the bottom. Inside storage for moisture control and to avoid freezing. Minimize internal use of floor space in crane bay.

Conveyor System 2 conveyors with a 61 m/min belt speed capable of moving approximately 19 m3 of soil per hour: 1 4.5 m long with a 3 m lift, 1 6.7 m long with a 4.5 m lift. Portability. Flexible configurations.

the anchors arranged in groups to anchor both ends of the low wall sections. Four of the

anchors are used in the high wall section to resist over-turning. The remaining two anchors

are used to anchor alternate locations for the low wall sections.

SOIL STORAGE AND CONVEYANCE

A soil storage system capable of holding and handling large quantities of soil for full-

scale and near full-scale soil-structure interaction experiments on pipelines and bridge

systems has been constructed in the crane bay area of the Winter Lab. The crane bay has 5.5

m high, 0.3-m-thick concrete walls spanning the 4.5 m horizontal distances between heavy,

laced, concrete jacketed columns that support the roof. The columns are jacketed for their

lower 5.5 m and unjacketed for the remaining 6.7 m. Steel beams with an exposed flange

were cast into the concrete columns. The flanges are used to connect other structural

members to the columns. The columns are approximately 1.2 m deep and there is

approximately 4 m between the inner edges of any two adjacent columns. This volume is

reduced in the lower portions of the units because of the tapered sections. Reinforced steel

plating has been placed between the inner steel flanges of adjacent columns to create the

basic storage unit. A conveyor belt assembly with a cleated belt trough slider bed belt will be

used to charge the soil bins. The front of the soil storage containment bins has sliding steel

discharge panels. Discharged soil will be moved with an existing small Bobcat loader, a trip-

release concrete bucket and overhead crane, or the conveyor belts.

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Table 5. Centrifuge Containers Performance Specifications Centrifuge Containers


Split Boxes Overall dimensions:108 cm L x 69 cm W x 36 cm H; Inside container dimensions: Model dimensions of 100 cm L x 36 cm W x 20 cm H; Prototype dimensions at 75g of 75m x 27m x 15m Empty weight of 900 N Displacement of movable sections = 0 to 8 cm Operating hydraulic pressure = 8.3 MPa Maximum Actuator force = 8.9 kN 1 box with 2 sections—1 capable of vertical movement, capable of horizontal movement 1 box with 3 sections—2 capable of horizontal movement

CENTRIFUGE CONTAINERS

The containers at the RPI centrifuge will use two hydraulic cylinders to produce localized

shear strains along one or two vertical interfaces in a soil model while being spun at

centrifugal accelerations of up to75g. Load cells directly connected between each actuator

and the movable portions of the container measure the shearing force applied by the

actuators. The maximum achievable displacement is 8 cm (6m prototype units). Motion of

each actuator is precisely controlled using a servo-valve and feedback control system. Using

a function generator or computer equipped with a DAC interface board, a variety of input

strain distributions and time histories can be created. The containers will be manufactured

from high-strength aluminum alloy. The moving portions of the container are supported and

guided using roller bearings to provide precise movement with minimal friction. The sliding

interface between the fixed and movable portions of the container utilizes low-friction Teflon

seals protected by steel shields. When used with a suitable Teflon sheet liner, this design

effectively excludes soil from the interface, maximizing the service life of the seals. One

container (Figure 3a) will have three sections having two actuators and a two-channel

displacement control system. In this concept, one section will be fixed, and either one or

both of the other sections can be moved. If two sections are moved, they can be moved either

together or independently. In this way a wide variety of strain configurations can be

modeled. The other container (Figure 3b) will have two sections having two actuators and a

two-channel displacement control system. In this concept, one section can be moved

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(a) 1 fixed segment, two segments capable of independent horizontal movement.

(b) 1 segment capable of independent vertical movement, 1 segment capable of independent horizontal movement

Figure 3. Schematic Diagram of Split Soil Containers for Use with the Centrifuge at RPI.

horizontally and the other can be moved vertically, allowing for experiments on pipes

experiencing either horizontal, vertical, or both horizontal and vertical PGD.

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ADDITIONAL TESTING EQUIPMENT

Figure 1 also shows several pieces of testing equipment that are not included in the

construction of the NEES facility at Cornell University—the most important of which are the

split test boxes and the vertical reaction frame.

The split boxes have traditionally been built by reinforcing a plywood box with steel

framing and resting the bottom beams of the moving box on Teflon strips to minimize

friction. Steel will often be available in the Winter Lab for framing of the split boxes but the

researchers using the facility are responsible for surveying the website

(www.nees.cornell.edu) and coordinating with the NEES Operations Manager at Cornell

University to determine the availability of steel beams. The website and/or Operations

Manager will also be helpful for identifying local fabricators and distributors who can

provide steel framing and Teflon.

A vertical reaction frame is anticipated to be an essential piece of testing equipment for a

number of applications: applying gravity load to structural members, applying bending loads

to pipes, etc. The current plans are to provide a vertical reaction frame capable of resisting

up to approximately 1 MN of force, pending a review of cost-savings on other equipment.

The original budget did not include an allowance for a vertical reaction frame. Again,

researchers should review the website and/or contact the NEES Operations Manager at

Cornell University to determine the availability of and specifications for a vertical reaction

frame.

In addition to the testing equipment described in the previous two paragraphs, researchers

will be responsible for providing one-time measuring devices, such as strain gauges and

fiber-optic gauges, and whatever soil they may want to use for testing. Guidelines will be

available on the Cornell NEES website or through the Operations Manager.

POTENTIAL RESEARCH PROJECTS

The NEES facility at Cornell University and RPI has been designed to address several

classes of research projects not covered by the other equipment sites in NEES. One project

class in particular (soil-structure interaction under permanent ground deformation) has been

prominent in planning the facility and is discussed in detail below. Other complementary

project classes are briefly described in the following subsections.

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SOIL-STRUCTURE INTERACTION UNDER PERMANENT GROUND DEFORMATION

It has long been recognized that the most serious damage to underground lifelines during

an earthquake is caused by PGD (e.g., O’Rourke 1998). It is not possible to model with

accuracy the soil displacement patterns at all potentially vulnerable locations. In fact, studies

of ground deformation patterns associated with surface faulting have shown complex patterns

of ground rupture and distributed deformation even for strike slip faults (Bray et al. 1994,

Lazarte et al. 1994). It is possible, nevertheless, to set an upper bound on deformation effects

by simplifying spatially distributed PGD as movement concentrated along planes of soil

failure. Detailed studies of fault deformation disclose that abrupt soil rupture and offsets are

indeed recurrent patterns of deformation (Bray 2001). Accordingly, they establish a baseline

with which to evaluate soil-lifeline interaction under large ground deformation.

Figure 4 illustrates the principal modes of soil-structure interaction under PGD. Figure

4a shows pipelines crossing a fault plane subjected to oblique slip. Reverse and normal faults

tend to promote compression and tension, respectively. Strike slip may induce compression

Figure 4. Soil-Pipeline Interaction Triggered by Earthquake-Induced PGD (after O’Rourke, 1998).

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or tension, depending on the angle of intersection between the pipeline and fault. As shown

in Figs. 4b and c, the pipeline will undergo bending and either tension or compression at the

margins of a slide where the deformation is similar to that at an oblique fault crossing. The

ground deformation at the head of the slide (Fig. 4d) is similar to normal faulting, where the

pipeline is subject to combined bending and tensile strain. At the toe of the slide (Fig. 4d),

the ground deformation is similar to reverse faulting, producing compressive strains in the

pipeline.

A number of approaches have been proposed to address the problem of lifeline response

to abrupt soil movement. Newmark and Hall (1975), for example, developed one of the first

analytical models for a pipeline intersecting a strike-slip fault at an angle, such that ground

rupture results primarily in pipe tensile strain. They assumed the pipe is firmly attached to

the soil (i.e., no relative pipeline displacement) at two anchor points some distance from the

fault trace and neglected the pipeline bending stiffness and horizontal interactions between

soil and pipe.

Kennedy et al. (1977) extended the ideas of Newmark and Hall by considering the effects

of lateral interaction. They also considered the influence of large axial strains on pipeline

bending stiffness, and modeled pipeline flexure.

Subsequent to the Kennedy et al. work, Wang and Yeh (1985) suggested modifications to

the closed form analytical model, while Ariman and Lee (1991) and Meyersohn (1991)

present results from FE models. An independent comparison of the results of the available

analytical approaches, as reported in O'Rourke and Liu (1999), suggest that the Kennedy et

al. model for strike slip faulting provides the best match to ABAQUS finite element results.

Relatively little analytical work is available for a pipeline crossing a normal or reverse

fault. For a normal fault, the pipe–soil system is no longer symmetric, and the transverse

interaction force at the pipe-soil interface for downward pipe movement is much larger than

that for upward movement. For a pipeline at a reverse fault, it appears that no analytical

approach is currently available. The ASCE Guidelines (1984) suggest using the FE method.

The behavior for both reverse and normal faulting is difficult to generalize, in part because

there are two angles of intersection (the angle in plan between the fault and the pipeline, as

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well as the dip angle of the fault) in addition to the aforementioned asymmetric nature of the

soil resistance in the vertical plane.

The existing analytical approaches are primarily directed at relatively small diameter-to-

thickness ratios (D/t) common in the gas and liquid fuel industries. For larger D/t, additional

complications are introduced. Ovaling behavior (i.e., the original circular pipe cross-section

deforms into an oval) now becomes a design consideration, and modeling procedures become

important. For FE analysis at low D/t, the pipe is frequently subdivided into elements,

typically about two pipe diameters in length. These pipe elements are connected at nodes

where a single axial/longitudinal soil spring and two transverse soil springs are attached.

However, for high D/t pipe, which may be susceptible to ovaling, a number of shell elements,

distributed around the pipe circumference would be needed. In addition, longitudinal and

transverse soil springs need to be attached in some manner to the nodes which connect the

individual shell elements.

Lack of fundamental knowledge about soil-pipeline interaction and reliance on analytical

simplifications result in a current state of practice characterized by a high degree of

uncertainty and the absence of design codes and in-depth guidelines. The opportunity for a

true breakthrough is therefore available with the NEES equipment sites at CU and RPI.

Furthermore, this breakthrough would have a profound, positive influence on the design and

construction of widespread critical facilities affecting public safety and security.

To address this very important problem, research can be performed using the combined

resources of the Cornell Large Displacement Lifeline Testing Facility and the RPI 150 g-ton

Geotechnical Centrifuge in combination with advanced computational simulation. Figure 5

illustrates the concept of split-box testing, which provides the basis for laboratory simulation

of the most severe PGD effects associated with surface faulting, liquefaction-induced lateral

spread, and landslides.

The laboratory and centrifuge equipment have the capability of imposing abrupt soil

displacements on buried lifelines consistent with PGD effects at fault crossings and the

margins of lateral spreads and landslides. As shown in Figure 5, relative displacement is

generated along a moveable interface between two test basins, or boxes, containing soil and

the buried lifeline. The lifeline is buried in soil that is placed and compacted according to

field construction practice. The scale of the experimental boxes is selected based on

computational modeling and previous test experience in an effort to minimize the effect that

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the boundaries of the test facility have on the soil-structure interaction. The experimental

facilities will have the capability of imposing horizontal movement and vertical

displacement.

The CU facility provides for full-scale testing that concentrates on detailed soil-structure

interaction. It permits accurate representation of both the soil and buried lifeline in the

vicinity of ground rupture where it is most important to duplicate pipe and soil material

behavior and the intricacies of soil-pipeline reactions. The size of the test facility, however,

is constrained by the practicalities of large-scale test box construction, soil placement, and

actuator load capacity. The RPI facility provides an excellent complement. Through multi-g

scaling, larger prototype dimensions and rates of loading can be tested. Soil-structure

interaction can be evaluated in considerable detail, although not to the same degree as is

possible with the large-scale facility. At both the CU and RPI equipment sites, the prototype

lifeline length is influenced by the maximum length of the split box used to simulate ground

rupture. Figure 6 shows generic types of ground rupture patterns that have impact for buried

lifelines. Table 6 summarizes the characteristics of each facility with respect to size of

pipeline/conduit that can be tested, geometry of ground deformation (as depicted in Fig. 6),

depth of pipe burial, and total length of pipeline.

PipeTrenchCross-section

Special Trenchand Backfill atFault Crossing

a) PGD Effect on Buried Pipelines

b) PGD Effect on Pipelines with Elbows

BuriedPipeline

Elbow

Permanent Ground Deformation(PGD)

Compacted Sand

Welded SteelPipeline

Fixed Box

c) Experimental Concepts

Straight Pipe

Pipe with Elbow

ElbowCompacted Sand

Welded SteelPipeline

Fixed Box

Figure 5. Simulation of Ground Rupture Effects on Lifelines by Split-Box Tests.

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Table 6 NEES Site Simulation Capabilities for Soil Lifeline Interaction

Figure 6. Abrupt Ground Rupture Pattern for Experimental and Numerical Investigations

There are three principal types of ground rupture patterns that are illustrated

schematically in Fig. 6: a) horizontal deformation, corresponding to strike slip displacement;

b) normal deformation, corresponding to normal faulting; and c) thrust deformation,

corresponding to thrust and reverse faulting. Combinations of a) with b) or c) are also

possible.

Parameter1 Cornell NEES Site RPI NEES Site Diameter, D 100-600 mm 200-5000 mm

Diameter to Thickness Ratio, D/t 10-120 10-250

Depth of Burial 0.6-1.5 m 0.6-20 m

Maximum Length of Pipeline2 18 m 46 m Pipeline Intersection Angle for Horizontal Deformation, α

+30 o to 90 o

90 o to -30 o 62 o to 90 o

90 o to -62 o Normal Deformation Angle, Nβ 30 o to -90 o 90 o

Thrust Deformation Angle, Tβ ≤30o NA

Maximum Displacement 1.8 m 4.0 m

Maximum Rate of Displacement 0.1 m/s 0.9 m/s 1 refers to prototype or actual field scale 2 refers to actual test box dimensions; the effective pipeline length can be increased experimentally through the use of actuators in the Cornell facility and special springs in the Rensselaer split box NA – not available

a) Horizontal Deformation Angle, α(Plan View)

b) Normal Deformation Angle, βN (cross-section)

c) Thrust Deformation Angle, βT(cross-section)

α - α

Pipeline

Ground Rupture

βN βT Pipeline

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SOIL-STRUCTURE INTERFACE INTERACTIONS

Soil-structure interface problems involve locations where abrupt transitions from

structure to soil create localized stresses and deformations. As illustrated in Figure 7,

Pipe/Conduit

Structural Vault

Soil

a) Bridges b) Vaults c) Base Isolation

Bridge Girder/Deck Abutment

Pipe/Conduit Structural Penetration

Soil

d) Experimental Concept

Soil

Building

Base Isolation Devices

Location of Interaction Between Structure

and Soil

Structural Vault or Bridge Abutment Equivalent

Box with Backfill Soil and Buried Conduit

Displacement from Actuator

Sliding Connection between Soil Box and Structural Vault

Displacement from Actuator

Teflon Strips

Figure 7. Soil-Structure Interface Interactions

examples include bridge abutments where a number of different cables and conduits may

transition from soil through the abutment and/or other structural elements. Additional

examples include basement and vault penetrations of cable and conduits. At these locations,

transient motion of the structure and adjacent soil can be significantly out of phase.

Furthermore, settlement can occur in the adjacent soil, thereby imposing permanent ground

deformation at the same time transient movements take place. Penetrations of structural

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walls and abutments have been identified as one of the most important issues for the

earthquake resistant design of lifelines (e.g., ASCE 1984).

This experimental facility will have the ability to simulate complex interactions at soil-

structure interfaces. The experimental concept is shown in Figure 2d. An actuator can apply

lateral displacements to a structural vault or bridge abutment element at the same time

another actuator applies displacements to a test box with backfill soil and a buried conduit

that penetrates the structural element. A special sliding connection can be fabricated to allow

relative movement between the test box and structural element. Teflon strips will allow for

low-friction sliding of the experimental members.

ACKNOWLEDGEMENTS

We would like to acknowledge Nathaniel A. Olson for creating all of the CAD drawings

of the modular reaction wall.

This work was supported in part by the George E. Brown, Jr. Network for Earthquake

Engineering Simulation (NEES) Program of the National Science Foundation under Award

Number CMS-0217366.

REFERENCES

American Society of Civil Engineering (ASCE), 1984, Guidelines for the Seismic Design of Oil and

Gas Pipeline Systems, Committee on Gas and Liquid Fuel Lifelines, Reston, VA.

Ariman, T. and Lee, B.J., 1991, Tension/bending behavior of buried pipelines under large ground

deformation in active faults, Proceedings of the Third U.S. Conference on Lifeline Earthquake

Engineering, Technical Council on Lifeline Earthquake Engineering, Monograph No. 4, ASCE,

226-233.

Bray, J. D., 2001, Developing mitigation measures for the hazards associated with earthquake Surface

fault rupture,” Workshop on Seismic Fault-Induced Failures: Possible Remedies for Damage to

Urban Facilities, Research Project 2000 Grant-in-Aid for Scientific Research (No. 12355020),

Japan Society for the Promotion of Science, Workshop Leader, Kazuo Konagai, University of

Tokyo, Japan, January 11-12, 55-79.

Bray, J.D., Seed, R.B., Cluff, L.S., and Seed, H.B., 1994, Earthquake fault rupture propagation

through soil, Journal of Geotechnical Engineering, ASCE, 120(3), 543-561.

Kennedy, R.P., Chow, A.W., and Williamson, R.A., 1977, Fault movement effects on buried oil

pipeline, Journal of the Transportation Engineering Division, ASCE, 103 (TE5), 617-633.

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Lazarte, C.A., Bray, J.D., Johnson, A.M., and Lemmer, R.E., 1994, Surface breakage of the 1992

Landers earthquake and its effects on structures, Bulletin of the Seismological Society of America,

84(3), 547-561.

Meyersohn, W.D., 1991, Analytical and Design Considerations for the Seismic Response of Buried

Pipelines, M.S. Thesis, Cornell University.

Newmark, N.M. and Hall, W.J., 1975, Pipeline design to resist large fault displacement, Proceedings

U.S. National Conference on Earthquake Engineering, Ann Arbor, Michigan, 416-425.

O'Rourke, M.J. and Liu, X., 1999, Response of Buried Pipelines Subject to Earthquake Effects,

Monograph No. 3, MCEER, Buffalo, NY.

O’Rourke, T.D., 1998, An overview of geotechnical and lifeline earthquake engineering,

Geotechnical Special Publication No. 75, ASCE, Reston, VA.

Wang, L.R.L. and Yeh, Y., 1985, A refined seismic analysis and design of buried pipeline for fault

movement, Journal of Earthquake Engineering and Structural Dynamics, 13, 75-96.

Yoshizaki, K., O’Rourke, T.D., and Hamada, M., 2003, Large-scale experiments of buried steel

pipelines with elbows subjected to permanent ground deformation, Structural

Engineering/Earthquake Engineering, JSCE 20(1), 1s-11s.

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The Promise of NEES Research

Application of the George E. Brown, Jr. Network for Earthquake Engineering Simulation in

Collaborative Research

Steven L. McCabe

Program Director, Structural Systems and Hazard Mitigation

Civil and Mechanical Systems National Science Foundation

Arlington ,VA

2

NationalAeronautic and Space

Administration

EnvironmentalProtection

AgencySmithsonian

InstitutionNuclear

Regulatory Commission

Other agencies

Commerce

Science Advisor

Other boards, councils, etc.

U.S. President

Independent Agencies

Major Departments

Science AdvisorOffice of Science and

Technology Policy

Office of Managementand Budget

Agriculture Health and Human Services

Interior Transportation Defense Energy

NSF-36

AssistantDirector forEngineering

Bioengineering &Environmental

Systems

Civil &Mechanical

Systems

Chemical &TransportSystems

Design,Manufacture, &

Industrial Innovation

Electrical &Communications

Systems

EngineeringEducation &

Centers

Directorate for Engineering

ENG-1

3

National Science Foundation

Lies within CMS– Structural Systems and Hazard Mitigation– Geotechnical Engineering– Emergency Response studies

Funding Levels at > $10 million per year with traditional individual investigator awards (IIA)

Earthquake Engineering program

National Science Foundation

– Major shift in funding levels and approachbeing launched this year to utilize NEES

– Initiating a three tiered plan for research• Grand Challenge Research Initiatives• Multiple Investigator teams• IIA

NEES Research: NEESR

4

Goal of NEES: National Shared Use Resources

• Experimental Sites funded by NSF (ES)• Experimental Data Repository

– Grid facilitates replication of results remotely or locally

• Computational Simulation Results Repository– Digital content for use in R&D, practice, education, outreach

• Simulation Software Tools Archive– Browsable and searchable library of community codes

• Collaborative technologies• Capabilities (e.g., HPC sites for numeric simulation)

– Grid facilitates ubiquitous access to computing resources, including high-performance parallel supercomputers

NEES Award Portfolio

Field Testing EquipmentUniversity of Texas, Austin

$2,937,036

Geotechnical CentrifugeUniversity of California, Davis

$4,614,294

Reconfigurable Reaction WallUniversity of California, Berkeley

$4,268,323

Fast Hybrid Testing LaboratoryUniversity of Colorado, Boulder

$1,983,553Multi-Axial Subassemblage Testing

SystemUniversity of Minnesota, Twin Cities

$6,472,049

Lifeline Testing FacilityCornell University

$2,072,716

Field Testing EquipmentUniversity of California, Los Angeles

$2,652,761

Three Biaxial Shake TablesUniversity of Nevada, Reno

$4,398,450

System IntegrationUniversity of Illinois at

Urbana-Champaign$10,000,000Tsunami Wave Basin

Oregon State University$4,775,832

Dual (relocatable) Shake Tables and High Performance Actuators

State University of New York,University at Buffalo

$6,160,785$4,379,865

Consortium DevelopmentConsortium of Universities for

Research in Earthquake Engineering$1,983,328

Permanently Instrumented Field SitesBrigham Young University

$1,944,423

Modular Simulation LaboratoryUniversity of Illinois at

Urbana-Champaign$2,958,011

Multi-directional Testing FacilityLehigh University

$2,593,317

Large Uniaxial Shake TableUniversity of California, San Diego

$5,890,000

Geotechnical CentrifugeRensselaer Polytechnic Institute

$2,380,579

5

NEES Resources: Equipment Sites

Actuator

Computer Model Test SpecimenActuator

ShearWall

Actuator

Fast Hybrid Structural Testing University of Colorado, Boulder

Structural and Geotechnical Field Testing University of California, Los Angeles

Geotechnical Field Testing University of Texas, Austin

Two Permanently Instrumented Field Sites in CA Brigham Young University

Wireless

NEES Resources: Equipment Sites

Geotechnical Centrifuge University of California, Davis

Geotechnical Centrifuge Rensselaer Polytechnic Institute

Tsunami Wave Basin Oregon State University

Reconfigurable Reaction Wall University of California, Berkeley

6

Compelling Technical Issues – what questions will NEES

Research answer? • Issues of scale

– Testing of models has been to reduced scale– Questions exists as to how the scaling affects the true

nature of performance involving nonlinear response– Material properties, time scale do not scale exactly

• e.g. fracture in concrete is a function of absolute size

– NEES will enable full or near full scale testing of com0plete structures and components

Compelling Technical Issues…• Issues of complexity

– Component test of individual components separated by geography and/or time are not the same as testing of a complete system

– Typical pseudo-dynamic tests or static tests have been extensively used but do not represent a true dynamic environment

– NEES will enable distributed tests to be conducted together with tests at other sites merging into large components or systems

– NEES will enable faster pseudo-dynamic tests that approach a true dynamic environment

7

Compelling Technical Issues…

• Issues of completeness– Soil-foundation-structure tests have not been

possible because of the different tests required to test the soil, foundation, soil-foundation interface and the structure

– NEES will enable true complete systems to be evaluated in dynamic or pseudo-dynamic tests for the first time

Compelling Technical Issues…

• Issues with ground motion– Recorded earthquake ground motions, primarily from recent

events, have exhibited accelerations, velocities and displacements that far exceed existing experimental capabilities

• Kobe• Northridge

– Using actual ground motions as test inputs for shaking table experiments is essential for developing improved understanding of response and damage mechanisms

– NEES will enable dynamic tests that will exhibit the true groundmotion characteristics

8

Japan also is developing a new modern testing environment

• Kobe earthquake revealed problems with existing data and decisions based on this data

• Japan independently recognized that scale issues are very important and have resulted in test results that are not as reliable as needed

• Tests of complete systems are needed to examine actual performance to develop better design codes

• Japan is developing the E-Defense shake table at Miki City to conduct full or near full-scale tests

• $450 million• One facility with limited throughput and participation• Agencies (BRI, NIED and PWRI) are running the show with

limited university participation

Examples of NEESR projects starting in FY2004

9

NEES Experimental Project for Verifying Full-Scale Semiactive Control

of Nonlinear Structures

PI: Richard ChristensonAssistant ProfessorDivision of EngineeringColorado School of Mines, Golden, CO

Amount: $196,811 ($223,823 w/ cost sharing)Duration: 36 monthsStarting Date: 09/15/03NEES site: UC Boulder Fast Hybrid Test System

Colorado School of MinesColorado School of Mines Network for Earthquake Engineering SimulationNetwork for Earthquake Engineering Simulation

Advancing the state of knowledge and acceptance of semiactive damping technology

More efficient and cost-effective than testing a physical structure.NEES provides equipment and facilities otherwise not available to the PI at the Colorado School of Mines.

Experimental Verification of SemiactiveControl

Applied to Full-Scale Structures Exhibiting Nonlinear Material Behavior

10

Collaborative Research: Testing and analyses of nonrectangular walls

under multi-directional loadsCatherine French

Department of Civil EngineeringUniversity of Minnesota, Minneapolis, Minnesota

Sri SritharanDepartment of Civil EngineeringIowa State University, Ames, IA

Ricardo LopezUniversity of Puerto Rico Mayaguez

Mayaguez, Puerto Rico

Suzanne Nakaki DowNakaki-Bashaw Group, Inc.

NSF George E. Brown Jr. NEES Program

Multi-Axial Subassemblage Testing System(MAST)

Unique features:large capacity6-DOF controlmixed mode

11

Innovative Bracing Systems• R. Leon and R. DesRoches – Georgia Tech • M. Bruneau and A. Reinhorn – U. at Buffalo• B. Shing – U. of Colorado• B. Stojadinovic and J. Moehle – UC-Berkeley• M. Abdollah – Florida A&M• A. Elgahzouli – Imperial College (London)

• Test at different loading rates (static, pseudo-dynamic, shake table)

• Tests at different structural scales (full-scale, subassemblies, members)

• Three NEES facilities linked in real time to conduct tests

Development of a PrecastFloor Diaphragm Seismic

Design Methodology (DSDM)Robert Fleischman, University of Arizona

Clay Naito and Richard Sause, Lehigh UniversityJose Restrepo and Andre Filiatrault, UC-San Diego

S.K. Ghosh, S.K. Ghosh Associates, Inc.

12

TeTeTe

Side Walls

Load Cell

Floor Diaphragms

Shake Table

ReactionWall

Steel Base withCantilever Outriggers

6 ft – 6 in

Research Approach:Integrated Analysis and Experimentation

• UA Analyses link UCSD structure level experiments with LU detail level experiments.

Demonstration of NEES for StudyingSoil-Foundation-Structure Interaction

University of Texas: S.L. Wood, E.M. Rathje, K.H. StokoePurdue University : J.A. RamirezSan Jose State University : T. Anagnos, K.M. McMullinUniversity of California, Berkeley: G.L. FenvesUniversity of California, Davis: B. Jeremic, B.L. Kutter, D.W. WilsonUniversity of Illinois: J.M. FutrelleUniversity of Kansas: A.B. MatamorosUniversity of Michigan: T.A. FinholtUniversity of Nevada, Reno: M. Saiidi, D.H. SandersUniversity of Washington: P. Arduino, M.O. Eberhard, S.L. Kramer

13

Soil-Foundation-Structure Interaction

• Prototype structure – reinforced concrete, continuous bridge on drilled shaft foundations.

• Behavior is influenced by ground motion and nonlinear characteristics of the soil, foundation, and structure.

• Not possible to test a single physical model and reproduce all the key aspects of system performance.

NEES Model for Research• Four series of complementary models will be

tested, each conducted at a different scale and designed to investigate a different aspect of the nonlinear response of the prototype structure.

• Computational simulations will be used to interpret the response of the individual experiments, quantify the limitations of each experiment, and model the response of the prototype system.

14

Prototype Structure

Centrifuge Tests

Field Tests

Structural Tests

Shaking Table Tests

NEES is an opportunity

• To improve performance under earthquake excitation

• To conduct research in a new way• To look at the future of collaborative

research

Proceedings, Third UJNR Workshop on Soil-Structure Interaction, March 29-30, 2004, Menlo Park, California, USA.

Opportunities for Soil-Structure Interaction Research Via ANSS

Mehmet Çelebi,a) and Janise Rodgersa)

The purpose of this paper is to introduce two integrated arrays each consisting

of building and free-field arrays that can be used for soil-structure interaction

(SSI) research. One of these arrays is funded by Advanced National Seismic

Systems (ANSS), a new initiative managed by the United States Geological

Survey. Through this new initiative, 6000 three-channel or equivalent

accelerometers are aimed to be deployed in seismic urban areas of three United

States. Of particular interest is the recommendation that SSI related deployment

be given high priority. The two arrays serve as examples for further deployments

in building structures to facilitate SSI research. Furthermore, limited data is

available from both arrays to facilitate SSI research.

INTRODUCTION

State-of-the-art knowledge and analytical approaches require, when warranted, the

structure-foundation system to be represented by mathematical models that include the

influence of the sub-foundation media. Identification of beneficial and adverse effects of soil-

structure-interaction (SSI) is a necessity. Adverse effects of SSI during the 1985 Michoacan

(Mexico) earthquake were addressed by Tarquis and Roesset (1988), who showed that, in the

lakebed zone of Mexico City, fundamental periods of mid-rise buildings (5-15 stories)

lengthened due to SSI. Thus, such buildings became vulnerable because their lengthened

periods were close to the now well known 2-s resonating site period of the lakebed zone.

Therefore, it is necessary to further study theoretically and verify through field experiments,

the implications of soil-structure interaction effects on the dynamic behavior and

performance of structures. To this end, since 1978, during several workshops and technical

meetings, specific recommendations have been repeatedly made to instrument a building for

soil-structure interaction studies (e.g. Lee, Marcuson, Stokoe and Yokel, 1978; Iwan, 1978

a) United States Geological Survey, Menlo Park , Ca. 94025

1

and 1981). On November 4--5, 1991, during the NSF workshop on ``Experimental Needs for

Geotechnical Earthquake Engineering,'' held in Albuquerque, New Mexico, strong-motion

instrumentation for soil-structure interaction was given a high priority. Of particular

significance is the high-priority recommendation in the recent USGS Circular 1079 titled

"Goals, Options, and Priorities for the USGS Earthquake Hazards Reduction Program" (Page,

Boore, Bucknam and Thatcher, 1992), ``Priority should be given to deploying both special-

purpose arrays and networks designed to provide data for a wide variety of purposes. These

deployments should include near-fault dense arrays and networks to determine earthquake

source processes, regional arrays to determine seismic-wave propagation characteristics

between the source and the site, downhole arrays to study the effects of local geologic

conditions on modifying ground motions, special deployments to study soil-foundation

interaction and the response of structures, and instrumentation of carefully chosen sites with

the potential for liquefaction or landsliding.''

Until 1992, there have been no meetings to directly discuss the detailing of a soil-

structure interaction experiment except the ones related to the nuclear power industry (e.g.

the Lotung array) – which is outside the scope of this paper.

In 1992, a workshop specifically dedicated to the subject, recommendations were made to

the effect that it is necessary to develop arrays for field conformation of soil-structure

interaction (SSI) effects to improve current methodologies and develop new ones for analyses

and design (Çelebi, Lysmer, and Luco, 1992). Recently, under the auspices of Panel on

Wind and Seismic Effects of the United States - Japan Natural Resources Development

Program (UJNR), two workshops on "Soil-Structure Interaction " (SSI) were organized.

(a) The first workshop was held in Menlo Park, CA on September 22-23, 1998. U.S. Geological Open-File Report 99-143 was issued as the proceedings of that workshop (Çelebi and Izuru, 1999).

(b) The second workshop was held in Tsukuba, Japan on March 6-8, 2001 (Proceedings, The 2nd UJNR Workshop on Soil-Structure Interaction, Tsukuba, Japan, March 6-8, 2001 – CD- ROM)

Both workshop presentations covered:

• Current methods of SSI used in design/analyses processes in both Japan and the United States,

• Recent research that is being carried out, and

2

• Experimental SSI research arrays and/or facilities developed and that are in the process

of being developed and • Searching ways to cooperate on future SSI research.

Another recent workshop identified evaluation of soil-structure interaction as one of the

most important measurement objective for strong-motion instrumentation of buildings

(COSMOS, 2001). Through recent Network for Earthquake Engineering Simulation (NEES)

initiative by National Science Foundation, several large-scale testing and field facilities that

can be used for SSI research (e.g. Youd et. al., 2004, this volume) are now funded. A new

initiative, Advanced National Seismic System (ANSS1) managed by the U.S. Geological

Survey (USGS) opens the door to opportunities to advance SSI research that can result in

evaluation of current methods on real-life structures as it proposes to deploy 3000 (3-

channel) instruments to monitor built environment in seismic urban areas of the United

States.

Thus, it is fair to state that opportunities for advancing field deployment of seismic

instruments in actual buildings for SSI research and assessment are being developed. In this

paper, two such prototype cases of buildings instrumented are presented. These cases can

provide opportunities for SSI research. The scope does not introduce results to date but rather

provide information relevant for SSI research.

TWO ARRAYS FOR SSI RESEARCH

ARRAY 1 - ATWOOD BUILDING (ANCHORAGE, AK)

The Building and Site Conditions

The Atwood Building is 20 stories tall and is located in downtown Anchorage. The

building is (1) a steel moment-resisting framed structure with only one level of basement, (2)

130’x130’ (39.6 m x 39.6 m) in plan and (3) 264’ (80.5 m) tall. The building foundation is

without any piles and consists of 5’ (1.52 m) thick reinforced concrete mat below core and

with 4’6” (1.37 m) thick reinforced concrete perimeter mat interconnected with grade beams.

1 ANSS: Advance National Seismic System – an intiative to expand and upgrade the seismic network system in the United States, authorized by U.S. Congress and administered by the U.S. Geological Survey (USGS Circular 1188).

3

It is well known that downtown Anchorage is underlain by an approximately 100-150-

feet (30.5 – 45.7 m) thick soil layer known as the Bootlegger Cove Formation, where

considerable ground failures occurred during the 1964 Great Alaska earthquake. Thus, during

earthquakes of various levels of shaking, recording the response and then assessing the

behavior of structures at such sites and the sites themselves is of interest to the engineering

community as the next large earthquake will most likely affect the performance of structures

at such sites.

Instrumentation

For that reason, it is important to take measures in advance not only to design structures

better with the best known methods but also to take it one step further by monitoring the

shaking response of the structures in the most efficient way to capture data to enable (a)

response studies, (b) assess the performance and (b) draw conclusions for future designs

and/or retrofit or strengthening of similar structures. In this specific case, seismic

instrumentation and monitoring of the Atwood Building is deemed to be important not only

to shed light on the behavioral issues related to this particular building but also overall

generic response issues related to such buildings on soft underlying geotechnical media such

as that beneath downtown Anchorage. Therefore, interest in the performance of this

particular building as well as similar buildings built on such a site and in a highly active

seismic environment makes this a very desirable building to monitor during strong shaking

events.

To meet the above objectives, the building instrumentation has two distinctive

components integrated to provide answers to shaking response issues as they pertain to the

particular building with its (a) specific structural system and foundation without any piles and

(b) associated free-field and borehole array in close proximity to the building. General three-

dimensional schematic of the building as well as the free-field surface and downhole array is

provided in Figure 1.

The instrumentation within the building is designed to record (a) its lateral swaying, (b)

twisting, (c) drifts (displacement between selected two consecutive floors) or average drifts

between any two floors, and (d) rocking of the building which is related to interaction of the

building with the underlying soil such that the shaking characteristics are altered due to such

interaction. Quantification of this phenomenon is of utmost importance for defining the role

of such soil-structure interaction in design and analyses of future structures.

4

The associated downhole array consists of surface and downhole instruments deployed at

various depths to capture the response of varying layers of soil and how such layering affects

the changes in the characteristics of earthquake motions as they travel and hit the surface and

affect the shaking of the structures.

With the integrated downhole, surface and superstructure arrays, propagation of motions

starting from the downhole to the roof of the building can be captured.

A Recorded Earthquake and Preliminary Analyses

Recorded acceleration and computed (double-integrated) displacements from the

superstructure array of the building2 during the December 15, 2003 (Ms=3.7) Point

MacKenzie, Alaska earthquake are provided in Figure 2. The building is 18.8 km distance

from the epicenter of the earthquake. The largest peak acceleration recorded in the building

array is less than 0.02 g. The figure shows clearly the propagation of waves from basement to

the roof of the building. Although at this low level shaking, clear SSI effects are not detected,

Figure 3 shows the amplitude spectra of the two parallel NS motions, their difference and the

EW motions at the roof and clearly identifies relevant structural frequencies. Figure 4 shows

that the two basement motions are coherent for several frequencies one of which may be due

to rocking. Further analyses on this subject is being carried out.

ARRAY 2 - PACIFIC PARK PLAZA BUILDING (EMERYVILLE, CA)

The Building and Site Conditions

Pacific Park Plaza Building is a thirty-story, 312 ft. (95.1 m) tall, ductile reinforced

concrete moment-resisting frame building. The three wings of the building are constructed

monolithically and are equally spaced at angles of 120 degrees around a central core. Shear

walls in the center core and wings extend to the second floor level only, but column lines are

continuous from the foundation to the roof. The foundation consists of a 5 ft. (1.8 m) thick

reinforced concrete mat over friction piles driven beneath column lines.

2 At the time of the earthquake, the surface and downhole free-field array was not activated.

5

Figure 1. General three-dimensional schematic of the Atwood Building (Anchorage, AK) showing the general dimensions and locations of deployed accelerometers within the structure and at free field with tri-axial downhole accelerometers.

6

0 10 20 30 40 50 60

0

10

20

30

40

50

TIME(S)

AC

CE

LER

AT

ION

(C

M/S

/S)

ATWOOD BUILDING: DECEMBER 15, 2003 EQ. [NS]

ROOF(CH30)

20TH FL.(CH27)

19TH FL.(CH24)

14TH FL.(CH21)

12TH FL.(CH18)

8TH FL.(CH15)

7TH FL.(CH12)

2ND FL.(CH9)

GR. FL.(CH5)

BASEMENT(CH2)

10 11 12 13 14 15 16 17 18 19 20

0

10

20

30

40

50

TIME(S)

AC

CE

LER

AT

ION

(C

M/S

/S)


BASEMENT(CH2)

GR. FL.(CH5)

2ND FL.(CH9)

7TH FL.(CH12)

8TH FL.(CH15)

12TH FL.(CH18)

14TH FL.(CH21)

19TH FL.(CH24)

20TH FL.(CH27)

ROOF(CH30)

0 10 20 30 40 50 60

-0.06

-0.04

-0.02

0

0.02

0.04

TIME(S)

DIS

PLA

CE

ME

NT

(C

M)


ROOF(CH30)

20TH FL.(CH27)

19TH FL.(CH24)

14TH FL.(CH21)

12TH FL.(CH18)

8TH FL.(CH15)

7TH FL.(CH12)

2ND FL.(CH9)

GR. FL(CH5)

BASEMENT(CH2)

10 11 12 13 14 15 16 17 18 19 20

-0.06

-0.04

-0.02

0

0.02

0.04

TIME(S)

DIS

PLA

CE

ME

NT

(C

M)


BASEMENT(CH2)

GR. FL(CH5)

2ND FL.(CH9)

7TH FL.(CH12)

8TH FL.(CH15)

12TH FL.(CH18)

14TH FL.(CH21)

19TH FL.(CH24)

20TH FL.(CH27)

ROOF(CH30)

Figure 2. (top and bottom left) Sixty seconds of the responses recorded from the NS oriented accelerometers on the west end of the Atwood Building, (top and bottom right) Ten seconds of the acceleration and displacement responses showing propagation of waves from basement to the roof.

0 5 100

100

200

300

Am

plitu

de(c

m/s

)

CH30-CH31

0 5 100

500

1000

FREQ (HZ)

Am

plitu

de(c

m/s

)

ROOF

CH30[360]

CH31

CH32

[90]

0 5 100

500

1000

FREQ (HZ)

Am

plitu

de(c

m/s

) CH32

0 5 100

0.5

1

Coh

eren

ce

0 5 10

100

0

100

FREQ (HZ)

Pha

se (

deg)

0 5 100

50

100

Sxy

ROOF [CH30 & CH31]

[360](d)

(b)

(c)

(e)

(f)

(a)

Figure 3. Amplitude spectra of accelerations recorded at the roof from the (a) two parallel translational accelerometers (Channels 30 and 31) in NS direction, (b) difference of Channels 30 and 31, (c) translational accelerometer (Channel 32) in the EW direction, and (d-f) the cross spectrum, coherence and phase angle plots of the two parallel motions (Channels 30 and 31).

7

0 2 4 6 8 10 12 14 16 18 200

0.5

1

CO

HE

RE

NC

E

0 2 4 6 8 10 12 14 16 18 20

-100

0

100

FREQ (HZ)

PH

AS

E(D

EG

.)

0 2 4 6 8 10 12 14 16 18 200

1

2

Sxy

ATWOOD: BASEMENT: VERTICAL(NE) AND VERTICAL(NW)

Figure 4. Cross Spectrum, coherence and phase angles of the two vertical motions at the basement.

Based on a relatively recent geologic log and shear wave velocity profile (Gibbs, et al.,

1994), the soils at the site consist of artificial fill, soft silty clay (Holocene Bay Mud), and

stiff to very stiff undifferentiated deposits composed of numerous layers of clay, loam, sand,

and gravel. The layer of Holocene Bay Mud, clearly evident on the shear wave velocity

profile shown in Figure 5a, begins at about 16 ft. (5 m) depth and is approximately 10 ft. (3

m) thick. Stiff deposits with shear wave velocity (Vs) of approximately 820 ft/s (250 m/s)

extend from below the Holocene Bay Mud to a depth of approximately 80 ft. (24 m). Very

stiff Pleistocene deposits with Vs approximately equal to 1300 ft/s (400 m/s) extend to a

depth of about 155 ft (48 m). The site transfer function calculated using Haskell’s shear-wave

propagation method (Haskell, 1953, 1960) using the shear wave velocity profile in Figure 5a

is plotted in Figure 5b, and indicates a site frequency at approximately 0.7 Hz.

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50

1

2

3

4

5

FREQ (HZ)

TRA

NS

FER

FU

NC

TIO

N

SITE TRANSFER FUNCTION: EMERYVILLE - SITE OF PPPLVE (KM/S)

DE

PTH

(M)

0

150

100

50

0.60.40.20

Figure 5. (a-left) Shear wave velocity profile and (b-right) Computed site transfer function

8

Instrumentation

A three-dimensional schematic of the Pacific Park Plaza Building and its integrated

structure, surface, and downhole arrays is shown in Figure 6. The instrumentation scheme is

uniquely designed to capture (a) the translational motions of the wings of the building

relative to its core, (b) the vertical motions of the mat foundation slab at the ground floor

level, and (c) free-field motions at the surface and at a downhole depth of 200 ft (61 m).

A Recorded Earthquake and Preliminary Analyses

The responses of the building and the surface free-field were recorded during the October

17, 1989 Loma Prieta earthquake. Significant research has already been done using these

records.

Important features of the particular data set from the Loma Prieta earthquake includes

amplified motions (Figure 7) at the site of the building as compared to the motions at Yerba

Buena Island (both approximately 100 km from the epicenter of the Loma Prieta earthquake).

Figure 8 shows cross spectra of orthogonal horizontal accelerations at the core of the

building roof and ground floor and SFF and their superimposed normalized spectra.

From the earthquake records, a building first mode frequency at 0.38 Hz is clearly

identified. Also identified is the site frequency at 0.7 Hz (Safak,and Çelebi,1992 and Çelebi

and Safak, 1992, Çelebi, 1998).

Extended data sets from this building include not only the Loma Prieta earthquake

response data but also those from forced and ambient vibration tests performed by Stephen

et. al (1985) as well as those by Marshall, Phan and Çelebi (1992) and Çelebi, Phan and

Marshall (1993). Dynamic characteristics of the building extracted from the data sets are

summarized in Table 1 and show considerable differences in the fundamental frequency

extracted from strong shaking versus low-amplitude shaking. The differences are attributed to

SSI effects during strong shaking (Çelebi, 1998, Kagawa, Aktan and Çelebi, 1993, Kagawa

and Al-Khatib, 1993, Kambhatla, Aktan, Kagawa and Çelebi, 1992).

9

Figure 6. A three-dimensional schematic of the building array with integrated surface and downhole array [Note: The downhole accelerograph was added after the 1989 Loma Prieta earthquake).

10

0 10 20 30 40

0

0.5

1

TIME (S)

AC

CE

L. [G

]

LPE (EW): PPP & YBI

ROOF

GR.FL.

SFF

YBI

PEAK=0.38 G

PEAK=0.21 G

PEAK=0.26 G

PEAK=0.06 G

101

100

101

0

0.5

1

PERIOD (S)

SP

EC

. AC

CE

L. [G

]

LPE (EW): PPP & YBI

YBI

ROOF

SFF

GR.FL.

.06

.38

Figure 7. Amplified (EW) motions and their corresponding response spectra (5% damped) at the South Free-Field (SFF), ground floor and roof of the Pacific Park Plaza array as compared to the motions at Yerba Buena Island (YBI).

Figure 8. Cross-spectra of roof, ground floor and SFF motions and their superimposed normalized plot (lower right).

11

Table 1. Dynamic Characteristics of Pacific Park Plaza

FREQUENCIES (HZ) DAMPING (%)

MODE MODE

1 2 3 1 2 3

1990 AMBIENT TESTS (from Çelebi, Phan and Marshall, 1992)

N-S 0.48 0.6

E-W 0.48 3.4

1989 (LPE) STRONG-MOTION (from Çelebi, Phan and Marshall, 1992)

N-S 0.38 0.95 1.95 11.6

E-W 0.38 0.95 1.95 15.5

1985 FORCED VIBRATION TESTS (from Stephen et.al, 1985)

N-S 0.590 1.660 3.09 1.7 1.3 2.9

E-W 0.595 1.675 3.12 1.8 1.9 3.2

Torsion 0.565 1.700 3.16 1.5 1.32 1.7

1985 AMBIENT VIBRATION TESTS (from Stephen et.al., 1985)

N-S 0.586 1.685 3.149 2.6 1.8 0.8

E-W 0.586 1.685 3.125 2.6 1.2 0.4

Torsion 0.586 1.709 3.125 3.8 1.4 1.0

MODAL ANALYSES (Rigid [R] & Flexible [F] Foundation) (from Stephen et.al. 1985) N-S

R

F

0.596 0.595

1.666 1.650

3.115 3.081

E-W

R

F

0.596 0.595

1.666 1.650

3.115 3.081

Torsion

R

F

0.565 0.562

1.711 1.686

3.275 3.220

CONCLUSIONS

Two integrated arrays of building and free-field arrays that can be used for soil-structure

interaction (SSI) research are introduced. One of these arrays is funded by the Advanced

National Seismic System (ANSS), a new initiative managed by the United States Geological

Survey. Through this new initiative, 6000 three-channel or equivalent accelerometers are

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intended to be deployed in seismic urban areas of the United States. In this initiative and

numerous scientific meetings, strong recommendations for SSI related deployment were

made. The two arrays can be an example for further deployments in building structures to

facilitate SSI research. However, very limited data is available from both arrays to facilitate

SSI research at this point.

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SFSI Monitoring at NEES Permanently Instrumented Field Sites

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