real-time dynamic hybrid testing for soil-structure interaction analysis

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Tsinghua UniversityHydraulic engineering

department

1Module und Variations_E

Real-time dynamic hybrid testingfor soil-structure interaction analysis

Wang Qiang & Zhang Chuhan

2009-10-15


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CONTENTS

2

3

4

5

Introduction of soil-structure interaction

RTDHT system in Tsinghua University

Soil-structure interaction model

SSI-RTDHT test setup

SSI-RTDHT test results

1

6 CONCLUSION


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Soil and structure should be considered as a whole system in dynamic analysis.

Introduction of soil-structure interaction1

Direct method Substructure method

the structure and the soil are treatedas two different substructures.

Each substructure can be analyzedusing a best-suited computational

technique.

Combining the force-displacementrelationship of the soil with the

discretized motion equation of the

structure, results in the final systemof equation of the total dynamic

system.

the structure and soil are treatedas a whole system.

The region of the soil adjacent tothe structure-soil interface is also

explicitly modeled.

Artificial boundary must beintroduced so as to cover the

unbounded soil domain.


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Considering SSI in shaking-table tests is still a problematic option.


Model box with finite region of soil Model boundary with damping material

(Chen, et al. 2005) (Li, et al. 2003)

Shaking

table

Finite

region ofSoil

structure


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Combining the numerical calculations of semi-infinite soil together withsuperstructure large scale model testing.


RTDHT


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RTDHT system in Tsinghua University2

Distributed real-time calculation system

Host PC Ordinarycomputer with

Windowsoperating system

Target PC Ordinarycomputer without

Windows operatingsystem (but xPC

kernel)

Software Matlab,Simulink,

Real-time workshop,xPC target

Shared common RAM network

high-speed:16.7 Mb/s

ultra-low-latency:250 ns

SCRAMNet cardSC150

Optical cableShaking table loading system

Area:1.5m 1.5 m

Bearing capacity:2 t

Max acceleration:3.6 g (bare table)1.2 g (full loaded)

Frequency:0~50 Hz

MTS 469D controller:Mathworks Simulink is integratedinto the controller platform


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Soil-structure interaction model3

Lumped parameter model used in this paper

Luan Maotian & Lin Gao 1996


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Lumped parameter model used in this paper


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If the system is excited by harmonic force, the external force and displacement vector can be rewritten as follows:

Dynamic stiffness coefficient


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Dynamic stiffness coefficient


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SSI-RTDHT test setup4

Motion equation


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Concretize2

Soil properties: Mass denscity

Soft Soil: Hard Soil:

Cfe=3.016107 Ns/m

Kfe=2.513108 N/m

Mfe=3.619106 kg

Kfe=4.021109 N/m

Cfe=1.2064108 Ns/m

Mfe=3.619106 kg


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Substructuring3

1

2

Physical substructure

Numerical substructure


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Model and measurements4

AccelerometerFor accelerationmeasurement

Strain gauges bridgeFor shear forcemeasurement

LVDTFor displacementmeasurement

NI DAQFor data acquisition


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Procedure of SSI-RTDHT5


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SSI-RTDHT test results5

The mesh boundary is far enough so that the effect of the wave reflection and scattering from boundary on

the structure-soil interface response can be avoided during the calculation duration.

1. Far boundary FEM


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2. Artificial wave


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3. Accuracy verification of lumped paremeter model

Peak comparison

LPM: 1.226 gFEM: 1.147 g.

Error: 6.9 %

Peak comparison

LPM: 0.793 gFEM: 0.773 g

Error: 2.6 %


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Peak comparison

LPM: 9.751 mmFEM: 9.594 mm

Error: 1.6 %


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Peak comparison

LPM: 635.1kNFEM: 597.3 kN

Error: 6.33 %

Peak comparison

LPM: 688.7kNFEM: 689.6 kN

Error: 0.13 %


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4. Accuracy verification of SSI-RTDHT

Peak comparison

SSI-RTDHT: 1.317 gFEM: 1.147 g

Error: 14.8 %

Peak comparison

SSI-RTDHT: 1.179 gFEM: 0.773 g

Error: 52.5 %


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Peak comparison

SSI-RTDHT: 10.39 mmFEM: 9.594 mm

Error: 8.3 %


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Peak comparison

SSI-RTDHT: 659.7 kNFEM: 597.3 kN

Error: 10.4 %

Peak comparison

SSI-RTDHT: 728.2 kNFEM: 689.6 kN

Error: 5.6 %


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5. SSI effect of different types of soil

Peak comparison

SOFT 0.40 gRIGID 0.55 g

REDUCT: 27.3 %

Peak comparison

SOFT 0.35 gRIGID 0.27 g

REDUCT: 22.9 %


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5. SSI effect of different types of soil

Peak comparison

SOFT 245 kNRIGID 399 kN

REDUCT: 38.6 %

Peak comparison

SOFT 196 kNRIGID 260 kN

REDUCT: 24.6 %


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CONCLUSION6

1. The lumped parameter model used in this paper can give a high accuracyapproximation of the infinite half space elastic foundation.

2. Comparing the SSI-RTDHT test results with the FEM results shows that SSI

-RTDHT can produce satisfying results in SSI analysis.3. Comparing the tests results under rigid foundation, hard soil foundation, and

soft soil foundation show that soil-structure interaction can affect the response of

the structure: softer the soil is, more obvious the SSI effect becomes.

Using the idea of RTDHT, the infinite soil foundation model calculation and

superstructure testing are combined together. Radiation damping of the infinitefoundation can be included in shaking-table tests.


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THE END

CONCLUSION

real-time dynamic hybrid testing for soil-structure interaction analysis

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