Sameh S. Badie, Ph.D., P.E.Research Assistant Professor

Civil Engineering DepartmentCollege of Engineering

and TechnologyUniversity of Nebraska-Lincoln

Omaha, Nebraska

Maher K. Tadros, Ph.D., P.E.Cheryl Prewett ProfessorConstruction Systems Technology DepartmentCollege of Engineering and TechnologyUniversity of Nebraska-LincolnOmaha, Nebraska

Elimination of expansion joints in bridge decksresults in initial economy and long-term durability. Itprovides a smooth-riding surface, minimizesmaintenance cost caused by water leakage, andprovides a relatively high span-to-depth ratio of thesuperstructure. This paper presents a summary of theresults of a project whose dual objectives were toreduce the cost of bearing devices used in jointlessbridges and to optimize the girder/pier joint detailsfor economy, constructability and aesthetics. Criteriafor selection of bearing devices as a function of loadlevels, translational and rotational capacities,simplified diaphragm details, simplified fixed andexpansion bearing details, and enhancements ofbridge aesthetics are presented. Cases where a sharpskew exists in the bridge are covered. With the largebottom flange of modern I-girder shapes, it is shownhow girder ends are produced with a skew tominimize the pier width.

Application of precast, prestressed girders to bridgeconstruction started in the United States in the early1950s. Since then, the use of pretensioned I-girders

with cast-in-place (CIP) concrete decks has grown rapidly. Until the early 1960s, bridges built with pretensioned

I-girders and CIP concrete decks were designed and con-structed as simply supported spans with expansion joints atpier supports. Although this type of construction providedsimple design and construction procedures, it created main-tenance problems. Leakage of deck joints combined withexcessive use of deicing chemicals resulted in serious main-

Re-Examination of I-Girder/Pier Connection in Jointless Bridges

62 PCI JOURNAL

Keith E. PedersenAssistant Professor

Construction Systems Technology Department

College of Engineering andTechnology

University of Nebraska-LincolnOmaha, Nebraska

March-April 2001 63

tenance and aesthetic problems in thesuperstructure bearing devices andsubstructure.

In the 1960s, a number of stateagencies1,2 started to build continuousjointless highway bridges with pre-stressed concrete girders. Jointlessbridges are bridges that are con-structed without any expansion jointsin the deck slab or girders at the piersor abutments.

The road surface is continuous fromone approach to the other and the su-perstructure is monolithically con-nected to the abutments. Superstruc-ture continuity for bridges is achievedby placing longitudinal reinforcementin the continuous deck slab above thepiers, providing negative moment ca-pacity for superimposed dead loadsand live loads.

Besides elimination of the mainte-nance costs associated with deckjoints, advantages of using jointlessbridges include improvement of ridingquality, increase of economy and im-provement of bridge aesthetics. Also,the ability to design the girders as con-tinuous for some of the load allows forlonger spans and higher span-to-depthratios.

In jointless bridges, longitudinalmovements that occur due to creep,shrinkage, and temperature effects, areaccommodated at the abutments usinga single row of steel HP piles. Thepiles are positioned with their weak

axis parallel to the transverse directionof the bridge deck and are embeddedin a flexible medium. Normally, this isloose sand which extends a short dis-tance to provide flexibility for the superstructure to expand and contract.

A number of states3 currently usejointless bridges as their standardsystem of construction. Among themare Nebraska, Oregon, Tennessee,Washington State, and West Vir-ginia. Examples of successful joint-less bridges include Route 50 Bridgeover Happy Hollow Creek, Ten-nessee,4 1175 ft (358 m) long, theU.S Highway 75 Viaduct in Ne-braska City, Nebraska,2 592 ft (180m) long, the I-469 Bridge over I-69,Fort Wayne, Indiana,2 270 ft (82 m)long, and the Deer Creek IndustrialPark Access Bridge, Barboursville,West Virginia,2 302 ft (92 m) long.

State agencies that use jointless pre-stressed concrete bridges generally putlimits on bridge length and skewangle2 as follows: (1) maximum bridgelength is between 600 and 800 ft (183and 244 m), and (2) maximum skewangle is between 40 and 45 degrees.

These limits have been set becauseof the significant movement that haveto be accommodated at the abutments.However, some states, such as Ten-nessee, have gone beyond these limitsand have built jointless bridges as longas 1175 ft (358 m) and a skew up to60 degrees.4

This paper covers the following topics:

1. Criteria for selection of bearingdevices that should be used with joint-less bridges; including effect of load-ing levels, movement levels, long-term durability and economics.

2. Role of pier diaphragms and howto simplify their details.

3. Simplified detailing of fixed bear-ings that restrain horizontal andvertical translations, and expansionbearings that restrain vertical transla-tion.

4. Recommendations for enhance-ment of bridge aesthetics.

SELECTION OF BEARING DEVICES

Bearing devices are used to transferloads from the bridge superstructure toits substructure in a controlled man-ner. Satisfactory bearing devicesshould:

1. Uniformly distribute concentratedvertical forces over an area largeenough to avoid high stress concentra-tions that may cause spalling andcrushing of the concrete.

2. Provide adequate flexibility toallow differential rotations of the con-nected members without transfer of sig-nificant moments into the substructure.

3. Allow translational movements ofthe superstructure relative to the sub-structure without inducing significant

Plain elastomeric Steel reinforced Cotton duck pads Fiber glass pads Random orientedParameter pads (PEP) elastomeric pads (CDP) (FGP) Pot bearings fiber pads

Users 65 percent 97 percent 13 percent Zero 42 percent Zero

Load, kips 100 800 300 150 2500 400-800(kN) (445) (3558) (1334) (667) (11,120) (1779-3558)

Rotation 0.010 0.040 0.003 0.015 0.020 0.080

Translation, in. 0.50 0.75 0.25 NA Zero if no sliding 0.75(mm) (13) (19) (6) surface is provided (19)

Initial cost$ per sq ft / per in. 28.00 280.00* 75.00 NA $2000 per bearing* 17.00✝

$ / m2 / mm (0.10) (1.05) (0.27) (0.06)

Maintenancecost Low Low Low Low High NA

Table 1. Summary of the survey results.

* Based on bid records of NDOR.✝ Price provided by the manufacturers.

64 PCI JOURNAL

horizontal forces into the substructure.Common types of bearing devices

that have been used in jointlessbridges are:

1. Elastomeric bearing pads that canbe produced in a plain or reinforcedform. Plain elstomeric pads (PEP)consist of an elastomer compoundblock that is extruded or molded intolarge sheets.

The sheets are polymerized and thencut to size. PEPs have low verticalload capacity and are susceptible to“slippage” from the contact area un-less they are adequately anchored.

Reinforced Elastomeric Pads (REP)can be reinforced with steel sheets,glass fibers (FGP), or other reinforce-ment materials. Reinforced pads arestiffer than plain elastomeric padsand can support higher vertical loads.The AASHTO Specifications5,6 allowthe use of reinforced elastomeric pads

as bearing devices in bridges. Also,plain pads are allowed within certainlimits.

2. Cotton Duck Pads (CDP) aremade of very thin elastomer layers,less than 1/60 in. (0.4 mm), and rein-forced with cotton ducks. CDPs arestiff and have larger compressive loadcapacities than PEPs, but they havevery little rotational and translationalcapacities. CDPs are sometimes usedwith a TEFLON or Polytetrafluorethy-lene (PTFE) sliding surface to accom-modate horizontal movements.

3. Pot bearings consist of a shallowcylinder or pot, an elastomeric pad, aset of sealing rings, and a piston. Ma-sonry plates and base plates are usedto allow attachment of the bearing andincrease the support area on the pier orabutment. Pot bearings are consideredas high-load multi-rotational bearingdevices. Pot bearings are more expen-

Fig. 1. Preliminary bearing selection diagram. CDP = Cotton Duck Pads, PEP = Plain Elastomeric Pads, ROF = Random Oriented Fiber Pads, SREP = Steel Reinforced Elastomeric Pads.

sive than other types mentioned aboveand have high maintenance costs.

In the 1980s, Random-Oriented-Fiber (ROF) pads were developed.ROF pads are a blend of an ozone-re-sistant rubber elastomer reinforced bya dispersion of synthetic fabric fiberscured together to form the final prod-uct. ROF bearing pads have under-gone some experimental investigationsfor more than 10 years.7-10 The experi-ments showed that ROF can supportcompressive stresses up to 8000 psi(55.2 MPa) in non-sliding bearingsand up to 2500 psi (17.2 MPa) in slid-ing bearings.9,10

ROF pads have the ability to accom-modate rotational deformation up to0.08 radians, which exceeds the practi-cal rotations for prestressed concretegirder ends under dead and live load.

Tests7,8 have shown that ROF padscan be used as an economical alterna-tive to steel reinforced elastomericpads. However, the AASHTO Specifi-cations5,6 do not recognize these padsas possible bridge bearing devices,which has significantly limited theiruse in bridge applications. It is recom-mended that the necessary steps betaken to develop an AASHTO ap-proval process to allow for the use ofthis product in bridge applications.

In a recent survey,3 sent by the au-thors to state agencies, PCI, ACI, andTRB concrete bridge committee mem-bers, participants were asked to statethe type of bearing devices currentlyused in bridges, and to comment ontheir economics and performance.Fifty-four responses were received, 31responses from state agencies and 23responses from consulting firms. Thesurvey results are listed in Table 1 andare discussed below:

1. The majority of state agencies (97percent) use steel reinforced elas-tomeric pads.

2. Plain elastomeric bearing pads(PEP) are used by 65 percent of the re-spondents. However, their use is lim-ited to short span bridges with lightloads and small horizontal move-ments. Most of the PEP users statedthat no “slippage” of the pads or mi-gration of anti-ozone waxes to the padsurface had been observed.

3. Forty-two percent of the respon-dents use pot bearings. However, their

March-April 2001 65

use is limited to extremely heavyloads.

4. Cotton duck bearing pads (CDP)are not common.

5. Fiberglass bearing pads (FGP) areseldom used in bridges.

6. Although ROF pads are struc-turally comparable to and significantlyless expensive than steel reinforcedelastomeric pads, they have not beenused by state agencies in bridges be-cause the AASHTO Specifications5, 6

do not recognize their use.Based on the literature review and

the survey,1-10 Fig. 1 can be used as apreliminary design guide for selectingbearing devices for bridges. The infor-mation shown in this figure has beenobtained from Refs. 9 to 11.

It is recommended to use ROF padsin bridges as a replacement of the steelreinforced elastomeric pads, unlesshigh bearing capacity is to be com-

bined with high translation, as shownin Fig. 1. Use of ROF will result insignificant dollar savings in bearingdevices.

Also, the authors recommend thatthe AASHTO Specifications5,6 recog-nize the use of ROF pads as accept-able bearing devices. Conservative re-quirements could be temporarilyimposed until more experience withsatisfactory performance of these padsis reported.

PIER-DIAPHRAGM DETAILS

Over the years, many details forjointless pier-diaphragm connectionshave been developed and used by stateagencies.

This section discusses the detailsthat have been used in recent years inthe United States.

Fig. 2. Fixed bearing detail. Note: 1 in. = 25.4 mm, #6 bar = 19 mm in diameter.

Fixed Bearing DetailsMost state agencies refer to a fixed

bearing as a joint that allows no hori-zontal or vertical translation but allowsrotation. Two alternatives have beenused for fixed bearing details. In bothalternatives, a continuous concrete di-aphragm is used. The difference be-tween them is the manner in whichvertical loads are transferred from thesuperstructure to the substructure.

The first solution fully relies on thebearing device with no contributionfrom the diaphragm. The second solu-tion provides for no special bearingdevice under the girder, and thus, fullyrelies upon the bearing between theconcrete diaphragm and the pier cap.Each concept has its advantages anddisadvantages.

An example of the first solution asused by the Nebraska Department ofRoads is shown in Fig. 2. The I-girders

66 PCI JOURNAL

are installed on reinforced elastomericbearing pads. A gap of about 8 in. (203mm) is usually maintained between thegirder ends.

Some strands from the girder bot-tom flange are extended beyond thegirder ends and bent into the gap be-tween the girders. These strands areused to resist the positive moment re-sulting from time-dependent effects.

Restraint of the joint against longi-tudinal and transverse translation isprovided by dowel bars extendingabove the pier cap for a distance two-thirds of the girder height. The dowelbars are located along the pier capcenterline. The diaphragm is cast to aheight of about two-thirds of thegirder height. The rest of the di-aphragm is cast with the deck con-crete. However, some state agenciescast the diaphragm totally with theconcrete deck. For more detailed dis-cussion of the merits of each construc-tion procedure, see Ref. 12.

Joint filler is generally installed be-tween the concrete diaphragm and thepier cap. Note that joint filler is usedto limit moment transfer between thegirders and the pier, and to make fu-ture superstructure replacement easier.

The bearing devices are designed totransfer the full vertical load. The sub-structure is designed to resist momentsdue to horizontal movement of the su-perstructure. This detail has been ex-tensively used in Midwestern andEastern states. Using this detail resultsin a relatively small pier cap width,but a high bearing device cost.

Fig. 3 shows an example of the sec-ond solution as used by the state ofWashington. The girders are temporar-ily supported on oak blocking wedgesplaced parallel to the diaphragm. Num-ber 7 or 8 (#22 or #25) reinforcing barsextend from the girder ends into thegap between the girders primarily forseismic resistance. A relatively widediaphragm is needed to develop these

bars. Also, some strands from the bot-tom flange of the girder are extendedand anchored into the diaphragm.

The girders are embedded in the di-aphragm for a distance of about 1 to 2in. (25.4 to 51 mm) only. This smallembedment length is intended to pro-tect the diaphragm from cracking dueto rotation of the girder ends. Thegirder ends are provided with sawtooth shear keys to help transfer verti-cal shear forces between the girderand the diaphragm.

A shear key is formed between thediaphragm and the pier cap to providethe diaphragm-pier joint with rota-tional capacity. Vertical dowel barsextending from the pier cap into thediaphragm are used to provide re-straint against longitudinal and trans-verse translations. After the diaphragmand the concrete deck are placed andcured, the oak blocks are removed.

This detail has been reported3 to bein use for over 25 years in several

Fig. 3. Washington State fixed bearing detail. Note: 1 in. = 25.4 mm.

March-April 2001 67

Western states. Using this detail re-sults in lower cost since no bearing de-vices are used. However, a wide piercap is needed to accommodate the oakblocks. In high seismic areas, di-aphragm reinforcement, if detailed asshown, would also result in wide di-aphragms and pier caps.

Expansion Bearing Details

Most state agencies refer to expan-sion bearings as a joint that allows novertical movement but permits hori-zontal and rotational movements. Fig.4 shows the expansion bearing detailwhere the I-girders are installed onsteel reinforced or fabric bearing padsthat accommodate the longitudinalmovement through shear deformationof the pad.

This detail is usually used withsmall longitudinal movements. It issimilar to the first fixed bearing detaildiscussed earlier except that no dowel

bars are used. Restraint against trans-verse movement of the superstructureis provided by the interlocking be-tween the cast-in-place diaphragm andthe pier cap pedestals.

If a large longitudinal movementthat cannot be accommodated by theelastomeric bearing pad is encoun-tered, a sliding bearing device is usedas shown in Fig. 5. The sliding bearingdevice consists of top and bottomparts. The top part is a steel sole platethat is welded to the girder base platein the field and attached to a thinstainless steel plate.

The sole plate is attached to the piercap by threaded anchor bolts embed-ded in the pier cap using slotted holesthat permit longitudinal movement,but restrain the transverse movementof the superstructure. The bottom partof the plate consists of a reinforcedelastomeric pad bonded to a TEFLONor Polytetrafluorethylene (PTFE) slid-ing surface.

RECOMMENDED JOINTLESS PIER DETAILSThis section discusses girder ends

with various skews, pier diaphragmusage, and fixed and expansion bear-ing details.

Girder Ends

For bridges with a large skew, a rel-atively wide pier cap is needed to sup-port the girders and maintain a 6 to 10in. (152 to 254 mm) wide gap betweengirder ends. Some state agencies, suchas Washington and Texas, use skewedgirder ends to reduce the pier capwidth. However, variable skewedgirder ends result in increased cost ofgirder production due to the fabrica-tion of many special end forms.

To minimize fabrication costs, it isrecommended that three standardgirder ends be used as follows: (1) forpiers with a skew between zero and 15degrees, do not skew girder ends; (2)

Fig. 4. Expansion bearing detail with non-sliding interface.

68 PCI JOURNAL

for piers with a skew between 15 and45 degrees, skew girder end 30 de-grees; and (3) for piers with a skew be-tween 45 and 65 degrees, skew girderend at 55 degrees, as shown in Fig. 6.

Steel Pier Diaphragms

Forming of continuous concrete di-aphragms over piers is usually timeconsuming and expensive becauseform dimensions depend on girderspacing, girder height, and skew angleof the pier. Thus, different forms haveto be used for each project.

According to a local contractor’s fig-ures in the Midwest area, forming, plac-ing reinforcement, and concrete placingfor a concrete diaphragm of a typicaloverpass bridge takes as much time asone week and costs about 500 dollarsper cubic yard of the diaphragm.

From a structural viewpoint, manydesigners believe that concrete di-aphragms over piers are required to:

1. Form the compression block forthe negative moment over piers that

occurs due to superimposed deadloads and live loads;

2. Transmit vertical loads from thesuperstructure to the substructure;

3. Distribute lateral forces due towind, braking, and collision to allgirders of the bridge; and

4. Accommodate reinforcement re-quired to resist positive moments dueto time-dependent effects.

Although these design issues arevalid, a concrete diaphragm may notbe the most economical solution tosatisfy these design concerns.

Fig. 7 shows a detail where the con-tinuous concrete diaphragm is omitted.Its function is satisfied through a com-bination of two elements, namely, asteel diaphragm and a concrete jointbetween girder ends.

A steel diaphragm, made of platesbent into channel shapes, is structurallydesigned to transmit the transverseforces from the girder to the substruc-ture. The connection between the gird-ers and the deck slab would be part ofthe transverse load resisting system.

Generally, one-half of the transversewind load is assigned at the deck slaband the other half is carried directly bythe girder bearing devices. The load atthe slab can be applied to a “rigidframe” that consists of the top slab, thegirder stems, and the steel diaphragm.

The steel pier diaphragm for skewedbridges may follow the pier skew orbe arranged in a stepped pattern per-pendicular to the longitudinal axes ofthe girders, as shown in Section A-Ain Fig. 7. If the girder depth is greaterthan 5 ft (1.5 m), the steel bent platesmay be replaced with diagonal bracingmembers. The Nebraska Departmentof Roads (NDOR) has already imple-mented this detail in the design of oneof its bridges.

Concrete is placed in the joint be-tween girder ends. It follows the sameprofile as that of the girders. The samesteel forms, as used for production ofthe concrete girder, can be used toform the joint. Strands that are ex-tended and bent into the concrete jointbetween girder ends, to resist positive

Fig. 5. Expansion bearingdetail with sliding

interface. Note: 1 in. = 25.4 mm.

March-April 2001 69

moment due to time-dependent ef-fects, should be of a length that allowsa 2 in. (50 mm) concrete cover, asshown in Detail C and Section D-D inFig. 8.

The ACI 318-99 Code13 states thatfor 270 ksi (1861 MPa) strands thatare used as non-prestressed reinforce-ment, a maximum tensile strength of90 ksi (620 MPa) can be utilized.

In an experimental program con-ducted at the Universi ty of Ne-braska,14 test results showed that a270 ksi (1861 MPa) low relaxationstrand that is embedded in the di-aphragm of a girder for a distance of10 in. (254 mm) is capable of devel-oping 90 ksi (620 MPa) tensi lestress. Therefore, the total embed-ment length of the strands in thejoint between the girder ends, withboth horizontal and vertical legs in-cluded, should be a minimum of 10in. (254 mm). If space allows formore strand extension, Ref. 13 gives

guidelines for the capacity that canbe developed.

Fixed Bearing Detail

Fig. 9(a) shows the proposed fixedbearing detail, where a random ori-ented fiber (ROF) bearing pad is usedto support two precast girder ends.The pier location and the girder endsare skewed according to the schemementioned above. A high strengthdowel rod is used to restrain the trans-verse and longitudinal movement ofthe girder.

The dowel rod extends in the jointbetween the girder ends, and in the piercap enough distance to develop its ca-pacity in direct shear. A standard 18 in.(457 mm) embedment length would beadequate in most practical applications.The size of the dowel rod is determinedfrom the expected longitudinal move-ment of the girders and the relative su-perstructure/substructure stiffness.

The standard practice in the state ofNebraska has been to use a #6 (#19)Grade 60 steel bar at 12 in. (305 mm)spacing for continuous concrete di-aphragm applications. It is suggestedthat the equivalent to this reinforcementbe also reasonable with the recom-mended details. Therefore, for a girderspacing of “S” in feet, it is suggestedthat the dowel rod resist a shear forceequal to (0.44 sq in./ft)(0.67x60 ksi)(Sft) = 17.7S kips. This detail may resultin a 3 ft (0.91 m) wide pier cap for askew angle as much as 45 degrees, andfor beams where bottom flanges are aswide as 48 in. (1250 mm).

Expansion Bearing Detail

Fig. 9(b) shows the recommendedexpansion bearing detail, where indi-vidual sliding bearing pads are used tosupport the girders. Steel side anglesare used to restrain the transversemovement. The angles are seated on

Fig. 6. Proposed skew angles of precast girder ends.

70 PCI JOURNAL

Fig. 7. Superstructure/pier details with steel diaphragm. Note: 1 in. = 25.4 mm.

Fig. 8. Anchorage of bottom flange strands into joint between girder ends. Note: 1 in. = 25.4 mm.

March-April 2001 71

1/4 in. (6 mm) pads to ensure full con-tact with the pier cap. The size of thebolts used to connect the angles to thepier cap is determined from the trans-verse load on the bridge superstructure.

The area under the girders that is notcovered with the bearing pads and thearea under the joint between girderends are covered with joint filler. Thisis to protect these areas from beingfilled with concrete while placing theconcrete joint, and from debris thatmay accumulate with time.

The sliding bearing device is installedparallel to the girder end to minimizepier cap width. It consists of bottom andtop parts as shown in Fig. 9(c). The bot-tom part is a bearing pad with TEFLON(PTFE) sliding surface, which is in-stalled in a 1/2 in. (13 mm) recess cre-ated in the pier cap top surface.

Based on the vertical load that needsto be transmitted, a random orientedfiber or a steel reinforced elastomericpad can be used. The top part consistsof a beveled steel plate with a stainless

Fig. 9. Recommended bearing details. Note: 1 in. = 25.4 mm.

Fig. 10. Hammer head pier currently used by Nebraska Department of Roads.

steel surface. The beveled plate is usedto accommodate the longitudinal slopeof the bridge, if desired.

The top part should be temporarilyattached to the girder base plate beforeinstallation of the girder. In the produc-tion of the girders, a 1/2 in. (13 mm)deep recess should be created under thebase plate of the girder to help confinethe top bearing part in its final position.

BRIDGE AESTHETICSBridge aesthetics are relatively im-

pacted by the difference in color be-tween various types of concrete used.For example, a color difference can beobserved on the side elevation of abridge between the pier cap and the di-aphragm, between the diaphragm andthe precast girders, and between the

72 PCI JOURNAL

precast girders and the barriers. Also,aesthetics are affected by leakage in thejoints between various concrete place-ments as shown in Fig. 10. In order toenhance bridge aesthetics, the follow-ing recommendations are offered:

• Add a bottom ledge to the barrier tohide the deck slab, as shown in Fig.7. This ledge is intended to hide thedifference in color between thedeck slab concrete and the barrier.Also, it will hide any stains that

Fig. 11. Recommended

details to enhanceaesthetics.

Aesthetic pier cap detail.

Fig. 12. Hammer head

pier with ledgesthat cover the

superstructure/pierjoint used by

Texas Departmentof Transportation.

may occur due to possible waterleakage.

• Use the steel diaphragm detail shownin Fig. 7. This would result in an un-interrupted exterior surface of theexterior girders. The exterior surfaceof the joint between girder ends willbe difficult to hide. Rather, attemptto accentuate it by using a form linerto create recess.

• A ledge should be added to the piercap to hide the side view of the di-aphragm, as shown in Fig. 11. Thisconcept has been used in Texas asshown in Fig. 12.

• Bridge aesthetics can be greatly en-hanced by modifying the shape ofthe pier support. Fig. 10 shows the“hammer head” pier that is cur-rently used by the Nebraska Depart-ment of Roads (NDOR). The piercap has side slopes and the pier col-umn has chamfers. Form liners areused to give the pier column vari-ous surface textures. For bridgeswider than 50 ft (15.2 m), a multi-hammer-head pier is used as shownin Fig. 10.

March-April 2001 73

• It is strongly recommended to stainthe outside surface of the barriers, ex-terior girders and pier with a colorsealing stain. This will conceal thedifference in color between variousconcrete pours and will work as asealant to protect concrete from mois-ture related discoloration. Also, it willsimplify graffiti removal, if present. Stain products should have the fol-

lowing properties: (1) uniformity ofappearance, (2) color retention, (3) nopeeling or flaking as it penetrates andmechanically locks into pores of theconcrete, (4) non-oxidizing as it doesnot contain any oxidizing ingredientssuch as vegetable or paraffin, and (5)fast drying. Some states, such as Washington,

have a long and successful experiencewith staining products. These productscan be brushed, rolled, or sprayed.They cost only 10 to 15 cents per sq ft of the covered area. Figs. 13(a)and 13(b) show photographs of theTacoma I-5 Interchange, Tacoma,Washington, before and after the exte-rior surface of the superstructure wascovered with color stains.

CONCLUSIONSI-girder/pier joint details for joint-

less bridges are proposed in this paper.Using these details will increase con-struction speed, enhance bridge aes-thetics, and reduce maintenance costs.Specific conclusions and recommen-dations of this study are summarizedas follows:

1. The current practice is to designbearing pads to transfer full vertical

load from the superstructure to thesubstructure, which results in largeand expensive bearing pads. Designersshould investigate the I-girder/pier detail before making this decision. Forexample, if a concrete diaphragm is indirect contact with the pier cap con-crete, the diaphragm is expected totransmit the large majority of the ver-tical load. This fact should be consid-ered in the bearing design. It would re-duce the size and cost of the bearingdevices.

2. Random oriented fiber (ROF)pads are an economical replacement ofthe more expensive steel reinforcedelastomeric and cotton duck pads(CDP). ROF pads can be used withvertical loads up to 800 kips (3558kN) and accommodate up to 3/4 in.(19 mm) of horizontal movement. Inbearings with horizontal movementlarger than 3/4 in. (19 mm), a two-component bearing device with aPTFE sliding surface should be used.

3. In order to reduce the width of thepier cap, it is recommended to skewthe girder ends using two or threestandard skew angles.

4. The concrete diaphragm over thepier should be replaced with a steel di-aphragm and the joint between thegirder ends should be filled with con-crete that takes the same shape as thegirder. The compressive strength ofthe concrete joint should match that ofthe concrete girder. This would sim-plify the construction process of thesuperstructure/substructure joint andreduce construction time and cost.

5. For fixed bearings, a ROF padthat covers the full contact area be-

tween the pier cap and the girders maybe used. This will result in reducingthe contact pressure and in providing amore uniform stress distribution in thepier cap. A high strength steel dowelrod should be used to restrain the jointagainst longitudinal and transversemovements.

6. For expansion bearing details, itis recommended to position the bear-ing pads parallel to the girder ends tominimize the pier cap width. Insteadof using a thick sole plate to restraintransverse movement of the girders,two steel side angles should be used ateach girder location.

7. To enhance bridge aesthetics andimprove durability, it is strongly rec-ommended to stain all exterior sur-faces of the bridge with a sealingstain; not to extend the concrete di-aphragm beyond the exposed surfaceof the exterior girder; and to add a bot-tom edge to the barrier to cover thedeck slab thickness.

ACKNOWLEDGMENTThis project was sponsored by the

Federal Highway Administration(FHWA), the Nebraska Departmentof Roads (NDOR), and the Center forInfrastructure Research (CIR), Uni-versity of Nebraska-Lincoln (UNL).Support of Mark Ahlman, Gale Barn-hill, Mike Beacham, Sam Fallaha,Lyman Freemon, Fouad Jaber, MoeJamshidi, Leona Kolbet, Steve Sabra,Samir Sidhom, and Daniel Sharp ofthe Nebraska Department of Roads(NDOR) is gratefully acknowledged.These individuals spent considerable

Fig. 13(a). A Washington State Department ofTransportation bridge before staining.

Fig. 13(b). A Washington State Department ofTransportation bridge after staining.

74 PCI JOURNAL

time discussing the contents of theproject and inspiring the researchteam.

Acknowledgment is due to bridgeengineers of the state DOT, consul-tant engineers, and members of thePrecast/Prestressed Concrete Institute

(PCI), American Concrete Institute(ACI), and Transportation ResearchBoard (TRB) bridge committees whoresponded to the survey and providedthe research team with their experi-ences.

Acknowledgment is due to Amgad

Girgis, research graduate student,University of Nebraska, for his helpin providing the sketches. Also, theauthors would like to thank the PCIJOURNAL reviewers of this paperfor their valuable and constructivecomments.

REFERENCES

1. Burke Jr., M. P., “Bridge Deck Joints,” National CooperativeHighway Research Program (NCHRP), Report 141, Washing-ton, DC, 1989.

2. PCI Committee on Bridges, “State-of-the-Art of Precast/Pre-stressed Concrete Jointless Bridges,” Precast/Prestressed Con-crete Institute, Chicago, IL (to be published).

3. Tadros, M. K., and Badie, S. S., “Superstructure/SubstructureJoint Details,” Final Report, Project PR-PL-1(035)P514, Ne-braska Department of Roads (NDOR), Lincoln, NE, October1999.

4. Wasserman, E. P., “Tennessee State Route 50 Bridge OverHappy Hollow Creek,” PCI JOURNAL, V. 44, No. 5, Septem-ber-October 1999, pp. 26-40.

5. AASHTO, LRFD Bridge Design Specifications, Second Edi-tion, American Association of State Highway and Transporta-tion Officials, Washington, DC, 1998.

6. AASHTO, Standard Specifications for Highway Bridges, Six-teenth Edition, American Association of State Highway andTransportation Officials, Washington, DC, 1996, and interim1997 and 1998.

7. Aswad, Alex and Tulin, L. G., “Responses of Random-Oriented-Fiber and Neoprene Bearing Pads Under SelectedLoading Conditions,” Second World Congress on Joint Sealingand Bearing Systems for Concrete Structures, San Antonio,TX, September 28 to October 2, 1986.

8. Aswad, Alex, “Assessment of Properties of Plain NeopreneBridge Bearing Pads with Design Recommendations,” PennState University, Middletown, PA, 1997.

9. FIBERLAST Bearing Design Manual, VOSS Engineering Inc.,Lincolnwood, IL 60645.

10. MASTICORD Design Guide, Structural Bearing Pad, ThirdEdition, JVI Inc., Skokie, IL 60077.

11. Steel Bridge Bearing Selection and Design Guide, V. II, Chap-ter 4, American Iron and Steel Institute, Chicago, IL, 1996.

12. Ma, J., Huo, X., Tadros, M. K., and Baishya, M. C., “RestraintMoments in Precast/Prestressed Concrete ContinuousBridges,” PCI JOURNAL, V. 43, No. 6, November-December1998, pp. 40-57.

13. ACI Committee 318, “Building Code Requirements for Struc-tural Concrete and Commentary (ACI 318-99/318R-99),”American Concrete Institute, Farmington Hills, MI.

14. Noppakunwijai, P., Tadros, M. K., and Ma, J., “Anchorage ofPrestressing Strands Into End Diaphragm of Girder.” Submit-ted to the PCI JOURNAL for publication consideration.