PCI Adjacent Box Beam Bridges 4-21-09

7/22/2019 PCI Adjacent Box Beam Bridges 4-21-09

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The State of the Art of

Precast/Prestressed

Adjacent Box Beam Bridges

209 West Jackson Boulevard, Chicago, IL 60606Phone: 312-786-0300 Fax: 312-786-0353http://www.pci.org email: [email protected]


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PCI Publication Number __-__

Copyright 2009By Precast/Prestressed Concrete Institute

First Edition, First Printing, 2009

All Rights Reserved

No part of this book may be reproduced inany form without the written permission ofthe Precast/Prestressed Concrete Institute.

ISBN 0-937040-XX-X

This report has been prepared and reviewed as a Precast/Prestressed ConcreteInstitute (PCI) Committee effort to present the state of the art for design of andconstruction of precast/prestressed adjacent box beam bridges. Substantial efforthas been made to ensure that all collected data and information included in thisreport are accurate. PCI, the committee members, and the quoted agencies cannot

accept responsibility for any errors or oversights in the use of this material or inthe preparation of any final design and engineering plans. This report is intendedfor reference by professional personnel who are competent to evaluate thesignificance and limitations of its contents and who are able to acceptresponsibility for the application of the material it contains. Actual conditions onany project must be given special consideration and more specific evaluation andengineering judgement may be required that are beyond the intended scope of thisstate of the art report. The contents of this report do not necessarily reflect theofficial views or policies of the agencies mentioned, and do not constitute astandard, or policy for design or construction. Details have been provided forinformation only.

Printed in U.S.A.


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ACKNOWLEDGEMENT

The subcommittee wishes to thank all those who participated in the developmentof this report. The subcommittee also extends its gratitude to the many individualsin the respective organizations of the members who contributed to this report fortheir active participation either in developing the material or in editing and typing.

The subcommittee expresses its appreciation to the support of thePrecast/Prestressed Concrete Institute Committee on Bridges to embark on amajor effort which will be a benefit to the precast concrete industry.

Members of the Subcommittee on Adjacent Members:

Kevin Eisenbeis, P.E., S.E. Harrington & Cortelyou, Inc. (Chair)Tess Ahlborn, Ph.D., P.E. Michigan Technological UniversityDave Bracewell Coreslab

Vijay Chandra, P.E. Parsons Brinckerhoff, Inc.David Deitz, Ph.D., P.E. Palmer Engineering Co.Keith Kaufman, Ph.D., P.E. Knife River Corp.Richard Miller, Ph.D., P.E. University of CincinnatiEric Steinberg, Ph.D., P.E. Ohio University

The subcommittee acknowledges the contribution made by Dr. Richard Miller,University of Cincinnati, for reduction of the survey data into electronic format.


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TABLE OF CONTENTS

Page1. Introduction

1.1 Overview .......................................................................................11.2 Executive Summary ......................................................................2

2. Adjacent Member Bridges2.1 Basic Characteristics .....................................................................32.2 Railroad Bridges ...........................................................................4

3. Composite Superstructure

3.1 General ..........................................................................................63.2 Types .............................................................................................6

4. Non Composite Superstructure

4.1 General ..........................................................................................8

4.2 Types .............................................................................................84.3 Typical Sections ............................................................................94.4 Design .........................................................................................12

5. Joints

5.1 General ........................................................................................135.2 Details .........................................................................................135.2.1 Shear Keys ..................................................................................135.2.2 Welded Connections ...................................................................165.2.3 Transverse Reinforcement ..........................................................17

5.2.4 Current Practice ..........................................................................195.3 Design .........................................................................................195.3.1 AASHTO Standard Specifications

for Highway Bridges (2002) .......................................................205.3.2 AASHTO LRFD Bridge Design Specifications (2004)..............20

6. Continuity ..................................................................................21

7. Bearings

7.1 General ........................................................................................227.2 Survey Questionnaire Response Summary .................................227.3 Railroad Structures......................................................................23

8. Maintenance Issues8.1 General ........................................................................................248.2 Inspection ....................................................................................248.3 Load Ratings ...............................................................................25


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Page

9. Survey of Current Practice9.1 Introduction .................................................................................279.2 Data Collection/Survey Response...............................................279.3 Lessons Learned ..........................................................................28

10. Summary of Case Studies10.1 NASA Road 1 Bridge over I-45..................................................3010.2 Mitchell Gulch Bridge, Colorado ...............................................3010.3 Quaker City Bridge, Ohio ...........................................................3010.4 BNSF Railway over Route 160, Missouri ..................................3010.5 Route 100 over I-44, Missouri ....................................................30

11. Summary of Current Research................................................3111.1 UHPC ..........................................................................................3111.2 NCHRP Projects .........................................................................32

12. Conclusions12.1 General ........................................................................................3412.2 Design .........................................................................................3412.3 Fabrication ..................................................................................3512.4 Construction ................................................................................35

13. References ..................................................................................36

14. Bibliography ..............................................................................38

Appendix A: Case StudiesA.1 NASA Road 1 Bridge over I-45A.2 Mitchell Gulch Bridge, ColoradoA.3 Quaker City Bridge, OhioA.4 BNSF Railway over Route 160, MissouriA.5 Route 100 over I-44, Missouri

Appendix B: PCI New England Recommendations

B.1 Sequence of Construction for Butted Box and ButtedDeck Beam Superstructures (Skews < 30)

B.2 Sequence of Construction for Butted Box and ButtedDeck Beam Superstructures (Skews > 30)

Appendix C: Survey Questionnaire Responses


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LIST OF FIGURES

Page

Figure 2.1 Elevation of a Continuous, Composite AdjacentMember Bridge ...................................................................................3

Figure 2.2 Typical Section of an Adjacent Member Bridge-

Composite Superstructure ...................................................................4

Figure 2.3 Typical Section of an Adjacent Member Bridge-Non-Composite Superstructure ...........................................................4

Figure 2.4 Typical Section of a Double-Cell Adjacent Member RailroadBridge - Non-Composite Superstructure ............................................5

Figure 2.5 Typical Section of a Single-Cell Adj. Member RailroadBridge - Non-Composite Superstructure ............................................5

Figure 3.1 AASHTO Composite Box Beam Bridge ............................................7

Figure 3.2 Inverted Tee Beam Bridge ..................................................................7

Figure 3.3 Composite Double-Tee Beam Bridge .................................................7

Figure 4.1 Non Composite Deck Bulb-Tee Beam Bridge ....................................9

Figure 4.2 AASHTO Box Beams, Solid and Voided Slab Beams .....................10

Figure 4.3 AASHTO Double-Tee Girders .........................................................11

Figure 4.4 AASHTO Deck Bulb-Tee Girders ....................................................11

Figure 5.1 Partial Depth Shear Key for Box Beams, Solid andVoided Slab Beams ...........................................................................14

Figure 5.2 Full Depth Shear Key for Box Beams ..............................................15

Figure 5.3 Large Width Shear Key for Box Beams ...........................................16

Figure 5.4 Welded Attachment with Plate and Grouted Shear Key ...................17

Figure 5.5 Welded Attachment with Rod and Grouted Shear Key ....................17

Figure 5.6 Skewed Bridge Square Post-Tensioning ........................................18

Figure 5.7 Skewed Bridge Skewed Post-Tensioning ......................................19


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Figure 5.8 Skewed Bridge Staggered Post-Tensioning ...................................19

Figure 7.1 Plan View of Three Point Bearing System .......................................23

Figure 8.1 Reflective Deck Cracking Along Shear Keys Between Beams ........24

Figure 8.2 Degradation of Box Beams Below Reflective Cracking ..................24

Figure 8.3 Spalling on Exterior Face of Box Girder ..........................................25

Figure 11.1 FHWA Pi Girder Test Section ..........................................................31


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1. Introduction

1.1 Overview

Precast pretensioned adjacent member bridges, consisting primarily of concrete boxbeams, have been in use since 1950 in the United States. Other non-box elements,including tee-beams, multi-stemmed tees, inverted tees, deck bulb-tees, solid andvoided slab beams, and U-shaped beams are also used in adjacent member bridges.Recent trends show an increase in the use of adjacent, non-box, non-I-beam bridgebeam elements.

Although box beam elements are frequently used in an adjacent configuration withtop flanges in close contact, they can also be used in a spread configuration, similar toconventional I-beam bridges. The 2006 National Bridge Inventory (NBI) shows thereare 53,874 box beam bridges presently in service in the United States. Of this total,9,988 (18.5%) are of spread configuration, with the balance adjacent. Of the total,

8,326 (15.5%) are multiple spans made continuous, with the balance simple spans.

According to the 2006 NBI, box beam bridges account for 9.0% of the total 597,340bridges in the United States. Since box beam bridges are typically used for shorterspans and the NBI only considers bridges with spans of 20 feet or more, the numberof these bridges is likely even higher. Precast concrete box beams are still widelyused in new bridge construction today. Approximately one-third of precast bridgesbuilt over the past decade are box beam bridges. Box beams are the most commonelement used in adjacent member bridges, and information on the usage of otheradjacent beam types is less readily available.

Many agencies have refined their design and construction practices to improve theperformance of box beam bridges. In the late 1980s and early 1990s, problemsassociated with longitudinal reflective cracking above joints were reported anddiagnosed. Refinements to previous practices have significantly reduced or eliminatedthis cracking issue.

In response to the wide use of concrete box beam bridges, improvements in designand construction practices, and the recent increase in use of non-box adjacent memberbridges, the Precast/Prestressed Concrete Institute (PCI) Committee on Bridges

established the Subcommittee on Adjacent Member Bridges. This subcommittee ischarged with the task of preparing this report on the state-of-the-art ofprecast/prestressed adjacent box beam bridges. This report presents a discussion ofcurrent practices, responses to a survey of US states and Canadian provincesregarding box beam bridges, and selected case studies. Also included is acomprehensive reference list for related information.

Conventional concrete spread I-girder and spread box beam bridges are not coveredin this report at this time. The designer is referred to the extensive publications in thebibliography for additional information on spread I-girder and box beam bridges.


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1.2 Executive Summary

This report presents the state of the art on precast pretensioned box beam bridges.Adjacent box beam bridges are widely used in new bridge construction and havemany advantages over other bridge types in speed and ease of construction,aesthetics, span to depth ratio and cost. Although early construction practices mayhave led to serviceability issues, improved practices have made the box girder bridge

a viable, cost-effective structural system. A discussion on current practice, historicalissues, lessons learned and improved performance of box girder bridges is provided.Much of the information presented is based on responses to a survey of US states andCanadian provinces.

In the late 1980s and early 1990s, problems associated with longitudinal reflectivecracking above joints were reported and diagnosed. Improvements in design andconstruction practice were developed and implemented. The PCI Committee onBridges established the Subcommittee on Adjacent Member Bridges to investigateand report on developments in adjacent member bridges. This subcommittee

developed the survey questionnaire, investigated case studies and prepared this report.Design, fabrication and construction practices that have been shown to improve theperformance of box beam girder systems are included.

The focus of the survey and this study is on box girder bridges. Box girder bridges areconsidered adjacent member bridges because the box beam elements are in closecontact with the adjacent beams. Other types of adjacent member bridges arediscussed in this report due to the similarity in construction and the applicability ofdetails as related to box beams bridges.

Lessons learned have been many, and indicate the importance of proper design,fabrication and construction to the effective performance of the integral structuralsystem. For maximum structural performance, all important components should beincorporated into the box girder system. The use of grouted shear keys, compositedeck slab, transverse tensioning and proper design, fabrication and constructiontechniques contribute to the successful performance of the system.

The appendix to the report includes case studies of box girder bridges and adjacentslab bridges where the use of precast adjacent elements, shear keys, transverse post-tensioning, and construction techniques are provided. The appendix also includesconstruction practice recommendations developed by the PCI Northeast TechnicalCommittee, and the compiled survey data from the responding states, provinces, andother agencies.


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2. Adjacent Member Bridges

2.1 Basic Characteristics

Adjacent member bridges incorporate a variety of precast prestressed beam types,spaced in close contact with adjacent beam elements. These bridges may includesimple or continuous spans, utilizing integral or non-integral construction. Most newbox beam superstructures utilize composite construction with cast-in-place (CIP)concrete deck slabs (Figure 2.1 & 2.2). Composite superstructures in a spreadconfiguration may incorporate conventional precast deck panels or precast concretedeck slabs mechanically anchored to the support beams. Some superstructures utilizenon-composite construction, with the adjacent member top flanges acting as theriding surface or non-composite overlays applied to the adjacent member top flanges,as shown in Figure 2.3. Various combinations of precast concrete deck panels, CIPdeck slabs and/or overlays are successfully used by the different US and Canadianagencies.

Figure 2.1Elevation of a Continuous, Composite Adjacent Member Bridge


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Span lengths of precast/prestressed adjacent member bridges typically range from 20feet to 130 feet. Simple span lengths of up to 168 feet have been achieved with theuse of adjacent deck bulb-tee girders. Longer span lengths are possible with the use ofcontinuity and longitudinal post-tensioning. Span lengths are dependent on specificproject design requirements, local beam availability and construction methodologiesused. The designer is referred to the PCI Bridge Design Manual, Chapters 6 and 8, foradditional design guidelines.

Figure 2.2Typical Section of an Adjacent Member Bridge - Composite Superstructure

Figure 2.3Typical Section of an Adjacent Member Bridge - Non-composite Superstructure

2.2 Railroad Bridges

The railroad industry utilizes adjacent member construction in a large percentage ofrailroad bridges. Many railroad bridges in the 25 to 50 feet range use curbed, non-composite double-cell box beams with the top flanges serving as the ballast pan forthe track structure. Standard single-cell box beams and box-tee beams are available inspan lengths from 19 to 48 feet and special designs can extend the span length to over80 feet. Figures 2.4 and 2.5 show typical double-cell and single-cell box beambridges. Shorter span railroad bridges, typically shorter than 20 feet, use adjacentsolid or hollow concrete slabs. Longer span precast/prestressed railroad bridgesincorporate multiple, adjacent I-beams with integral concrete deck ballast pans ornon-composite single-cell adjacent box beams.


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Figure 2.4Typical Section of an Adjacent Member Railroad Bridge - Non-compositeSuperstucture

Figure 2.5Typical Section of an Adjacent Member Railroad Bridge - Non-compositeSuperstucture


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3. Composite Superstructure

3.1 General

Composite adjacent member bridges incorporate a variety of precast prestressed beamtypes, spaced in close contact with adjacent beam elements. For adjacent sections,composite toppings in the 5 to 6 inch range are common, compared to spread beamsystems that use composite topping commonly in the 8 inch thickness range. In someinstances, a non-structural overlay is provided over the cast-in place deck slab toprovide a replaceable wearing surface.

Transverse connections are typically made between beams to prevent differentialdeflection and improve the distribution of live loads. Composite deck slabs can alsoassist in distributing the live load to the beam elements. Transverse connections,when used, are typically made using threaded rods, post-tensioning bars or post-tensioning strands. In some instances, welded or bolted connections are utilized.

The small longitudinal joint between abutting beams, typically referred to as theshear key or keyway, is normally filled with grout or an appropriate non-structural sealant to prevent water leakage and moisture penetration between beams.Shear keys also assist with the load transfer between beams. Without an adequatetransverse connection, differential movement between beams may lead to longitudinalcracking of grouted keyways and reflective cracking in the deck slab and overlay, ifone is present.

Several different types of grouted keyways and transverse connections have been

reported to provide good performance when used in conjunction with adequatetransverse connections. The selection of a system for connecting adjacent memberbridges should consider initial cost, long-term maintenance costs, experience of theowner, capabilities of local contractors, and availability of materials.

3.2 Types

Composite adjacent member bridges may be constructed with box beams (Figure3.1), solid or voided slab beams, tee beams, inverted tees (Figure 3.2), doublestemmed tees (Figure 3.3), deck bulb-tees, U-shaped beams or tub sections. Abutting

top flanges or beam sections are in close contact and allow the use of thinnercomposite toppings. The American Association of State Highway and TransportationOfficials (AASHTO) standard box beams, spanning from 40 to 127 feet, arecommonly used by many agencies. Other adjacent member sections, such as the deckbulb-tee girders, are regional in nature and subject to local availability.

A number of states have their own standard products. Designers should check withtheir local precast producers or agencies on product availability before they begindesign. The designer is referred to the PCI Bridge Design Manual, Chapters 6 and 8for design procedures, design aids and examples.


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Figure 3.1AASHTO Composite Box Beam Bridge

Figure 3.2Inverted Tee Beam Bridge (Shown in Spread Configuration)

Figure 3.3Composite Double-Tee Beam Bridge


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4. Non-composite Superstructure

4.1 General

Non-composite adjacent member bridges are constructed by placing precast,prestressed concrete box or other adjacent member beams next to each other so that adeck slab is not required to complete the structure. Often, a non-structural overlaysuch as a 2-inch thick asphalt concrete wearing surface is used to provide the ridingsurface. In some instances, such as secondary roads, a topping is not used because thesurface of the precast beam adequately serves as the riding surface. The use of awaterproofing membrane is beneficial to reduce the intrusion of water and deicingsalts between the adjacent members.

The transverse connections and keyways used between adjacent non-compositemembers are similar to those used for composite members. Refer to Section 3.1 ofthis report.

4.2 Types

Non-composite adjacent member bridges are typically constructed with box beams,solid or voided slab beams, double-tee beams or deck bulb-tee girders. Abutting topflanges or beam sections are placed in close contact to serve as the wearing surface orto support a non-structural overlay. AASHTO standard box beams, spanning from 40to 132 feet, are commonly used by many agencies. Other adjacent member sections,such as the deck bulb-tee girders are regional in nature and subject to localavailability. Deck bulb-tee girders generally span from 65 to 168 feet. A typical non-

composite deck bulb-tee girder bridge is shown in Figure 4.1.

A number of states have their own standard products. Designers should check withtheir local precast producers or agencies on product availability before they begindesign. The designer is referred to the PCI Bridge Design Manual, Chapters 6 and 8for design procedures, design aids and example designs.


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Figure 4.1Non Composite Deck Bulb-Tee Beam Bridge

4.3 Typical Sections

Several typical sections are included for reference. See Figure 4.2 for typicalAASHTO box beams, solid slab beams and voided slab beams. Typical AASHTOdouble-tee sections and deck bulb-tee sections are shown in Figures 4.3 and 4.4.Maximum spans shown in Figures 4.2 through 4.4 are for simply supported and non-composite HS25 live load, with fc = 7,000 psi. However, the sections are suitable for

use in composite construction as well.


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Figure 4.2

AASHTO Box Beams, Solid and Voided Slab Beams


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Figure 4.3 Figure 4.4AASHTO Double-Tee Girders AASHTO Deck Bulb-Tee Girders


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4.4 Design

Continuity over piers is not normally used with the various standard beam sections innon-composite construction. Therefore, non-composite adjacent member bridges aretypically designed as simple spans.

Adjacent member highway beams have been designed according to AASHTO

Standard Specifications or AASHTO LRFD Specifications. Railroad bridges aredesigned in accordance with the American Railway Engineering and Maintenance ofWay Association (AREMA) Manual for Railway Engineering.

A number of states and Canadian provinces utilize their own or other states standardproducts. Designers should check with their local precast concrete producers onproduct availability before they begin design.


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5. Joints

5.1 General

Adjacent member bridges require longitudinal joints between their members. Variousdetails for this interface have been used to connect the adjacent members. Connectingadjacent members can serve two purposes. First, the joint can act as a water seal,

preventing water from seeping between the members which can lead to deterioration.Second, if certain details are applied, the connection can prevent differentialdeflections between adjacent members, transmitting loads applied to one member tothe next, allowing the members to share live load during service.

Different agencies have taken widely varying approaches to the treatment oflongitudinal joints. When joints are intended to transmit loads, some form of shearkey is often employed. Welded connections details are also in use by a few agencies.In some cases transverse reinforcement in the form of post-tensioning is extendedacross the joints to tie the elements together while for some systems no connectionbetween the adjacent members is provided. A composite deck slab can be utilized toboth reduce moisture penetration and contribute to the distribution of loads. Non-composite toppings, sometimes used on secondary roads, can be used to provide adriving surface and water stop without participating in load distribution. In otherinstances, the top flanges of the adjacent members serve as the riding surface.

5.2 Details

Joint details are largely based on regional preferences. Variations occur in the size,

type and location of the joint as well as type and strength of material used to fill thejoints when shear keys are used.

Transverse reinforcing details also vary considerably. Differences occur based onregional preferences in the amount, spacing, and type of reinforcement used.Placement of transverse reinforcement in the construction sequence also varies.Regions differ on whether the transverse reinforcement is installed and stressedbefore or after the joint material is placed. The PCI Northeast Region TechnicalCommittee (PCINE) recommends stressing the transverse reinforcement after thegrout is placed for a square structure, but prior to grout placement for skewed bridges

(see Appendix B).

5.2.1 Shear Keys

Shear keys consist of blockouts on the faces of adjoining elements of adjacentmembers as shown in Figures 3.1, 4.1, 4.2 and 4.4. After the members are in place onthe structure, the joints are filled with mortar grout, epoxy or concrete, linking theadjacent members together. Shear keys are used in combination with transversereinforcement or composite slabs by some agencies. Current practice indicates the


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most effective systems utilize an epoxy grout or non-metallic, non-shrink grout inshear keys which extend the full length of the box beam.

Figure 5.1Partial Depth Shear Key for Box Beams, Solid and Voided Slab Beams

The size, shape and location of shear keys vary widely. Locating the joints near the

top of the member facilitates filling the blockouts. Deck bulb-tee sections and othersections with a top flange have relatively small, narrow shear keys that are usuallyfilled with a non-shrink grout. Box beams may use partial depth shear keys locatednear the top of section (Figure 5.1), but other details take advantage of the largecontact area between adjacent boxes to utilize a longer, nearly full depth, but narrowshear key (Figure 5.2). Improved results have been reported with systems utilizingfull depth shear keys instead of smaller keys. Some agencies have developed a simplebox girder system that utilizes standard AASHTO I-girder shapes to form the sides ofa box girder. The forms are placed far enough apart that a void is placed in the middle


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creating a box shape with a large shear key formed by the abutting I shaped sides(Figure 5.3).

Figure 5.2

Full Depth Shear Key for Box Beams


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Figure 5.3Large Width Shear Key for Box Beams

The most common material used to fill precast joints in adjacent member bridges is anon-shrink cement grout. However, epoxy grout is also used for the small shear keysand conventional deck concrete is commonly allowed to flow into the large shear keyshown in Figure 5.3.

Proper grout quality and grouting procedures have been found to be critical to thelong term performance of the joints. Thoroughly cleaning the blockouts forming thejoints by pressure washing, then wetting the surface of the blockout prior to groutplacement improves the bond between the adjacent member and grout.

Materials and grouting practices are generally based on regional preferences. Someregions report the most effective systems utilize shear keys in combination with atransverse reinforcing system to tie adjacent members together.

5.2.2 Welded Connections

Welded connections between adjacent precast members are constructed by castingweld plates and blockouts into the edges of the adjacent elements at several locationsalong the length of the member. After the components are erected, the plates are fieldwelded to each other, typically using a filler plate (Figure 5.4) or rod (Figure 5.5), tomake the connection between members. Various details have been used to allow forconstruction tolerances both in the precasting process and erection. One agency notedthat welding can be difficult when differential camber occurs.


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Figure 5.4Welded Attachment with Plate and Grouted Shear Key

Figure 5.5Welded Attachment with Rod and Grouted Shear Key

5.2.3 Transverse Reinforcement

Transverse reinforcement installed after the adjacent members are in place affects the

performance of the joints. The reinforcement passes through the adjacent members,

(BETWEEN WELD TIES)


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locking them together during loading. The reinforcement may be post-tensioned.Mild, non-prestressed reinforcement is usually placed continuously along the lengthof the members, either in a composite slab, or across a closure pour. Post-tensionedreinforcing is generally installed at discrete locations along the member length. Thenumber of locations, type of reinforcement (bars or strands of varying strengths) andamount of prestressing force applied ranges widely. Transverse post-tensioningreinforcement can be installed before or after the grout has been placed in shear keys.

Skewed bridge construction brings another set of varying details. Many states try toavoid use of skewed bridges when feasible. Adjacent member bridges with transversepost-tensioning have been constructed with the post-tensioned reinforcement placedperpendicular to the beams across the full width of the bridge (Figure 5.6), placed fullwidth across the bridge along the skew (Figure 5.7) and placed perpendicular to thebeams and staggered to connect only two adjacent girders per post-tensioninglocation (Figure 5.8). Post-tensioned ties are typically installed in sleeves cast inintermediate diaphragms, where the loading can be distributed throughout the system.Some agencies have found that installing skewed, transverse post-tensioning in

bridges with large skew angles can cause the box girders to slide longitudinally pasteach other, causing the girders to rack. See Appendix A.4 for a case study on howthis problem was addressed for one railroad bridge. Other agencies have reported atendency for skewed beams to walk and separate when not adequately tied togetherwith a tension tie.

Figure 5.6Skewed Bridge - Square Post-tensioning


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Figure 5.7 Figure 5.8Skewed Bridge - Skewed Post-tensioning Skewed Bridge - Staggered Post-

tensioning

5.2.4 Current Practice

Currently twenty-eight agencies use shear keys between adjacent members. Of these,seventeen report the use of keyways that differ in size or shape from those found onthe standard AASHTO box beams. Thirteen agencies require that the shear keys besandblasted. Sandblasting is performed at the precast plant in eight jurisdictions,while four require sandblasting at the job site; two prior to erection of the beams andtwo after girders are placed.

Transverse post-tensioning is used in combination with shear keys by twentyagencies. Of these, eight report that post-tensioning is performed before the shearkeys are grouted, nine reverse the order of these operations and one agency varies theorder dependent upon the skew angle of the bridge. The type of transversepost-tensioning also varies, with twelve agencies reporting the use of strands, elevenusing bars (some agencies use both). The strands are typically 0.5 inch strands, butthe bars vary widely in both size and yield strength, from 1.5 inch, 36 ksi bars to #7bars, 150 ksi. The post-tensioning bars are usually installed mid-depth of the beamsor below, but some agencies utilize post-tensioning near the top of the beam. The

number of post-tensioning locations along the girder generally increases with thelength of the girder with post-tensioning typically applied every 25 to 30 feet. Someagencies define skew angle limits for the use of square, skewed or staggeredtransverse post-tensioning.

5.3 Design

Typically, a detailed design for shear or flexure in the joints is not performed. In mostcases, standard details based on regional preferences are used without calculatingjoint design loads. A general overview of design code requirements is given below.


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5.3.1 AASHTO Standard Specifications for Highway Bridges (2002)

Specific guidelines were not provided for designing or detailing the longitudinaljoints. The specification does stipulate that a continuous longitudinal shear key andtransverse tie reinforcement be provided to use the live load distribution factorequations for multi-beam decks. Transverse tie reinforcement may or may not beprestressed. Since the Standard Specifications are currently being phased out of use,

this information is included here for historical reference only.

5.3.2 AASHTO LRFD Bridge Design Specifications (2004)

The specifications provide requirements for both the depth of the joint, or shear key,and minimum compressive strength of the non-shrink grout used to fill the joint.

Based on the specific design method and detailing requirements used, the joints caneither be considered Shear Transfer Joints or Shear-Flexure Transfer Joints.Meeting the more stringent design requirements of the latter allows for an improved

live load distribution. Additionally, the specifications require the adjacent membersbe prestressed transversely. The amount of transverse prestressing required must bedetermined by the strip method or a two-dimensional analysis, and meet minimumrequirements for compressive force across the joint. Both El-Remaily et al. (1996)and Bakht et al. (1983) provide guidance and examples for the two-dimensionaldesign of adjacent box beam bridges.


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6. Continuity

Adjacent member bridges can be made continuous for live load and othersuperimposed dead loads by connecting the precast simple span members overinterior supports. This requires a negative moment connection over the support whichtypically consists of a cast-in-place concrete diaphragm and composite deck.

Providing continuity decreases the positive design moments allowing for longer spanlengths. Continuity also removes expansion joints over interior supports that canrequire significant long term maintenance.

Many transportation departments design and construct bridges using this practice.However, there are important aspects of continuous bridges that need consideration.NCHRP Report 519 (2004), Connection of Simple-Span Precast Concrete Girdersfor Continuity, provides recommendations for design and construction for this typeof bridge. Significant conclusions from this report include the following:

Due to the time dependent behavior of the prestressed concrete beams, positivemoments can form at interior supports. Proper detailing of positive momentconnections at these supports is important.

Temperature effects on the beam/deck slab system can be significant.

Current analytical models show that differential shrinkage between the deck slaband the girders can cause negative moments in the system.

The presence of positive moment cracks at the connection does not affect thenegative moment capacity of the system.

A link slab system (Caner and Zia 1998) can be used as an alternative to a continuousfor live load superstructure while still maintaining a jointless deck. In a link slabsystem, the continuous deck at interior supports is designed to allow the beams inadjacent spans to act as simple spans for all loadings. The deck is designed towithstand beam end rotations over the pier. This system has the added advantage ofallowing for the use of state DOT standard beam tables typically based on simplespans.


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7. Bearings

7.1 General

Bearings for precast prestressed adjacent member bridges typically consist ofneoprene pads. Plain pads are typically used for shorter spans, with laminatedneoprene pads for longer and heavier girders. When used, laminate embedded in the

pads is typically steel.

In box beam bridges, support configurations include 4-point support where bearingpads are located under each corner of each box beam; continuous support, wherebearing pads are continuous under each end of each box beam; and 3-point support,where one bearing pad is located under each corner of the box at one end of the span,and a wider single pad is centered under the opposite end of the beam. Two singlecorner pads can be located side by side to form the single pad. The center pad andcorner pad layout of the three-point system can also alternate end to end at adjacentgirders to provide a more uniform overall bearing of the system.

Lateral restraint is typically provided to minimize lateral movement at supports andsecure the structural system to the substructure. Shear keys or blocks can be used toprovide lateral restraint in seismic and non-seismic regions.

7.2 Survey Questionnaire Response Summary

Nearly all respondents reported using neoprene pads for the support of box beam

superstructures. Only three of thirty-one respondents did not use neoprene pads, withtwo using fabric pads, and one using 0.5 inch preformed joint filler. The largestvariation for the neoprene pad users was related to the use of plain or laminated pads.Seven agencies reported using only plain pads, fourteen use only laminated pads, andeight use either plain or laminated pads, depending on the design requirements.

Fourteen respondents indicated uneven seating of the box beams has occurred.Skewed ends and variations in box geometry can cause the uneven seating, and insome cases, rocking of the boxes during construction. Several states have recentlyswitched to a 3-point bearing system (Figure 7.1), particularly on skewed bridges, in

an attempt to minimize these conditions. Primary concerns with the uneven seatinginclude problems with alignment and grouting during construction, and excessbearing pressure.

Some form of lateral restraint is required by most agencies. Eighteen report the use ofdowel pins, typically steel, for lateral restraint. Five use blocks or shear keys, and fouragencies utilize either dowel pins or shear keys. Three agencies consider theembedment of reinforcing steel into integral concrete diaphragms as sufficient forlateral restraint. Only one respondent reported using no lateral restraint other thanshear stiffness of the bearing pads.


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Figure 7.1Plan View of Three Point Bearing System (TxDOT)

7.3 Railroad Structures

Bearing pads utilized for railroad double-cell box beams typically consist of 0.75 inchurethane pads, continuous under the ends of the beams. Heavier single-cell boxes aresupported on laminated neoprene pads, continuous under the ends of the beams.Design of bearings for railroad structures is based on procedures outlined in theAmerican Railway Engineering and Maintenance of Way (AREMA) Manual forRailway Engineering.


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8. Maintenance Issues

8.1 General

Early design and construction practices have created serviceability problems with boxgirder bridges. The predominant distress observed in adjacent box girder bridges isreflective cracking of the deck along the shear keys between beams (Figure 8.1) andthe associated degradation of the box beams below the reflective cracks (Figure 8.2).The reflective cracking constitutes a serious problem, as it allows penetration ofsurface water and deicing chemicals through the deck and between the beams.

Reflective cracking occurs more readily on bridges utilizing asphalt wearing surfaces,although the problem also occurs on bridges with concrete deck surfaces.Deterioration of individual box beams and the related structural system comes inmany forms. Visual symptoms usually consist of cracks and/or spalls. These areas areof concern because they may allow salt-laden water to penetrate into the structural

member and cause further deterioration of the concrete, prestressing strands andreinforcing steel. Deterioration of transverse tensioning elements and substructureunits may also occur.

Figure 8.1 Figure 8.2Reflective Deck Cracking Along Shear Degradation of Box Beams BelowKeys Between Beams Reflective Cracking

8.2 Inspection

Proper identification, diagnosis and timely maintenance are essential to preserveadjacent member bridges. As load ratings are affected by the current condition of thebridge, it is important to recognize and document the forms of distress and theirlocations while conducting inspections.

Bridge inspections should, as a minimum, identify size and depth of cracks, areas ofspalling, extent of delaminated concrete, exposed reinforcement and prestressing


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strands, section loss, evidence of water staining, efflorescence and corrosion, andcondition of the various structural elements. Spalling on the exterior face of anexterior box girder with exposed prestressing strands is shown in Figure 8.3.

Figure 8.3Spalling on Exterior Face of Box Girder

Corrosion of the prestressing strands greatly impacts the capacity of the structure, notonly because it causes a loss of a key component in a prestressed system, but

corroding steel may also expand three to six times the original volume and causefurther loss of concrete section due to cracking and spalling (Teng 2000).

A Michigan DOT (MDOT), Michigan Tech and Wayne State Universities project,Condition Assessment and Methods of Abatement of Prestressed Concrete Box-Beam Deterioration, (MDOT 2007) describes thirteen types of common degradationspecific to prestressed box beams. These are reprinted in the Prestressed Box-BeamAssessment Handbook. This handbook developed for prestressed box-beamassessment has been designed to serve as a supplement to the Pontis BridgeInspection Manual (MDOT 1999), and should serve as a guide to aid bridgeinspectors and engineers while assessing the condition of box-beams for the purposeof scoping or damage evaluation inspections. The level of detail called for in theassessment handbook may be greater than needed for routine biennial inspections.

8.3 Load Ratings

Bridge load ratings are used by bridge owners to assess the structural integrity of theirbridges, and are reported to the Federal Highway Administration in the form of theNational Bridge Inventory (NBI). Damage and deterioration of the structural


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members of the bridge are incorporated into the load rating, and structural repairsmay be required if a load rating falls below accepted standards.

Load rating a prestressed concrete box-beam requires six conditions for the inventoryrating and three conditions for the operating rating. Each rating requires a strengthcheck of the member, both flexural and shear, and a service limit check. Theinventory rating requires a service level check of concrete tension, concrete

compression, and prestressing steel tension. The operating rating only requires thatthe prestressing steel tension be checked.

Four properties are directly influenced by deterioration: compressive strength of theconcrete, moment of inertia, cross-sectional area of the beam, and the cross-sectionalarea of the prestressing steel. The compressive strength of the concrete is the onlyproperty directly related to material related distress. The cross-sectional area of thebeam, moment of inertia, and total area of prestressing strand are all related to thephysical condition of the box beam. Changes to the cross-section of the beam alsoresult in different values for centroid and eccentricity of the prestressing strands. All

of these components must be updated to reflect the capacity of a beam in a distressedstate. These properties are used directly in the calculation of the service level stressesfor both the inventory and operating ratings, and are used by the strength ratings todetermine the moment and shear capacity of the beam.

Parameters such as applied loads do not need to be reassessed unless the location ortype of deterioration indicates that load patterns may change. For example, if loadtransfer mechanism deterioration lessens the load sharing capabilities of the adjacentbox beam design, the load distribution will be influenced. If this type of deteriorationhas occurred, it may be necessary to revise the distribution factors for live and dead

loads to reflect the current condition of the bridge.


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9. Survey of Current Practice

9.1 Introduction

To obtain current information on the use of box beam bridges, the Subcommittee onAdjacent Member Bridges distributed a questionnaire to the departments oftransportation in all fifty states and to the ministries of transportation in thirteenCanadian provinces. In addition, the survey was sent to nine additional agencies orentities. The questionnaire solicited specific information in the following generalcategories:

1. Organizations experience with box beam bridges

2. Deck slab and overlays

3. Box beam construction

4. Keyways

5. Prestressing

6. Bearings

7. Lessons learned

The questionnaire also requested drawings and photographs of representative box

beam bridges.

The response was good, with forty five of the fifty states, three of the thirteenCanadian provinces, plus the New Jersey Turnpike Authority and PrestressEngineering Corp. responding to the questionnaire.

9.2 Data Collection/Survey Response

The effort for this report began by developing a questionnaire. The first questionasked was whether or not the responding entity used box beam bridges. If the answer

was negative, further response was not required. If the answer was affirmative,information in the above-mentioned areas was collected.

A wide variety of responses to the various box beam related questions weresubmitted. Box beams are currently used in twenty nine of the forty five states and thethree Canadian provinces which responded to the questionnaire.

Based on the information available, the matrix shown in Appendix C was prepared tosummarize the survey responses.


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9.3 Lessons Learned

A number of important lessons were reported by the respondents:

Many respondents discussed the importance of minimizing longitudinal cracking toprevent water penetration into the longitudinal joints. Surveys of adjacent box beambridges made in the late 1980s and early 1990s revealed that reflective cracks in the

wearing surface were a recurring problem in some areas. These cracks should beprevented because water and deicing chemicals may penetrate the cracks and causeconcrete staining and eventual structural deterioration.

One state reported many detail changes over the last twenty years that considerablyimproved performance and reduced water leakage between adjacent boxes. Theseincluded placing the bearing pads under the edge of the beam rather than under themiddle to prevent rocking of the beams during grouting of the shear keys, blastcleaning the key surfaces, the use of non-shrink grout instead of sand/cement mortarin the keys, and the use of corrosion inhibitor in the concrete mix for the box beam.

The combined use of sufficient transverse connections, non-shrink grout orappropriate sealant in the keyways, and a composite deck slab provides a reasonableassurance against longitudinal deck cracking.

The use of a cast-in place composite slab can prevent leakage between box beams.

Transverse tie post-tensioning helps control differential deflection in adjacent box orslab construction.

Two states report that reflective cracking and associated leakage have beeneliminated with the use of the full depth shear key developed by the PCINE TechnicalCommittee.

One state is considering eliminating the use of welded connections between adjacentboxes due to longitudinal cracking associated with this detail. This is the only statethat reported using welded connections between boxes.

Lack of adequate positive transverse tie force is the primary cause of shear keyfailure.

Dimensional tolerances in tall box sections may create gaps which are difficult toseal, allowing grout to drip through the longitudinal joints during grouting ofkeyways. Inadequate sealing has presented problems when used over traveledroadways.

To provide a more uniform overlay thickness, one Canadian province varies the topflange thickness to offset upward beam camber.


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Two states report instances of poor seating for some box beams embedded into CIPdiaphragms. However, these have not resulted in any actual in-service distress.

Jointless bridges are the best way to avoid problems with bearings and substructurecorrosion.

One state expressed concern that concrete cover within the box may not be provided,

but no inspection process is available for checking.

Sloping the bearing seats to match the cross slope helps with seating the boxes.

One state limits the use of box beams to small bridges with spans of 40 feet or less.

Minimize skews where practical.

Provide lateral restraint at piers and abutments.

Utilize polystyrene material for form voids. Cardboard forms may react withconcrete, creating gases that can cause concrete to crack and split off.


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10. Summary of Case Studies

Five case studies appear in Appendix A representing the application of differentadjacent member systems by various agencies. The following projects were included:

10.1 NASA Road 1 Bridge over I-45

The NASA Road Bridge 1 over I-45 is a Texas Department of Transportation projectthat replaced a 300 foot long, four span bridge over six lanes of the interstatemainline, and dual two lane frontage roads in just nine days.

10.2 Mitchell Gulch Bridge, Colorado

The reconstruction of the single span bridge carrying Colorado Highway 86 overMitchell Gulch was a value-engineered project that demonstrated how adjacentmembers can be used to greatly reduce the length of construction time, and to

minimize inconvenience to the public on a heavily traveled road.

10.3 Quaker City Bridge, Ohio

The superstructure of this two span bridge was replaced with a precast, adjacentmember superstructure, reusing the existing intermediate pier and abutments. Theproject uses laterally post-tensioned, precast reinforced concrete slab beams.

10.4 BNSF Railway over Route 160, Missouri

The BNSF Railway Bridge over Missouri Route 160 is a grade separation structure inSpringfield, Missouri. This 158 foot long, triple track, three span structure replacedtwo existing structures that did not provide sufficient horizontal clearance to widenRoute 160 beneath. An intricate staging sequence and a temporary shoofly structurewas constructed in conjunction with the replacement bridges to maintain a minimumof two sets of tracks in service at all times during construction.

10.5 Route 100 over I-44, Missouri

The Missouri Route 100 Bridge over I-44 is a two span overpass near Gray Summit,

Missouri, just west of Saint Louis. The replacement structure was value-engineeredfrom a four span rolled beam bridge to a two span, adjacent box girder bridge aftercontractors encountered cost penalties from the steel industry associated with therapid construction schedule.


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11. Summary of Current Research

11.1 UHPC

The FHWA is investigating ultra high performance concrete (UHPC) for use inbridge design utilizing an optimized bulb-double-tee shape (Graybeal and Hartman,2005). Figure 11.1 provides the cross-section. Two girders using these sections wereerected side by side to form an adjacent member bridge at the FHWA Turner-Fairbank Highway Research Center. Testing on these members to determine theelastic lateral load distribution of the members has been performed (Graybeal andHartman, 2005(2)).

Figure 11.1

FHWA Pi Girder Test Section

Buchanan County, Iowa, with the assistance of the Iowa DOT and Iowa StateUniversity, is the site of the first bridge in the U.S. built with Pi-shaped girders madeof ultra high performance concrete. The Bridge Engineering Center staff of Iowa

State University is assessing the behavior of the individual elements duringconstruction as well as their long-term performance and overall behavior of thecompleted bridge.

Based on results of testing by FHWA, changes are being made to the optimized Pisection shown above, including thicker webs, thicker deck and consideration oftransverse tensioning.


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11.2 NCHRP Projects

Other NCHRP research projects directly or indirectly related to adjacent membersinclude:

10-71 Evaluation of CIP Reinforced Joints for Full-Depth Precast Concrete BridgeDecks

10-72 Bridge Deck Design Criteria and Testing Procedures

10-73 Guide Specification for the Design of Externally Bonded FRP Systems forRepair and Strengthening of Concrete Bridge Elements

12-56 Application of the LRFD Bridge Design Specifications to High-StrengthStructural Concrete: Shear Provisions

12-57 Extending Span Ranges of Precast, Prestressed Concrete Girders

12-58 Effective Slab Width for Composite Steel Bridge Members

12-60 Transfer, Development, and Splice Length for Strand/Reinforcement inHigh-Strength Concrete

12-62A Simplified Live Load Distribution-Factor Equations-Phase II

12-64 Application of the LRFD Bridge Design Specifications to High-StrengthStructural Concrete: Flexure and Compression Provisions

12-65 Full-Depth, Precast-Concrete Bridge Deck Panel Systems

12-68 Improved Rotational Limits of Elastomeric Bearings

12-69 Design and Construction Guidelines for Long-Span Decked Precast,Prestressed Concrete Girder Bridges

12-71 Design Specifications and Commentary for Horizontally Curved ConcreteBox-Girder Highway Bridges

12-72 Blast-Resistant Highway Bridges: Design and Detailing Guidelines

12-73 Design Guidelines for Durability of Bonded CFRP Repair/Strengthening ofConcrete Beams

12-74 Development of Precast Bent Cap Systems for Seismic Regions

12-75 Design of FRP Systems for Strengthening Concrete Girders in Shear


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12-77 Structural Concrete Design with High-Strength Steel Reinforcement

12-80 LRFD Minimum Flexural Reinforcement Requirements

12-83 Calibration of LRFD Concrete Bridge Design Specifications forServiceability

18-12 Self-Consolidating Concrete for Precast, Prestressed Concrete BridgeElements

18-14 Evaluation and Repair Procedures for Precast/Prestressed Concrete Girderswith Longitudinal Cracking in the Web

18-15 High-Performance/High-Strength Lightweight Concrete for Bridge Girdersand Decks

20-5 Synthesis Topic 39-10, Adjacent Precast Box Beam Bridges: ConnectionDetails


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12. Conclusions

12.1 General

This report presents the state-of-the-art on precast, prestressed adjacent box beambridges. Although early construction practices may have lead to serviceability issueswith box girder bridges, improved practices have made the box girder bridge a viable,cost-effective structural system. Adjacent box beam bridges have many advantagesover other bridge types in speed and ease of construction, aesthetics, span to depthratio and cost. Lessons learned have been many, and indicate the importance ofproper design, fabrication and construction to the effective performance of theintegral structural system. For maximum structural performance, all importantcomponents should be incorporated into the box girder system. Design, fabricationand construction practices that have been shown to improve the performance ofadjacent box girder systems are summarized below. What follows are conclusionsdrawn from the survey.

12.2 Design

Utilize high performance or high strength, low permeability concrete in the beamsand deck slab.

Provide shear key geometries that allow deck concrete to fill the key, or use full depthshear keys.

Provide a minimum of 1 in. cover to all reinforcing. Use 2 in. where practical.

Utilize strand patterns which omit use of prestressing strands in the exterior corners.

Design for composite action with a reinforced concrete deck slab (minimum thicknessof 5 in.).

Minimize skews where practical.

Provide lateral restraint at piers and abutments.

Consider 3-point bearing system to minimize rocking of girders.

Utilize corrosion inhibitor in the concrete mix design for the beams.

Provide waterproofing between top of structural member and overlay if a non-composite overlay is to be used.


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12.3 Fabrication

Utilize polystyrene material for form voids.

Provide consistent casting conditions to minimize differential camber in beams.

Properly anchor void forms to prevent floating of forms during casting.

Provide vent holes for beam curing, in addition to drainage holes in boxes.

When extending stirrups for shear connection to slab, consider bent shape of bar inrelation to placement of void forms.

When extending mild reinforcing steel at the ends of beams, provide straight bars andbend after fabrication.

12.4 Construction

Provide transverse post-tensioning to compress joints and minimize differentialdeflections between boxes.

Sandblast shear keys prior to grouting or concreting.

When using small shear keys, utilize epoxy grout in keyways. Some agencies reportsuccess with non-metallic, non-shrink grout.

Post-tension transverse ties prior to grouting shear keys on skewed bridges, aftergrouting on square bridges.

Grind concrete pier and abutment surfaces if necessary to achieve uniform bearingsurface.

Offset longitudinal deck joints a minimum of 1 foot from edge of adjacent box instaged construction.

When differential camber occurs, force beams together when practical or providesmooth transition with joint grout material.


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13. References

Chapter 5

1. El-Remaily, Ahmed, Tadros, Maher, Yamane, Takashi, and Krause,Gary Transverse Design of Adjacent Precast Prestressed ConcreteBox Girder Bridges,PCI Journal, 41(4), July/August 1996.

2. Bakht, Baidar, Jaeger, Leslie, and Cheung, M.S., Transverse Shear inMultibeam Bridges,ASCE Journal of Structural Engineering, 109(4),April 1983.

3. AASHTO, LRFD Bridge Design Specifications, 3rd Edition,American Association of State Highway and Transportation Officials,Washington, D.C., (2004).

4. AASHTO, Standard Specifications for Highway Bridges, 17th Edition,American Association of State Highway and Transportation Officials,Washington, D.C., (2002).

Chapter 6

1. Miller, Richard, Castrodale, Reid, Mirmiran, Amir, and Hastak,Makarand, Connection of Simple-Span Precast Concrete Girders forContinuity, NCHRP Report 519, Transportation Research Board,Washington, D.C., 2004.

2. Caner, Alp, and Zia, Paul, Behavior and Design of Link Slabs forJointless Bridge Decks,PCI Journal, 43(3), May/June 1998.

Chapter 8

1. AASHTO. (2003). Interim Revisions to the Manual for ConditionEvaluation of Bridges, Second Edition. American Association of StateHighway and Transportation Officials, Washington DC.

2. MDOT (2007) Condition Assessment and Methods of Abatement ofPrestressed Concrete Box-Beam Deterioration Phase I. MichiganDepartment of Transportation, Report # RC-1470.

3. MDOT. (1999). Pontis Bridge Inspection Manual. MichiganDepartment of Transportation, Lansing Maintenance Division, LansingMI.


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4. Miller, R.A., Hlavacs, G.M., and Long, T.W. (1998). Testing of FullScale Prestressed Beams to Evaluate Shear Key Performance. FHWAreport # OH-98/019, Federal Highway Administration. FHWA report# OH-98/019

5. Teng, T. P. (2000). Materials and Methods for Corrosion Control ofReinforced and Prestressed Concrete Structures in New Construction.

FHWA-RD-00-081. Federal Highway Administration.

Chapter 12

1. Graybeal, B. and Hartmann, J., (2005), Experimental Testing ofUHPC Optimized Bridge Girders: Early Results, Proceedings of thePCI National Bridge Conference, Palm Springs, CA, October 16-19.

2. Graybeal, B. and Hartmann, J., (2005(2)), Lateral Load Distributionin Optimized UHPC Bridge Girders, Proceedings of the InternationalConference on Advanced Materials for Construction of Bridges,

Buildings and Other Structures, IV, Maui, Hawaii, August.

3. Miller, Richard, Castrodale, Reid, Mirmiran, Amir, and Hastak,Makarand, (2004), Connection of Simple-Span Precast ConcreteGirders for Continuity, NCHRP Report 519, Transportation ResearchBoard, Washington, D.C.


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14. Bibliography

AASHTO LRFD Bridge Design Specification (2005), 3rd ed., American Associationof Highway and Transportation Officials, Washington, D.C.

AASHTO Standard Specifications, (2002), 17th ed. American Association of

Highway and Transportation Officials, Washington, D.C.

Bakht, B., Jaeger, L., and Cheung, M., (1983), Transverse Shear in Multi-beamBridges, Journal of Structural Engineering, ASCE, v. 109, n. 4, April, pp. 936-949.

El-Remaily, A., Tadros, M., Yamane, T., and Krause, G., (1996), Transverse Designof Adjacent Precast Prestressed Concrete Box Girder Bridges, PCI Journal v. 41, n.4, July-August, p. 96-113.

Grace, N., Enomoto, S., Sachidanandan, S., and Puravankara, S., (2006), Use of

CFRP/CFCC Reinforcement in Prestressed Concrete Box Beam Bridges, ACIStructural Journal, v. 103, n. 1, p. 123-132.

Gulyas, R., Wirthlin, G., and Champa, J., (1995), Evaluation of Keyway Grout TestMethods for Precast Concrete Bridges, PCI Journal v. 40, n. 1, p. 44-57.

Hlavacs, G., Long, T., Miller, R., and Baseheart, T., (1997), NondestructiveDetermination of Response of Shear Keys to Environmental and Structural CyclicLoading, Transportation Research Record, n. 1574, pp. 18-24.

Huckelbridge, A., El-Esnawi, H., and Moses, F., (1995), Shear Key Performance inMulti-Beam Box Girder Bridges, Journal of Performance of Constructed Facilities,v. 9, n. 4, p. 271-285.

Lall, J., Alampalli, S., and DiCocco, E., (1998), Performance of Full Depth ShearKeys in Adjacent Prestressed Box Beam Bridges, PCI Journal, v. 43, n. 2, March-April, pp. 72-79.

Martin, L., and Osborn, A., (1983), Connections for Modular Concrete BridgeDecks, FHWA-82/106, NTIS Document PB84-118058, Consulting EngineersGroup, Glenview, IL, August.

Miller, R., and Parekh, K., (1994), Destructive Testing of a Deteriorated PrestressedBox Beam Bridge, Transportation Research Record, n. 1460, pp. 37-44.

Miller, R., Hlavacs, G., Long, T., and Greuel, A., (1999), Full-Scale Testing ofShear Keys for Adjacent Box Girder Bridges, PCI Journal v. 44, n. 6, p. 80-90.


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Nottingham, D., (1995) Discussion of Evaluation of Keyway Grout Test Methodsfor Precast Concrete Bridges, by Gulyas, R., Wirthlin, G., and Champa, J., (1995),PCI Journal v. 40, n. 4, p. 98-103.

Osborn, A., and Preston, H., (1990), Post-Tensioned Repair and Field Testing of aPrestressed Concrete Box Beam Bridge, ACI SP-120, p. 229-256.

Precast Prestressed Concrete Bridge Design Manual, (1997), PCI, Chicago, IL.

Stanton, J., and Mattock, A., (1986), Load Distribution and Connection Design forPrecast Stemmed Multibeam Bridge Superstructures, NCHRP Report 287,Transportation Research Board, Washington, D.C.

Yamane, T., Tadros, M., and Arumugasaamy, P., (1994), Short to Medium SpanPrecast Prestressed Concrete Bridges in Japan, PCI Journal, v. 39, n. 2, March-April,pp. 74-100.


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Appendix A: Case Studies

Five examples of adjacent member bridges are discussed in this section:

A.1 NASA Road 1 Bridge over I-45, Texas - 2002

A.2 Mitchell Gulch Bridge, Colorado - 2002

A.3 Quaker City Bridge, Ohio - 2003

A.4 BNSF Railway over Route 160, Missouri - 2002

A.5 Route 100 over I-44, Missouri - 2006


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A.1 - NASA Road Bridge 1 over I-45, Texas

At the NASA Road 1 Bridge over I-45 between Houston and Galveston, the Texas Departmentof Transportation (TxDOT) makes use of a unique adjacent member system that eliminates the

necessity of either grouting or post-tensioning operations to connect the adjacent girders. Thisstructure is one of a pair of parallel bridges that carries four lanes of traffic over I-45; the otherstructure is a traditional steel girder bridge. The 300 foot long bridge crosses three lanes of I-45and a two lane frontage road in each direction with four equal spans of 75 feet (Figure A.1.1),replacing a six span structure with one that matches the span layout of the eastbound bridge.

The NASA Road 1 overpass was designed in accordance with the 1996 AASHTO StandardSpecification for Highway Bridges for HS-20 Live Loading. The bridge crosses I-45 on a squarealignment and has a broad vertical curve centered on the bridge. Precast concrete was used forboth the superstructure and substructure as part of an accelerated construction scheme. The

abutments and piers are supported on five 24 inch square precast, prestressed piles, which varyfrom 49 to 76 feet in length, and from 105 tons to 135 tons in capacity. The abutment wingwalls,caps and intermediate bent caps were also designed with a precast option, however the C.I.P.alternate was chosen.

The precast abutment and intermediate bent caps were cast with the tops sloped to match the2.08% roadway cross slope. This places the boxes slightly out of square; however this did notpresent any problem for the torsionally stiff boxes. In the past, TxDOT had experiencedproblems with box girders rocking transversely when supported on bearings at each corner. Toalleviate this problem, box girders are now supported on a 3-point bearing system consisting of

Figure A.1.1: NASA Road 1 Bridge Elevation


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two smaller bearings placed near the corners at one end of the girder and a single, wider bearinglocated at the centerline of the girder at the opposite end (Figure A.1.2). The box beams arerestrained transversely by concrete ears that are cast on each end of the caps. The abutment capsalso have a backwall to provide longitudinal restraint.

The 75 foot spans of this structure are supported by nine, adjacent TxDOT Type 4B28 girders(Figure A.1.3). These 28 inch deep precast beams are formed by using two side forms fromTexas Type A Standard Prestressed Concrete Beams that are spaced approximately four feetapart. Concrete is poured around a styrofoam block placed between the side forms that creates

Figure A.1.2: Bearing Pad Layout

Figure A.1.3: Bridge Cross Section


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the void for the box beam(Figure A.1.4). The boxgirders are prestressedwith 24 straight, in.diameter, 270 ksi low-relaxation strands locatedin the bottom flange. A

vertical, 1 in. diameterPVC pipe is cast in thebottom slab of the boxbeam at each corner toprovide drainage for anywater that mightaccumulate inside thevoid. A 7 in. deep, 12 in.long blockout is alsoprovided at each end of

the girders. Reinforcingbars are placed in thisvoid and it is filled withconcrete from the slabpour to create an enddiaphragm (FigureA.1.5). A plastic joint former is located in the slab over the piers between the end diaphragms tocreate a control joint and silicone sealant is used to fill the 1 in. gap between the end diaphragmat the abutments and the approach pavement.

After the adjacent boxgirders are placed, a 5in. thick, reinforced,cast-in-place slab ispoured on top. Theordinary slab concretein this pour is alsoallowed to flow intothe large shear keyprovided by the Ishaped sides of theadjacent box girders(Figure A1.5). Achamfer strip isplaced in the gapbetween the boxgirders to retain theconcrete in the shear

Figure A.1.4: Typical Section of Box Beam

Figure A.1.5: Detail of Shear Key and End Diaphragm


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key (Figure A.1.6). U shapedreinforcing bars at 12 in. spaces extendfrom the top slab of the girders into theslab to insure composite action of the slaband box beams. The exterior girders alsohave U shaped bars embedded near theoutside edge that project through the slab

and into the barrier curb, which is pouredon top of the slab. Bridges that utilize anasphalt driving surface have post-tensioning bars located in internaldiaphragms; however TxDOT does notrequire interior diaphragms for adjacentbox beam bridges that utilize a cast inplace slab.

Summary Discussion

Through their use of box beams since the1960s, TxDOT has encountered andsolved several issues. The concrete in thebox beams is required to be placed in atwo-stage monolithic pour. Fabricators hadexperienced difficulties holding the voidforms in place; the void forms would try toshift laterally when concrete is placedunequally on the two sides of the box, and would be forced upwards by buoyancy when thebottom and both sides were placed. Attempts to prevent the lateral movement of the void form

by filling both sides of the box equally resulted in air voids in the concrete of the bottom slab. Toavoid these problems, TxDOT specifies that the concrete in the bottom slab be placed first, andremain in the plastic state until the concrete in the second stage, the walls, is placed. In the pastcardboard forms had been used to create the void; however TxDOT had found that this couldlead to problems when a reaction between the cardboard and the concrete created gases thatwould cause the bottom flange of the boxes to split off.

The use of this simple adjacent member superstructure system allowed TxDOT to completelyreconstruct the NASA Road 1 Bridge in just nine days, greatly minimizing the disturbance to thetraveling public.

Figure A.1.6: Detail of Plug


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A.2 - Mitchell Gulch Bridge, Colorado

The reconstruction of the bridge carrying Colorado Highway 86 over Mitchell Gulch (FigureA.2.1) illustrates how adjacent girders can be part of a rapid construction solution to drasticallyreduce construction delays typically associated with bridge construction projects. This bridgereplacement project was completed over one weekend with a total road closure of only 46 hours.

The Mitchell Gulch Bridge project originally was designed as a typical bridge replacementproject with an anticipated two month road closure and detour required to construct a cast-in-place box culvert on the same alignment as the aging wooden bridge it was to replace. After theoriginal design was bid, the winning bidder submitted a value engineering proposal to drasticallyreduce the inconvenience to the approximately 12,000 daily vehicle drivers that travel this stretchof Highway 86, just southeast of Denver. This proposal significantly compressed theconstruction schedule for a total cost of $360,000, approximately the same as the originalwinning bid.

Figure A.2.1: Colorado State Route 86 Mitchell Gulch Bridge


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The new single span bridge carrying Highway 86 spans 35 ft over Mitchell Gulch is on a squarealignment (Figure A.2.2). The bridge was designed in accordance with the AASHTO 16thEdition Load Factor Design Manual for HS-25 Live Loading and a future overlay of 36 psf. Thestructure makes significant useof precast elements for bothsuperstructure and substructure.Precast abutment backwalls and

wingwalls were welded to steelH-piles that were placed outsideof the existing bridge androadway. This arrangementallowed piling to be pre-drivenprior to the road closure. The 44ft long backwalls are split intoan upper and lower section andeach 24 ft long wingwall is aseparate piece. Embedded weld

plates were cast into each of theelements to allow weldedconnections to the pile supportsand other elements. After theabutments were constructed,they were backfilled withflowable fill.

The superstructure of the Mitchell Gulch Bridge is composed of eight adjacent, precast,prestressed slab beam members. The 18 in. thick by 5 ft-4 in. wide beam slabs (Figure A.2.3)

Figure A.2.2: Bridge Alignment

Figure A.2.3: Section through slab beam


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span 37 ft-4 in. from bearing to bearing to provide the 35 ft opening. Each girder contains 20straight prestressing strands; 0.6 in.diameter with a total initialprestress force of 820 kips. Afterrelease the strands were cut 1 in.inside the surface of the concreteand the ends were patched with an

epoxy grout. The girders aresupported on a in. by 6 in.continuous bearing pad and areheld in place on the abutments byangles that are welded toembedded plates in the abutmentbackwalls and girder ends (FigureA.2.4).

The adjacent deck girders are

laterally connected to each otherby 1 in. post-tensioning rods anda shear key as shown in FigureA.2.5. Four inch diameter PVCsleeves were placed at the and points of the span and thegalvanized post-tensioning rodswere placed through these ductsafter the girders were placed. Therods were then post-tensioned to

10% of the final post-tensioningforce of 131 kips per rod prior tothe grouting of the shear keys withan epoxy grout capable of attaininga compressive strength of 3000 psiwithin 12 hours. After the grouthad hardened sufficiently toprevent spalling, the full 131 kippost-tensioning force was applied.The contractor was allowed toweld the two interior girders to theabutments after just the initial 10%post-tensioning force was applied,however the remaining girderswere not to be welded until theshear keys had been grouted andthe full post-tensioning forceapplied.

Figure A.2.4: Embedded weld plates at beam slab ends

Figure A.2.5: Longitudinal Shear key

DETAIL "1"Cont. Shear Key


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The exterior girders have a 7 in. square blockout on the exterior face for the post-tensioninghardware. The exterior girders also differ from the interior girders due to the 18 in. wide by 19high curb that was cast on the slab beams in the plant after the girder was removed from theprecasting bed. Anchor bolts were cast in the curb to attach a traffic railing to the curb prior tothe erection of the girders (Figure A.2.6).

The laterally post-tensioned adjacent beam slab members function as the bridge deck as well asspanning longitudinally, eliminating the need for a cast-in-place slab. Eliminating slab forming,pouring and curing from the critical path greatly reduced the construction time. The drivingsurface consists of 6 in. of asphalt placed over an aggregate base course. The curbs on the

exterior girders also serve to retain the base course and pavement on the bridge. The girderbearings at the abutment were level to facilitate the post-tensioning and alignment of the shearkeys, so it was necessary to taper the thickness of the base course to achieve the required 2%cross slope (Figure A.2.7). PVC pipes, 2 in. in diameter, are cast near each end of the girdersand at midspan to function as drain holes for the base course material.

Figure A.2.6: Exterior beam slab with integral curb and attached traffic rail


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Summary DiscussionThe Colorado Department of Transportations willingness to allow the use of a new bridgesystem paid large dividends. The adjacent precast members for the superstructure were combinedwith a precast substructure to facilitate the replacement of a highway bridge in less than twodays, minimizing the impact on the traveling public. To achieve this rapid construction, thoroughorganization and contingency planning was required. As with most construction projects, therewere some difficulties that arose during construction. One such problem occurred when theepoxy grouting process was begun before the transverse post-tensioning had been completed.The fast setting epoxy began to harden before the post-tensioning operation was complete whichnecessitated chipping out the epoxy and re-grouting the joints after the post-tensioning was

completed.

The post-tensioned adjacent beam slab design added some complexity to construction process;however this system allowed several time consuming steps from typical bridge construction to beeliminated. Careful planning, the construction teams ability to react to issues and the use of anadjacent member superstructure all contributed to the success of this project.

Figure A.2.7: Transverse section showing tapered subgrade material used to create cross slope


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A.3 - Quaker City Bridge, Ohio- Rapid Replacement Using Adjacent Post-tensioned Slabs

GUE-513-1.80 located in the town of Quaker City, Ohio (approximately 50 miles east ofColumbus). The existing bridge was a 2 span, concrete slab bridge, with each span beingapproximately 30 foot long. The superstructure was to be replaced, but the existing pier andabutments were to be re-used after repair. Another slab bridge was the logical replacementstructure but the time required to construct a slab bridge was a concern. Because the site is in arural area, the detour was approximately 25 miles for cars and 40 miles for trucks and largebusses. Local officials were concerned about detouring school busses over this long distance andwanted the bridge built after the school year ended and with as little interference with thesummer school term as possible. Another major factor in the decision to accelerate theconstruction was a festival held in Quaker City each summer. The festival is a major revenue

source for the local community and it was desirable to have the bridge completed before thefestival. As a result, the bridge had to be completed in less than 3 weeks.

The engineer decided to use a post-tensioned, adjacent concrete slab unit for the superstructure.The rail would be precast concrete as well. Figures A.3.2 A.3.5 show the details of the bridgestructure. The slab panels used a full depth joint with a mid-height shear key (Figure A.3.6).

After demolition of the old slab, the abutments and the center support were reworked toaccommodate the precast slabs. The precast slabs were reinforced elements. They were notpre-tensioned to simplify the fabrication and to avoid any camber problems.

Figure A.3.1: Quaker City Bridge


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To insure proper alignment of the PT ducts, a mock up assembly of the slabs was required in theprecasting yard. Unfortunately, no one thought to account for the crown in the bridge. When theslabs were delivered to site, there was some misalignment due to the crown which had to befixed by shimming the supports.

After the slabs were assembled, the joints were grouted. Grout was a major problem on thisstructure. The engineer had specified a high early strength, fast setting grout. The contractor did

not pick this up in the bid phase and did not have an acceptable grout available. When thecontractor attempted to purchase an acceptable grout, he could not find a grout which both metthe engineers specifications and was on the Ohio DOT approved list. Eventually, the engineerand the contractor found a grout acceptable to all parties. Grout placement was a problem as thegrouting company was not familiar with grout. After post-tensioning, the grout cracked and thecracks were sealed with high molecular weightMethacrylate (HMWM). In a post constructionmeeting, both the contractor and ODOT acknowledged that grout is, in general, a problem inadjacent girder bridges.

After grouting was complete, the bridge was post-tensioned in both the longitudinal and

transverse directions. The longitudinal post-tensioning made the bridge continuous for live load.Three, 0.6 in diameter strands were used in each duct to post-tension the structure. After post-tensioning, the ducts were grouted for corrosion protection (Figure A.3.7). To further reduceconstruction time, the bridge was precast with an integral wearing surface. After assembly of thebridge, the surface was ground to profile and grooves were sawcut into the surface. A precast railwas used. The rail was post-tensioned to the fascia girder when the transverse post-tensioningwas done.

The bridge met expectations for speed of construction. Although originally scheduled for 16 day,unavoidable delays extended the construction time to 19 days; but this was well within

acceptable limits.

Figure A.3.2: Elevation of the Replacement Structure

Figure A.3.3: Longitudinal Section of a Single Panel


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Figure A.3.4: Longitudinal Section of the Deck

Figure A.3.5: Cross Section of the Deck

Figure A.3.6: Slab Placement - Longitudinal PT Ducts and Shear Keys Are Visible

Bridge Railing


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Figure A.3.7: PT Tendons


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A.4 - BNSF Railway over Route 160, Missouri

The BNSF Railway Bridge over Missouri Route 160 is a grade separation structure inSpringfield, Missouri. This 158 ft long, triple track, three span structure (Figure A.4.1) replacestwo existing structures that did not provide sufficient horizontal clearance to widen Route 160beneath. An intricate staging sequence and a temporary shoofly structure was constructed inconjunction with the replacement bridges to maintain a minimum of two sets of tracks in serviceat all times during construction.

The railroad crosses Route 160 at a skew of 14 50 and is supported by three independentsuperstructures on individual intermediate piers, but all three share a common abutment at eachend. The boxes were cast with skewed ends to match the skew angle of the structure, except

abutment ends, which are cast square. Each set of tracks is supported by adjacent box beams; the38 ft end spans are carried by two adjacent, 42 in. prestressed concrete double-cell box beams

Figure A.4.1: Elevation at Project Baseline

Figure A.4.2: Section Through End Span


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(Figure A.4.2), while the 82 ft center span is supported on four 72 in. prestressed concrete singlecell box beams (Figure A.4.3). The structure was designed in accordance with the 1999 editionof the AREMA Manual for Railway Engineering and was designed for Cooper E-80 loading. Allgirders are designed as simple span, non-composite beams. The prestressing strands in all girdersare in. diameter, 7 wire uncoated, low-relaxation strands. After detensioning, the strands arecut flush with the end of the beam and painted with a waterproofing substance. All strands are

straight, no draped strands are used.

The double cell box girders in the end spans are placed adjacent to each other, but are notconnected. The girders are completely independent and each was assumed to support one half ofthe total dead and live load. Each girder contains 48 prestressing strands stressed to 31 kips perstrand for a total prestressing force of 1488

Documents

PCI Adjacent Box Beam Bridges 4-21-09