assessing the cost/benefits of employing thicker bridge decks in alabama

282 Pages·2012·14.25 MB·English

IR-00-03
Final Report
ASSESSING THE COST/BENEFITS OF
EMPLOYING THICKER BRIDGE DECKS
IN ALABAMA
Submitted to
Highway Research Center
Auburn University
Prepared by
G. Ed Ramey
Daniel M. Balmer
AUGUST 2000
Final Report
on
Highway Research Center Research Project
ASSESSING THE COSTSIBENEFITS OF EMPLOYING
THICKER BRIDGE DECKS IN ALABAMA
Prepared by
G. Ed Ramey
Daniel M. Balmer
Department of Civil Engineering
Auburn University
October 2000

ABSTRACT
Alabama employs thinner decks on their highway bridges than all other states in the U.S.
Up until about two years ago, ALDOT deck depths ranged from 6 114" to 7 3/4 ", with the depth
depending primarily on the girder spacing. About two years ago, the minimum depth was
increased to 7" and thus ALDOT's deck depths now range from 7" to 7 3/4". While this increase
in minimum value is viewed by most parties as being a step in the right direction, this upgrade
does not affect bridge decks with the very common girder spacings of 8 feet or more. Also, even
with the upgrade, ALDOT still employees the thinnest decks in the country.
Thicker bridge decks are stiffer, stronger and should provide a longer servIce life;
however, they cost more and require a stronger and more costly support girder system. Thus, the
cost/benefits of using thicker decks is not clear and this was the impetus for this study.
The results of performing a parameter sensitivity study, talking with ALDOT bridge
design engineers and bridge contractors, and a survey of other state DOTs all point to increasing
bridge deck thickness to a minimum of 8 in. All of the parameters investigate in the parameter
sensitivity study, with the exception of two (deck unit weight and initial cost), support increasing
Alabama's bridge deck thicknesses to 8". An increase in deck thickness from 7" to 8" will cause
the deck unit weight to increase 6-12 psf depending on whether the concrete is added to the top
or underside of the deck. This will increase the cost of the bridge deck around $0.20ft2, and
would translate into an increase in deck/bridge initial cost of around 2%-3%. However,
increasing the deck thickness from 7" to 8" would also increase the deck service life (10-50%)
which would reduce the life cycle cost of the deck/bridge.
From the information developed and collected in this study, it is recommended that
bridge deck thicknesses in Alabama be increased from a minimum of 7" to a minimum of 8".
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This will increase the durability and longevity of the bridge decks and in turn lower the life cycle
cost of decks/bridges. Additionally, a deck thickness of 8" should become the standard and used
throughout the state except for unique circumstances. This will improve construction quality and
lower cost by simplifying the construction process. Also the deck top bar cover should be
increase from 2" to 2 Yz" to allow for construction errors and errors in overestimating the deck
DL deflection. This will help insure a minimum cover of 2". These changes will help improve
the quality of bridge decks in Alabama with minimal increase in initial cost and an anticipated
reduction in life cycle cost.
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ACKNOWLEDGMENTS
This research was supported by the Highway Research Center (HRC) and Civil Engineering
Department at Auburn University. The PI is grateful to these sponsors for their support of this
work. The PI is also grateful to Mr. Keith Mims, President of Alabama Bridge Builders, Inc.,
Mr. Tim McInnis, Vice President of McInnis Corporation, and Mr. Charles Davis, Jr., Chief
Engineer for Scott Bridge Company, Inc., for meeting with him to discuss the effects of
increasing the thickness of bridge decks from construction and cost perspectives. Lastly, the PI
appreciates the cooperation and assistance of the state DOT's via their timely and conscientious
response to our mail survey questionnaire.
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TABLE OF CONTENTS
ABSTRACT ................................................................................................... .i
ACKNOWLEDGMENTS ................................................................................... .iii
1. INTRODUCTION ...................................................................................... 1-1
1.1 Statement of Problem ......................................................................... 1-1
1.2 Project Objectives .............................................................................. 1-1
1.3 Scope of Work .................................................................................. 1-2
1.4 Work Plan ....................................................................................... 1-2
2. BACKGROUND AND LITERATURE REVIEW ................................................ 2-1
2.1 Background ..................................................................................... 2-1
2.2 Literature Review .............................................................................. 2-3
3. RESULTS OF CIP REINFORCED CONCRETE BRIDGE DECK
THICKNESS SURVEy ............................................................................... 3-1
3.1 GeneraL ......................................................................................... 3-1
3.2 Results of State DOT Survey ................................................................ .3-1
3.3 Southern States Survey Results .............................................................. 3-6
3.4 Closure ...........................................................................................3 -6
4. THEORETICAL CONSIDERATIONS ............................................................ .4-1
4.1 General ...........................................................................................4 .1
4.2 Behavior of Beam-and-Slab Decks ......................................................... 4-1
4.3 Influence Lines for Beam-and-Slab Load Distribution Coefficients .................... 4-12
4.4 Stresses in Bridge Decks Due to Wheel Loads ......................................... .4-22
4.5 Deck Punching Shear .........................................................................4 -31
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4.6 Approximate LL Deflections, Girder Spacing and LID Ratios ........................ .4-34
4.7 Transverse Vibrations of Plates/Decks ....................................................4 -38
4.8 Deck Design .................................................................................. 4-46
4.9 Plastic Collapse Analysis of Plates/Decks .............................................. ..4-53
4.10 Construction Tolerances and Errors ..................................................... .4-60
5. PARAMETER SENSITIVITY TO DECK THICKNESS ........................................ 5-1
5.1 General .......................................................................................... 5-1
5.2 Deck Weight and Transverse Cross-Section Properties .................................. 5-1
5.3 Deck/Girder Longitudinal Properties ...................................................... .5-3
5.4 Deck Thermal and Drying Shrinkage Stresses and Cracking Propensity .............. 5-8
5.5 Deck Cracking, Deflection, and Vibration Characteristics ............................. 5-10
5.6 Deck Flexural, Punching Shear, and Strength Characteristics ......................... 5-12
5.7 Influence Lines for Girder-and-Slab Load Distribution Coefficients ................. 5-14
5.8 Deck Fatigue/Service Life .................................................................. 5-20
5.9 Deck/Bridge Costs ............................................................................ 5-22
6. EFFECTS OF INCREASING BRIDGE DECK THICKNESS ..................................6 -1
6.1 GeneraL .......................................................................................... 6-1
6.2 Effect on Support Girders .....................................................................6 -1
6.3 Increasing Deck Thickness-Example Case ................................................. 6-3
6.4 Effects on Other Bridge Components ....................................................... 6-8
6.5 Girder Cost Example ........................................................................ 6-14
6.6 Results of Girder Design Examples ........................................................6 -16
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7. CONSTRUCTION AND COST CONSIDERA TIONS-
CONTRACTOR PERSPECTIVE .................................................................... 7-1
7.1 General .......................................................................................... 7-1
7.2 Contractor Meeting Results .................................................................. 7-2
7.3 Closure ......................................................................................... 7-10
8. CONCLUSIONS AND RECOMMENDATIONS ................................................. 8-1
8.1 Conclusions .................................................................................... 8-1
8.2 Recommendations ............................................................................. 8-3
REFERENCES ..............................................................................................R -1
APPENDIX A MAIL SURVEY QUESTIONNAIRE ON BRIDGE DECK THICKNESS ....A -1
APPENDIX B DECK SUPPORT GIRDER DESIGN EXAMPLES ...............................B -1
APPENDIX C EXAMPLE ILLUSTRATING ADDITIONAL COST OF DECK
CONCRETE CAN BE CAPTURED IN REDUCED DECK REBAR COST ... C-1
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