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Distribution Factors for Design of Bridge Girder with FRP Decks

I. Research Problem Statement

Building bridges with non-corrosive FRP decks is one of the promising applications for the use of composite materials in the civil infrastructure. Several states have embarked on pilot projects to explore the feasibility of this promising application. It is well known that the number one item of maintenance cost is fixing/replacing bridge decks that have deteriorated due to harsh environmental conditions. The advantages that FRP decks have to offer (non-corrosive, light weight, etc.) outweigh its disadvantages (connection details, vulnerability to dynamic loads, etc.), which can all be improved by further research. However, as it is always the case with civil infrastructure applications, FRP decks have not been widely accepted, and rightly so, by the bridge community. This research will address one of the major barriers that prohibit many designers from adopting the use of FRP decks. AASHTO has always provided simplified means by which the design of a complex bridge system can be carried out without resorting to costly refined methods. Since the 1930s, designers have used simplified distribution factors that isolate the transverse design of a bridge from its longitudinal design. It is the common practice and the training that all bridge designers get accustomed to. The distribution factor expressions in AASHTO-Standard were overhauled in AASHTO-LRFD based on the results from NCHRP Project 12-26. AASHTO-LRFD recognizes the impact of relative stiffness between the deck (transverse direction) and girder (longitudinal direction) on the distribution factor which was lacking in AASHTO-Standard. The calibration of the current AASHTO-LRFD expressions was intended for concrete decks and was not intended to be applicable for FRP decks which have a different stiffness that may be non-uniform if some of its portions are cast in place concrete to ensure composite action or provide shear keys. Another project (NCHRP Project 12-62) which was meant to address some shortcomings in the current expressions in AASHTO-LRFD does not address FRP decks as well. Lacking simplified expressions for the distribution factor of girder bridge with FRP decks puts a huge burden on designers, which normally would opt for a more common, well-understood, and easily designed alternative; i.e. cast-in-place deck. Providing these expressions would eliminate this unnecessary barrier, which would give designers the tools they are accustomed to, the industry a boost it needs, and bridge owners the low-cost decks they need.

II. Research Proposed

The objective of the project is to provide bridge engineers with tools for the design of FRP decks that conform to current AASHTO-LRFD design specifications. The research should include a survey of the properties of FRP decks available in the market. This information will be synthesized and categorized based on their structural properties. Distribution factors will be obtained from intensive analytical studies that need to be conducted to cover a wide range of parameters. The analytical models will first be verified through load testing of existing bridges with FRP decks. Results from this research will need to be presented in the form of provisions in preparation fro adoption in AASHTO-LRFD. The goal of the research should include the development of design specifications for inclusion in the AASHTO LRFD manual.

Key Words:

Bridges, FRP decks, distribution factors.

Related Work:

1. AASHTO, LRFD Bridge Design Specifications, American Association of State Highway and Transportation Officials, Washington, D.C.,

2. NCHRP Project 12-26, FY 1992 (Completed). Distribution of Wheel Loads on Highway Bridges

3. NCHRP Project 12-62, FY 2003 (Active). Simplified Live-Load Distribution-Factor Equations

III. Estimate of Problem Funding and Research Period Recommended Funding:

$300,000 Research Period: 24 mos.

IV. Urgency/Priority

The design of FRP bridge decks is not documented in AASHT- LRFD, which creates a barrier to the greater use of this system with high potential. The elimination of this barrier will allow for wider adoption of the system, which adds another tool by which rapid bridge construction can be achieved. This will add another tool that helps achieve the goal of designers, contractors, and everyone involved in the transportation industry: Get in, Get out, and Stay out. User Community Results of the research will be directly applicable to the AASHTO LRFD Specifications and will benefit the whole bridge community. Implementation Research results will be implemented with proposed revisions to the AASHTO LRFD Bridge Design Specifications. Effectiveness The long-term benefits of this research include faster construction times, potential lower initial costs, lower maintenance costs and longer life for bridges. This results in less cost and less inconvenience to society. Thrust/Business Need Enhanced Materials, Structural Systems, and Technologies Modular construction Rapid replacement techniques Efficient Maintenance, Rehabilitation, and Construction Efficient construction methods Enhanced Specifications for Improved Structural Performance Design and construction concepts for rapid replacement and repair .

V. Person(s) Developing the Problem

Ayman M. Okeil, Ph.D., P.E. Department of Civil and Environmental Engineering CEBA 3502, LSU Baton Rouge, LA 70803 Phone (225) 578-7048 Fax (225) 578-8652 e-mail aokeil@lsu.edu

VI. Date and Submitted by

Issam Harik

E-Mail: iharik@engr.uky.edu

Sponsoring Committee:AKB10, Innovative Highway Structures and Appurtenances
Date Posted:12/28/2006
Date Modified:10/29/2010
Index Terms:Bridge decks, Girder bridges, Bridge design, Fiber reinforced polymers, Fiber reinforced materials, Dynamic loads, Load transfer, AASHTO LRFD Bridge Design Specifications, Cast in place structures, Longitudinal strength, Infrastructure, Designers,
Cosponsoring Committees: 
Bridges and other structures

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