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SWUTC Research Project Description

Spread Prestressed Concrete Slab Beams

University: Texas A&M University

Principal Investigator:
Mary Beth Hueste
Texas Transportation Institute
(979) 845-1940

Funding Source: SPR Program

Total Project Cost: $236,565

Project Number: 0-6722

Date Started: 9/1/12

Estimated Completion Date: 8/31/13

Project Summary

Project Abstract:
TxDOT uses prestressed slab beam bridges for shorter spans, such as stream crossings. These bridges have precast, pretensioned slab beams placed immediately adjacent to one another with a cast-in-place slab made composite with the beams. While these bridges are used extensively, they are more expensive than traditional prestressed I-beam and I-girder structures on a per square foot basis.  The objective of this project is to explore the use of slab beams that are spread apart. This modified bridge type could significantly reduce the cost of shorter span bridges, while being easily mass produced, transported and constructed.

Project Objectives:
The overall objective of this project is to explore the possible benefits of utilizing a spread prestressed slab beam configuration in bridges.  The major goal is that TxDOT will implement spread prestressed slab beams with greater economy than currently possible with conventional slab beam bridges. The research will include an experimental assessment of the performance of a spread slab beam bridge system, along with determination of appropriate live load distribution factors. Based on this objective, the following work plan will be executed with specific tasks identified to meet the desired project outcomes.

Task Descriptions:

Task 1:   Synthesize Literature and State-of-the-Practice

Task 2:  Preliminary Designs

Task 3:  Full-scale Bridge Field Test

Task 4:  Laboratory Testing

Task 5:  Analysis of Experimental Results

Task 6:  Live Load Distribution Factors

Task 7:  Develop Design Guidelines and Example

Task 8:  Report Preparation

Implementation of Research Outcomes:
Preliminary designs were developed to assess the potential of a spread slab beam bridge system. A full-scale spread slab beam bridge was constructed at the Texas A&M University Riverside Campus and tested to assess constructability, in-service performance, and behavior.  Field testing was conducted for the Riverside bridge and a US 69 on-system bridge to evaluate load distribution behavior and to provide data to guide analytical modeling of this bridge system. Analytical models were developed to investigate an array of possible bridge geometries. Based on these models, recommendations were developed for shear and moment load distribution factor (LDF) relationships for the design of spread slab beam bridges.

Impacts/Benefits of Implementation:
LDF relationships for shear and moment were developed to facilitate implementation of the spread slab beam system. The American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) LDF equations for spread box beams were reviewed for applicability to spread slab beams. The AASHTO LDFs range from being unconservative to very conservative. For example, the AASHTO expressions slightly underestimate shear for interior spread slab beams.  Unique LDF expressions were developed for spread slab beam bridges to provide an appropriate level of conservatism. The proposed moment LDF for interior slab beams (multiple lanes loaded) is identical to the AASHTO LRFD spread box beam equation.

Web Links:
Final Technical Report