Behavior and Design of Spread Prestressed Concrete Slab Beam Bridges

Abstract

The Texas Department of Transportation (TxDOT) uses precast prestressed concrete slab beam bridges in a side-by-side configuration for short span bridges in low clearance areas. A new bridge type called a spread slab beam bridge was recently developed using the same concept as spread box beam bridges in which the beams are spaced apart with precast panel stay-in-place forms between beams and a cast-in-place concrete deck. This research presents an evaluation of spread slab beam bridges in terms of design, constructability and performance. The main objective of this project is to develop appropriate design guidelines for this alternative spread slab beam bridge system. Forty-four bridge geometries are designed using standard TxDOT slab beam types to determine the feasible design space. One of the most aggressive geometries with widely spaced slab beams is constructed as a full-scale test bridge and tested under static and dynamic vehicular loads to evaluate constructability and structural performance. Load distribution behavior is investigated during field testing and the measured data is utilized to validate modeling techniques including orthotropic plate analysis, grillage analysis and finite element method based on research findings.

It is concluded that spread slab beam bridges that utilize precast concrete panels with a cast-in-place concrete deck provide a viable construction method for short-span bridges. For the tested bridge, the desired performance is achieved for in-service loading. Field testing shows that beam live load deflections are within the design limits, with no significant cracking or reduction in the overall stiffness of the bridge observed. Experimental load distribution factors (LDFs) are evaluated using alignments that provided the most adverse loading cases. Bridge responses under dynamic loads are larger compared to the static counterparts. The American Association of State Highway Transportation Officials (AASHTO) Load and Resistance Factor Design (2012) LDF equations for spread box beams are reviewed for applicability to spread slab beams and shown to range from being unconservative to very conservative when applied to spread slab beam bridges. Unique LDF expressions are developed for spread slab beam bridges to provide an appropriate estimate of load sharing for beam design.