Load and Resistance Factor Design of Integral Bent Caps

Abstract

Cast-in-place concrete box girder highway bridges with integral bent cap substructures are the preferred bridge type in California. In the AASHTO LRFD Bridge Design Specifications, two methods are available for the design of integral bent caps: the sectional method for flexural members and the strut and tie method (STM) for flexural and deep members. Although many bent caps are considered deep beams according to the AASHTO load and resistance factor design provisions, practicing engineers elect to use the sectional method exclusively for design because of its familiarity and the lack of guidance for using STM. Design examples that used STM have been published, but none of these examples deals with integral bent caps. When applying STM to integral bent caps, several issues, unique to this geometry, need to be addressed. These issues are discussed, and three different integral bent cap design examples are presented. The design of the three bent cap examples was also carried out by using the sectional method. The application of the sectional method to integral bent caps presented its own issues. These issues are discussed, and the results of both methods are compared.