Precast, Prestressed Concrete Bent Caps: Volume 1 Preliminary Design Considerations and Experimental Test Program

Precast prestressed concrete bent caps may provide significant benefits by enabling accelerated construction of bridge substructures and improve longevity by reducing the propensity for cracking. The Texas Department of Transportation enables the use of precast reinforced concrete (RC) bent caps through standard connection details that allow contractors the option of cast-in-place or precast caps. A largely unrealized benefit of precast caps is the use of prestressing to enable additional fabrication options and to reduce or eliminate cracking. To enable widespread use, the design and behavior of pretensioned bent caps is explored through a comprehensive study consisting of a literature review, a design study, experimental tests, and with a discussion of the results. Design for flexure is based upon the concept of zero tensile stresses under dead loads, thereby ensuring any cracks close upon removal of live loads. A modified pocket connection is designed to improve constructability and minimize the potential negative effects of prestressing at the reduced cross-section. Full-scale bent caps were tested under indeterminate loads representative of those in multicolumn bents. An RC specimen was designed, constructed, and tested to serve as a performance baseline. Pretensioned caps investigate the spacing of shear spacing, use of voids, and void detailing. Pretensioned caps exhibit significantly reduced flexure cracking, with the ability to fully close upon removal of live load. Bent caps with voids were susceptible to minor shear cracking under design loads, with minimal impact of void detailing. Pocket connections provided adequate performance under design loads. The experimental findings validate the design and construction concepts, which may be useful in developing design and construction recommendations.