Cracking in Reinforced Concrete Bent Caps: Summary Report (0-1851-S)

Unexpected cracking in reinforced concrete (RC) bent caps at outside column locations (canti-levered regions) occurs occasionally in Texas bridges (see Figure 1). Smaller vertical flexural cracks exist in the bent over the supporting column and larger inclined flexure-shear cracks propagate from the girder loading region to the supporting column. This cracking typically occurs during service loading. From engineering drawings of a sample bent cap constructed prior to 1989, several reinforcing details are noted with regard to their possible contribution to cracking: (1) top longitudinal reinforcement without hooks or end plates at the bent cap end may have bond (or slip) problems due to insufficient embedment; (2) shear span-to-depth ratio of about 1.5, which is close to the deep beam classification in the American Association of State Highway and Transportation Officials (AASHTO) and American Concrete Institute (ACI) 318 codes; and (3) longitudinal skin reinforcement evenly distributed through the member depth or concentrated in the web tension region of the bent cap side faces per previous and current codes, respectively.