Research is reported that was planned to develop design procedures for bent caps which would include consideration for the location and distribution of critical AASHTO loading for a bent cap, the effect of flaring a column, the effective width of a bent cap, the effect of spreading bent cap reinforcement into an adjacent box girder slab, and the location of critical cross sections. The research which was conducted in two phases (analytical and experimental) consisted of studies of load distribution in bridge entireties and stress distribution in bent caps on two prototype bridges, and the construction and testing of seven scale models. Two of the models, built to one-fifth scale of the prototype bridges, were representative of popular reinforced concrete box girder designs. Model tests provided information on the distribution of loads in the vicinity of integrated bent caps. Another five models represented transverse strips of bridge superstructures parallel to, and including, the bent caps and columns. Column flare and the amount and distribution of bent cap reinforcement varied in these models. These tests provided information about critical sections and the effective width of bent caps. The recommendation is made (based on the results of the investigation) for the use of present AASHTO design methods. It is also recommended that for an integral support to be considered effective, the angle of greatest slope of the surface of the support shall not exceed 45 degrees from the vertical. Conditions governing the effective width of an overhanging compression flange on either side of the web of an integral bent cap are listed as well those conditions governing the effective width of an overhanging tension flange on either side of an integral bent cap. Regarding the design section for negative moment, it is recommended that moments at the face of support may be used for design of the bent cap. The face of support is defined as the limit of the effective support along the center line of the bent cap. The recommendation related to the effect of spreading reinforcement urges the use of provisions specified for the effective flange width tension. Observations are also reported which relate to one of the primary aims of this study, namely, to determine if current design methods resulted in more reinforcement than needed in the bent cap.
Samenvatting