Effective Width of Integral Bent Caps in Reinforced-Concrete Box-Girder Bridges

The objective of this paper is to revise the effective slab width of integral bent cap beams in reinforced concrete box-girder bridges. Currently, a conservative code-based value of 12 times the slab width plus the cap beam width is used to define the beam’s top and bottom flange widths to account for the box-girder slab contribution as part of the cap beam analysis and design. A comprehensive experimental study was utilized to revise the integral bent cap beam effective slab width for more accurate design and capacity estimation. Two large-scale column-cap beam-box-girder bridge subassemblages were tested under combined vertical and lateral loading. The first specimen was tested using quasi-static cyclic loading and the second was tested using hybrid simulation earthquake loading. A strain-based approach was used to estimate the bent cap effective slab width at different loading levels. The study concluded that 12 times the slab width is a conservative estimate for the box-girder slab contribution to the bent cap stiffness and capacity, and 18 times the slab width is a more accurate representation.