Lateral-Load Response of Two Reinforced Concrete Bents

Two reinforced concrete bridge bents were subjected to large, transverse displacements. The bents contained detailing deficiencies typical of the 1960s, including minimal transverse reinforcement, short reinforcing splices, and a lack of top reinforcement in the footings. Spalling of the concrete cover at the column tops began at a drift ratio of 1.5. At this drift ratio, the column displacement ductility was approximately four, the curvature ductility was eight, and nominal curvature in the plastic hinges corresponded to a nominal maximum concrete strain of 0.01. In spite of their deficiencies, the bents resisted transverse loads equal to nearly 40% of the bridge's weight at a drift ratio of 3%. The ductile response was attributed to a low shear demand and to the influence of the soil in redistributing the rotational demands away from the column splices. The measured response was reproduced well by an analytical model that considered the nonlinear force-deformation relationships of the columns and soil. The results of a parametric study indicated that the soil surrounding the column bases increased the column shear demand by 25%.