Experimental Assessment of Second-Generation Hybrid Sliding-Rocking Bridge Columns under Reversed Lateral Loading for Free and Fixed End Rotation Conditions

Hybrid sliding-rocking (HSR) bridge columns are among the resilient column designs recently developed to allow accelerated bridge construction for bridge substructures in seismic areas. HSR columns are precast concrete segmental columns with unbonded posttensioning, end rocking joints, and intermediate sliding joints. This design provides significant energy dissipation and partial self-centering capabilities. This paper describes Second-Generation HSR columns and assesses their seismic performance through experimental testing. The Second-Generation HSR columns have fewer sliding joints than the original HSR columns, employ high-performance materials at their sliding joints to better control their frictional properties, and are designed to minimize the columns' seismic damage at target hazard levels through large joint sliding and relatively small end joint rocking. The experimental results discussed herein are from 15 selected tests performed on two half-scale identical column specimens tested under cantilever and fixed-fixed conditions. Both column specimens were tested under reversed lateral loading, including a variety of cyclic and arbitrary loading protocols with various loading rates, representing quasi-static and quasi-dynamic conditions. Satisfying their performance objectives, the damage sustained by both columns under the peak drift ratios representing 975- and 2475-year ground motions representative of Los Angeles, California, was minimal. Under those peak drift ratios, the residual drift ratios remained below 1.1% and 0.7% for the cantilever and fixed-fixed columns, respectively, and more than 90% of those residual drifts were from joint sliding and, thus, recoverable. The damage observed under even more rare ground motion demands included concrete spalling near the rocking joints and strand wire fractures in both the cantilever and fixed-fixed column specimens, as well as concrete cone failures near the sliding joints in the fixed-fixed specimen.