Development of Rocking Column Systems

Current seismic bridge design practices rely on the development of damage and the potential for residual deformations following a seismic event due to the formation of a flexural plastic hinge. Improved response can be realized through the use of rocking column systems that employ a combination of unbonded post-tensioning and bonded mild reinforcement. Rocking column systems can produce significantly less damage and residual displacements when compared to a traditional cast-in-place concrete column. As a part of a broader research program investigating seismic accelerated bridge construction, a total of three rocking column systems are being studied both analytically and experimentally. The first specimen is a conventional system employing tightly spaced spiral reinforcement to provide confinement at the column base. The second specimen uses a concrete filled steel tube for confinement and flexural reinforcement. Mild reinforcement only passes across the joint and develops in the column and is then terminated. The third specimen is a hollow column that used two shells as confinement and lateral resistance. Again the mild reinforcement extends only a short distance into the column to allow for development. This paper presents the basic design requirements that must be satisfied to ensure the benefits of a hybrid system are achieved. Basic results of the testing of the first two specimens are also included.