Seismic behavior of post-tensioned column base for steel self-centering moment resisting frame

Abstract

This paper presents experimental and analytical investigation of cyclic response of a post-tensioned column (PT) base connection. The PT column base connection is designed to eliminate structural damage at column bases in self-centering moment resisting frames (SC-MRFs) under seismic loading; the softening behavior at the connection is provided by gap opening and elongation of PT bars rather than yielding in the column. Additional shear resistance is provided by bolted keeper plates; additional energy dissipation is provided by buckling restrained steel (BRS) plates. To investigate the cyclic behavior of the PT column base connection, a series of PT column base connection subassemblies were subjected to axial load and cyclic lateral displacements. Test parameters included initial post-tension force, initial axial force in column (constant or varying), column size and loading history. Limit states investigated for the PT column base connections included PT bar yielding and fracture of BRS plates. The test results demonstrated that properly designed PT column base connections were able to undergo lateral displacement up to 4% interstory drift while the columns and grade beams remained elastic. Also, the BRS plates showed good energy dissipation capacity by yielding in tension and compression without fracture. Structural damage at column bases was limited to the replaceable fuse BRS plates. In addition, analytical models were developed to predict the moment–rotation relationship of the PT column base connection and showed good correlation with the experimental data.