Cyclic experimental response of self-centering concrete frames with slotted columns

Abstract

A slot, which is a partial separation between a column and a base, provides the rotation of columns in a moment-resistant frame under strong ground motion, and prevents severe concrete crushing due to concentrated plastic deformation at the bottom end of the column. In a slotted column, unbonded post-tensioned tendons are arranged at the centerline of the cross-section to reduce residual drift, that the moment-resistant concrete frame performed the capacity of self-centering. The aim of this study was to determine the cyclic lateral response of a self-centering concrete frame with slotted columns. Three 1/2.5 scale frames, with different graded longitudinal reinforcements as energy dissipators in the slots, were tested under cyclic lateral loads combined with different axial loads. The failure of specimens was observed without the presence of plastic hinges near the column end, and the energy dissipation capacity was quantitatively analyzed. The fracture of several exposed longitudinal reinforcements in the slots during the test had a lesser influence on the energy dissipation capacity. The residual drifts of the three specimens were less than 1.00% for the elastoplastic seismic design at 2.00% lateral drift, and less than 1.75% at failure. By investigating the rules of the loading and unloading stiffnesses at different loading stages, a hysteretic model was developed to provide a satisfactory prediction of the structural residual drift, in which the residual drift was considered as constant after the fracture of several longitudinal reinforcements in the slots.