Seismic behaviour of framed tubes

Abstract

A framed tube, consisting of closely spaced columns connected by deep spandrel beams, is designed in reinforced concrete for building code loads. The members of the frame are proportioned using strength concepts. A planar model of the tube is developed and its behaviour is compared to that of the three‐dimensional structure. The planar model is then used to evaluate the inelastic behaviour of the framed tube when subjected to strong ground motion. The effects of the finite element discretization and the ground motion characteristics are investigated. Results show that ductility requirements of the spandrel beams are minimum at the top and maximum at the bottom of the tube. Ductility requirements in the columns are well controlled and are within acceptable limits. Participation of the higher modes of vibration is significant and requires increasing damping. It also is shown that the increased stiffness due to finite member sizes at a joint cannot be neglected.