Seismic collapse resistance performance on out-jacketing frames with concrete-encased CFST columns for adding storeys

Abstract This research paper conducted a hysteretic behavior simulation on a single-span and single-storey frame composed of prestressed concrete-encased steel beams and concrete-encased concrete filled steel tube (CFST) columns. The hysteretic parameters of stiffness degradation, strength degradation and pinching behavior for members were suggested according to tested results. After that, an analytical model for corresponding out-jacketing frames with single-span and multi-storey was developed, and amounts of elastoplastic seismic response analysis were conducted for seismic fortification intensities 7 and 8 with various site-classes and design earthquake groups under rare earthquake. The results indicated that, the out-jacketing frames assigned to Intensity 7 with Site-classes I0 to III behaved perfectly in seismic collapse resistance performance, which could be designed as regular frames by using China's current codes; while referring to Intensity 8, a certain amount of out-jacketing frames assigned to Site-classes I0 to III had inter-storey collapse mechanism, and several design proposals were developed to prevent collapse failure by measurements of enhancing seismic grade.