Experimental research on seismic behavior of enveloping steel strengthened seismic-damaged exterior joints in composite frame consisting of CFSST columns and steel beams

In order to study the seismic performance of seismic-damaged exterior joints in composite frame consisting of concrete-filled square steel tubular (CFSST) columns and steel beams strengthened with enveloping steel, one half scaled models of five exterior joints in composite frame consisting of CFSST columns and steel beams were designed and manufactured. One model was prototype control specimen, one was strengthened by enveloping steel, and the others were pre-damaged and strengthened. The destruction tests under lateral cyclic load on the models were carried out. The test results show that seismic-damaged joints in composite frame consisting of CFSST columns and steel beams strengthened with enveloping steel can meet the strong column-weak beam requirement of seismic design, and the failure modes of all joints are the flexural failure of steel beam. Compared with the prototype control specimen, the ultimate loading and the ultimate displacement of the mildly damaged specimen after retrofit are increased by 20.8% and 19.8% respectively, the ultimate loading and the ultimate displacement of the moderately damaged specimen after retrofit are increased by 12.3% and 11.3% respectively, and the ultimate loading and the ultimate displacement of the severely damaged specimen after retrofit are increased by 4.8% and 6.1%. In general, the strengthening method of seismic-damaged joints by enveloping steel is an effective method for seismic strengthening. ©, 2015, Science Press. All right reserved.