Abstract： In order to study the performance and mechanism of progressive collapse resistance of RC column-steel beam (RCS) composite structure under the condition of removing penultimate column (the most dangerous condition), the experiment took the beam flange cut through RCS structure joint members as the research object, and the characteristics of different lateral stiffness and beam end restraint capacity of the remaining structure when penultimate column fails were simulated by the difference of beam span. The characteristics of test curve and failure mode were studied, and the development of internal force and resistance mechanism of control section were analyzed. The results show that: after the failure of the second side column in the bottom layer, the weak part of the beam through RCS structure joint appears on the upper flange of the beam, and it is easy to appear local buckling at the upper flange of the side with less lateral stiffness; the resistance mechanism of the structure is changed from the beam bending mechanism to the joint action of the bending mechanism and the catenary mechanism. Then, due to the severe local buckling of the upper flange and web, the structure will be destroyed asymmetrically before the catenary effect is fully exerted.
