MECHANISM OF PROGRESSIVE COLLAPSE RESISTANCE OF REINFORCED CONCRETE SPATIAL FRAME STRUCTURE

Progressive collapse is spatial, and effected by structural redundancy. Therefore a spatial frame is more realistic than a plane frame to reflect the spatial characteristic of progressive collapses. Based on the experimental research on progressive collapse performance, mechanism of progressive collapse resistance of reinforced concrete spatial frame structure is analyzed in this paper. In the case of the initial local damage of the middle-side column of the first floor, the entire collapse process can be divided into four stages, namely elastic stage, elastoplastic stage, plastic hinge development phase and compound mechanism stage. Progressive collapse resistance consists of beam mechanism and catenary mechanism. As for the longitudinal frame, beam mechanism and catenary mechanism both play a part in resisting progressive collapse, while only catenary mechanism works as for the transverse frame. In the compound mechanism stage, progressive collapse resistance is not the simple addition of utimate capacity of beam mechanism and catenary mechanism. With the displacement development, beam mechanism gradually reduced, but catenary mechanism enhance little by little. They are changing. The degree of role of beam mechanism or catenary mechanism is related to the plastic deformation ability of frame beams.