Progressive collapse-resisting capacity of RC beam-column sub-assemblage

Experiments were carried out to investigate the progressive collapse-resisting capacity of reinforced concrete beam-column sub-assemblages designed with and without seismic load. The two-span sub-assemblages were designed as part of five-and eight-storey reinforced concrete moment-resisting frames. The exterior columns of the right-hand girders were designed to be 1.5 times larger in size than the middle columns to take into account continuation of the girder. A monotonically increasing load was applied at the middle column of the specimens and force-displacement relationships were plotted. It was observed that the non-seismically designed specimen failed by crushing of concrete at the exterior column-girder joint of the left-hand girder before catenary action was activated. However, the force-displacement relationship of the specimen designed for seismic load kept increasing after fracture of the girder lower rebars near the middle column due to the catenary force of the upper rebars. Based on the test results it was concluded that significant catenary action of girders could be induced in reinforced concrete moment-resisting buildings designed as per current seismic design codes against progressive collapse initiated by sudden loss of a column.