Experiments were carried out to investigate the progressive collapse-resisting capacity of reinforced concrete beamcolumn 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 forcedisplacement 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.

Passive energy dissipation devices are generally used to reduce structural responses caused by earthquake or wind loads. This study presents combined system of rotational friction dampers connected to high strength tendons to enhance both seismic and progressive collapse-resisting capacity of existing structures. Friction dampers were designed using the capacity spectrum method to satisfy given performance objectives against seismic load, and their seismic-and progressive collapse-resisting capacities were investigated. According to the nonlinear dynamic analysis results, the structures retrofi tted with rotational friction dampers generally satisfi ed the given performance objectives against seismic load. Both the nonlinear static and dynamic analysis results showed that the progressive collapse potential of the model structures was signifi cantly enhanced as a result of the seismic retrofi t.

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