In this study the vertical push-down analysis was conducted to investigate the resistance of steel moment frames for progressive collapse. The analysis was carried out by gradually increasing the vertical displacement in the location of the removed column and the vertical load in all spans corresponding to the increase of vertical displacement. The analysis results showed that the load resisting capacity increased as the number of stories and the number of spans increased. However, as the length of a span increased, the load resisting capacity against progressive collapse decreased. The load-displacement relationships obtained from push-down analyses were compared with those obtained by incremental nonlinear dynamic analyses, and the results showed that the maximum load factors resulted from the dynamic analyses were a little less than those from the push-down analyses. This implies that the push-down analysis might overestimate the inherent capacity of structures against progressive collapse.

In this research a seismic retrofit system consisting of a pin-jointed steel frame and rotational friction dampers is developed for the seismic retrofit of reinforced concrete soft-first-story structures, and its efficiency is evaluated through theoretical formulation, cyclic loading test, and analysis of a case study structure. In this system, pin-jointed steel frames are attached to a framed structure at the first story, and a rotational friction damper is installed at each corner of the steel frames. A theoretical formulation is derived for the amplification mechanism of the rotational friction damper and is used to design the geometry of the damper in such a way that its rotation is maximized for a given lateral drift of the structure. The experimental and analysis results show that the proposed system can be used efficiently to prevent the collapse of the case study structure and reduce interstory drift ratios to the code-stipulated limit states.

In this study the progressive collapse resisting capacity of a RC beam-column subassemblage with and without strengthening was investigated. Total of five specimens were tested; two unreinforced specimens, the one designed as gravity load-resisting system and the other as seismic load-resisting system, and three specimens reinforced with: (i) bonded strand, (ii) unbonded strand, and (iii) side steel plates with stud bolts. The two-span subassemblages were designed as part of an eight-story RC building. Monotonically increasing load was applied at the middle column of the specimens and the force–displacement relationships were plotted. It was observed that the gravity load-resisting specimen failed by fractures of re-bars in the beams. In the other specimens no failure was observed until the maximum displacement capacity of the actuator was reached. Highest strength was observed in the structure with unbonded strand. The test result of the specimen with side steel plates in beam-column joints showed that the force–displacement curve increased without fracture of re-bars. Based on the test results it was concluded that the progressive collapse resisting capacity of a RC frame could be significantly enhanced using unbonded strands or side plates with stud bolts.