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The subject of progressive collapse assessment in RC structures has been concerned in various studies. In contrast, most of these studies have attended to a scenario in which an instantaneous removal of a column due to unexpected impact or explosion has occurred. The present study addresses progressive collapse in RC structures resulting from both instantaneous and gradual removal of columns. The scenario for a gradual removal is the result of slow decreasing strength due to fire propagation in a specific zone of structure which is partially fire-proved. A five-story building model was selected as a case study for which the nonlinear model is later developed. Vertical displacement in the upper node of the removed column, redistribution of forces after removing the column, plastic deformations in adjoining elements, and the stress imposed on the sections of the beams adjacent to the removed column in both instantaneous and gradual cases are studied.

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This paper presents the results of a study that was carried out to investigate the use of small-diameter CFRP strands for strengthening steel plates subjected to uniaxial compression. This study is part of a comprehensive research program to evaluate the use of the small-diameter CFRP strands for shear strengthening of steel girders. The research in this paper was undertaken to examine the bond characteristics of the proposed material which is expected to eliminate the debonding failure observed for CFRP laminates strengthening system and to resist the compressive stresses induced in high shear zones. The small-diameter CFRP strands are stitched together with a gap between the strands to allow each strand to be completely covered by the adhesive material. The effectiveness of the strengthening system was investigated by varying various parameters believed to affect the overall behavior including the slenderness ratio of the steel plates as well as mechanical properties and reinforcement ratios of the CFRP strands. Strengthened plates exhibited higher buckling capacity in comparison to similar plates without CFRP strands. In addition, the small-diameter CFRP strands did not show any signs of debonding at large lateral deformation associated with elastic buckling.

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The Khorjinee connection is a special connection that was widely used in the construction of low-rise steel structures in Iran before the national seismic code was established. However, catastrophic experiences from recent earthquakes have shown that these connections are highly vulnerable to seismic loads. In fact, it is recognised that such connections should be classified as non-seismic, semi-rigid connections with unknown rotational stiffness. As a result of this issue, many structures with these connections may need to be rehabilitated to ensure their safety in future earthquakes. In this study the dynamic properties of a half-scale model of a four-storey steel structure with Khorjinee connections were determined by a forced vibration test. The structure was then separately rehabilitated by means of four different bracing configurations (X bracing, chevron bracing, eccentrically braced frames (EBFs) and knee braces) and the structural responses were investigated. The results, which include the natural frequencies, mode shapes and damping ratios for each case, present a realistic approach to enable engineers to select the best way of strengthening steel structures with Khorjinee connections according to diverse structural limitations. The structural displacement ratios were found to be significantly larger in structures with EBFs and knee bracing systems when the number of braced spans is high compared with the first mode.