Progressive collapse occurs when a sudden event such as a blast or an impact load influences a structure. Wherein, loss of continuity and low ductility of the remaining structural members result in total collapse of it. Alternate Path Method (APM) is an efficient method to study progressive collapse that is recommended in common guidelines such as GSA and UFC. APM check outs alternate paths in remained structure to resist progressive collapse due to key elements loss. This research surveys different scenarios of column elimination in planar regular and irregular frames by conducting non-linear dynamic analysis. Verification of the selected methods is conducted via analyzing an experimental model. Generally removal of corner column leads to significant responses compared with other scenarios. Moreover, eliminating a column in irregular frame causes large displacements and beam rotations which could be attributed to uneven distribution of forces in structural members; so regularity is an important factor to resist collapse.

1. Introduction Progressive collapse of building structures typically occurs when an abnormal loading condition causes a sudden loss in the structural capacity of one or more critical members, which leads to a chain reaction of failure and ultimately catastrophic collapse (Tohihi et al, 2014). In this research, based on the alternative load path (ALP) approach, using the three-dimension (3D) finite element (FE) method, numerical studies were conducted for the investigation of progressive collapse resistance of beam-column joints in Reinforced concrete (RC) frame under loss of exterior ground column. The paper presents a simple and reliable FE model that predicted the nonlinear load-deflection response of tested RC joints conducted by other researchers. Experimental models including two sets of interior and exterior subassemblages were analyzed under monotonic loading to simulate gravity load on the damaged frame after a blast. In the numerical simulations, the nonlinear behavior of materials was modeled by appropriate constitutive laws. The comparisons between numerical and experimental responses highlighted the reliability of the proposed FE model. In addition, a parametric study is conducted using the validated models to investigate the effect of slab on the behavior of the subassemblages and the transverse reinforcement ratio and slab effects on the performance of substructures that covering both the interior and exterior joints...

This paper is devoted to assess the behavior of the exterior concrete beam-column connections Reinforced with Glass Fiber Reinforced Polymers (GFRP) bars under cyclic loading. For this purpose, 8 different beam-column connections were experimentally investigated. In these specimens, concrete with compressive strength of 30 and 45 MPa was employed. In four of these connections, GFRP bars were used while the others were Reinforced with steel bars. The confinement of longitudinal bars was different in the connections. The GFRP-Reinforced beam-column connection showed an elastic behavior with very low plasticity features under cyclic loading. This resulted in lower energy dissipation compared to the steel-Reinforced beam-column connections. The GFRP-Reinforced beam-column connections showed lower stiffness than that of the steel-Reinforced beam-column connections. Load-story drift envelope for specimens with GFRP bars showed an acceptable drift capacity. These specimens had the essential requirements for acting as a member of a moment frame in seismic regions. In case of GFRP strengthened specimens with low and high strength concrete, increasing the cyclic loading results in flexural failure of the beam in the beam-column connection region. Increasing the confinement of concrete beams leads to the reduction of crack width. Furthermore, at higher drifts, spalling was not observed in concrete surface in beam-column connection region. In the analytical parts of the study, specimens were simulated using the SeismoStruct software. Experimental and analytical results showed a satisfactory correlation.

This paper presents the effect of Reinforced high performance concrete (HPC) in exterior beam-column joint with and without fibre under monotonic loading. In this experimental investigation, cross-diagonal bars have been provided at the joint for reducing the congestion of reinforcement in joints, and also M75 grade of concrete with optimum mix proportion of 10 % silica fume and 0.3 % glass fibre was used. Four exterior beam-column joint sub-assemblages were tested. The specimens were divided into two types based on the reinforcement detailing.Type A comprises two joint sub-assemblages with joint detailing as per construction code of practice in India (IS 456-2000), and Type B comprises two joint subassemblages with joint detailing as per ductile detailing code of practice in India (IS 13920-1993). In each group there was one specimen of control mix and the remaining one specimen of fibre-Reinforced mix. All the test specimens were designed to satisfy the strong column–weak beam concept. The performances of specimens were compared with the control mix and the fibre-Reinforced mix. The results show that exterior beam-column joint specimens with silica fume and glass fibre in the HPC mix showed better performance.

Composite special moment frames represent a novel type of special moment frames (SMFs) where a combination of concrete columns and steel beams is used. This paper evaluates the modeling of composite special moment frames and the behavior of the steel beam-concrete column connection. Due to the focus on hinge formation, the behavior of the connection with a hole drilled on the beam flange was analyzed. Numerical simulations were carried out in ABAQUS. The beam-column connection was subjected to one-five rows of holes. It was observed that the beam-column connection with three rows of holes had the optimal hinge formation behavior, stress distribution, and load. The connection with five rows of holes showed plastic strains in the first four rows, while the fifth row had no plastic strain. This suggests an increased drilling space since the fifth hole row did not contribute to the improvement of stress distribution uniformity. It was numerically found that the bending moment change varied from 8% to 46%; the model with three rows of holes had the lowest bending moment change, whereas the model with a single hole row showed the highest change in the bending moment. Moreover, energy absorption changed by 4-20%.

In recent years, the use of larger Reinforced concrete (R.C.) column-supported hyperboloid cooling towers has been increased significantly. Thus, the investigation on failure criteria for structural components of such structures under different loads has been found as an essential need. Construction of cooling towers in seismic zones initiated the study on the dynamic behavior of such structures due to seismic loads. In this paper, finite element analyses have been performed to obtain the stress concentration, nonlinear behavior, stability or safety factor of the R.C. tower due to earthquake loads. Outcomes of the study show that considerable plastic hinges were created in the X shape long columns of the R.C. hyperboloid cooling tower due to seismic loads, which resulted in a significant decrease in the stability safety factor and, thus, an increase in concerns.

This paper presents an experimental investigation on the behaviour of retrofitted beam-column joints subjected to cyclic loading. The beam-column joints were designed for gravity loading. The same joints were retrofitted for seismic loading with four different retrofitting strategies essentially to achieve equal strength of the segment under sagging and hogging bending moments. The results obtained from the experimental investigation gives better understanding of the strengthening and repair methodology of FRP strips, FRP sheets, MS flats and embedded additional reinforcement in RC beam–column joints under cyclic loading. A simple analytical model proposed by Ibarra et al. is shown to be an excellent tool for performance evaluation of the retrofitted beam column joints. The progressive damage in the retrofitted elements can also be well predicted.