Beam-column connection flexural behavior and seismic collapse performance of concentrically braced frames

This dissertation investigates the flexural behavior of beam-column connections with gusset plates and their ability to improve the seismic collapse performance of concentrically braced frames. Previous experimental and field observations demonstrated that reserve lateral force-resisting capacity due to the flexural strength of connections outside the primary lateral force-resisting system of steel frames can maintain structural stability if the primary system is damaged. Several experimental studies were conducted to quantify the flexural behavior of these connections, but there has only been limited investigation of beam-column connections with gusset plates. Thus, the focus of this study was two-fold. First, expand existing knowledge about the flexural behavior of braced frame connections. This task was accomplished through a series of large-scale experiments of beam-column subassemblies. The braced frame connections in the experimental program were double angle and end plate details that were proportioned based on the design loads from a prototype braced frame. The results from the experiments suggested that beam-column connections with gusset plates have appreciable flexural stiffness and strength. In addition, the flexural stiffness and strength of the connections could be increased, with minimal ductility loss, by thickening the double angles and adding a supplemental seat angle. The stiffness, strength, and ductility were limited, however, by weld failure, angle fracture, and bolt fracture. Since only one beam depth was used in the large-scale testing, it was desirable to investigate the effect of beam depth on the flexural behavior of braced frame connections using three-dimensional finite element analyses. Three additional beam sizes were selected: W14x53, W18x46, and W21x44. Additional thicknesses for the double angles were also considered. The computational studies revealed that increasing beam depth increases the flexural stiffness and strength of beam-column connections with gusset plates. Nevertheless, the critical limit states occurred at smaller story drifts as the beam depth increased. Larger angle thicknesses were also found to increase flexural stiffness and strength. The results from the experimental and computational studies were used to develop a simplified procedure for evaluating the flexural stiffness and strength of a braced frame connection. After completing the experimental and computational studies on the flexural behavior of braced frame connections, a series of incremental dynamic analyses were conducted on a suite of concentrically braced frames designed for a moderate seismic region to determine if beam-column connections with gusset plates can provide adequate reserve capacity to insure collapse prevention performance under maximum considered earthquake level demands. Collapse performance data were generated by analyzing the results of the incremental dynamic analyses using a reliability-based performance assessment. The results from the collapse performance assessment revealed that beam-column connections with gusset plates can function as a reserve lateral force-resisting system. The results from the incremental dynamic analyses, in conjunction with the collapse performance data, were used to synthesize recommendations for the minimum level of strength a reserve lateral force-resisting system must possess in order to insure adequate collapse prevention performance