Seismic Behavior, Performance and Design of Steel Concentrically Braced Frame Systems
Palmer, Keith David
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This dissertation describes a research program on special concentrically braced frame (SCBF) and buckling-restrained braced frame (BRBF) systems. The study builds upon previous work performed as part of a research program supported by the George E. Brown Network for Earthquake Engineering Simulation (NEES) entitled ``International Hybrid Simulation of Tomorrow's Braced Frame.'' This program was initiated due to practical and experimental evidence that SCBFs were not performing as intended by current seismic design provisions. The current study includes a comprehensive experimental and analytical program which included two first-of-its-kind, two-story, one-bay by one-bay SCBF and BRBFs experiments. The experiments were performed at the University of Minnesota NEES laboratory to take advantage of its ability to apply large-displacement bi-directional loading. The two specimens were configured with braces in two orthogonal bays framing into a ``shared'' column with a floor system designed and constructed to simulate realistic conditions. The first specimen, the SCBF, employed HSS3x3x1/4 braces in a single-story X-configuration with one continuous brace and a pair of spliced braces in the opposing direction. The second test specimen, the BRBF, employed pin-ended, collared BRBs in a single-diagonal configuration. The analytical study consisted of a large suite of finite element simulations aimed at identifying the main parameters that influence the damage at the beam-column-gusset connection region in BRBFs and to make recommendations for the design and detailing of this connection region. This research has resulted in a number of findings including the observation that out-of-plane loading and deformation had little impact on the drift and ductility capacity of the system when compared to planar frame test results. In fact, the drift capacity of the SCBF test frame was only 6\% less than that of comparable planar frames while the ductility and cumulative ductility capacities of the BRBF exceeded that of many of the planar BRBF system tests. Based on the experimental and analytical findings, design and detailing recommendations were developed for the connection at the brace splice point in the single-story, X-configured system. Design and detailing recommendations were also made for the corner gusset plate connection region in BRBFs.
- Civil engineering