In recent years, typical steel construction in regions of high seismic risk has shifted from moment-resisting frames to concentrically braced frames. As a result of the increased popularity of braced frames, the poor performance of some conventionally braced frames in past earthquakes, and the limited experimental data available on the inelastic response and the failure characteristics of braced-frame systems, a series of experimental and analytical investigations were initiated. The tests reported on herein contain some of the first data available on braced frames constructed in accordance with modern construction practices in the western U.S. Extensive analytical studies were undertaken to assess the analysis methods used for the research, and improved models were developed to better understand the complete range of behavior, including yielding, lateral buckling, and rupture due to low-cycle fatigue.
The primary objectives of this research are to (1) improve understanding of the behavior of this common type of structural system under cyclic inelastic deformations, (2) permit validation and improvement of computer models for predicting global and local response, and (3) improve understanding of the relation between system, member, and connection behavior.
As such, a series of investigations have been conducted, aimed at understanding and improving the seismic performance of concentrically braced steel-frame structures. Extensive analytical studies have been carried out on systems with conve ntional and buck ling-restrained bracing. Tests on a limited number of full-scale pipe and square, hollow structural section (HSS) braces were carried out. These te sts were supplemented with large-scale tests of three buckling- restrained braced-frame (BRBF) specimens and a single two-story special concentrically braced frame (SCBF). In the latter case, specimens incorporated traditional bracing elements susceptible to lateral and local buckling. Thes e component and system test results, along with existing data, were used to develop, calibrate, and validate im proved numerical models capable of realistically simulating the behavior of braced frames, including possible failure due to buckling and low-cycle fatigue. An array of numerical simulations assessed the likely performance of braced-frame structures subjected to severe earthquakes of the type expected in California. The applicability of performance-based earthquake engineering evaluation methodologies to concentrically braced frames is assessed using these results. Based on this research, recommendations are offered regarding the design, analysis, modeling, and detailing of concentrically braced frame structures.
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