10-24-2009, 04:06 PM
Toward Earthquake-Resistant Design of Concentrically Braced Steel-Frame Structures
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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 conventional and buckling-restrained
bracing. Tests on a limited number of full-scale pipe and square, hollow structural section (HSS)
braces were carried out. These tests were supplemented with large-scale tests of three bucklingrestrained
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. These component and system test results, along with existing data,
were used to develop, calibrate, and validate improved numerical models capable of realistically
simulating the behavior of braced frames, including possible failure due to buckling and lowcycle
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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