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Chevron-braced frames are preferred structural systems by architects and contractors in low to mid-rise buildings for seismic design because they accommodate architectural elements such as doors and windows while providing the necessary lateral stiffness and resistance. This system was more common prior to the advent of new seismic provisions, specifically in braced frame building designed prior to 1988. Today, chevron braced frames are not as prevalent because of the seismic design requirements of the beam connecting the chevron-configured braces. Modern seismic design provisions require that the full-strength beam meets the vertical component of idealized unbalanced capacities of full yielding of the tension and degraded capacity of the compression brace. This results in large and costly beams and these configurations are now rarely designed. Instead, alternatives such as buckling restrained braced frames, diagonal bracing or reinforced concrete shear walls are used.

With funding from the American Institute of Steel Construction (AISC), a collaborative research team from the University of Washington (UW) and National Center for Research on Earthquake Engineering (NCREE) is exploring the use of an alternative plastic mechanism to reduce the beam size and meet or possibly improve the performance. In the first experimental phase, a series of one-story frames tested at UW to study the impact of the relative strength of the beam and demand of the braces. These tests demonstrated that this mechanism improved the deformability of the SCBF without compromising the capacity of the system if beam yielding follows brace buckling. However, if the beam is too weak, the idealized strength of the system using elastic systems (corresponding to developing the critical buckling capacity in tension and compression) cannot be achieved. The UW research used only simple beam-to-column connections. The second phase of the research studied the response of multi-story, specifically 3, systems with chevron-configured bays using high-resolution finite-element analyses (FEA). The FEA results show that the beam-to-column connection is critically important and the gusset plate above the beam at the beam-to-column connection provides rigidity. To study this impact experimentally, a three-story, full-scale chevron-configured SCBF will be tested at the NCREE laboratory. The test will be extensively instrumented and the results used to validate high-resolution finite element models. The experimental and analytical results will be combined to propose to design equations for inclusion in AISC seismic provisions.


© 2018 National Center for Research on Earthquake Engineering