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Abstract:
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Seismic -resistant steel eccentrically braced frames (EBFs ) are designed so that that yielding during earthquake loading is restricted primarily to the ductile links . To achieve this behavior , all members other than the link are designed to be stronger than the link , i .e . to develop the capacity of the link . However , satisfying these capacity design requirements for the beam segment outside of the link can be difficult in the overall design process of an EBF . In some cases , it may be necessary to make significant changes to the configuration of the EBF in order to satisfy beam design requirements . If this discovery is made late in the design process , such changes can be costly .
The overall goal of this research was to develop guidelines for preliminary design of EBFs that will result in configurations where the beam is likely to satisfy capacity design requirements . Simplified approximate equations were developed to predict the axial force and moment in the beam segment outside of the link when link ultimate strength is developed . These equations , although approximate , provided significant insight into variables that affect capacity design of the beam . These equations were then used to conduct an extensive series of parametric studies on a wide variety of EBF configurations . The results of these studies show that the most important variables affecting beam design are 1 ) the nondimensional link length , 2 ) the ratio of web area to total area for the wide flange section used for the beam and link , 3 ) the angle between the brace and the beam , and 4 ) the flexural stiffness of the brace relative to the beam . Recommendations are provided for selection of values for these variables in preliminary design . |