Seismic Demand Estimation of Steel Moment Resisting Frames in Near Field of Fault

Forward directivity effects in near field of fault causes the creation of long-period pulse-like records with low effective duration and high amplitude at velocity time history of ground motions that lead to increase in ductility demand for structures [1-3]. Because of widespread use of linear methods for structural design in order to estimate and control the structural drift by engineers and according to standing some of the Iran''s cities in near field of fault [3]، in this study the base shear and relative displacement demand of steel moment frame are studied under the effects of forward directivity with height changes in near and far field of fault. The seismic demand of 5 steel moment-resisting frames under 20 earthquake records is determined for estimating forward and neutral directivity effects on the demand of steel moment-resisting frames (base shear and relative displacement of stories)، using linear static، linear dynamic and nonlinear dynamic methods. Then the accuracy and correctness of linear methods for the estimation of structural demands are discussed، comparing results of demands obtained from linear methods with nonlinear dynamic method in near field and far field of fault. At last، based on the far field of fault''s data some relations are proposed for estimation of base shear and drift demand of steel moment frames in near field of fault.