Seismic Demand and Capacity of Steel Moment Resisting Frames Under Near-Fault Earthquakes Using Incremental Dynamic Analysis

In seismic performance based design procedures، nonlinear static pushover analysis (SPO) and incremental dynamic analysis (IDA) are usually used for determining seismic demand and capacity of moment resisting frames (SMR). The results of these methods are often presented using curves of intensity measures (IM) Vs damage indexes (DI). For far field earthquakes، different intensity measures، such as acceleration spectral intensity of the first mode of vibration with 5% damping i. e. Sa (T1، %5) factor are used. But for near field earthquakes، it is necessary to consider other suitable IM''s. In this article، the difference between IDA and SPO curves for near field earthquakes compared to that for far field earthquakes are shown for three SMR frames which are designed according to Iranian code of practice using 15 pairs of near and far field earthquakes. Then some other intensity measure factors which may be suitable for near and far field earthquakes، are considered. These IM''s are compared with the use of standard definitions of «efficiency» and «sufficiency». It is concluded that intensity measure IM1I&2E which considers second mode effects and nonlinear behavior، is much more efficient and better sufficient than more often used Sa (T1، %5) factor.