The effect of fling step and forward directivity the near-fault earthquake on the seismic behavior of high-rise steel moment frames by EBF and determine the point collapse preventation performanced

This paper focuses on the interstory drift ratio (IDR) demands of building structures subjected to nearfault ground motions having different impulsive characteristics based on generalized interstory drift spectral analysis. The near-fault ground motions considered include the idealized simple pulses and three groups of near-fault ground motions with forward directivity pulses, fling-step pulses and without velocity pulse. Meanwhile, the building systems are equivalently taken as shear-flexural beams with representative lateral stiffness ratios. The IDR distribution of continuous beams subjected to three groups of near-fault ground motions is acquired. It is illustrated that the maximum IDR shifts from the upper half to the lower half of buildings with an increase in lateral stiffness ratio. For long-period systems, the average IDR under impulsive ground motions is significantly greater than that under nonpulse motions. Finally, for moment-resisting frame buildings the forward directivity pulses amplify the drift response of higher modes, while the fling-step pulses excite primarily their contribution in the first mode and generate large deformation in the lower stories. The essential reason for this phenomenon is revealed according to the distinct property of near-fault impulsive ground motions and generalizedmdrift spectral analysis. High-rise buildings behavior subjected to near-fault records is different than the far-fault records. Because of this difference, the characteristics of near-fault records that alters the behavior of the structure in the near-fault records. The effect of the characteristics of near-fault earthquakes on seismic behavior of steel moment frames with eccentricity brace and determine the collapse prevention. The aim of this study was to analyze the IDA tall buildings and obtain the point of collapse prevention (CP) of the curve by IDA under the near-fault records, the effect of height and weight stories on the point of collapse prevention , to obtain the Immediate Occupancy performance level (IO) and life safety (LS) of the curve IDA, determining the impact feature near-fault records (forward directivity, backward directivity, fling step) at the time of forming the point collapse prevention and determine the amount of spectral acceleration records at the time of forming the point collapse prevention , To obtain the point of collapse prevention (CP) by capacity spectrum method (determining the performance level CP) and compare the result with the result of IDA and the reasons for the difference in results of these two methods and proposals for closer results in future research. To achieve these goals, 6 frames 15, 20 and 25 floors with two extra-axial value of 1 and 2 m were designed. Then, 30 near-fault records to determine the point of collapse prevention with IDA and capacity spectra. To evaluate the effect of the characteristics of near-fault records to determine the point of collapse prevention, near-fault records of the three categories including feature a forward directivity, backward directivity, fling step, was divided. The frame is designed for IDA analysis was performed and the results for of these records have been examined individually. In order to characterize the structural response over the near-fault records showed that near-fault records with the fling step in spectral acceleration lower than the near-fault records with the forward directivity the point collapse prevention arrive. Structural response to near-fault records with backward directivity was also very similar to far-fault records. The comparison between the response of structures to analyze the IDA and NSP analysis to determine the point collapse prevention became clear answers obtained by NSP smaller amounts of IDA method show.