دانلود رایگان مقاله انگلیسی نیاز به برش قاب مقاوم خمشی فولادی در معرض لرزش - اشپرینگر 2018

Abstract

Strength capacity checking and instability control of building structures require the prediction of story shear demands and other actions produced by seismic excitations. Impulsive feature and large vertical accelerations associated with near-fault ground motions may lead to instability of the structural systems with severe damaging outcomes. The seismic demands depend on structural and ground motion characteristics. In this paper, the effect of ground motion impulsive characteristics on the story shear demands of steel moment frames is investigated for different hazard levels. For this purpose, incremental dynamic analysis is conducted on five steel frames with 3–15 stories subjected to different types of ground motions. Moreover, the accuracy of conventional pushover and static linear procedures is examined and some modification factors are suggested for each analytical approach. Finally, the effect of vertical component of near-fault records is investigated for two case studies. The results of the study demonstrate that story shear demands obtained from static procedures must be amplified for stories located at the upper one-third of the structure by a modification factor of up to 2.5 to find more precise shear demands, depending on parameters such as structure height, story level, analysis method and ground motion type. Among pushover cases, the first-mode load pattern gives more reliable results compared to other load patterns. Also, it was found that the application of vertical component of long-period pulse-like accelerograms increases the column axial forces by up to 100%.

5 Conclusions In this study, the effect of near-fault ground motions on the global response and seismic shear demands of steel moment-resisting frames is investigated. In addition, the accuracy of static procedures to predict the shear demands is examined. Nonlinear time-history analyses as well as static linear and nonlinear procedures with different load patterns were conducted to assess the seismic response of five sample steel moment-resisting frames with 3–15 stories. The results of study are summarized as follows:

1. Long-period pulse-like ground motions tend to impose up to 35% larger global drift in comparison with farfault ground motions with the same peak ground acceleration, but they do not necessarily impose larger base shear demands.

2. Scaling ground motion records either based on the spectral acceleration corresponding to first mode of vibration or based on the scaling methodology proposed by Iranian seismic design code (or other similar standards) do not capture the damaging potential of near-fault ground motions.

3. The base shear amplification factor is estimated 3 by pushover analysis and 3.5 using time-history analysis.