همبستگی بین پارامترهای جنبش نیرومند زمین در زلزله‌های دور و نزدیک گسل و پاسخ سازه‌های قاب خمشی فولادی

شدت جنبش نیرومند زمین توسط پارامترهای مختلفی قابل شناسایی است که میزان همبستگی آنها با پاسخ سازه به عوامل مختلفی از جمله نوع و ارتفاع سازه، پاسخ اندازه‌گیری شده، نوع خاک، پارامتر لرزه‌ای مورد بررسی و ... بستگی دارد. در این پژوهش به ارزیابی همبستگی پارامترهای زلزله در حوزه دور و نزدیک از گسل با شاخص‌های خرابی قاب‌های خمشی فولادی پرداخته شده است. بدین‌منظور قاب‌های دو بعدی با 3، 6، 9، 12، 15 و 20 طبقه و سه دهانه در نظر گرفته شدند. تعداد 107 جفت رکورد زلزله شامل 100 رکورد حوزه دور و 114 رکورد حوزه نزدیک به گسل از بانک داده‌های peer انتخاب شدند. تحلیل‌های تاریخچه زمانی غیرخطی توسط نرم‌افزار opensees بر روی سازه‌ها انجام شد. سپس همبستگی بین پارامترهای جنبش نیرومند زمین با شاخص‌های خرابی حداکثر جابه‌جایی نسبی طبقات و انرژی مستهلک شده در قاب با استفاده از رابطه‌ی پیرسون محاسبه گردید. نتایج به‌دست‌آمده نشان می‌دهد که پارامترهای شتاب طیفی در مود اول نوسان cordova ، (sa(t1))، شدت طیف سرعت و شدت هاوزنر در هر دو حوزه دور و نزدیک به گسل قوی‌ترین همبستگی را با پاسخ حداکثر جابه‌جایی نسبی طبقات و انرژی مستهلک شده دارند. همچنین نتایج نشان داد که در بیشتر موارد، تفاوت معنی‌داری در همبستگی اکثر پارامترهای لرزه‌ای با پاسخ سازه برای هر دو نوع خاک c و d وجود ندارد. همچنین اختلاف به وجود آمده در همبستگی بین پاسخ سازه و پارامترهای زلزله در اثر تغییر ارتفاع قاب در زلزله‌های نزدیک به گسل مشهودتر است.

correlation between seismic parameters of far and near fault ground motion and response of moment resisting steel frames

in seismic countries, with regard to the damages and losses caused by ground motion, the earthquake resistant design of structures is a critical matter. previous earthquakes have shown that the regulation in seismic codes does not guarantee the buildings to resist against seismic forces and may cause severe damage in the structures. this subject goes back to the design philosophy in seismic code and also weakness in the hypothesis of seismic design of structures. noted that, the earthquake records include many inherent parameters affected the response of the structures. meanwhile the seismic codes use only a few of them in the designing process such as spectral acceleration at the first mode period, i.e., sa(t1) and wellknown parameter pga. in recent decades, many studies focus on the correlation between seismic parameters and the response of structures and found out that the used parameters in the codes do not have the best correlation with the response of structures. this finding depends on the databank of the records including the sitetofault distance intensity of the earthquake, frequency content etc. as well as the type of earthquake resistant structure. this paper deals with a comprehensive study on the correlation between both farfield and nearfield earthquake parameters and response of moment resisting steel frames. for this purpose, a series of nonlinear time history analyses were carried out on 3, 6, 9, 12, 15 and 20 moment resisting steel frame using opensees. 107 records pair included 100 farfield records and 114 nearfield records were selected from fema p695 as well as pacific earthquake engineering research (peer) databases. 26 seismic parameters were extracted from these records, i.e. 5564 earthquake parameters were considered. two damage indices including maximum interstory drift (misd) and the amount of absorbed energy were calculated in studied frames. to assess the relationship between seismic parameters and structural damage pearson correlation coefficient was determined. the results show that corvoda, sa(t1), pgv, velocity spectral intensity (vsi), housner intensity have the best correlation with response of structure in misd and structure absorb energy in both farfield and nearfield earthquakes. also, the correlation coefficient of displacement dependent parameters is enhanced by increasing the number of stories. moreover, the results indicate a weak correlation between pga and response of structures for both misd and absorbed energy as reported by previous researches. it should be noted that due to the rich frequency content of nearfield earthquakes, the correlation of their parameters with seismic response of the studied frames was sensitive to the frames height. noted that the short period structures (short height) are named acceleration sensitive and the medium and high rise building are recognized as velocity and displacement sensitive, respectively. therefore, because of rich frequency content of nearfield earthquakes, the correlation between acceleration based parameters such as pga and displacement response of the structures are reduced by increasing the frame height. in a contrary manner, the correlation between damage indices of the structures with displacement based parameters is increased by increasing the frame height. meanwhile, the correlation between damage indices of the structures with velocity based parameters such as pgv is the most for midrise structures. according to the result it can be concluded that the parameters depended on velocity like housner intensity and velocity spectral intensity have the best correlation with misd and absorbed energy. also, the parameters depended on earthquake duration like significant duration and effective duration have weak correlation with the response of structures. it is shown that one cannot expect the longer duration earthquake result in more damage i.e. maximum story drift in structures.