پديد آورندگان :
بهنام‌فر ، فرهاد نويسنده استاديار دانشكده مهندسي عمران Behnamfar , F , بهمن‌زاد، عليرضا نويسنده كارشناس ارشد دفتر فني استانداري اصفهان Bahmanzad, A
كليدواژه :
سازه‌ي فولادي خمشي , بم و نورث‌ريج , حوزه‌ي نزديك , زلزله‌هاي طبس , آيين‌نامه‌ي ايران , رفتار لرزه‌يي
چكيده فارسي :
در اين پژوهش، به‌منظور بررسي ايمني فراهم‌شده‌ي آيين‌نامه‌يي براي سازه‌هاي فولادي خمشي ابتدا ساختمان‌هاي4، 6، 8، و10 طبقه طبق استاندارد 2800 ايران و مبحث دهم مقررات ملي ساختمان طراحي و سپس همين ساختمان‌ها تحت اثر شتاب‌نگاشت زلزله‌هاي طبس، بم، و نورث‌ريج مورد تحليل تاريخچه‌ي زماني غيرخطي واقع و عملكرد آنها ارزيابي شده‌اند. و نيز به منظور مقياس‌كردن شتاب‌نگاشت‌هاي اين زلزله‌ها از روشي كارامد، موسوم به روش توازن طيفي در 2 سطح خطر مختلف استفاده شده است.
نتايج اين بررسي نشان‌دهنده‌ي عملكرد ضعيف ساختمان‌هاي مذكور است، به‌طوري كه خسارات بيش از حد مجاز و گاه فروريزش سازه‌ي طراحي‌شده طبق آيين‌نامه مشاهده مي‌شود. براي اصلاح رفتار و ارتقاي ايمني لرزه‌يي، روش كاهش تغييرمكان نسبي طبقه‌يي مجاز پيشنهاد مي‌شود. نتايج بررسي مجدد نشان‌گر بهبود رفتار و كفايت لرزه‌يي ساختمان‌هاي اصلاح‌شده است.
چكيده لاتين :
Iran, as a vast country, has frequently witnessed destruction of many of its cities due to earthquake. Many times the occurrence of short-duration ground motion has affected a society, economically, socially, politically, and culturally, and essentially changed the destiny of generations. The near-field earthquakes of a Tabas, Bam and Northridge, which displayed destructive effects, differed from other seismic events, and acted as an incentive for many researchers to focus on such kinds of earthquakes. Due to the proximity of active faults to populous regions, the possibility of occurrence of near-field earthquakes is high in Iran, justifying special consideration of this type of earthquake in the design or retrofit of structures. In this research, to assess the safety provided through a code-based design for moment resisting steel structures, first, structures 4, 6, 8, and 10 stories tall are designed for Standard 2800 and Chapter 10 of National Building Regulations. Second, the same buildings are nonlinearly analyzed and evaluated under Tabas, Bam and Northridge earthquakes, for hazard levels with 475 and 2475 return periods. The method of Spectral Balancing is used to scale the time histories of the ground motion for the two levels of seismic risk. In this method, the response spectrum is displaced vertically to a position where the area between the design and 1.4 times the response spectra are the same between periods 0.2T and 1.5T, with T being the natural period of the building under study. Tables of beam and column responses are provided, in which the number of plastic hinges in each member and the number of hinges with rotations over the code limit are shown. As a result, the buildings investigated are evaluated as weak under these earthquakes, meaning that damage is beyond allowable limits and that even collapse is observed in certain cases. To modify the behavior and enhance seismic safety, it is proposed to decrease the allowable story drift for structures subjected to near-field earthquakes. An equation for calculating the modified drift limit is proposed based on regression analysis. The suggested equation gives the value of a reduction factor, as a function of number of stories, to be multiplied to the code-based drift limit. Evaluating the structures designed, according to the reduced drifts, shows a satisfactory seismic behavior, to the extent that rotations of plastic hinges remain below acceptable limits for each performance level. In addition, where nonlinear behavior may not occur, the section forces do not exceed the member capacities.
