تاثيرسطوح عملكردي حاصل از تحليل استاتيكي و ديناميكي غيرخطي بر مقدارمصالح مصرفي قاب هاي خمشي فولادي با سيستم دوگانه

The effect of Performance Levels on the Material Quantity of Steel Moment Resisting Dual Systems Utilizing Nonlinear Static and Dynamic Analysis

هريك از روش‌هاي مقاوم سازي داراي معايب و محاسني است كه معمولا براي رفع معايب يك روش ازتركيب آن با روش ديگراستفاده مي‌شود. در اين پژوهش دو دسته ساختمان‌هاي فولادي داراي سيستم قاب خمشي و ساختمان‌هاي با سيستم دوگانه يا تركيبي قاب خمشي و ديواربرشي بتن مسلح در دو سطح شكل پذيري مبه وسيله‌ي و زياد و به دو روش تنش‌هاي مجاز وحالات حدي با تعداد طبقات 3، 5، 8، 12 و 15 بر اساس استاندارد 2800 و نيز ويرايش قبلي و فعلي مبحث دهم مقررات ملي ايران به صورت سه بعدي طراحي شده و در گام بعد سطح عملكردي كليه سازه‌هاي گفته شده در دو سطح خطر مورد ارزيابي قرار گرفته است. به منظور ارزيابي سطح عملكرد اين ساختمان ها تمامي آن‌ها در نرم افزار Perform-3D به صورت سه‌بعدي مدل شده و تحليل بارافزون روي آن‌ها با استفاده از چهار روش‌ شامل روش ضرايب تغييرمكان، روش طيف ظرفيت، روش خطي‌سازي معادل و روش ضرايب اصلاح شده، انجام شد. نتايج تحليل استاتيكي غيرخطي روي ساختمان‌هاي مطالعه شده نشان مي دهد كه تحت اثر زمين‌لرزه طرح، سطح عملكردي ايمني جاني با ميزان خسارتي كمتر از آنچه در سطح ايمني جاني بوجود مي‌آيد پيش‌بيني مي‌‌شود. اين نتيجه با هدف پيش‌بيني شده در استاندارد 2800 به گونه محافظه كارانه مطابقت دارد. همچنين مقايسه نتايج تحليل‌هاي بار افزون با نتايج تحليل تاريخچه زماني غيرخطي نشان مي‌دهد كه روش‌هاي ارايه شده درFEMA-440 (روش‌ خطي‌سازي معادل و روش ضرايب اصلاح شده) براي تغييرمكان هدف بسيار دقيق‌تر از ساير روش‌ها بوده و تغييرمكان‌هاي به دست آمده از اين روش‌ها به نتايج تحليل ديناميكي نزديك‌تر است. در ادامه دو دسته ساختمان طراحي شده از لحاظ ميزان مصالح مصرفي مورد مقايسه قرارگرفته است.

Retrofitting of structures to resist lateral loads induced by earthquake, various lateral load resistance systems may be used. Each of these systems has advantages and disadvantages. Sometimes, to eliminate the disadvantages of one system, the combination with other system may be used.In this research, two sets of three dimensional building systems composed of Steel moment resistant frame system and dual system (consisted of steel moment resisting frame with reinforced concrete shear wall) have been selected for investigation. These three dimensional (3D) building structures which have been considered for the two levels of medium and high ductility with 3,5,8, 12 and 15 stories. All 3D structures were designed (utilizing ETABS software) in accordance to allowable stress deign (ASD) method and load and resistance factor design (LRFD) method based on the Iranian code of practice for seismic resistant design of buildings (standard 2800) and the last and new version of the Iranian national building code for steel structures Part -10. Then performance levels of all structures are evaluated in two hazard level-1 (with the return period of 475 years) and level-2 (with the return period of 2475 years).In order to evaluate performance level of the aforementioned structures, they were modeled three dimensionally using CSI Perform-3D software for both nonlinear static and dynamic analysis. In the case of nonlinear static analysis (pushover analysis) different codes methods such as: ”Displacement Coefficients Method (DCM)” in accordance to the FEMA-356, ”Capacity Spectrum Method (CSM) ” as per ATC-40, ”Equivalent Linearization Method (ELM)” and “Modified Coefficient Method (MCM)” given by FEMA-440 have been implemented.The results obtained from the nonlinear static analysis exhibit that the performance level corresponded to the life safety cause less damage compared to the damage due to expected life safety performance. This result is in good agreement with the aim of Iranian code of practice for seismic resistant design of buildings (standard 2800). For nonlinear time history dynamic analysis (NTHY) out of thirteen coupled ground motion accelerations from the strong motion data base of PEER, seven accelerations with minimum of 20 km from the source and magnitude range of 5.9 to 7.3 were selected. The soil type II was considered having shear wave limit between 375 to 750 m/sec. The result and the accuracy of pushover analysis has been compared with the nonlinear time history analysis. This indicates that the results obtained by ELM and the MCM methods given by FEMA-440, are closer to the results of NTHA. The CSM results are not as accurate as methods given by FEMA-440 specifically for the structures having reinforced concrete shear walls provide upper bound results. Finally, this research evaluates and compares these two set of designed buildings with respect to material consumption.The relevant results of medium and high ductility levels obtained for both ASD and LRFD method, indicate that the steel used for steel moment resisting frames are more compare to that of dual systems. This is due to the presence of RC shear wall that causes the reduction in columns stiffness and controls the lateral drift of the buildings.