19577

۱۹۵۷۷

ارزيابي لرزهاي قاب هاي خمشي فولادي ويژه كوتاه و ميان مرتبه طراحي شده براساس روش نيرو و تغييرمكان مستقيم

كارشناسي ارشد

زلزله

۱۳۹۴

۱۳۹۷/۰۲/۲۴

دكتر مرتضي رئيسي دهكردي

دكتر مهدي اقبالي

عمران

روش‌هاي طراحي عملكردي با هدف طراحي سازه‌هايي كه رفتار آنها در هنگام زلزله قابل پيش بيني باشد در دهه هاي اخير مطرح شده اند، در اين ميان روش طراحي مستقيم بر‌اساس تغييرمكان از جديدترين روش‌هاي طراحي براساس عملكرد است كه امروزه مورد توجه محققين زيادي قرارگرفته است. اما اين روش هنوز به صورت آئين نامه‌اي كامل و استاندارد مناسب جهت به‌كارگيري در طراحي كليه سازه‌هاي قابي در نيامده است. در اين تحقيق رفتار سه سازه قاب خمشي ويژه فولادي منظم با تعداد پنج، هفت و نه طبقه كه با دو روش متفاوت طراحي مستقيم بر‌اساس تغييرمكان و نيرويي ولي با يك طيف (طيف طرح منطقه‌ي مورد نظر در ويرايش چهارم استاندارد 2800) طراحي شده‌اند، مورد بررسي و ارزيابي قرار گرفته اند. به منظور ارزيابي عملكرد لرزه‌اي اين سازه‌ها و مقايسه اين دو روش‌ مختلف طراحي، تحليل تاريخچه‌ زماني ديناميكي غيرخطي تحت هفت شتاب نگاشت‌ واقعي كه طيف پاسخ آنها منطبق بر طيف طرح منطقه‌ي مورد نظر در ويرايش چهارم استاندارد 2800 مي‌باشد، انجام شده است. بررسي‌ها نشان مي‌دهند كه سازه‌هاي طراحي شده به روش تغييرمكان مستقيم در مقابل روش نيرويي در حين وقوع زلزله رفتاري مناسب تر و قابل پيش بيني‌تر داشته اند. ولي نياز به يافتن روشي براي بهينه‌تر كردن روش طراحي مستقيم براساس تغيير مكان احساس مي‌شود.

1397/08/02

Seismic Evaluation of short and mid Steel Moment Frames with Force Based Design and Direct Displacement Based Design method

10/24/2018 12:00:00 AM

To date, the most commonly used method for seismic design is the force-based method. The basis of this method is to provide a minimum lateral resistance to seismic loads. In this method, the design process begins with the estimation of structural component dimensions and the conservative estimate of the main natural periods of the structure, whose values are less than those obtained from the actual period of the structure. Then, the behavior coefficient is determined. For numerous structures, it is also unreasonable to assume seismic forces among structural elements based on initial stiffness, because there was an improper assumption that different structural elements are forced to be yielded simultaneously. In this method, displacements values are only controlled at the end of the design phase. Therefore, the modification of the design method is needed. Performance-based design methods aiming at designing structures with predictable seismic behaviours have been proposed in recent decades. Meanwhile, the direct displacement-based design method is among the latest performance-based methods which is nowadays considered by many scholars. The direct displacement-based design method has the following advantages over the force-based method. In this method, the displacements play a major role in the initial design. Moreover, due to the fact that Target Displacement Criteria are selected for Service and Ultimate limit states, damage control is performed automatically. Furthermore, the strength and stiffness of the lateral load-bearing system is chosen to meet the criteria for the desired displacement, and it is not necessary to use the estimation empirical approximative relations to the main period of the structure in the initial design. Additionally, the shape and composition of the allowable story drifts are practically considered by choosing the deformed profile at the beginning of the design. The correction factor of R is not used in this method as an empirical, uncertain and partially selective variable. However, this method has not yet been developed as a complete and standard standard to be employed in the design of all framing structures. In this study, the behavior of three regular special steel moment-frame structures with 5, 7 and 9 floors, designed with different design methods but same spectrum (the design spectrum of the desired region in the fourth edition of standard 2800), has been studied and evaluated. In order to evaluate the seismic performance of these structures and compare these two different design methods, the nonlinear time history dynamic analysis for 7 real accelerograms was performed, which their response spectrum was designed by "Seismomatch 2016" software. Comparison of the time history analysis results of the floor displacement ratios with their allowable values has shown that they differ in behavior due to different design methods and basics, although both methods are based on satisfaction of the applied conditions by a code-design spectrum. Designed structures have more suitable and predictable seismic behaviour based on direct displacement method than force-based method. It also needs to find a way to make the direct displacement-based design method more optimized.