بررسی ایمنی لرزه‌ای در قاب های مهاربندی بهینه سازی شده براساس عملکرد

هدف از‌ این تحقیق، ارزیابی ایمنی لرزه‌ای قاب ‌های فولادی با مهاربندی همگرای ضربدری بهینه‌سازی شده در چهارچوب نگرش طراحی مبتنی بر عملکرد می‌باشد. این تحقیق مشتمل بر دو گام اصلی می‌باشد. در گام اول، دو قاب سه دهانه ده طبقه با سیستم مهاربند ضربدری با موقعیت قرارگیری مهاربند در دهانه وسط و دهانه‌های کناری، با استفاده از الگوریتم فرا ابتکاری مرکز جرم در چهارچوب روش طراحی مبتنی بر عملکرد و با در نظرگیری وزن سازه به‌عنوان تابع هدف و روش تابع جریمه خارجی، بهینه‌سازی شده‌اند. در این فاز از مطالعه، از نرم‌افزار opensees، جهت انجام مدل‌سازی و تحلیل‌های غیرخطی و از نرم‌افزار متلب جهت پیاده‌سازی مسئله بهینه‌سازی استفاده شده است. در گام دوم به بررسی ایمنی لرزه‌ای قاب‌های حاصل از روند بهینه‌سازی، با استفاده تحلیل دینامیکی افزایشی پرداخته شده است. با توجه به نتایج به‌دست‌آمده، مشاهده گردید که قرارگیری مهاربند در دهانه‌های کناری موجب کاهش تقریباً 10% ایمنی لرزه‌ای نسبت به قاب‌های مهاربندی با قرارگیری مهاربند در دهانه وسط، می‌شود.

investigation of seismic safety in performance based optimally designed bracing frames

throughout history, structural engineers have always been trying to design optimal structures that are always cheap due to limited resources, and at the same time meet all existing design limitations. after the great damages caused by the earthquakes in the 1990s in america and japan, the seismic design regulations made significant changes. although there were not many casualties in these earthquakes, huge economic losses were left, which clearly revealed that the goal of life safety should not be only the design criteria should be used, and more performance levels should be controlled and verified in the designs. during the last few years, performance-based design has been introduced in regulations and expanded significantly, on the other hand, the improvement of computing power of computers and hardware systems has made it possible for people to use optimization methods and use advanced nonlinear analysis. therefore, today we can use a meta-heuristic algorithm for the design of new structures to find the best design and perform a dynamic analysis to find the response of the structure. this possibility was previously only possible for the evaluation of existing buildings, and the performance evaluation methods at that time were defined by regulations. and various recipes were introduced. the main goal of performance-based design is to design structures whose behavior is predictable. the current method of designing structures is based on design by resistance method and includes estimating the base shear in the structure and its distribution in height and determining the required resistance of structural components against incoming loads, regardless of the deficiencies that exist in this method, expressing the behavior of the components a structure, only through resistance, in many cases does not give a suitable answer. in fact, the purpose of seismic design based on performance is to enable designers to design structures whose performance is predictable, because the involvement of employers in choosing the level of risk in the design in question at different earthquake levels requires knowing. the way the structure works in different earthquake levels. according to the design regulations, structural members are designed in such a way that they can withstand the incoming forces with a suitable safety margin that depends on the design method. after designing the structural members for the incoming forces, displacement controls are also performed in some cases the purpose of this research is to evaluate the seismic safety of steel frames with optimized cross convergent bracing in the framework of performance-based design approach. this research consists of two main steps. in the first step, two three-span ten-story frames with a cross bracing system with the position of the bracing in the middle opening and the side openings, using the meta-heuristic algorithm of the center of mass in the framework of the performance-based design method, and considering the weight of the structure as the objective function and the external penalty function method have been optimized. in this phase of the study, opensees software was used to perform nonlinear modeling and analysis, and matlab software was used to implement the optimization problem. in the second step, the seismic safety of the frames resulting from the optimization process has been investigated using incremental dynamic analysis. according to the obtained results, it was observed that placing the brace in the side openings reduces the seismic safety by almost 10% compared to the bracing frames with the placement of the brace in the middle opening.