توسعه یک روش تحلیل غیرخطی نموی-تکراری جهت پیمایش مسیر ایستایی گنبدهای فضاکار کم عمق

دراین مقاله یک روش جدید نموی تکراری برای تحلیل سازه های خرپایی، شامل هر دو رفتار غیرخطی هندسی و مصالح پیشنهاد شده است. معادلات تعادل غیرخطی با استفاده از یک روش نموی تکراری بر مبنای روند کنترل جابجایی حل می شوند. مبنای روند غیرخطی هندسی بر اساس فرمول بندی هم چرخشی و غیرخطی مصالح براساس ردیابی رابطه تنش کرنش داده شده برای رفتار پس کمانشی عضو خرپایی می باشد. در این روش فرض شده که اندازه بردار نمو جابجایی به اندازه بردار جابجایی کل در شروع هر نمو بار مقداری ثابت است. بر اساس این ایده و تفکر، معادلات مربوطه نوشته شده است و فرمول بندی جدید استخراج گردیده است. روش پیشنهاد شده قادر است نقاط حدی شامل فروجهش و پس جهش را نیز به خوبی عبور دهد. برای روش پیشنهاد شده مثال های متعددی در نظر گرفته شده و با حل آنها کارایی الگوریتم پیشنهادی مورد بررسی قرار گرفته است. نتایج نشان می دهد که روش توسعه داده شده در این مقاله منحنی تعادل را به خوبی روش طول کمان اصلاح شده با اختلاف اندک ردیابی می کند.  

an incremental-iterative method of static nonlinear analysis to trace the equilibrium path of shallow space dome structures

nowadays, non-linear analysis of structures has become an attractive matter and appears necessary for most structural engineering applications, whereas tendency for more accurate structural analysis has increased by many engineers. in general, nonlinear analysis is divided into two main parts: geometrical and material nonlinearity. in some cases, both nonlinear types are used simultaneously in the analysis process. in this paper, a new incremental iterative method for the analysis of truss structures, including both geometric and material nonlinearity behavior, is proposed. nonlinear equilibrium equations are solved using an incremental iterative method based on the displacement control process. the basis of geometric nonlinear process is based on rotational formulation and material nonlinearity is based on tracing the stress strain relationship for post buckling behavior of the truss members. in this proposed method, it is assumed that the magnitude of the displacement increment vector to the size of the total displacement vector at the beginning of each load increment, is a fixed value. based on this idea and thinking, the corresponding equations are written and a new formulation has been developed based on the displacement control scheme, as, by employing a specified displacement, the corresponding load will be obtained. using fixed incremental displacement algorithm, this paper, proposed a novel method that has a possibility of passing the limit points in the case of highly nonlinear behavior state. the proposed method, is able to pass the limit points including snap through and snap back. some examples are provided for the proposed method and by solving them, the efficiency of the proposed algorithm is examined. a limit point refers to the turning point for the equilibrium path of a structure, which can be further considered as the transition point from stable to unstable equilibrium states or vice versa. in analysis of such structures, the simple incremental iterative methods unable to pass this limit points. the simple incremental iterative methods couldn’t trace the equilibrium path after the limit points. for resolving such disadvantages, advanced analysis methods have been developed numerical examples demonstrate the feasibility and accuracy of the proposed algorithm, to be highly suitable in predicting nonlinear response of structures with multiple limit points and snap back points, and trace the equilibrium path accurately. the results show that the method developed in this paper, traces the equilibrium curve as well as the modified arc length method with a small difference. in spite of the fact that the procedure herein explained is only implemented for truss structures, it is possible to generate the proposed method for other structures. this paper is organized as follows. in the first section, we will have a brief review of nonlinear analysis of trusses, including both geometric and material nonlinearity. a literature review is done and a number of available methods in this field is describe. in the second section we explained the basic concepts in nonlinear analysis. the third section geometric and material nonlinear behavior of trusses are reviewed. section four is allocated to implementation of proposed method for nonlinear analysis. in section five, the validity of the proposed method is illustrated with some examples.