يك مدل بزرگ مقياس خرپايي براي تحليل غيرخطي ديوارهاي بنايي

A truss element based model for nonlinear analysis of masonry walls

در اين تحقيق يك مدل بزرگ­ مقياس خرپايي براي شبيه­ سازي رفتار درون صفحه ديوارهاي بنايي در مودهاي خرابي مختلف معرفي مي­شود. در مدل پيشنهادي، اعضاء سازه­اي بنايي به پانل­هاي دو بعدي كوچكتر تقسيم شده سپس براي مدل­ سازي هر پانل،­ از يك سيستم خرپايي استفاده مي­ شود. نحوه تعيين مشخصات مربوط به هندسه، ابعاد و مدل رفتاري اين المان هاي خرپايي با توجه به مكانيزم رفتاري و مودهاي خرابي داخل صفحه ديوارهاي بنايي معرفي مي­شوند، سپس نتايج حاصل از تحليل با استفاده از مدل پيشنهادي و روابط پيشنهادي آيين­ نامه­ ASCE41 در مودهاي خرابي مختلف مورد ارزيابي و مقايسه قرار مي­ گيرد. همچنين به منظور صحت­ سنجي، دو نمونه ديوار محصورشده توسط دو لبه، سه نمونه ديوار با مقطع مستطيلي و يك نمونه ديوار قوسي با استفاده از مدل پيشنهادي مدل­ سازي شده و نتايج تحليل عددي و آزمايشگاهي بررسي مي­ شود. نتايج بدست آمده نشان دهنده آن است كه مدل پيشنهادي در عين سادگي، قابليت مناسبي در تخمين رفتار داخل صفحه ديوارهاي بنايي دارد.

In this research, a truss model is introduced to simulate the in-plane behavior of masonry walls in different failure modes. In the proposed model, the structural members are divided into smaller two-dimensional panels and then a truss system is used to model each panel. The geometry, dimensions and behavioral model of these truss elements are introduced according to the behavior mechanism and failure modes of the masonry walls. It is shown that the masonry walls can be well modeled by choosing the appropriate dimensions for the horizontal, vertical and diagonal elements and also using the appropriate material models. The dimensions of the truss members are determined in such a way that the stiffness of the truss model is the same as the stiffness of the initial panel, under different loading conditions. In this regard, the computational method introduced by Aghababaei is used. The elasto-plastic-fracture model developed at the University of Tokyo is applied for compressive behavior of elements. Barimani et al. evaluated and verified the accuracy of this model. Also for tensile and post cracking behavior of masonry, the tension softening model of Maekawa et al. is used. The proposed model is implemented in the nonlinear finite element software, TaRa, developed at Tarbiat Modares University. In addition to the ability to model the reinforced concrete frame systems under monotonic, cyclic and dynamic loads, this software is capable of modeling the behavior of structures in large deformations, progressive failure and elements removal. The capability, accuracy and validity of the program in simulating the structural behavior of reinforced concrete have been shown in previous researches. In this research, this software is used to develop the proposed truss-based method for modeling the in-plane behavior of masonry structures. In order to apply the effects of cracking on the compressive behavior of diagonal elements, a softening model dependent on the crack width is introduced. The idea used is generally based on the smeared track approach. In this model, after identifying the pair of each diagonal element and as soon as a crack occurs in one diagonal element, by multiplying the force values in a proposed function, the behavior of the other diagonal element is modified. Although in the proposed model, the friction angle is not defined as the main input parameter, but the results show that based on the compressive strength of the masonry, an equivalent friction angle can be expected for the masonry. The results of the parametric study in shear sliding mode showed that the capacity and behavior of these samples are affected by the tensile and compressive strength of diagonal elements. In such a way that the tensile strength is related to adhesion in the Mohr-Coulomb model and the compressive strength is effective on the friction angle. Analytical results are evaluated based on ASCE41 code in different failure modes. Also, for verification, two I-shaped masonry walls, three masonry walls with rectangular cross-section and an arched walls are numerically analyzed using the proposed model and the results of numerical and experimental tests are compared. The results show that the proposed model, while simple, has a good ability to estimate the nonlinear behavior of masonry wall.