توسعه روش اجزاء مجزا براي تحليل غيرارتجاعي اعضاء بنايي غيرمسلح

هدف از اين تحقيق توسعه رويكرد ريز مدلسازي برمبناي روش اجزاي مجزا (بلوك صلب و فنر)، براي شبيه‌سازي رفتار داخل صفحه سازه‌هاي بنايي آجري غيرمسلح است. به منظور ارزيابي ترك‌خوردگي در آجر از فرضيات ترك دو جهته و براي رفتار پس از آن، از ايده روش ترك پخشي ثابت استفاده شده است. همچنين مشخصات فنرهاي نرمال و برشي شبيه‌سازي كننده رفتار ملات و اندركنش مابين آن با آجر، بطور مجزا از هم با ارزيابي ميزان بازشدگي ترك و تغييرشكل برشي در سطح ترك تعيين مي‌شوند. جهت ارزيابي ميزان تنش برشي در فنرهاي برشي از معيار موهر-كولمب استفاده مي‌شود. الگوريتم محاسباتي و نرم‌افزار توسعه يافته، تشريح و مورد اعتبارسنجي قرار مي‌گيرد. مقايسه نتايج تحليلي و آزمايشگاهي حاكي از آن است كه برنامه توسعه يافته از قابليت مناسبي براي ارزيابي رفتار غيرخطي سازه‌هاي بنايي به همراه مكانيزم‌هاي مختلف مودهاي شكست و الگوهاي ترك‌خوردگي برخوردار مي‌باشد.

One of the oldest and most durable building materials used for a large number of ancient structures by mankind is the masonry material. The advantages of this material such as few maintenance costs of masonry building and beautiful sight view of this structure, as well as its proper resistance to fire, have caused to be the boost building materials nowadays. Although numerical analysis of the seismic behavior of masonry structures due to their geometrical and behavioral complexities is difficult, it is possible to accurately evaluate them by using an appropriate recently developed modeling method. In order to select the appropriate numerical method in addition to the accuracy of the results, the simplicity of the modeling and the necessary parameters to determine the behavioral characteristics of the masonry materials must also be considered. Two major modeling approaches for simulating the behavior of masonry members are micro-modeling (heterogeneous model) and macro-modeling (homogeneous model). In the micro-modeling approach, the failure mechanisms and cracking pattern are precisely determined; but because of the required specifications and details, it is considered as a sophisticated modeling approach. In this study, the main purpose is to develop a micro-modeling approach based on the discrete element method (i.e. rigid block and spring method) for simulating in-plane behavior of unreinforced brick masonry buildings. For modeling each brick masonry wall in this paper, the masonry unit is defined which is consisted of a rigid block in the transverse direction and four blocks in the horizontal direction with two different types of springs. This unit represents, in fact, two bricks and connecting mortar in real condition. According to the assumption of the rigid block and spring method, the properties of the normal and shear springs are considered independently. In this situation, it is not practically possible to accurately estimate the behavior of masonry member in shear dominated case. In order to model cracking in brick, the two-way crack hypothesis and for subsequent behavior in each masonry unit, the idea of fixed smeared crack approach is implemented in this research. The properties of the normal and shear springs, simulating behavior of the mortar and the brick-mortar interaction, are determined separately by estimating the cracking opening and shear displacement in the crack surface. The Mohr-Coulomb criterion is used to evaluate the behavior of mortar-brick interface. The computational algorithm and developed FORTRAN code are described and validated. Comparison of analytical and experimental results showed that by applying corrections to evaluate the stiffness of springs attached to the blocks and also the application of behavioral models introduced in this paper for the masonry material, it is possible to evaluate the different mechanisms of failure of the masonry building along with their cracking pattern. Therefore, an accurate evaluation of the structural responses can be obtained by applying the smeared crack approach in the modeling assumptions of the rigid block and spring method for different loading conditions. The lateral load-displacement diagrams of the masonry walls in analytical and numerical models illustrate the appropriate accuracy of the developed numerical models.