منحني رفتاري ديوارهاي بنايي محصور شده با كلاف‌هاي بتن مسلح

Behavioral Curve of Unreinforced Masonry Walls Confined by RC Ties

ضوابط موجود در آيين‌نامه‌هاي مختلف در مورد ديوارهاي بنايي كلاف‌دار عموماً بر‌مبناي مطالعات آزمايشگاهي و مشاهده خسارت‌هاي وارد بر اين دسته از سازه‌ها در زلزله‌هاي گذشته مي‌باشد. از اين رو اين ضوابط اغلب به‌ صورت تجويزي بوده و روابط تحليلي مناسبي براي ارزيابي مقاومت لرزه‌اي آن‌ها وجود ندارد. در اين تحقيق با استفاده از روش اجزاي محدود غيرخطي به بررسي رفتار درون صفحه‌اي ديوارهاي بنايي كلاف‌دار پرداخته مي‌شود. پس از اعتبار‌سنجي مدل عددي و مدل‌هاي رفتاري استفاده شده، اثر وجود بازشو و هم‌چنين چيدمان ديوارهاي بنايي مجاور هم بر رفتار لرزه‌اي هر كدام از ديوارها به صورت عددي مطالعه مي‌شود. مطالعات انجام شده نشان مي‌دهد كه با افزايش مساحت بازشو در قسمت مياني پانل ديوار، حداكثر مقاومت ديوار به صورت لگاريتمي كاهش پيدا مي‌كند. نتايج به‌دست آمده نشان مي‌دهد كه ديوارهاي مجاور سبب افزايش نيروهاي اندركنشي بين كلاف‌هاي بتني و ديوار بنايي شده است، در نتيجه ظرفيت باربري هر كدام از ديوارها به صورت مجزا افزايش پيدا مي‌كند. در ادامه با بررسي پاسخ‌هاي به‌دست آمده از نمونه‌هاي تحليلي، يك منحني جامع سه خطي براي به‌دست آوردن ظرفيت ديوارهاي بنايي كلاف‌دار پيشنهاد مي‌شود.

Confined masonry consists of load-bearing walls with some slender cast-in-place tie columns connected with tie beams. These confining elements are usually made of reinforced concrete and especially located around the critical points such as openings and corners. Although the response of confined masonry walls has been extensively studied in experimental tests worldwide, the analytical models capable of capturing deformation and strength characteristics of these walls and also technical guidelines which can help engineers to numerically evaluate the seismic resistance of confined masonry structures are rate. In this study, the micro-modeling strategy is adopted for the numerical simulation of unreinforced masonry walls confined by reinforced concrete tie columns and beams. A modified version of general path dependent contact density model is used to simulate the complicated response of brick-mortar interaction in the mixed mode of shear and axial deformations. A nonlinear finite element analysis program called “WCOMD_SJ” is used for this purpose. This program has been developed at University of Tokyo and is an analytical tool for two-dimensional static and dynamic nonlinear analysis of reinforced concrete structures based on fixed smeared crack approach. This program has been modified by the second author for nonlinear macro and micro analysis of masonry structures. In order to validate the analytical approach, experimental test results and gathered data from literature are used. The comparison between experimental and analytical results shows good agreement between analytical and experimental findings. Then through a parametric study, the effect of opening and also the interactional effect of adjacent walls on the lateral response and strength of confined masonry walls are numerically investigated. Finally a simple but rational method for modeling the nonlinear behavior of confined masonry walls is proposed. The comparison between this model and numerical results confirms the reliability of the proposed model. Since available experimental results are rare, an analytical study is also performed for investigating the accuracy of the proposed relations.