بررسي تاثير مشخصات المان مرزي در رفتار ديوارهاي برشي بتني كوتاه

The Effect of Boundary Element Characteristics on the Behavior of Squat Concrete Shear walls

در اين نوشتار، با تحليل 30 مدل از ديوارهاي برشي بتني كوتاه به بررسي تاثير متغيرهايي از قبيل نسبت ارتفاع به طول ديوار، ميزان بار محوري و به ويژه تاثير المان مرزي و برخي مشخصات آن از قبيل ميزان آرماتور طولي و ميزان آرماتور عرضي (محصورشدگي بتن) در رفتار اين‌گونه ديوارها پرداخته شده است. پارامترهاي پاسخ بررسي‌شده عبارت‌اند از: مقاومت بيشينه و تغييرشكل نظير آن و همچنين مود گسيختگي ديوار. نتايج حاصله نشان مي دهد كه المان مرزي با توجه به نسبت ارتفاع به طول ديوار و شرايط طراحي‌اش، تاثيرات متفاوتي از خود نشان مي دهد. با افزايش آرماتور طولي المان مرزي، تغييرشكل در مقاومت بيشينه در ديوارهاي با نسبت ارتفاع به طول 5/0، افزايش و در ديوارهاي با نسبت 0/1 و 5/1، كاهش مي يابد. اين پديده تابعي از مود گسيختگي ديوار است. در بعضي از موارد تغيير در مشخصات المان مرزي باعث تغيير مود گسيختگي ديوار مي شود.

Squat shear walls are common in low-rise buildings, their seismic rehabilitation and lower stories of high-rise buildings. Wall segments formed by openings also have the same behavior as squat shear walls. Usually walls with aspect ratio less than 1.5 are known as low-rise or squat shear walls. Shear stresses have significant effect in lateral strength and ductility of such walls. Concrete structures with shear dominant behavior are more complex for Analyzing and their seismic behavior may be poor. Also squat shear walls have various failure modes under lateral loading. Few researches can be found related to the effect of boundary elements characteristics on the behavior of squat shear walls. Accordingly, in this paper, the effect of some variables such as wall aspect ratio, amount of axial force, and specially effect of boundary elements and some of their characteristics such as longitudinal reinforcement and horizontal reinforcement (concrete confinement) on the behavior of squat shear walls are investigated, and this is done by analyzing 30 models of such walls. Response parameters include maximum lateral strength, lateral displacement in maximum strength and failure mode of walls. Results suggest that the effect of boundary elements characteristics on the response parameters will differ depending on wall aspect ratio and details of design. In walls with aspect ratio of 0.5, displacement in maximum strength found to increase with increasing longitudinal reinforcements of boundary elements and in walls with aspect ratio of 1.0 and 1.5 found to decrease. Lateral strength increase with increasing longitudinal reinforcements of boundary elements and its increase has rising rate with increasing wall aspect ratio. Accordingly, the conclusion here is that with increasing longitudinal reinforcement of boundary elements, ductility increases in models with diagonal tension failure mode and decreases in models with flexural failure mode. In some cases change in boundary element characteristics result in change in failure mode of models.