پديد آورندگان :
غني زاده، محمد پژوهشگاه بين المللي زلزله شناسي و مهندسي زلزله , فرزام، مسعود دانشگاه تبريز - دانشكده مهندسي عمران , سروقدمقدم، عبدالرضا پژوهشگاه بين المللي زلزله شناسي و مهندسي زلزله - پژوهشكده مهندسي سازه
كليدواژه :
ديوار برشي كوتاه , المان محدود , مقاومت برشي , مقاوم سازي
چكيده فارسي :
ديوارهاي برشي كوتاه با نسبت عرض به طول كمتر از 2 در تقويت سازه هاي كم ارتفاع بكار گرفته مي شوند. اين ديوارها معمولاً مقاومت جانبي قابل توجه ليكن شكل پذيري كم دارند. به دليل استفاده از دهانه هاي به طول متعارف (در فاصله محور به محور ستون ها)، اغلب به تمامي ظرفيت برشي اين ديوارها نيازي نمي باشد و مي توان با بسيج بخشي از ظرفيت برشي، به مقاومت هاي كافي براي چنين سازه هايي دست يافت. در اين مقاله نشان داده مي شود كه مي توان با استفاده از شكل و طول مناسبي از فونداسيون و به حساب آوردن اثر انعطاف پذيري بستر ، شكل پذيري و مقاومت اين ديوارها را افزايش داد. همچنين تاثير پارامترهاي خاك بر شكل پذيري مطالعه شده است. بدين منظور ابتدا يك نمونه ديوار برشي كوتاه كه به صورت تجربي آزمايش شده و در ادبيات فني گزارش شده است، با نرم افزار تحليل غيرخطي ATENA 3D صحت سنجي شده و نتايج براي مطالعه حساسيت رفتار به پارامترهاي طول، شكل فونداسيون و سختي خاك بكار گرفته مي شود.
چكيده لاتين :
Short reinforced concrete shear walls with aspect ratio less than 2 are commonly utilized for strengthening of low rise masonry structures. These walls demonstrate adequate lateral load strength, while having low ductility compared with high rise walls with same lengths. Shear failure is the dominant failure mode of short walls while the bending failure is the most likely failure mode of tall walls. The bending strain distribution over the section of the wall is nonlinear due to shear deformation contribution; therefore, adding longitudinal reinforcements slightly increases the total lateral load strength of the short walls. Considering typical span length of such walls –between adjacent column distances–, and due to the fact that walls are usually distributed symmetrically over the plan of building, there is no need to motivate all their lateral load strength. Taking into account merely a portion of strength will be sufficient for the purpose of strengthening of the structure. In this paper it will be shown that taking the shape and length of foundation into account, and the interaction of soil-structure, the ductility of the wall is increased. Furthermore, the effect of soil stiffness on the behavior of the wall is studied. The short shear wall which has been studied experimentally by the NUPEC of Japan is adopted for numerical simulation by the commercial nonlinear analysis software ATENA 3D. Fracture plastic model, taking the smeared cracking method into account, is used for concrete and the bilinear hardening plasticity model is assumed for rebar. The wall is subjected to the predefined level of axial load and the increasing cycling lateral deformations. Sensitivity of the wall behavior to mesh dimensions and the affecting parameters of concrete models such as fracture energy, tension softening and tension stiffening coefficient, shear modulus reduction after cracking, fixed or rotating crack modeling among the other affecting parameters are investigated to verify the model. Because of symmetry, only one half of the wall is modeled. Reinforcing bars are modeled discretely taking into account the bond-slip between concrete and bars. A typical shear wall, introduced by IIESE for strengthening low rise masonry buildings, is adopted to study the effect of soil and foundation parameters on its behavior. The wall behavior under lateral loads is studied numerically, based on the results of the above mentioned numerical verification on short shear walls, which have been tested by NUPEC. The sensitivity of wall to the parameters of length and shape of the footing together with soil properties has been investigated. It is shown that by increasing the length of footing, base reaction coefficient and the embedment depth of footing the bearing capacity of shear walls showing rocking behavior increased, while the ductility decreased. The U shaped foundations show better behavior in comparison with the straight foundation having the same length. For structures which need a limited level of strength increase or a required ductility, the length or embedment length of the footing may be chosen intentionally, to motivate the rocking behavior of foundation.
