تاثير آرماتورگذاري قطري در رفتار لرزه‌اي ديوارهاي سازه‌اي بتن مسلح به روش المان محدود

Influence of Diagonal Web Reinforcement on Structural Walls’ Behavior Using Finite Element Method

ساختمان هاي داراي سيستم ديوار يا تركيب ديوار- قاب داراي مقاومت موثري در برابر نيروي زلزله هستند و خرابي كم‌تري نسبت به ساختمان هايي كه مقاومت جانبي آن‌ها تنها بر قاب‌ها استوار است، از خود نشان مي دهند. سه نمونه‌ي ديوار سازه اي بتن مسلح (RC) با هدف مطالعه‌ي تاثير آرماتورگذاري قطري به روش المان محدود توسط نرم‌افزار ABAQUS بارگذاري دوره اي شده‌اند. متغيرهاي تحقيق شامل مقدار و وضعيت قرارگيري آرماتورها در جان بودند. ديواري كه به‌صورت معمولي آرماتورگذاري شده، ظرفيت بارجانبي كمي داشت و به‌دليل شكست جان با يك افت ناگهاني در ظرفيت باربري، گسيخته شد. در حالي كه ديوارهاي مسلح شده با آرماتورهاي قطري، توانايي تحمل بار بسيار بالايي داشته و با يك مد نرم‌تر گسيخته شدند. نتايج تحقيق به‌وضوح نشانگر افزايش قابل ملاحظه‌ي ظرفيت بارجانبي ديوار و نرم‌تر شدن مد شكست به‌وسيله‌ي آرماتورگذاري قطري جان است.

Shear walls are structural elements which have high in plane lateral resistance. The failure mode in these walls is important because collapse in whole structure is generally dominated by their crashing modes. The behavior of properly designed walls with an aspect ratio of around 1.5 is a mixed mode of failure by flexure and shear so for many years researchers are looking for ways to prevent this brittle behavior. The inelastic behavior of RC structural walls subjected to cyclic loads has received considerable attention and gradually the importance of the cross – inclined 45 degree web reinforcement usage to control the shear brittle failure has been proved; however, most related tests have not included the influence of axial loading on the walls and the level of shear stresses which are higher than codes limits. In this paper three reinforced concrete (RC) structural walls with boundary elements and an aspect ratio of 1.5 were simulated in ABAQUS software. To develop verification between numerical and experimental results first specimen conventionally reinforced and its behavior was compared with similar experimental specimen. The other two models are the same with first model although they have diagonal web reinforcement. In second wall the spaces of web deformed bars are the same with first model and in third specimen the weight of web reinforcement is equal with first wall. Considering that all specimens were subjected to a cyclic loading and the nonlinear dynamic analysis is done so to define RC the Concrete Damage Plasticity model should be used. The walls were subjected to a cyclic lateral displacement history based on first yield displacement. The displacement history consisted of several stages and each stage consisted of three loading cycles. During the first stage the specimen was pushed (pulled) under load control until the first cracking of the concrete was observed. In subsequence stages the specimen was loaded under displacement control to integer multiplies of the measured first yield displacement until failure. After the first wall analysis the results were compared with experimental results and considering available differences the numerical results are acceptable. Comparing the numerical analysis results for all specimens with together it is obvious that the wall with conventional reinforcement from the beginning has inelastic and unpredictable behavior and finally failed due to web crushing as a brittle made of failure. In spite of that the other two models after showing an elastic behavior failed in more ductile modes. The energy dissipation capacity of the diagonal reinforcement was a little more than conventional reinforcement however lateral load capacity in diagonal reinforcement almost equals with two fold of similar specimen with conventional reinforcement.