بررسي تاثير دستك فلزي بر رفتار غيرخطي قاب‌هاي بتن آرمه به كمك روش المان محدود

Investigation of Steel Prop Effect on Inelastic Beahavior of RC Frames Using FE Method

- به دلايل گوناگون ممكن است سازه‌هاي موجود نياز به بهسازي داشته باشند، اين بهسازي، شامل احياسازي سازه‌هاي آسيب ديده به وسيله‌ي يك زلزله يا عوامل ديگر، يا مقاوم سازي و تقويت يك سازه خسارت نديده كه با آيين‌نامه‌هاي بارگذاري و طراحي ويرايش قديم يا حتي بدون كد، طراحي و ساخته شده است، مي‌شود، پس احياسازي و مقاوم سازي سازه‌هاي آسيب پذير در برابر زلزله امري ضروري است. در اين مقاله نتايج روش عددي غيرخطي المان محدود FE يك قاب بتن آرمه معمولي و همچنين قاب‌هاي تقويت شده با روش پيشنهادي دستك و طوقه فلزي، تحت بار جانبي افزاينده نشان داده مي‌شود. تاثير دستك فلزي بر رفتار خطي و غيرخطي قاب بتن آرمه و همچنين افزايش سختي، مقاومت نهايي و ميزان جذب انرژي و پارامتر شكل پذيري قاب مورد بحث قرار مي‌گيرد. نتايج آزمايشگاهي يك قاب بتن آرمه يك دهانه يك طبقه انتخاب شده و پس از كاليبراسيون مدل عددي و اطمينان از صحت و دقت نتايج، اين پارامترها بررسي مي‌شوند. نتايج روش عددي المان محدود نشان مي‌دهد كه استفاده از طوقه و دستك فلزي به صورت فشاري و كششي با مساحت مقطع 5 تا 10 سانتي‌متر مربع در اين قاب ، باعث افزايش قابل توجه سختي و مقاومت نهايي و كاهش تغيير مكان نهايي قاب بتن آرمه مي‌شود. همچنين دستك با جاري شدگي خود به عنوان سيستم دفاعي اول در برابر بارهاي جانبي، مي‌تواند مانند فيوزي، جذب انرژي و ميزان شكل پذيري آن را افزايش دهد و همچنين تنش‌هاي ناشي از بار جانبي در محل چشمه اتصال را كاهش داده و مفصل پلاستيك را از چشمه اتصال دور كند.

It is required to rehabilitate the existing structures due to many reasons including the retrofitting of damaged structures under earthquakes or the need to strengthen or retrofit an undamaged structure designed based on old building codes. So, the rehabilitation and retrofitting of structures against seismic loads is unavoidable. In recent years, different methods such as braced systems, shear wall, energy dissipation systems and dampers, fiber reinforced polymer, high performance fiber reinforced cementitious composites HPFRCC, used for retrofitting of deficient RC frames. Each of these mentioned methods can be used for upgrading and improving of linear and nonlinear behavior of RC frames such as rigidity, ultimate strength and ductility. In this paper, by proposed technique of steel elements called steel prop and curb, an ordinary reinforced concrete frame are retrofitted. The technique is usable for local and global strengthening of reinforced concrete frames. Therefore it can be inferred that this method is usable for strengthening of deficient frames with reduced height beams that it due to increase of vertical deflection of beam under gravity loads and sometimes increase of the horizontal drift against lateral loads base on provisions of design cods. The results of a nonlinear finite element analysis of an ordinary reinforced concrete frame and also strengthened frame by steel prop and curb under monotonic lateral load are presented. The effect of different area sections of steel prop on linear and nonlinear behavior of reinforced concrete frame and also increasing the rigidity, ultimate strength, rate of energy absorption and ductility parameter of frame are investigated in this paper. Therefore, the experimental results of an one-bay and one-story reinforced concrete frame are considered for calibrating the numerical results, and then the mentioned parameters have been investigated. The numerical results showed that by adding steel curb and prop box in both compression and tension position with 5,7.5,10 cm2 area at an one-bay and one-story reinforced concrete frame, the stiffness of strengthened frame at linear and nonlinear state are increased considerably. Also the ultimate strength and energy absorption of strengthened frames under monotonic load 43 to79% and 18.5 to 22% relative to un- strengthened frame were increased respectively. But in strengthened frame, by increasing of section area of the steel prop, the ultimate displacement and ductility factor µ were decreased. Furthermore, with a valid selection of steel prop area section, the yielding of steel prop as a preliminary defensive system against lateral loads increased the energy absorption and ductility and also decreased the stresses in panel zone and finally it changed the place of plastic hinge