تحليل عددي رفتار ستون بتن مسلح تقويت شده با قفس فولادي

امروزه سازه­هاي بتني بصورت گسترده در سراسر جهان احداث گرديده و شمار قابل توجهي از اين سازه‌ها بنا به دلايل مختلفي از جمله ضعف در طراحي، خرابي در اثر زلزله، ارتقا يك سازه جهت تغيير كاربري و ...، نيازمند مقاوم­سازي هستند؛پس احياسازي و تقويت سازه‌هاي آسيب پذير در برابر عوامل مختلف امري مهم محسوب مي‌شود. در اين پژوهش رفتار ستون بتن مسلح تقويت شده با قفس فولادي، كه نوعي روكش فولادي محسوب شده و روشي موثر، ساده و اقتصادي مي‌باشد كه براي محصورسازي مقاطع بتني مربعي و مستطيلي شكل استفاده مي گردد، مورد بررسي قرار گرفته است. دراين راستا، ابتدا مدل المان محدود ستون بتن مسلح تقويت شده با قفس فولادي در نرم افزار ABAQUS، تحت نيروي محوري و لنگرخمشي مدل­سازي گرديد و پس از كاليبراسيون مدل عددي و اطمينان از صحت نتايج و دقت مدل، مطالعه‌ي پارامتريك هفتگانه‌اي بر روي عوامل موثر در رفتار ستون تقويت شده نظير تعداد، اندازه و ضخامت نوار هاي فولادي و مكانيزم انتقال بار و ...، در مقايسه با ستون مبنا انجام گرديد. نتايج حاصله از اين بررسي ميزان تاثير پارامترهاي مختلف در رفتار ستون تقويت شده را مشخص نمود و علاوه بر آن بيانگر افزايش قابل توجه در ظرفيت بار نهايي و لنگر خمشي ستون تقويت شده با قفس فولادي است.

Nowadays, reinforced concrete structures are widely being constructed all over the world and some of them need to be strengthened for variety of reasons such as poor design, damages caused by earthquakes, etc. Nowadays, engineering attitude toward demolition and renovation of structures have been changed to retrofitting and upgrading. By retrofitting, the structural reliability increases and saves both time and cost. In some of special cases that the structure can not be demolished and rebuilt, retrofitting plays an important role. The columns of the structures are one of the main elements that are subjected to axial, shear forces, and bending moments, and their strength and ductility have an important impact on their seismic capacity. Different methods are used for strengthening of columns. These methods include concrete jacketing, steel jacketing and composite jacketing (FRP). Among the various retrofitting methods of reinforced concrete columns, steel jacketing is one of the methods used to strengthening of RC structures, especially for confining RC columns with rectangular and square cross sections. Steel cage is a type of steel jacket and because of its effectiveness, ease of use, light weight and the availability of material, it has become an affordable, effective, economic and simple option. This method involves the use of four longitudinal angle steel profiles fixed to the corners of the RC columns, to which some transverse steel strips are welded. The gap between steel cage and column is filled with cement or epoxy mortar. Different parameters affect the behavior of the column reinforced with steel cage. Studies carried out on this strengthening method have mostly focused on the axially loaded columns. The parameters have been studied are the number of steel strips, the size of the steel strips, the size of the steel angels, the thickness of the steel strips, the yield stress of the steel of the cage, the compressive strength of the concrete used in the column, and, finally, the use of capitals in the beam-column connection joint zone. Capitals are welded to the steel cage and located at each end of the cage, loads applied to the beam are transmitted to the steel cage through the capitals. Loads from an upper floor of the building are also transmitted to the cage through the beam via the capitals. Current study investigates the behavior of RC columns strengthened with steel cage under axial force and bending moment. In this regard, the strengthened RC column with steel cage was modeled using finite element method using ABAQUS software and calibrated by experimental results obtained from other laboratory research works. Then, the parameters affecting the behavior of the strengthened columns were examined. Seven different parametric studies carried out in order to grasp the behavior of the retrofitted columns by using parameters such as the number, size, thickness and yield strength of the steel jacket plates, compressive strength of concrete, condition of the beam to column connection and the mechanism of load transmission. The results of this study show a good agreement with experimental results and demonstrate a considerable increase in the ultimate axial force and bending moment