تحلیل عددی رفتار ستون بتن مسلح تقویت شده با قفس فولادی

امروزه سازه های بتنی بصورت گسترده در سراسر جهان احداث گردیده و شمار قابل توجهی از این سازه‌ها بنا به دلایل مختلفی از جمله ضعف در طراحی، خرابی در اثر زلزله، ارتقا یک سازه جهت تغییر کاربری و ...، نیازمند مقاوم سازی هستند؛پس احیاسازی و تقویت سازه‌های آسیب پذیر در برابر عوامل مختلف امری مهم محسوب می‌شود. در این پژوهش رفتار ستون بتن مسلح تقویت شده با قفس فولادی، که نوعی روکش فولادی محسوب شده و روشی موثر، ساده و اقتصادی می‌باشد که برای محصورسازی مقاطع بتنی مربعی و مستطیلی شکل استفاده می گردد، مورد بررسی قرار گرفته است. دراین راستا، ابتدا مدل المان محدود ستون بتن مسلح تقویت شده با قفس فولادی در نرم افزار abaqus، تحت نیروی محوری و لنگرخمشی مدل سازی گردید و پس از کالیبراسیون مدل عددی و اطمینان از صحت نتایج و دقت مدل، مطالعه‌ی پارامتریک هفتگانه‌ای بر روی عوامل موثر در رفتار ستون تقویت شده نظیر تعداد، اندازه و ضخامت نوار های فولادی و مکانیزم انتقال بار و ...، در مقایسه با ستون مبنا انجام گردید. نتایج حاصله از این بررسی میزان تاثیر پارامترهای مختلف در رفتار ستون تقویت شده را مشخص نمود و علاوه بر آن بیانگر افزایش قابل توجه در ظرفیت بار نهایی و لنگر خمشی ستون تقویت شده با قفس فولادی است.

Numerical Analysis of RC Columns Retrofitted with Steel Cage

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 beamcolumn 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. 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.