بررسی رفتار لرزه‏ای سیستم دوگانه دیوار برشی– قاب خمشی با در نظر گرفتن اندرکنش بین خاک و سازه

در اکثر موارد در طراحی و ارزیابی سازه‏ها، تکیه‏گاه سازه به‌صورت گیردار فرض شده و اثرات اندرکنش خاک و سازه لحاظ نمی‏شود؛ در‌صورتی‌که در نظر گرفتن اثرات اندرکنش خاک و سازه ویژگی‏های دینامیکی سیستم را عوض می‏کند. در این مطالعه رفتار لرزه‏ای سیستم دوگانه دیوار برشی قاب خمشی با در نظر گرفتن اثرات اندرکنش خاک و سازه بررسی شده است. بدین‌منظور سه سازه با تعداد طبقات 5، 10 و 15 در محیط نرم‌افزار opensees مدل‌سازی شده و تحلیل‏های استاتیکی غیرخطی در دو حالت پایه گیردار و پایه انعطاف‏پذیر انجام شده است. نتایج نشان می‏دهد که در نظر گرفتن ssi  باعث افزایش زمان تناوب سازه و کاهش برش طبقات می‏شود. همچنین با در نظر گرفتن اثرات اندرکنش خاک و سازه ظرفیت سازه کوتاه کاهش پیدا می‎کند درحالی‌که با افزایش ارتفاع سازه مقدار ظرفیت آن تفاوت چندانی ندارد. از سوی دیگر در اثر اندرکنش خاک و سازه فونداسیون دیوار برشی حرکت دورانی دارد و این باعث می‏شود که دیوار برشی در آغاز بارگذاری مقدار کمی از بار جانبی را تحمل نماید و هرچقدر بار جانبی بیشتر می‏شود سهم دیوار برشی در تحمل بار جانبی بیشتر ‏شود.

Investigating the Seismic Behaviour of the RC Wall-Framed System Considering Soil-Structure Interaction

In most cases of design or assessment of the buildings, the fixed foundation assumption is used and the effect of soilstructure interaction (SSI) is neglected. In fact, considering the SSI effects in analysis leads to substantial changes in the dynamic properties and the dynamic responses of the structure. On the other hand, the shear wallframe lateral load resisting system is one of the most popular systems for resisting the earthquake and wind loads because of its ability to provide high energy dissipation, high lateral stiffness and high lateral capacity in comparison with shear wall or bare frame only. In this paper, a comprehensive study of the seismic behavior of the RC wallframe system with and without SSI effects is performed. For this aim, three 5, 10 and 15story buildings were simulated in OpenSees software so that the wallframe dual system for each of them is located at the perimeter of the structure. The shear wall modeling was performed using the shear flexure interaction (SFI) model, which was developed by (Kolozvari et al., 2015). For nonlinear modeling of beams and columns, the beamWithHinges and nonlinearBeamColumn elementswere used, respectively. Also, by using the beam on nonlinear Winkler foundation (BNWF) theory the SSI phenomena was simulated. Modal and pushover analyses were carried out in two cases, namely, fixed and flexible bases. The lateral load capacity, structure period, base shear contribution ratios of the shear wall and moment frame and the story drifts were studied in details. Also, for different performance levels, the base shear, story shear force and the development of the plastic hinges were investigated. The results of the modal analyses show that the SSI effects increase the first mode period of the structure and the percentages of increase in the first mode period for the 5, 10 and 15story models are 75.2, 23.8 and 13.2%, respectively. In addition, considering the SSI effects in eigenvalue analysis leads to change in the first mode shape of the 5story model, so that it will be close to linear case. Also, the SSI effects lead to decrease in the base shear capacity of the 5story model and by increasing the height of structure its effects on the base shear capacity are negligible. The results indicate that the foundation of the shear wall under SSI effects has a rotational movement that decreases the shear wall contribution in bearing the lateral loads and increases the frame base shear contribution at the linear stage. Besides, by increasing the lateral load level, the shear wall base shear contribution ratio increases and more nonlinearity will take place at this stage. In case of flexible base, the story drifts increase, especially in the lower stories and at the high damage stage the base shear contribution ratios of the shear wall and frame will be equal. Also, the SSI effects lead to increase in the seismic demands of the structural components in the lower stories and decrease them at the higher stories.