تاثیر نامنظمی سختی جانبی بر نیاز زاویه درز انقطاع قاب های خمشی فولادی مجاور تحت زلزله های حوزه نزدیک گسل

به دلیل عدم رعایت درز انقطاع لازم بین ساختمان های مجاور، پدیده برخورد (ضربه) در هنگام وقوع زلزله رخ می دهد. ضربه می تواند منجر به خسارات موضعی به ستون های محل برخورد، خسارات موضعی یا کلی کف ها در تراز برخورد و یا منجر به فروریزش کلی ساختمان شود. از طرفی وجود نامنظمی سختی جانبی(طبقه نرم یا خیلی نرم) به دلیل تغییر در نوع کاربری اولین طبقه ساختمان، از رایج ترین انواع نامنظمی است. این مقاله به تخمین نیاز زاویه درز انقطاع در بالاترین تراز برخورد دو سازه مجاور در ترکیب قاب های خمشی فولادی منظم و دارای نامنظمی سختی جانبی با تغییر در ارتفاع طبقه اول، تحت رکوردهای زلزله حوزه نزدیک گسل می پردازد. بدین منظور قاب های خمشی فولادی 2 تا 20 طبقه 3 دهانه منظم و نامنظم در هفت گروه از ترکیبات دوتایی در مجاورت یکدیگر قرار می گیرند و زاویه درز انقطاع آنها با تحلیل دینامیکی تاریخچه زمانی غیرخطی محاسبه و مقایسه می گردد. نتایج بدست آمده حاکی از آن است که افزایش مقدار نامنظمی سختی جانبی در اولین طبقه سازه، می تواند منجر به افزایش زاویه درز انقطاع در 84 % از ترکیبات همجواری بررسی شده گردد. ضریب میانگین این افزایش در کلیه حالات تحت تاثیر مورد بررسی از ترکیب قاب های منظم و نامنظم با ارتفاع طبقه اول 4.5 و 5.5 متر، به ترتیب 1.19 و 1.38 برابر ترکیبات قاب های منظم است.

The Effect of the Irregularity of Lateral Stiffness on the Demand of Separation Gap Angle in Steel Moment Frames UnderNear-Field Earthquakes

In crowded cities, building structures are usually constructed in close proximity to one another because of restricted availability of space. In many cases, every building in a block is in full or partial contact with its neighboring buildings. Because of insufficient separations, their different heights and seismicresisting systems collision can occur between adjacent buildings during strong ground motions. This collision can make partial or general damages to the structural elements and accelerate their failure by affecting their stiffness. This phenomenon is commonly referred to as structural pounding. Pounding between inadequately separated buildings has been observed in most previous major earthquakes. Each time pounding occurs, building structures will sustain short duration large impact force not specifically considered in conventional designs. The severity of the impact depends on the dynamic characteristics of the adjacent buildings in combination with the earthquake characteristics. options to minimize the effect of pounding have to do with the decreasing of lateral motion by joining adjacent buildings at critical positions so that their motion could be inphase or by increasing the damping capacity of building pounding by means of energy dissipation, for example, by passive structural control systems. Modern seismic design codes have many pioneering provisions on the nonlinear behavior of structures, but amongst others, they do not consider structural pounding, a phenomenon with strong nonlinearities, for which codes usually suggest a sufficient separation between adjacent buildings. On the one hand, irregularity in lateral stiffness (a soft or very soft story) due to the different use of the first floor of the building is one of the most common types of irregularity. Aiming to prevent such collisions, these study estimates demand of separation gap angle at the highest level of collision between two adjacent structures in regular steel moment frames with irregularity in the lateral stiffness (with changes in the height of the first floor) under seismic records of a nearfield earthquake. Models were considered as twodimensional, ductile, steel moment frames of 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20story 3span buildings. In order to create an irregularity in the lateral stiffness on the first floor, the height of this story was increased from 3.5 m to 4.5 and 5.5 m while the crosssection of the column at the first two stories was kept unchanged. These frames can be placed alongside in seven binary groups considering priority in the arrangement. Each group represents 100 different binary arrangements of the frames. In total, 700 cases of various adjacency were studied. The OPENSEES software was used to analyze the dynamics of the nonlinear history considering 20 perpendicular components to the fault with a progressive orientation of nearfield earthquake records of pulselike faults. The results suggest the increase in the irregularity in the lateral stiffness in the first floor of the building can increase the separation gap angle. On average, the combination of regular and irregular frames with the firstfloor height of 4.5 and 5.5 m, is increased 1.19 and 1.38 times, respectively, compared to the combinations of regular frames. Moreover, among various adjacent combinations of regular and irregular frames, in case the taller structure is associated with lateral stiffness (soft floor), the average increase in the separation gap angle is larger than other cases.