پديد آورندگان :
خاتمي، مصطفي دانشگاه سمنان , گرامي، محسن دانشگاه سمنان - پژوهشكده فناوري هاي نوين مهندسي عمران , خيرالدين، علي دانشگاه سمنان - دانشكده مهندسي عمران
كليدواژه :
زاويه درز انقطاع , تراز برخورد , نامنظمي سختي جانبي , ساختمان هاي مجاور , تحليل تاريخچه زماني
چكيده فارسي :
به دليل عدم رعايت درز انقطاع لازم بين ساختمان هاي مجاور، پديده برخورد (ضربه) در هنگام وقوع زلزله رخ مي دهد. ضربه مي تواند منجر به خسارات موضعي به ستون هاي محل برخورد، خسارات موضعي يا كلي كف ها در تراز برخورد و يا منجر به فروريزش كلي ساختمان شود. از طرفي وجود نامنظمي سختي جانبي(طبقه نرم يا خيلي نرم) به دليل تغيير در نوع كاربري اولين طبقه ساختمان، از رايج ترين انواع نامنظمي است. اين مقاله به تخمين نياز زاويه درز انقطاع در بالاترين تراز برخورد دو سازه مجاور در تركيب قاب هاي خمشي فولادي منظم و داراي نامنظمي سختي جانبي با تغيير در ارتفاع طبقه اول، تحت ركوردهاي زلزله حوزه نزديك گسل مي پردازد. بدين منظور قاب هاي خمشي فولادي 2 تا 20 طبقه 3 دهانه منظم و نامنظم در هفت گروه از تركيبات دوتايي در مجاورت يكديگر قرار مي گيرند و زاويه درز انقطاع آنها با تحليل ديناميكي تاريخچه زماني غيرخطي محاسبه و مقايسه مي گردد. نتايج بدست آمده حاكي از آن است كه افزايش مقدار نامنظمي سختي جانبي در اولين طبقه سازه، مي تواند منجر به افزايش زاويه درز انقطاع در 84 % از تركيبات همجواري بررسي شده گردد. ضريب ميانگين اين افزايش در كليه حالات تحت تاثير مورد بررسي از تركيب قاب هاي منظم و نامنظم با ارتفاع طبقه اول 5/ 4 و 5/5 متر، به ترتيب 19/ 1 و 38/ 1 برابر تركيبات قاب هاي منظم است.
چكيده لاتين :
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 seismic-resisting 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 in-phase 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 non-linear behavior of structures, but amongst others, they do not consider structural pounding, a phenomenon with strong non-linearities, 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 near-field earthquake. Models were considered as two-dimensional, ductile, steel moment frames of 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20-story 3-span 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 cross-section 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 near-field earthquake records of pulse-like 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 first-floor 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.
