ارايه‌ي منحني‎هاي شكنندگي تحليلي براي ساختمان‎هاي بنايي مدارس ايران

Development of Analytical Fragility Curves for Iran’s Masonry School Buildings

هدف اين نوشتار به‌دست‎آوردن منحني‎هاي شكنندگي ساختمان‎هاي بنايي متداول مدارس ايران است. در اين مطالعه با استفاده از يك روش تحليلي منحني‎هاي شكنندگي براي ساختمان‎هاي بنايي در 3 حالت 1 ، 2،‎ و 3 ‎طبقه و روي انواع خاك‎هاي ذكرشده در استاندارد 2800 به‌صورت مجزا توسعه داده شده‎اند. از ديگر مزاياي اين پژوهش اين است كه به منظور دستيابي به منحني‎هاي شكنندگي واقعي‎تر براي هر ساختمان 24 تحليل انجام شده و اين موارد مد‎نظر قرار گرفته‎اند: اعمال نيرو در هر دو جهت اصلي x و y، توزيع نيروي جانبي به‌صورت مود اول و يكنواخت، خروج از مركزيت، اعمال نيروي جانبي در جهت مثبت و منفي محورها. براي تحليل ساختمان‎هاي بنايي، نرم‎افزار سازه‌يي Tremuri مورد استفاده قرار گرفته، تحليل‎هاي استاتيكي غيرخطي انجام شده‎ و منحني‌هاي ظرفيت سازه به‌دست آمده‌اند. همچنين از طيف آيين‎نامه‌ي 2800 به‌عنوان طيف تقاضا استفاده شده است. نهايتاً با فرض توزيع لوگ ‎نرمال براي تابع چگالي احتمال منحني‎هاي شكنندگي به‌دست‎ آمده‎اند. شايان ذكر است كه شتاب بيشينه‌ي زمين (PGA) به‌عنوان پارامتر نمايان‌گر شدت حركت لرزه‎‎‌يي زمين انتخاب شده است.

Earthquakes are undoubtedly a most important natural disaster and, therefore, in recent decades, the seismic vulnerability assessment of existing buildings has become an important issue. One of the latest achievements in seismic vulnerability assessment is the seismic fragility curve. Fragility curves describe how the reliability of a structure changes over a range of loading conditions to which a structure may be exposed. Approaches to developing fragility curves can be classified into four main categories: judgmental, empirical, analytical, and hybrid. Fairly extensive studies have been done for concrete and steel structures and also for different types of bridges, while, for masonry buildings, only limited studies are available. Iran is in a high seismicity area in the world where a large number of masonry buildings have been constructed. In this study, an analytical approach was used to develop fragility curves for 1 story, 2 story and 3 story masonry school buildings on different soils. In order to achieve more realistic fragility curves, 24 analyses were performed for each building. The following conditions were considered in these analyses: applying lateral force in 2 main axes (x and y) and 2 main directions (positive and negative), eccentricity, applying lateral force in 2 cases (first mode and mass). The computer program, Tremuri, and the design spectrum of Standard No. 2800 have been used in this study. Finally, by assuming a log-normal distribution probability function, fragility curves were obtained. It is worth noting that the peak ground acceleration (PGA) is selected as a parameter that represents the intensity of seismic ground motion.