برآورد تابع خسارت براي ساختمان‌هاي غيرمهندسي‌ساز در منطقه‌ي زرند

EVALUATION OF DAMAGE FUNCTIONS FOR NON-ENGINEERING BUILDINGS DURING THE 2005 DAHOOIYEH-ZARAND EARTHQUAKE, IN IRAN

يكي از مهم‌ترين علل تلفات انساني و زيان‌هاي اقتصادي‌ ـ اجتماعي ناشي از زمين‌لرزه‌ها، آسيب‌‌پذيري شديد ساختمان‌هاي مسكوني در مناطق شهري و روستايي است. از جمله روش‌هاي موجود براي بررسي آسيب‌‌پذيري لرزه‌يي ساختمان‌ها، استفاده از منحني هاي آسيب‌پذيري يا تابع خسارت است كه با توجه به نوع سازه، مصالح به‌ كار رفته و روش‌هاي ساخت‌و‌ساز براي هر منطقه يا كشور متفاوت است. در اين مطالعه، تابع خسارت برحسب شدت و بيشينه‌ي شتاب جنبش زمين براي ساختمان‌هاي غيرمهندسي‌ساز (خشتي و مصالح بنايي) منطقه‌ي زرند با استفاده از داده‌هاي جمع‌آوري‌شده از خرابي ساختمان‌ها در زمين‌لرزه‌ي داهوييه ـ زرند (1383)، ارايه شده است. بدين منظور شدت زمين‌لرزه در شهرها و روستاهاي خسارت ديده با توجه به رده‌ي آسيب‌‌پذيري ساختمان‌ها و ميزان خرابي آن‌ها براساس دستورالعمل EMS-98 تعيين ‌شده است. همچنين، ميزان خسارت در سطح خرابي سنگين براي ساختمان‌هاي منطقه محاسبه شده و در نهايت با توجه به تعداد بالاي ساختمان‌هاي غيرمهندسي‌ساز در منطقه‌ي زرند تابع خسارت براي اين نوع ساختمان‌ها ارايه شده است. براين اساس، آستانه‌ي تخريب سنگين در منطقه‌ي زرند معادل 2cm/s 100 بر حسب شتاب و شدت VII در مقياس EMS-98 برآورد ‌شد.

Several aspects of an earthquake, including those of a seismological, engineering, and socio-economical nature, must be understood and incorporated effectively before the impact of an earthquake can be predicted. Earthquake damage and loss modeling requires comprehensive assessment of earthquake hazard, the seismic vulnerability of the built environment and associated exposure. One of the steps in hazard mitigation and the realistic modeling of damage, fatalities and causality due to future earthquakes, is to apply appropriate damage and fatality functions. Among different methods for evaluating damage functions, the most robust method is the empirical method, which is based on the damage information of different building types from past earthquakes. The application of appropriate damage functions could provide an essential input for the seismic hazard mitigation plan before an earthquake, as well as preparedness and response plans after an earthquake. Damage functions vary for each region or country, based on the types of structure, materials and construction methods. Therefore, the damage data from a past earthquake should be carefully gathered and analyzed. Then, the ground motion level, in the form of seismic intensity, peak ground acceleration or velocity, needs to be estimated in damaged areas and their relation to the observed damage of structures should be investigated. To this end, the recent earthquakes in Iran provide a unique opportunity to develop damage functions, and to study their relations with different levels of damage experienced by different types of structure. In this paper, the empirical damage functions for non-engineering buildings (adobe and masonry structures) were evaluated in terms of intensity and peak ground acceleration for the Zarand region. The building damage data were collected from the damage survey of the 2005 Dahooiyeh-Zarand earthquake, by the first author, and those gathered from the damage report provided by different organizations. The earthquake intensity was evaluated in the damaged areas considering the vulnerability class and the damage grade of buildings using the European Macroseismic Scale (EMS-98). Furthermore, peak ground acceleration was estimated from the recorded data and by application of an interpolation technique to those estimated by attenuation relationships in damaged areas, where no recorded data were available. Then, the damage functions for a heavy damage level (G4+G5) were evaluated for adobe and masonry structures, which were the major types of structure in the Zarand region. The introduced damage functions revealed that the heavy damage threshold for non-engineering buildings in the Zarand region is about 100 cm/s2 or VII on the EMS-98 intensity scale.