مطالعه‌ي پارامتري اثر عوامل مختلف در نيروي وارد بر اجزاي غيرسازه ‌يي

A Parametric Study on Input Acceleration for the Design of Non-Structural Components

آيين نامه هاي معتبر ساختماني در يكي دو دهه‌ي اخير، روابطي را براي محاسبه‌ي نيروي وارد بر اجزاي غيرسازه‌يي ساختمان ها ارايه كرده اند. در اين مطالعه، روابط پيشنهادي آيين نامه‌ي يوروكد با مقادير حاصل از تحليل هاي تاريخچه‌ي زماني قاب هاي فولادي 3، 5، و 7 طبقه‌ي خمشي، مهاربندي هم محور و مهاربندي برون محور با رفتار كشسان و خميري تحت ركوردهاي حوزه‌ي دور و نزديك مقايسه و نشان داده شده است كه مقادير حاصل از اين روابط در بسياري از موارد، غيرمحافظ كارانه و كمتر از حد لازم است. بر اين اساس و با استفاده از نتايج تحليل هاي ذكرشده براي اصلاح مقادير اين آيين نامه، اصلاحاتي پيشنهاد مي ‌شود. اين اصلاحات عمدتاً مرتبط با اثر محل قرارگيري عضو غيرسازه ‌يي در ارتفاع سازه و نيز ضريب تشديد ارايه‌شده در آيين نامه‌ي مذكور است. در اين نوشتار، همچنين اثر زلزله هاي حوزه‌ي نزديك و شدت زلزله در نيروي وارد بر اعضاي غيرسازه ‌يي نشان داده شده است.

The importance of non-structural components in the seismic performance based design of buildings is well known nowadays. Impaired Non-Structural Components (NSC) in earthquakes could cause heavy loss of life and property and loss of serviceability. The response of NSC depends on various parameters, among them are the behavior of the primary structure, location of non-structural elements in the structure, interaction between NSC and the structure, type and number of NSC attached points, the geometry, shape and condition of the mass distribution of NSC and etc. Researchers have used different methods for calculating NSC responses. Among them are the direct method and the Floor Response Spectrum (FRS) method. In the first method, analysis is performed by modeling the primary structure and NSC simultaneously. In case the weight of the NSC is less than 10% of the total weight of the structure and 20% of the weight of the floor, then, the effect of NSC on the structure can be neglected and simpler methods can be implemented. One of the simpler methods is the FRS method. In this method, the behavior of the primary structure at the attached point or points of NSC is determined, neglecting their interaction. Then, the obtained FRS is used as an input for analyzing non-structural elements. This method is used in many design codes in order to determine the design force on the NSC. The present research studies the effect of various parameters, including the inelastic behavior of the system, natural periods of primary and secondary systems and type of structural system, on NSC response. A method for calculating the NSC response is suggested, which accounts for the location of the NSC and the inelastic behavior of the structure more precisely. For this research, a variety of moment resisting frames, eccentric and concentric braced frames were examined. These frames are designed in accordance with ASCE 2005 requirements. 15 records of far-field earthquakes and 15 records of near-field earthquakes were chosen for performing parametric studies. To perform expanded parametric studies on various frames with different stiffness and strength, modified shear building models for these frames were constructed. The shear building frame is set to have an equivalent lateral force-deformation behavior in each storey of a given MRF, CBF or EBF frame. Consequently, the base shear-roof displacement curve of both frames became approximately the same. It has been demonstrated that the structure system type does not significantly affect the suggested relations. Moreover, in this study, it has been shown that earthquake intensity causes minimum acceleration (in the first floor) to decrease, and peak acceleration (in higher floors) to increase.