تعيين نيروهاي معادل استاتيكي زلزله بر روي شبكه‌هاي تخت و بررسي كارايي آنها

Assessment of Equivalent Static Earthquake Loadings on DLG and their Versatility

سازه‌هاي مشبك فضايي يكي از انتخاب‌هاي رايج براي پوشش فضاهاي بزرگ است. همچنين به عنوان سرپنا‌‌ه‌‌هاي موقت پس از زلزله‌هاي قوي و مخرب مورد استفاده قرار مي‌گيرند و سبك و با درجه‌ي نامعيني بالايي هستند. اين دو خصيصه باعث شده است كه مدت‌ها تصور رود كه آن‌ها در برابر زلزله، آسيب‌پذير نيستند. با اين‌حال، رخدادهاي زلزله در كوبه (1995) نشان داده است كه سازه‌هاي مذكور هر چند نسبت به سازه‌هاي متعارف ايمن‌تر هستند، ولي نبايد آن‌ها را مطلقاً مصون پنداشت. در پژوهش حاضر، خصوصيات ديناميكي، رفتار خطي، و غيرخطي شبكه‌هاي تخت دولايه مورد مطالعه قرار گرفته و نشان داده شده است كه شبكه‌هاي ذكرشده در زلزله آسيب‌پذير هستند، بنابراين بايد به دقت طراحي شوند و براي محاسبه وتوزيع بار زلزله‌ي استاتيك معادل در جهت قايم بر روي شبكه‌هاي تخت دولايه فرمول‌هايي ارايه و با روابط موجود در آيين‌نامه‌ي چين، در رابطه با ارزيابي نيروي زلزله‌ي قايم بر روي شبكه‌هاي دولايه مقايسه‌هايي انجام شده است.

Reticular space structures are widely selected as cover for large spaces, and are also used as refuge spaces for earthquake hit areas. Space structures are light and highly indeterminate and, for some time, these two properties caused researchers to take them as a-seismic structures. However, the 1995 Kobe earthquake in Japan showed that although space structures are safer than conventional buildings, they are not completely a-seismic. Double layer grids (DLG) are one of the most frequently used types of space structure. The aim of this research is to introduce some relations for calculating the earthquake induced forces on these structures. The relations comprise of a) assessing the static equivalent vertical base shear of earthquake action on DLGs and b) assessing the distribution pattern of the vertical base shear on the nodes of these structures. These relations make assessment of the earthquake action on the double layer grids very easy and versatile. In this research, for assessment of the vertical equivalent static earthquake loading on double layer grids, a set of double layer grids are established. These grids have the same configuration but different dimensions. Also, five strong ground motions with high vertical components are selected. The acceleration records of the earthquakes are scaled for a very high seismic area. By numerous linear and nonlinear analyses, a formula for assessing the earthquake vertical base shear on DLGs is produced. Also, a set of equations for distribution of the base shear on the nodes of these structures is developed. In the final stage, the versatility of the equations is examined on some double layer grids, and a comparison is made with the results of the equations of the code of practice of China. It is shown that the introduced equations in this research make the DLGs safer against strong ground motions.