تحليل آسيب پذيري و بهسازي سيستم دال و ديوار بتني به‌روش استاتيكي غيرخطي

DAMAGE ASSESSMENT AND RETROFITTING OF WALL & SLAB SYSTEMS BY NONLINEAR STATIC ANALYSIS

سيستم دال و يوار بتني درجا از سيستم هاي متداول در ايران و ساير نقاط جهان است كه به علت عملكرد مناسبِ آن در زلزله‌هاي گذشته، كاربردش گستردگي بيش تري يافته است. در دستورالعمل هاي مربوط به ارزيابي آسيب پذيري، عموماً براي سازه‌هاي موجودِ از اين دست رويكرد جداگانه‌يي منظور نشده است. به‌دليل موجود نبودن استانداردهاي ويژه‌ي اين ساختمان‌ها و كمبود اطلاعات در‌مورد نحوه‌ي ارزيابي عملكرد لرزه‌يي با در نظر گرفتن امكان ايجاد رفتار غيرخطي در ديوار، انجام مطالعات كاربردي بهسازي روي سيستم دال و ديوار از اهميت خاصي برخوردار است. در اين نوشتار براي بررسي دقيق تر عملكرد سيستم، از روش استاتيكي غيرخطي به جاي روش هاي ساده تر و غيرواقعي تري كه رفتار ديوار را تنها در حالت خطي در نظر مي گيرند، بهره گرفته شده است. بررسيِ سازه‌هاي دال و ديوار با پلان متقارن و طراحي اوليه براساس استاندارد 2800 ايران در سازه‌هاي 4، 8 و 12 طبقه با هدف بهسازي مطلوب دستورالعمل بهسازي لرزه‌يي انجام گرفته و براي اجراي تحليل هاي غيرخطي، از نرم افزار Ram Perform 3D استفاده شده است.

The Wall & Slab system is one of the most widespread conventional systems used in Iran and other countries like Turkey, Chile, and Canada, etc. Buildings with a Wall & Slab system diverge from other conventional reinforced concrete structures due to the absence of beams and columns in their structural system. Post-earthquake reconnaissance missions reported the surprisingly good seismic behavior of structural wall buildings, and, because of their good performance in past earthquakes, this system has been widely used since then. Instructions of damage assessment have not mentioned any separate procedure for structures of this type. Practical studies on Slab & Wall systems specifying nonlinear behavior to the walls are very important because there is no special standard for these buildings and information about how to evaluate their seismic behavior is not sufficient. Vulnerability assessment has become more important than ever since structural designers started to employ performance based design methods, which require that structural and member behaviour at different limit states be predicted precisely. For investigation into the performance of systems, this article uses nonlinear static analysis instead of other simple and unreal methods that only estimate wall behavior in linear form. Investigations into Slab & Wall structures with simple symmetric plans and primary designs, on the basis of the 3rd version of the Iranian Seismic Building Code (2800), in four, eight and twelve stories, is done for the basic safety objective (BSO) level of instruction for seismic rehabilitation. These buildings are made as three-dimensional space frame structures, with shear walls in both orthogonal directions, in ETABS 9.1.6 software, according to ACI 2005 for the initial design, and Ram Perform 3D 4.0.1 software is used for nonlinear analysis. For modelling the nonlinear behaviour of the wall, in this analytical program, a section analysis using a fibre model was employed. The results of analysis showed that the structures had the expected performance.