مطالعه‌اي بر عملكرد لرزه‌اي سازه‌هاي بتن‌آرمه قالب تونلي با پلان نامنظم

A Study on Seismic Performance of RC Tunnel-Form Building Structures With Irregular Plan

به علت غلبه مود پيچشي بر مود انتقالي بر اساس نتايج تحليل مقادير ويژه بر روي مدل‌هاي سازه‌اي قالب تونلي، كاربرد اين سيستم با پلان نامنظم توسط متوليان تهيه استانداردها چون مركز تحقيقات ساختمان و مسكن ايران غير مجاز اعلام شده و اين در حالي است كه هيچ اطلاعاتي در خصوص رفتار لرزه‌اي سازه‌هاي بتني قالب‌تونلي با پلان نامنظم از زلزله‌هاي گذشته موجود نيست. ضرورت منظم بودن سازه‌هاي بتني قالب‌تونلي در پلان و ارتفاع، علي‌رغم مزايايي چون تسريع روند ساخت و تضمين كيفيت بالاتر، محدوديت‌هاي زيادي از نظر طراحي معماري بدنبال دارد كه از مشكلات اساسي كاربرد اين سيستم سازه‌اي در مناطق شهري است. در اين مطالعه، رفتار لرزه‌اي سازه‌هاي قالب‌تونلي5 و10 طبقه با پلان نامنظم كه بر اساس آيين‌نامه‌هاي موجود طراحي شده‌اند در محدوده تغييرشكل‌هاي غيرخطي مورد بررسي قرار گرفته و سطح عملكرد اين سازه‌ها، در سطح خطر طرحي آيين‌نامه ايران، با استفاده از تحليل‌هاي تاريخچه زماني و بار‌افزون و با تحريك مدل‌ها در دو راستاي طولي و عرضي پلان به صورت همزمان، تعيين شده است. نتايج حاكي از عملكرد لرزه‌اي مناسب اين سازه‌ها علي‌رغم وجود نامنظمي در آنهاست. هر دو سازه در زلزله طرح در سطح عملكردي قابليت استفاده بي‌وقفه قرار گرفتند. به نظر مي‌رسد كه بند پنجم از ضوابط ابلاغي از سوي مركز تحقيقات ساختمان و مسكن ايران در خصوص طرح و اجراي سازه‌هاي قالب‌تونلي كه بر منظم بودن در پلان تاكيد مي‌كند، حداقل براي سازه‌هاي مورد مطالعه سختگيرانه است.

The tunnel-form falls under the category of industrial construction methods which is one of the modern construction methods for building houses. A current tendency in the building industry in many countries around the world with increasing city populations, is toward utilizing the modular construction system for development of multistory residential units. The tunnel-form system is an industrialized construction technique in which structural walls and slabs are cast in situ simultaneously using steel forms composed of vertical and horizontal panels set at right angles.The wall and slab frameworks consist of joining horizontal (table) and vertical parts that are reused on multiple stories of a building without being dismantled. The assembled sections are flown by crane from one story to the next. Once in position the gaps between the tables are filled with fillers. They vary in shape and size. The use of these systems can greatly reduce the time and manual labor involved in setting and striking the formwork. Their advantages are best utilized for mass building construction and also for simple designed structures. The main characteristic of a tunnel-form system are its relatively thinner components, i.e. walls and slabs compared to those of traditional reinforced concrete buildings.Through reduction of the construction time and proper performance during the past earthquakes, this type of building construction is recognized as a suitable method used in mass production projects. Despite its widespread use and different behavior in respect of other systems, in the current building design codes, this system has not been considered as an independent structural system. Unfortunately no special seismic code is published for reinforced concrete wall-slab system with tunnel-form and there is only little information about the seismic behavior of this structural system type in technical and research docs. Therefore based on reasonable numerical results, seismic behavior and performance of structures constructed with this technique considering the effective factors on response is highly noteworthy in a seismic code development process. Due to domination of the natural torsion mode respecting to the natural transverse mode based on eigen value analysis of their structural model, use of this system with an irregular plan by the authority building standards departments like the Building and Housing Research Center of Iran has been declared illegal. However, so far no information on their seismic behaviors and vulnerability reports subjected to past earthquakes are available. Necessitating regularity of tunnel-form constructions in the plan and elevation, despite superior advantages such as high-speed manufacturing process and high quality assurance, several limitations in terms of architectural design requirements are one of the basic problems of using this structural system in urban zones. In this paper, the seismic behavior of the two-tunnel-form structures of 5 and 10 stories with an irregular floor plan which were designed based on current building codes in range of nonlinear behavior, is studied. Indeed, performance levels under the design earthquake using the response history and pushover analysis are specified through excitation in two longitudinal and traversal plan directions simultaneously. The results showed the appropriate seismic performance despite the irregularities. Both structures subjected to the design earthquake are placed in the immediate occupancy performance level. It seems that the provision no. 5 of the regulations issued by the Building and Housing Research Center of Iran pertaining to tunnel form building design and construction that stipulate regularity requirement of the tunnel-form plan , at least, are strict and scrupulous for the studied structures.