مطالعه‌ای بر عملکرد لرزه‌ای سازه‌های بتن‌آرمه قالب تونلی با پلان نامنظم

به علت غلبه مود پیچشی بر مود انتقالی بر اساس نتایج تحلیل مقادیر ویژه بر روی مدل های سازه ای قالب تونلی، کاربرد این سیستم با پلان نامنظم توسط متولیان تهیه استانداردها چون مرکز تحقیقات ساختمان و مسکن ایران غیر مجاز اعلام شده و این در حالی است که هیچ اطلاعاتی در خصوص رفتار لرزه ای سازه های بتنی قالب تونلی با پلان نامنظم از زلزله های گذشته موجود نیست. ضرورت منظم بودن سازه های بتنی قالب تونلی در پلان و ارتفاع، علی رغم مزایایی چون تسریع روند ساخت و تضمین کیفیت بالاتر، محدودیت های زیادی از نظر طراحی معماری بدنبال دارد که از مشکلات اساسی کاربرد این سیستم سازه ای در مناطق شهری است. در این مطالعه، رفتار لرزه ای سازه های قالب تونلی5 و10 طبقه با پلان نامنظم که بر اساس آیین نامه های موجود طراحی شده اند در محدوده تغییرشکل های غیرخطی مورد بررسی قرار گرفته و سطح عملکرد این سازه ها، در سطح خطر طرحی آیین نامه ایران، با استفاده از تحلیل های تاریخچه زمانی و بار افزون و با تحریک مدل ها در دو راستای طولی و عرضی پلان به صورت همزمان، تعیین شده است. نتایج حاکی از عملکرد لرزه ای مناسب این سازه ها علی رغم وجود نامنظمی در آنهاست. هر دو سازه در زلزله طرح در سطح عملکردی قابلیت استفاده بی وقفه قرار گرفتند. به نظر می رسد که بند پنجم از ضوابط ابلاغی از سوی مرکز تحقیقات ساختمان و مسکن ایران در خصوص طرح و اجرای سازه های قالب تونلی که بر منظم بودن در پلان تاکید می کند، حداقل برای سازه های مورد مطالعه سختگیرانه است.

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

The tunnelform 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 tunnelform 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 tunnelform 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 wallslab system with tunnelform 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 tunnelform constructions in the plan and elevation, despite superior advantages such as highspeed 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 twotunnelform 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 tunnelform plan , at least, are strict and scrupulous for the studied structures.