بررسي و مقايسه‌ي روش طراحي عملكردي براساس كنترل جابهجايي و روش نيرويي در طرح لرزه‌يي ساختمانهاي با اهميت خيلي زياد

STUDY ON DISPLACEMENT-BASED AND FORCE-BASED DESIGN METHODS FOR SEISMIC DESIGN OF ESSENTIAL BUILDINGS

طراحي براساس جابهجايي يكي از جديدترين روشهاي طراحي و ارزيابي ساختمانها در برابر سطوح مختلف زلزله با استفاده از تحليلهاي غيرخطي است. در اين نوشتار، روش جديد و ساده‌ي طراحي براساس جابهجايي (DBD) (قربانياصل و هيومار، 2007) معرفي شده است. ويژگيهاي خاص اين روش بي‌نياز به محاسبه‌ي زمان تناوب اصلي سازه و لحاظ اثرات مودهاي بالاتر در حوزه‌ي غيرخطي در طراحي است. در اين مطالعه دو قاب بتن مسلح با دو شيوه‌ي نيرويي و DBD طراحي و عملكرد آنها با استفاده از تحليل استاتيكي غيرخطي بررسي شده است. در اين رابطه چرخشهاي خميري مفاصل، ظرفيتهاي شكلپذيري و باربري، سطوح عملكرد و تغييرمكانهاي نسبي طبقات در دو شيوه‌ي طراحي با هم مقايسه شده است. نتايج نشان‌دهنده‌ي بهبود ظرفيت شكلپذيري و باربري و عملكرد قابهاي طراحي‌شده به روش DBD است.

In recent years many research efforts have been undertaken in order to develop design methods and structural performance-based evaluation. One of the most recent methods for the design and evaluation of structures at different levels of earthquake and performance, using nonlinear analyses, is displacement-based design. The main issue in displacement-based design is the development of simple and accurate methods for the analysis and design of new buildings, and evaluation of existing buildings at different performance levels. In this paper, the new and simple displacement-based design method (DBD) (Ghorbanie-Asl and Humar, 2007) is introduced. The main characteristics of this method concern higher mode effects in design, with no need to estimate or calculate the fundamental period of the buildings. In this paper, two reinforced concrete frame structures (essential building, hospital) were designed using the traditional force method (linear static method of standard No. 2800) and the new DBD method, and then frame sections, weight and fundamental periods were compared. Then, the seismic performance of the mentioned frames was compared using nonlinear static analysis. In this regard, inelastic rotation of plastic hinges, ductility and load-carrying capacities, performance levels and story drifts of both designed frames were compared. The results indicate that design base shear, dimension of structural members and weight of reinforced concrete frame structures, designed using DBD, are more than those designed using the force method. It is due to using a ductility capacity instead of a response modification factor (R) in reducing elastic demand spectra. Also, results indicate improvement in the ductility, load-carrying capacity and performance of frame structures designed by the DBD method, because of the increased percentage of longitudinal and stirrup reinforcements and increased section dimensions. Frame Structures designed using the force method become inelastic under earthquake with smaller acceleration than design acceleration and experience large displacements; whereas this is unlike the objective of design of essential buildings in the code. Evaluation of frame structures, designed by the force method, indicates that they are not appropriate for desired performance levels (Immediate Occupancy), unlike the frames designed by controlled displacement. It could be concluded that the displacement-based method could be a suitable substitute for the force-based (traditional) method in the seismic design of essential buildings.