عنوان مقاله [English]
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.