Performance Comparison of Concrete Moment Frames Designed by Direct Displacement Based and Force Based Methods

Abstract

Performance-Based Design Methods idea is based on decreasing the structural damages in earthquake, according to client requirements, it seems be an economical design method. There are two different Performance based design approaches, the former is direct approach and the latter is indirect approach. In direct approach the level of performance is assumed at the beginning of design procedure and design has been performed to achieve the assumed performance. Direct displacement-based design method (DDBD) is known as direct approach. In DDBD procedure performance of the structure is predefined by assuming the total structural drift against specified earthquake level. In DDBD method, structural base shear is calculated according to occurrence of mechanism in earthquake. Therefore DDBD seems to be more realistic in comparison to force based design (FBD) because of considering the structural nonlinearities directly in calculations. In this paper, the principles of DDBD are explained, then concrete special moment frames of 4, 8, 12, 16 stories were designed by both of DDBD and FBD methods. It is concluded that columns dimensions and reinforcement in DDBD will be obtained equal or greater than FBD. In addition, longitudinal reinforcements at the middle span of beams in the frames of DDBD are more than the two ends which are the possible locations of plastic hinges. Frames evaluation by push-over analysis shows that DDBD frames responses are more compatible with plastic mechanism which is supposed in design procedure. Also it is concluded that the maximum drift of DDBD frames before collapse are usually greater than FBD ones and in DDBD frames plastic hinge formation in upper stories is more than FBD frames.

Keywords

• performance comparison
• direct displacement-based design
• force-based design
• concrete moment frame
• push-over analysis