ارزیابی شکنندگی لرزه ای قاب خمشی فولادی
Abstract
1- Introduction
2- Performance-based design optimization
3- Seismic damage indices
4- Collapse margin ratio
5- Margin ratio for different levels of damage
6- Proposed methodology
7- Numerical examples
8- Conclusions
References
Abstract
This study is devoted to seismic performance assessment of optimally designed steel moment frames (SMFs) in the framework of performance-based design (PBD). The methodology presented in this work includes three phases. The first phase involves the optimization of SMFs by employing an efficient metaheuristic algorithm to meet the PBD requirements according to FEMA-350 code. Subsequently, the overall damage index (ODI) is calculated for the obtained optimal SMFs based on the Park-Ang local damage index (DIPA). In the second phase, incremental dynamic analysis (IDA) is conducted for the optimally designed SMFs and their fragility curves are derived and their collapse margin ratios (CMRs) are determined based on FEMA-P695. In the last phase, the fragility curves of the optimal SMFs are generated for different damage levels ranging from slight damage to collapse state and a new damage measure termed as damage margin ratio (DMR) is introduced to assess the damage-resistance capacity of the SMFs at the different damage levels. In order to illustrate the efficiency of the proposed methodology, three numerical examples of 3-, 6-, and 12-story SMFs are presented and the total cost of optimal SMFs, including initial and seismic damage costs, are determined. The numerical results demonstrate that the SMF with the best total cost has the best CMR, DMR, and degree of repairability.
Introduction
In the last years, performance-based design (PBD) has emerged as one of the most efficient seismic design approaches which its main purpose is to design structures that present a predictable and reliable behavior against seismic actions through their lifespan. It is expected that the structures designed according to the PBD methodologies will resist earthquakes by tolerating levels of seismic damage. The structures designed in the framework of PBD satisfy a sort of predefined performance levels about their corresponding hazard levels. An efficient design framework may be offered by integrating PBD methodologies and structural optimization techniques. During the last few years some researches have been conducted in this context for steel structures. Choi and Park [1] employed a non-dominated sorting genetic algorithm-II (NSGA-II) for seismic PBD optimization of SMFs to ensure beam-hinging mechanism. Saadat et al. [2] achieved multi-objective PBD optimization of a SMF taking into account two conflicting objective functions: direct social and economic losses. Gholizadeh [3] utilized a combination of neural network (NN) and a modified firefly algorithm (MFA) for PBD optimization of SMFs. Gholizadeh and Poorhoseini [4] proposed a methodology for optimal placement of braces in steel braced frames (SBF) in the framework of PBD using an improved dolphin echolocation algorithm. Xu et al. [5] employed generalized pattern search (GPS) algorithm to implement multi-objective PBD optimization of steel frames subject to random excitation. Gholizadeh and Baghchevan [6] proposed a chaotic multi-objective firefly algorithm (CMOFA) for finding the Pareto front of the multi-objective PBD optimization problem of SMFs.