Performance-based Seismic Design of Nonlinear Steel Structures Using a Novel Reliability Technique

Abstract

A unified performance-based seismic design procedure is proposed and successfully implemented in this dissertation. It provides an alternative to the currently used life safety design requirement. To successfully develop the concept, structures are represented by finite elements and excited by the seismic loading in time domain. To implement the performance-based seismic design concept, a novel reliability evaluation technique is proposed, integrating the finite element method, first order reliability method, the response surface method, and advanced factorial design concept, producing compounding beneficial effects. Following the 1994 Northridge earthquake, several improved connections in steel buildings were proposed to eliminate brittle fractures in welds. Making connections more flexible was considered to be an attractive option. One type of flexible connection considered in this study is expected to be economical and improve the behavior of steel structures, making them more seismic load-tolerant. However, the partial rigidities of connections need to be considered. To consider rigidities of connections, the 4-parameters Richard model is incorporated in the finite element algorithm. The accuracy of the procedure is demonstrated by comparing it with respect to Monte Carlo Simulation. The efficiency and robustness are verified with the help of several steel structures of different height. Performances are defined in terms of immediate occupancy, life safety, and collapse prevention. The corresponding risks are evaluated by exciting steel structures designed by experts satisfying all post-Northridge seismic design requirements. In order to incorporate uncertainties in frequency contents of ground motions, the structures are excited by 20 earthquake time histories for each performance level, and the corresponding reliability indexes and probabilities of failure are estimated. Only hundreds of deterministic finite element analysis are required for extracting the corresponding risk. The superiority in extracting reliability information is demonstrated with respect to Monte Carlo Simulation, which requires thousands or millions of deterministic finite element analysis. The study confirms the benefits of multiple deterministic analyses suggested in recent design guidelines. The behavior of post-Northridge design is demonstrated to be superior to that of the pre-Northridge design, as expected. The performance criteria suggested by the Federal Emergency Management Agency appear to be reasonable and are expected to satisfy the intent of the performance-based design concept. Several other advantages of the novel reliability technique are presented in terms of corresponding risk of steel structures excited by simulated ground motions. A broadband platform developed by the Southern California Earthquake Center is used for the artificial generation of time histories. Then, the structural risk is calculated using simulated ground motions. Designing a structure using multiple time histories, as suggested in recent design guidelines, is a step in the right direction. Based on the results and the observations documented in this dissertation, a robust, efficient, and accurate reliability technique is proposed, and its implementation potential for the performance-based seismic design of steel structures is demonstrated.