2033Performance Based Design

Following the 1989 Loma Prieta Earthquake, bridge engineers [3] have faced three essential challenges:

• Ensure that earthquake risks posed by new construction are acceptable.

• Identify and correct unacceptable seismic safety conditions in existing structures.

• Develop and implement the rapid, effective, and economic response mechanism for the recovering structural integrity after damaging earthquakes.

Performance-based project-specific criteria [28-30] and design memoranda [24] have been developed and implemented for the design and retrofitting of important bridges by California bridge engineers. These performance-based criteria included guidelines for development of site-specific ground motion estimates, ductile design details to preclude brittle failure modes, rational procedures for concrete joint shear design, and the definition of limit states for various performance objectives [15]. The performance-based criteria usually require a two-level design approach. The first level of design is to ensure the performance (service) of a bridge in small-magnitude earthquake events that may occur several times during the life of the bridge. The second level of design is to achieve the performance (no collapse) of a bridge under severe earthquakes that have only a small probability of occurring during the useful life of the bridge. Figure 20.5 shows a flowchart for development of performance-based SDC.

0 0

Post a comment