Calibration of the Load-Resistance Factors for the Reliability-based Design of Cable-supported Bridges Seung Han Lee
ABSTRACT This paper presents the determination of the target reliability index and the calibration of the load-resistance factors, which is the most important research for the reliability-based design of cable-supported bridges. As the basic research for the determination of the target reliability index and the calibration of the load-resistance factors, the probabilistic models of several loads acting on the cable-supported bridge are estimated. In particular, the focus is on the estimation for the probabilistic models for variable loads and accidental loads by the consistent definition. The probabilistic models for live load and wind load are estimated by reflecting the previous researches about ordinary bridge and domestic datas. And probabilistic model for earthquake load is estimated by reflecting the previous researches about probabilistic seismic hazard analysis. Target reliability of cable-supported bridge is deteminated by considering the two main aspects. First, it is needed the consideration of the reliability level, which the existing design guildlines guarantee. For this, the reliability assessment of the cable-suppored bridge designed by existing design guildlines is performed. Second, it is needed the establishment of philosophy, which the determination of target reliability is based on. By anlayzing the design philosophy of the existing design guildlines and considering the importance and design life of the cable-supported bridge, the target reliability of cable-supported bridge is deteminated. Furthermore, this paper presented the method of setting up the target reliability differently, according to the limit state and structural component. Load and resistance factor which guarantee the target reliability is calibrated by the establishment of the load and resistance factor system using resistance modification factor. First, the load factor of each load and the resistance factor of each structural component are determinated by AFORM for guaranteeing the representative target reliability for the limit state, regardless of the importance and design life. Second, the resistance factors of the structural components are fixed and the load factor is calibrated for guaranteeing same the target reliability. Finally, the target reliability which is set differently according to the importance and design life of components is guaranteed by using resistance modification factor.
Key Word cable-supported bridge, probability of failure, reliability, reliability analysis, reliability-based design, load and resistance factor design, probabilistic model, target reliabily, calibration of load and resistance factor, code calibration
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