Reliability Assessment and Investigation on the Development of Secondary Stresses in Main Cables of Suspension Bridge Keun Won Lyu
ABSTRACT This paper presents the main causes of secondary stress factors that are caused at the main cable of a suspension bridge. Each of the secondary stress factors caused by the size and impact to the main cable are analyzed. The probability of failure is calculated as the largest value at the saddle on pylon and the second largest on the cable band which is closest to the pylon. Therefore, the sizes of the stress are calculated on the most dangerous two points and change of the probability of failure by influence of secondary stress is suggested. On the saddle, secondary stress is occurred by the bending of the cable caused by shape of saddle and cable bending at the edge of the saddle. On the cable band, cable bending at the edge of the cable band caused by concentrated load through hanger and compression of the band itself for prevention of sliding make secondary stress. The difference of the stress by the length differences of the strand is occurred in whole cable section. Then the analytic solution of the impact of each factor is suggested dividing the saddle and cable band. Finally, magnitude of stress is proposed by analysis with whole suspension bridge modeling. If each cause of occurrence of secondary stress be a random variable, reliability assessment can be performed. To grasp distribution characteristics of secondary stress, Monte-Carlo Simulation is performed based on the variability of a random variable. To determine influence of the proposed analysis techniques of secondary stress and distribution characteristics, examples is performed by applying them to real bridge model. Target bridges are Yisunsin bridge, Ulsan bridge, and Newmillennium bridge. Through result of the example, safety factor and reliability index of main cable of suspension bridge including secondary stress is presented and safety factor and the value of reliability index is verified. Analysis in terms of safety factor and the results of reliability analysis are shown including the secondary stress and are validity of stress magnitude is verified by the result of these examples. This paper presents target reliability index in accordance with safety factor and basic data for set up of the load factor in design guide lines reflecting limit state design methods.
Key Word suspension bridge, main cable, secondary stress, length difference of strand, bending angle of cable, compression of cable band, safety factor, reliability assessment
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