Reliability Assessment of Tie-Down Cables for Cable-Stayed Bridges Subject to Negative Reactions: Case Study

Abstract

This paper presents a reliability assessment for tie-down cables of cable-stayed bridges subject to negative reactions. The advanced first-order second-moment reliability method (AFOSM) is used to evaluate the reliability indexes. The strength of a tie-down cable and load parameters are selected as random variables. A Newton-type solution scheme with double iteration loops is used to solve the minimization problem defined in the AFOSM. Reactions at supports are calculated through the stiffness equation formed by a finite-element model, and the sensitivities of the reactions with respect to the random variables are obtained by the direct differentiation of the stiffness equation. The reliability indexes of the tie-down cables are evaluated for two cable-stayed bridges in service in Korea: the Second Jindo Grand Bridge and Incheon Grand Bridge. Three limit states on the pretension, required strength, and design strength are considered for the load combination of the Strength I limit state in LRFD bridge design specifications. The required strength is evaluated with the load factors defined in the specifications and the resistance factor recommended for tension members. Design vehicular live load and pedestrian load are applied to the bridges. The reliability indexes and corresponding most probable failure points of the tie-down cables installed in the bridges are presented and discussed in detail. The effects of the partial failure of the tie-down cables and the variation of the resistance factor on the reliability index are investigated.