Reliability Assessment of the Operating Mechanism of a Movable Bridge

Large movable bridges in the Netherlands are often equipped with an electromechanical operating mechanism (for opening, closing, and locking) consisting of a panama wheel system. Many of these operating mechanisms are reaching the end of their design lifetime. Currently, there is no standard to assess the structural safety of existing operating mechanisms. The standard for new-built operating mechanisms is used, but it is unknown to which level of safety it leads. The goal of this research is to recalibrate the partial factor for the wind load effect. The partial factor for wind is calibrated to meet target probabilities set for both consequence class 2 and 3 and a reference period of 50 years according to EN 1990. In the static ultimate limit state, the tooth root stress of the panama wheel is assumed to be critical. The analysis focuses on the load combination holding the bridge deck in a fixed position by the operating mechanism. A dedicated wind load model was developed taking into account the number and duration of openings over the design life of the bridge. The ISO 6336-3 standard was used to model the strength of the teeth. Three typical movable bridges are used as case studies. Results show that the partial factor for wind load of the aforementioned scope could be set to 1.5 for maximum opening durations with possible reductions for shorter opening durations. Future research will focus on modelling of dynamic load combinations and calibrating partial factors for the failure mechanism fatigue.