Cable hanger plate replacement; a case study on BosporusBridge

摘要

Fatigue at steel bridge structures is one of the major problernproblems that often s times dornnot reveal itself until later stages of damage. Design of fatigue prone members or connections isrnvital especially for non-redundant fracture critical elements. Cyclic traffic and/or wind loads onrnbridges can further aggravate stress variations at connections. Bridge members or connectionsrnthat reach their fatigue life or get damaged due to other reasons may become difficult to replacernor rehabilitate especially for suspension bridges. This paper addresses cable hanger plate fatiguernproblem of a suspension bridge, Bosporus-Istanbul, and also discusses alternatives forrnhanger plate replacement procedures that will not result in disruption of the traffic. Transfer ofrncable tensile load to the bridge through alternative paths is necessary for replacing the cablernconnection plate. Four alternatives are generated for load transfer: a) bypass by supplementaryrn'V' cables connected to the original cable, b) in-plane cable transfer, c) direct connection to thernmain suspension cable, and d) inverted 'U' shape bypass frame for improved stability. Cablernstrain measurements that will be taken during the load transfer process would allow measurementrnof axial load existing on cables. The strain based measurement of cable force can be comparedrnagainst vibration based measurement to calibrate for the unknowns such as I) cablernboundary conditions, ii) cable bending rigidity, and iii) cable inclination. Furthermore, measurementrnof cable strains during cable plate replacement enables comparison of axial load on therncable prior to and after the connection plate replacement. Permanent instrumentation of cablesrnwould allow health monitoring of cables and determination of traffic-temperature loading versusrncable force relations.