« Previous | Contents | Next »
Listen
2 Background
Within the United States of America, there are nearly 50 major suspension bridges with over half of them being more than 50 years old. These bridges represent major investments and are essential transportation links. As the age of these structures increase, the need to assess their condition, load carrying capacity and remaining service life will also increase. In the absence of any reliable and nationally recognised procedures to inspect and evaluate the condition and strength of suspension bridge parallel wire cables there was concern that unreliable methods may result in unnecessary major refurbishment works or in unexpected failures. In 1998, The Transportation Research Board identified a priority need for the development of cable inspection, sampling and testing guidelines as well as the development of models to predict the strength of deteriorated cables. As a result, guidelines were produced and issued by the National Cooperative Highway Research Programme ( NCHRP). The document is referred to as NCHRP Report 534 and is entitled "Guidelines for Inspection and Strength Evaluation of Suspension Bridge Parallel Wire Cables". It is worth noting that the principal compilers of the guidelines are the American consultants, Weidlinger. It is this firm which has advised, supported and assisted Faber Maunsell with the Forth Bridge main cable investigation works.
In the United Kingdom, there are three major suspension bridges with parallel wire cables; these are the Forth Bridge, the Severn Bridge and the Humber Bridge. The Forth Bridge is the oldest of these bridges, opening in 1964. FETA was aware of the development of the American guidelines and the recommendation that an initial series of intrusive inspections should be carried out after thirty years of service. As the Forth Bridge had been operating for nearly forty years, FETA commissioned Faber Maunsell, in conjunction with Weidlinger, to undertake an intrusive inspection of the main cables of the Forth Bridge. In the absence of any recognised UK or European standard or procedure, FETA required their intrusive inspection and associated strength assessment to be based upon the NCHRP Guidelines. (2.1) Figures in Brackets refer to sections of the audit trail document, Appendix A.
« Previous | Contents | Next »