Assessment of concrete bridges
Bridges are key parts of the road network and it is therefore essential that they should be able to carry the required traffic loads, which may be greater than those for which they were originally designed. The emphasis today is very much on asset management. This means moving away from reactive management and towards targeted schemes which increase the overall value of the bridge stock but at lowest whole life cost. An important activity in asset management is the inspection and assessment process. It is necessary to determine the general condition and structural safety of each item in the overall asset, i.e. each bridge. Having established the current state, it is also necessary to estimate deterioration rates, so that some idea of the residual life of the structure can be determined.
To assist in this process, the Concrete Bridge Development Group has prepared Technical Guide 9, Guidance on the assessment of concrete bridges. The intention of the Guide is to address the assessment of all types of concrete bridges irrespective of their ownership. Nevertheless, it is recognised that a significant proportion of such structures are reinforced concrete highway structures and that many of the standard procedures that are currently used are founded on the requirements of the Highways Agency and/or, when road over rail, Railway Group Standards. As such, much of the guidance that is given in the Guide is also based on these requirements, but wherever possible reference is also made to new research and alternative points of view, which is believed will both aid and advance the assessment process.
The Chapters of the Guide are as follows: The assessment process, Technical approval and documentation, Inspection for assessment, In-situ and laboratory testing, Loading, Analysis for assessment, Hidden strengths, Specific structural forms, Specific material and assessment factors, Load testing, Reliability and risk-based techniques, Bridge management and assessment.
There is an extensive list of References is at the end of each Chapter and an Appendix lists relevant historical references to design and materials specifications and standards used in concrete bridge construction.
If details of the Standards to which the bridge was designed and constructed are available, these can obviously be used to obtain an indication of the expected concrete and steel strengths. Further information on the development of specified steel and concrete strengths for bridges over the years is given in Concrete Society Technical Report 70, Historical approaches to the design of concrete buildings and structures.