SCI P154: Design of steel bridges for durability

[ir_71]

SCI P154: Design of steel bridges for durability

Author: C W BROWN, D C ILES | Size: 0.2 MB | Format: PDF | Publisher: SCI | Year: 1995 | pages: 21 | ISBN: 1859420281

The design of a new bridge can directly affect the durability and the maintenance costs, and hence the whole-life cost. Careful consideration should be given to whether an increase of initial capital cost may be warranted in order to reduce the subsequent maintenance costs. Such consideration would be particularly important in the case of a bridge where the notional costs of traffic delay and disruption during maintenance were disproportionately high - in such cases large increases in initial
capital cost can be justified to reduce the duration of maintenance. Steel bridges have an unjustified reputation for high cost maintenance. For instance, to some designers, the one word “rust” is a serious disincentive to the use of a steel bridge; this is a shortsighted and unreasonable attitude, for several reasons. To a large extent this view has been based upon experience of older structures where the choice of steelwork details and protective coating had been based on lower relative labour costs than currently prevail. Furthermore, it cannot be emphasised too strongly that corrosion of structural steel is a surface phenomenon; it is readily detectable in its early stages and, provided remedial action is taken, will not affect the overall
integrity of the structure in any significant way. Another perceived “problem” with steel bridges is that of fatigue. The resistance to fatigue of some early bridges in high strength structural steel was not adequate: some of these bridges are showing evidence of premature fatigue failure, although in most cases this can be repaired relatively easily. In the last twenty years a vast amount of research into fatigue has been carried out and this, together with extensive test programmes, has ensured that the subject of fatigue is much better understood now than it was in, say, 1950. Designers can now design bridges that have a high probability of lasting without serious fatigue problems for more than 100 years, using well-proven details. It is important not to become complacent, since there are unfortunately occasional examples of steel bridges where unexpected and unwelcome problems have occurred. However, it is pertinent to point out that repair or strengthening of deficient steel bridges can be a comparatively straightforward process, usually involving in-situ welding or bolting on additional steelwork without restricting
traffic. To summarise, a steel bridge is durable, when properly designed and maintained, and its whole-life cost is competitive with that of a bridge in any other material. In particular, it should be noted that:
C Design for durability is a well known and proven technology
C Steel bridges have more than 100 years proven record of durability
C Corrosion of structural steel is a surface phenomenon; it is readily detectable in its early stages and, provided remedial action is taken, will not affect the overall integrity of the structure in any significant way
C When deterioration is noted, it can readily be rectified
C Reliable coating systems, both for initial painting and maintenance painting, are available
C Modern steel bridges are designed to be easily inspectable and maintainable
C Maintenance should be regular; it is a known technology with quantifiable costs, and is thus easy to discount to present values that can be included in the whole life cost of the bridge
C Satisfactory design against fatigue has now become routine for steel bridge designers.

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