Large structures, such as road and rail bridges often need repair and reinforcement... either due to damage, fatigue or corrosion, or because they need uprating to carry heavier loads. The typical approach is to use large reinforcing elements or patches - often composites patches where saving weight is important.
But when these patches are first applied they carry no load. Only when additional load is applied do they start to share some of it. And coupling the new structure to the old does not make it a single integrated whole.
While the new load is shared between them, the existing structure still carries all the existing load. So if the bridge is already close to its limit, this rather limited load sharing is not 100% efficient.
A better solution is to remove or shift some of the top load, before coupling in the new structure. This allows more load to be carried overall, but the load still is not shared equally - and the work involved in removing and then restoring heavy weights can be time-consuming, expensive and difficult. |
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