Roads - bridge strengthening
Do you assess whether a bridge is strong enough?
We assess bridges in Derby for their weight carrying ability. This means we do calculations to look at the strength of a bridge.
The permissible load that lorries can carry was raised to 40 tonnes in 2000. As a result, the government instigated a programme of assessments for bridges.
How do you assess a bridge?
An assessment involves a detailed on-site inspection taking measurements, details of the condition of the bridge and samples of materials. We then work out whether the bridge can safely carry 40 tonnes.
If it isn't strong enough, what do you do?
If we find that a bridge cannot safely carry 40 tonnes, we then decide whether to strengthen it, or part of it, or whether we need to rebuild it completely. In the short-term, we may put a temporary weight restriction on the bridge. We sometimes use concrete barriers or traffic lights so that traffic crosses the bridge in a single lane and avoids weak areas of the bridge. We also sometimes reduce the number of vehicles that can cross the bridge at the same time. Sometimes we make a weight limit permanent. This may be appropriate:
- In residential areas.
- For a bridge that isn't used much.
- For one that only carries farm traffic.
Loads that may need to use the bridge, including fire engines, can be individually assessed.