Dynamic Load Testing of a Bridge
A load test shows how a bridge actually behaves under a defined load. The deformation of the bridge is measured during a controlled vehicle passage and compared with the calculated structural behaviour.
The key advantage is the direct comparison:
calculated behaviour → measured behaviour
This complements calculations and existing structural documentation with a measurement of the actual structure.
Defined load – measured response
A known vehicle load is used for a load test. As the vehicle crosses the bridge or is positioned at a defined location, the deformation of the structure is measured.
The measurement shows directly how much and in what spatial pattern the bridge responds to this load.
This is not only about the maximum deformation. The interaction of several measurement areas provides information about the actual structural behaviour.
Compare calculated and actual behaviour
The expected deformation can be calculated from the geometry, structural system and applied load.
A highly complex calculation model is not necessarily required for this comparison. The key is that the load case, measurement positions and model assumptions correspond sufficiently well to provide a traceable reference.
The calculated and measured deformations are then compared:
Expected behaviour → Calculation
Actual behaviour → Measurement
Any deviations can subsequently be assessed technically.
Multiple measurement points show spatial behaviour
A bridge does not respond to a vehicle load at only one location.
Multiple laser measurement lines make it possible to measure deformation simultaneously in different areas of the structure. This shows how the load is distributed through the structure.
Particularly in multi-span structures, this allows interactions between different areas to be observed.
Recovery after loading
After the vehicle has crossed the bridge, the maximum deformation is not the only relevant parameter.
It is equally important to observe whether and how quickly the structure returns to its initial position.
Measuring recovery therefore complements the maximum deformation and provides additional information about the structural response.
Comparison over time is particularly informative
A single load test describes the condition of a structure at a specific point in time.
If the same or a comparable load test is repeated later, a much stronger statement becomes possible:
Does the bridge respond to a comparable load today in the same way as it did during the previous measurement?
This turns a one-time load test into a reproducible comparison of actual structural behaviour.
Load testing and long-term monitoring complement each other
A load test uses a load that is known as precisely as possible. Long-term monitoring, by contrast, observes the structure continuously under real traffic.
The two approaches answer different questions and can complement each other.
Load test: known load → defined structural response
Long-term monitoring: real traffic loads → long-term changes
Together, they provide a robust basis for observing the actual behaviour of the structure.
Load testing with Bridge LDM
Bridge LDM measures structural deformation at several defined measurement areas using non-contact laser measurement lines.
The time-synchronised measurement data allow maximum deformation, spatial deformation patterns and recovery after loading to be analysed.
Repeated measurements can also be compared with previous reference conditions.