The dilapidated state of many bridges in Germany regularly hits the headlines. Most of Germany's approximately 39,000 motorway bridges were built between the 1960s and 1980s out of reinforced concrete. Today traffic levels are nearly twice as high. This means that the loads placed on these materials have increased significantly. In addition, road salt and the weather are particularly hard on the concrete.
Repairing or rebuilding dilapidated bridges leads to high costs for national, regional and local authorities. According to the Federal Ministry of Transport and Digital Infrastructure [Bundesministerium für Verkehr und digitale Infrastruktur (BMVI)] around €1.13 billion should be invested in bridge repairs on motorways in 2016, and a further €1.22 billion in 2017.
But when should we repair and when rebuild? And which method is more cost-effective? BAM is examining how the lifespan and safety of bridge constructions can be assessed in an interdisciplinary research project involving experts in safety of structures and non-destructive testing.
Projecting the lifespan of bridges
The aim of BAM's research project is to discover how the load-carrying capacity of bridges that are 40 to 50 years old can be extended. Building on an analysis of the current situation, various maintenance and repair measures will be examined and assessed. The monitoring methods developed by BAM can then be used as a basis for cost estimates. In this way, BAM is contributing to the safety of bridge structures and the calculation of repair costs.
The modern sensor technology developed by BAM can be used to continually monitor the condition of bridges. The sensors capture the tremors and loads caused by traffic that affect the reinforced concrete. BAM experts can use the measurement data to establish how cracks, inclinations and vibrations can affect the material, and when repairs or maintenance are necessary. The aims of BAM's research are long lifespans and measures for increased safety that are as cost-effective as possible.
BAM test bridge for ageing experiments
To test the innovative monitoring methods, BAM built a reference bridge for stress tests at its Test Site for Technical Safety (BAM TTS) in Horstwalde. The results obtained here should complement the existing theoretical calculation models.
For example, fibre optic measurement techniques can be implemented here, in which sensors that are several metres long are embedded directly into the concrete of the reference bridge. They measure the strains that occur in the material under stress over the total length of the structure. Signal analysis techniques take signals from different sensors, form correlations and use these to identify a type of pattern. If the pattern changes, then damage has occurred. BAM is also examining how reliable the sensors are. Increased safety of usage and certainty of costs are also objectives of the project.
BAM's innovative monitoring methods and research results can be used to continually monitor the safety of bridges in the future. Damage can be repaired in a timely and cost-effective manner as it occurs and projections for the life span of the bridges can be calculated.