Modification of the partial safety factor for dead loads of existing concrete bridges

The assessment of the load bearing capacity of existing structures is a task with growing importance, especially within the context of the aging infrastructure in Germany. This is usually done with information based on old documents from the construction phase. One of the main load cases of a concrete bridge is its own weight (dead loads) which depends on the geometry and material weights. As there are always some deviations between the real structure and the target state based on documents, a partial safety factor is applied to the loads. In contrast to the assessment of a new structure that is yet to be built these deviations are not theoretical for existing structures but can instead be measured. However, the acquisition and usage of the actual weight distribution of a bridge can be very work intensive and expensive. Therefore, it can be more practical to instead modify the safety elements for the dead loads as a function of the measured deviations based on a certain number of samples. This approach was applied on three existing concrete valley bridges resulting in lower partial safety factors and therefore more efficient assessments of the load bearing capacities.