Contribution to the probabilistic calculation of the remaining service life of steel bridges
Author: Karsten Geißler
Abstract
The assessment of existing bridges with regard to their further use has become increasingly important in recent years. In this context, the verification of fatigue safety for steel road and railway bridges is a decisive criterion. It can be carried out both on the basis of the Wöhler curve concept and with the help of the fracture mechanics concept.
Two basic objectives were pursued and realised with this work.
Firstly, the development of a computer-aided fracture-mechanical evaluation algorithm makes it possible to determine the influencing parameters that are essential for fatigue analyses.
- Load spectrum
- Supporting structure
- (fracture mechanically idealised) detail
- Material properties
which is an easy-to-handle tool for the remaining service life evaluation in practice. The fact that the stress is taken into account according to its frequency distribution is very important. The traffic load parameter is examined in great detail and the possibilities of continuous measurement of stress collectives are demonstrated. Furthermore, a procedure is developed that allows fracture mechanics results of FE calculations for special construction details to be integrated into the algorithm.
Secondly, by combining the fields of fatigue, fracture mechanics and reliability theory, a fracture-mechanical safety concept for the probabilistic verification of the remaining service life of steel bridges is developed and implemented. Based on the reliability-theoretical investigations, an order for the influence of the individual parameters is derived. The results of the probabilistic calculations are the temporal course of the BETA safety index as well as (systematically derived) design values for all individual parameters, which can then find their way into the deterministic fracture-mechanical verification with the result of a generally sustainable extension of the remaining service life.