Crack-Detection in old riveted steel bridge structures

Abstract

In light of the scarcity of resources, the fundamental demand for economic and sustainable use of existing structures is becoming increasingly important. A large number of existing steel bridges fulfill their purpose in principle. But almost 30% of steel railway bridges in Germany are up to 100 years old. Considering deterioration as well as significantly increased loads, however, they must meet the current requirements of stability and fatigue resistance. Of fundamental importance is the realistic assessment of the state of fatigue of the steel bridge structures.If no sufficient remaining fatigue life can be determined based on normative S-N-curve assessment, initiation of fatigue cracks has to be assumed. Steel bridges from the period 1880 to 1940 are usually riveted steel structures. Therefore, crack initiation occurs primarily at the edge of the rivet holes. In this early phase of crack growth, however, a crack at the rivet hole is still below the rivet head and therefore cannot be found in a visual inspection of the structure. For this reason, the remaining cyclic lifetime based on fracture mechanics is determined assuming a start length of the crack beyond the rivet head.Currently, there is no practicable non-destructive testing method to detect hidden cracks in riveted joints. X-ray inspection requires complex precautions for occupational safety. Ultrasonic tests are also very expensive, since each rivet would have to be examined separately. This paper describes investigations using Lock-In-Thermography for crack detection in riveted joints.