Fatigue and Wear of Steel Eyebars from Historic Railroad Bridges

Fatigue of steel is a major cause of mechanical failure and as such is very important to the safe design of railroad bridges. Fatigue phenomena are governed by the creation and growth of cracks, which can propagate through the material under stress until the material fails from fracture. Since these cracks take time to form and grow, cyclic loading is the main driver of fatigue in steel. Two historic steel-truss railroad bridges were dismantled and several joints were extracted intact from each bridge. Historic railroad bridges built around the turn of the 19th century were mostly not designed for fatigue, so it has become necessary to study these bridges to understand their fatigue behavior. Additionally, many in-service bridges in the United States are very old, are approaching the end of their useful service lives, and do not have accurate as-built information readily available. Much research has been done to develop and evaluate experimental methods to evaluate the structural health of bridges in situ, however these often rely heavily on certain assumptions that may or may not hold. Often historic bridge behavior is a surprise to engineers and gives unexpected results. Accurate knowledge of material properties is of utmost importance in understanding how these bridges will behave. Therefore, several aspects of the structural form are investigated including the wear of the components during service life, material test results, and fatigue behavior of the eyebars