Fatigue Testing of Post-Tensioned Steel-Concrete Composite Beams

Steel-concrete composite (SCC) bridge superstructures are widely used today extensively in highway bridges. Post-tensioning (PT) has been commonly used in this type of structure as a repairing or strengthening technique. As bridges are typically subjected to cyclic loading, understanding their performance under fatigue is vital. In this paper, two specimens were tested to study the performance of SCC beams with external post-tensioning under the effect of fatigue loading. Because the external PT is mostly added to existing bridges as a retrofitting technique, one of the specimens has undergone some damage prior to experiencing fatigue loading. The strains in the shear connectors as well as the midspan deflections were monitored during the fatigue tests. The results show that as the number of fatigue cycles increases, both the deflection and strain in the shear connectors also increase. The pre-existing damage decreased the effectiveness of the PT to enhance the fatigue behavior of the SCC beam. For the pre-damaged specimen, the increase in the shear connector strain and the midspan deflection was 4.5 and 1.4 times those for the undamaged specimen, respectively.