Steel–Concrete Composite Beams Strengthened with Externally Post-Tensioned Tendons under Fatigue

Abstract

External post-tensioning (PT) by means of high‐strength steel cables can be used to effectively increase the ultimate capacity of steel–concrete composite beams. Limited research exists on the fatigue behavior of such strengthening, and therefore, this paper presents static and fatigue tests on four steel–concrete composite specimens to evaluate the effect of externally post-tensioned tendons on the ultimate strength and fatigue behavior of composite beams. Fatigue tests are conducted to a million cycles under four-point bending. In addition, static tests are performed on the fatigued specimens to evaluate the residual strength of the strengthened specimen. The static test results indicate that the external PT force improved the flexural behavior of the strengthened specimen by increasing the beam capacity and reducing the tensile strain in the bottom flange of the steel beam. The external PT improved the overall performance of the composite beam under fatigue by decreasing the strains in the shear connector, in the concrete flange, and in the steel beam at all stages of loading. However, the concrete flanges experienced additional longitudinal fatigue cracks in comparison to the reference specimen, which could negatively impact the overall fatigue life of the composite beam. The strengthened fatigued specimen experienced a reduction in the residual stiffness and ultimate capacity compared with the strengthened unfatigued specimen, which are attributed to the partial loss of composite interaction between the concrete flange and steel beam during fatigue testing.