Rehabilitation and strength sustainability of fatigue damaged concrete–encased steel flexural members using a newly developed polymeric carbon–fiber composite

Abstract

The retrofit of fatigue-damaged concrete–encased steel girders is investigated using a newly developed composite wrap that stabilizes the damage in retrofitted beams via an energy dissipation mechanism, resulting in significant ductility and high-strength sustainability. Three large-scale fatigue-damaged concrete–encased steel girders were retrofitted using either conventional carbon–fiber reinforced polymers (CFRP) or the new prototype composite, referred to as “CarbonFlex.” Following the peak strengths of the beams, the CFRP-retrofitted beam exhibited a sharp, yet expected, decrease in strength with minimal ductility until failure, whereas the CarbonFlex-retrofitted beam was able to sustain over 68% of its peak strength, showed tremendous relative displacement ductility, and had an ultimate displacement three times greater than that of its counterpart. A Concrete Structural Retrofitting Analysis Program-for-Flexural (CSRAP-Flex) behavior was subsequently developed using a linear elastic fracture mechanics (LEFM) approach to analyze the initial crack propagation. Subsequent moment capacity and curvature relationships were derived and verified using the experimental test results.