This paper presents an experimental and numerical investigation into the bending behaviour of reinforced concrete (RC) T-beams damaged by overheight vehicle impact strengthened with ultra-high performance concrete (UHPC). Four-point bending tests were conducted on one RC T-beam and six UHPC-strengthened RC T-beams, and the primary parameters included the length and thickness of the UHPC strengthening layer, as well as the filling area of UHPC for the damaged region. The test results demonstrated that the UHPC strengthening layer effectively delayed the development of concrete cracks, improved the bending stiffness, cracking load, and resistance of the T-beams. The UHPC-strengthened T-beams exhibited an increase in cracking and ultimate loads by 39–339 % and 26–113 %, respectively, compared to the RC T-beam. Subsequently, a finite element (FE) model of the UHPC-strengthened T-beams was developed and validated using the experimental results. A parametric study using the validated FE model was conducted, revealing that insufficient strengthened length or excessive strengthened thickness of the UHPC layer increased the risk of debonding failure. Furthermore, for T-beams experiencing bending failure, increasing the thickness and height of the UHPC layer, as well as the UHPC filling area for the damaged region, significantly improved the bending resistance, while the UHPC layer length had little effect on the bending resistance. Finally, based on the calculation theory of RC beams under bending loads and considering the strain-hardening behaviour of UHPC in tension, a design method for the bending resistance of damaged RC T-beams strengthened with UHPC was proposed and verified using the experimental and numerical results.
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