Behavior of Existing Box Beams Repaired with High-Strength Mortar Layer and Ultra-High-Performance Concrete (UHPC) Overlay: Experimental, Numerical, and Theoretical Investigations

Box beams constructed earlier were prone to inadequate bending capacity owing to low construction standards, overloading, and environmental degradation. To resolve the challenge, three full-scale box slab beams in service for 15 years were strengthened with a high-strength mortar layer and an ultra-high-performance concrete (UHPC) layer in this paper. The flexural performances of unstrengthened beams (control beam) and strengthened beams (mortar beam, UHPC beam) were investigated by in situ four-point bending tests and numerical simulations. The experimental results showed that the cracking of box beams, strengthened with high-strength mortar and UHPC layers, was effectively mitigated. In comparison to the control beam, the cracking load of the mortar beam and the UHPC beam increased by 20%, and the ultimate load increased by 23.5% and 35.3%, respectively. The high-strength mortar layer had little influence on the elastic-phase stiffness of box beams. In contrast, the stiffness of the elastic phase of the box beam, strengthened by the UHPC layer, increased by 32.9%. In the numerical simulations, the load-deflection curves obtained from finite elements and tests coincided well. The characteristic loads showed relatively good agreement with the test results, with errors below 10%. Combined with the tests and numerical analyses, the proposed equations for predicting the ultimate bearing capacities of the control beam, mortar beam, and UHPC beam were presented with a better prediction accuracy.

This creative work has been published under the Creative Commons Attribution 4.0 International (CC-BY 4.0) license which allows copying, and redistribution as well as adaptation of the original work provided appropriate credit is given to the original author and the conditions of the license are met.