Flexural behavior of 15-year-old full-scale hollow slab beams strengthened with fiber-reinforced composites

A large number of early hollow slab beams suffer from inadequate load carrying capacity, stiffness and durability, resulting from the overloading, environmental deterioration mechanism and poor maintenance. Most of the existing studies on the reinforcement of pre-damaged reinforced concrete beam carried out in scale-down models. However, the artificial pre-damage (mechanical damage and accelerated corrosion) alters the deterioration mechanism of reinforced concrete beam. The scale effect leads to disparities in force ratios acting on scale-down models and full-scale structures. To solve these problems, three 15-year-old full-scale hollow slab beams (taken from a serving bridge in Guangxi, China, with 15.96 m long) were respectively strengthened with steel-reinforced UHPC layer, GFRP-reinforced UHPC layer and CFRP layer. The flexural behaviors of the strengthened beams and the control beam were investigated by field four-point bending test and numerical simulation. The experimental results indicate that the ultimate flexural load capacity and stiffness of hollow slab beams after strengthened are respectively increased by 17.6%-47.1% and 4.7%-17.9%, and the deflection under service load is decreased by 7.6%-19.1%. Meanwhile, UHPC is beneficial to improve the energy absorption capacity of hollow slab beams. Moreover, the main bearer of load is the tensile steel bars in the hollow slab beams and the reinforcement layers played an auxiliary role in load bearing. Finally, the accurate prediction formulas for the ultimate flexural load of strengthened hollow slab beams with a maximum error of only 3.5% were proposed.