Tensile performance of rebar welded joints jacketed with SCC and UHPC for repair applications

The replacement of longitudinal rebars through welded joints is a technique used to restore the structural performance of bridge piers damaged by earthquakes or corrosion. In such repairs, the welded joints between new and existing rebars are typically embedded in newly cast concrete. However, the influence of this surrounding concrete on the tensile performance of the welded joints has not been thoroughly investigated. This study explores this effect by testing specimens with welded rebar joints embedded in self-compacting concrete (SCC) and ultra-high-performance concrete (UHPC). A series of uniaxial tensile tests were conducted. Two practical splice geometries were investigated: (i), named R4V*, an indirect butt weld supported by two short lap bars welded on one side of the joint with auxiliary direct butt welding, and (ii), named R6V*, an indirect butt weld executed against a V-angle backing with auxiliary direct butt welding, each tested at different weld lengths and bar diameters (d). Results showed that for weld lengths of 1.0d, only the R4V* weld satisfied the failure criterion of fracture occurring in the base metal. At 1.5d, both weld types met this criterion. Tests with SCC and UHPC jackets revealed that fibre-reinforced concrete sustained load-sharing even after initial cracking, delaying the failure of the embedded joint. Three mechanical models were evaluated to predict the tensile-yield capacity of the specimens: (1) Rebar-only model, which assumes the welded rebar alone carries the load. (1) Rebar + full-jacket model, which adds the contribution of the entire concrete jacket in tension. (3) Rebar + UHPC-ring model, which augments the steel capacity with the tensile resistance of a calibrated UHPC annulus; calibration showed that an annular thickness of three bar-diameters yields the best overall fit.