Strengthening R/C beams with opening by externally installed FRP rods: Behavior and analysis

This paper discusses the strengthening of opening in R/C beams by FRP rods. A total number of thirteen beams with circular and square opening have been tested. The opening is shown to significantly reduce the shear capacity of beam. Two patterns of strengthening by FRP rod are investigated: one is to place FRP rods enclosing the opening and the other is to place FRP rods diagonally throughout the entire depth of the beam. It is found that simply placing FRP rods around the opening is not fully effective because a diagonal crack can propagate through the beam with the crack path diverted to avoid intersecting with the FRP rod. When FRP rods are placed throughout the entire beam’s depth, a significant improvement in loading capacity and ductility is achieved, similar to strengthening by pre-fabricated internal steel bars. The flexural failure mode is restored. A nonlinear finite element analysis, based on smeared crack approach, is conducted for numerical verification and examining the effect of length, position and inclination of FRP rods. The plot of analytical principal compressive stress illustrates two strut mechanisms associated with FRP rod. The inclined rods are found to be more effective than vertical ones.