Remediation of Punching Shear Failure Using Glass Fiber Reinforced Polymer (GFRP) Rods

The results of an experimental program on shear-strengthening of flat slabs using Glass
Fiber Reinforced Polymer (GFRP) rods are presented. A total of seven specimens were tested under
an upward concentric monotonic loading until failure. One specimen served as a control and was
tested without any modification. The remaining six specimens were strengthened with post-installed
GFRP rods in single (SG), double (DB), and radial (RD) patterns within shear critical parameters
around the centric column. The results of this experimental study suggest that GFRP rods are
capable of enhancing both the peak load and deformation capacity. Furthermore, brittle failure associated
with punching shear failure was successfully avoided by all strengthening patterns. Of all
of the patterns, the RD pattern resulted in maximum peak load increase and corresponding deformation
capacity while the lowest bound was created by the SG pattern. The results suggested that
SG, DB and RD patterns enhanced ultimate loads up to 9.1, 11.3 and 15.7% while corresponding
deflections increased up to 109, 136 and 154%. Strain measurement on flexural reinforcement suggested
that all strengthened specimens were able to withstand higher longitudinal strains than
yield. It was further shown that reducing the spacing between the GFRP rods efficiently enhanced
peak loads, nevertheless, neither this change was proportional, nor did it result in an enhanced
energy dissipation capacity. In the end, recommendations of American Concrete Institute (ACI) for
the shear strength of two-way systems were modified to incorporate the contributions from GFRP
rods. The results indicate that the proposed analytical approach provides an excellent match with
the experimental results.