Improvement of punching shear strength of reinforced lightweight concrete flat slab using different strengthening techniques

This paper investigates the strengthening techniques of lightweight concrete (LWC) flat slabs vulnerable to punching shear failure. Thirteen reinforced LWC flat slab specimens were experimentally tested. The main investigated parameters were the type of shear reinforcement (steel bars, high strength bolts, or glass fiber reinforced polymers (GFRP) rods), spacing, shear reinforcement configuration around the column and the fixation method of shear reinforcement. The test results showed that using radial shear reinforcement with spacing of (d/2) resulted in the most efficient strengthening technique. The punching shear capacities were improved by 77%, 61% and 54% by using steel bars, glass fiber rods and high strength bolts, respectively, compared to the reference specimen. Moreover, using high strength steel bolts fixed to the slabs with steel plates showed the highest ductility compared with the other strengthening techniques Also, the failure mode converted from being brittle shear failure to flexural-shear mode. Non-linear finite element analysis (NLFEA) was carried out for the numerical verification. The analysis adequately reflected the trend of experimental results. Finally, the experimental test results were evaluated with code equations. The evaluation showed that the ACI 318 code underestimated the punching shear capacity of the tested specimens. On the other hand, Euro Code showed good prediction of the punching shear strength of the tested slabs. •Strengthening techniques showed an improvement in the punching shear strength of the specimens.•Using diagonal shear reinforcement considered one the most effective ways for strengthening of LWC flat slabs.•Radial reinforcement spaced with 0.5d was the most efficient strengthening technique to enhance the punching shear strength of LWC flat slabs.•Strengthening with GFRP rods as shear reinforcement improves the punching shear capacity.•Utmost enhancement in the ductility was achieved for specimens strengthened using high strength steel bolts with steel plates.