Strengthening of reinforced concrete slabs with mechanically-anchored unbonded FRP system

The potential use of mechanically-anchored unbonded fibre reinforced polymer (MA-UFRP) system to upgrade reinforced concrete (RC) slabs deficient in flexural strength is examined in this paper. A total of six RC slabs, each having 500 mm width, 100 mm thickness, and 1800 mm length, were constructed and tested to failure under four-point bending. Each slab was reinforced with three No. 10 deformed steel bars at tension side that corresponded to 0.8% steel reinforcement ratio. One slab was used as a control while the other five slabs were strengthened with various fibre reinforced polymer (FRP) strengthening systems, each having 0.12% external FRP reinforcement ratio. Two slabs were strengthened with externally-bonded FRP (EB-FRP) system, one slab with end-anchorage and one slab without end-anchorage. The remaining three slabs were strengthened with MA-UFRP system having various anchors’ locations. Test results showed that MA-UFRP system resulted in up to 43% enhancement in the slab flexural strength. The strength of the slabs strengthened with MA-UFRP system was on average 18% lower than that of the slab strengthened with EB-FRP system with end-anchorage but only 8% lower than that of the slab strengthened with EB-FRP system without end-anchorage. The mid-span deflection at ultimate load of the slabs strengthened with MA-UFRP system was on average 56% higher than that of the slab strengthened with EB-FRP without end-anchorage, 5% higher than that of the slab strengthened with EB-FRP with end-anchorage, and only 15% lower than that of the control.