Structural Response of Flexure-Deficient Reinforced Concrete Continuous Slabs Strengthened With Composites

Jwan Ahmad Al Khalil


Accidental reduction in the amount of steel in continuous reinforced concrete (RC) floor slab is a typical problem that might occur due to an error in design, unclear drawings, or overlooked verification of reinforcement prior to concrete casting. Existence of such deficiencies would compromise the load capacity and serviceability of RC floor slab. This research examines the effectiveness of using fiber-reinforced polymers (FRP) to improve the structural response of flexure-deficient continuous RC slab strips. The study comprised experimental testing and finite elements (FE) modeling. Sixteen two-span RC slap strips, 400 x 125 x 3800 mm each, were tested. Test parameters included the deficiency location, strengthening regime, and amount of FRP.

The unstrengthened slab strip deficient in the sagging region had 22% lower load capacity and 64% higher deflection-based ductility index compared with those of its counterpart deficient in the hogging region. Strengthening with FRP improved the load capacity and stiffness of the deficient slab strips. The FRP strengthening tended to decrease the ductility index of the slab strips deficient in the sagging regions. Conversely, the ductility index of the slab strips deficient in the hogging region tended to increase after strengthening. The strength gain caused by strengthening was in the range 29% to 69% for the slab strips deficient in the sagging regions and 14% to 44% for those deficient in the hogging region. Increasing the amount of FRP resulted in an increase in the load capacity but the additional strength gain was, generally, not proportional to the added amount of FRP. Increasing the amount of FRP had, typically, less significant effect on the load capacity of the slabs deficient in the hogging region than in the sagging region.

Strengthening of deficient regions reduced the moment redistribution ratios. The ratios further decreased as the amount of FRP in the deficient region increased. A maximum moment redistribution ratio of +32% was recorded for the strengthened slab strips. The FE model developed in this study predicted the nonlinear structural response of the tested continuous RC slab strips with a high level of accuracy. The numerical and experimental results were in good agreement.