Performance of FRP-Upgraded RC One-Way Ribbed Slabs with an Opening in Flexure Zone

Reinforced concrete (RC) one-way ribbed slabs serve as a prevalent flooring solution in the Middle East. In this region, the occurrence of openings within these slabs is frequent, particularly when making modifications to existing buildings. However, these openings compromise the stiffness and load-bearing capacity of the slabs, necessitating strengthening measures. All of the available investigations were carried out on strengthening RC one- and two-way solid slabs with openings. However, a noticeable research gap exists, as none of these studies have delved into the strengthening of RC one-way ribbed slabs with openings. This gap was bridged in this study by conducting a comprehensive experimental inquiry into the effectiveness of utilizing fiber-reinforced polymer (FRP) laminates to restore the flexural capacity of RC one-way ribbed slabs featuring flexure openings. The experimental program comprised four half-scale one-way ribbed slabs (having three ribs) divided into one unstrengthened specimen without openings to act as a reference, one unstrengthened specimen with a single opening located in the peak-moment region, and two FRP-strengthened slabs each having a single opening located in the peak-moment region. The dimensions of each slab were 2600 mm (length) × 825 mm (width) × 175 mm (thickness). The openings were square (side length = 400 mm), which included cutting the middle rib. The slabs were tested under four-point flexure until failure. It was revealed that strengthening slabs using FRP sheets fully restored the flexural capacity, which was even exceeded by up to 8%. However, the secant stiffness and dissipated energy were partially restored compared with the unstrengthened slab without opening, and these response parameters were reduced by up to 19% and 32%, respectively. Moreover, the displacement ductility for strengthened specimens was moderately reduced compared with the unstrengthened specimen without opening. Furthermore, an analytical procedure was suggested based on section analysis for quick and reasonable assessment of the peak load for both unstrengthened and strengthened one-way ribbed slabs with and without flexure openings.

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