Abstract
Openings in slabs are usually required for many different applications such as aeriation ducts and air conditioning. Opening in concrete slabs due to cutouts significantly decrease the member stiffness. There are different techniques to strengthen slabs with opening cutouts. This study presents experimental and numerical investigations on the use of Carbon Fiber Reinforced Polymers (CFRP) as strengthening material to strengthen and restore the load carrying capacity of R.C. slabs after having cutout in the hogging moment region. The experimental program consisted of testing five (oneway spanning R.C. flat slabs) with overhang. All slabs were prismatic, rectangular in cross-section and nominally 2000 mm long, 1000 mm width, and 100 mm thickness with a clear span (distance between supports) of 1200 mm and the overhang length is 700 mm. All slabs were loaded up to 30 kN (45% of ultimate load for reference slab, before yielding of the longitudinal reinforcement), then the load was kept constant during cutting concrete and steel bars (producing cut out). After that operation, slabs were loaded till failure. An analytical study using finite element analysis (FEA) is performed using the commercial software ANSYS. The FEA has been validated and calibrated using the experimental results. The FE model was found to be in a good agreement with the experimental results. The investigated key parameters were slab aspect ratio for the opening ratios of [1:1, 2:1], CFRP layers and the laminates widths, positions for cutouts and the CFRP configurations around cutouts.
Highlights
The ACI 318-14 code allows reinforced concrete slabs to have openings with the condition of performing full structural analysis to assure slab safety, strength, and serviceability under different expected loads
Enochsson et al (2007) tested two-way slabs strengthened with carbon fiber reinforced polymers (CFRP) and the results showed that the stiffness and ultimate load of the slabs with large opening is higher than the small opening with the same opening locations
The relationships between the applied load, deflection, and the longitudinal strains for concrete, steel, and CFRP of the tested slabs were typical for all tested slabs, a linear increase behavior followed by a nonlinear behavior until failure has been observed
Summary
The ACI 318-14 code allows reinforced concrete slabs to have openings with the condition of performing full structural analysis to assure slab safety, strength, and serviceability under different expected loads. Whereas the ACI 318-14 (ACI 318-14) Code gives procedures and limits for opening location and size If designer satisfies those requirements the analysis could be abandoned, problem becomes more complex when openings are planned to be made in existing slab, the most common way to substitute additional steel reinforcement is to apply CFRP strengthening before cutting a hole. The use of carbon fiber reinforced polymers (CFRP) as external reinforcement to strengthen existing slabs due to openings is becoming more popular, partly due to ease of installation and partly due to space saving. In these situations, CFRP sheets are applied to the slab before the opening is made even though CFRP is used for strengthening of openings, very
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