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The Prestressed Hollow Core Slabs (PHCSs) are mostly used in the construction industry nowadays owing to the economic benefits they achieve. Openings are probable to be needed in a PHCS after construction to allow the installation of an equipment or the passage of facilities ducts due to changes that could appear in the use of the building.
Moreover, the presence of openings along the span of an existing slab can severely decrease the ultimate capacity of the slab due to the discontinuity resulting from cutting the concrete and the prestressing steel reinforcement according to Saint-Venant’s principle.
The Near Surface Mounted (NSM) strengthening technique is among the practical and feasible solutions to rehabilitate or enhance the performance of the PHCSs with openings. Compared to the strengthening of other concrete elements, a limitation exists in the case of strengthening of the PHCSs. The longitudinal voids of the PHCSs constrain the positioning of the FRP reinforcement and make it limited to be at the location of the webs , due to the smaller thicknesses of the PHCSs’ flanges.
In this study, Finite Element (FE) numerical simulations for PHCSs with openings provided and consequently strengthened with NSM FRP strips. The Concrete Damage Plasticity (CDP) model was successfully implemented to model the non-linear behaviour of concrete. The bond failure for the strengthened specimens was accommodated in this research, where shear stress-slip and normal stress-gap models were utilized to consider different debonding modes. An acceptable accuracy, in terms of the cracking, ultimate loads and the corresponding deformations, as well as, the PHCSs failure modes, was monitored. Maximum differences, compared to the experimentally attained results in the ultimate loads and the corresponding deformations of nearly 4% and -8.4%, respectively, were detected.
Additionally, an extensive set of parametric study variables influencing the PHCSs response were investigated. The PHCS cross-sectional shape, openings locations and sizes, the average precompression and the FRP reinforcement percentages were among the considered parameters. This made it possible to visualize ranges in which the proposed strengthening technique is feasible in restoring and further enhancing the ultimate-load carrying capacities, together with others in which changes in the failure modes hinders the utilization of the NSM strengthening.
Moreover, the suggested FE modelling approach along with the parametric study results could assist to formulate design guidelines that evaluate reductions in the ultimate capacities of the PHCSs associated with the presence of openings at multiple locations along their spans and improvements experienced by employing the NSM strengthening technique.
Finally, an analytical investigation to determine the flexural capacities of the PHCSs using the strain compatibility method was conducted. In addition, the shear capacities were calculated according to the American Concrete Institute (ACI) guidelines.