Strengthening of RC slabs with circular composite patches – a high-order approach

A new approach for the strengthening of existing reinforced concrete slabs using circular patches made of composite materials, and a mathematical model for the analysis of such strengthened slabs are presented. The model follows the concepts of the High-Order theory and fulfills all equilibrium and compatibility requirements as well as boundary and continuity conditions. The field equations and the boundary and continuity conditions are derived via the variational principle of virtual work assuming axisymmetric behavior. The constitutive relations of laminated materials are used for the composite patch and unique constitutive relations are derived for the RC member. The proposed model is used for the investigation of a square slab strengthened with circular patches of various materials and sizes through a sub-structuring approach. The results include the overall behavior of the strengthened slab and the localized shear and vertical normal stresses near the edges of the bonded patch throughout the entire loading process. The effects involved with pretensioning of the circular patch are also examined. The study reveals that the proposed strengthening approach improves both the serviceability and the load resistance of the slab, however it is associated with severe stress concentrations near the edge of the bonded patch.