Technical and economic substantiation of the choice of a strengthening method for reinforced concrete floor slabs in the reconstruction of civil buildings

Abstract

Reconstruction of civil buildings involving a change of function increases the design loads on interfloor slabs, so that existing reinforced concrete slabs cease to satisfy the ultimate limit state conditions and require strengthening. The choice of a strengthening method usually relies on the designer's experience and is rarely accompanied by a formalized comparison across technical and cost attributes, which reduces the reproducibility of design decisions. The aim is to construct a procedure for the technical and economic substantiation of the choice of a strengthening method for typical reconstruction conditions. Four methods – compression-zone enlargement with a bonded overlay, external carbon-fibre reinforcement, unloading by rolled steel beams and full slab replacement – are compared using the analytic hierarchy process across six criteria with a sensitivity analysis. For a required capacity gain of up to 55-60%, external composite reinforcement is rational by the composite indicator (K = 0.76), outperforming the other methods; full replacement remains unavoidable only when the required gain exceeds 70%. The rationality of a method is determined by the ratio of the achievable gain to the actual strength deficit rather than by the absolute capacity.