Pohoryles, DA; (2017) Realistic FRP seismic strengthening schemes for interior reinforced concrete beam-column joints. Doctoral thesis , UCL (University College London).

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Abstract

The observation, in recent earthquakes, of brittle collapses of reinforced concrete (RC) structures built before the introduction of detailed seismic design codes (pre-1970’s), underlines the need for significant upgrades to the existing RC building stock. In particular, weak-column/strong-beam mechanisms and shear failures have potentially catastrophic impacts that could be addressed by repair and retrofit solutions. In recent years, retrofits with fibre reinforced polymers (FRP) are becoming increasingly popular due to the benefits of corrosion resistance, high strength-to-weight ratio and reduced labour time. Experimental evidence for the efficiency of such schemes for joint strengthening can be found in the literature. An analysis of all available literature shows that the reduced scale of most tested specimens, as well as the omission of slabs and transverse beams in many studies, may lead to an unrealistic assessment of FRP retrofit schemes. In this study, pre-1970’s full-scale interior beam-column joints with slab and transverse beams are hence tested under realistic conditions in order to propose and assess new and practical FRP retrofit solutions for seismic actions. Three carbon FRP (CFRP) retrofit schemes with selective retrofit objectives are designed using outcomes from the literature and from calibrated finite-element models. The retrofit schemes are composed of a combination of FRP strengthening and selective weakening components to ensure failure of inadequately reinforced RC beam-column joints according to capacity design principles. The objectives of the schemes include the enhancement in lateral capacity and ductility, as well as changing the failure mechanism of the joint. Results from full-scale cyclic tests on the CFRP retrofitted specimens are compared to the behaviour of a deficient specimen and a specimen designed to modern guidelines (EC8), highlighting the successful achievement of the respective retrofit objectives. To evaluate the effect of the realistic set-up, the results are also compared to specimens without slab and transverse beams, highlighting their importance. Finally, new design equations, to be used in conjunction with existing guidelines, are formulated to ease the practical adoption of the proposed retrofit scheme.

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