Strengthening of RC slabs with penetrations using unanchored and anchored FRP composites

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Reinforced concrete (RC) slabs are one of the most commonly occurring structural forms. Penetrations (otherwise known as openings or cut-outs) in new as well as existing concrete slabs are commonly introduced due to structural and/or functional reasons. The introduction of a penetration, if large enough, may cause weakening of the slab which will then require the installation of strengthening. Traditional methods of strengthening RC slabs with penetrations, such as the addition of extra supports or bolted steel plates, can be expensive and cumbersome. Such traditional methods can however be replaced by the bonding of high strength, light-weight and durable fibre reinforced polymer (FRP) composites. In recent years, externally bonded FRPs have become popular as a means to strengthen or rehabilitate RC infrastructure, such as the flexural, shear or torsional strengthening as well as seismic retrofitting of beams, slabs, columns and connections. The effectiveness of the FRP strengthening may however be compromised by premature debonding failure of the FRP prior to its ultimate strength being reached. In order to optimise the use of FRP composites, such premature debonding failure should be prevented or delayed. To date, several different types of anchorage systems have in tum been introduced to FRP strengthened RC members, namely embedded metal threads, U-jackets, near surface mounted rods, and anchors made using FRP. FRP anchors are particularly attractive as they are non-corrosive and can be applied to slabs and walls. This dissertation is concerned with the strengthening of existing RC slabs with large penetrations with externally bonded FRP composites. FRP anchors are also researched and utilised in order to address the debonding issue. A review of the relevant literature is firstly given which justifies the need for the research presented herein. The remainder of the dissertation is then divided into four main sections, namely (i) pullout strength and behaviour of FRP anchor systems, (ii) shear strength and behaviour of FRP anchor systems, (iii) unanchored FRP-strengthened RC slabs with penetrations, (iv) FRP-strengthened RC slabs with penetrations with the addition of FRP anchors. In each of these four sections, experimental tests are reported. Overall, the slab strengthening schemes were found to be effective and the effectiveness of FRP anchor associated with the debonding issue was proved to be positive. Also reported in each of the four sections is the development of analytical models which have been derived from first principles and calibrated from the various Jest data. The results of parametric studies are then reported using the various analytical models and the influence of key geometrical and material properties identified. Design recommendations, which can be readily incorporated into existing design guidelines, are then given and future research needs are finally identified.
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