PSI - Issue 64

Annalisa Napoli et al. / Procedia Structural Integrity 64 (2024) 975–982 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction The use of either epoxy-bonded or bolted steel plates for external strengthening of reinforced concrete (RC) members in bending, shear, or for column j has been a long-standing practice. Known in the 60’s as “beton plaqué ”, this relatively low-cost technique, which does not require skilled labor and employes material (steel) with optimal mechanical properties, attracted in the ‘90s the interest of the scientific community as corroborated by a significant number of experimental investigations performed at that time (Swamy et al. 1987; Ziraba et al. 1994; Hussain et al. 1995; Ziraba et al. 1995; Swamy et al. 1996; Mohamed et al.1998; Oehlers et al. 1998;). However, already toward the end of 1990s, the increasing demand on the market for the use of Fiber Reinforced Polymer (FRP) composite materials as alternative strengthening technique caused a corresponding reduction of steel plate applications. The shift towards FRPs was driven by their lightweight nature, ease of storage, transport, and application, as well as their resistance to corrosion (Teng et al. 2002). Despite the advantages of FRPs, steel plates still remain a viable option for strengthening interventions thanks to the ductile stress-strain behavior, high stiffness properties, the ability to strengthen structures while in use, and potential for material reuse, leading to cost savings and greater environmental sustainability. However, despite being a traditional technique, the number of FRP applications is far greater than those available for steel applications, the former being supported by the widespread of several international guidelines for the FRP strengthening design of RC structures. Conversely, the in-situ applications with steel plates are still very common and often preferred to FRPs, but they are not well supported by clear design indications. This paper aims at contributing to fill this knowledge gap by presenting a large experimental database compiled from the literature, which includes three/four- point bending tests performed on rectangular or T-shape RC members variably reinforced with external steel plates. A typological description of the database was performed by accurately accounting for relevant parameters, such as: beam geometry, amount of internal and external steel reinforcement, strengthening layout and failure modes experienced during the tests. The analysis of the collected data represents a useful basis for carrying out a theoretical study on the prediction of the bending moment capacity of the beams. E-DB end debonding of the steel plate FL flexural failure mode FL+Bolt shearing = flexural crisis associated to the shearing of one or more bolts nearest to the plate ends. I-DB intermediate debonding of the steel plate L s shear span length of the beam L c clear length of the beam MF mechanically fastened steel strengthening system b beam width h beam height b w web width in a T-shape beam f c 0.85 f’ c f’ c cylinder compressive strength of concrete f r,y yielding strength of external strengthening steel plate f s,y yielding strength of longitudinal steel reinforcement of beam in tension t p external steel plate thickness  r mechanical percentage of external strengthening steel plate  s mechanical percentage of longitudinal steel reinforcement of beam in tension Nomenclature A s total area of longitudinal steel rebars in tension area of external strengthening steel plate externally bonded steel strengthening system A r EB