Issue 38

S. Bennati et alii, Frattura ed Integrità Strutturale, 38 (2016) 377-391; DOI: 10.3221/IGF-ESIS.38.47 377 Evaluation of the increased load bearing capacity of steel beams strengthened with pre-stressed FRP laminates S. Bennati, D. Colonna, P.S. Valvo Università di Pisa, Dipartimento di Ingegneria Civile e Industriale, Largo Lucio Lazzarino, 56122 Pisa, Italy s.bennati@ing.unipi.it, p.valvo@ing.unipi.it A BSTRACT . We analyse the problem of a simply supported steel beam subjected to uniformly distributed load, strengthened with a pre-stressed fibre-reinforced polymer (FRP) laminate. We assume that the laminate is first put into tension, then bonded to the beam bottom surface, and finally fixed at both its ends by suitable connections. The beam and laminate are modelled according to classical beam theory. The adhesive is modelled as a cohesive interface with a piecewise linear constitutive law defined over three intervals (elastic response, softening response, debonding). The model is described by a set of differential equations with suitable boundary conditions. An analytical solution to the problem is determined, including explicit expressions for the internal forces and interfacial stresses. As an application, we consider the standard IPE series for the steel beam and the Sika® CarboDur® system for the adhesive and laminate. For each considered cross section, we first carry out a preliminary design of the unstrengthened steel beam. Then, we imagine to apply the FRP strengthening and calculate the loads corresponding to the elastic limit states in the steel beam, adhesive, and laminate. Lastly, we take into account the ultimate limit state corresponding to the plasticisation of the mid-span steel cross section and evaluate the increased load bearing capacity of the strengthened beam. K EYWORDS . Steel beam; FRP strengthening; Adhesive; Beam theory; Cohesive-zone model; Analytical solution; Pre-stressing; Ultimate limit state; Load bearing capacity. Citation: Bennati, S., Colonna, D., Valvo, P.S., Evaluation of the increased load bearing capacity of steel beams strengthened with pre- stressed FRP laminates, Frattura ed Integrità Strutturale, 38 (2016) 377-391. Received: 15.08.2016 Accepted: 08.09.2016 Published: 01.10.2016 Copyright: © 2016 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION ibre-reinforced polymers (FRP) are increasingly used in civil engineering for the strengthening of existing constructions. In such applications, the existing structural elements (made of traditional materials such as, for instance, masonry, wood, concrete, steel, etc.) are strengthened by adhesively bonding FRP laminates onto their external surfaces. The type of fibre, shape, thickness, and other characteristics of the laminate vary according to the F