On the delamination phenomenon in the repair of timber beams with steel plates Giovanni Metelli ⇑ , Marco Preti, Ezio Giuriani Department of Civil, Environmental, Architectural Engineering and of Mathematics, University of Brescia, Italy highlights  A non-invasive technique for the repair of ancient wooden floors is presented.  Steel plated were glued on one side into longitudinal routed grooves.  The plate delamination was studied with the Moiré interferometry analysis.  The plastic strain of sapwood markedly reduced the risk of delamination.  The continuous monitoring of the floor confirms the effectiveness of the technique. article info Article history: Received 14 January 2015 Received in revised form 5 September 2015 Accepted 21 September 2015 Available online 1 October 2015 Keywords: Timber Repair Delamination Stress concentration Bond Interferometry analysis Creep abstract This paper presents a non-invasive technique for the repair of ancient wooden floors. Steel plates are glued on one side only by epoxy-adhesive into longitudinal grooves in order to allow the free swelling and shrinkage of the wood in the direction transversal to the plate glueing surface, thus reducing the risk of plate delamination. A set of high strength steel nails provides load transmission from the steel plates to the wooden beam in the case of loss of adhesion due to fire or delamination. This technique was used to repair a precious beam in a 15th-century wooden floor in Palazzo Calini (Brescia, Italy). The technique requires particular attention because it might be affected by the delamination of the glued reinforcement due to stress concentration, which occurs at the end of the repairing element or at any cracks in the repaired beam. Results of experimental studies on delamination phenomenon investigated by means of the Moiré interferometry analysis are also presented. These show that the risk of plate debonding can be markedly reduced by the capability of the sapwood to develop plastic strain. The wooden floor has been monitored for more than fourteen years, confirming the effectiveness of the adopted technique. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction In the rehabilitation of ancient buildings the problem of strengthening and repairing wooden beams is encountered often. In recent years, theoretical, numerical and experimental studies have been carried out to find valid techniques to enhance the stiff- ness and the strength of ancient wooden floors. These techniques are essentially based on the use of thin collaborating concrete slab or steel plates [1,2]. Several techniques have been developed since the 1960s, which are especially focused on strengthening and repairing local fractures or defects in wooden beams with steel plates bonded by epoxy adhesive [3–6]. More recently, fibre- reinforced polymer (FRP) sheets have been proposed to replace steel plates because they are easily installed and provide good durability [7–11]. Generally these techniques require wide steel plates or FRP strips which cover a large part of the surface of the wooden beam. This aspect makes it difficult to apply these techniques to the repair of precious ancient wooden floors. The restoration technique proposed by Gentile et al. [12], Alhayek and Secova [13] and by Alam et al. [14] seems to be more acceptable. It uses glass-fibre (GFRP) or carbon-fibre reinforced polymer (CFRP) reinforcements that were glued into narrow longi- tudinal grooves routed out of the wood beam. This limits the inter- vention to a reduced portion of the beam, which remains mostly visible. This technique was adopted to efficiently strengthen 75 timber beams of a bridge in Canada [12]. All of the previously mentioned techniques, based on the collaboration between two elements of different materials, pose the issue of stresses occurring between the reinforcing element and the wood, induced by the http://dx.doi.org/10.1016/j.conbuildmat.2015.09.038 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: DICATAM, University of Brescia, via Branze 43, Brescia, Italy. E-mail address: giovanni.metelli@unibs.it (G. Metelli). Construction and Building Materials 102 (2016) 1018–1028 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat