Experimental and numerical evaluation of composite repairs on wood beams damaged by cross-graining R.D.S.G. Campilho a,b, * , M.F.S.F. de Moura b , A.M.J.P. Barreto b , J.J.L. Morais c , J.J.M.S. Domingues d a Departamento de Economia e Gestão, Universidade Lusófona do Porto, Rua Augusto Rosa n°24, 4000-098 Porto, Portugal b Departamento de Engenharia Mecânica e Gestão Industrial, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal c CITAB/UTAD, Departamento de Engenharias, Quinta de Prados, 5001-801 Vila Real, Portugal d Departamento de Engenharia Mecânica, Instituto Superior de Engenharia do Porto, Rua Dr. António Bernardino de Almeida 431, 4200-072 Porto, Portugal article info Article history: Received 4 May 2009 Received in revised form 20 September 2009 Accepted 15 October 2009 Available online xxxx Keywords: Wood Composite Repair Cohesive zone models Finite element analysis abstract An experimental and Finite Element study was performed on the bending behaviour of wood beams of the Pinus Pinaster species repaired with adhesively-bonded carbon–epoxy patches, after sustaining dam- age by cross-grain failure. This damage is characterized by crack growth at a small angle to the beams longitudinal axis, due to misalignment between the wood fibres and the beam axis. Cross-grain failure can occur in large-scale in a wood member when trees that have grown spirally or with a pronounced taper are cut for lumber. Three patch lengths were tested. The simulations include the possibility of cohe- sive fracture of the adhesive layer, failure within the wood beam in two propagation planes and patch interlaminar failure, by the use of cohesive zone modelling. The respective cohesive properties were esti- mated either by an inverse method or from the literature. The comparison with the tests allowed the val- idation of the proposed methodology, opening a good perspective for the reduction of costs in the design stages of these repairs due to extensive experimentation. Ó 2009 Published by Elsevier Ltd. 1. Introduction Wood is amongst the oldest construction materials in the world and has been widely used to build large-scale structures like bridges, railroad infrastructures, lightweight warehouses and resi- dential buildings [1,2]. This natural and renewable material is characterized by high strengths under parallel to grain tension and compressive loads, which are nearly unique as specific proper- ties (i.e., divided by its weight). Moreover, it performs well under the influence of wind and especially earthquake loads, due to the low stiffness of wood, especially in the direction perpendicular to fibres, providing a redistribution of loads in the structure [3–7]. However, without proper maintenance, wood deteriorates due to fungi and insects, and swelling and shrinkage caused by variations on ambient humidity. Poor initial design or construction, or short duration episodes such as overloads and earthquakes, can also be pointed out as origins of damage [8]. Some studies were published in the last decades about the reinforcement [9] and repair [2,6] of wood structures with aluminium/steel and composites. In recent years, composite materials, which are already extensively used in several high performance applications in the aerospace, automo- tive, marine and military industries (Carbon–Fibre Reinforced Plas- tics; CFRP), and in house-hold and leisure appliances (Glass-Fibre Reinforced Plastics; GFRP), are gaining acceptance for structural strengthening and repair. In fact, composites offer a set of benefits over conventional engineering materials, such as higher strength and lighter weight than conventional materials, availability in the form of thin pultruded elements of different shapes (e.g. Sika Ò Car- boDur strips) with continuously decreasing costs, corrosion resis- tance and flexibility. Transversely to these issues, wood is tolerant to large strains before failure, necessary to develop the characteristic high strength of composite materials [9]. The study of wood structures reinforced with composites dates back to the 1980s and has been under research since then [5,10–15]. The work of Borri et al. [5] is a comprehensive experimental and numerical study on the reinforcement of wood beams with unidirectional CFRP laminates and pultruded bars. The four-point bending (4 PB) test was used to evaluate the effectiveness of the proposed methods. Reinforcing with CFRP sheets in the tension face signifi- cantly increased the bending characteristics of the beams (three sheets of CFRP resulted on a 60% increase of the flexural strength). Results were not so impressive with CFRP bars, with the sole advantage of this technique being related to its aesthetics, since the bars are not visible. Regardless of the reinforcement method, failure always occurred within the wood beams, with an adhesion failure between the reinforcement and the wood taking place only afterwards. Oppositely to the reinforcement studies, not many 0950-0618/$ - see front matter Ó 2009 Published by Elsevier Ltd. doi:10.1016/j.conbuildmat.2009.10.006 * Corresponding author. Address: Departamento de Economia e Gestão, Univer- sidade Lusófona do Porto, Rua Augusto Rosa n°24, 4000-098 Porto, Portugal. Tel.: +351 939526892; fax: +351 225081584. E-mail address: raulcampilho@hotmail.com (R.D.S.G. Campilho). Construction and Building Materials xxx (2009) xxx–xxx Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat ARTICLE IN PRESS Please cite this article in press as: Campilho RDSG et al. Experimental and numerical evaluation of composite repairs on wood beams damaged by cross- graining. Constr Build Mater (2009), doi:10.1016/j.conbuildmat.2009.10.006