Effect of temperature on the mechanical performance of glued-in rods in timber structures Julie Lartigau a,b,n , Jean-Luc Coureau b , Stéphane Morel b , Philippe Galimard b , Emmanuel Maurin c a ESTIA, Technopôle Izarbel, 97 allée Théodore Monod, F-64210 Bidart, France b I2M, Université de Bordeaux, 351 Cours de la Libération, F-33400 Talence, France c LRMH, 29 rue de Paris, F-77420 Champs-sur-Marne, France article info Article history: Accepted 17 October 2014 Available online 4 November 2014 Keywords: Epoxides Destructive testing Finite element stress analysis Joint design abstract Structural bonding technology has proven to be an economically and attractive connection process in timber engineering. Within old or historical wooden buildings, local reinforcement of weak zones is often performed with glued-in rods. This kind of connection typically allows the transfer of loads within wooden elements by means of threaded steel rods glued with a structural adhesive. This paper relates to experimental and numerical investigations on small sized specimens, with the aim of providing a better knowledge about the elastic behavior according to temperature. Experimental results reveal that stiffness of bonded-in rods significantly decreases once the glass transition temperature of the adhesive is reached. However, the ultimate shear strength is constant and sudden failures occur in the wood close to the adhesive whatever the temperature is. Then, an elastic finite element model allows the evolution of the Young modulus of the adhesive with temperature changes and also reveals the stress distribution along the glued-in depth during the elastic regime. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction Structural bonding technology and connections in timber engi- neering have undergone an important growth in the last few years. Connections with concealed rods bonded into timber are often used for rehabilitation (repair or reinforcement) of wooden structural members. This process appeared for the first time in French historical monuments in 1979. Such connections make the transfer of loads within wooden elements possible. They also offer esthetic benefits; the joint is inconspicuous and rods are hidden in the cross sections of the members. A large part of the original timber is preserved, since only the damaged part of the member is changed and replaced by a sound one. Many experiments have been carried out to understand the short- term behavior of connections by glued-in rods and their dependence on geometric or material parameters [1–4]. The durability of structural adhesives, when bonding secondary materials into wood, has been examined by some researchers in relation to combined thermal moisture effects [5,6]. Aicher et al. [7] and Cruz and Custodio [8] revealed that glue lines inside timber structural members followed the outer temperature regime both in heating and cooling phases. Temperature inside roofs, recorded in summer 2004 in Portugal, did not exceed 45 1C, but peak temperatures of 75 1C have been measured in the USA [9]. The European standard EN301 [10] accepts 50 1C to be the limit between normal conditions and hot service conditions, to which different requirements are imposed concerning the adhesives performances (type I and type II). Currently, the European structural timber code [11] does not cover the design of structures subject to prolonged exposure to temperatures over 60 1C. Besides, other studies [12,13] disclosed that the load bearing capacity of bonded-in rods significantly decreased when the epoxy resins reached an intrinsic critical temperature also called the glass transition temperature (T g ). Once this temperature was attained, irreversible modifications of the inner structure of the polymer occurred. From this temperature, it is known that mechanical properties of the adhesive, and consequently of the corresponding connection, significantly decrease. Design rule proposals, predicting the pull-out strength of glued-in rods, are available [14,1,15] but the temperature is not taken into account in design. The lack of information regarding the performance of these connections under temperature changes is still a drawback for their use and the influence of temperature needs to be further analyzed. In this work, the effect of temperature on the mechanical behavior of glued-in rods is studied through experiments and Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ijadhadh International Journal of Adhesion & Adhesives http://dx.doi.org/10.1016/j.ijadhadh.2014.10.006 0143-7496/& 2014 Elsevier Ltd. All rights reserved. n Corresponding author at: ESTIA, Technopôle Izarbel, 97 allée Théodore Monod, F-64210 Bidart, France. Tel.: þ335 59 438 458; fax: þ335 59 438 401. E-mail address: j.lartigau@estia.fr (J. Lartigau). International Journal of Adhesion & Adhesives 57 (2015) 79–84