## 2 Problem Definition  
Connections and reinforcements with bonded-in rods have been used in building for several decades. For instance, this solution appeared for the first time in 1980, in French historical monuments [22]. Besides, adhesive bonds for timber applications are notoriously sensitive to several aspects, including:  
1. wetting ability of the adhesive in relation to the surface;
2. bulk properties of adhesive after complete hardening;
3. severe environmental conditions.  
(Point 1) relates to the substrate (type of surface, its treatment, any kind of ageing and chemical modification, etc.), and to the adhesive in use (viscosity, density, chemical affinity with the substrate, etc.). (Point 2) is particularly relevant when the thickness is high (as usual for structural applications in timber buildings). Finally, environment conditions in 3) can include elevated thermal distortions (due to fires or repeated hygrometric variations), such as wood deformations that induce additional coactive stress at the interface between the adhesive and timber.  
From a practical point of view, the applied bond strength design values and the explicit strength modification factors are in most cases not retrievable. This is closely related to the fact that the current lack of worldwide standards or commonly accepted specifications exist for assessing and approving adhesives to be used for BiR applications. It is obvious from a chemistry view point that different adhesive types, which may have rather similar short-term bond strengths, can behave differently under variable climates. The design of BiR joints is implemented in European prestandards and technical documents [23; 24; 25], which specify the modification factors for accumulated duration of load in different climates (service classes in Table 1, as described in [26]). The final result takes the form of the well-known factor. On the other hand, this factor is irrespective of the adhesive type.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Service Class**} \\ \cline{2-4}  & **1** & **2** & **3** \\ \hline \multirow{2}{*}{Climatic condition} & 20 \({}^{\circ}\)C, relative humidity \textgreater{}65\% & 20 \({}^{\circ}\)C, relative humidity \textgreater{}85\% except & \multirow{2}{*}{Climatic conditions worse than class 2} \\  & for few weeks/year & & \\ \hline \multirow{2}{*}{Average moisture content in timber} & \multirow{2}{*}{about 12\%} & \multirow{2}{*}{always \textless{}18\%} & \multirow{2}{*}{\textgreater{}18\%} \\  & & & \\ \hline \multirow{4}{*}{Examples} & Interiors; warmed and & Covered exteriors; unconditioned & \\  & conditioned environments, & environments (shelters, cold roofs, & \\ \cline{1-1}  & with limited hygthermal & terraces) or humid ones (swimming & \\ \cline{1-1}  & variations & pools); beam ends on interior walls, & \\ \cline{1-1}  & well ventilated and drained & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Service classes for timber structures and typical examples.  
The current investigation presents experimental tests of BiR connections in different humid climates, in order to explore their actual load-bearing capacity (strength and slip modulus, failure mechanism), as a function of two different adhesive types and rod arrangements.