## 3 Results and Discussion
### Experimental Results
#### 3.1.1 Splitting Loads and Failure Modes
It is worth noting that bending failure only occurred in the beams with the greatest slenderness and \(\alpha\) ratio of 0.64, where the ultimate loads shown in Table 4 caused stresses in the outermost wood fibres of around 90 N/mm\({}^{2}\), which are in line with the limit values reported in the literature [15]. It was observed that the experimental tests reached the maximum load by developing two different fracture patterns: one completely brittle (pure splitting) and the other in a combination of failure modes (a non-negligible plastic behaviour of the wood develops before splitting occurs), as shown in Figure 5. The behaviour of the combined failure mode is directly related to the formation of small cracks in the wood at the bottom of the dowel and, in some cases, to the yielding of the wood around the connection, as these areas are singular points subjected to high stress concentrations perpendicular to the grain. A summary of the load-displacement curves (_P-\(\delta\)_) for each of the tested specimens is shown in Figures 6 and 7. In these graphs, the load and displacement of the connection are plotted, according to the placement of LVDTs depicted in Figure 1. However, in Figure 7b, the total load on the beam (_2P_) is plotted in order to compare the results between the graphs depicted in Figure 7.  
Figure 5: Governing failure modes in the experimental tests. Figure 6: Experimental _P-\(\delta\)_ curves of beams with one dowel: (**a**) 1D with connection at mid-span; (**b**) 1D with the connection placed at off-centre of the beam. As can be seen, a single-dowel-type connection tends to develop a mixed-mode behaviour, but a double-dowel-type connection tends to collapse in a brittle manner. In particular, all beams with two dowels located in the centre of the span and those with two off-centre connections closer to the centre of the span break in a completely brittle manner. However, the rest of the beams showed a mixed-mode behaviour. This difference in behaviour depends on the configuration of the connection and is in line with the results of other research in the literature for other wood species [29, 34, 38, 40, 66]. In the series investigated, the splitting failure was characterised by the propagation of a main crack, which extended along the beam length and through the full entire thickness. This failure mode appeared suddenly and in a brittle manner. In some tests, the splitting failure was preceded by the formation of small cracks around the dowel, but eventually only one crack propagated and in a forceful manner. In some specimens, the crack shape that developed along the beam was very straight and continuous (see Figure 8a), but in other cases, the shape was oblique and/or discontinuous (see Figure 8b). The crack propagation patterns across the width of the beam also exhibited similar differences between the specimens (see Figure 9). However, the results showed that the less straight and continuous the crack propagation was, both longitudinally and transversely, the higher the splitting capacity. Figure 8: Typical failures: (**a**) straight and continuous crack; (**b**) oblique and discontinuous crack. Figure 7: Experimental _P-\(\delta\)_ curves of beams with two dowels: (**a**) 2D with connection at mid-span; (**b**) 2D with the connection placed at off-centre of the beam. Figure 9: Typical crack patterns. In all the series with two dowels and a span of 950 mm in group 2, the crack was propagated to the end of the beam, splitting it into two parts. In addition, this also happened in the beams of group 1 with a span of 450 mm and in all the series with two connections except for the one where the connections are closer to the supports (100/2D/950/0.13L). However, this did not happen in the rest of the series, where the crack did not reach the ends. Some of these crack patterns are shown in Figure 10.