Issue 31

C.L. dos Santos et alii, Frattura ed Integrità Strutturale, 31 (2015) 23-37; DOI: 10.3221/IGF-ESIS.31.03 28 diameter. The previous relations consider that failure occurs due to embedding failure at the wood members. The required embedment strengths for previous formulae were obtained in the literature, specifically for the same wood species, using embedding tests with the same thicknesses ( 1 2 30  t t mm   ) and dowel diameter 14  d mm  ( h,1 h,2 21.13.6 MPa; 46.44.2 MPa  f f   ) [26, 27]. Since the investigated connection shows one dowel and two shear planes, the strength values given by Eq. (1) – (2) were multiplied by 2 to result the total failure loads. It is interesting to note that EC5 produced similar strength values to the experimental results. However, a slightly higher strength value is observed when the failure coincides with the embedment of the centre member. According to the EC5, the smallest strength value from all possible failure modes should be considered for the definition of the design failure load of the joint. In this case, the EC5 would suggest the failure mode corresponding to the embedment of the side members, which agrees with the experimental results that showed the majority of failures at the side members. Despite showing apparent success in the prediction of the ultimate loads, the EC5 does not predict accurately the failure modes since it considers the embedding of the wood members as a failure mode when in the reality the situation is distinct, since crack initiation and propagation controls the ultimate loads (see Fig. 5) and the ductility of the joint. Experimental EC5 [3] F max (N) Side members 17213±1041 17724 Centre member 17228±1868 19488 D (1/2)max (mm) 4.7±1.7 - D (3/4)max (mm) 1.9±0.6 - k 1 (N/mm) 7416±1356 - k 2 (N/mm) 14445±3303 - k 3 (N/mm) 15546±2480 - Table 2 : Average strength and ductility of the T-joint. (a) (b) Figure 5 : Failure modes of the T-connection: (a) failure at the centre member; (b) splitting at the side members. N UMERICAL MODELLING 3D FE model of the tested joint was built and simulation results are presented and discussed in this section. The commercial FE code ANSYS ® was used for this purpose [19]. The ANSYS ® parametric design language capabilities – APDL language – were used for this purpose. Both wood members and steel dowel were accounted for in the model. They were modelled using hexahedra isoparametric 20-node elements (SOLID95) with full integration. The contact between the dowel and wood members was modelled applying the contact elements available in ANSYS ® , using a surface-to-surface option. The contact between the central and side wood members was also simulated. The CONTA174 and TARGE170 elements were used to model, respectively, the contact and target surfaces, forming the so- called contact pairs. Both surfaces of each contact pairs were assumed flexible. Three contact pairs were considered: A