PSI - Issue 78

Martina Sciomenta et al. / Procedia Structural Integrity 78 (2026) 253–260

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values that deviated by more than 20% from the mean). For each testes sample, F ' max,i is equal to the actual maximum load F ' max,R when the corresponding slip value was less than 15 mm, otherwise the load corresponding to a 15 mm slip F 15 was used. According to EN 12512 (CEN, 2011), the yield point ( F y , v y ) was determined, taking into account the pronounced non-linear behaviour of the load-slip curves. The ultimate slip v u corresponds to the attainment of the first of the following conditions: i) failure of the specimen, ii) slip at 0.8 F ' max,R times on the descending branch, and iii) a slip value of 30 mm (CEN, 2011).The ductility D is calculated as the ratio between ultimate slip and yield slip according to (CEN, 2011). 4. Results The force-displacements curves in terms of shear force versus slip of the entire specimen for all the configurations and screwed connections is represented for three specimens from the three series with VGZ screws in Fig.1b. Figure 2 shows the mean values of the experimental results in terms of max F and s K (assessed according to EN 1995-1-1 (CEN, 2011)). For the glulam beech specimens VGS screws showed higher strength and stiffness values than VGZ screws, instead for the hybrid and glulam chestnut specimens there is not much difference. From the results obtained for the beech series, it can be seen that the greater the diameter and length of the screw, the greater the maximum force and the stiffness.

Fig. 2. Experimental results in terms of maximum load and slip modulus.

The percentage differences of all mechanical properties, including ultimate load

max ' F , slip modulus

s K (assessed

according to EN 1995-1-1 [8]), yield force y F (evaluated according to EN 12512 case B (CEN, 2011)), yield y v and ductility D (calculated according to EN 12512 (CEN, 2011))were evaluated using the glulam beech series as a reference, the results obtained for the VGZ 9x160 with a 40 mm side board and for the VGS 9x160 with a 40 mm side board were compared. For VGZ 9x160 with a 40 mm side board (Fig.2) the hybrid beech-Silver fir configuration achieves the highest ultimate force max ' F , surpassing glulam beech by 36.75% while the chestnut series achieves an ultimate force 18.09% lower than the reference configuration. In terms of slip modulus, s K , the screws in hybrid configuration were characterized for an increased stiffness (40.26% higher than these in glulam beech configuration), instead the values achieved with chestnut configuration is slightly higher (12.75%) compared to the reference. The ductility of fasteners displacement