A / \ 50%

A /\ I \





Figure 4. Load procedure applied in the carrying tests.

Figure 5. Instrumentation layout.

Figure 5. Instrumentation layout.

the main global displacement of the trusses, the relative displacements between the king post and the tie beam and the rotation of each joint were measured, using sixteen transducers, Figure 5.

Two hydraulic jacks, supported by a steel counter -frame fixed to the reaction slab of the laboratory, were used for applying the loads. As boundary conditions, two supports restraining the vertical displacement and the right support restrained also the horizontal movement were applied.

4.2 Evaluation of the trusses behavior

The response of the timber trusses under the carrying tests performed is highly depending of the variability, previously detected and reported, along the truss members in terms of cross sections area and principal moments. Moreover, it is recognized the difficulty associated with tests over existing structures, in which the members can present residual deformations and signs of decay and/or the connections are not well tight. The tests results shows that even under symmetric loading conditions, the behavior of both trusses is asymmetric. This conclusion is more evident in the response of Truss 1 under symmetric loading corresponding to SLS, Figure 6.

The connection between the king-post and the tie beam, made by a steel rod of 20 mm diameter fixed in the king-post, aligned in the longitudinal direction, passing through the tie beam, with a nut at one end, fastening the two elements, performs adequately. The king post suspends the tie beam, Figure 7.

As a consequence of the truss deformations under the vertical loads applied, horizontal displacement at the free support was recorded, Figure 8.

Figure 6. Asymmetric behavior of Truss 1 under symmetric loading condition (SLE).

Figure 7. Behaviour of the connection between the king-post and the tie beam under symmetric loading conditions.

Figure 7. Behaviour of the connection between the king-post and the tie beam under symmetric loading conditions.

Figure 8. Horizontal displacement recorded in the support under symmetric loading.

Under asymmetric loading conditions, the asymmetric behavior of the trusses, already pointed out, is emphasized. Channels A6 and A7 shows asymmetric displacement, Figure 9.

This asymmetric behavior of the trusses introduces bending stresses in the rafters and tie beam. Because of the rotational stiffness offered by the king-post/tie

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