samples is graphically compared in Figure 10. Both specimens showed a failure characterized by a relative rotation between the boards and the beams (Figure 9), which involved the resistant mechanism of the moment of the couple provided by the pair of nails fastened at each beam.
The contribution of additional friction due to the tongue-and-grove connection during the relative slip at the board sides, influenced the better performance of the F2.M sample, in comparison with the F1.M one. By considering the conventional displacement of 30 mm as reference (UNI EN 12512), an increment of strength of 37% was found (Figure 10 and Table 2).
To analyze the results, by assuming that monotonic curves usually constitute the envelope of cyclic tests, for general timber structure built with metal fasteners, the UNI EN 12512 standard can be also used (Ceccotti et al. 2005).
The results are summarized in Table 2 and represented in Figure 10, where symbols are as follows: Fmax is the maximum load at 300 mm of displacement, Fy,est is the estimated load at yielding, Vy,est is the displacement correspondent to Fy est, and a and f are the angles of the slope of first and the second branch of the rectified curve, respectively, built as described in the box of Figure 10.
Also in terms of yielding load the F2.M sample performed better (Table 2), with an increment of 16% of the reference load. Moreover, it showed an initial
Figure 11. Comparison between in-plane floor and in-plane masonry wall deformations.
and an ultimate stiffness respectively 256% and 42% higher than those provided by F1.M.
A first estimation of the effect of the in-plane deformation of timber floors in the behaviour of masonry subjected to lateral actions can be also suggested, by considering a simplified case, represented by a masonry box having common dimensions of walls (4 m long and 3 m high, as in Figure 11) and covered by a plain floor. The estimation of drifts (5) normalized to the height of the wall (H) for masonry piers available from literature, led to the following values: 0,2 ^ 0,3% is the common range for the achievement of the first cracking, 0,4% for the shear cracking, 0,5 ^ 0,6% for the attainment of the maximum load, whereas 0,8% refers to the rocking behaviour (da Porto 2005, Tomazevic et al. 1996, Tomazevic & Lutman 1996, Tomazevic 1999).
By dividing the shear load by the span length (L = 4 m), and referring it to the ratio between the maximum relative floor shear displacement (5f) and the height of the wall (H = 3 m), see box in Figure 11, the previous limits become: 0,23% for first cracking; 0,30% for shear; 0,45% for maximum load; and 0,60% for rocking. It can be seen how the already poor capability in redistributing the horizontal seismic forces is worsened by the loss of shear stiffness in correspondence of the damage zone of masonry walls, when the redistribution needs are very desirable to assure a good seismic behaviour (Figure11).
Since the F2.M sample showed better performances than the F1.M one, its results will be considered for the calibration of a FE numerical model, as described in the following. Moreover, the boarding with tongue-and-groove connection will be used as basic type for the planned strengthened cases.
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