PSI - Issue 44

Agnese Natali et al. / Procedia Structural Integrity 44 (2023) 2334–2341 Agnese Natali, Francesco Morelli / Structural Integrity Procedia 00 (2022) 000–000

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Fig. 3. Test set up.

With regard to the monotonic tensile tests (Fig. 4), tensile resistance is the same for all the layouts (as expected, the cross-section in correspondence of the reduced part is the same, see sec. B-B in Table 1). The failure mode for all the layouts is consists in the yielding and final fracture of the brace in the reduced section which is the nearest to connection (Fig. 4b). Most of the deformations seems to be placed in right in correspondence of those sections. No sign of damage has been detected in correspondence of connection, neither at upright nor diagonal side. This may mean that the capacity design rules are properly defined to guarantee the over-resistance of the connection. Concerning monotonic compression tests, buckling resistance is comparable for all the layouts (Fig. 4a). Regarding the failure modes (Fig. 5), L1, L2 and L3 are characterized by global buckling (torsional-distortional mode) followed by local buckling of the reduced sections. Local buckling occurs with the increase of lateral deformations of the element due to global buckling, and mainly occurs in correspondence of the reduced sections in the middle-length of the element – which is indeed mainly affected by the deformations due to the global buckling mode. The L4 layout is characterized by immediate local buckling. This may occur due to connected factors: the length of each reduced section is the highest, so the slenderness of each segment of reduced part is higher; the number of the reduced sections is reduced, with a high and localized change of stiffness along the length of the element. For cyclic tests (Fig. 6 and Fig. 7) the behaviour is characterised by: global, followed by local buckling of the brace in the region containing the reduced sections; consequent fracture of the brace in the reduced section which experienced local buckling or in the one closest to the connection. Indeed, the consequent load-unloading cycles may induce little cracks formation in the locally buckled zone, which drives failure under tension in the so damaged reduced section. In any case, no damage in connection is detected.

a

b

L1

L2

L3

L4

Fig. 4. (a) Load-displacement curves for the 4 layouts from the monotonic tests; (b) failure modes under tensile load.