PSI - Issue 44

Agnese Natali et al. / Procedia Structural Integrity 44 (2023) 2326–2333 Agnese Natali, Francesco Morelli / Structural Integrity Procedia 00 (2022) 000–000

2332

7

3.2. Outcomes from the AD HOC TESTS The same C section is also tested in the AD HOC configuration. Fig. 8 shows the force – displacement curves resulting from the monotonic load tests and the first cyclic test (standard loading protocol – similar results are obtained for the second loading protocol). Under tensile load, plastic ovalization is mainly developed in correspondence to the upper connection. Fig. 9a shows the final aspect of the diagonal end sections tested under monotonic tensile load, with complete tearing of the end plate of the diagonal in the upper node. No damage is detected in the other elements. Under compression load, the profile buckles before detecting significative deformations in the connections. Fig. 9b shows the final aspect of the diagonal end sections tested under monotonic compression load: although some deformation is detected in both lower and upper node, with some local buckling of the plate between the outer and inner holes, the profiles buckles. This outcome is relevant for the POS strategy, according to which buckling of the diagonal should not occur and be anticipated by reaching the bearing resistance of the connection. No damage can be observed in the upright pieces or bolts. Under cyclic load, the behaviour in tension is driven by the plastic deformation due to bearing in correspondence to the node, while the behaviour in compression in driven by the buckling of the element. A close correspondence appears between the behaviour under cyclic and monotonic load, with very limited reduction of resistance in tension. Pinching behaviour can be observed from the curves, with zero force in the part of the cycles where bolts are in loose contact with the hole borders: the more the hole is ovalized and plastic deformation increased, the larger is the zero contact/force zone. Energy dissipation is very similar to the one under monotonic load, with an increase only when the displacement demand increases, but with no increment for the same displacement demand. The connections experience large plastic deformation in tension, and limited in compression, due to the buckling of the diagonal (which in any case is anticipated by ovalization of the connection). Almost complete tearing can be observed in the lower node (Fig. 9b). No damage is detected in upright pieces or bolts.

Fig. 8. Force – displacement curves for the monotonic tensile test (MT), monotonic compression test (MC), and cyclic test 1 (standard loading protocol - SP). Force is the load acting on the diagonal, displacement is measured in correspondence to the upper contrast beam.

a

b

c

Fig. 9. View of the lower (left) and upper (right) sides of the diagonal after: a) monotonic tension test, and b) monotonic compression test; and c) cyclic test 1 (standard protocol).