PSI - Issue 78

Agnese Natali et al. / Procedia Structural Integrity 78 (2026) 2015–2021

2018

for additional data collection. During reloading, a higher stiffness was observed compared to the first loading phase, due to slip effects in bolted connections that occurred right during the first loading phase.

Fig. 4. Force-displacement curve of the composite configuration.

Notably, the test revealed significant relative rotation between the composite beams and the CHS column. This resulted in tearing at the lower weld of the left beam flange, while no damage was observed in the upper continuity plate. Cracking in the slab was concentrated near the column, particularly on the side of the beam subjected to hogging bending. Cracks were documented at specific top displacement intervals: initial transverse cracks formed around 57 mm; additional diagonal and transverse cracks emerged at ~100 mm; full slab-column separation and concrete crushing were evident around 150 mm. These damage states were mapped on the slab surface in Fig. 5 and correlated with the force-displacement curve in Fig. 4.

Fig. 5. Highlight of crack formation and propagation on top of concrete slab.

Strain gauge data from slab reinforcement bars confirmed the development of a strut-and-tie mechanism. The transverse bars near the column experienced high tension, especially on the side of the beam subjected to a sagging bending moment. Longitudinal bars crossing cracked areas showed that tension also increased after the formation of cracks, while those away from the cracks remained nearly undeformed.