PSI - Issue 64

Carmine Lima et al. / Procedia Structural Integrity 64 (2024) 849–856 Lima et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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For the three tests C25/30 characterized by a slab thickness of 150 mm, a maximum load ranging between 870 kN and 916 kN were recorded (see also Fig. 5a). The failure occurred at about 20 mm of slip between the concrete slab and steel profile. The observed behavior was almost symmetric on the two sides of the slab as confirmed by means of the LVDTs positioned on all alignments in correspondence with the eight connectors. The observed failure (see also Fig. 6a) can be defined as ductile as was observed an area around the perimeter of connectors where slab concrete was undergone high concentration of stress and therefore was deteriorated, allowing high deformation of connectors with consequent shrinkage of the same and final failure due to shear stress in the section immediately upstream of the weld which remained attached to the steel beam.

a c Fig. 6 Push-out test failure mode for (a) C25/30 samples; (b) C60/75 samples and (c) UHP-FRC samples b

On the other hand, the three tests performed on C60/75 samples, characterized by a 120 mm slab thickness exhibited a maximum strength ranging between 1000 kN and 1100 kN and the failure occurred at differential slip between slab and beam equal about to 15 mm (see also Fig. 5b). Also in this case, the response behavior was almost symmetrical on the two sides as confirmed by the displacement control by means of the LVDTs. The failure mechanism in this case can be defined mixed as it can be observed that some connectors had ductile failure with constriction similar to C25/30 samples, while other ones suffered of detachment of the weld from the flange (see also Fig. 6b). As a matter of the principle, it was observed that the ductile rupture of the connectors occurred on the side where the concrete slab offered the minimum covering and therefore the strength offered by the concrete cone was lower, while the immediate detachment of the weld took place on the side with greater contrast of the slab, where the high strength of the concrete allowed a more constant distribution of stresses over the length of the connector, shifting the failure from a flexural mechanism to a shear one. In those points, therefore, the failure was due to detachment of the weld at the connection with the beam at the cutting section between slab and beam. Finally, the three tests performed on the UHP-FRC slab samples, characterized by a 75 mm slab thickness reached an ultimate strength variable between 733 kN and 818 kN. In this case, the failure occurred at differential slip between slab and beam equal to 6mm to 8 mm (see also Fig. 5c).Unlike the previous C25/30 and C60/75 testes, the observed failure was characterized by a generalized detachment of all connectors from the beam at the section of the weld (see also Fig. 6c). Specifically, it was found that the high strength of UHPC prevented the connector deformation, and the behavior was completely governed by shear mechanisms in the cutting section between the slab and the steel beam resulting in the detachment of the weld. 3.2. Theoretical simulation of the push-out test results In order to further analyze the obtained results and understand the mechanisms observed in the experimental phases, a data processing was also carried out in order to derive generalized laws such as the one considered by Ollgaard et al. (1971) which contemplate the phenomenon observed for high performance concretes up to at the point of maximum strength. Specifically, the force-displacement relationship was determined with reference to the following law: = ∙ (1− − ∙ ) (4)