PSI - Issue 78

Sabatino Di Benedetto et al. / Procedia Structural Integrity 78 (2026) 1697–1704

1701

3. Experimental activity An experimental investigation was conceived with the aim of acquiring meaningful and representative data on the mechanical behaviour of the steel – concrete interface under axial loading conditions. This would allow for a more detailed understanding of the stress transfer mechanisms between the two materials and enable the evaluation of possible variations in the structural response due to the presence of a construction joint. Specifically, the experimental activity included one test setup conducted at the Strength Laboratory of the University of Salerno. This test was designed and executed with the objective of providing data for the calibration of a numerical model capable of accurately reproducing the bonding behaviour of steel micropiles embedded in concrete under tensile loads. The plinth was constructed with a height equal to 80 cm, and a plan dimension of approximately 85×85 cm, inspired on a real footing taken as an example. Specifically, the considered footing is the footing installed at the base of a noise barrier structure of a road. The reinforcement used in the in-situ structural elements was adapted to the dimensions of the footing, while keeping unchanged both the spacing and the diameters of the reinforcement bars used on site, thus ensuring effective anchorage of the bars within the footing. As a result, the reinforcement implemented in the laboratory specimen was identical in to that of the cross-section of the foundation. As for the Circular Hollow Section micropile, it was made of S275 steel with a diameter of 137 mm, a thickness of 8 mm, and a total length of approximately 1.20 m. During installation, it was embedded 50 cm into the concrete casting, while the remaining portion was inserted into a predrilled hole in the ground in order to replicate the construction procedures used on site, by casting the footing from top to bottom. The specimen was carried out to investigate the bond between the steel micropile and the concrete in the presence of a construction joint, using a concrete sample representative of the foundation slab at the head of the micropiles to which the noise barrier panels are anchored. Specifically, two classes of concrete (C32/40 and C50/60) were used according to the heights of the plinth depicted in Fig. 2: 30 cm of the plinth height are made of C50/60 concrete, while the remaining 50 cm are constructed using C32/40 concrete. After the curing of concrete, the specimen was tested in the laboratory using a servo-hydraulic testing machine, equipped with a load cell, with a maximum capacity of 600 kN. The steel micropile was connected to the testing machine by means of a steel plate, properly welded to the head of the micropile and linked to the machine through a metal pin. The test was conducted under displacement control, with acquisition of the applied load and a displacement rate imposed on the actuator equal to 1.25 mm/min. The test output is represented by the force – displacement graph shown in Fig. 2. The force at which the sliding of the tube occurs corresponds to a value equal to 330 kN.

Fig. 2. Tested specimen (left) and results of the experimental test expressed according to the force-displacement curve (right)