PSI - Issue 78

Martina Sciomenta et al. / Procedia Structural Integrity 78 (2026) 253–260

256

3.2. Test setup Tests were carried out at the laboratory of the Department of Civil, Construction-Architectural and Environmental Engineering (DICEAA) of the University of L’Aquila. It consisted of push-out tests carried out by applying the loading procedure of EN 26891 (British Standards Institute, 2001) on each specimen. Firstly, according to the Standard, an estimated maximum load est F was determined for each of the three series. Then, the load was applied up to est 0.4 F and maintained for 30 s. The load was then reduced to est 0.1 F and maintained for 30 s. Thereafter the load was increased until the slip of 30 mm was reached in accordance with the EN 12512 (European Committee for Standardization (CEN), 2005) but the setup was designed to reach a maximum displacement of 30 mm. The load was introduced by a Controls Uniflex 300 flexural frame (300 kN cap.) through a vertical rod hydraulically controlled (Fig. 1a) and measured by a high precision strain gauge load cell. A constant slip rate of 0.06 mm/s was adopted (it was kept in the range between 0.02 mm/s and 0.2 mm/s recommended by the Eurocode 5 (CEN, 2011)). The specimen is equipped with two 100 mm travel LVDTs displacement transducers to measure the vertical slip between the central element and the sides (Fig. 1a). Furthermore, the cross-head displacement was recorded with another 100 mm LVDT. The recording was done continuously with a frequency rate of 20 Hz via a multi-channel data recording and control device (Controls Automax Multitest).

Fig. 1. Experimental setup: a) Specimen and instrumentation; b) force-displacement curves for three specimens belonging to each series and VGZ screws

3.3. Calculation methods The standards adopted as reference for the evaluation of the connection performance parameters (yield point, secant stiffness, ultimate conditions and static ductility) were EN 12512 (CEN, 2011) and EN 26891 (CEN (European Committee for Standardization), 1991). The slip modulus s K of the connections (corresponding to the slip modulus ser K provided by EN 1995-1-1 (CEN, 2011)) was calculated by means of the following equation:

0.4 F ' max - 0.1 F ' max v 0.4 - v 0.1

(1)

K s =

Where v 0.1 and v 0.4 are the connection slips (evaluated for each specimen) corresponding to the load levels of 0.1 F ' max and 0.4 F ' max respectively; F ' max is the mean value of the maximum load recorded for each specimen of the same series: F ' max,i (consistently with EN 26891 (CEN (European Committee for Standardization), 1991) excluding