PSI - Issue 62

Gianluca Bottin et al. / Procedia Structural Integrity 62 (2024) 177–184 G. Bottin et al./ Structural Integrity Procedia 00 (2019) 000–000

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The most critical phase of the entire demolition process was lifting the girders (Fig. 5b), since the static scheme has been modified compared to the on-site conditions. The lifting points were defined so as not to induce cracking of the girders as well as the support points on the truck bed. 3.2. Design four points bending test set-up A preliminary literature review on bending test conducted on cast-in-place reinforced concrete beams was carried out in order to identify the critical issue of the experimental activities. Analyzing past testing experiences available in literature (e.g. Savino et al. 2023, Pape and Melchers 2013, Tonelli et al. 2023, Jiang et al. 2023), it was observed that tests on large spans girders require a detailed design of the setup with special attention to: the end constraint conditions; the magnitude/extent of the middle deflection; the horizontal displacements and the end rotations. The test scheme involves a simply supported condition with two load points applied symmetrically at a distance of 1.0m from the center line of the girder itself. A special test setup equipment was specifically designed to carry out the full scale four points bending test on girders extracted from the deck (Fig. 6).

Fig. 6. Schematic view of the designed experimental equipment.

The setup equipment, consists of two specifically designed steel reaction frames, each equipped with a 500 kN MTS servo-hydraulic actuator with a maximum stroke equal to 450 mm. In order to ensure a higher midspan deflection of the tested girder, four RC shimming elements are used at the base of the reaction frame pillars. These elements can be removed at a certain step of the test to increase the actuator stroke, permitting to reach a maximum midspan deflection of 900 mm. Two RC basements are used as support of the girder by means of two special constraint devices designed to reproduce the ideal static scheme of simple supported beam. In detail the hinge support is realized using a cylinder resting on a crescent-shaped hollow plate. The cylinder is anchored to the RC basement by means of a thick plate. The sliding support is realized with a double steel plate system. Sliding is allowed by the steel roller placed between the two plates. The maximum reachable horizontal sliding is equal to 400 mm while the maximum end rotation allowed by the device is equal to 12°. All the contact surfaces in the support devices that rotate or slide are machined to limit friction phenomena. The validation of the setup was carried out using an extensive FE numerical campaign focusing on the critical setup parameters such as: maximum force applicable by the actuators, maximum mid-span deflection and therefore stroke of actuators; maximum horizontal displacement of sliding support; maximum end rotation of supports.