PSI - Issue 64

Andrea Armonico et al. / Procedia Structural Integrity 64 (2024) 604–611 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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research, a predictive model for calculating the maximum crack amplitude has been proposed and validated based on an experimental study A. Armonico et al . (2024). In order to validate the previous study, new experimental tests have been done on large scale beams. Beams with a T-section has been therefore studied. The response of these structures has been evaluated with respect to displacement and crack monitoring to evaluate the effectiveness of a monitoring system and compare the most innovative measurement methods with those typically used in laboratory tests. Four T beams has been tested, a first group of two beams under monotonic loading a second one of 3 beams under fatigue loading. All beams are cast in the same time. 1.1 Specimens Four T-shaped beams are tested in four-point bending. The size of the test specimens are shown in Figure 1. The concrete characteristic strength is 45 MPa and the geometry is given by figure 1. The composite strengthening system is made of two layers of 150 mm CFRP externally bonded with wet-lay up technics.

Figure 1: Strengthening layout used in T-shaped monotonically tested beam

2 Testing device The testing device is equipped with a hydraulic load actuator with a capacity of 500kN placed between the actuator and the steel frame a displacement measurer range of500 mm. The centered load was applied using a non-deformable steel beam that was simply supported, allowing a 4-point loading with a wheelbase equal to 1340 mm. The load cell is a Class I element with a standard output equal to 2mV/V. 2.1 Instrumentation The scope of the experimental campaign is to obtain an amount of data to study the effect of a structural strengthening provided using externally bonded CFRP sheets. The main objective is to measure the load-displacement evolution, to monitor the distributed strain along the FRP and the crack opening. Local Measurement of Displacement Displacement monitoring plays a significant role in diagnostics. During loading, displacement monitoring has high validity for the proper functioning of structures and the prediction of structural damage. The vertical displacement has been measured in the center of the beam with LVDT and the displacement is also monitor with digital image and structure by motion tool. Distributed Measurement of Displacement – Structure From Motion Laboratory tests allow an exhaustive knowledge of the geometry of the interested specimen. However, in real cases, displacement is an information that frequently cannot be accurately or safely acquired. In this scenario, a no-contact methodology that provides this information with a low level of geometric uncertainty is required. In the last years, Unmanned Aerial Vehicles (UAVs), also known as “Drones” (ENAC, 2014), are frequently used in civil engineering as a photogrammetry tool (Linder, 2009) able to detect complex geometries (Barrile et al., 2016; Chen et al., 2019; Kassotakis et al., 2021; Micelli and Cascardi, 2020;) with good accuracy (Elkhrachy, 2021; Ridolfi et al., 2017). At the same time, its potential to safely reach places not easily accessible make this tool very useful for mapping material decay (Biscarini et al., 2020; Stepinac and Gašparović, 2020). The procedure is based on analyzing an extensive photo set captured using a high-definition camera and post-processed in dedicated photogrammetry software. The computer analysis results in a points cloud containing GPS and RGB information, which can be used in several fields. The computer elaboration is performed by the Structure from Motion (SFM) algorithm (Faugeras et al., 2001). It employs