PSI - Issue 64

Tahreer M. Fayyad et al. / Procedia Structural Integrity 64 (2024) 708–715 Tahreer M. Fayyad / Structural Integrity Procedia 00 (2019) 000–000

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2.4. Testing In order to obtain stable loading conditions, all the tests were performed under displacement control. Consequently, the load was applied as a function of the mid span deflection. This allowed a gradual increase in the mid span deflection and crack mouth opening, as well as a steady decrease of the load in the post-peak regime. The Zwick machine was set to a loading rate of 0.01 mm/sec (0.6 mm/min). During the test, the images were continuously captured every 10 seconds. The Zwick machine and the StrainMaster were interconnected ensuring that the collected images were synchronised with the loading values from the data logging system. Before commencing the damage testing, vibration tests were conducted on specimens from both series in their undamaged state. The first series underwent continuous loading during three-point bending tests. The results of the first series were used to determine the stopping points for the next series' tests and to conduct vibration testing on the beams in damaged state. Concrete compressive test cubes were crushed on the same day as the testing to accurately define the concrete’s actual strength. 3. Results and Discussion All the specimens exhibited a ductile behaviour and failed due to central crack propagating through the middle of the beam. The load-displacement results of the first series are shown in Fig. 4. All the beams exhibited a ductile behaviour and stain softening after reaching the peak load. The effect of the concrete strength and the effect of reinforcement ratio can be noticed in the Fig. 4. The beams with the same reinforcement ratio showed a similar behaviour but the higher concrete strength (C60_0.3_1 and C60_0.5_1) got a higher ultimate strength comparing with the beams cast from lower concrete strength (C45_0.3_1 and C45_0.5_1 respectively). The difference was very small because the cube compressive strength of the C45 was 49 MPa and the cube compressive strength of the C60 was 54 MPa leading to a small difference in the concrete strength. It is of note that the behaviour of the beams is similar before the steel yields; however, after yielding the beams with lower reinforcement ratio exhibited a more flat strain hardening which is connected with crack opening.

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Fig. 4. Load-displacement results of the first series StrainMaster DIC is meant for the optical examination of material strain. The software utilizes image-tracking algorithms to process images through the DIC system. StrainMaster is compatible with the raw data that was collected and generated by LaVision software DaVis 10.2 that was used during testing. The DIC analysis was performed for all the beams after performing the required scaling with a subset size of 19 pixels. A full displacement profiles were gained for the process of crack propagation (Fig. 5(a)).