A low-cost digital image correlation system is used to visualize the formation and propagation of concrete cracking in a reinforced concrete beam. The system employed comprises an ordinary digital camera, a remote image recording controller (a smartphone) and a freely-available, open-source image correlation software package Ncorr. In this paper, the application of this system is demonstrated to obtain a comprehensive time-lapse of longitudinal strain fields developing before and after the onset of shear cracking, thus allowing one to appreciate the mechanisms of shear failure in the beam fully. It is shown that the longitudinal strain fields obtained from the DIC system are in a good agreement with hand-drawn crack maps and that obtained from nonlinear finite element analysis.
Three reinforced concrete beams, one with no shear reinforcement and two others with shear reinforcement ratios of 0.4% and 1.1%, were tested to investigate the influence of stirrup spacing on the mode of failure, overall strength and ductility. The results show that the beam reinforced with closely-spaced shear reinforcement failed in a ductile manner, whereas the other two beams with large stirrup spacing and no stirrup exhibited only a small measure of ductility and failed in a brittle manner. The importance of the provisions of maximum spacing is highlighted to ensure adequate anchorage for the stirrups and prevent a premature shear failure to occur. The application of a non-contact monitoring system employing the open source digital image correlation software Ncorr, an ordinary digital camera and a smartphone is demonstrated to provide a visualization of the cracking process throughout the load history.
This paper presents the application of a smeared fixed crack approach for nonlinear finite element analysis of shear-critical reinforced concrete beams. The experimental data was adopted from tests undertaken on twelve reinforced concrete beams by Bresler and Scordelis in 1963, and from duplicate tests undertaken by Vecchio and Shim in 2004. To this end, all beams were modeled in 3D using the software package ATENA-GiD. In the modeling, the nonlinear behaviors of the concrete were represented by fracture-plastic constitutive models, which were formulated within the smeared crack and crack/crush band approaches. The applicability of nonlinear analysis was demonstrated through accurate simulations of the full load-deflection responses, underlying mechanisms, crack patterns, and failure modes of all 24 beams. Detailed documentation of the results is presented to demonstrate the potential and practical value of nonlinear finite element analysis in providing an informed assessment of the safety and performance of reinforced concrete structures.
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