Finite Element Modelling of RC Beams with CFRP Strengthened Web Openings

Web openings are commonly used in reinforced concrete (RC) beams to accommodate pipes, ducts, and utilities. The expected reduction in strength can be compensated by locally strengthening the beam opening with carbon-fiber-reinforced polymer (CFRP). In this paper, a robust nonlinear finite element model (FEM) is developed to simulate the behavior of RC beams with/without openings. The model can simulate the strengthening of the beam opening with CFRP sheets. The developed FEM is validated using seven simply supported RC beams that were previously tested under monotonic two concentrated loads. One specimen was considered as a control beam that did not have any openings, while the six other beams had a web opening with various dimensions and locations from support, two of them were strengthened with CFRP. The crack pattern and load-deflection relationship, from the FEM, were compared to those obtained from the experiments. The developed FEM was utilized to conduct a parametric study on 32 beams to investigate the behavior of RC beams with CFRP strengthened openings. The parametric study showed that the opening width did not significantly affect the load at failure. However, both the opening depth and distance from support had a clear effect on the failure load. Increasing the stirrups diameter from 8 mm to 10 mm increased the shear capacity of RC beams by 3∼16%. Also, it was concluded that strengthening the web opening with CFRP sheets increased the shear capacity by 1∼26% compared to similar beams without CFRP. The failure loads obtained from the proposed FEM were compared to those obtained from international design codes; the ACI 318-19 (2019), CSA A23.3-14 (2014), ACI 440.1R (2015) and CSA-S806 (2012). Differences between the FEM and predicted failure loads ranged between −30% to +50% for ACI 318-19 (2019) and −19% to +63% for CSA A23.3-14 (2014) for beams without CFRP. The differences became −18% to +54% for ACI 440.1R (2015) and +5% to +80% for CSA-S806 (2012) for beams with CFRP.