Numerical and experimental investigation on the shear resistance of functionally graded concrete (FGC) beams

Functionally graded concrete (FGC) is one of the most innovative materials combining two or more different concrete strength in building elements to optimise the construction cost. Studies focussing on the behaviour of graded concrete in flexural strength have been conducted by several researchers, whilst the research on the shear behaviour of FGC beam has not been initiated yet. Investigation on the shear behaviour of RC graded concrete beam is necessary due to the fabrication process could create a cold-joint that lower the load-carrying capacity of the element. Delamination possibly presents on the casted concrete layer during the loading and turns the beam behaviour more brittle in action. To further investigate these hypotheses, a laboratory testing and a numerical analysis are conducted in this research. Three pieces of RC beams with an identical dimension of 120 x 240 x 2200 mm are prepared with the concrete strength of 20 MPa, 30 MPa, and 20-30 MPa. The specimens are then tested using a four-point bending method in the age of 28 days. A set of strain gauge is mounted in stirrups surface to record the strain response on each incremental load. To validate the result, the specimens are also modelled in three-dimension using Abaqus. The results show that there is a significant difference in the stress-strain curve resulted from the experimental works and the model simulation. It is due to the limitation of programme to model the real interaction between the rebars and the concrete. In reality, the presence of aggregate interlocking, concrete contribution in withstanding compression stress, dowel effect improves the shear resistance of beams. Additionally, the interfacial failure did not present during the testing owing to the support of stirrups that confine the transition zone of concrete layers. (paper)