Experimental and numerical assessment of deflections in circular reinforced concrete beams

Methods for calculating deflections (at service loads) prescribed in codes such as EC2 and ACI 318 are largely based on semi-empirical methods validated for beams with rectangular cross sections. The applicability of these methods to beams with circular cross section is validated in this paper using experimental studies on eight circular beams with different grades of concrete and different percentages of reinforcing steel. Similar beams with square cross section have also been studied for comparison and it is found that the code estimates have more-or-less the same degree of conservatism for square and circular beams. The complete load-deflection behavior generated by the test specimens could also be simulated numerically using a layered approach, considering material nonlinearity in concrete and steel rebar. Using the proposed procedure, the influences of percentage of reinforcing steel and axial compression on the load-deflection behavior have also been studied. This study shows that the postcracking stiffness increases and ductility decreases with increase percentage of reinforcing steel. The circular beams are found to have less strength and ductility when compared to square beams (with the same area of cross section) owing to differences in distribution of steel rebar.