Axial–flexure–shear strength interaction of solid and hollow reinforced concrete rectangular members

Abstract The paper provides an analytical method to estimate the combined axial force P – shear force V – bending moment M capacity of solid and hollow reinforced concrete sections including effects of confinement. A fiber model is employed to perform the parametric study to understand the effects of section size and amounts of longitudinal and transverse reinforcements on the strength interaction. The confined P–M envelope can be smaller than the unconfined P–M envelope; the reduction is significant if the concrete cover is more than 15% of the member dimension. In hollow sections, the reduction in strength is independent of absolute section size and is majorly influenced by the percentage opening. The maximum shear force capacity occurs at axial load demand lesser than the uniaxial capacity; it varies with increase in bending moment but remains constant at zero axial load. Design recommendations are made along with a design P–V–M interaction surface.