Critical Inclination of Compression Struts in Concrete Beams

In design for shear forces with stress fields, three failure criteria are usually considered: failure of the chords, of the compression struts, and of the stirrups. Bond failure along the chords is usually not explicitly checked. The effective concrete strength in the struts and the bond strength along the chord are combined with the stresses in the stirrups to determine critical inclinations of the compression struts. An expression for the effective concrete strength is proposed considering compression softening, while the proposed expression for bond strength considers concrete strength, bar roughness, and the beneficial effect of lateral pressure exerted by the stirrup forces. Parametric studies are discussed and conclusions are drawn on the governing failure criteria and the critical inclination of the compression struts in the ultimate limit state. An Appendix summarizes the calibration of the proposal for the effective concrete compressive strength and compares it to other proposals from the literature.