Behaviour of nodal regions of reinforced concrete frames subjected to opening moments and proposals for their reinforcement

The strength and deformation capacity of concrete frames is typically governed by their nodal regions behaviour. This is particularly relevant for frame corners subjected to opening bending moments, where premature brittle failures may develop depending on the reinforcement arrangement. Although some previous investigations have shown a significant dependence of the nodal regions behaviour as a function of the corner angle (α, measured between frame axes), most research has concentrated on orthogonal corners (α = 90°). However, design recommendations obtained for orthogonal corners may not be directly applicable (neither optimal) for other corner angles, and particularly for larger corner angles. In this paper, the result of an experimental and theoretical investigation on frame corners with a corner angle (α = 125°) is presented. Sixteen tests were performed on 400-mm thickness specimens representative of actual frame corners subjected to opening bending moments. The experimental results are investigated by means of Elastic–Plastic Stress Fields and strut-and-tie models leading to a number of recommendations for their design in practice.