Enhanced Radial Stress Method (RSM) for cellular beams in EN 1993-1-13 to account for elasto-plastic behaviour

In cellular beams with circular openings, Vierendeel bending failure is caused by the local bending around the web openings in regions of high shear. In BS EN 1993-1-13, a Radial Stress Method (RSM) is presented, which is based either on the elastic resistance of the inclined T-sections around the openings or on their plastic bending resistance dependent on the section classification of the inclined T-section, which results in a step between elastic and plastic properties. The RSM method also fails to account for stress redistribution between the lower moment side and the higher moment side of openings. This study investigates the RSM for circular openings in a typical UB 457x152x52 beam, that is modelled and analysed using Abaqus. The RSM is extended to an elasto-plastic analysis of the inclined T-sections that gives a way of evaluating the development of the Vierendeel bending mechanism and may be used for slender webs. The elasto-plastic analysis around the openings subject to axial force, shear and bending is based on a multiple of the yield strain at the edge of the opening. This is compared to the non-linear FEA results, which show good agreement for the stress distribution around the openings on the lower moment and higher moment sides of the openings for all combinations of applied shear and moment. The results of the method are also compared to cellular beam tests results failing in Vierendeel bending. • FE models agree with the Radial Stress Method (RSM) in the elastic range • The Enhanced RSM considers elasto-plastic behaviour of the Tee sections • The Enhanced RSM tracks plasticity levels in inclined Tee sections with increasing shear. • Redistribution of moment in the Tees allows for an increase in the shear capacity. • The proposed method results in 78 % higher shear capacity than the elastic RSM.