Discussion of the paper 'Equivalent representations of beams with periodically variable cross-sections' by Tianxin Zheng and Tianjian Ji [Eng Struct 39 (2011)1569-1583]

摘要

The paper [1] studies equivalent representations of a beam with periodically variable cross-sections using a different but simple approach that utilizes the periodic characteristics of variable cross-sections. The equivalent method assumes a constant bending moment in each unit. The stepped beam is represented by a uniform beam based on the equivalence of the maximum rotation, maximum deflection and fundamental natural frequency of the two beams. The equivalent angles are obtained by matching equivalent and finite element analyses results of 221 variations of a stepped beam with misaligned neutral axes. In practice, the change in the location of the centroidal axis over the length of a stepped beam is ignored in structural analysis. However, because of the arching action of the non-prismatic members, the change or discontinuity of the centroidal axis produces axial forces under vertical loadings when the ends of the non-prismatic members are restrained. Although the study presented by authors is interesting, the discusser wants to mention the following observations.