Steel beam upstands as a strengthening approach for doubly symmetric I-shaped sections

Abstract

Sustainable design with minimization of carbon footprint requires the consideration of opportunities for optimal material use as well as for re-use and repurposing existing steel members. For steel beams susceptible to lateral-torsional buckling one such opportunity is the use of flange upstands to strengthen existing beams if a change in use requires that the member have more bending strength or stiffness. Flange upstands employed in the study convert a doubly symmetric section into a monosymmetric section. The monosymmetry effect is studied and reveals the existence of a range of upstand heights that can be exploited for increased critical elastic buckling moment. Beyond a given upstand height, the effect of monosymmetry then reduces the critical elastic buckling moment. It is shown that the critical upstand height relates closely to the point at which the monosymmetric section attains a coincident shear center and centroid, a property typically associated with doubly symmetric sections. Elastic and elastic-plastic analysis approaches are used to demonstrate how the stiffeners influence flexural capacity and stiffness properties of the beams. Application of a desirable range of upstand heights for strengthening I-shaped doubly symmetric beams is demonstrated with an example.