At the IESL NSW Chapter YED 2019, Nilakshi presented her PhD thesis work. Nilakshi graduated from the University of Moratuwa in 2014, attaining her bachelor’s degree in Civil Engineering with First Class Honours. Shortly after completing her studies, she worked as a lecturer at the University of Moratuwa for one year. She then pursed her PhD in Structural Engineering at Queensland University of Technology in 2018. Currently, she is working as a graduate engineer at SMEC.

The use of cold-formed steel members has increased rapidly due to the benefits they offer when compared to hot-rolled steel members. Most of the open cold-formed steel sections are used in short span applications. However, since these open cold-formed steel sections are susceptible to unfavourable buckling modes, Hollow Flange Steel Plate Girder (HFSPG) formed by welding industrially available cold-formed rectangular hollow sections (RHS) as flanges to a web plate were introduced to increase the structural efficiency of steel sections.

In this research, experimental studies and a detailed parametric study were conducted on fully laterally restrained HFSPGs to understand their flexural behaviour involving local buckling of flange and/or web elements and determine their section moment capacities.

Comparison of experimental capacities with the section moment capacities predicted by the currently available design equations showed that they under-estimate the capacities of HFSPGs. Both experimental and numerical results were used to review Australian cold-formed and hot-rolled steel design standards and suitable recommendations were made.

A thorough finite element analysis based parametric study was conducted on the member moment capacities of medium/long span, laterally unrestrained HFSPGs subject to lateral distortional, lateral torsional and local-global interacting buckling failures. Currently available design equations for global and interaction buckling were studied and suitable recommendations were provided.

A brief comparison on the moment capacity per unit area of steel between the proposed HFSPGs and industrially available universal beams (UBs) demonstrated their efficiency in terms of cost and structural performance.