Behaviour and design of high strength steel structural elements and frames

Abstract

The behaviour and design of high strength steel (HSS) welded I-section structural elements and frames subjected to different loading configurations are studied in this thesis. The thesis is intended to evaluate and improve the current Eurocode 3 (EC3) design provisions for HSS structures, and to facilitate the deformation-based advanced design of HSS welded I-section structural elements by means of second-order inelastic analysis with strain limits. Normal strength steel (NSS) counterparts are also studied for comparison purposes.

A novel residual stress model for welded I-sections made of varying steel grades has been firstly developed and calibrated based on a large data pool of residual stress measurements collected from literature. This model was employed in subsequent numerical studies throughout the thesis. A comprehensive experimental programme on HSS welded I-section structural elements and frames was then carefully conducted. At the member level, a total of six three-point bending tests and five column flexural buckling tests were performed, while at the system-level, eight fixed-base single-storey HSS frames were tested in-plane under different combinations of horizontal and vertical loads. Digital image correlation (DIC) was used in the experimental programme to trace the spread of plasticity at critical cross-sections as well as the full-range deformation-field of the frame specimens. The test results, together with existing test data on HSS welded I-section members collected from literature, were used for the validation of finite element (FE) models. Numerical parametric studies were then carried out using the validated FE models to generate extensive structural performance data. Based on the experimental and numerical data, modified EC3 design rules for individual members under compression and combined loading were developed, showing improved levels of accuracy and consistency relative to the current EC3 design rules. In addition, the test results of the frames highlighted the potential for extending plastic design to HSS structures, which is currently prohibited in EC3. Finally, an advanced deformation-based design method by second-order inelastic analysis with strain limits was extended to HSS welded I-section structural members and has been shown to provide superior resistance predictions compared with the current EC3 design methods.