Jean-François Demonceau

Within the framework of Connect4C project, which is funded by the European Union and aims to develop innovative joints to enhance the reusability of steel structural elements in order to reduce the carbon footprint of the steel industry, the use of High-Strength Steel (HSS) is contemplated in the parts of the joints that should be protected against yielding, i.e. remain in the elastic domain, for the sake of reusability. Therefore, several test campaigns on components made of HSS S690 and S960 were carried on within this project, with the aim of extending the current design rules of Eurocode up to these grades. This paper focuses on the T-stub component and presents results from an experimental test campaign. Firstly, a review of the current normative design rules is proposed. Secondly, the test setup and the T-stub specimens to be tested are described. Then, the experimental test results are provided, analyzed and compared with the code predictions to evaluate their suitability for T-stubs made of HSS. Finally, in view of the characterization of both materials, the results of tensile coupon tests are also presented.

Local damages to key structural members may originate from different causes, including localised fires or earthquakes, and, as far as the affected area remains small and the damage is contained, the risk is reduced. However, if the structure does not have the capacity to absorb the damage and bridge over the lost components, progressive collapse may be initiated, with serious consequences for the life of the occupants and the costs of losses. Even if some inherent structural properties, like redundancy and ductility, bring a beneficial contribution to the resistance of structures subjected to such scenarios through the activation of alternate load paths, these properties can be affected when working under elevated temperatures, and thus structural integrity can be at risk. This paper investigates the cumulative effects of seismic events and elevated temperature on the progressive collapse resistance of two-way frames with steel and composite steel-concrete floors. Numerical models are calibrated against relevant test data. The results show that, even if fire protection is an effective way in increasing the resistance of structural components under elevated temperatures, the failure may propagate due to the attainment of the bearing capacity of the surrounding elements and connections that are still at ambient temperature. Also, the interaction between concrete slabs and steel beams may provide additional capacity to stop the progressive collapse.

This paper presents the results of 10 laboratory tests performed on closely spaced built-up members fabricated from hot-rolled angle sections. Such members are of special interest in the construction and reinforcement of steel lattice towers used for telecommunication or electrical transmission lines. The angle sections used in this study were star-battened with pinned support conditions. In particular, two configurations were studied: star-battened angles with equal sections (SBE) (composed of two chords with the same section), and star-battened angles with unequal sections (SBU) (composed of two chords with different sections). The influence of connection spacing along the members and different types of connections (fully preloaded bolts, partially preloaded bolts) were also studied. In addition, the important influence of geometric imperfections on failure load and failure mode were analyzed. In this paper, a numerical model is introduced after the laboratory tests are presented. The model was built in ANSYS version 18.2 and was validated based on the results obtained during the experimental campaign. The numerical results highlighted the sensitivity of failure modes to initial imperfections (out-of-straightness, load eccentricity). Last, the validated numerical model is thought to be used in a wider parametric study with the aim of developing new design recommendations.