Innovative One‐way Connections between I‐beams and CHS columns

Abstract

Very good resistance against high axial forces and bending in all directions [1], lightweight structures [2], lesser requirement of fire protection materials [3] and excellent aesthetics have emphasized upon the encouraging potential offered by CHS columns and their advantages compared to equivalent H-sections. They have also proved to be the best shape for elements under wind-, water-or wave-loading scenarios [4]. Additionally, as filling the hollow sections with concrete provides a simple way to achieve a composite behaviour (and add strength and stiffness), it also offers an extra advantage towards fire resistance. Therefore, over the past few decades, researches have tried to implement such hollow sections in structures to improve their overall resistance by exploiting the significant advantages in offer. Several different types of open-to-hollow section joints have been developed in the current industry and CIDECT has provided significant understanding [5] regarding their strength, fire protection, wind loading, composite construction and their static and fatigue behaviour based on successful identification of the force-transfer mechanism. The current Eurocode rules regarding their design and practical implementation of such structural hollow section connections are largely based on the foretold CIDECT research works. However, in today's construction industry, the I-beam-to-CHS column connections are constructed either by directly welding the beams to the CHS column wall or by using diaphragm connections (both referred to as "conventional CHS connections" in this contribution). While in the first technique, concentrated stresses develop on the CHS wall leading to its local distortions , the second technique demands a substantial number of gusset plates and/or stiffeners, which have unfortunately limited their preference from a designer's perspective. The complex detailing requirements of these joints are noticed to compromise around 1/4 th of the total structural weight, increase constructional expenses and slow down the fabrication process. Several studies have suggested that the additional stiffeners and gusset plates can cause both economic as well as practical difficulties [6] during the fabrication process and can also spoil the aesthetics. They have also shown significant vulnerability towards extreme loads such as fatigue or seismic loading ORIGINAL ARTICLE Abstract Although stiffeners and gusset plates are often used in conventional I-beam-to-CHS-column connections for an efficient load transfer, they usually result in high welding quantities. Directly welding the beams to the column exposes the beams to premature flange fractures and the columns to severe local distortions. Both approaches therefore hinder the use of such connections in the industry. However, if designed efficiently, the CHS connections can offer a viable solution with an excellent structural behavior in tension, compression and bending in all directions. In this context, the present contribution proposes two new moment resisting one-way connection configurations with I-beams or steel plates passing through the CHS column, developed within the European research project LASTTS, with the aim of simplifying the fabrication process and increasing the structural performance of such joints with an effective reduction of the foretold drawbacks. The "passing-through" system is developed using a laser cut & weld technology and avoids the localized damages, premature flange failures as well as the excessive usage of stiffening plates required by the conventional CHS connections. These connections are first designed based on a recently developed code-like procedure and are then assessed through nonlin-ear finite element models-primarily calibrated on experimental results to validate the modelling assumptions-in order to characterize the influence of the different parameters of the joints.