Finite element modelling of concrete-filled double-skin steel stiffened tubular chord-to-SHS steel brace T-joints : behaviour and design

Abstract

Although concrete-filled double-skin stiffened steel tubular (CFDSST) members have been researched and applied in recent years, their use in truss T-joints has been lacking. This paper therefore examines the mechanical behaviour of CFDSST chord-to-hollow steel section (SHS) brace T-joints under axial brace loading. Detailed finite element models for CFDSST-to-SHS T-joints are firstly validated by assessing the modelling approaches against recent tests for CFDSST columns and other types of T-joints. The models are subsequently used to conduct parametric assessments into the influence of key factors, including the brace-to-chord width ratio, brace-to-chord thickness ratio, material strengths, hollow ratio of CFDSST chord, and the axial load applied on the chord. It is shown that the ultimate load capacity of the T-joints increases with the increase in the brace-to-chord width ratio as well as with higher steel tube and sandwiched concrete material strength, with a much less pronounced influence from the brace-to-chord thickness ratio. A new parameter representing the flexural stiffness-to-member length ratio of the chord to the brace is also introduced, based on which the failure modes are separated into two categories related to either the failure of the brace or of the chord. Using the detailed results and observations, existing methods for determining the bearing capacities of T-joints are evaluated, leading to the development of a new design approach. The proposed design procedure is shown to provide accurate predictions for CFDSST-to-SHS T-joints, indicating its suitability for use in practical application.