Flexural Behavior of Concrete-Filled Double-Skin Hexagonal Tubular Beams Using Finite Element Analysis

Abstract

The Concete-Filled Double Steel Tube (CFDST) members usually prepared from Concrete-Filled Steel Tube (CFST) member with additional internal steel tube, in order to increase strength and reduce the selfweight of the composite member. The  conventional square cross-sections are usually used for the CFDST beams. However, these sectionsthis square section are usually facing an outward buckling failure at the compression zone stress that usually occurred at the top flange of the CFDST beams under high bending loads. Additionally, using cross-section shapes with hexagonal and/or octagonal and/or decagonal could be to reduce the flatness width of the CFDST beam’s top flangem since they have smaller flatness width of their flanges than the square/rectangular tube’s cross section. Therefore, the aim of this research is to numerically study the flexural behavior of CFDST beam with hexagonal tubular cross-section under pure bending static loads by using finite element (FE) software named ABAQUS. First, the FE model was devloped and verified with the rated experimental tested results, then devloped and analysed additional models of hexagonal CFDST beams to investigate further parameters that not yet been investiated. Generally  a total of 19 hexagonal CFDST models were analysed for this project to investigate the influnce of varied tube’s thickness (t), steel yielding strength (fy), concrete strength (fcu), inner to outer tube’s dimensions ratio (Di/Do), and different inner tube’s cross-sections shape (hexagon, square and circle). The result of the paper showed that by using double steel tube for the beam, the failure due to outward buckling can be reduced significantly. The ultimate bending capacity of the hexagon CFDST models were increased with increases of their steel/concrete strength, tube’s thickness and Di/Do  ratio. For example, increasing the tube thickness from 1.5 mm 2.5 mm achieved an improvement in Mu values of about 41%. Meanwhile less improvement percentages was recorded when only the concrete strength increased. Furthermore, there are no much improvements have been recorded in the model’s bending capacity when used square or circle shape of inner tube’s cross-section the than the hexagonal shape. The energy absorption of the hexagon CFDST model have been improved according to the improvement of their loading strength capacities