Concrete filled double skin circular tubes : a review

A review of the research conducted on the compressive strength of concrete filled double skin circular tubes (CFDSCT) columns is conducted. Variables of the CFDSCT considered in this review include the concrete strength, steel strength, inner and outer tube diameter, steel thickness and length of the stub columns. Test results show that the composite columns had compressive strengths of up to 41% higher than the sum of the individual strengths of the section. All the outer tubes of these composite columns by failed local buckling. A review of the design equations proposed are presented and discussed. The paper also identifies gaps for further research for these types of columns

Behaviour of grout-filled double-skin tubular steel stub-columns: Numerical modelling and design considerations

The use of grout-filled double-skin tubular (GFDST) sections in civil, bridge and offshore engineering applications is rapidly increasing. The design of such composite members is not directly covered by design codes, despite recent research studies investigating their performance, proposing design equations or modifying existing codified methods. Aiming to extend the available pool of structural performance data, the current study reports the results of an extensive numerical investigation on GFDST stub-columns. Finite element (FE) models, are developed and validated against published test data. A parametric investigation is conducted to evaluate the effect of key parameters, including cross-sectional slenderness, hollow ratio and the effect of concrete infill on the capacity of GFDST members. The numerically obtained load capacities along with collated test data are utilised to assess the applicability of design strength predictions based on European Code (EC4), the American Concrete Institute (ACI) and the analytical models proposed by Han et al. and Yu et al. Overall, the modified Yu et al. provided strength predictions with low scatter, whereas ACI yielded overly conservative predictions particularly for smaller hollow ratios

Performance of concrete-filled double-skin circular tubes in compression

Abstract: CFDSCT columns are structural members that are filled with concrete and supported by circular steel tubes on the interior and exterior. These steel tubes serve as formwork and hence these members are economical and quicker to construct when compared to conventional concrete reinforced columns. They are also efficient because they take advantage of the high compressive strength of the concrete and high tensile strength of steel. Despite the fact that much research is ongoing internationally in the field of CFDSCTs, no experimental tests have been conducted on intermediate and slender CFDSCTs. Current research has been focused on short CFDSCT columns and varying amounts of confinement have been found in these tests. Design codes also do not cover CFDSCTs. In order to gain a more comprehensive understanding of the behaviour of CFSDSCTs, experimental tests were conducted on 32 concrete-filled double-skin circular tube (CFDSCT) columns. The CFDSCT columns were loaded in axial compression till failure. The parameters that were varied were the lengths and diameters of the outer steel tubes, and the strength of the outer steel tubes. The lengths ranged from 1 and 2.5 m, in half a metre increments. The CFDSCTs of one metre lengths, failed by yielding of the steel tubes. All the other CFDSCTs failed by overall buckling due to their large slenderness. Using the same philosophy as SANS 10162-1 and EC4, new formulas were developed to predict the results of the strengths of the CFDSCTs. The new formulas are in a similar format to SANS 10162-1 and EC4, and are 5% and 6% more conservative than the tests results, respectively. The ratio of the predicted results over the test results versus the slenderness was plotted and shows that the results were predicted fairly well.M.Ing. (Civil Engineering

Ultra-high Strength Concrete on Eccentrically Loaded Slender Circular Concrete-filled Dual Steel Columns

[EN] This paper presents an experimental study which was undertaken to investigate the effect of ultra-high strength concrete (UHSC) on the mechanical response of concrete-filled dual steel tubular columns (CFDST) subjected to eccentric loads. This campaign is a continuation of a previous program on axially loaded members and consists in testing 12 CFDST specimens and two concrete-filled tubular (CFST) columns which serve as references. The location of the dual-grade concretes (outer ring and inner core) and the steel thicknesses configuration were the parameters analysed. Therefore, in this program, two series can be distinguished: 6 columns with normal strength concrete in their outer rings and, conversely, 6 with ultra-high strength concrete. In addition, two different steel tube thicknesses configurations were considered: columns with thin outer steel tube and thick steel tube (thin-thick); and the opposite pattern (thick-thin). Moreover, the experiments on the CFST columns of reference served to investigate the effect of the extra inner steel tube and its filling in CFDST columns. Since the number of campaigns on eccentrically loaded slender CFDST columns is scarce, the results presented in this work become particularly relevant. The analysis of the results revealed that, for both series, the response of the specimens showed similar trend but the effect of UHSC differed from that observed for axially loaded columns. Finally, the experimental data were contrasted to the predictions given by Eurocode 4 for the design of composite columns resulting, in general, in slightly unsafe predictions.The authors would like to express their sincere gratitude to both the Spanish Ministry of Economy and Competitiveness and to the European Community through the FEDER funds for the help provided to finance the project BIA2012-33144.Ibáñez Usach, C.; Romero, ML.; Espinós Capilla, A.; Portolés, JM.; Albero Gabarda, V. (2017). Ultra-high Strength Concrete on Eccentrically Loaded Slender Circular Concrete-filled Dual Steel Columns. Structures. 12:64-74. https://doi.org/10.1016/j.istruc.2017.07.005S64741

Experimental and numerical study on the behaviour of CFDST columns subjected to close-in blast loading

The dynamic behaviour of concrete-filled double-skin steel tube (CFDST) columns under close-in blast loading was investigated using experimental and numerical approaches in the present study. Field test results on three large scale CFDST column specimens subjected to different blast loading conditions were presented. High-fidelity physics-based numerical models were developed utilizing the Arbitrary-Lagrangian-Eulerian (ALE) formulation coupled with Fluid-Structure Interaction (FSI) algorithm available in the nonlinear dynamic analysis program LS-DYNA. The numerical models were verified with the experiment results and were then used to investigate the dynamic response, damage mechanism and energy absorption capacity of CFDST columns subjected to close-in explosions. The results indicated that the typical failure pattern of CFDST columns under close-in blast loading is dominated by localized denting of the cross-section directly facing the explosion with minor global deformation of the column. The concrete core suffers severe damage while the steel tubes remain almost undamaged except in a limited region in the vicinity of the detonation. The energy absorbed by each part of the CFDST columns demonstrates that the severe plastic damage of concrete core plays a significant role in the energy absorption mechanism of CFDST columns under blast loading from close-in explosion. The primary function of the steel tubes is to provide confinement to the concrete core therefore prevent concrete spall damage. In addition, the influence of explosive charge setups and level of axial loads on the structural response and damage was assessed and discussed