•Rubberised concrete-filled double skin tubular (RuCFDST) columns are investigated.•Outer and inner square hollow sections are considered.•RuCFDST columns with different rubber ratios are tested.•The ...best design formula for the strengths of RuCFDST columns is found.
Waste tyres are among the largest and most problematic sources of waste in modern society due to their durability and high rate of dumping in landfills. One possible recycling alternative is to incorporate waste tyre rubber as an aggregate replacement in concrete to promote sustainability and utilise the elastic properties of rubber. Rubberised concrete has not reached its full potential because of the decrease in compressive strength and a lack of research to solve such challenge. Recent research suggests that combining rubberised concrete with confinement increases ductility and energy absorption. Specifically, confined rubberised concrete using single skin or double skin square hollow section tubular columns present higher ductility than those made of normal concrete. This study explored experimentally the use of rubberised concrete filled single skin and double skin steel tubes under concentric axial compression. The experimental investigation included changing the confinement of the outer and inner square hollow sections and explored how confinement affected normal concrete compared to rubberised concrete. Four variations of double skin steel tubes with a total of twelve 300 mm long columns of 0%, 15%, and 30% rubber replacement were created and tested concentrically. Three single skin short columns with 0%, 15%, and 30% rubber content were also tested and compared. The compressive strengths were determined theoretically and compared against those measured experimentally. An interesting spring back phenomenon occurred where the infill rubberised concrete moved upwards after testing due to the large confinement of the core and elasticity of the rubber. This study examined the use of rubberised concrete filled double skin steel tubular columns as a promising construction technique for applications such as columns in buildings located in seismic active zones, security bollards and flexible road side barriers.
•The shear strength of BGCWs should consider the realistic initial imperfection.•The strength proposed with n=0.6 cannot be used over the full range of behavior.•A modified shear capacity of BGCWs ...based on Sause and Braxtan formula is presented.•Stocky corrugated webs cannot practically reach the yield shear strength.
The current paper focuses on the shear strength of bridge girders with corrugated webs (BGCWs) using the realistic initial imperfection amplitudes. Firstly, the results of full-scale experimentally tested BGCWs, available in literature, are used to check the validity of the available design shear strengths. Secondly, they are checked using the same equations utilizing the interactive shear buckling strength formula, recently, proposed by the current authors to account for the realistic support condition at the juncture between the web and flanges which was found to be nearly fixed. However, the comparison indicated that the available design shear strengths in the literature are conservative and need to be improved. Hence, the ABAQUS software is used to construct a nonlinear finite element (FE) analysis, including geometric and material nonlinearities, on full-scale BGCWs failing by shear. To ensure the accuracy of the FE models, the models are verified using the available experimental results provided by other researchers. The available design shear strength formulae were in addition compared with the FE shear strengths of the corrugated webs. However, among the strengths using the proposed interactive shear buckling strength formula, the one adopting Sause and Braxtan (2011) 7 equation was found to be the most suitable. It was as well found that stocky corrugated webs cannot practically reach the yield shear strength. At the end, an illustrative example for the calculation of the shear strength of BGCWs using the currently proposed formula is provided.
•The corrugated web plate segments with fixed junctures need to satisfy that b/hw⩽0.2.•1st-order interactive buckling strength is unconservative for fixed juncture webs.•A new interactive shear ...buckling strength formula is proposed for fixed juncture.•It is found that the support condition at the juncture is nearly fixed for tf/tw⩾3.0.•A proposed interactive shear buckling strength formula using (n=0.6) should be used.
In this paper, the real behavior at the juncture between the corrugated web and flanges of bridge girders is studied. An elastic bifurcation buckling analysis is carried out using ABAQUS computer package for corrugated webs with simple (S) and fixed (F) boundary conditions at their juncture with the flanges. The dimensions of the generated corrugated webs are assumed based on the average dimensions of the available bridges with corrugation webs. The principle aim is to firstly compare them with each other. Secondly, the critical shear buckling strengths of the corrugated webs with both boundary conditions are compared with the interactive shear buckling strength formulae available in the literature. The paper is then extended to compare girder segments composed from corrugated webs and flanges with corrugated webs with well-defined boundary conditions; simple (S) and fixed (F). Based on the numerical results, the relative critical shear stress of the corrugated webs of simple juncture to that of the corresponding fixed boundary condition has an average value of 0.96. The comparison with the available interactive shear buckling strength formulae shows that the 1st-order interactive buckling strength is suitable for the case of corrugated webs with simple-juncture, while it is unconservative for the case of fixed-juncture corrugated webs. Hence, a new interactive shear buckling strength formula is proposed for the case of fixed (F) juncture in the current paper. The results as well obviously indicated that when the flanges are rigid enough (tf/tw⩾3.0), the girder segments exhibit shear failure mechanisms. Whereas, if the corrugated web plates are relatively rigid (tf/tw<3.0), the strengths of the girders become controlled by the deformation of flanges. Finally, it is found that the realistic support condition at the juncture is nearly fixed.
•The buckling behavior of bridge girders with corrugated webs (BGCWs) is presented.•Using ABAQUS, 3D finite element models for BGCWs under shear are developed.•The behavior of Tapered BGCWs differs ...from the prismatic girders.•Buckling stresses are proposed for tapered corrugated webs of bridge constructions.•The suggested shear strengths predict well the shear strengths of BGCWs.
The existing literature on bridge girders with steel corrugated webs (BGCWs) is focused on prismatic girders; i.e. with constant depth. To the authors’ best knowledge, no work has been done on the shear stability of tapered BGCWs although they have been increasingly used in bridges in recent years. Research presented in this paper focuses, first, on the critical shear buckling stress (τcr) of the corrugated webs of tapered BGCWs. This is made by carrying out elastic bifurcation buckling analyses using ABAQUS software on isolated corrugated webs with simple and fixed boundary conditions. Webs in different typologies of tapered girders with steel corrugated webs are considered. The corrugation dimensions of the considered corrugated webs are taken typical of those used in Shinkai and Matsnoki bridges. Opposite to prismatic corrugated webs which may buckle globally, it is found that the tapered corrugated webs buckle interactively without nothing buckling globally. It is additionally found that predicting τcr values for tapered webs based on prismatic web calculations are not accurate. Therefore, critical buckling stresses of the tapered webs based on the prismatic ones with different equation for each typology are proposed. The paper is, then, extended to investigate the nonlinear shear strengths of the BGCWs. The available design shear strength formulas for prismatic girders are compared with the FE shear strengths of the tapered BGCWs. Based on these comparisons, design strengths for the different cases of the tapered BGCWs are suggested. An illustrative example is given at the end to explain the application of the proposed predictions.
•Axisymmetric model for circular CFST short columns with UHSC is developed.•UHSC in CFST columns reduces the section area by 50% when compare with NSC.•Steel contribution ratio above 0.3 is needed to ...ensure ductility of UHSC.•Australian and European codes safely predict strength of CFST column with UHSC.
A nonlinear axisymmetric simulation of axially loaded ultra-high strength circular short Concrete-Filled Steel Tubular (CFST) columns is reported in this paper. An efficient material law of Ultra-High Strength Concrete (UHSC) is employed in this axisymmetric simulation to consider the confining effects which increase the ultimate strain, stress and axial ductility. The peak loads and load-strain responses of short CFST columns predicted by the axisymmetric model are verified with the independent test data and those predicted by the three-dimensional (3D) model. The structural characteristics of circular short CFST columns having different material and geometric parameters are subsequently examined by the axisymmetric analysis. The numerical results indicate that the column size can approximately be reduced by 50% when UHSC is used in the composite construction instead of Normal Strength Concrete (NSC). Comparisons of the current test data are made with the current structural codes including AS/NZS 5100.6, Eurocode 4, AISC and GB 50936. The comparisons demonstrate that the Australian/New Zealand and European design codes provide consistent predictions for the ultimate axial strengths of ultra-high strength circular short CFST columns. On the other hand, the North American design code is conservative, whereas the Chinese code is unconservative.
•Flat and corner material properties of the stainless steel tubes are presented.•Using ABAQUS, 3D finite element models CFFSSTs under axial compression are developed.•The fundamental behaviour of the ...CFFSST columns is discussed in detail..•The feasibility of current design codes to the design of the CFFSST columns is evaluated.•The proposed design model is shown to predict well the strengths of CFFSST columns.
Concrete-filled stainless steel tubes (CFSSTs) are increasingly applied in current composite structures owing to their excellent performance characterized by aesthetic appearance, high corrosion resistance and durability, and ease of maintenance. Compared with austenitic and duplex stainless steels, ferritic stainless steels have not or contain very low nickel content, achieving lower and more stable material costs. This provides a more viable alternative for structural applications. Additionally, it has been used successfully in corrosive marine environment in a few countries, such as South Africa. However, structural applications of concrete-filled ferritic stainless steel tubular (CFFSST) columns are still limited owing to the dearth of performance data and design guidance. To understand their structural behaviour and to include relevant design recommendations in current design specifications, this paper aims at investigating the compressive behaviour of axially loaded rectangular CFFSST short columns using the nonlinear finite element (FE) modelling. The FE models are developed using ABAQUS software, where two different material constitutive models for the flat and corner portions of the rectangular ferritic stainless steel tubes are incorporated. Close agreement is found between the outputs of FE analysis and existing test results with respect to the failure modes, cross-sectional strengths and axial load-shortening curves. Parametric analysis is then conducted to ascertain the impacts of key variables on the compressive behaviour of the studied CFFSST columns. The obtained numerical results as well as available test results are employed to evaluate the feasibility of current design specifications to design the examined CFFSST columns. Finally, a novel strength design model is proposed and shown to achieve a higher degree of accuracy and consistency of the design predictions.
•A finite element model for CFSCT short columns under axial loading is presented.•A new accurate constitutive model for concrete confined by two tubes is proposed.•The verified finite element model ...is used to study the behaviour of CFSCT columns.•The proposed design model is shown to predict well the strengths of CFSCT columns.
Recently, a concrete-filled austenitic stainless steel–carbon steel tubular column has been introduced as a new form of composite members. This column is composed of an external stainless steel tube and an internal concentrically placed carbon steel tube with concrete filling in the whole tubular section. However, the excellent performance of such composite columns can additionally be achieved by utilising the low-cost lean duplex stainless steel material. In this paper, the behaviour of circular concrete-filled lean duplex stainless steel–carbon steel tubular (CFSCT) short columns under axial loading is investigated by using the general purpose finite element analysis program ABAQUS. A new constitutive model for the concrete core confined by both the external stainless steel tube and the internal carbon steel tube is proposed and incorporated in the finite element model developed. The accurate two-stage stress–strain relationships are employed to model cold-formed lean duplex stainless steels. The finite element results obtained by the proposed concrete model are shown to be in good agreement with test results. Parametric studies are then conducted to investigate the effects of concrete compressive strength, carbon steel yield stress and cross-section geometry on the behaviour of CFSCT columns. The ACI code is found to significantly underestimate the ultimate axial strengths of CFSST columns. Therefore, a new design model is proposed for CFSCT short columns. It is shown that the proposed design model provides excellent predictions of the ultimate axial strengths of circular CFSCT columns over a wide range of diameter-to-thickness ratios of the stainless steel tubes.
•The lateral–distortional buckling (LDB) of tubular flange plate girders is investigated.•Based on finite strips, a parametric study on LDB of HTFPGs is performed.•An analytical model for the ...calculation of critical LBD moment is proposed.•The European specifications are unconservative compared to the FE models.
In this paper, the lateral–distortional buckling (LDB) of hollow tubular flange plate girders (HTFPGs) with slender unstiffened webs is investigated. Firstly, shell finite element analyses are performed in order (i) to study the elastic buckling behaviour of simply supported HTFPGs under uniform bending and (ii) to compare it with the behaviour of I-section plate girders (IPGs) with unstiffened and stiffened webs. The results show that HTFPGs (without stiffeners) have much higher critical moments than IPGs (with stiffeners). Secondly, the LDB behaviour of HTFPGs is investigated using finite strip analyses and the results show the girder length range in which LDB is relevant. After that, an analytical model to estimate the critical LDB moment is proposed and validated by comparison between analytical and numerical values. Thirdly, the investigation is extended to the inelastic domain and non linear shell finite element analyses are performed to evaluate the ultimate strengths of the HTFPGs. Several remarks regarding the flexural strength of HTFPGs are presented. Finally, the predictions given by Eurocode 3 are compared with the numerical results and it is found that the predictions given by the design equations are unconservative. Therefore, it is recommended to use the European specifications by adopting the proposed expression to estimate the critical LDB moment.
•The finite element model for axially loaded hexagonal CFST short columns is proposed.•The confining pressure model for regular hexagonal CFST short columns is given.•The developed finite element ...model accurately predicts the nonlinear characteristics of hexagonal CFST short columns under axial compression.•An extensive parametric study on hexagonal CFST with confinement effect is conducted.
Concrete-filled steel tubular (CFST) columns have frequently been utilised in the construction of mid-rise and high-rise buildings as they offer smaller cross-sectional size to load carrying capacity ratio than ordinary reinforced concrete or steel solutions. The steel tube component of CFST columns can be shaped into different forms to further increase its strength and this article focuses on hexagonal CFST short columns in compression. Firstly, the literature is revised and it was found that the available experiments on the hexagonal columns cover relatively limited hexagonal dimensions and material properties. Additionally, existing design models were observed to be inaccurate for certain diameter-to-thickness (D/t) ratios of the columns. Accordingly, this paper intends to widen the available pool of data and proposes a new design model to design hexagonal CFST short columns in compression. This is made herein through comprehensive finite element (FE) models by using Abaqus software, carefully validated against experimental results and subsequent parametric studies covering a wide range of hexagonal dimensions of regular cross-section (circular-like). The effect of various D/t ratios, material steel grades and concrete compressive strengths (fc′) on both the behaviour and strength of the hexagonal CFST short columns is investigated. Based on observations made and conclusions drawn upon analysing numerical data generated, a new design model is presented which provides better strengths compared with available design models and with accurate predictions for the full range of D/t ratios.
The current slenderness limits in international design codes are often based on certain rotation capacities obtained from plastic bending tests of Concrete Filled Tubes (CFT). In the past, a plastic ...slenderness limit of λs=188 was obtained by the first author based on a fracture rotation limit of the steel tube. However, such limit may be questionable being brittle and insufficient for plastic design of CFT members, sub-assemblies and frames where adequate strain/deformation ductility is required. The main aims of this paper are to present (i) a new method to determine new ductile slenderness limits suitable for plastic design of structures based on the measured strains in plastic bending tests on CFT; (ii) a closed-form solution for the elastic and inelastic buckling strains of CFT under pure bending using a new simplified energy approach employing the well-known Ritz method. The critical strains obtained from such analysis were used to derive new slenderness limits for CFT; and (iii) finite element modelling of CFT and compare the experimental and numerical moment-rotation responses. The effect of concrete filling on the post-buckling strength of restrained tubes is quantified. The current design rules for unrestrained Circular Hollow Sections (CHS) in steel specifications are also compared with the restrained strength obtained from the tests. Two new compact and yield slenderness limits were derived based on the strength corresponds to the appearance of the plastic ripples during the test. The experimentally obtained and the theoretically derived slenderness limits are compared against the available limits in the design codes and standards. The newly derived compact limit of λp=79 was found in a good agreement with λp=72 specified for CFT in the ANSI/AISC 360-10 specification. However, the new yield limit of λy=150 was found considerably lower than λy=254 for CFT specified in the ANSI/AISC 360-10.
•A new method to determine new ductile slenderness limits for CFT is presented.•A closed-form solution is derived for the inelastic buckling strains of CFT is derived.•A new finite element model of CFT is presented.•The effect of concrete filling on the post-buckling strength of CFT is quantified.
PDF
