•Axial performance of ultra-high strength CFST columns is presented.•Measures to improve ductility are provided.•Confinement effect should be ignored for calculating axial resistance.•Modified ...Eurocode 4 method is applicable to ultra-high strength CFST columns.
The use of high strength concrete and steel have significant advantages for composite members subject to significant compression as in the cases of high-rise buildings. Current design codes place limits on the strengths of steel and concrete due to limited test data and experience on the behaviour of composite members with the high strength materials. To extend their applications, a comprehensive experimental program has been carried out to investigate the behaviour of concrete filled steel tubes (CFSTs) with high- and ultra-high- strength materials at ambient temperature. This article presented some new findings on the axial performance of 56 short CFSTs. High tensile steel with yield strength up to 780MPa and ultra-high strength concrete with compressive cylinder strength up to 190MPa were used to prepare the CFST test specimens. The key issue is to clarify if the plastic cross-sectional resistance could be used at ultimate limit state as for CFSTs with the normal strength materials. To address this, experimental and analytical methods were adopted where the test results were compared with the predictions by various design codes world widely, and design recommendations were therefore proposed so that the prediction methods could be safely extended to the short CFSTs with the high- and ultra-high- strength materials.
•A method to predict premature cover spalling was introduced and validated.•A concrete confinement model was proposed for composite sections.•A new model was proposed to predict the axial load ...shortening relation of composite section.•Recommendations were proposed to enhance the capacity and ductility of composite sections.
Experimental work on steel H-section fully encased by high strength concrete showed the occurrence of premature failure due to concrete cover spalling. This failure mode limits the utilization of full material strength and hence impedes the attainment of anticipated load-carrying capacity. This paper proposes an analytical model to predict the full range axial load-displacement behaviour of concrete encased steel composite section made from concrete grade up to C130 and steel section grade up to S690. The analytical model captures the compression behaviour of concrete encased steel composite section at the constitutive level including premature cover spalling, concrete confinement from stirrups and steel section. Concrete fracture energy is used to estimate the cover spalling strain, and a confinement model is proposed to evaluate the confining pressure provided by the steel section. Good agreement is observed between the analytical predictions and test results in terms of initial stiffness, peak load, residual strength, and the full range of load-displacement response. Based on the findings, recommendations are put forward for practical design of high strength concrete encased steel composite columns.
•Structural test is conducted on 14 high strength Concrete Encased Steel (CES) composite short columns.•The axial compression capacity of high strength CES columns is evaluated and compared with ...various design codes.•A concrete strength reduction factor is proposed to account for the brittleness of high strength concrete.•Parametric studies are carried out to determine the critical parameters affecting strength and ductility of CES columns.•An empirical equation is proposed to assess the ductility of high strength CES columns.
This paper presents an experimental program that studies the structural behaviour of high strength Concrete Encased Steel (CES) composite columns. The structural performance under compression, including the damage pattern, load-carrying capacity, post-peak ductility, and load-displacement response is experimentally investigated. A total of 14 specimens were tested under concentric compression. The parameters studied in this program include concrete compressive strength, steel yield strength, stirrup spacing, incorporation of steel fiber, as well as the shape of the structural steel section. To evaluate the material compatibility between high strength concrete and high strength steel, two concrete grades (C90, C130) and two steel grades (S500, S690) were used to prepare the test specimens. In addition, 0.5% volume fraction of steel fiber was added in concrete mix to minimize the inherent brittleness of high strength concrete. The comparison between test results and analytical predictions reveals the inability of existing design codes to estimate high strength CES columns, unless steel fiber and dense reinforcement are used in combination. The effect of material strength, steel fibers, volumetric ratios of hoop reinforcement, and shape of steel section on both strength and ductility of CES columns was assessed through a comprehensive parametric study. The analysis of test results demonstrates that steel contribution ratio plays a dominant role in the ductility, whereas increasing hoop reinforcement ratio and adding steel fiber has negligible effect. Finally, a simplified formula is proposed to evaluate ductility of high strength CES columns.
AbstractCorrugated steel tube (CST) confined reinforced concrete (RC) sections, which consists of galvanized corrugated steel tubes infilled with concrete and steel reinforcements, provide a solution ...for their practical application in the outdoor and offshore corrosive environment. To investigate their compression-bending, cross-sectional behavior, a fiber model is established by treating it as a confined reinforced concrete section. The model considers the nonuniformity of concrete confinement pressure across the cross-sectional depth and tensile axial-strain concentration at the lock seam. The ultimate strength and lateral deflection of the CST confined RC sections are investigated. Further in-depth analyses are carried out to study the influence of the eccentricity ratio, geometric parameters (thickness, helical angle and corrugation profile of tubes, and reinforcing bars ratio), as well as materials strength (concrete and tube). Finally, a design method is proposed to predict the compression-bending strength of CST-confined RC sections, and its precision is verified by comparison with tests and numerical results.
•New joint for connecting aluminum rectangular hollow section members is proposed.•Six different full-scale ARH joints are tested under an out-of-plane bending moment.•The M-Φ curves, stress ...variation, and failure modes of the ARH joint are obtained.•A bilinear model is proposed to summarize the M-Φ curves of the joint.•The influence of different factors on mechanical behavior of ARH joints is analyzed.
A new joint system for connecting aluminum alloy rectangular hollow section (ARH) members is proposed to overcome the problem of connecting rectangular tubes using the traditional Temcor joint. The structural performance of the ARH joint system under an out-of-plane bending moment is studied experimentally. The moment-rotation (M-Φ) curves, stress variation, and failure modes of the ARH joint obtained from the tests are discussed. A bilinear model is proposed to summarize the M-Φ curves of the joint. The influence of the key parameters, gusset thickness and bolt quantity on the mechanical behavior of the ARH joint is analyzed. Subsequently, finite element analysis is conducted to investigate the moment rotational behavior of the ARH joint. The comparison between the experimental and numerical results proves that the proposed finite element model is accurate enough and can be used to study the moment resistance behavior of the ARH joint system. The results show that the proposed ARH joint, for connecting rectangular hollow section members, can be considered as a semi-rigid connection. This study provides a reference for the practical application of the ARH joint in reticulated structures made of aluminum rectangular members.
A foam sol clay (FSC) mixture, mainly composed of fly ash (FA), surfactant (n-amylamine) and polyethylene oxide (PEO), was proposed for coal dust control. The FA surface, modified by a FSC solution, ...stability and foamability were investigated. It was found that the FA surface in alkaline solution was deprotonated to form a negative charge, which could be adsorbed by the polar head group of n-amylamine via electrostatic interactions. As a result, with increasing surfactant, the particles gradually converted from hydrophilic to hydrophobic and attached at gas-liquid interfaces so that the contact angle, zeta potential, froth stability and foamability increased. At a surfactant concentration (ca) of 35 g/L, a monolayer three-dimensional network was formed and the maximum foamability and half-life were obtained. Upon further increasing ca, a bilayer and particle clusters were formed by surfactant chain-chain interaction, resulting in particles becoming hydrophilic again, and the FSC solution having stronger mechanical resistance against flowing, so that the viscosity rapidly increased and the diffusion of free surfactant molecules was hindered at the froth surfaces. Thus, the contact angle, froth stability and foamability decreased. PEO could bond sodium dodecyl sulfate and water to form a dual adsorption layer and hydrogen, respectively, which enhanced the wettability of the FSC on coal dust surfaces. PEO could adsorb and curl FA particles to form a thin layer of armor after froth air-drying. It was concluded that the froth generated by the FSC solution, including 200 g/L FA, 35 g/L ca and 1 g/L PEO, could control coal dust with a long-term effect.
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•Foam sol clay for controlling coal dust was proposed.•Fly ash particles surface modified by n-amylamine was analyzed.•The mechanism of fly ash for froth stability was studied.•The mechanism of polyethylene oxide for froth stability and wetting dust was studied.
•Finite difference model is proposed for temperature prediction in composite columns.•A database containing 15,200 composite column specimens is established.•Equivalent temperature method is proposed ...for temperature calculations.•Artificial neural networks method for fire resistance design of composite columns.•Closed-form equations are derived for predicting fire resistance of composite columns.
Concrete encased steel (CES) columns, also known as steel reinforced concrete (SRC) composite columns, exhibit superior fire resistance due to concrete acting as a protection layer for the embedded steel section. While modern design codes have provided design guides for the fire resistance of CES columns, they are only applicable to those made of normal strength concrete. For high strength CES columns, advanced analysis is needed to capture the brittleness of high strength concrete at elevated temperature. In this paper, two methods, namely the artificial neural network (ANN) and the analytical equations, are proposed to predict the fire resistance of axially-loaded CES columns made of high strength concrete. To train the ANN, a finite difference model is developed to compute the temperature field in CES columns and it is used to establish a database containing 15,200 specimens. The cross-sectional dimensions and materials grades of the specimens are carefully selected to cover a wide range of values including those commonly adopted in real-life applications. The inputs of the ANN are identified through an extensive parametric analysis. The selected ANN consists of 7 inputs, 3 outputs and 2 hidden layers and achieves a high determination coefficient R2 value of 0.999. For practical implementation, analytical equations are also derived and achieve high R2 values above 0.953. The predictive power of the ANN and the analytical equations are examined against the observations obtained from actual fire tests, showing reasonable accuracy of prediction. Both methods are simple, of high accuracy and have implicitly accounted for temperature-dependent material degradation, and hence do not require input of temperature-dependent material properties and advanced analysis software.
This paper provides an insight into the buckling behavior of high strength concrete encased steel (CES) columns through a comprehensive investigation including experimental, numerical and analytical ...analyses. Three long CES column specimens made of high strength concrete C100 and S355 H-section were tested under axial compression. The maximum test loads obtained from these tests were compared with the buckling resistance predicted by EN 1994-1-1, AISC 360-10 and ACI 318-08. Nonlinear finite element analyses were performed to predict the buckling resistance and trace the load displacement behaviour of these columns. In the finite element model, the column initial imperfections were carefully chosen to predict the maximum resistance and the load-displacement response, and compared with the equivalent imperfection values stipulated in the modern design codes. In order to examine the validity and limitation of the current design approaches in predicting the buckling resistance of CES columns made of high strength concrete, a statistical study was undertaken based on the established database covering a wider range of material strength and geometric configurations. In the statistical study, the buckling resistance and effective flexural stiffness obtained from the tests were compared with the codes' predictions from EN 1994-1-1, AISC 360-10 and ACI 318-08. Finally, the reliability of the current design methods is assessed by correlating their accuracy with respect to the variation of material strength, column slenderness ratio, load eccentricity and steel contribution ratio.
•The compression behaviour and maximum resistance of high strength concrete encased steel composite columns were investigated.•New test database including 3 large scale tests carried out on high strength composite columns subject to axial compression was reported.•The test failure loads were compared with codes' predictions and numerical results from nonlinear finite element analyses.•The effective flexural stiffness of high strength composite members predicted by design codes was comparatively studied.
This paper presents a novel buckling-restrained steel plate shear wall with inclined slots called slotted SPSW to be used as an energy dissipation device for earthquake resistance. In the slotted ...SPSW, a steel plate with inclined slotted holes is sandwiched in between two external concrete panels which provide lateral restraint to achieve stable energy dissipation under cyclic reversal loading. Theoretical analysis and finite element monotonic pushover analyses are conducted to investigate the stability of slotted SPSWs. Global buckling and local buckling resistances of slotted SPSWs are determined. Some key parameters, such as the gap between steel plate and concrete panels, bolt spacing, width of steel strips, and steel panel slenderness, are investigated through numerical analyses. The shear force and lateral drift behavior of the slotted SPSW is found to be affected by the physical gap between the concrete panels and inner steel plate. The minimum concrete panel thickness for providing the effective lateral restraint to prevent buckling failure of the inner steel plate is determined based on the bolt spacing.
•The stability of slotted SPSWs under shear force is investigated through theoretical studies.•The effect of the gap between steel plate and concrete panels is investigated numerically.•The minimum concrete panel thickness is determined by the parametric analyses.•The general behavior of slotted SPSWs with sufficient lateral restraint is provided.
•Eccentric compression tests were conducted on seven high strength CES beam-columns.•The strength, ductility, and deformability of specimens were analysed.•Numerical simulation was performed to ...predict the ultimate strength and load-deflection behaviour.•A refined formula was proposed to estimate the effective flexural stiffness .
This paper investigated the structural performance of Concrete Encased Steel (CES) beam-columns made of C90 concrete and S690 welded steel section. Seven large-scale beam-column specimens including four steel reinforced concrete encased specimens and three fiber-reinforced concrete encased specimens were tested under axial compression and end moments. The end moment was applied by a compression load acting at an eccentricity. The test results in terms of failure mode, load-carrying capacity, deformation capability and second-order moment were presented. In addition, the effects of load eccentricity, steel fiber content, steel contribution ratio, and stirrup configuration on the column strength and ductility were analyzed. The existing design methods suggested in EN 1994-1-1 and AISC 360-16 were examined in constructing the axial force-moment interaction diagram and in predicting the effective flexural stiffness for second order analysis. A fiber element analysis method was developed and the predicted results were verified against the load displacement response and the failure loads from the tests. The analysis method was then used to generate additional data for beam-columns of various design parameters. Finally, an analytical method was proposed based on regression analysis to estimate the short-term effective flexural stiffness for the design of high strength CES beam-columns.
