Lightweight Aggregate Concrete-filled Steel Research Articles

Size Effect on Nominal Strength of Lightweight and Normal Concrete-Filled Steel Tube Columns under Axial Compression: Mesoscale Simulations

With the devolvement of large-span structures and super high-rise buildings, lightweight aggregate concrete (LWAC) materials have been widely utilized. The main content of this work is to explore the failure and size effect of lightweight aggregate concrete-filled steel tube (LWACFST) columns under uniaxial compression. A three-dimesnional mesoscale simulation approach considering concrete heterogeneity was developed, in which the ideal bond was assumed between the steel tube and inner concretes. The failure of geometrically similar square and circular LWACFST/CFST columns under axial compression having different structural sizes and transverse constraints was modeled and explored. The size effect on the nominal compressive strength of the columns was examined. The influences of aggregate type, column cross-sectional type, and constraint effect generated by the steel tube on the size effect in axial compressive failure are also investigated. The results indicate that an obvious size effect in axial-compressive failure can be found for both LWACFST and CFST columns. With the increase of the confinement degree of steel tube, the size effect on nominal compressive strength would be weakened. The LWACFST columns exhibits a more obvious size effect than the CFST columns. Moreover, the size effect on the compressive strength of the circular columns is obviously weaker than the effect on square columns. Finally, considering the quantitative influence of confinement coefficient, a novel size effect law (SEL) for quantitatively describing the size effect in axial-loaded CFST columns was proposed. The accuracy and reasonability of the proposed SEL was verified by the available test data.

Effect of section shape on the behaviour of thin walled steel columns filled with light weight aggregate concrete: Experimental investigation

The paper presents the results of an experimental investigation to study the behaviour of 19 light weight aggregate concrete-filled steel tubular (CFST) columns subjected to concentric loads. The intermediate CFST columns consisted of 19 different cross-sections. In order to study the most effective section in terms of confinement and stability, All sections were designed to have approximately the same outer perimeter (P), and thus approximately the same cross sectional area, since all sections were manufactured using a mild steel plates with constant thickness. During the experimental tests, the ultimate strength, column shortening, lateral displacement and failure modes were recorded. The results showed that all the CFST columns failed by outward local buckling around the mid-height of the column due to the crushing of the light-weight concrete core, and during the final stages of loading, additional local buckling occurred close to the ends of the column. Furthermore, the results also showed that as the number of steel plates welded together to form the section increases, the section becomes more stable and more confinement can be achieved. Thus, the Octagonal (CO) CFST columns exhibited the largest failure stress followed by the Plus-Shaped (CPS) shaped section. On the other hand, sections formed using a hybridization of the circle and square shapes such as the D-Shaped (CD), Hexagonal Asymmetric (CHA) and Semi- Circular (CSC) showed the lowest failure stress amongst all other section. In terms of ductility, the CFST column with octagon section showed the highest ductile behaviour amongst all other shapes, while the CFST column with L-shaped cross section showed the lowest value of ductility. Also, CFST columns with conventional cross-sectional shapes such as circle and square seem to have a relatively high ductility index. On the other hand, as the shape becomes more irregular, its ductility index decreases.

Behaviour of lightweight aggregate concrete-filled steel tube under horizontal cyclic load

A horizontal cyclic test was carried out to study the seismic performance of lightweight aggregate concrete filled steel tube (LACFST). The constitutive and hysteretic model of core lightweight aggregate concrete (LAC) was proposed for finite element simulation. The stress and strain changes of the steel tube and concrete filled inside were measured in the experiment, and the failure mode, hysteresis curve, skeleton curve, and strain curve of the test specimens were obtained. The influence of axial compression ratio, diameter-thickness ratio and material strength were analysed based on finite element model. The results show that the hysteresis curve of LACFST indicated favourable ductility, energy dissipation, and seismic performance. The LACFST failed when the concrete in the bottom first crushed and the steel tube then bulged, thus axial force imposed by prestressing was proved to be feasible. The proposed constitutive model and hysteretic model of LAC under the constraint of its steel tube was reliable. The bearing capacity and ductility of the specimen increase significantly with increasing thickness of the steel tube. The bearing capacity of the member improves while the ductility and energy dissipation performance slightly decreased with the increasing strength of the steel and concrete.

Behavior of Reinforced Lightweight Aggregate Concrete-filled Circular Steel Tube Columns Under Axial Loading

The use of lightweight aggregate concrete (LWC) is the most obvious way to reduce the self-weight of concrete-filled steel tube (CFST) columns. This paper reports an investigation of the properties of reinforced lightweight aggregate concrete-filled steel tube (RLWCFST) columns subjected to axial compression. Eighteen specimens with three length-to-diameter (L/D) ratios (short, medium, and long) and two diameter-to-thickness (D/t) ratios (thin and thick) were tested. The LWC compressive strength is 30.58 MPa. The test results are given in terms of the compression loading against end shortening curves, and the failure modes of eighteen specimens are compared and discussed. In addition, the predictions of AISC360-16 and EC4 design specifications were compared to the test results to confirm the predictions of these specifications hold for RLWCFST columns. According to the experimental results, the use of the steel-bar reinforcement improves the mechanical behavior of LWC and increases the compressive strength capacity, toughness, and ductility of the composite column. The failure modes of the columns were affected by the behavior of the reinforced and unreinforced LWC and the geometric properties of the steel tube (L/D and D/t ratios). Steel-bar reinforcement combined with thinner steel tube provided excellent performance and using larger-diameter steel-bars instead of thick steel tube can offer improvement in compression capacity and ductility for short, medium, and long columns.

Bending Performance of Lightweight Aggregate Concrete-filled Steel Tube Composite Beam

A composite beam, which consists of a Lightweight Aggregate Concrete Filled Steel Tube (LACFST), and a reinforced concrete slab deck, was investigated. Bending tests were performed to study its behaviour. Based on the test results and the assumptions therein, calculation methods proposed and design suggestions were proved by finite element analysis. The results shows that the composite beam had good ductility and high bearing capacity. The design bearing capacity can be calculated using a force balance method. The flexural stiffness, at the serviceability-level, can be found by superposition of the slab deck and LACFST beam stiffness. A three-line M-δ model was proposed for the lightweight aggregate concrete steel tube composite beam moment–deflection evolution. After validation by finite element analysis, the neutral axis was suggested as lying between the top of the steel tube and the bottom of the concrete deck when the composite beam failed.

Bending behaviour of lightweight aggregate concrete-filled steel tube spatial truss beam

A lightweight aggregate concrete-filled steel tube (LACFST) spatial truss beam was tested under bending load. The performance was studied by the analysis of the beam deflection and strains in its chords and webs. According to the test results, several assumptions were made to deduce the bearing capacity calculation method based on the force balance of the whole section. An optimal dimension relationship for the truss beam chords was proposed and verified by finite element analysis. Results show that the LACFST spatial truss beam failed after excessive deflection. The strain distribution agreed with Bernoulli-Euler theoretical prediction. The truss beam flexural bearing capacity calculation results matched test evidence with only a 3% difference between the two. Finite element analyses with different chord dimensions show that the ultimate bearing capacity increases as the chord dimensions increase when the chords have a diameter smaller than optimal one; otherwise, it remains almost unchanged as the chord dimensions increase.

Combined strength of lightweight aggregate concrete-filled steel tube

The strength characteristics of lightweight aggregate concrete confined by steel tube were studied experimentally. Based on the superposition of two materials, a method was established to calculate the combined strength of lightweight aggregate concrete steel tube: the accuracy of this calculation was verified experimentally. The research indicated that the confining effect of steel tube on lightweight aggregate concrete increased as the steel area ratio is enlarged. The confining effect coefficient of lightweight aggregate concrete can be taken as 3·4, which reflected the stress–performance improvement of lightweight aggregate concrete under trip–direction compression. Comparison between calculation and test results showed that the calculations were precise. The calculated result could be regard as ultimate strength at a coefficient of lateral deformation of 0·5, and as its design strength at a coefficient of lateral deformation of 0·3.

The behavior of lightweight aggregate concrete filled steel tube columns under eccentric loading

This paper consists of two parts; the first part describes the laboratory work concerning the behavior of lightweight aggregate concrete filled steel tubes (LACFT). Based on eccentricity tests, fifty-four specimens with different slenderness ratios (L/D= 3, 7, and 14) were tested. The main parameters varied in the test are: load eccentricity; steel ratio; and slenderness ratio. The standard load-strain curves of LACFT columns under eccentric loading were summarized and significant parameters affecting LACFT column\'s bearing capacity, failure mechanism and failure mode such as confinement effect and bond strength were all studied and analyzed through the comparison with predicted strength of concrete filled steel tube columns (CFT) using the existing codes such as AISC-LRFD (1999), CHN DBJ 13-51-2003 (2003) and CHN CECS 28:90 (1990). The second part of this paper presents the results of parametric study and introduces a practical and accurate method for determination of the maximum compressive strength of confined concrete core ( fmax), In addition to, the study of the effect of aspect-ratio and length-width ratio on the yield stress of steel tubes ( fsy) under biaxial state of stress in CFT columns and the effect of these two factors on the ultimate load carrying capacity of axially loaded CFT/LACFT columns.

Experimental Research on Seismic Behavior for Lightweight Aggregate Concrete-Filled Steel Tubular Frame

In order to research the seismic behavior of lightweight aggregate concrete-filled rectangular steel tubular (CFRST) frame, four test specimens were experimentally studied under constant axial load and cyclically lateral load. The form of beam section and steel ratio of column section were considered as experimental parameters. The results show that the lightweight aggregate CFRST frame has plump hysteretic loops without obvious shrinkage phenomenon; the displacement ductility coefficients is between 3.00 and 3.74, which can meet the requirement of ductile frames; the bearing capacity, ductility and energy dissipation capability improve with the increase of the steel ratio; when the steel ratio is the same, the steel beam frames have plumper hysteretic loops, the ductility and energy dissipation capability increase to some extent, the stiffness degradation is slower compared with the CFRST beam frames. Conclusively, the lightweight aggregate CFRST frame has excellent seismic behavior and mechanical performance and there is the value to further research.

Failure of lightweight aggregate concrete-filled steel tubular columns

Tests on steel tubular columns of square, rectangular and circular section filled with normal and lightweight aggregate concrete were conducted to investigate the failure modes of such composite columns. Thirty-six full scale columns filled with lightweight and normal weight aggregate concrete, eighteen specimens for each, were tested under axial loads. Nine hollow steel sections of similar specimens were also tested and results were compared to those of filled sections. The test results were illustrated by a number of load-deflection and axial deformation curves. The results showed that both types of filled columns failed due to overall buckling, while hollow steel columns failed due to bulging at their ends (local buckling). According to the above-mentioned results, and due to low specific gravity and thermal conductivity of the lightweight concrete the further interest should be concentrated in replacing the normal concrete by the lightweight aggregate concrete.