Aggregate Concrete-filled Steel Tube Research Articles

Properties of Recycled Aggregate Concrete Filled Steel Tubes

A review on the properties of recycled aggregate concrete filled steel tubes (RACSFT) was presented, followed by the short overview on the related researches. The uniaxial mechanical behavior, flexural performance, creep performance as well as eccentric loaded behavior of RACSFT specimens were discussed. It was found that the differences between the element made of recycled aggregate concrete (RAC) and that of natural aggregate concrete (NAC) could not be ignored. The performance of the RACFST is inferior to that of natural concrete filled steel tube (CFST). But, the RACSFT can be applied into structural elements safely. Based on the test results, it was also concluded that the RACSFT is an effective method to improve the application of RAC.

Reliability Analysis on Load-Bearing Capacity of Axially Loaded of Recycled Aggregate Concrete-Filled Steel Tube

The first degree second order moment method (JC method) is applied to analyze the reliability of recycled aggregate concrete-filled steel tube (RACFST). Several performances are studies, which are the influences of different load combinations, specific values of loads,confinement coefficients and recycled coarse aggregate replacement percentage on the reliability of the column. It is found that the reliability index varied with the load combination and specific value of loads. The analytical results indicate that the reliability index of the round steel tube is higher than square steel tube and the influence of recycled coarse aggregate replacement percentage can almost be ignored It can be concluded that the formula had great influence on reliability index and the revised formula can meet the requirements of the ductility of structure reliability.

Seismic Behavior of Recycled Aggregate Concrete Filled Steel and Glass Fiber Reinforced Plastic Tube Columns

This paper presents the results of seismic tests on the recycled aggregate concrete filled steel tube (RCFS) and recycled aggregate concrete filled glass fiber reinforced plastic (GFRP) tube (RCFF) columns. The objective of this study is to evaluate the seismic behavior of steel/ GFRP tube in-filled recycled aggregate concrete (RAC) columns. The main parameters in the tests are the recycled coarse aggregate (RCA) replacement percentage and the tube material. The results show that both deformation and bearing capacities of RCFF and RCFS columns are greatly improved. The seismic behavior of RCFS columns is better than that of RCFF columns. Research findings also indicate that the energy dissipation capacity and the ductility slightly change with the variation of recycled coarse aggregate replacement percentage, whereas the bond-slip has little effect on the seismic behavior. Besides the experiments, a finite element method (FEM) analysis is also conducted. It is found that the seismic behavior of both RCFS and RCFF columns is decreased with the increase of the axial load ratio.

Numerical Analysis on the Seismic Resistance of Steel Tube Columns Filled with Recycled Aggregate Concrete

Horizontal bearing capacity and seismic resistance of Recycled aggregate Concrete Filled Steel Tube (RCFST) columns under low cyclic loads have been analyzed by nonlinear finite element software in this paper. A three-dimensional nonlinear finite element (FE) model was developed, and some parameters that affect the restoring force model of RCFST columns were studied, including axial compression ratio, steel ratio, steel yield strength, strength of core recycled aggregate concrete and recycled aggregate substitution rate. Analysis results show that, along with steel ratio, steel yield strength and recycled aggregate substitution rate increasing, seismic resistance of RCFST becomes better. However, the increase of core recycled aggregate concrete and axial compression ratio will weaken seismic resistance of RCFST columns.

Study of Post-Fire Axial Compressive Behavior of Self-Stress Ceramsite Concrete Filled Steel Tubular Short Columns

The post-fire axial compressive behavior of a set of self-stress lightweight aggregate concrete filled steel tubes (noted as SSLC-ST) after exposure to fire was studied. Effect of the fire temperatures of the specimens and some parameters on the axial compressive behavior of the specimens was especially discussed. The results show that the initial circumferential strain of surface of the steel tubes is much larger than the longitudinal strain of the steel tubes, and the specimens of SSLC-ST have higher post-fire axial compression bearing capacity and better plastic deformation. It was concluded that the local buckling and overall failure of the specimens take place in succession while the specimens are axially loaded, and there are a lot of slip lines with angle of 45oon surface of the steel tubes.

Experimental Study of Performance of Self-Stress Lightweight Aggregate Concrete Filled Steel Tubes after Exposure to Fire

The post-fire behavior of a set of self-stress lightweight aggregate concrete filled steel tubular short columns (noted as SSLC-SSC) after exposure to fire was experimentally studied. Effect of the maximum value of fire response temperatures of the tubes and their geometric parameters on the strength and the other mechanical property of the specimens were especially discussed. The experimental results show that the specimens of SSLC-SSC have higher post-fire bearing capacity and better plastic deformation, there was no obvious descent segment in post-fire load-displacement curves of the most specimens subjected to fire load. It was concluded that the maximum response temperature of specimens has great effect on the post-fire bearing capacity of self-stress concrete-filled steel tubes subjected to fire load, and the value of self-stress corresponding to 10% of dosage of expansive agent has the greatest effect on post-fire bearing capacity of specimens of SSLC-SSC.

Influence of Amount of Recycled Coarse Aggregate on Mechanical Properties of Steel Tube Columns

This paper presents the experimental results of recycled aggregate concrete filled steel tube columns prepared with different amount of recycled coarse aggregate (RCA) subjected to axial loading. The recycled coarse aggregates are obtained from the earthquake waste in Sichuan. Based on the studying of the physical and mechanical properties of recycled coarse aggregate, the mechanical property of recycled aggregate concrete (RAC) with five concrete mixes with 0%, 25%, 50%, 75% and 100% RCA respectively are prepared. The behaviour of the circular solid steel tube columns are studied in terms of the load carrying capacity, ductility and strain response under axial compressive loading in addition to the physical and mechanical characteristics of RCA and RAC. The results show that the steel tube column gives lower ultimate bearing capacities when the RCA were added. However, no obvious difference on the failure modes were found between the steel tube columns filled with recycled aggregate concrete and normal concrete.

EXPERIMENTAL STUDY AND THEORETICAL ANALYSIS ON AXIAL COMPRESS CAPACITY OF ERCYCLED AGGREGATE CONCRETE-FILLED CIRCLE STEEL TUBE SHORT COLUMN

In order to study the axial compress capacity of recycled aggregate concrete-filled steel tube short-columns, 22 specimens were designed to test, and the recycled coarse aggregate replacement percentage and confinement index were regarded as major variable parameters. By the experiment, the whole mechanical process and failure mode of all specimens were observed, and stress-strain curves of the specimens were obtained. The influence of the aggregate replacement rate and confinement index on the bearing behaviour of the specimens was analyzed. The test results indicate that the failure mode of the columns is similar to that of an ordinary concrete-filled steel tube, and recycled coarse aggregate replacement rate has little effect on a recycled aggregate concrete-filled steel tube, but confinement index has a significant effect on the bearing behaviour and deformation performance. The bearing capacity of the specimens was calculated and analyzed according to the theories of Unified Strengthen, Confinement and Superposition Calculation. Compared with the experimental values, the results show that calculated values are low on the basis of the first and the third calculation theories, but the calculated values are slightly high based on the second calculation theory. Finally, stress-strain curves were fitted and analyzed according to experimental data. Stress-strain whole curve equations of specimens were put forward. The research conclusions could be a reference for the scientific study and engineering application of recycled aggregate concrete-filled steel tubes.

Structural behaviour of recycled aggregate concrete filled steel tube columns strengthened by CFRP

This paper presents experimental research on structural behaviour of normal and recycled aggregate concrete filled steel tube (RACFT) columns externally strengthened with carbon fibre reinforced polymer (CFRP) sheets and subjected to axial loading. A total of 22 specimens were tested to investigate the influence of the following variables: (1) tube configurations, circular or square, solid or hollow; (2) types of concrete, normal or recycled aggregate concrete; and (3) strengthening arrangements, full wrapping or partial wrapping. The results show that the recycled aggregate concrete may degrade the concrete strength during the curing period for the first 28days. However, the ultimate strength and stiffness (90-day curing period) for the square and circular solid steel tubes filled with recycled aggregate concrete show slightly higher values than the ones filled with normal concrete, but this is reversed for the steel hollow section tubes. The test results indicate that both reinforcing arrangements enhance the ultimate strength greatly in comparison to the control column, and that the full wrapping arrangement is much more effective than the partial wrapping one. Moreover, stiffness of the strengthened columns is increased significantly due to the restraint offered by the external CFRP wrapping on hoop deformations during compressive loading. In addition, theoretical calculations of the bearing capacity of the composite columns are presented and compared with the experimental results.

Experimental Study of Post-Fire Behavior of Steel Fiber Reinforced Ceramsite Concrete Filled Steel Tubes

The axial compressive mechanical behavior of steel fiber reinforced ceramsite concrete filled steel tubes (noted as SFR-CCST) after exposure to fire are experimentally studied. Effect of furnace temperature, dosage of steel fiber in specimens on the post-fire mechanical performance of the specimens after exposure to fire was especially discussed. The results show that all the specimens of SFR-CCST have higher post-fire bearing capacity and better plastic deformation, and there was no obvious descending segment in the load-strain curves of the most specimens after exposure to fire. It was concluded that the furnace temperature applied to the specimens and dosage of steel fiber in the specimens of SFR-CCST has some effect on the post-fire mechanical performance of the ceramsite concrete-filled steel tubes after exposure to fire, and the dosage of steel fiber of 0.5% has the most effect on the post-fire performance of lightweight aggregate concrete filled steel tubes after exposure to fire.

Experimental behaviour of RACFST stub columns after exposed to high temperatures

The experimental studies on the behaviour of recycled aggregate concrete-filled steel tube (RACFST) stub columns after exposed to high temperatures are reported in this paper. Forty specimens, including 32 RACFST stub columns and 8 normal concrete-filled steel tube (CFST) stub columns as reference, were tested, and the failure pattern, load versus strain relation and ultimate strength of the specimens were presented and analysed. Five types of concrete were produced: one reference concrete with natural aggregates, two concrete mixes with recycled coarse aggregate (RCA) replacement ratios of 50% and 100%, and two concrete mixes with recycled fine aggregate (RFA) replacement ratios of 50% and 100%. The specimens were exposed to 300°C, 600°C and 800°C for 3h. The test results showed that, due to the existence of the recycled aggregates, the post-fire performance of RACFST stub columns was lower than the corresponding normal CFST specimens under the same maximum temperature suffered, and the RACFST specimens with RCA had a better behaviour than those with RFA under the same recycled aggregate replacement ratio.

Mechanical Research on Bond-Slip Behaviors of Recycled Aggregate Concrete-Filled Square Steel Tubes

In order to research the interface bond-slip behaviors of recycled aggregate concrete-filled square steel tube (RACFSST), ten specimens using waste concrete were designed for launch test. The three changing parameters were concrete strength grade, embedded length and recycled coarse aggregate replacement rate. The load–slip curves of square steel tubes and recycled aggregate concrete were obtained, and starting bond strength and ultimate bond strength influenced by each changing parameter were analyzed. The results show that the replacement rate had a slight influence on the starting bond strength and ultimate bond strength, while the embedded length had the opposite effect. The shorter embedded length specimens had larger bond strength. The concrete strength had a relatively large influence on them.

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.

Pure Bending behavior of Lightweight Aggregate Concrete Filled Circular Steel Tubes

Based on appropriate numerical constitutive model of lightweight aggregate concrete filled steel tubes (LCFST), layered method was adopted to predict the complete moment-curvature curves of LCFST composite section subjected to pure bending. A FORTRAN program for the moment-curvature curves was developed. Applying the layered method, the influences of the significant parameters, such as steel ratio, yield strength of steel and strength of lightweight aggregate concrete on the moment-curvature curves of the composite section subjected to pure bending were discussed. The practical composite flexural stiffness, ultimate moment and practical moment- curvature relationship of LCFST composite section were presented. The predicted results of both layered method and practical moment-curvature relationships of LCFST composite section are in good agreement with the test results from reference. Compared with the layered method, practical calculate method could remove the step of composite section layered and improve the calculation speed while achieving similar results.

Behaviour of Recycled Aggregate Concrete-Filled Steel Tubular Columns under Long-Term Sustained Loads

Recycled aggregate concrete-filled steel tube (RACFST) causes the recycled aggregate concrete (RAC) to be in a state of protection with the outer steel tube and thus the RAC is hardly affected by harmful environmental factors (e.g. wind, rain, moist). However, shrinkage and creep are the phenomena commonly associated with concrete-related structures, so studies on the behaviour of RACFST columns under long-term sustained loads are essential for the design of structures which include RACFST members. This study is an attempt to predict the time-dependent behaviour of RACFST columns by using the age-adjusted effective modulus method. The concrete shrinkage and creep in RACFST columns were studied experimentally, and the static bearing capacity of the tested specimens was also investigated. A theoretical model to account for the effects of concrete shrinkage and creep on RACFST columns under long-term sustained loading is developed, and comparisons of the results predicted using this model show good agreement with the test results. Formulae for the calculation of the bearing capacity of RACFST columns under long-term sustained loads are suggested.

Concrete Shrinkage and Creep in Recycled Aggregate Concrete-Filled Steel Tubes

Concrete shrinkage and creep in recycled aggregate concrete-filled steel tubes (RACFST) were experimentally studied and the results were presented in this paper. The measurements on the shrinkage and creep lasted for about eighteen months. The main parameters varied in the tests are: (1) sectional types, circular and square; (2) in-fill concrete types, recycled aggregate concrete (RAC) and normal concrete; and (3) long-term sustained load levels, 0.3 and 0.6. The test results showed that the time-history of the concrete shrinkage and creep in RACFST was similar to that of the corresponding normal CFST. However, the shrinkage and creep strains of RACFST specimens were larger than those of the normal CFST specimens. Finally, the predictive models based on previously issued provision for time-dependent behaviour of the composite member were calibrated with the tests, and recommendations for the calculations on the shrinkage and creep of the concrete core in RACFST were also suggested.

Compressive and flexural behaviour of recycled aggregate concrete filled steel tubes (RACFST) under short-term loadings

The behaviour of hollow structural steel (HSS) stub columns and beams filled with normal concrete and recycled aggregate concrete (RAC) under instantaneous loading was investigated experimentally. A total of 40 specimens, including 30 stub columns and 10 beams, were tested. The main parameters varied in the tests were: (1) recycled coarse aggregate (RCA) replacement ratio, from 0 to 50%, (2) sectional type, circular and square. The main objectives of these tests were threefold: first, to describe a series of tests on new composite columns; second, to analyze the influence of RCA replacement ratio on the compressive and flexural behaviour of recycled aggregate concrete filled steel tubes (RACFST), and finally, to compare the accuracy of the predicted ultimate strength, bending moment capacity and flexural stiffness of the composite specimens by using the recommendations of ACI318-99 (1999), AIJ (1997), AISC-LRFD (1999), BS5400 (1979), DBJ13-51-2003 (2003) and EC4 (1994).

Ultimate moment capacity of foamed and lightweight aggregate concrete-filled steel tubes

An experimental investigation of lightweight aggregate and foamed concrete contribution to the ultimate strength capacity of square and rectangular steel tube sections is presented in this study. Thirty-four simply supported beam specimens, 1000-mm long, filled with lightweight aggregate and foamed concretes were tested in pure flexural bending to calculate the ultimate moment capacity. Normal concrete-filled steel tubular and bare steel sections of identical dimensions were also tested and compared to the filled steel sections. Theoretical values of ultimate moment capacity of the beam specimens were also calculated in this study for comparison purposes. The test results showed that lightweight aggregate and foamed concrete significantly enhance the load carrying capacity of steel tubular sections. Furthermore, it can be concluded from this study that lightweight aggregate and foamed concretes can be used in composite construction to increase the flexural capacity of the steel tubular sections.