scholarly journals Experimental Studies on the Effect of Properties and Micro-Structure on the Creep of Concrete-Filled Steel Tubes

Materials ◽  
2019 ◽  
Vol 12 (7) ◽  
pp. 1046 ◽  
Author(s):  
Rongling Zhang ◽  
Lina Ma ◽  
Qicai Wang ◽  
Jia Li ◽  
Yu Wang ◽  
...  
Keyword(s):  
Pore Structure ◽  
Steel Tube ◽  
Creep Tests ◽  
Steel Tubes ◽  
Concrete Filled Steel Tube ◽  
Steel Ratio ◽  
Air Content ◽  
Lateral Restraint ◽  
Concrete Filled Steel Tubes ◽  
Core Concrete

To study different lateral restraints, different constituents of expansion agents, the influence of different steel ratios, and concrete creep properties, we carried out experiments with lateral restraint and without lateral restraint conditions separately on 12 specimens with the expansion agent content accounting for 4%, 8%, and 12% respectively. In addition, the creep tests were performed on specimens with different steel ratios of 0.0%, 3.8%, 6.6%, and 9.2%. The test results show that the lateral restraint improves the strength of the system (concrete-filled steel tubes) which resists further load after the concrete ultimate strength is surpassed and reduces the creep. The creep degree of the concrete-filled steel tube with lateral restraint is about 0.09–0.30 times smaller than that of the tube without lateral restraints. The creep degree of the concrete-filled steel tube increases as the steel ratio decreases. Creep tests with different amounts of expansion agent indicate that the creep degree of the concrete structure increases as expansion agent content decreases. To study the internal mechanism of the creep of concrete-filled steel tubes with different lateral restraints and different expansion agent concentrations, a microscopic pore structure test on the steel core concrete was conducted using the RapidAir457 pore structure instrument. Microscopic studies show that the air content and the length of the bubble chord of the laterally restrained core concrete are lower than those without lateral restraint core concrete. The amount of air content and the length of the bubble chord of core concrete specimens increase as the expansion agent content in the core concrete specimens decreases from 12% to 4%. Under the same external loading conditions, as steel ratio increases, the lateral restraint causes a further reduction of creep. The results of this study suggest that the creep of concrete can be reduced by selecting appropriate lateral restraint conditions and an optimal amount of expansion agent in the mix design of concrete for concrete-filled steel tubes.

scholarly journals Theoretical Analysis on Mechanical Behavior of Axially Loaded Recycled Aggregate Concrete Filled Steel Tubes

2015 ◽  
Vol 2015 ◽  
pp. 1-14 ◽  
Author(s):  
Yijie Huang ◽  
Yuedong Sun ◽  
Huangsheng Sun ◽  
Qing Wang
Keyword(s):  
Mechanical Behaviour ◽  
Mechanical Model ◽  
Confining Pressure ◽  
Steel Tube ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Steel Tubes ◽  
Concrete Filled Steel Tubes ◽  
Numerical Program ◽  
Core Concrete

A new mechanical model for analysing the behaviour of axially loaded recycled aggregate concrete filled steel tubes (RACFSTs) stub columns is presented in this study. The model is derived from the typical elastoplasticity, the nonlinear elastic mechanics, and the properties of materials. Based on the mechanical model, a novel numerical program is developed. The mechanical model and the numerical program are adopted to study the effect of recycled coarse aggregate (RCA) replacement percentage on RACFST mechanical behaviour. The complete load-deformation relationship of specimens, the steel tube axial and circumferential stresses, and the performance of the confined core concrete and the variation of interaction are also investigated. The analytical results indicate that this model is able to capture the mechanical behaviour of RACFST. It is also found that the axial and circumferential stresses of steel tube change nonlinearly during the loading stages. It is concluded that the behaviour of the confined core concrete is significantly influenced by the confining pressure. The steel tube confinement could improve the mechanical behaviour of RAC effectively and the RCA replacement percentage slightly changes the response of core concrete. Finally, the relations between confined core concrete and confining pressure are analysed.

Study on Stress-Strain Relationship of FRP-Confined Concrete Filled Steel Tubes

2010 ◽  
Vol 163-167 ◽  
pp. 3826-3829
Author(s):  
Feng Yu ◽  
Ping Wu
Keyword(s):  
Main Parameter ◽  
Steel Tube ◽  
Confined Concrete ◽  
Stress Strain ◽  
Steel Tubes ◽  
Concrete Filled Steel Tube ◽  
Strain Relationship ◽  
Relationship Of ◽  
Concrete Filled Steel Tubes ◽  
Strain Model

FRP-confined concrete filled steel tube may fully use the character of FRP-confined concrete and concrete filled steel tube. Based on the analysis of existing experimental data, the formula of ultimate bearing capacity of FRP-confined concrete filled steel tube is proposed. The mechanical behavior of FRP-confined concrete filled steel tube is mainly related to the equivalent confinement effect coefficient before the rupture of FRP. Based on the static equilibrium condition, the equivalent conversion section is adopted; taking as main parameter, the simplified stress-strain model of FRP-confined concrete filled steel tube is established. The predictions of the model agree well with test data.

Influence of concrete mix proportions on axial performance of concrete-filled steel tubes made with self-compacting concrete

2019 ◽  
Vol 23 (5) ◽  
pp. 835-846 ◽  
Author(s):  
Y Ouyang ◽  
JJ Zeng ◽  
LG Li ◽  
AKH Kwan
Keyword(s):  
Steel Tube ◽  
The Self ◽  
Use Of Self ◽  
Self Compacting Concrete ◽  
Steel Tubes ◽  
Concrete Filled Steel Tube ◽  
Concrete Mix ◽  
Key Factor ◽  
Air Void ◽  
Concrete Filled Steel Tubes

Self-compacting concrete is quite commonly used in concrete-filled steel tube structures, but the compaction level of the self-compacting concrete, that is, the percentage of volume occupied by materials other than air void, within the steel tube is seldom investigated. The authors are of the view that the concrete mix proportions of the self-compacting concrete may have significant effects on the compaction level of the self-compacting concrete, which will be quantified by the ‘compaction index’ proposed in this study and thus the performance of the concrete-filled steel tube. Moreover, the mix proportions would also influence the performance of the concrete-filled steel tube by affecting the aggregate–aggregate and aggregate–paste interactions of the concrete, albeit this important issue is rarely addressed in previous studies either. Herein, a pilot study is conducted to investigate the influences of the self-compacting concrete mix proportions on the axial performance of concrete-filled steel tube. Four groups of concrete-filled steel tube specimens made with different self-compacting concrete were tested, and the investigated concrete mix parameters included the paste volume, fine to coarse aggregate ratio, and 9.5–19.0 mm aggregate ratio. It was found that the compaction index of the self-compacting concrete is a key factor enabling the successful use of self-compacting concrete in concrete-filled steel tube. Moreover, the paste volume and aggregate proportions of the concrete mix have certain effects on the post-peak behaviour and ductility of concrete-filled steel tube.

scholarly journals Influence of Red Mud Proportion on Circular Concrete-Filled Steel Tubular Short Columns

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Wu Bin ◽  
Tan Zhuoying ◽  
Li Fan ◽  
Wang Sun
Keyword(s):  
Red Mud ◽  
Longitudinal Strain ◽  
Ultimate Load ◽  
Steel Tube ◽  
Steel Tubes ◽  
Concrete Filled Steel Tube ◽  
Short Columns ◽  
Calculation Results ◽  
Concrete Filled Steel Tubes ◽  
Stub Columns

Tests on twelve circular concrete-filled steel tube stub columns with mixed red mud and three circular concrete-filled steel tube stub columns to investigate the influence of the mixed proportion of red mud on the mechanical behavior of axial compressive circular concrete-filled steel tube stub columns are reported. It is found that with the increase of red mud content, the ultimate load increases first and then decreases; on the contrary, the ultimate displacement decreases first and then increases; the specimen stress reaches the proportion limitation as the steel tube longitudinal strain is around 160 με and reaches the yield limitation as the steel tubes’ longitudinal strain is around 4400∼5000 με. The axial compressive bearing capacity empirical formulation of concrete-filled steel tubes stub columns mixed with red mud is proposed. The theoretical calculation results agree well with those experimental data.

The Seismic Behavior of Strengthened Joints between Concrete-Filled Steel Tubes and Beams Based on the Numerical Simulation Technology

2010 ◽  
Vol 150-151 ◽  
pp. 571-575
Author(s):  
Yun Peng Chu ◽  
Yong Yao ◽  
Shu Lian Xiao ◽  
Yue Chen
Keyword(s):  
Energy Dissipation ◽  
Bearing Capacity ◽  
Double Layer ◽  
Seismic Behavior ◽  
Steel Tube ◽  
Ultimate Bearing Capacity ◽  
Steel Tubes ◽  
Concrete Filled Steel Tube ◽  
Energy Dissipation Capacity ◽  
Concrete Filled Steel Tubes

As a key part in concrete-filled steel tubular frames, the seismic behavior of joints between concrete-filled steel tubes and beams needs more research because of the complexity of stress under the reciprocating load. the behavior of 9 strengthened joints connecting concrete-filled steel tube with H-shaped steel beam have been analyzed under reversed cyclic loading condition by using finite element analysis software ANSYS, and the result show that: (1) The ultimate bearing capacity, energy dissipation capacity and ductility of strengthened joint are obvious better than that of ordinary welded joint; (2) Compared to concrete-filled steel tube the ultimate bearing capacity, energy dissipation capacity and ductility of double-layer concrete-filled steel tubes are better; (3) For the joints connecting double-layer concrete-filled steel tubes with beams, the shape of inner tube have certain effect on the ultimate bearing capacity but little on the energy dissipation capacity and ductility. (4) The shape of stiffened plate has significant influence on the ultimate bearing capacity, energy dissipation capacity and ductility of nodes.

Experimental behaviour of concrete-filled steel tubes under cyclic axial compression

2019 ◽  
Vol 23 (1) ◽  
pp. 74-88 ◽  
Author(s):  
Vui Van Cao ◽  
Quoc Dinh Le ◽  
Phuoc Trong Nguyen
Keyword(s):  
Axial Compression ◽  
Maximum Stress ◽  
Axial Loading ◽  
Peak Stress ◽  
Steel Tube ◽  
Monotonic Loading ◽  
Steel Tubes ◽  
Concrete Filled Steel Tube ◽  
Loading And Unloading ◽  
Concrete Filled Steel Tubes

This study experimentally investigated the behaviour of concrete-filled steel tubes under cyclic axial compression. A total of 42 concrete-filled steel tube specimens of two groups were tested to failure. In each group, 18 specimens were subjected to three cyclic axial loading histories while three specimens were subjected to monotonic loading for comparison. The results indicated that concrete-filled steel tube specimens under cyclic axial compression failed in the form of buckling and still kept their form which was similar to the failure of specimens under monotonic loading. Effect of cyclic axial loading slightly reduced (approximately 2%–3%) the maximum stress but it increased 25% of the strain corresponding to the maximum stress. Loading and unloading moduli in post-peak stress phase were, respectively, about 70% and 85% higher than initial moduli because better interaction and confinement were resulted from the initial loading cycle. In addition, the absorbed energy exhibited a heavy dependence on strain and confinement while it was insignificantly affected by cyclic loading histories. Details and application of obtained experimental results are reported in this article.

The Study on Static Force Behavior of Concrete Filled Steel Tube Lattice Wind Generator Tower Joints

2013 ◽  
Vol 671-674 ◽  
pp. 833-837
Author(s):  
Yang Wen ◽  
Fei Zhou
Keyword(s):  
Tube Wall ◽  
Local Buckling ◽  
Steel Tube ◽  
Wall Region ◽  
Steel Tubes ◽  
Concrete Filled Steel Tube ◽  
Wind Generator ◽  
Nonlinear Static ◽  
Angle Steel ◽  
Section Form

In order to discuss the failure mechanism of concrete filled steel tube lattice wind generator tower joints. Based on the parameters of web member section form, and using nonlinear static numerical simulation, this dissertation research on the stressed complex joints. The results of the study show that the abdominal rod for circular steel tubes joint (JD1) is instability failure which is led to the local buckling of compressive bar; the abdominal rod for single angle steel (JD2) or double angle steel (JD3) joint is instability failure because of the local buckling of the joint board. Under the web members and joint boards all fitting their own capacity requirements, JD1 is very easy to make draw bar broken on both sides of the pillar tube wall region, JD2 and JD3 are apt to damage on the weak positions of joint board ends and pillar tube wall joint. In the three forms of web member joints, the best ultimate bearing capacity is JD1 , JD3 is the second and JD2 is minimum.

scholarly journals Analytical Model for Restraint Strains and Self-stressed in Expansive Concrete Filled Steel Tubes (ECFST) estimation

2020 ◽  
pp. 93-98
Author(s):  
Viktar V. Tur ◽  
Radoslaw Duda ◽  
Dina Khmaruk ◽  
Viktar Basav
Keyword(s):  
Experimental Data ◽  
Experimental Studies ◽  
Steel Tube ◽  
Development Model ◽  
Steel Tubes ◽  
Concrete Core ◽  
Expansive Concrete ◽  
Proposed Model ◽  
Comparison Results ◽  
Concrete Filled Steel Tubes

In this paper, a modified strains development model (MSDM) for expansive concrete-filled steel tube (ECFST) was formulated and verified on the experimental data, obtained from testing specimens on the expansion stage. The modified strain development model for restraint strains and self-stresses values estimation in concrete with high expansion energy capacity under any type of the symmetrical and unsymmetrical finite stiffness restraint conditions was proposed. Based on proposed MSDM a new model for expansive concrete-filled steel tubes is developed. The main difference between this model and other previously developed models consists in taking into account in the basic equations an induced force in restrain that is considered as an external load applied to the concrete core of the member. For verification of the proposed model-specific experimental studies were performed. As follows from comparison results restrained expansion strains values calculated following the proposed model shows good compliance with experimental data. The values predicted by the proposed MSDM for concrete-filled steel and obtained experimental data demonstrated good agreement that confirms the validity of the former.

Experiment Study on Interfacial Normal Bond Strength of Concrete Filled Steel Tube

2012 ◽  
Vol 594-597 ◽  
pp. 947-954 ◽  
Author(s):  
Zhen Yu Liu
Keyword(s):  
Bond Strength ◽  
Temperature Change ◽  
Concrete Strength ◽  
Steel Tube ◽  
Test Method ◽  
Bending Test ◽  
Concrete Filled Steel Tube ◽  
Normal Bond ◽  
Core Concrete ◽  
Test Result

To study the debonding of concrete filled steel tube (CFST), pulling and bending methods were used to test the normal bond strength. Based on the test result, debonding due to temperature change and shrinkage of core concrete in CFST was analyzed. The test and analysis result shows that the bending method is a better test method; the concrete strength has little influence on bond strength while the surface condition of steel has much influence on it. The bond strength of steel which is rust is greater than that of the steel with smooth surface. According to the analysis on the bending test result, the normal bond strength of 0.86MPa was got and the debonding of CFST arch was analyzed, the analysis result shows that debonding will easily happen under the action of temperature change and shrinkage of core concrete. The test methods and results can provide a reference for engineering applications.

Axial impact behaviors of stub concrete-filled square steel tubes

2019 ◽  
Vol 22 (11) ◽  
pp. 2490-2503 ◽  
Author(s):  
YT Zhang ◽  
B Shan ◽  
Y Xiao
Keyword(s):  
Finite Element ◽  
Failure Modes ◽  
Steel Tube ◽  
Experimental Results ◽  
Parameter Analysis ◽  
Steel Tubes ◽  
Simple Method ◽  
Concrete Filled Steel Tube ◽  
Drop Weight ◽  
The Impact

Existing research on the widely used concrete-filled steel tubes is mainly focused on static or cyclic loading, and the studies on effects of high strain rate are relatively rare. In this article, seven stub concrete-filled steel tubular columns with square section were tested under both static and impact loads, using a large-capacity drop-weight testing machine. The research parameters were variable height of the drop-weight and different load types. The experimental results show that the failure modes of the concrete-filled steel tube columns from the impact tests are similar with those under static load, characterized by the local buckling of the steel tube. The time history curves of impact force and steel strain were investigated. The results indicate that with increasing impact energy, the concrete-filled steel tube stub columns had a stronger impact-resistant behavior. The dynamic analysis software LS-DYNA was employed to simulate the impact behaviors of the concrete-filled steel tube specimens, and the finite element results were reasonable compared with the test results. The parameter analysis on the impact behavior of concrete-filled steel tube columns was performed using the finite element model as well. A simple method was proposed to calculate the impact strength of square concrete-filled steel tube columns and compared favorably with experimental results.

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