Aggregate Concrete-filled Steel Tubular Columns Research Articles

A Restoring Force Correction Model for Enveloped Steel Jacket-Confined Seismic-Damaged Rectangular Recycled Aggregate Concrete-Filled Steel Tubular Columns

In order to establish a suitable restoring force correction model for enveloped steel jacket (ESJ)-confined seismic-damaged rectangular recycled aggregate concrete-filled steel tubular (RRACFST) columns, based on experimental research, a study of the seismic performance and parameters of ESJ-confined seismic-damaged RRACFST columns was carried out. The restoring force theory, model test, and OpenSees simulation of ESJ-confined seismic-damaged RRACFST columns were conducted. Firstly, a trilinear model of the skeleton curve and a suitable restoring force model for ESJ-confined seismic-damaged RRACFST columns were established. The results were compared with the model test results, and it was found that the two results had good consistency. Secondly, the initial damage of the RRACFST column was simulated by the reducing material properties method, and a correct numerical model for ESJ-confined seismic-damaged RRACFST columns was proposed. The influence mechanism of seismic parameters of the RRACFST column was clarified. Finally, the seismic parameter combination with the best seismic performance for ESJ-confined seismic-damaged RRACFST columns was established; namely, the replacement rate of recycled coarse aggregate is 50%, the concrete strength is C40, the axial compression ratio is 0.3, the strength of the rectangular steel tube is Q345, the wall thickness of the steel tube is 4 mm, and the slenderness ratio is 7.5.

Axial compressive behavior of recycled ceramic coarse aggregate concrete-filled steel tubular columns

A series of axial compressive tests were performed on recycled ceramic coarse aggregate concrete (RCCAC) cubes and prisms, as well as 36 recycled ceramic coarse aggregate concrete-filled steel tubular stub columns (RCCAC-FSTs) in the present study. RCCAC failure mechanisms, compressive strength, elastic modulus, and microstructure were studied. In addition to the cross-sectional type, the steel content, the confinement factor, and the replacement ratio of recycled ceramic coarse aggregate (RCCA) were chosen as primary variables to investigate the passive confinement effect of RCCAC-FSTs. Analysis of the typical failure modes, the Load (Nue)-longitudinal strain (εL) curve, the Load (N/Nue)-hoop strain (εh) curve, the ultimate bearing capacity, the ductility, and the effect of RCCA replacement ratio were successively performed. The results suggest that the confinement factor determines the development pattern of the load–strain curves, while the use of RCCA influences the failure mode, the elastic modulus, the ultimate strength, the critical strain, and the ductility of specimens. The critical confinement factor for circular and square specimens was also determined. A stress–strain model of RCCAC restrained by steel tube was established and verified through finite element analysis based on a database of test results presented in the present study and existing research.

Seismic performance evaluation of recycled aggregate concrete-filled steel tubular columns with field strain detected via a novel mark-free vision method

In this study, low cycle reciprocating load tests were conducted on nine recycled aggregate concrete-filled steel tube columns (RACSTCs) and a solitary ordinary concrete-filled steel tube contrast column (OCSTC). The axial compression ratio and steel-tube wall thickness were considered as the parameters of interest. Accordingly, the failure mechanism, hysteresis performance, skeleton curve, ductility coefficient, energy consumption performance, and stiffness degradation of the two types of columns were compared. A vision measurement system was developed to track the full field deformations of specimens, and a quadocular vision system was constructed to determine the concrete column deformations. The deformations were compared with those obtained from laser measurements using an image and point cloud stitching algorithm. The results show that the hysteresis curves of RACSTCs are non-pinched with large ductility coefficients for all the specimens and the equivalent viscous damping coefficients are in the range of 0.462–0.975. RACSTC specimens exhibit good seismic and deformation performance. A three-fold restoring force model was established for RACSTC specimens based on skeleton curve test data. The theoretical hysteresis curve obtained using the skeleton curve model and hysteresis rule shows good agreement with the hysteresis curve obtained from experiment. This can be used as a reference for research on the restoring force characteristics of RACSTCs. The results obtained using the vision measurement system show that the measured mean relative error values are less than 0.504%. This confirms that the multiple vision measurement method can be used to accurately measure curved surface deformations as well as the full field strain values of RACSTCs. Therefore, the proposed method can be used to evaluate the asymmetric deformation of structures subjected to vibrations, impact, and other load types, thereby providing early warning decision data.

Performance of recycled aggregate concrete-filled steel tubular columns under combined compression and shear load

This paper presents the behavior of recycled aggregate concrete-filled steel tubular columns under combined compression and shear load. A total of 30 recycled aggregate concrete-filled steel tubular specimens were tested, with their failure modes and shear capacities investigated. The main parameters considered include the cross-section type, the axial load ratio, the shear span-to-depth ratio, the steel ratio and the replacement rate of recycled coarse aggregates. A finite element analysis model is established, which is verified and then used to conduct analysis on the shear performance in terms of the failure modes, the full-range load-deflection relations, the stress distributions and the load transfer mechanism. The results show that both the axial load ratio and the shear span-to-depth ratio have influence on the failure modes. A strut-tie mechanism model is proposed to reveal these influences. Four failure modes are identified, while recycled aggregate concrete-filled steel tubular columns tend to fail in a shear manner with a smaller shear span-to-depth ratio and a higher axial load level. Finally, an existing simplified model is assessed to predict the shear capacity of recycled aggregate concrete-filled steel tubular columns under combined compression and shear load.

Numerical Study on Temperature Field of Recycled Aggregate Concrete-Filled Steel Tubular Columns Under Fire

In order to study the characteristics of the temperature field and variation law of steel pipe recycled aggregate concrete column in a fire hazard, this paper takes the thickness of steel pipe and the type of concrete material as the main parameters to carry out fire resistance test of six concrete steel columns simulated by ABAQUS and conducts finite element analysis of the temperature field inside the test piece. The result shows that both the steel pipe recycled concrete column and the ordinary steel tube concrete column have a temperature platform during heating, and their temperature rise is feature hysteresis; the thickness of the steel pipe has little effect on the internal temperature rise while the concrete material is the main factor affecting the heating rate, so steel pipe recycled aggregate concrete column is better fire-resistant. The constitutive model based on the modified parameters in European EC4 specification is used for finite element analysis, and the FEM simulation result is well fitted with the experimental data.

Seismic performance of circular recycled aggregate concrete-filled steel tubular columns: FEM modelling and sensitivity analysis

Recycled concrete aggregates (RCAs) generated from waste concrete have been recognized as a potential alternative to natural aggregates (NAs) for utilization in structural concrete to reduce the environmental impact and achieve the sustainability of resources in engineering constructions. However, it is well known that the overall performances, such as strength, ductility, energy dissipation, durability, etc., of recycled aggregate concrete (RAC) are slightly lower than those of conventional concrete made by NAs. An innovative structural component, namely RAC-filled steel tube (RACFST), was proposed to improve the deficient properties of RAC by using a steel tube to confine concrete. However, literature at large lacks methods to predict the structural performance of RACFST under seismic-induced actions. To address the scarcity of technical information on modelling the seismic performance of circular RACFST, in this study, a fiber-based FEM model is first proposed and then validated using the available experimental data on the hysteresis loops of these columns. The so-validated numerical model is then used to conduct a complete parametric study to investigate the influence of the key parameters governing the mechanical properties of the RAC and of the steel tube on the hysteretic characteristics of circular RACFST columns. Additionally, the compiled database is used to conduct a grey correlation analysis that aims to establish quantifiable evidence of the parametric sensitivity of the seismic performance of circular RACFST columns. The evaluation results show that the use of the additional water method absorption of RCAs in manufacturing RAC reduces the lateral load capacity of the columns, whereas the opposite occurs when this method is not employed. It is also demonstrated that RCA percentage has a less remarkable effect on the seismic performance of CFST manufactured using RCAs, although this effect should be considered in the seismic assessment.

Real-time detection of surface deformation and strain in recycled aggregate concrete-filled steel tubular columns via four-ocular vision

• A mark-free vision-based dynamic real-time measurement technique is proposed for full field strain and 3D deformation detection. • Point cloud combination and 3D reconstruction are applied. • The non-contact method results truly reflect the deformation process and full-field strain values. • The standard deviation mean value measured by the proposed method relative to the true value is 1.23%. • The proposed method can be used as a reasonable alternative to traditional contact methods. This study presents a dynamic real-time detection method for surface deformation and full field strain in recycled aggregate concrete-filled steel tubular columns (RACSTCs). Automatic calibration and dynamic surface tracking measurement are utilized and mathematical models combining the four-ocular visual coordinates and point cloud matching are proposed. The 3D deformation of the RACSTCs under low cyclic loading are gathered every 60 s as sample images. The four-ocular vision system constitutes two groups of binocular stereoscopic vision systems. The 3D deformation surface is reconstructed by multi-ocular vision coordinate association, image preprocessing, and point cloud registration. The measurement results are validated by comparison against laser range finder data. The standard deviation mean value of 10 specimens measured by the proposed method relative to the true value is 1.23%; the mean error of the maximum absolute value is 2.82%.

Behaviors of recycled aggregate concrete-filled steel tubular columns under eccentric loadings

The paper investigates the behaviors of recycled aggregate concrete-filled steel tubular (RACFST) columns under eccentric loadings with the incorporation of expansive agents. A total of 16 RACFST columns were tested in this study. The main parameters varied in this study are recycled coarse aggregate replacement percentages (0%, 30%, 50%, 70%, and 100%), expansive agent dosages (0%, 8%, and 15%) and an eccentric distance of compressive load from the center of the column (0 and 40 mm). Experimental results showed that the ultimate stresses of RACFST columns decreased with increasing recycled coarse aggregate replacement percentages but appropriate expansive agent dosages can reduce the decrement; the incorporation of expansive agent decreased the ultimate stresses of RACFST columns but an appropriate dosage can increase the deformation ability. The recycled coarse aggregate replacement percentages have limited influence on the ultimate stresses of the RACFST columns and has more effect than that of the normal aggregate concrete-filled steel tubular columns.

Study of seismic behavior of recycled aggregate concrete-filled steel tubular columns

This paper discusses the effects of recycled aggregate concrete strength, axial compression ratio, slenderness ratio and steel tube thickness on the seismic performance of recycled aggregate concrete-filled steel tubular columns. The failure process, hysteresis behavior, skeleton curve, stiffness degeneration, ductility coefficient, and energy consumption function were investigated by conducting low cyclic loading test on six recycled aggregate concrete-filled steel tubular columns and two normal concrete-filled steel tubular columns. The finite element method was applied to investigate the effects of slenderness ratio, steel tube thickness, and axial compression ratio on the seismic behavior. A restoring force model for the recycled aggregate concrete-filled steel tubular columns was constructed accordingly and used to compare the experimental and simulated results. The recycled aggregate concrete-filled steel tubular columns showed excellent seismic performance and deformability compared to the normal concrete-filled steel tubular columns, suggesting that they may feasibly and effectively be applied to load-bearing structures in seismic regions.

Mechanical Behavior of Recycled Aggregate Concrete-Filled Steel Tubular Columns before and after Fire.

Recycled aggregate concrete (RAC) is an environmentally friendly building material. This paper investigates the mechanical behavior of recycled aggregate concrete filled steel tube (RACFST) columns exposed to fire. Two groups of 12 columns were designed and tested, under axial compression, before and after fire, to evaluate the degradation of bearing capacity due to fire exposure. Six specimens were subjected to axial compression tests at room temperature and the other six specimens were subjected to axial compression tests after a fire exposure. The main parameters of the specimens include the wall thickness of the steel tube (steel content) and the type of concrete materials. Several parameters as obtained from the experimental results were compared and analyzed, including the load-bearing capacity, deformation capacity, and failure characteristics of the specimens. Meanwhile, rate of loss of bearing capacity of specimens exposed to fire were calculated based on the standards EC4 and CECS28:90. The results show that concrete material has a large influence on the rate of loss of bearing capacity in the case of a relatively lower steel ratio. While steel content has little effect on the rate of loss of bearing capacity of concrete-filled steel tube (CFST) columns after fire, it has a relatively large influence on the loss rate of bearing capacity of the RACFST columns. The loss of bearing capacity of the specimens from the experiment is more serious than that from the calculation. As the calculated values are less conservative, particular attention should be given to the application of recycled aggregate concrete in actual structures.

Time-Dependent Behavior of Recycled Aggregate Concrete–Filled Steel Tubular Columns

AbstractRecycled aggregate concrete–filled steel tube (RACFSTs) are attracting increasing attention from academics as a solution to use recycled aggregate concrete (RAC) as main load bearing members in multilevel or even high-rise buildings. Despite their promising future for structural use, limited attention has been devoted to investigate the time-dependent behavior of such elements. This paper reports on an investigation of how the incorporation of recycled aggregates (RAs) affects the long-term responses of these composite specimens. To achieve this, 21 RACFST specimens with different aggregate replacement ratios have been prepared for the long-term tests. The accuracy of currently available RAC concrete models in predicting the creep behavior of the RACFST specimens has been investigated based on the related experimental results. Replacing natural coarse aggregates with recycled aggregates can increase the long-term deformation of the composite columns by 22% but barely affects the rate of creep deve...

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.

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.