Aggregate Concrete-filled Steel Tube Research Articles

Concentric and Eccentric Compression Behaviour of Recycled Aggregate Concrete Filled Steel Tube Columns Strengthened with CFRP

Concentric and Eccentric Compression Behaviour of Recycled Aggregate Concrete Filled Steel Tube Columns Strengthened with CFRP

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.

Seismic Behaviors of Tailings and Recycled Aggregate Concrete-Filled Steel Tube Columns

Seismic Behaviors of Tailings and Recycled Aggregate Concrete-Filled Steel Tube Columns

Residual axial capacity of square recycled aggregate concrete-filled steel tube columns after blast loads

To study the residual axial capacity of square recycled aggregate concrete-filled steel tube (RACFST) columns after close-range explosion loads, the explosion tests and the axial compression tests were performed. Firstly, 18 square RACFST columns were fabricated, and 15 of them were subjected to explosion tests. Secondly, the axial loads were applied to 3 intact columns and 9 blast-damaged columns. The curves of the load-displacement, the load-strain, and the load-mid-span deflection of all columns are analyzed. After the tests, the failure modes of the columns and core concrete were analyzed. Furthermore, the theoretical axial capacity of the RACFST columns was calculated according to the Chinese standard GB50936-2014. Based on the residual load-bearing capacity, the damage index is adopted to assess the damage degree of 9 blast-damaged columns. It indicates that both the blast-damaged and intact columns show diagonal shear failure under axial compression; the range of bearing capacity loss of the blast-damaged columns is approximately 1.9–32.1%, of which 5 columns are slightly damaged and 4 columns are moderately damaged, indicating that the columns still maintain a strong axial capacity reserve after explosion loads.

Study on the hysteretic behavior of recycled aggregate concrete-filled steel tube columns containing ferronickel slag

To study the hysteretic behavior of recycled aggregate concrete-filled steel tube (RACFST) columns containing ferronickel slag (FNS), this paper designed and fabricated nine specimens with the recycled coarse aggregate replacement ratios (RCAs), diameter-thickness ratio, and axial load ratios as the design parameters, which were tested using low-cycle reciprocation loading tests. The damage patterns of all specimens were observed; the hysteresis and skeleton curves of each specimen were obtained. Comparative analyses of the ultimate strength, hysteretic behavior, ductility, stiffness degeneration, energy dissipation capacity, and other seismic parameters were performed. Additionally, a series of numerical models of RACFST columns were established and the relevant parametric studies were discussed. The test results showed that the damage position of the specimen was located in the plastic hinge area at the bottom of the column, which was mainly characterized by the bulging and fracturing of steel tubes. The hysteresis curves of all specimens were relatively full, and the RCAs had a negligible influence on the hysteretic behavior of the columns. With the increasing axial loading ratio, the degeneration rates of ultimate strength and stiffness were accelerated, the deformation capacity was inversely deteriorated, while the hysteretic energy dissipation was unexpectedly enhanced. As the diameter-thickness ratio declined, both the ultimate strength and ductility of the columns were improved accordingly. Furthermore, an applicable numerical model was established and compared with the test results. The numerical results were in good agreement with the test results and especially could reflect the hysteretic behaviors of columns. Moreover, the results obtained from the parametric analyses showed that the slenderness ratio, axial load ratio, and steel ratio all exhibited a relatively large effect on the ultimate strength and ductility of the specimens, while the effect of the RAC strength was relatively small.

Experimental study on the seismic behavior of CFRP-strengthened seismic-damaged recycled aggregate concrete-filled rectangular steel tube frame columns

The seismic performance of rectangular steel tube steel tube frame columns filled with recycled aggregated concrete and reinforced with carbon fiber cloth was evaluated. Four frame columns were designed and fabricated at a scale of 1:2, seismic damage was simulated, and low-cycle reciprocating load tests were conducted. The results showed that the damage process and damage pattern of the specimens were similar to those of concrete-filled steel pipe frame columns. The hysteresis curve of the reinforced specimens was fuller than that of the unreinforced specimen, and the shape of the hysteresis curve changed from a shuttle to a bow shape; The carbon fiber cloth improved the specimen's bearing capacity and stiffness, significantly improved the ductility, energy dissipation capacity and seismic performance. The reinforcement effect of the carbon fiber cloth was related to the pre-damage level of the specimens, and used of carbon fiber cloth improved the seismic performance of the specimens. The hysteresis curve and skeleton curve obtained from the test were used to establish the restoring force model of the specimens, and the displacement amplitude of the bearing capacity obtained from the model and experiment were compared. The restoring force model can be used for the elastic-plastic seismic analysis of the seismically damaged rectangular steel tube frames filled with recycled aggregate concrete.

Seismic behavior of full-scale square high-strength RACFST columns

The research purpose was to investigate the seismic behavior of full-scale square high-strength recycled aggregate concrete-filled steel tube (RACFST) columns. With the recycled coarse aggregate (RCA) replacement ratio, shear-span ratio and axial compression ratio as the variation parameters, seven column specimens were subjected to low-frequency cyclic loading tests. The test results showed that square high-strength RACFST columns had reliable seismic performance, their failure modes were similar to those of normal CFST columns, and the damage was mainly concentrated at the column roots. The bearing capacity and ductility of high-strength RACFST columns were less affected by the RCA replacement ratio, while the shear-span ratio and axial compression ratio had a greater impact on the peak bearing capacity, ductility, and other hysteretic behavior indexes. Meanwhile, a restoring force model established based on the test research and theoretical analysis agreed well with the test hysteresis curves. Finally, a fiber element model (FEM) using Opensees software was developed and a good agreement was achieved between the test and predicated results. The so-validated numerical model was then used to investigate the influence of the key parameters, such as the RCA replacement ratio, diameter-to-thickness ratio, axial compression ratio, shear-span ratio, and steel yield strength on the seismic performance of square high-strength RACFST columns.

Experimental investigation on recycled aggregate concrete filled steel tubular stub columns under axial compression

This paper presents an extensive experimental investigation of the circular recycled aggregate concrete filled steel tubes (RACFST) stub columns under to axial compression to assess their cross-section behaviour. Recycled aggregate concrete is a sustainable concrete produced with recycled coarse aggregate (RAC) from demolition wastes generally used to fabricate non-structural elements. When compared with natural coarse aggregate (NCA), the recycled coarse aggregate presents lower mechanical properties due to physical and chemical changes that occurred during the recycling process, and thus the resulting RAC possess lower strength than the conventional natural aggregate concrete. However, the confinement provided by the circular steel tube can increase the strength and ductility of RAC in recycled aggregate concrete filled steel tubes (RACFST) columns. The test programme presented in this paper comprised twenty-three composite columns with replacement ratios (the mass percentages of the NCA replaced by RCA in concrete) corresponding to 0% (nature coarse aggregate), 30 and 50% (recycled aggregate concrete), plus four steel columns used for comparison. The experiments have shown that, as anticipated, the concrete core enhances the composite section load-carrying capacity. However, the control over the contents of this concrete core influences the composite section's ductility. If the fill material presents a brittle behaviour, stress redistributions occur in both steel and concrete to compensate for this effect. Since the behaviour of natural aggregate concrete filled steel tubes (NACFST) and RACFST columns are similar, the present paper starts from a study based on a comparative assessment of the recommendations presented in ABNT NBR 8800, ABNT NBR 16239, AISC 360–16, Eurocode 4 and Australian/New Zealand AS/NZS 2327 design standards. These design recommendations proved to be consistent and in line with the performed experiments. Additionally, the results indicated that the cross-section slenderness ratio (D/t) and the confinement ratio directly influence the composite section response.

강섬유 보강 순환골재 콘크리트 충전 각형강관의 전단성능 실험

강섬유 보강 순환골재 콘크리트 충전 각형강관의 전단성능 실험

Impact of aggregate content and tube thickness on semi‐lightweight aggregate concrete filled steel tube subjected to uniaxial compression

AbstractArtificial lightweight aggregates (LWA) generally can be more deformable in lateral expansion than that of natural crushed stone. Therefore, concrete made of LWA can exhibit a higher Poisson effect, and this characteristic could be advantageously used in the confined elements. In the present study, experimental research on behaviors of semi‐lightweight aggregate concrete filled steel tube (LWACFT) under axial compression is performed, in which the key parameters such as the volume content of LWA and the thickness of steel tube are involved. The results showed that the bearing capacity of LWACFT columns is influenced by the compressive strength and Poisson effect of LWAC in dual‐facets. With a rational LWA volume fraction, the bearing capacity of LWACFT columns is not less than that of traditional CFT. Furthermore, the experimental results of bearing capacity are compared with the results by current design codes. With the volume content of LWA and the steel thickness as the variable, the modified and simplified models have been proposed to predict the axial load versus strain curves and the bearing capacity of LWACFT columns. The research results have demonstrated that the predicted results by the model proposed in this study agree well with the experimental ones.

Axial behavior of carbon fiber-reinforced polymer–confined recycled aggregate concrete-filled steel tube slender square columns

The behavior of fiber-reinforced polymer (FRP)–confined recycled aggregate concrete-filled steel tube (RACFT) columns is barely studied. Especially, that of slender specimens has not been investigated so far. In this article, an experimental test of FRP-confined RACFT slender square columns was conducted to study the influences of recycled aggregate (RA) replacement ratios, FRP thicknesses, and wrapping schemes on their axial behavior. Results in this article suggest that the RA replacement ratio barely affects the initial stiffness of load-deflection curves of specimens. Moreover, the specimen with a higher RA replacement ratio has a lower axial stress but larger strain at the peak point. The external FRP jackets (either partial or full wrap) can effectively improve the performance of axially loaded RACFT columns, and the improvement of ductility due to the increase of the FRP thickness is more significant than that of axial compressive strength. Additionally, it was found that the axial strength and ultimate axial strain decrease with increasing slenderness ratios. Furthermore, the influences of slenderness ratios on the behavior of such columns are more significant for the column with a larger length-to-width ratio. Finally, a design model for FRP-confined RACFT slender square columns is developed, which can predict the results of the present test accurately.

Study on axial compressive stiffness of RAC-encased RACFST composite columns

Twenty four specimens were designed to investigate the axial compressive stiffness of the recycled aggregate concrete(RAC)-encased recycled aggregate concrete-filled steel tube (RACFST) composite columns. The working mechanism of the RAC-encased RACFST composite column was investigated and the full range load–displacement curves of the composite columns were obtained. The interaction of each component of the composite column, i.e. the effect of the outer RAC from the stirrup and the steel tube, and the effect of the core RAC from the stirrup and the steel tube, were analyzed. The constitutive models of the outer unconfined RAC, the outer confined RAC, the core RAC were discussed. Thereupon, simple formulas were proposed to calculate the axial compressive stiffness of composite columns. These formulas can assist engineers to predict the axial deformation of structure in high-rise buildings more accurately.

Experimental and numerical investigations of circular recycled aggregate concrete-filled stainless steel tube columns

This paper reports a comprehensive experimental and numerical study of the flexural buckling behaviour and resistances of circular recycled aggregate concrete-filled stainless steel tube columns. The experimental programme, adopting four series of column specimens designed with various stainless steel tube sizes, recycled coarse aggregate replacement ratios and member lengths, included material tests on both recycled aggregate concretes and stainless steel tubes, initial global geometric imperfection measurements and pin-ended column tests. The obtained experimental results, including the failure loads, load–mid-height lateral deflection curves and flexural buckling failure modes, were reported in detail. The effects of the stainless steel tube size, recycled coarse aggregate replacement ratio and member length on the flexural buckling resistances of the column specimens were examined. The lateral deflection distributions along the column specimen lengths and the development of the longitudinal strains of the outer stainless steel tubes were discussed. The experimental programme was supplemented by a numerical modelling programme, in which finite element models were developed and validated against the test results and then used for conducting parametric studies to generate further numerical data over a wide range of cross-section dimensions and member lengths. Given that there have been no existing design codes for recycled aggregate concrete–stainless steel composite structures, the relevant codified design rules for circular natural aggregate concrete-filled carbon steel tube columns failing by flexural buckling, as used in Europe, Australia/New Zealand and America, were assessed for their applicability to circular recycled aggregate concrete-filled stainless steel tube columns, based on the test and numerical data. The assessment results revealed that the design rules, as given in the Australian/New Zealand standard and American specification, result in unsafe flexural buckling resistance predictions when used for circular recycled aggregate concrete-filled stainless steel tube columns, while the Eurocode design rules lead to more safe and accurate flexural buckling resistance predictions.

Response and modeling of axially-loaded concrete-filled steel columns with recycled coarse and fine aggregate

Recycled aggregate concrete-filled steel tube (RACFST) could be a practical structural application of recycled aggregate concrete (RAC) with fine recycled aggregate (FRA). Despite its great potential, limited attention has been devoted to the compressive response of RACFST with FRA. This study investigates the effects of FRA on the structural response of RACFST with different coarse recycled aggregate (CRA) replacement ratios (rC), and how FRA influences the confinement effect of RACFST. Fifty-four RACFST specimens were tested to failure with different FRA and CRA replacement ratios (rF and rC), concrete strengths (fcm) and effective steel ratios (α). Experimental results show that FRA and CRA have a significant compounding effect (i.e., FRA effect is different at varying rC) on the strain at the maximum load (ε0) of RACFST. Unlike CRA which has an insignificant influence on the confinement effect, the use of FRA significantly reduces the confinement of RACFST. The test results were used to modify the existing mathematical expressions for normal concrete-filled steel tube (CFST) to predict the stress-strain relationships for RACFST. The predicted results matches well with the available test data.

Behaviour of rectangular RACFST slender columns under eccentric compression

Experimental and numerical studies on the static behaviour of eccentrically compressed recycled aggregate concrete filled steel tube (RACFST) slender columns with rectangular cross-section are reported in this paper. Fifteen specimens were tested under eccentric compression. The factors considered in the experimental investigation included: 1) depth-to-width ratio (β), from 1.0 to 2.0; 2) load eccentricity ratio (m), from 0 to 0.6; 3) slenderness ratio (λ), from 20 to 40; and 4) recycled coarse aggregate (RCA) replacement ratio (r), from 0 to 100%. The experimental results show that failure of the eccentrically compressed specimens is manifested with major local buckling of the steel tube coving compression flange and part of side walls near the mid-height section and the crushing of the concrete core at the same location. The eccentrically compressed specimens generally possess stable load versus deformation curves including the initial linear and the subsequent nonlinear stages before reaching the peak load and the post-peak descending stage. In addition, when other parameters keep constant, the specimens with larger m, λ and r possess smaller bearing capacity (Nue), and m has more significant effect on Nue than λ and r. Numerical simulation of the eccentrically compressed rectangular RACFST slender columns is also carried out by a finite element analysis (FEA) model built in ABAQUS, and the model is verified by experimental results. The typical mechanism of rectangular RACFST slender columns under eccentric compression is further revealed by the FEA model. Finally, simplified formulae for the bearing capacity are developed, and the comparison between simplified and experimental results indicates that the simplified model is accurate in predicting the bearing capacity of rectangular RACFST slender columns.

Axial compressive behavior of recycled aggregate concrete-filled square steel tube stub columns strengthened by CFRP

Fiber-reinforced polymer (FRP)-confined recycled aggregate concrete-filled steel tube (RACFT) columns significantly mitigate the defects of RAC, and hence can be potentially used in structural engineering, e.g., column and pile. However, the existing studies on the behavior of recycled aggregate concrete-filled steel tube (RACFT) columns strengthened by the fiber-reinforced polymer (FRP) are scarce, especially those on square specimens. This paper presents an experimental study to investigate the compressive behaviors of FRP-confined RACFT square columns. The results in this paper suggest that the FRP-confined RACFT column with a higher RA replacement ratio has a smaller axial strength of the specimen, but tends to exhibit more ductile behavior. The specimen confined by a thicker FRP tends to have a higher axial strength and larger ultimate strain due to the better confinement effect of thicker FRP on the RACFT column. Additionally, compared with the partial wrapping scheme, the full wrapping scheme mainly improves the ductile behavior of the RACFT columns rather than their axial strengths. Based on the test results, a design model of the axial load bearing capacity for FRP-confined RACFT columns is proposed, which is found to predict the results of experimental tests accurately.

Seismic experiment and performance index studies on recycled aggregate concrete filled steel tube frames infilled with recycled hollow block filler walls

AbstractTo study the seismic behavior of recycled aggregate concrete filled steel tube (RACFST) frames infilled with recycled hollow block filler walls (RHBFW), four frame specimens were designed subjected to low cycle loading experiments. Through the test, the failure process and pattern of specimens were observed and the seismic performance indexes were obtained. The results show that the hysteretic curves of RACFST frames infilled with RHBFW are full; the equivalent viscous damping coefficients he of specimens when destroyed both exceed 0.2, and the interlayer displacement angle is between 1/34 and 1/33 when destroyed, meaning the frame structures having good energy dissipation and good collapse resistance abilities. The RAC beam section height has little effect on the ductility and stiffness degradation of specimens; however, the bearing capacities of specimens increase gradually with the increase of beam section height. The existence of RHBFW can be the first seismic defense line of RACFST frames, and they can improve the ductility of specimens, as well as the bearing capacities and initial elastic stiffness. Before RHBFW failed, the specimens with filler wall have better energy dissipation abilities than those without filler wall. After RHBFW failed, the specimens without filler wall have better energy dissipation abilities than those with filler wall.

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.

Flexural behavior of steel fiber reinforced self-stressing recycled aggregate concrete-filled steel tube

Recycled aggregate concrete (RAC) has the potential to escape the predicament of our cities being surrounded by construction waste, while its application is limited due to the defective mechanical properties. This paper aims to improve the performance behavior of RAC, thereby extending its engineering application. A new-style green RAC is prepared by recycled aggregate, steel fiber and sulphoaluminate cement, as infilling into steel tube to manufacture CFST columns. A comprehensive study for 41 concrete mixes and 54 CFST columns subjected to bending is presented. The parameters are steel fiber volume content, recycled aggregate dosage, water cement ratio, cement type and steel tube thickness. The test result reveals that, through reasonable mix design, steel fiber reinforced self-stressing recycled aggregate concrete-filled steel tube can exhibit similar flexural behavior with the normal CFST. Steel fibers prolong the elastic extent and improve the flexural capacity, meanwhile 1.2% of steel fiber is recommended for the optimal improvement. Self-stress induced by the expansive sulphoaluminate cement contributes to the elastic stage, and is beneficial to flexural capacity and stiffness.

Tests and numerical simulation of rectangular RACFST stub columns under concentric compression

Tests and numerical simulation of rectangular recycled aggregate concrete filled steel tube (RACFST) stub columns under concentric compression are carried out. Eighteen specimens, including 12 RACFST specimens and 6 concrete filled steel tube (CFST) specimens as reference, with varied width-to-thickness ratio (B/t), depth-to-width ratio (β) and recycled coarse aggregate replacement ratio (r) are tested. The test results show that rectangular RACFST stub column specimens have similar failure pattern as their counterparts. However, the bearing capacity and the composite elastic modulus of RACFST specimens are lower than those of CFST ones while they both decrease with higher r. Moreover, the specimens with larger B/t and β possess a smaller ductility index. Numerical simulation of rectangular RACFST stub columns under concentric compression is executed using a finite element analysis (FEA) model developed based on the ABAQUS software, and the predicted results are verified by the experimental observations. The mechanism of concentrically loaded rectangular RACFST stub columns is further revealed by the FEA model. Finally, simplified formulae for the bearing capacity of rectangular RACFST stub columns are proposed, with the comparison between simplified and experimental results showing that the simplified model is a good predictor.