Self-compacting Concrete-filled Steel Tube Research Articles

Resilience-based seismic design and cyclic behavior of assembled joints between self-compacting concrete-filled rectangular steel tube frame columns and H-shaped steel beams

The overall stability of prefabricated steel structures depends significantly on the strong seismic resilience exhibited by the connections between beams and columns. This paper introduces a novel beam–column connection approach, referred to as the welded upper and lower flanges and two diagonal web plates (WULF-TDWP). Unlike conventional methods, this approach replaces bolted connections with butt-welded joints between steel beams and employs short cantilever beams to achieve plastic hinge displacement. The steel-column cross-section was designed with a larger aspect ratio to better absorb and distribute energy. Six full-scale specimens were subjected to cyclic loading tests to investigate the seismic performance of the WULF-TDWP system. The main test parameters included the axial load ratio, welding configuration in the node region, and presence of reinforcement plates. The specimens exhibited two distinct failure modes: plate buckling deformation and beam–column end weld tearing. The experimental results included the hysteresis curves, skeleton curves, ductility coefficients, stiffness degradation curves, and strength degradation curves of the specimens. The experimental findings highlighted the favorable hysteresis performance, load-carrying capacity, and deformation capacity of all the nodes. Additionally, the plastic hinges were observed to shift, thereby delaying the premature failure of the node region. Notably, the omission of welding between the cantilever short beam flange and steel column significantly reduced the initial stiffness of the node. Through finite element analysis, the seismic performance of the beam-column joints with upper and lower flange welded connections and cantilever short beams was elucidated. The reliability of the finite element model for assessing the seismic performance of the nodes was confirmed through validation using experimental findings. Furthermore, this paper categorizes the nodes and introduces a simplified calculation model based on the moment–rotation method.

Self-compacting concrete filled steel tube specimens with RHA and M-Sand replacement subjected to axial compression

ABSTRACT Because the cement content is inexorably growing, CO2 emissions from the cement industry are becoming unavoidable. The use of rice husk ash (RHA) makes the system environmentally benign. This paper investigates the effect of RHA and manufactured sand (M-Sand) on the axial capacity of circular Concrete Filled Steel Tube (CFST) specimens subjected to axial compression. Thirty-two CFST specimens infilled with self-compacting concrete (SCC) with a replacement of RHA and M-Sand to cement and fine aggregate in 0%, 15%, 20% and 25% proportions are subjected to axial compression. Results show that use of RHA beyond 20% decreased the compressive strength of concrete and eventually decreased the axial capacity of CFST and occurred higher local buckling irrespective of their L/D ratios. Failure modes, strength index, confinement along with steel and concrete contribution on axial capacities of CFST specimens are studied. The axial capacities of the specimens were compared with various design code results such as: American concrete institute, Australian Standards, Chinese code, Eurocode, and Japanese code. Among all the codes, Chinese code overestimated the test results and hence, the axial capacity equation is altered and compared the results with test data along with 278 circular CFST data available from literature and found the results to be accurate.

Eccentric Compression Behaviors of Self-Compacting Concrete-Filled Thin-Walled Steel Tube Columns.

For the sake of solving sustainability issues and analyzing the complicated service force states, eccentric compression experiments on self-compacting concrete-filled thin-walled medium-length steel tube columns with a circular cross-section were carried out in the present study. Thereafter, the influence of the eccentric ratios and the wall thickness factors on the mechanical behavior and failure characteristics of both the eccentrically loaded and axially loaded columns was comprehensively analyzed. Finally, prediction formulas for the ultimate load of the columns under eccentric compression were proposed, and a comprehensive comparison of the ultimate loads between the predicted values and experimental values was also conducted. The results indicated that the typical failure characteristics of the eccentrically loaded columns presented lateral deflection together with buckling, while the axially compressed columns displayed expansion and rupture at local positions. Moreover, the ultimate loads of the eccentrically loaded columns decreased by 43.0% and 34.5% in comparison to the columns under axial compression, with the wall thickness factor decreasing from 116.7 to 46.7, respectively. Meanwhile, the ratios of the ultimate loads calculated using design codes to the tested values were in the range of 0.70~0.90, which demonstrated that the design codes could predict the ultimate loads conservatively. Additionally, the ratios of the ultimate loads calculated using the proposed formulas to the tested values were within the range of 0.99~1.08, implying that the proposed formulas were more accurate than the design codes. At the same time, the initial stiffness of the columns under eccentric compression was correspondingly lower than that of the columns undergoing axial compression. The lateral deflections along the height of the columns were almost symmetrical at different loading levels. This study could provide a meaningful approach for designing columns and facilitate their application in civil industry.

Influence of recycled large-aggregate self-compacting concrete-filled steel tube mechanical properties under pure bending load

ABSTRACT In this study, the influence of different factors on pure bending members of recycled large-aggregate self-compacting concrete-filled steel tubes (RLA-SCCFSTs) was analyzed. Seven RLA-SCCFST members and one SCCFST member were designed to study their failure under a pure bending load and the influence of the steel tube wall thickness, RLA strength, and RLA particle size. The flexural bearing capacity was calculated using various codes. Based on the test results, ABAQUS and MIDAS FEA NX finite element analysis software were used to simulate and verify the test conditions. The results showed that under a pure bending load, the failure process of the RLA-SCCFSTs was much the same as that of an ordinary concrete-filled steel tube. Moreover, changes in the influencing factors resulted in different degrees of improvement in the flexural bearing capacity of the RLA-SCCFSTs. The factors most affecting the flexural members of the RLA-SCCFSTs – from large to small – included the steel tube wall thickness, RLA strength, and RLA particle size. The finite element simulation shows that the model based on the modified constitutive relation of core concrete was in good agreement with the experimental results. Among the various calculation methods for the bearing capacity, the results using the DBJ13-51-2003 specification were in good agreement with the test results. This study provides a reference for the reuse of waste concrete.

Seismic Performance of RC Circular Columns Strengthened with Self-compacting Concrete-Filled Steel Tubes

Seismic Performance of RC Circular Columns Strengthened with Self-compacting Concrete-Filled Steel Tubes

Experimental study on self-compacting concrete-filled steel tube samples containing shrinkage-controlling admixtures

Once again, the earthquake disaster in Turkey and Syria indicates the significance of aseismic structures. Concrete-filled steel tube (CFT) columns are key components in such structures. In this study, the effect of shrinkage control admixtures on the performance of self-compacting mixes that are often used in CFT column construction was evaluated. They were confined to a 3 mm thick cylindrical hollow steel tube and the infilled concrete shrinkage was monitored with the embedment of a vibrating wire strain gauge. The concrete length of this compound was found to be reduced as the length of the confining tube expanded. However, this change in concrete length was reduced by 70% with the use of a commercial grade liquid mixture that reduces shrinkage in the early stages. A substantial reduction in concrete shrinkage was observed with the use of limestone powder and a compensating admixture for shrinkage. The use of limestone also improved the resistance of concrete to water permeation and chloride ion transport by pore filling effects. Although steel confinement reduced concrete shrinkage by 50% at 28 days, the addition of specialty admixtures is still highly recommended to avoid the effect of debonding, induced by the shrinkage discrepancy between confining steel and the inner concrete mass.

Experimental Study on Self-Compacting Concrete-Filled Thin-Walled Steel Tube Columns

Concrete-filled steel tubes present excellent structural and constructional performances because they ideally combine the advantage of concrete and steel tube. Thus, they are widely used in civil infrastructures. However, they inevitably suffer from either hard compacting or high costs. Thus, convenient and rapid construction for compacting concrete and cost saving are the urgent challenges for concrete-filled steel tubes. Therefore, this study investigates filling a thin-walled steel tube with self-compacting concrete to solve the challenges presented by traditional concrete-filled steel tube columns, such as poor compacting performance and high costs. This experimental study tests self-compacting concrete-filled thin-walled steel tube (SCCFTST) columns under concentric compression from loading to failure. Effects of wall thickness of the thin-walled steel tube on the failure modes, load-deformation behaviors, and the ultimate loads of the SCCFTST columns are comprehensively investigated. The ultimate loads between experiments and their calculated values in terms of design codes are also compared. The results suggest that buckling on thin-walled steel tube surface is the typical failure mode. The amount of local buckling increases with decreasing wall thickness, and the decreasing rate of the load-deformation curves in the descending branch decreases by increasing the wall thickness, as well as the ultimate load increasing with increases wall thickness. The ACI and CECS are the most conservative and accurate design codes, respectively, for predicting the ultimate load. Therefore, the SCCFTST columns can be used as structural components in civil infrastructures and their peak loads can be calculated using design codes for conventional concrete-filled steel tube columns. However, modification measures must be taken while predicting the ultimate loads of the SCCFTST columns by design codes. The experimental results of this paper can contribute towards the application of SCCFTST columns in practice.

Axial Compressive Properties of Self-Compacting Concrete Filled Steel Tube Short Columns with Ground Desulfurization Slag.

Desulfurization slag (DS) is the solid waste discharged from the bottom of the circulating fluidized bed (CFB) boiler. It has good pozzolanic activity, self-hardening property and large expansibility. In this paper, ground desulfurization slag (GDS) is used as mineral admixture to replace cement to prepare self-compacting concrete (SCC). In order to find out the influence laws of different factors on the axial compressive properties of the self-compacting concrete filled steel tube (CFST), seven types of SCC are prepared and nine groups of CFST short column are fabricated. Filling ability test, compressive strength test and axial compressive test are performed. The filling ability and the compressive strength of the SCCs are investigated, and the axial compressive properties of the CFSTs are researched. The results show that the amount of polycarboxylate superplasticizer (PS) increases with the amount of GDS, and the addition of GDS decreases the 3d, 7d and 28d compressive strength of the SCCs. The optimum amount of GDS for SCCs and CFSTs is 30%. When the amount of GDS is 30%, the ultimate bearing capacity of CFST short column (GP3) is the highest, which is 33.6% higher than that of GP1 without GDS. The influence law of the GDS’s amount on the CFSTs’ ultimate bearing capacity is quite different from that of the GDS’s amount on the SCCs’ compressive strength. The ultimate bearing capacity of CFSTs can be significantly improved by adding GDS. Sodium sulfate can improve both the compressive strength of the SCC and the bearing capacity of the CFST.

Experimental and numerical investigations of interfacial bond in self-compacting concrete-filled steel tubes made with waste steel slag aggregates

New self-compacting concrete (SCC) mixtures were designed to improve the interfacial bond strength in concrete-filled steel tubes (CFST) at 30 days and one year. The proposed SCC mixtures involved the strengthening of bond strength by using waste steel slag aggregates (SSA). A total of thirty-six circular and squared tube specimens with different ratios (0%, 25% and 50%) of SSA as a replacement by weight of coarse and fine aggregates in SCC were initially prepared. The results revealed that the using of SSA in SCC enhanced the specimens' bond strength for both shapes of steel tubes and the bond strength was reduced with an increase of concrete's age. Additionally, the incorporating of SSA did not decrease the loss in bond strength at one year. A three-dimensional non-linear finite element (FE) analysis was further conducted to simulate the interfacial bond-slip mechanism between two surfaces of the infill concrete and inner steel tubes.

Performance of fly ash and silica fume self-compacting concrete filled steel tube stub columns under axial compression

Experimental research on the performance of fly ash and silica fume selfcompacting concrete filled steel tube (FSS CFST) stub columns under axial compression were conducted. The main parameters varied in the tests are steel tube’s diameter to thickness ratio, D/t (from 20 to 33), and yield strength (from 275.83 MPa to 350.51 MPa). The self-compacting concrete grade used as infill is M60 concrete with 50% and 10% addition of fly ash and silica fume, as partial replacement of Portland cement. The performance of FSS CFST stub columns is examined via the axial compression capacity, load-shortening response, and mode of failure of 12 specimens. The results indicate that the ultimate axial load capacity of the columns increases as the D/t ratio decreases. The FSS CFST columns have a maximum concrete contribution ratio of 3.72, a strength index greater than unity, and a ductility index of 2.431 and below. The predicted values obtained using Eurocode 4 closely estimate the test results with a mean of 0.927 and a standard deviation of 0.073. Conversely, the predicted values using ACI code are more conservative with a mean of 1.341 and a standard deviation of 0.089.

Experimental Study on Short Steel Tube Columns Filled with Recycled Large Aggregate-Self Compacting Concrete Subjected to Compression

The mechanical characteristics of recycled large aggregate concrete show poorer performance than that of Portland-cement concrete due to the internal defects of recycled large aggregate (RLA). To improve the mechanical characteristics of recycled large particle size aggregate concrete, the recycled large aggregate Self-Compacting Concrete filled steel tube (RLA-SCCFST) is proposed. The external steel tube can not only keep the core recycled large aggregate concrete in the three-dimensional state of stress, but also prevent the crack expansion of the core recycled large aggregate concrete. RLA-SCCFST subjected to compression is studied experimentally. The compression failure tests use 20 specimens of circular section short column with different steel content rate, particle size of RLA, strength of RLA, strength of SCC, and eccentricity of the load. The influence of different factors on mechanical characteristics of RLA-SCCFST short cylindrical components subjected to compression is analyzed. The results indicate that the load-bearing performance of RLA-SCCFST short columns increases following with the augmentation of RLA particle size, strength of RLA particle size, strength of SCC and steel content rate. The load-bearing performance of RLA-SCCFST short columns reduced with the augmentation of the load eccentricity. And the experimental results are in high coincidence with those calculated by different formulas.

Axial compressive behaviour of steel fibre reinforced self-stressing and self-compacting concrete-filled steel tube columns

This study attempted to explore the effects of initial self-stress in concrete and steel fibre on the compressive behaviour of concrete-filled steel tube (CFST) columns. A total of 36 CFST columns with a radial self-stress ranging between 3.31 MPa and 6.66 MPa and a steel fibre volume percentage of 0, 0.6% and 1.2% were tested under axial compression. The steel tube thickness of 2.5 mm, 3.5 mm and 4.25 mm was used to achieve different confining stiffness to the expansion of concrete core. The concrete strength grade of C40, C50 and C60 was used to obtain different expansion deformations. The failure mode, axial load-axial shortening curve, ultimate load and ductility of CFST columns were investigated. Experimental results showed that all specimens exhibited shear failure, and neither self-stress nor steel fibre had obvious influence on the failure mode. Self-stress in concrete enhanced the ultimate load of the CFST columns by 9.8%–27.6%, but decreased their deformability significantly. Adding steel fibres could enhance the ultimate load and slightly improve the post-peak behaviour and ductility of CFST columns with self-stress. Based on the results of this study and literature, an optimum self-stress level (the ratio of radial self-stress and concrete strength) of 0.10 is proposed. Finally, formulas are proposed to predict the load carrying capacity of FSS-SCCFST columns under axial compression, and the predictions agree well with the test results.

Finite element simulation of recycled large aggregate self-compacting concrete short columns with steel tubes

In order to study the mechanical properties of recycled large aggregate self-compacting concrete filled steel tube(RLA-SCCFST) and promote the research and application of the structure, the mechanical properties of nine groups of RLA-SCCFST short columns under axial compression were studied by ABAQUS simulation. Comparing the results of finite element simulation with the test results, it is found that: 1. The simulation results of the load-vertical strain curve are in good agreement with the test results, and the maximum error of the ultimate bearing capacity measured by the simulation and the test is within 3%; 2. The ultimate bearing capacity and ductility of RLA-SCCFST specimen increase with the increase of steel pipe wall thickness, recycled large aggregate strength and self-compacting concrete strength, and the ultimate bearing capacity of specimen decreases with the increase of recycled large aggregate content.

自密实钢管混凝土合理膨胀剂参量研究

自密实钢管混凝土合理膨胀剂参量研究

Flexural behavior of lightweight concrete and self-compacting concrete-filled steel tube beams

The study presents a comparative experimental analysis of the flexural behavior of lightweight concrete and self-compacting concrete filled square steel tube beams subjected to pure bending. A total of 20 specimens including eight lightweight concrete-filled steel tube (LWCFST) beams, eight self-compacting concrete-filled steel tube (SCCFST) beams, and four hollow steel tubes were tested. The main parameters varied during the experiment include (1) type of concrete core, lightweight concrete (LWC), and self-compacting concrete (SCC); (2) width to thickness ratio; and (3) confinement factor (ξ). The flexural capacities, flexural stiffness, ductility, failure modes, deflection curves, and bending moment versus mid-span deflection curves were examined. Several performance indexes were used to discuss the flexural strength, stiffness, and ductility of the tested beams. The test results revealed that LWC and SCC significantly improved the overall flexural behavior of square hollow steel tubular sections. The results indicated improvements in flexural strength, stiffness, and ductility. Furthermore, a comparison was performed, and the findings indicated that LWCFST beams exhibit increased flexural stiffness, comparable moment resistance, and lower ductility when compared to SCCFST beams. The moment capacities and flexural stiffness were compared with the predicted values by using various design codes, and the comparisons indicated that all the design codes are conservative with respect to the estimation of the moment capacity. However, all the design codes are not conservative with respect to the prediction of the serviceability level flexural stiffness. The test results and comparisons motivate application of LWCFST and SCCFST beams as a potential alternative for normal weight CFST beams.

Bond behavior of steel-fiber-reinforced self-stressing and self-compacting concrete-filled steel tube columns for a period of 2.5 years

The aim of this study is to explore the influence of concrete age on the bond behavior of steel-fiber-reinforced self-stressing and self-compacting concrete-filled steel tube (FSSCFST) columns. The push-out tests of 36 FSSCFST columns are conducted at ages corresponding to 28 d or 2.5 y. All specimens with an age of 2.5 y are tested under four cycles of repeated loading. The variables considered in the test are as follows: (a) concrete age (28 d and 2.5 y); (b) thickness of the steel tube (2.5 mm, 3.5 mm, and 4.25 mm); (c) steel-fiber volume percentage (0% and 1.2%). The experimental results indicate that an increase in the concrete age increases the bond strength and corresponding slip (Su) of FSSCFST columns. The addition of steel fibers improves the bond behavior at an early age and it generally loses its effect with increases in the concrete age. With increases in the loading cycle, the bond strength in the same direction exhibits a decreasing trend. However, steel fibers delay the degradation in bond strength.

Performance of Retrofitted Self‐Compacting Concrete‐Filled Steel Tube Beams Using External Steel Plates

Self‐compacting concrete‐filled steel tube (SCCFST) beams, similar to other structural members, necessitate retrofitting for many causes. However, research on SCCFST beams externally retrofitted by bolted steel plates has seldom been explored in the literature. This paper aims at experimentally investigating the retrofitting performance of square self‐compacting concrete‐filled steel tube (SCCFST) beams using bolted steel plates with three different retrofitting schemes including varied configurations and two different steel plate lengths under flexure. A total of 18 specimens which consist of 12 retrofitted SCCFST beams, three unretrofitted (control) SCCFST beams, and three hollow steel tubes were used. The flexural behaviour of the retrofitted SCCFST beams was examined regarding flexural strength, failure modes, and moment versus deflection curves, energy absorption, and ductility. Experimental results revealed that the implemented retrofitting schemes efficiently improve the moment carrying capacity and stiffness of the retrofitted SCCFST beams compared to the control beams. The increment in flexural strength ranged from 1% to 46%. Furthermore, the adopted retrofitting schemes were able to restore the energy absorption and ductility of the damaged beams in the range of 35% to 75% of the original beam ductility. Furthermore, a theoretical model was suggested to predict the moment capacity of the retrofitted SCCFST beams. The theoretical model results were in good agreement with the test results.

Performance of the High-Strength Self-Stressing and Self-Compacting Concrete-Filled Steel Tube Columns Subjected to the Uniaxial Compression

To improve the compactness of concrete and prevent the debonding between steel tube and concrete core, a high-strength self-stressing and self-compacting concrete-filled steel tube (HSS–CFST) column is introduced. This paper deals with an experimental study on the uniaxial compression of HSS–CFST. A total of 51 specimens subjected to axial compression were investigated. Important variables, including self-stress level, concrete strength, tube thickness, and length-to-diameter ratio, were studied. The failure modes, ultimate bearing capacity, and post-peak ductility were analyzed. The results showed that the use of HSS concrete in CFST yielded a better uniaxial compression performance in comparison with the conventional CFST specimens. An increase of 12.4% in ultimate bearing capacity was observed for an HSS–CFST specimen having a self-stress of 5 MPa. The improvement becomes more pronounced as the length-to-diameter ratio increases. Besides, increasing concrete strength can also contribute significantly to the ultimate bearing capacity, while improvement on the post-peak ductility is not obvious. Furthermore, a numerical analysis considering the self-stressing was carried out, which provided good agreement between the experimental results. Finally, predictive equations specially to calculate the ultimate bearing capacity of HSS–CFST columns were proposed and then validated by the experimental results.

Behaviour of small-diameter self-compacting concrete-filled steel tubes

This study explores the effect of length to diameter (L/D) ratio on the axial load capacity of small-diameter self-compacting concrete-filled steel tube (SCFT) specimens. The SCFT specimens with L/D ratio of 2 to 14 were tested. Two different cold-formed steel tubes with diameters of 26·9 and 33·7 mm were used in the construction of the SCFT specimens. The behaviour of the SCFT specimens was compared with the unfilled steel tube (UT) specimens. The axial load capacity of SCFT specimens was found to be higher than the axial load capacity of UT specimens. The compressive failure of SCFT and UT specimens with a ratio of 2 and 4 occurred due to local buckling, and with L/D ratio ≥ 6 failure occurred due to global buckling. However, the self-compacting concrete inside the steel tubes improved the ductility and the post-peak axial load–axial deformation response of SCFT specimens compared to the UT specimens.

Bond behavior of steel fibers reinforced self-stressing and self-compacting concrete filled steel tube columns

This paper investigates the bond behavior of steel fibers reinforced self-stressing and self-compacting concrete filled steel tube (FSSCFST) columns. A series of push-out tests on ninety CFST columns are conducted. The variables considered in the test are: (a) concrete type (self-compacting concrete and steel fibers reinforced self-stressing self-compacting concrete); (b) the thickness of steel tube (2.5–4.25 mm); (c) concrete strength (C40, C50 and C60); and (d) steel fibers volume percentage (0%, 0.6% and 1.2%). Experimental results show that the bond strength of FSSCFST specimens varies from 0.50 MPa to 2.51 MPa, which is generally higher than the self-compacting CFST specimens. Self-stress significantly improves the bond strength of CFST specimens, and the average improvement level is 42.7%. The bond strength firstly decreases and then increases with the increase of steel fiber volume percentage. Finally, formulas are proposed to predict the bond strength of FSSCFST columns, and the proposed formulas give a more accurate prediction than the existing design codes.