Concrete-filled Steel Research Articles

Seismic Behavior of Composite Columns with High-Strength Concrete-Filled Steel Tube Flanges and Honeycomb Steel Webs Subjected to Freeze-Thaw Cycles

To investigate the seismic behavior of composite columns with high-strength concrete-filled steel tube flanges and honeycomb steel webs (STHHC) after being subjected to freeze-thaw cycles, 36 full-scale STHHCs were designed with the following main parameters: the shear span ratio (λs), the axial compression ratio (n0), the number of freeze-thaw cycles (Nc), the concrete cubic compression strength (fcu), and the steel ratio of the section (αs). Compared with existing experimental data, the validity of the finite element modeling method was verified. Parameter analysis was conducted on 36 full-scale STHHCs to obtain the hysteresis curve of the composite columns and to clarify the impact of the different parameters on the skeleton curve, the energy dissipation capacity, the stiffness degradation, and the ductility of the composite columns. The results showed that the hysteresis curves of all specimens after freeze-thaw cycles exhibited an ideal shuttle shape, reflecting that this kind of composite column has good energy dissipation ability and freeze-thaw resistance. The specimens’ maximum bulging deformation and maximum stress both occurred at the column base. Finally, the restoring force model of this kind of composite column is therefore established, and design recommendations based on these results are proposed.

A STUDY ON BEHAVIOUR OF CONCRETE FILLED STEEL COLUMN IN FRAMED STRUCTURE

A STUDY ON BEHAVIOUR OF CONCRETE FILLED STEEL COLUMN IN FRAMED STRUCTURE

Experimental study on the interfacial bonding performance of concrete-filled steel tubes at different ambient temperatures

In this study, the interface bonding properties of CFST at different ambient temperatures (T) were studied through the push-out test of 20 CFST specimens. The effects of diameter-to-thickness (D/t) ratio and concrete strength (fcu) on the interfacial bonding strength at different ambient temperatures were studied. At the same time, the distribution characteristics of the strain on the steel tube along the axial direction of CFST columns at different temperatures were analyzed. Subsequently, a formula for calculating the inter-facial bonding strength of CFSTs considering the effect of T was proposed. The results showed that the bonding strength calculated using the formulas pro-posed in this paper was in good agreement with the test results, which could serve as a theoretical reference for the design of CFST structures in high-cold regions.

Experimental study on seismic behaviour of thick-flange steel beam to square CFST column joints with internal diaphragms

Composite structures made of concrete-filled steel tubular (CFST) columns and steel beams have gained widespread usage in high-rise and long-span structures, and beam-to-column joints strengthened by an internal diaphragm (ID) are expected to be efficient joint patterns. However, the thickness ratio (ηbc) limit of beam-to-column flanges is not considered sufficiently in current design codes and existing studies. Moreover, the previous tests rarely included specimens with a beam flange thickness reaching 40 mm. Thus, three joint specimens were designed and tested under cyclic loadings to further investigate the mechanical properties of the ID-type joints and guide engineering applications. The effects of the thickness ratio of the beam-to-column flange were mainly considered in this study. All beam flange thicknesses were 40 mm. Two failure modes were observed, including excessive development of beam plasticity and failure of local connections. Specifically, as the thickness of column walls decreased, the seismic behaviour, such as the resistance, stiffness and ductility of the joints, deteriorated obviously. Two out of three joint specimens satisfied the AISC requirements for composite special moment frames (C-SMF). Based on the test results, the limit value of the thickness ratio of beam-to-column flange (ηbc) has been proposed for design purposes.

Behaviour and design of prestressed stayed circular concrete-filled double skin steel tubular (PS-CCFDSST) columns under axial compression

An innovative type of steel-concrete composite column, named the prestressed stayed circular concrete-filled double skin steel tubular (PS-CCFDSST) column, is introduced in this study, aiming to achieve both structural efficiency and economic advantages. Numerical simulation and theoretical analysis on the axial compressive behaviour of PS-CCFDSST columns were carried out, to understand and reveal their fundamental working mechanisms. Nonlinear finite element analysis (FEA) utilising ABAQUS was performed and validated against collected test data of CCFDSST columns and PS columns. Properly designed PS-CCFDSST columns could gain cost savings of over 30 % while maintaining identical load-bearing capacity as prestressed stayed hollow steel tube (PS-HST) columns with the same steel usage. The effects of initial pretension, nominal steel ratio, hollow ratio, column’s slenderness ratio, relative length of struts, column diameter, strut diameter and cable area on the buckling mode and buckling capacity of PS-CCFDSST columns were evaluated via parametric studies. The stiffness ratio β could be used as an index to comprehensively assess the structural efficiency of PS-CCFDSST columns, and a critical threshold of β = 2 corresponds to the transition between symmetric and anti-symmetric buckling modes. Linear calculation formulae for the theoretical buckling capacity and optimal initial pretension of PS-CCFDSST columns were derived. Finally, practical design equations for predicting the column’s buckling capacity were developed, and recommended values for the actual optimal initial pretension and other primary parameters were provided for PS-CCFDSST columns under axial compression. This study, for the first time, provides the fundamental mechanical behaviour, identification of the critical stiffness ratio for buckling mode transition, and design framework for buckling capacity of the PS-CCFDSST column, which is useful for advancing theoretical exploration and informing engineering practices for this new column type.

Experimental behavior of connection between composite columns and reinforced concrete flat slab

The combination of concrete-filled steel tube (CFST) columns and reinforced concrete flat slabs provides a suitable structural solution that can be used to replace traditional structures in high-rise buildings. The connection between the CFST column and the RC flat slab is an important factor for this construction system to operate efficiently. In this study, a new form for the connection between the CFST column and the RC flat slab has been proposed. This connection has more constructability, where the steel tube is cut at the level of the slab to prevent the separation between the slab and the concrete inside the steel tube as the slab reinforcement is allowed to continue in the connection zone. The joint zone is strengthened with rebar rings to compensate for the loss in confinement caused by cutting the steel tube at the slab level. In addition to using longitudinal rebar in the joint zone to bear part of the vertical load and to ensure bending rigidity. The behavior of the proposed connection was investigated by testing three sets of small-sized samples. In addition, an equation based on the outcomes of the second set of tests has been carried out to determine the joint bearing capacity for the vertical load.

Behavior of eccentrically loaded slender concrete-filled steel tubes with defect representing random local corrosion

This paper focuses on the eccentric compression behavior of slender concrete-filled steel tubes (CFSTs) subjected to random localized corrosion and the localized corrosion was represented by a local defect. The randomness of corrosion includes the random locations and the random geometric characteristics that involve irregular corrosion profiles and uneven surfaces. Corrosion on the steel tube was represented by a defect in the experiment. The influence of spatial characteristics of local corrosion was investigated by seven CFST beam-column specimens, each featuring the defect in different locations along both height and circumferential directions. It was indicated through test results that both dimensions and locations of the defect considerably affected the failure mode and ultimate strength of the CFSTs. A numerical analysis was performed to confirm that local corrosion with irregular shape and uneven surface on a CFST beam-column can be approximated by a constant-depth circumscribed rectangular defect. Subsequently, a parametric analysis was conducted to find out how the corrosion dimensions, locations, and other critical parameters such as steel ratio, slenderness ratio, and material strengths influence the eccentric compression behavior of CFST. It revealed that negligible effects from local corrosion were observed in cases where slight corrosion was located near the column end. Finally, a calculation method was introduced to predict the ultimate strength of randomly localized corroded CFST beam-columns, with high precision.

Fiber-based model for rectangular/square concrete-filled steel tubular columns under arbitrary end moment ratios considering member imperfection

This paper develops a fiber-based model for rectangular/square concrete-filled steel tube (CFST) columns under arbitrary end moments considering the member imperfection. The accuracy of the proposed model regarding the prediction of capacity, deflection curves and full range curves is verified using a collected test database. The verified model is further used to investigate the behaviour of rectangular/square CFST columns under arbitrary end moments. It was found that the varying trends of strength and deformation capacity of rectangular/square CFST columns under arbitrary end moments are opposite while increasing the end moment ratio β, L/r ratio and fc, whereas those are the same if increasing b/t ratio and fy. Higher fy and/or smaller b/t ratio may be adopted in order to achieve larger strength and deformation capacity simultaneously. The location of maximum deflection at peak state hkp/L is only significantly affected by end moment ratio β, whereas the location of critical section at peak state hcp/L is significantly affected by end moment ratio β, L/r ratio and yield strength fy. Moreover, current design codes, i.e., EC4, AISC 360 and GB50936–2014, were found to poorly predict the resistance to axial load and bending moment of rectangular/square CFST columns under arbitrary end moments.

Seismic Vulnerability Analysis of Concrete-Filled Steel Tube Tied Arch Bridges Using Symmetrically Arranged High-Damping Rubber Bearings

Seismic Vulnerability Analysis of Concrete-Filled Steel Tube Tied Arch Bridges Using Symmetrically Arranged High-Damping Rubber Bearings

Investigation of interfacial debonding identification for concrete filled steel tube columns based on acoustic signals

A method was proposed to address challenges in detecting debonding in concrete-filled steel tube (CFST) columns by analyzing acoustic signals. In this approach, wavelet time-frequency diagrams are initially derived through the application of continuous wavelet transform to acoustic signals acquired from tapping on columns. The wavelet time-frequency diagrams serve as data samples for training the MobileNetv2 convolutional neural network model in order to identify concrete debonding. The laboratory test results show that the MobileNetv2 model achieved 100 % accuracy for both the training and verification sets, and 99 % accuracy for the test set. Four CFST columns in a high-rise building under construction were also measured. The findings indicate a recognition accuracy ranging from 86.7 % to 90 % and an error rate that falls within an acceptable range. These results confirm the viability of the method outlined in this paper for detecting debonding in CFST columns using acoustic signals.

Behavior of circular ultra-high-strength concrete-filled steel tube columns subjected to combined high-axial and cyclic lateral loads

The present study examined the seismic performance of circular concrete-filled steel tube (CFST) columns infilled with ultra-high-strength concrete (UHSC >100 MPa) as well as the beneficial effect of embedded spiral confining (SC) reinforcement at high axial load ratios (0.53–0.70) in order to enhance the safety and structural integrity of high-rise buildings. Seven specimens, including four CFST columns and three SC-CFST columns, were investigated under combined high axial and quasi-static cyclic lateral loads. The test parameters included axial load ratio (0.53–0.70), concrete compressive strength (64–111 MPa), embedded spiral confining reinforcement (pitch of 30 mm and 60 mm), and concrete vibration state. The test results demonstrated that adding spiral reinforcement improved the deformation capacity of CFST columns, which was reduced by the increased concrete strength. By embedding spiral confining reinforcement (volumetric ratio 3.3 %), the SC-CFST columns attained a deformation capacity comparable to that of CFST columns with normal concrete (64 MPa) for an axial load ratio of 0.53. The higher axial load ratio and concrete strength of composite columns led to a significant P-Delta moment effect, resulting in a substantial drop in columns' lateral load capacity. Composite columns with UHSC showed a larger contribution from the column base rotation to the specimen's lateral deformation when compared to composite columns with normal-strength concrete because the rigidity offered by UHSC made the column more rigid and reduced its flexural deformation. The unvibrated core concrete of the CFST column did not influence the initial stiffness and energy dissipation capacity. However, during the later stages of loading, the damage in core concrete rapidly accumulated, resulting in instant degradation of the load capacity and stiffness, considerable axial shortening, and poor deformation capacity. The experimental investigation offered a reliable reference on the performance of CFST columns constructed under high-axial load ratios (0.53–0.7) using ultra-high-strength concrete (>100 MPa) and spiral confining reinforcement so as to promote their application in practical engineering.

Experimental study on seismic behavior of concrete-filled steel tubular columns subjected to localized corrosion

The seismic behavior of a circular concrete-filled steel tubular (CFST) subjected to localized corrosion was investigated experimentally. The effects of localized corrosion parameters (corrosion depth ratio, circumferential corrosion ratio, longitudinal corrosion ratio, and longitudinal location of the corrosion) on the seismic behavior were analyzed. The experimental results showed that localized corrosion significantly influenced the failure mode of the CFST columns. The hysteresis curves exhibited a pinching phenomenon and were asymmetrical about the coordinate origin for the specimens under one-sided corrosion at the bottom of the column. The seismic performance deteriorated with increasing corrosion depth ratio, circumferential corrosion ratio, and longitudinal corrosion ratio for CFST columns corroded at the bottom. Corrosion at the mid-height of the CFST columns had less adverse effects on seismic performance than corrosion at the bottom. Moreover, the plastic hinge varied with the corrosion depth ratio and circumferential corrosion ratio but was minimally influenced by the longitudinal corrosion ratio. The specimen exposed to corrosion at the mid-height yielded plastic hinges at both the bottom and middle of the column.

The ultimate capacity of geopolymer recycled aggregate concrete filled steel tubular columns: Numerical and theoretical study

Concrete-filled steel tubular (CFST) columns have been extensively used due to their numerous advantages including high load-bearing capacity, stiffness, energy absorption, and ductile failure mode. Human awareness toward environmental problems is increasing and research on geopolymer recycled aggregate concrete (GRAC) has gained much attention as a green and sustainable material. However, there is little experimental and numerical research on the behavior of CFST columns with the GRAC as an infill material with the available design codes not yet modified for addressing the utilization of unconventional concrete mixes, such as the GRAC. This research introduces a critical modification of the ACI code provisions using the nonlinear finite element analysis method (FEA) on the behavior of square GRACFST columns under axial compression where the proposed modification was verified using experimental data from the literature. The influence of the length-to-width ratio, width-to-thickness ratio, geopolymer concrete strength, and the recycled aggregate replacement ratio was investigated. Results show that the outward local buckling was the primary failure mode for both short and slender columns. Considerable improvements were observed in the column's load-bearing capacity, initial stiffness, ductility, and energy absorption by (81.0, 101.9, 46.5, and 87.8)%, respectively, achieved upon increasing the steel tube thickness from 3 mm to 9 mm. However, the increase in length-to-width ratio negatively affects the energy absorption by 39 % while the ductility was reduced up to 20.4 %. The predictability of the AISC360-16, ACI318-19, and BS5400-5 codes on the capacity of GRACFST columns was evaluated where conservative predictions were guaranteed with the closest one recorded for the ACI318-19 code with a 24.5 % overestimation percentage. Finally, a modification was proposed to the ACI code prediction, taking into account the inclusion of recycled aggregate and geopolymer concrete with only a 2 % average error.

Reinforcement of Insufficient Transverse Connectivity in Prestressed Concrete Box Girder Bridges Using Concrete-Filled Steel Tube Trusses and Diaphragms: A Comparative Study

To address the issue of insufficient transverse connectivity in prestressed concrete box girder (PCB) bridges, this study investigates two transverse strengthening methods—installing diaphragms and utilizing concrete-filled steel tube trusses (CFSTTs). A finite element model was developed for a typical 30 m PCB bridge and was validated by on-site load test results for reliability. Based on the deflection and load distribution of PCB bridges before and after reinforcement, as well as the maximum stress and strain of the diaphragms and the CFSTTs, comparative analyses were conducted on diaphragms of different thicknesses and materials, as well as on CFSTTs of various strength grades. The results show that the addition of a transverse partition and CFSTTs can effectively improve the load distribution of the PCB bridge and reduce the maximum deflection of the girder, especially when using the CFSTT reinforcement method. The unique structural design improves the reinforcement effect of the material in the post-elastic stage. When using CFSTTs, increasing the steel tube wall strength significantly reduces the maximum deflection of the main girder. For example, using steel tubes with yield strengths of 235 MPa and 420 MPa filled with concrete of 50 MPa compressive strength reduced the maximum deflections by 15.32% and 24.55%, respectively, and improved the load distribution coefficients by up to 7.31% and 11.57%. Additionally, steel diaphragms demonstrated better reinforcement effects compared with concrete diaphragms. The load transverse distribution coefficients for the CFSTT-reinforced PCB bridge were calculated using the hinge plate (beam) and the rigid plate (beam) methods, showing minimal differences between the two approaches. The findings of this study provide valuable insights into the design of diaphragm and CFSTT reinforcement in PCB bridges, aiding in the selection of optimal reinforcement strategies.

Behaviour of steel-fibre-reinforced geopolymer concrete-filled square steel tubular stub column under axial compression

Resource utilisation of industrial waste has become a crucial issue in construction aiming for sustainable development. Research on geopolymer concrete-filled square steel tubular (GCFST) structures is limited. Moreover, methods for calculating the bearing capacity of steel-fibre-reinforced GCFST (SFRGCFST) structures require further investigation. This study presents an experimental and analytical investigation of the axial compression performance of SFRGCFST stub columns. Twenty-four specimens were tested to assess the effect of steel tube thickness, steel fibre (SF) volume fraction, SF aspect ratio, and concrete strength grade on failure modes, load–deformation behaviour, load–strain response, ultimate resistance, and ductility of SFRGCFST columns. The results indicated that the failure modes of SFRGCFST columns are influenced by the coefficient index, which varies with the test parameters. When the coefficient index exceeded 0.88, the failure mode of the specimens transitioned from shearing failure to waist-drum-shaped failure. The average ultimate bearing capacity of the SFRGCFST columns increased by 35.13 % compared with that of the plain concrete-filled steel tubes (CFSTs). When the SF volume fraction reached 0.9 %, the ultimate bearing capacity of the SFRGCFST columns increased by 21.85 % compared with that of steel-fibre-reinforced concrete-filled steel tube (SFRCFST) columns. The incorporation of SF significantly improved the deformation capacity and ductility of the SFRGCFST columns and moderated the slope of the post-peak load–displacement and load–strain curves, slowing the descent of the curve. Utilising the multi-axial strength criterion and mechanical equilibrium equation for square CFSTs, a formula for calculating the ultimate bearing capacity of SFRGCFST stub columns was developed. This formula enables accurate prediction of the axial compressive load capacity of SFRGCFST stub columns and provides a basis for revising relevant standards.

Axial compressive mechanical behavior of a CFRP-confined composite member composed of bamboo strips and a thin-walled steel tube

To utilize fully the excellent mechanical properties of bamboo, thin-walled steel, and carbon fiber-reinforced polymer (CFRP), a CFRP-confined composite member composed of bamboo strips and a thin-walled steel tube (CBSC) was proposed to design a bamboo member with high-bearing capacity and ductility. The axial compressive tests were conducted on 26 CBSC members. Based on the validated finite-element (FE) model, a parametric analysis was performed to investigate the effects of different parameters on the axial compressive mechanical behaviors of CBSC members. Finally, the predictions of the ultimate axial compressive bearing capacity derived from the unified theory of concrete-filled steel tube columns agreed well with the test and FE results. The results showed that the failure mode of short CBSC members was strength failure, including material damage in the middle of the member, and end-crushing failure. However, the slender CBSC members exhibited typical global buckling failure. CBSC members can fully utilize the mechanical characteristics of the three materials to exert their combined effects. In terms of improving the bearing capacity, the recommended number of CFRP layers for all CBSC members is one except for the short CFRP-confined bamboo strip, thin-walled, circular steel-tube composite members, which is equal to two. The critical slenderness ratios of the CBCSC specimens and CBSSC specimens for distinguishing strength failure and global buckling are 19 and 36, respectively. The proposed predicted equations can accurately estimate the ultimate bearing capacity of CBSC members under axial compression.

Failure mechanisms and reinforcement support of soft rock roadway in deep extra-thick coal seam: A case study

The soft rock roadway in deep extra-thick coal seam is prone to large deformation disaster. In order to solve this problem effectively, taking the W3101 coalface of Xiao’kang coal mine as the engineering background, the failure mechanisms and the corresponding control technology were investigated by the methods of laboratory test, numerical simulation and field measurement. First, a series of tests were carried out on the basic mechanical properties of rock mass, in-situ stress and loose zone, and it was found that the failure mechanisms of soft rock roadway in deep extra-thick coal seam are poor lithology of surrounding rock, high in-situ stress, large loose circle and unreasonable original support. Then, based on the supporting mechanisms of grouting cable and concrete-filled steel tube (CFST) of bottom angle, a new collaborative reinforcement support (CRS) technology combining the two was proposed. Next, the numerical simulation shows that the CRS technology has good applicability in controlling large deformation of soft rock roadway in deep extra-thick coal seam. Finally, to exhibit the engineering application effect of the proposed CRS scheme, it was also applied in Xiao’kang coal mine. Comparing to the controlling effect of original support scheme, it can be seen that the average deformation of soft rock roadway reduces by 73.2 % under the proposed CRS scheme, and the steel arch frame of bottom angle is slightly deformed. Meanwhile, it is found that the grouts diffusion radius is nearly 1.21 m, and the deepest diffusion depth is 4.25 m, which also indicates again that the feasibility of the proposed CRS scheme in controlling large deformation of soft rock roadway in deep extra-thick coal seam.

Failure mechanism analysis and support strength determination of deep coal mine roadways – A case study

In order to solve the problems related to deformations, failures, and difficulties in support controls of deep coal mine roadways, the typical failure forms and characteristics of deep coal mine roadways were investigated and analyzed in this study. The distribution laws of plastic zones of circular roadways under different lateral pressure coefficients were expounded using a theoretical analysis method, and the influence of plastic zone scopes on the failure forms of roadways was explained. In addition, considering the distribution characteristics of plastic zones, a calculation method of the required support strength based on the plastic zone scopes was proposed. The primary and secondary factors affecting the support strength were then determined. A numerical simulation method was applied in order to analyze the distribution characteristics of the displacements and plastic zones of deep mine circular roadways under the conditions of no support scheme, an existing support scheme, and a support scheme determined by the proposed support strength calculation method (referred to in this study as the optimized support scheme), respectively. The simulation results showed that the support effects of the optimized support scheme were superior to those of the existing support scheme, and thereby more conducive to maintaining roadway stability. In addition, an on-site engineering test method was used to identify support schemes for bolting and shotcrete with wire mesh + concrete-filled steel tubular supports based on the plastic zone scopes and the support strength of roadways in order to determine the support parameters. As indicated by the field monitoring results, the proposed support strength calculation method and optimized support scheme had shown the ability to effectively control the large deformations of the tested roadway, and thereby guarantee its overall stability.

Numerical Study on the Axial Compression Behavior of Composite Columns with High-Strength Concrete-Filled Steel Tube and Honeycombed Steel Web Subjected to Freeze–Thaw Cycles

To investigate the axial compression behavior of composite columns with high-strength concrete-filled steel tube flanges and honeycombed steel web (STHHC) under load during freeze–thaw cycles, 48 full-scale composite column specimens were designed with different parameters: the restraint effect coefficient (ξ), concrete strength (fcu), number of freeze–thaw cycles (nd), slenderness ratio (λ), space–height ratio (s/hw), and hole–height ratio (d/hw). The finite element models of STHHC composite columns were simulated using ABAQUS finite element software (Version: 2021). The modeling method’s rationality was verified by comparing simulation results with experimental outcomes. Based on the finite element model, a parametric analysis of the composite columns under freeze–thaw cycles was conducted, analyzing their failure modes and load-bearing processes. The results indicate that the bearing capacity of the STHHC increased with increases in ξ and fcu, and decreased with a rise in λ. In contrast, the influence of s/hw and d/hw on the ultimate bearing capacity of the composite columns was relatively minor. An equation for calculating the axial bearing capacity of the STHHC composite columns under freeze–thaw cycles was derived using statistical regression methods and considering the impact of different parameters on the axial compressive performance of the composite columns, laying the foundation for the promotion and application of this type of composite column in practical engineering projects.

Force-displacement relation for lumped plasticity model of compact square concrete-filled steel tube columns

Integration of steel and concrete benefits in square concrete-filled tube columns (SCFTs) makes them be utilized extensively worldwide. To evaluate the seismic behavior of special moment frames having SCFT columns, an accurate macro-modeling tool with little complexity is necessary. Although the fiber section can consider both linear and nonlinear behavior of SCFT, it fails to allow for deterioration, which is vital in assessing a seismic resisting system. This study proposes a new deterioration tool based on the Ibarra-Krawinkler model for compact SCFT columns using artificial neural networks (ANNs) through numerical simulation. Initially, 96 specimens with variations in geometry, material, and axial loading conditions were simulated in ABAQUS and then were analyzed using displacement control loading protocol to obtain hysteretic curves, which were used to prepare the data sets for training, testing, and validating the neural networks. Finally, the performance of ANN models was evaluated by statistical relations such as regression and mean square error. Through FEMA 356 and Ibarra-Krawinkler approaches, parameters defining linear and nonlinear phases of SCFTs behavior were derived. By employing efficiently trained neural networks, equations predicting the parameters of the deterioration model were established, and the obtained results show the accuracy and efficiency of the proposed model.