Binding Bars Research Articles

Experimental and numerical investigations of the octagonal concrete-filled thin-walled tube columns with binding bars (O-CFT-WBB) under compressive pressure and thermal loads

An experimental and theoretical investigation is conducted to evaluate the behavior of CFT columns with a unique geometric cross-section under axial loading and in a thermal environment. In this study, based on previous research on octagonal CFT columns, this geometry was chosen as a favorable option compared to other possible configurations. Additionally, binding bars were employed to enhance these columns' mechanical and thermal behavior. A thermal gradient (temperature changes ranging from 0 to 600 degrees) was applied in the laboratory to replicate extreme environmental conditions. By experimental results, a theoretical investigation was conducted to derive suggested formulas for considering confinement effects in O-CFT-WBB columns, and the results were then compared with experimental results and the closest existing formulas. After examining the experimental results, it was shown that the presented formulas had more accuracy than the existing ones. Additionally, based on the experimental results, the presence of binding bars at different temperatures led to different behaviors in the axial capacity of the columns. According to the results, the binding bars in the O-CFT-WB columns can lead to different behaviors in the axial capacity of the columns. Based on a constitutive model of confined concrete, a method for calculating the maximum strength of L-shaped CFT columns with and without binding bars is proposed. The method is verified with experimental results from this test program and data from other experiments.

Seismic Behavior of T-Shaped Concrete-Filled Steel Tubular Column to Steel Beam Joints with Side Plates

This study investigates the seismic behavior of the T-shaped concrete-filled steel tubular (CFST) column to steel beam joints, aimed at expanding their applicability in areas with high-seismic fortification intensity. A construction form of T-shaped CFST column to steel beam joint with side plates is presented. The variables studied in these experiments include the side plate length, the axial compression ratio, the presence of side plates, and the presence of binding bars. The force mechanism, failure modes, load–displacement curves, strength, stiffness, ductility, and energy dissipation capacity of seven specimens were evaluated under low-cycle reciprocating load. The experimental results demonstrate that the joints of side plates show a full hysteresis curve, with the ductility coefficient ranging from 1.67 to 2.49, and the equivalent viscous damping coefficient between 0.147 and 0.234. The joint panel zone displays strong deformation and energy dissipation capacity. The inclusion of side plates and binding bars improves the seismic behavior of the joint. The setting of side plates enables the formation of a plastic hinge on the steel beam, creating a beam hinge failure mechanism and satisfying the seismic design principle of “strong column and weak beam, strong joint and weak member” as required by the building structures.

Axial compressive behavior of corroded double-steel-plate composite shear wall with binding bars

Steel structure is susceptible to corrosion, and corrosion will seriously affect its own load-bearing capacity and service life. In this paper, the axial compressive behavior of double-steel-plate composite shear wall (DSCW) with binding bars under different corrosion degrees is experimentally studied. The typical failure modes include the steel plate local buckling, binding bars fracture, concrete crushing, and steel plate weld tearing. The increase of corrosion rate has unfavorable influence on the axial compressive bearing capacity, initial stiffness, and ductility of DSCW. Finite element (FE) models are established to further investigate the axial compressive behavior of DSCW. It is concluded that the concrete and steel plate strength grade, the concrete section area, the steel plate thickness, and the binding bars diameter and spacing significantly affect the axial compressive bearing capacity of DSCW. A formula calculating the axial compressive bearing capacity of corroded DSCW with binding bars is proposed. The formula agrees well with the test results and can provide a reference for the engineering application.

Gas7 is a novel dendritic spine initiation factor.

Brain stores new information by modifying connections between neurons. When new information is learnt, a group of neurons gets activated and they are connected to each other via synapses. Dendritic spines are protrusions along neuronal dendrites where excitatory synapses are located. Dendritic spines are the first structures to protrude out from the dendrite to reach out to other neurons and establish a new connection. Thus, it is expected that neuronal activity enhances spine initiation. However, the molecular mechanisms linking neuronal activity to spine initiation are poorly known. Membrane binding BAR domain proteins are involved in spine initiation, but it is not known whether neuronal activity affects BAR domain proteins. Here, we used bicuculline treatment to activate excitatory neurons in organotypic hippocampal slices. With this experimental setup we identified F-BAR domain containing Growth Arrest-Specific Protein (Gas7) as a novel spine initiation factor responding to neuron activity. Upon bicuculline addition, Gas7 clustered to create spine initiation hotspots, thus increasing the probability to form new spines in activated neurons. Gas7 clustering and localization was dependent on PI3-kinase activity and intact F-BAR domain. Gas7 overexpression enhanced N-WASP localization to clusters as well as it increased the clustering of actin. Arp2/3 complex was required for normal Gas7-induced actin clustering. Gas7 overexpression increased and knockdown decreased spine density in hippocampal pyramidal neurons. Taken together, we suggest that Gas7 creates platforms under the dendritic plasma membrane which facilitate spine initiation. These platforms grow upon neuronal activation, increasing the probability of making new spines and new connections between active neurons. As such, we identified a novel molecular mechanism to link neuronal activity to the formation of new connections between neurons.Significance StatementWhen we learn something new, neurons change their connections to other neurons. We know that active neurons connect to each other, but we have poor understanding on the cellular or molecular mechanisms which link neuronal activity to the formation of new connections. Here we show how neuronal activation can facilitate formation of new connections to wire the firing neurons together.

Behavior of square and rectangular concrete-filled steel tube (CFST) columns with horizontal reinforcing bars under eccentric compression

A series of eccentric compression tests on square CFST columns with horizontal reinforcing bars were conducted, focusing on the effects of eccentricity ratio, different types of horizontal reinforcing bars (binding bars and inclined tension bars), and bar spacing. In addition, the results of a previous study on rectangular CFST columns with binding bars were also included for comparison, aiming to investigate the strengthening performance of installing horizontal reinforcing bars for both rectangular and square CFST columns. It is found that the restraining effect provided by the reinforcing bars could not only delay and restrain steel tube buckling, but also enhance the ultimate strength and lead to a more ductile post-peak descending branch for the load-axial strain, load-lateral strain, and moment–curvature curves. For square CFST columns under eccentric compression, installing binding bars which led to a 30%–40% enhancement in ultimate strength was more efficient than installing inclined tension bars of the same reinforcement ratio which only had less than 20% enhancement. Meanwhile, the ductility of the columns was significantly improved by reinforcing bars. Furthermore, the columns with binding bars had better ductility than those with inclined tension bars. Generally, binding bars can more efficiently improve the eccentric load behavior of CFST columns than inclined tension bars. For rectangular CFST columns under eccentric compression, reducing the spacing of binding bars can slightly increase the ultimate strength by around 7% while the ductility of the columns can be increased significantly by reducing the bar spacing. In addition, increasing the cross-sectional aspect ratio of the rectangular CFST columns would offset the restraining effect of the binding bars. In the end, a discussion was provided for a design code assessment against the test results.

AXIAL COMPRESSION TESTING OF BAMBOO PLYWOOD-ENCASED THIN-WALLED STEEL TUBE/STONE DUST CONCRETE COLUMNS

A novel structural member, the bamboo plywood-encased thin-walled steel tube/stone dust concrete composite column (BSDCC), was investigated in this study. Axial compression tests were conducted on 10 BSDCC specimens; their failure characteristics and modes were examined, and the effects of the stone-dust concrete content ratio and strength, specimen slenderness ratio, cross-sectional composition and binding bar confinement pattern, and binding bar spacing ratio on the bearing capacity and deformation of the columns were investigated. Two main compressive failure modes were observed: (1) adhesive failure by cracking and debonding between the bamboo plywood boards and between the bamboo plywood and the steel tube and (2) compressive-flexural failure of the bamboo plywood between the binding bars in the middle of the specimen. For specimens with the same cross-sectional dimensions, the cross-sectional content ratio of the stone dust concrete impacted the deformation and failure mode but did not significantly affect the ultimate bearing capacity. The bearing capacity decreased with increasing specimen slenderness and binding bar spacing ratio and increased with increasing stone dust concrete strength and bamboo plywood constraint (in terms of the cross-sectional composition and binding bar restraint pattern). A model for the ultimate bearing capacity of BSDCCs was established through regression analysis.

Compressive behaviour of stone dust concrete composite columns confined with bamboo plywood and thin-walled steel-tube systems

A novel bamboo plywood and thin-walled steel-tube dual-confined stone dust concrete composite column (BSDCC) is proposed to integrate the utilization of industrial solid waste and bamboo materials. Compression tests are performed on 12 BSDCC specimens. The failure mechanism is elucidated by analysing the entire process of specimen damage, the failure modes of the thin-walled steel tubes, the load-displacement curves, and the strain development patterns of different composite components. The test results show that the failure modes of the BSDCC specimens under compression were dominated by adhesive cracking failure of the bamboo plywood between the transverse binding bars in the middle of the column and the bamboo plywood on the tension side and yielding of the inner steel tube. Throughout the loading process, the specimens showed ideal elastoplastic behaviour, but the plastic capacity was not advantageous, and the plastic strengthening effect was not obvious. The bearing capacity of the stone dust concrete accounts for less than 10% of the total bearing capacity of the composite column, so the concrete strength is not the main factor improving the bearing capacity. The inner steel tube filled-with low-strength stone dust concrete can result in a composite column configuration with better mechanical properties, changes the failure mode of the composite column and the deformation mode of a cross-section, and delays the overall failure of the composite column. The setting of binding bars can effectively delay the bamboo plywood failure, and the outward partial buckling of the slab and steel tube enhances the restraint effect of the steel tube on the core concrete. Setting the binding bar in the middle of the column body can improve the column eccentric load bearing capacity and ductility. A formula for calculating the bearing capacity of BSDCCs under eccentric compression is established based on nonlinear regression analysis.

Unified solutions on axial bearing capacity of T-shaped concrete-filled steel tube short columns with binding bars

Based on the unified strength theory, according to the characteristics of axial bearing capacity of T-shaped concrete-filled steel tubular stub short columns with binding bars, the cross shaped section was divided into 3 rectangular sections which have binding bars and one rectangular section which has no bars. Considering intermediate principal stress, the ration of width to thickness of pipe to the bearing capacity of steel tube was in consideration too, the paper analyzed force mechanism. In the end, the mathematical formulation of bearing capacity for the T-shaped concrete-filled steel tube stub column with binding bars was obtained. The formula calculation values are in good agreement with the test value of the relevant literature.

Constitutive relation of stiffened square CFST Columns

Using the constitutive model of a square CFST column with binding bars, the constrained mechanism of the stiffened square CFST columns is analyzed in great detail. The equivalent constitutive model under uniaxial compression is established for square CFST columns. The model is then used to describe the stress-strain curve process for concrete and to calculate the bearing capacity. Models of ten concrete-filled square steel tubular columns under axial compression specimens are created with constitutive relation. The results are compared with the axial compression test of an ordinary square CFST specimen column and stiffened square CFST specimens. Our results show that the bearing capacity and stress-strain curves under axial compression are consistent with the actual test measurements. Analysis can be applied to the square stiffened CFST columns, the square CFST columns with binding bars, and the ordinary square CFST columns.

Unified solutions on axial bearing capacity of round-ended concrete-filled steel tube short columns with binding bars

Based on the unified strength theory, according to the characteristics of axial bearing capacity of round-ended concrete-filled steel tubular stub short columns with binding bars, the cross shaped section was divided into a rectangular section which has bars and two round-ended sections which have no bars. Considering intermediate principal stress, the ration of width to thickness of pipe to the bearing capacity of steel tube was in consideration too, the paper analyzed force mechanism. In the end, the mathematical formulation of bearing capacity for the round-ended concrete filled steel tube stub column with binding bars was obtained. The formula calculation values were in good agreement with the value of the relevant literature. Theoretical formulas are expected to be helpful for engineering applications.

Axial Compression Testing of Bamboo-Laminated Encased Steel Tube Composite Columns

To resolve the problem of premature glue failure in square, thin-walled steel tube/bamboo-laminated composite hollow columns (SBCCs) under compression, a new type of SBCC with transverse binding bars (SBCCB) is proposed. An axial compression test was performed on nine SBCCBs to observe the compressive failure mode and analyse the influence of the net cross-sectional dimension, slenderness ratio and cross-sectional composition on the glue failure and the ultimate bearing load; the results were compared with the known limit stress of SBCCs without transverse binding bars. The experimental results indicate that the compressive damage to SBCCBs is primarily the breaking of the bamboo plywood material and glue failure between the matrix interfaces at the end and middle of the column between the binding bars. The ultimate bearing load is not only related to the dimensions of the cross section and the slenderness ratio but also impacted by the cross-sectional composition. Installing transverse binding bars can effectively reduce glue failure in the test specimens, alter the limit failure mode and significantly increase the ultimate bearing load. Compared to the limiting compressive stress on an SBCC, the limiting compressive stress on an SBCCB is 26% higher on average. A formula for calculating the axial compressive load capacity of an SBCCB was established using nonlinear regression analysis.

Local buckling of rectangular concrete-filled steel tubular columns with binding bars under eccentric compression

Based on the energy method, this article presents a theoretical study on the elastic local buckling of steel plates in rectangular concrete-filled steel tubular columns with binding bars subjected to eccentric compression. The formulas for elastic local buckling strength of the steel plates in eccentrically loaded rectangular concrete-filled steel tubular columns with binding bars are derived, assuming that the loaded edges are clamped and the unloaded edges of the steel plate are elastically restrained against rotation. Then, the experimental results are compared with these formulas, which exhibits good agreement. Subsequently, the formulas are used to study the elastic local buckling behavior of steel plates in rectangular concrete-filled steel tubular columns with binding bars under eccentric compression. It is found that the local buckling stress of steel plates in eccentrically loaded rectangular concrete-filled steel tubular columns with binding bars is significantly influenced by the stress gradient coefficient, width-to-thickness ratio, and the longitudinal spacing of binding bars. With the decrease of width–thickness ratios or the longitudinal spacing of binding bars or with the increase of the stress gradient coefficient, the local buckling stress increases. Furthermore, the influence of the longitudinal spacing of binding bar is more significant than the stress gradient coefficients. Finally, appropriate limitation for depth-to-thickness ratios ( D/ t), width-to-thickness ratios ( B/ t), and binding bar longitudinal spacing at various stress gradient coefficients ( α0) corresponding to different cross-sectional aspect ratios ( D/ B) are suggested for the design of rectangular concrete-filled steel tubular columns with binding bars under eccentric compression.

Axial Compression Behaviors of the Steel Tube Confined Reinforced Concrete Columns with Binding Bars

An experimental study on the steel tube confined reinforced concrete (STCRC) column with binding bars under axial compression is conducted. The bearing capacity and failure modes are obtained. It can be known that the axial deformation of concrete occurred under compression. The core concrete is wrapped and constrained by the steel tube wall, and the steel tube wall is constrained by binding bars locally, so the local buckling shape of the wall between the binding bars is like wave shape. The 3D finite element model is also developed to analyze the behavior of this type of column under axial compression. Good agreement is shown between the test and predicted results in terms of the load‐deformation curves and ultimate strength. The parametric studies indicate that the spacing of binding bars, diameter of longitudinal bars, concrete strength, thickness of the steel tube wall, and section dimension of the column generate different influence on the mechanical properties and bearing capacity. The diameter of longitudinal bars, concrete strength, and section dimension of the column have a great effect on the ultimate bearing capacity. The numerical results also show that the spacing of binding bars has little effect on the ultimate bearing capacity. The larger thickness of the steel tube wall leads to adverse effect on the specimen performance. Finally, the theoretical calculation is carried out, and the result is good.

Axial Compressive Behavior of Steel-Damping-Concrete Composite Wall

This paper presents a novel steel-damping-concrete (SDC) composite wall as a vertical element for high-rise buildings and nuclear power plants etc. In an SDC composite wall, a damping layer is sandwiched between the concrete core and steel plates to reduce structural response based on its damping characteristics under axial and seismic loads. To ensure that an SDC composite wall exhibits a comparable compressive resistance as a steel-concrete-steel (SCS) composite wall, two types of reinforcing approaches including steel sheets and sleeves are utilized to enhance the weakness of the damping layer on the concrete core. The compressive performance of the reinforced SDC composite wall is numerically and analytically investigated using finite element (FE) simulations by ABAQUS. The influences of several key parameters including the type of reinforcement, the thickness of the damping layer, steel plates, and concrete core, the binding bar spacing as well as the diameter of steel sheets on the compressive performance of the composite walls are investigated through numerical analyses. The results show that while only embedding the rubber interlayer in the composite wall leads to the decrease of compressive resistance of the composite wall, the steel sheets and sleeves can provide the confinement effect on concrete core efficiently and improve the compressive resistance and ductility of walls. Based on the available methods in the current design codes such as Eurocode 4, AISC-360, a theoretical model is developed to predict the ultimate compressive resistance of SDC walls. The predictions show a reasonable correlation when compared with the numerical results.

Study on the Eccentric Compression Performance of Stiffened Rectangular CFST

Concrete-filled steel tubular columns (CFST) have high bearing capacity, high stiffness and good ductility. The columns with rectangular section are more suitable for compression bending than round. However, its lateral binding force is small in the middle of the section, and local buckling is easy to occur.Stiffened Rectangular Concrete Filled Steel Tubular columns(SRCFST) are proposed to solve the problem that ordinary rectangular concrete filled steel tubular columns(RCFST) are prone to appear local buckling before reaching the limits of carrying capacity in 3 cases such as the thin steel tube wall, the larger diameter to thickness ratio or width to to thickness ratio. SRCFST are RCFST added with stiffening ribs, stiffening hoops and binding bars. By its set, the latera stiffness and the resistance ability of the local buckling of the steel tube are effectively enhanced, so the confinement effects of the steel tube to core concrete become stronger and more uniform. To compare the improved effects of SRCFST and RCFST with binding bars under eccentric compression, the paper compiles the solving procedure of the cross section grid unit method which can accurately solve the whole process curve of SRCFST under eccentric compression. The whole process curves show that the eccentric bearing capacity and ductility of SRCFST are obviously improved with respect to RCFST with binding bars.

Study on the Eccentric Compression Performance of Stiffened Square CFST

Concrete-filled steel tubular columns (CFST) have high bearing capacity, high stiffness and good ductility. The columns with square or rectangular section are more suitable for compression bending than round. However, its lateral binding force is small in the middle of the section, and local buckling is easy to occur. Stiffened Square Concrete Filled Steel Tubular columns (SSCFST) are proposed to solve the problem that ordinary square concrete filled steel tubular columns(SCFST) are prone to appear local buckling before reaching the limits of carrying capacity in 3 cases such as the thinner steel tube wall, the larger diameter to thickness ratio or width to thickness ratio. SSCFST are SCFST added with stiffening ribs, stiffening hoops and binding bars. By its set, the lateral stiffness and the resistance ability of the local buckling of the steel tube are effectively enhanced, so the confinement effects of the steel tube to core concrete become stronger and more uniform. To compare the improved effects of SSCFST and SCFST with binding bars under eccentric compression, the paper compiles the solving procedure of the cross section grid unit method which can accurately solve the whole process curve of SSCFST under eccentric compression. The whole process curves show that the eccentric bearing capacity and ductility of SSCFST are obviously improved with respect to SCFST with binding bars.

Experimental Study on the Hysteresis Performance ofStiffened Square CFST

Stiffened Square Concrete Filled Steel Tubular Columns (SSCFST) were proposed to solve the problem that ordinary square concrete-filled steel tubular columns (SCFST) are prone to appear local buckling and poor hysteresis performance before reaching the limits of carrying capacity in 3 cases such as the thin steel tubular wall, the larger diameter to thickness ratio or width to thickness ratio. In order to investigate its hysteresis behavior, based on introducing its basic concept, the manufacturing method was expounded, and the low cyclic loading tests of 15 SSCFST and 1 SCFST with binding bars were carried out. The author observed experimental phenomena, failure process and failure mode, then analyzed hysteresis loop area and energy dissipation of SSCFST columns under reciprocating loading, and discussed the effect of various factors to its anti-seismic behavior. Compared to SCFST with binding bars, SSCFST has superior anti-seismic performance.

A refined model for local buckling of rectangular CFST columns with binding bars

This paper presents a refined model for local buckling of rectangular concrete-filled steel tubular (CFST) columns with binding bars under axial compression due to a deficiency in the previous model i.e. the influences of horizontal spacing and diameter of binding bars were not considered. The influences of longitudinal spacing, horizontal spacing and diameter of binding bars on the critical local buckling stress can be reasonably considered in the proposed model, which is applicable to both elasto-plastic phase and elastic phase. The refined model is verified against the experimental results, showing better agreement than the previous model. Then, the proposed model is employed to investigate the influences of longitudinal spacing, horizontal spacing, diameter of binding bars and cross-sectional aspect ratios on the critical local buckling stress. It is found that the critical local buckling stress increases considerably with the decrease of the spacing of binding bars. Furthermore, the influence of longitudinal spacing of binding bars on the critical local buckling stress is more significant than that of horizontal spacing. It is also found that the critical local buckling stress increase modestly with the increase of diameter of binding bars in the case of small spacing of binding bars. In addition, the cross-sectional aspect ratio have little influence on the critical local buckling stress, which can be ignored. Aiming at delaying the occurrence of local buckling of steel plates in rectangular CFST columns with binding bars, it is suggested that decreasing longitudinal spacing as an efficient measure has priority over other measures.

Performance of T-shaped CFST stub columns with binding bars under axial compression

This paper investigates the axial compressive behaviour of T-shaped concrete-filled steel tube (CFST) stub columns with blinding bars. In this column system, binding bars are applied cross-through the section and produce confinement effects. Eleven specimens with binding bars and five ones without binding bars were tested under axial compressive loading. The experimental results demonstrate that, by setting binding bars, the local buckling failure modes are changed and the occurrence of local buckling is delayed, and the global outward bulge of the steel tube at the concave corners can be effectively restrained. The ultimate strength and ductility of the columns with binding bars can achieve up to 1.53 and 7.5 times higher than those of the columns without binding bars, respectively. Taking into consideration the contribution of binding bars, the confinement effects of steel tube and the other sectional characteristics, a method for predicting the ultimate axial compressive strength of the columns with or without blinding bars is established. The accuracy of the method is validated through comparisons of the experimental results reported in this paper and in other available open literatures.

Compression performance of thin-walled square steel tube/bamboo plywood composite hollow columns with binding bars

A new type of thin-walled steel tube/bamboo plywood hollow composite column with binding bars was developed in which transverse binding bars were used as reinforcement. The compression performance of 12 specimens was tested to examine the failure modes of the steel tube/bamboo plywood hollow composite column with binding bars, and the influences of the slenderness ratio, the net cross-sectional area of the bamboo plywood, the load eccentricity distance, and the binding bars on the ultimate load-bearing capacity were analyzed. The results indicated that the compression failure modes of the steel tube/bamboo plywood hollow composite column with binding bars were mainly bamboo plywood material failure and debonding failure of the adhesion interface; the ultimate bearing capacity of the steel tube/bamboo plywood hollow composite column with binding bars increased with an increasing net cross-sectional area of the bamboo plywood and decreased with an increasing slenderness ratio and eccentricity distance. Transverse binding bars were introduced to ensure the integrity of the composite column, to effectively reduce the debonding failure of the adhesion interface, to change the life-limiting damage mode, and to significantly improve the load-bearing capacity of the steel tube/bamboo plywood hollow composite column with binding bars. Finite element numerical simulations were performed to extend the influential factor analysis based on the test results. Furthermore, based on a non-linear regression analysis of the experimental data, a model for calculating the load-bearing capacity was formulated to determine the allowable compressive capacity of an steel tube/bamboo plywood hollow composite column with binding bar for engineering applications.