Tube Thickness Research Articles

Tensile Behavior of Anchored Stainless Steel T‐Head Blind Bolts within Concrete‐Filled Steel Square Tubes

AbstractBased on a recent review on blind bolted connections to concrete‐filled steel tubes, there is a need to improve the performance of anchored blind bolts in such composite connections. This paper presents a study on the pull‐out behavior of anchored blind bolts under applied tensile load in terms of stiffness, yield strength, ultimate strength and load‐displacement response. A finite element (FE) model with concrete damage plasticity model was developed for parametric study. Effects of key parameters, such as concrete strength, bolt grade, embedment length, tube thickness and tube grade, on the tensile behavior of the connection were studied to identify the key parameters influencing the behavior. Finally, a predictive model based on component method was proposed to estimate the structural behavior of the blind‐bolted connections.

Numerical studies on the torsional behavior of octagonal concrete‐filled linked double steel tubes

AbstractThe concrete confinement is improved in octagonal concrete‐filled double steel tubular (OCFLDST) columns by linking the steel tubes with steel plates and thereby it enhances ductility. It has the potential to improve the torsional resistance in concrete‐filled steel tubular cross‐sections. This paper investigates the torsional behavior of OCFLDST through analytical and numerical investigations. The numerical model for OCFLDST is developed in ABAQUS and validated using test data available in the literature for axial loading conditions. The validated model is then subjected to pure torsion to study the torsional behavior of OCFLDST. In comparison with bare steel tubes, concrete filling of linked steel tubes has increased the torsional resistance by 33%. Further, parametric studies are conducted to understand the influence of various parameters like yield strength and thickness of the outer steel tube, compressive strength of concrete, the thickness of the linking plates, and axial load ratio. The numerical results are compared with the proposed expression for finding the torsional capacity based on St. Venant's torsion theory. The proposed capacity prediction is in good agreement with the numerical results.

Influence of GFRP Confining Tube Parameters in Double-Skin Tubular Short Columns under Axial Loading

Abstract Composite construction with steel and concrete has become a widespread solution in modern construction practices because of its inherent properties such as high strength-to-weight ratio, good corrosion resistance, and high stiffness. Concrete-filled fiber-reinforced polymer (FRP) steel double-skin tubular compression members as vertical load–carrying members in buildings helps in optimizing the advantages of three materials: steel, concrete, and FRP. This study investigates the axial compressive behavior of short, concrete-filled glass fiber–reinforced polymer (GFRP) steel double-skin tubular (GSDST) columns and concrete-filled GFRP tubular (CFFT) columns. Parameters such as the number of FRP layers, hollow section ratio (HSR), variation of diameter of the inner steel tube, and the angle of orientation of the fibers have been examined in this investigation. The experimental study was carried out by performing a monotonic axial compressive loading condition. Three different angles of fiber orientation, 0° along the hoop direction, 45°, and 0°/90° with respect to the axis of the column, were adopted in this study. The ultimate load-carrying capacity, axial displacement, axial and horizontal strains, and failure modes were observed. The experimental results indicate that the structural performance of GSDST columns is significantly influenced by GFRP tube thickness, inner steel-tube diameter, and fiber-orientation angle. Maximum displacement was observed in the specimens with high HSR, thus showing a ductile characteristic in the axial load-displacement behavior. The load-carrying ability of the specimens decreased as the HSR increased. The load-carrying capacity of the specimens increased with the increase in outer GFRP tube thickness. This study demonstrates that GFRP tubes can be used efficiently in the construction field as vertical load–carrying components by enhancing the axial behavior of FRP steel double-skin tubular columns.

Analysis of the stress-strain state of problematic sections of the shaft of the mine using computer simulation

The article presents the computer simulation results for the stress-strain state of the lining sections of the shaft No. 1 of mine 3 of JSC Belaruskali that were obtained using visual and instrumental investigation of the mine lining state. The loading parameters of the shaft take into account the specific feature of the lateral pressure calculation in the considered location. This means that the shaft intersects vertically rocks different in their physical and mechanical properties. Computer simulation of loading of the most problematic vertical mine shaft sections observed by the lining examination results was performed using the Static Structural component of the ANSYS Workbench engineering software package. Distribution diagrams of longitudinal normal, shear and von Mises equivalent stresses in the vertical mine shaft lining are obtained for the design and residual values of the cast-iron tubing thickness. A comparative analysis of the mine shaft residual bearing capacity for various parameters of the lining elements was carried out. Based on the computer simulation results, the conclusions were made on the bearing capacity of the shaft No. 1 of mine 3 of JSC Belaruskali and the recommendations for a further safe operation of the mine shaft were suggested.

Anthropomorphic Carotid Artery Phantom for Ultrasound Flow and Vessel Wall Elastography Imaging.

Shear wave elastography imaging (SWE) is a non-invasive US technique that has been developed to provide quantitative information about tissue elasticity. This technique might be useful in the identification of vascular risk factors. Arterial wall thickness and inner diameter vary with age and disease, which may impact shear wave propagation. The effect of arterial geometry on SWE has not yet been thoroughly investigated. Therefore, this study aimed to investigate the impact of different wall thickness, pulsation and imaging planes on YM estimates, to gain more information about the source of variability associated with SWE. Poly(vinyl alcohol) cryogel (PVA-c) fabrication has been used for phantom design and construction. The agar-based TMM was used to surround the tubes. The inlet and outlet of the phantom were connected to a programmable gear pump using c-flex tubing to form a closed loop. Image J profiling was used to clarify the anomalies further detected using SWE. The 4 F/T cycle vessel phantom has shown less YM variability than in the 6 F/T cycle. YM ranged from 8 kPa for a 1 mm thickness tube to 53 kPa for the thickest 6 mm wall thickness for the softer 4 F/T cycle tube. Vessel phantoms embedded in TMM show higher variability than vessel phantoms submerged in water. YM ranged from 32 kPa for a 1 mm thickness tube to 117 kPa for the thickest 6 mm wall thickness for the softer 4 F/T cycle tube. SWE variability in measurements was higher in phantoms embedded in TMM compared to those submerged in water. It is recommended that combine the transverse and longitudinal imaging planes to provide a better understanding of disease over the full vessel circumference.

Steel fiber-reinforced recycled aggregate concrete-filled GFRP tube columns: Axial compression performance

The enhancement of the mechanical properties of recycled aggregate concrete (RAC) has long piqued the interest of researchers. Based on a brief review of the existing methods for improving the mechanical properties of RAC, this paper proposed a new composite column—steel fiber-reinforced recycled concrete-filled GFRP tube (SF-RACFFT) column. To investigate the axial compressive performance of concrete-filled GFRP tube (CFFT) columns, 36 specimens were designed and fabricated. The variables considered included the mass replacement rate of recycled coarse aggregate (MRCA: 0, 50%, and 100%), steel fiber volume content (VSF: 0, 0.6%, 1.2%, and 1.8%), and GFRP tube thickness (T: 4 mm, 6 mm, and 8 mm). The failure patterns of these CFFT columns were compared, the contribution of the GFRP tube to the axial bearing capacity was quantified, and the axial stress–strain responses were analyzed. Results showed that as the GFRP tube thickness increased, the peak axial stress of the CFFT columns increased by 20.8%∼54.2%. Replacing natural coarse aggregate (NCA) with 100% recycled coarse aggregate (RCA) resulted in a reduction of 8.6%∼12.4% in peak stress; while adding an appropriate amount of steel fibers could improve the peak stress. Finally, based on the evaluation of existing models, a strength enhancement model and a strain enhancement model for SF-RACFFT columns were proposed.

A First Analysis of the Ensemble of Local Maxima of Maximal Center Gauge

Maximal center gauge (MCG) aims to detect some of the most important vacuum configurations, suggesting thick magnetic flux tubes quantized to non-trivial center elements of the gauge group being responsible for confinement. Due to the NP-hardness of a global maximization of the gauge functional only numeric procedures aiming for local maxima are possible. We observe a linear decrease in the string tension with increasing gauge functional value of the local maxima. This implies that the request to get as close as possible to the absolute maximum is unattainable. We compare global properties of the ensemble of local maxima with other methods to detect center vortices and with determinations of the string tension from full configurations. This comparison indicates that the information about the number and positions of center vortices is contained in the structure of the ensemble of local maxima. This may pave the way for a future more successful formulation of the gauge condition.

Axial compressive property of square and rectangular UHPC-filled duplex stainless steel tube stub columns

This study presents experimental and numerical investigations of the axial compression performance of square and rectangular ultrahigh performance concrete (UHPC)-filled duplex stainless steel tube (UFSST) stub columns. A total of twelve UFSST stub columns, six ordinary concrete filled duplex stainless steel tube (CFSST) stub columns, and six hollow duplex stainless steel tube (HSST) stub columns were tested under axial compression. The test parameters include the section type, three kinds of concrete strength grades, and three kinds of duplex stainless steel tube thicknesses. The test results showed that UFSST stub columns behaved with high bearing capacity and favourable ductility. In the UFSST stub columns with ξ ≥ 1.87, the square and rectangular duplex stainless steel tubes could well confine the shear failure of UHPC. The developed finite element model could effectively reflect the compressive behavior of the HSST, CFSST and UFSST stub columns. The available experimental database was employed to evaluate the feasibility of current design codes and existing calculation models in the literature to design UFSST stub columns. Finally, a modified computational model was proposed that takes into account the nonuniform confinement effect induced by square and rectangular section tubes on concrete and showed a higher prediction accuracy.

Parametric study of steel-beam to flat-rectangular CFST column connections with small-size diaphragms

This paper studies the influence of various design parameters on the hysteretic behavior of beam-to-column connections between steel beams and flat rectangular concrete filled steel tubular (CFST) columns with small-size external diaphragms. Finite element models for the corner and exterior connections in a frame structure are developed and validated using test results. The influence of the parameters including the axial compression ratio, the thickness and flatness of the rectangular steel tube, and the size of the diaphragm on the hysteresis, load capacities, ductility, and energy dissipation capacities of the connections are particularly evaluated. Based on the evaluation, recommendations on the optimum design of the parameters are provided to ensure reliable hysteretic behavior of the connections for the seismic design of steel structures. This study provides the knowledge for the use of small-size external diaphragms beyond the limitation of existing design specifications for beam-to-column connections, which is meaningful to best exploit the unique properties of flat rectangular CFST columns and widen their applications in residential buildings.

Comparative analysis of acoustic anisotropy of pipes and sheets using SH- and tH-waves

The results of comparative studies of acoustic anisotropy of tH-waves and SH-waves in plates and tubes of different thickness are presented. Turning of polarization direction due to the corresponding orientation of transducers allowed to estimate the angular indicatrix of wave velocity relatively to the rolling direction. Significant differences in acoustic anisotropy of tH-waves and SH-waves are shown for both tubes and sheets.

Experimental and theoretical study on elliptical rubber concrete filled double-skin GFRP short tubes under axial compression

This study proposed a double-skin section consisted of an elliptical glass fiber reinforced polymer (GFRP) outer tube, a circular steel inner tube and rubber concrete filled between them, which had the features of aesthetic appeal, structural efficiency and waste recycle. Axial compressive test was conducted on the elliptical rubber concrete filled double-skin GFRP tubular (CFDST) short columns with various void ratios and rubber contents. Load-axial strain-hoop strain data was obtained from the experiments and the contribution of each component (i.e., concrete, GFRP tube, steel tube) to resist the applied load was clarified. Experimental results indicated that the void ratio and rubber content had the most significant effects on the dilation property (i.e., hoop and axial strains) and confinement effect of the rubber concrete. Nevertheless, effects of steel tube thickness and rubber particle size were insignificant. Based on the experimental results and confining concrete theories, a theoretical model, with proper considerations on the effects of void ratio, rubber content and aspect ratio, was proposed to estimate the ultimate load-carrying capacity and ultimate strain of the stub columns under axial compression. Finally, reasonability and accuracy of the proposed model were verified by the experimental results.

Study of Bearing Capacity of Aluminum Alloy Thin-Walled Circular Tube Filled with Lightweight Filler

In this study, experimental research, a numerical simulation, and a theoretical analysis were performed on the bearing capacity of an aluminum alloy circular tube filled with a lightweight filler (ATLF). Bearing capacity tests were conducted for six ATLF columns and two aluminum alloy hollow tubes (AAHTs), and their local buckling failure modes and mechanical properties were obtained. A finite element model was developed using ABAQUS software (ABAQUS 2016, ABAQUS Inc., Palo Alto, CA, USA) for numerical calculations. Furthermore, a large-scale numerical analysis was performed to investigate the effect of structural parameters, such as the tube thickness, diameter, column length, and initial geometric imperfections, as well as the aluminum alloy’s properties and the lightweight filler’s properties, on the bearing capacity of the ATLF columns and AAHTs under axial compression. Based on the test and numerical analysis results, a formula for calculating the local buckling stress of AAHTs under axial compression is proposed. An improved coefficient of bearing capacity for the ATLF columns caused by the internal lightweight filler was obtained by fitting, and based on the results, a formula for computing the bearing capacity of ATLF columns under axial compression is proposed in this study.

Cyclic loading tests and numerical modeling of concrete-filled 700 MPa high-strength steel tubes incorporating deep plasticity

Concrete-filled high-strength steel tubes (CFHST) could improve structural efficiency with lighter weight and higher capacity. However, the relative lower ductility and higher yield-to-tensile strength ratio of high-strength steel arouse worries about seismic performance of CFHST. In order to reveal the influence of high-strength steel on the elastoplastic hysteretic behavior of CFHST, 8 cantilever columns with Q550 and Q690 steel were subjected to constant axial load and cyclic top displacement. The actual yield strength of the steel was over 700MPa and the maximum axial load ratio was over 0.5. Based on the experimental observations, a finite element model was developed in ABAQUS that could consider deep plasticity behavior of CFHST members more precisely by introducing full-range elastoplastic constitutive model of high-strength steel and damaging–crushing behavior of infill concrete. The model was validated by the 8 tests of this study and other 34 cyclic-loaded CFST specimen from different researchers. 288 cyclic-loaded CFHST models were simulated by the effective numerical model in the parametric study on the elastoplastic deformation capacity of CFHST columns. The experimental and numerical investigations show that the CFHST could still have considerable deformation capacity if the local deformation of the steel tubes develop moderately. For heavy loaded CFST columns, high-strength thin-walled steel tubes have satisfying elastoplastic deformation capacity and ductility that are not worse than CFST with thick conventional steel tubes. The application of high-strength steel could delay the steel yield and control the damage of the concrete, leading to larger pre-peak deformation capacity. Finally, the empirical formulas were proposed to roughly yet efficiently estimate the ultimate drift θu of cyclic-loaded CFSTs with fy=345∼ 690 MPa, fc’=24∼72 MPa, ξ=1.0∼6.0 and n=0.20∼0.80, which is fairly practical in plastic inter-story-drift check and seismic design of CFHST structures.

Roles of Carbon Nanotube Confinement in Modulating Regioselectivity of 1,3-Dipolar Cycloadditions.

DFT-based calculations were employed to investigate mechanisms of 1,3-dipolar cycloadditions between phenylacetylene and an azide (phenylazide or benzylazide) inside carbon nanotubes, whose diameters range from 10 to 14 Å, by obtaining their reaction species (reactant complex, transition state (TS), and product (Pro)). The reactions yield 1,4- and 1,5-triazoles, whose paths are denoted by 1,4- and 1,5-approaches, respectively. We found different geometrical features of reaction species between 1,4- and 1,5-approaches. Reflecting different reaction species, nanotube confinement has the power to enhance kinetically and thermodynamically controlled regioselectivity of 1,3-dipolar cycloadditions to form 1,4-triazoles. In inner 1,4-approaches, the reaction species have planar structures, being small relative to the cavity of tube hosts, and then, their activation energies are slightly lowered relative to those without tube surroundings, independent of the tube diameter. In inner 1,5-approaches, reaction species have phenyl groups overlapping each other, depending on the tube diameter: L-shaped and stacking fashions are found in thick and thin tubes, respectively. Particularly, the stacking fashion in thin tubes results in repulsive orbital interactions between two phenyl rings, destabilizing their TS and Pro. The presence of overlapping phenyl groups increases the activation energies in the 1,5-approaches with a decrease in the tube diameter, being larger than those without tube surroundings.

Behavior of square concrete-filled stainless steel tube columns after high-temperature sliding

This paper presents herein pertains the experimental and numerical investigations on axial compressive behavior of square concrete-filled stainless steel tube (CFSST) columns after high-temperature sliding. A total of 117 CFSST specimens were tested under axial compression loading. The design variables included tube thickness, temperature, duration, and concrete compressive strength. Test results indicated that the initial stiffness of square CFSST short columns was degenerated due to high-temperature sliding. CFSST specimens exhibited a 62.7% lowest residual strength at 1000 °C. The influence of high-temperature duration on the residual strength of square CFSST short columns after high-temperature sliding was limited. The residual strength of specimens was positively correlated with the thickness and concrete strength. All square CFSST columns after high-temperature sliding experienced an outward local buckling under axial compression. Finite element models of square CFSST columns after high-temperature sliding are established and validated against the experimental results. In addition, the parameter formulae of residual strength for CFSST columns after high-temperature sliding were proposed, which achieved high accuracy. This research results could provide strengthening reference for the application of CFSST columns after high-temperature sliding.

Mechanical behavior of GFRP-recycled concrete-steel multitube concrete columns under axial compression

This paper proposed a novel GFRP-recycled concrete-steel multitube concrete column (RA-MTCC), which consisted of an external circular GFRP tube, a group of small internal steel tubes in a circular array, and recycled aggregate concrete filling for all the space inside of these tubes. The mechanical behavior of eleven specimens were investigated under uniaxial compressive test considering parameters of the GFRP tube thickness, the configurations of internal steel tubes, the strength and the replacement ratio of recycled coarse aggregates (RCAs). Test results indicated that: (1) the replacement ratio of RCAs had no significant impact on the failure mode and ultimate load bearing capacity but noticeable adverse effect on the stiffness of RA-MTCCs; (2) the small internal steel tube could significantly increase the ultimate load bearing capacity and stiffness of RA-MTCCs, with a maximum enhancement of 82% and 114%, respectively; (3) specimens with GFRP outside exhibited excellent ductility behavior due to the effective confinement provided by GFRP jacket and steel tubes. An analytical model considering the replacement ratio of RCAs was proposed and verified with the present test results. The predicted results showed that the proposed model could accurately predict the full range stress–strain response of RA-MTCCs. Finally, based on the proposed analytical model, a simplified calculation formula for the ultimate bearing capacity of RA-MTCC was proposed.

A novel mechanical joining method for sheet-tube structures by annular ring compression

Joining by forming has lately received great attention for connection between sheets and tubes due to its high joining efficiency, simple operation, and excellent joining strength. However, protrusion or indentation often occurs adjacent to the joints and, in some cases, the sheet warps, seriously affecting the performance of the connector. To overcome this problem, we propose a novel joining by forming process by compressing an accessory ring to produce the annular squeezing of the sheet, thus forming high-quality joints with smooth surfaces. A numerical-experimental analysis was adopted to identify the influence of the ring width and height on the joint cross-section, effective strain, tube thickness, and flow velocity. To assess the performance of the enhanced joint, its mechanical properties, microstructure, and failure modes were also analyzed. The results showed that the ring width and height have a significant effect on joint strength. Compared with the original joining process without the ring, the joint utilizing a wider ring can obtain higher pull-out loads (58.9% higher) to detach the sheet from the tube, while no sheet warpage happens for excessive local deformation. The utilization of larger and higher rings also motivates the increase of the pull-out strength. In some cases, tube plastic instability can be triggered during the pull-out tests, thus avoiding the full detachment of the components and contributing to the safety of the mechanical joint. Compared with the non-deformation zone, the grains in the deformation zone of the sheet are compressed and become elongated, and there are inclined separation bands between the two regions. This paper provides a new and efficient method for manufacturing sheet-tube structures with high joining strength.

Nonlinear finite element and analytical modelling of reinforced concrete filled steel tube columns under axial compression loading

Local buckling of steel and excessive spalling of concrete have necessitated the need for the evaluation of reinforced concrete columns subjected to axial compression loading. Thus, this study investigates the behaviour of concrete filled steel tube (CFST) columns and reinforced concrete filled steel tube (RCFST) columns under the axial compression using the finite element modelling and machine learning (ML) techniques. To achieve this aim, a total of 85 columns from existing studies were analysed utilising the finite element modelling. The ultimate load of the generated datasets was predicted employing various ML techniques. The findings showed that the columns' compressive strength, ductility, and toughness were improved by reducing transverse reinforcement spacing, increasing the number of reinforcing bars, and increasing the thickness and yield strength of outer steel tube. Under the axial compression loading, the finite element modelling analysis provided an accurate assessment of the structural performance of the RCFST columns. Compared to other ML approaches, gradient boosting exhibited the best performance metrics with R2 and root mean square error values of 99.925% and 0.00708 and 99.863% and 0.00717 respectively in training and testing stages, to predict the columns' ultimate load. Overall, gradient boosting can be applied in the ultimate load prediction of CFST and RCFST columns under the axial compression, conserving resources, time, and cost in the investigation of the ultimate load of columns through laboratory testing.

Damage analysis and energy absorption capacity of hollow square steel tubes subjected to conical hammer impact

ABSTRACT Steel tubes find widespread applications in various structural elements, including load-bearing columns, stair guardrails, and security bollards, due to their high strength and durability. However, these structures are susceptible to damage under impact loading conditions. While prior studies have focused on drop hammer shapes like rectangles, wedges, cylinders, and hemispheres, research on the impact of a conical-shaped hammer on square and rectangular steel tubes remains limited. Therefore, this study aims to analyse the damage resulting from the impact of a conical-shaped hammer on square steel tubes using nonlinear Finite Element Analysis (FEA) software ABAQUS/Explicit. The investigation explores the effects of various parameters, including tube geometry, impact location, impactor mass, and impact height, on tube deformation and fracture behaviour of tube. Through comprehensive analysis, it was observed that the impacted site exhibited punching failure accompanied by inward bending of the tube, while outward buckling occurred at the support. The energy absorption process was examined, and the effect of the aforementioned parameters on the energy absorption capacity (EAC) was assessed. The findings indicate that the thickness of the steel tube has the most significant impact on the impact force and EAC. Additionally, the deflection of the tube was primarily influenced by the length of the hollow section.

Modal analysis of concrete filled steel tubular structure under lateral impact loading

In this paper, deformation mode and the large deflection of the concrete filled steel tubular (CFST) structural member with fixed ends under lateral impact loading was studied by rigid-plastic modal approximation method and finite element analysis by ABAQUS. Using the yield criterion and beam-on-foundation model, the modal analytical solution for plastic behavior of CFST member under lateral impact is obtained considering the interaction of bending and axial stretching. The rigid-plastic modal solution captures the FE results and the deformation mode is accordance with the available experimental results. It shows that lateral deformation of CFST member can be effective predicted by the modal solution consisting of geometric and physical parameters variations. The influence of steel tube thickness, cross-section diameter, effective length, strength and density of concrete and steel, and initial impulsive are discussed in detail. The results show that deflection of the CFST member increase with the increase of the length to diameter ratio, initial impulse and smaller thickness to diameter ratio. Finally, the relationship between lateral deformation and geometric variations are established by optimal sets of modal solution.