Core Tube Research Articles

Compressive performance of bamboo scrimber and concrete-filled steel tube columns

The light and high strength bamboo scrimber was buried in the core of concrete-filled steel tube (CFST) to form bamboo scrimber and concrete-filled steel tube column (BCFST), which was expected to reduce the amount of concrete and weight in CFST and promote the use of bamboo scrimber. To investigate the influences of key design parameters on the compressive performance, namely bamboo scrimber dimension, design concrete strength, and diameter to thickness of steel tube, ninety BCFSTs and eighteen CFSTs specimens were tested under axial compression. According to the experimental results, the improvement of the BCFST bearing capacity resulted from the contribution of the inner sandwich concrete and the bamboo scrimber under the constraint from the steel tube. The ultimate load rose with the increase of the bamboo scrimber dimension, concrete strength, and steel tube thickness. Note that the increase range of ultimate load of BCFSTs is 3.9% higher than that of CFSTs by increasing the dimension of bamboo scrimber, with a maximum increase at 43.9%. The damage modes of BCFSTs can generally be categorized into local buckling failure mode and shear failure mode. In addition, owing to the different compactness between the bamboo scrimber and the concrete, the stress-strain curve of the C80 concrete characterized the strain hardening tendency rather than the strain softening tendency in the C50 concrete. According to the load-strain curves of the BCFSTs and the contribution of the composite actions between the three parts of the member to the load-carrying capacity, the characteristic points were defined. A calculation model for accurately predicting the ultimate capacity of BCFSTs was proposed by considering the boundary conditions for both non built-in and fully built-in bamboo scrimber in CFSTs.

Design of a sheathed water condensation particle counter with variable saturation ratio

We consider a particle condensation device where a cold aerosol enters at one open end of a tube. The wall of the tube is porous beyond a certain section. A stream of cold air is injected radially and symmetrically through an initial focusing region of the porous wall, and a stream of warm humid air with a saturation ratio S is injected in a condensation region further downstream. The configuration offers several advantages over existing water condensation particle counters (WCPCs). First, S may be varied by mixing a dry gas stream with a humid stream prior to their passage through the porous tube wall. Second, radial entry of the humidified flow accelerates the penetration of the vapor into the core of the tube, such that the maximal saturation ratio is reached within axial distances comparable with the tube radius. Third, the aerosol is partially confined within the tube core by the radially entering dry and humid gases. The particles then sample the relatively uniform saturation field near the tube axis, resulting in sharp responses of the activation probability versus particle diameter. Calculations with various combinations of axial and radial Reynolds numbers are carried out in search of conditions resulting in the smallest possible variation of the maximal supersaturation reached along the various flow streamlines.

Intensity analysis of frictional heat source during core tube sampling and drilling

AbstractCurrently, the heat generated during coal core tube sampling causes rapid gas desorption, leading to substantial measurement errors in laboratory gas content assessments. Reducing these errors requires studying frictional heat from core tube friction against the hole wall and coal core temperature rise. Combining the independently developed device to simulate the thermal effect of coring and the COMSOL finite element analysis software, the intensity of the frictional heat source during the core tube sampling and drilling process was analyzed under different coring depth and rotational speed conditions. The research results show that: At constant speed, frictional heat intensifies as the core depth increases. However, the rate of temperature rise decreases with increasing core depth; when the coring depth is constant, the frictional heat is proportional to the rotational speed. For example, at a depth of 140 m and a rotational speed of 120 r/min, the intensity of frictional heat generated by drilling is 2.21 ∗ 10E6J. Similarly, at 180 r/min, the strength is 2.28 ∗ 10E6J, and at 240 r/min, the strength reaches 3.65 ∗ 10E6J; Under certain conditions, core tube wall temperature will not rise indefinitely but will stabilize to a certain value.

Seismic response analysis of a new staggered storey isolated structure under mainshock-aftershock sequences

ABSTRACT Based on a new type of isolated structure, this paper studies the seismic response of the structure under single mainshock and mainshock-aftershock sequences. The new structure developed from the base-isolated structure and the inter-storey isolated structure. To compare its seismic performance with a fixed-base structure, a new staggered storey isolated structure model is developed using ETABS software. The results indicate that during both single mainshock and mainshock-aftershock sequences, the maximum inter-storey displacement of the staggered storey isolated structure is concentrated in the isolated layer, while the stress damage of the core tube mainly occurs between the upper and lower isolated layers. Under mainshock-aftershock sequences, the displacement of the isolated layer is larger than that under the single mainshock, and the distribution of plastic hinges of the frame is greater than that under the single mainshock, compared with the single mainshock sequences, the stress distribution of the core tube and the inter-story displacement of the structure increase by 19.80% anc23%% respectively. Consequently, the damage to the structure under mainshock-aftershock sequences is more severe. The hysteresis curve of the upper isolated layer bearings is more pronounced and demonstrates better energy absorption than that of the lower isolated layer bearings. Overall, the staggered storey isolated structure exhibits better seismic performance than the fixed-base structure. The isolated effectiveness and energy dissipation of the new staggered storey isolated structure improve when the upper isolated layer is lowered.

Development of a pressure coring system for the investigation of deep underground exploration

To provide a more accurate evaluation of the scale of deep underground resources, a new pressure coring system was carefully developed and its strength and safety of the engineering were verified by theoretical analyses and numerical simulation. The designed pressure coring system can obtain cores with length of 3 m and diameter of 50 mm at 70 MPa. The results of the ball-drop operation experiment demonstrate that differential motion assembly can effectively cut a safety pin by applying a tensile force of 4852 N, and it can lift the core tube through the center pole to complete a series of mechanical actions to seal the pressure. Additionally, by maintaining pressures at 70 MPa for 30 min, the pressure sealing capacity of the system was proven. Furthermore, a core sample with a diameter of 50 mm was obtained through a core drilling experiment and the coring performance of the pressure coring system was verified. This study can not only enrich the existing onshore coring technology but also provide a theoretical guide and design criteria for the development of similar pressure coring systems to meet the demand for deeper underground exploration.

Morphological Performance of Vegetated and Non-Vegetated Coastal Dunes with Rocky and Geotextile Tube Cores under Storm Conditions

Coastal dune restoration projects are increasingly seen as a means of protecting the coast against storms, especially with the use of natural (plants), artificial (geotextile tube cores) and hybrid (plants and geotextile tube) elements. As geotextile tube cores have been found to negatively affect dune and beach natural morphodynamics, rocky cores are thus seen as a potential alternative. We carried out laboratory experiments to compare the performance of dunes with rocky cores, geotextile cores, and both types when coupled with planted vegetation. We investigated these elements in the context of scaled mild, moderate, and intense storm conditions. The results showed that dunes with either type of core lost more sand than dunes without cores. The addition of plants generally reduced the erosion across the various options, but most strongly for rocky cores under mild and moderate storm conditions. We also found that dunes with a high density of plants were best for intense conditions. Overall, the use of rocky dune cores, when coupled with plants, is the most suitable and sustainable alternative option in hybrid engineering projects.

CFD wind tunnel investigation for wind loads of steel television tower with grid structure

Television(TV) towers with grid structures serve as broadcasting frequency modulation or television transmission signals and provide sightseeing opportunities. Accurate wind load information is critical to the design of these towers to ensure their resistance to wind. Due to the scaling ratio of the test model, wind tunnel test can only determine the overall wind load, resulting in the loss of wind load information on specific rods. However, there is currently a lack of research on the wind loads of the specific rods of a core tube with a grid structure. This article focuses on this special topic. Computational fluid dynamics (CFD) technology, which was validated based on the Commonwealth Advisory Aeronautical Research Council (CAARC) model, was employed in simulation for a towering television tower with a grid structure. Wind load distributions of the grid structure and core tube were studied, including flow streamlines, velocity profiles and wind pressure distributions. The results indicate that the wind pressure distribution on the outer surface of the cross rods is similar at different heights. Net wind pressures of the rods in the flow separation zone are close to 0, which significantly reduces the across-wind load. Different wind direction angles significantly influence the wind load of the grid structure but slightly influence the core tube. The simulation results can provide a reference for wind load design of similar grid structures.

Experimental investigation of axially loaded circular ultra-high performance concrete with coarse aggregate (CA-UHPC) filled steel tube slender columns

This paper presents an experimental investigation on circular ultra-high performance concrete with coarse aggregate (CA-UHPC) filled steel tube (CA-UHPCFST) slender column subjected to axial compression. A total of 42 specimens were manufactured and tested to determine the effects of CA-UHPC strength, steel tube thickness, steel strength, and length-to-diameter ratio on axial compressive behavior of circular CA-UHPCFST slender columns. The test results show that elastoplastic instability failure with local buckling in the compression region is observed for intermediate columns, while overall buckling failure is occurred for slender columns. The inclusion of steel fibers significantly alleviates the tensile cracking and compressive crushing of CA-UHPC core, which in turn improves the ultimate strength and ductility of CA-UHPCFST slender columns. The ultimate bearing capacity and ductility index decrease remarkably with an increase in length-to-diameter ratio, while increase with steel yield strength and tube thickness. The interaction between steel tube and CA-UHPC core decreases as the length-to-diameter ratio increases, which mainly exists in compression zone but is weak or even nonexistent in tension zone. Finally, the feasibility of current design guidelines concerning the concrete-filled steel tubes for calculating the stability bearing capacity of circular CA-UHPCFST slender columns is evaluated, and a simplified model is proposed to estimate the stability carrying capacity. The simplified model demonstrates good accuracy in predicting the ultimate carrying capacity of axially loaded circular CA-UHPCFST slender columns.

Effect of geometrical parameters on compression performance and energy absorption of pyramidal thin-walled tube core sandwich panel

Sandwich panels with pyramidal cores made of thin-walled tubes absorb energy very well, but their main limitation is the complexity of producing such a structure. This study utilized a novel self-interlocking assembly technique to fabricate the lattice core, significantly reducing fabrication time and material requirements. Experimental tests and finite element analyses were performed to investigate the effect of geometrical parameters on the out-of-plane characteristics of sandwich panels with pyramidal thin-walled tube cores and relative densities ranging from 1.39% to 3.96%. Finite element predictions for deformation mechanisms, compressive strength, and energy absorption match experimental results. The results reveal that the proposed approach for producing the nodes worked successfully, with no brazed nodes breaking. The amount of energy absorbed per unit of mass reduces by 22% and 27%, respectively, when the slenderness is increased from 3 to 5 and subsequently from 5 to 7. In addition, when the angle of the tubes is increased from 50° to 55°, it makes them 23% stronger and absorbs 13% more energy per unit mass. Regarding strength and energy absorption per unit volume, pyramidal thin-walled tube cores are better than traditional lightweight sandwich panels, especially at lower relative densities.

Seismic fragility analysis of the steel frame with new layered assembled joints

In order to improve the assembly efficiency of the steel frames, a new fully-bolted core tube joint was proposed in combination with the seismic performance requirements of the joint. Cyclic loading tests were carried out on both new and traditional joints to study their seismic performance, and the joint parameters obtained from the tests were introduced into the overall frame model in SAP2000 to perform Incremental Dynamic Analysis. Based on the single-parameter damage model and the two-parameter damage model, the structural performance level limits were defined, the damage states were classified, and the seismic fragility analysis of the structure was performed. The results showed that the fragility curves of the steel frame with the new joint were enveloped within the fragility curves of the steel frame with the traditional joint under both single and double damage indices, and the collapse resistance reserve factor of the steel frame with new joint was larger. That is, the use of the new joint could reduce the failure probability of the structure under each damage state and improve the collapse resistance of the frame. The median PGA values of the structure based on the single-parameter damage index were smaller than those based on the two-parameter damage index in the LS1 ∼ LS2 limit states, and the opposite was true in the LS3 ∼ LS4 limit states, meaning that the cumulative energy dissipation had an obvious influence on the evaluation of the seismic performance of the structure, and the combination of the two-parameter damage index could better predict the damage degree of the structure. Additionally, increasing the inner sleeve height in the joint domain improved the overall performance and reduced the failure probability of the structure.

Detection of brazing defects in stainless steel core plate using the first peak value of pulsed eddy current testing signals

As a novel building structure element, stainless steel core plate (SSCP) has seen growing application in modular construction. It is composed of two stainless steel skin panels and a number of stainless steel core tubes, which are brazed by elevated temperature inert gas. The underlying defects in brazing joints severely damage the SSCP’s structural integrity and weaken its mechanical properties. In this study, a nondestructive testing (NDT) method based on pulsed eddy current testing (PECT) was employed to contactlessly detect the missing solder and non-bonding brazing defects from the plate surface. The defect-free and defective brazing joints are simplified to stratified structures and analytical modeling for a PECT probe over the brazing joint is thus performed. The time-domain features of the calculated PECT signal due to the structure parameter variation are investigated. The first peak value is selected to characterize the brazing quality due to its distinct variation w.r.t. well-bonded brazing, missing solder, non-bonding and skin panel. Experiments are also carried out to validate the analytical modeling. With the aid of an industrial robotic arm, one-dimensional (1D) line-scan and two-dimensional (2D) planar scan of the PECT probe over the SSCP specimen are implemented and the detection results are represented in images. In contrast to the well-bonded joint, the brazing joints with missing solder defects are imaged as notched rings, on which the notch orientations and sizes agree with the actual openings of the brazing foils, while the non-bonding brazing joint is imaged as a full ring with faded color. The proposed method shows a promising aspect in practical application for automated NDT of the brazing defects in SSCPs.

Numerical simulation and load-bearing capacity of concrete-filled steel tubes strengthened with CFRP grid-reinforced ECC under axial compression

A numerical study on the compressive behavior and load-bearing capacity of the concrete-filled steel tube (CFST), strengthened with a carbon fiber-reinforced polymer (CFRP) grid-reinforced engineered cementitious composite (ECC), is presented. The numerical simulation, which was based on a previous test performed by the authors, indicated that an increase in the number of CFRP grid layers results in a significant increase in the bearing load on the concrete core. The confinement is provided to the concrete core by the strengthening layer only after the yielding of the steel tube, which occurs because of the contact pressure between the steel tube and ECC. Parameter studies that considered the effect of the number of CFRP grid layers and the strength of the CFRP, compressive strength of the ECC and concrete core, diameter-to-thickness ratio, and yield strength of the steel tube were conducted. The increase in fcu and decrease in Ds/t weakened the function of the confinement of the strengthening layer, and the influence of fcu was more significant. Furthermore, an analysis model that considered the nonlinear confining behavior and stress history for predicting the load-bearing capacity of the CFST columns strengthened with CFRP grid-reinforced ECC was established. The stress increment iteration method was employed to determine the varying confining pressure during loading. The proposed model showed high accuracy for predicting the load-bearing capacities of the strengthened columns.

Energy Analysis of a Damped Substructure Outrigger System

A damped outrigger system (DO) has been proposed to enhance the seismic performance, in which links between outriggers and perimeter columns are artificially disconnected and implemented by dampers. Such an operation essentially destroys the structural integrity and becomes a potential threat for structural safety. Moreover, its performance is very sensitive to the stiffness of perimeter columns. In this study, a mega-sub controlled system is employed to propose a novel outrigger system, i.e., a damped substructure outrigger system (DSO). The novel system has good structural integrity due to its main structure consisting of the core tube, outrigger, and perimeter column. To present further investigation, the govern equations of DSO are derived by the simplified model which is regard as a cantilever beam system with a multirotation spring and energy dissipation substructure. Then, the energy distribution and seismic performance are parametric investigated. Finally, the damping effects of DSO are discussed. The results indicate that DSO possesses the superiority of damping performance. Compared with DO, DSO is less sensitive to perimeter column stiffness. Moreover, the proposed system can obtain the high efficiency in energy dissipation but with less damping cost than that of the viscous damper. Also, the larger stroke of the viscous damper can be found for DSO.

Dynamic model, performance analysis and evaluation of frame-distributed rocking-core tube structure

To obtain adequate lateral stiffness for frame-core tube (FCT) structures, the core tube area proportion is often increased and/or overly reinforced which often limits the layout flexibility and economy of the structure. A new high-rise configuration named frame-distributed-core tube (FDCT) is proposed to reduce the tube area proportion of the FCT structure. Combined with a rocking system, the frame-distributed rocking-core tube (FDRCT) structure is further proposed, which aims to reduce the damage caused by soft-stories due to by the weakening of the stiffness of the FDCT structure. Simplified models are built, and the structural dynamics are derived based on the Lagrangian equation. Through numerical simulation of three structures under ground motions, it is shown that the FDRCT structure has good energy dissipation and damping performance. The inter-story drift ratios of the structure decreases with the increase of the distributed rocking tubes mass. Under different site conditions and long-period ground motions, numerical simulations and shaking table tests show that the distributed rocking tubes can effectively reduce the structural response and improve the seismic performance. The FDRCT configuration gives better damping performance under long-period ground motions. A performance-profit evaluation shows that the proposed high-rise structure system of FDRCT provides a safe and cost-effective design solution.

Behavior of CA-UHPC filled circular steel tube stub columns under axial compression

Ultra-high performance concrete with coarse aggregate filled steel tube (CA-UHPCFST) is a sustainable and high-performance structural form with high carrying capacity. This paper presents experimental and numerical investigations on the axial compressive behavior of circular CA-UHPCFST stub columns. Forty-four specimens were tested to determine the effects of concrete strength, steel fiber content, steel tube thickness, and steel yield strength on the axial compressive behavior. A finite element (FE) model was developed and validated for composite action analysis between steel tube and concrete core. The results show that the failure modes of CA-UHPCFST stub columns depend on confinement coefficient (ξ) categorizing as shear failure (ξ < 0.9) and bulge failure (ξ > 1.4). Correspondingly, as the confinement coefficient grows, the load-shortening curve after the ultimate resistance demonstrates three categories: descending, plateau, or hardening stage. The steel tube exhibits a prominent confinement effect on the CA-UHPC core, with a strength index ranging from 1.066 to 1.225; however, the enhancing effect is not as significant as that of the ordinary concrete-filled steel tubes. The incorporation of steel fiber can improve the ultimate resistance, but has a limited effect on strength index. By comparing the measured ultimate resistances to the predictions, the feasibility of current design codes for the prediction of load carrying capacity is evaluated, and a simplified model is proposed to predict the ultimate resistance of circular CA-UHPCFST stub columns under axial compression.

Crashworthiness behavior assessment and multi-objective optimization of horsetail-inspired sandwich tubes based on artificial neural network

The crashworthiness behavior of horsetail-inspired sandwich tubes was analyzed in this study. Multilayer perceptron (MLP) algorithms with the Levenberg-Marquardt training algorithm (LMA) were used to predict force-displacement curve and optimize the geometrical parameters according to minimum peak crushing force and specific energy absorption. Based on the non-dominated sorting genetic algorithm II (NSGA-II) optimization results, the specimen with four core tubes and a thickness of 1 mm, and a height of 92 mm has the optimal crashworthiness performance. Finally, the optimal specimen is fabricated and the results of the numerical and MLP methods are validated versus experimental approach.

Soil flowing characteristics during flexible tube coring for lunar exploration: Modeling and verification

Obtaining planetary soil samples and returning them to the Earth is the most effective solution to detect the distribution and reserves of planetary resources. In order to maintain the stratification and a high coring ratio of soil samples during the sampling process, China National Space Administration adopted a flexible tube coring (FTC) method for the upcoming Chang’e-6 mission. In this paper, the lunar regolith FTC characteristics, coupled with its spiral debris discharge were modeled. Orthogonal experiments were carried out with different drilling parameters using the prepared high-density lunar regolith simulant. The results show that the coring height and coring ratio are greatly determined by the penetration per revolution (PPR) index. The lunar regolith simulant’s coring ratio was as high as 90% when the PPR was optimized. The physical and mechanical parameters of artificial lunar regolith were characterized with respect to the PPR index as well as the dynamic flowing of the internal core, with a resulting accurately tuned coring ratio prediction model. Furthermore, the drilling load analysis can be applied to the optimization of drilling parameters employed by Chang’e-6 when collecting lunar regolith.

Seismic resistance of post-tensioned bridge column improving post-earthquake recovery

This study aims to improve the recovery of bridge columns after being damaged subjected to an earthquake and also proposes a PC column that reduces residual displacement by prestressing. The proposed column has a repairability of the damaged part of the column by arranging a concrete-filled steel tube at the column core. The seismic performance and post-earthquake recovery of the proposed columns were verified by conducting cyclic loading tests. Test results showed that the residual displacement was not reduced enough to improve the post-earthquake recovery. However, after investigating the column core at the end of the test, almost no visible damage, such as fracture or buckling, was found in the steel tube at the core, which means that the concrete-filled steel tube core itself can support the structure above. Therefore, the proposed system can be repaired quickly after being damaged if the residual displacement can be reduced.

Study on the seismic response of new staggered story isolated structure under different parameters

The new staggered story isolated structure is developed according to the base-isolated structure and the mid-story isolated structure. Quantitative calculation and evaluation of seismic damage are very important for structural safety. In this paper, the seismic damage evaluation of a new staggered story isolated structure is studied by numerical simulation and damage index calculation. A new staggered story isolated structure is established, and the effects of different layers and different chassis areas on the seismic response of the structure are studied. When the position of the bottom isolated layer stays the same, the upper isolated layer is set at different layers, which is set to the top of the 3rd, 6th and 9th layers. When the upper isolated layer keeps at the top of the 3rd layer, the chassis area is set at a different area, which is 26 m × 26 m, 36 m × 36 m and 46 m × 46 m. The results show that the new staggered story isolated structure has good isolated effects under the ground motion. For the structure set upper isolation layer is lower, the inter-layer shear force, inter-layer acceleration and inter-layer displacement are reduced. The energy dissipation effect of the structure improves. The core tube is less damaged and the plastic hinge is smaller. With the increase of chassis area, the isolated effect of the part above the upper isolated layer is good, while the shear force and acceleration of the part below the upper isolated layer of the structure increase, the damage at the core tube changed little and the appearance of the plastic hinge increased. Under earthquakes, with the change in position of the upper isolated layer and the area of the chassis of the new staggered story isolated structure, the displacement, tensile stress and compressive stress of the isolated bearing still meet the requirements of the standard.

Self-sacrifice-template epitaxial growth of hierarchical MnO2@NiCo2O4 heterojunction electrode for high-performance asymmetric supercapacitor

Constructing three-dimensional (3D) hierarchical bimetallic pseudocapacitive materials with abundant opening channel and heterojunction structures is rather promising but still challenging for high-performance supercapacitors. Herein, a self-sacrifice-template epitaxial growth strategy was proposed for the first time to construct 3D hierarchical bimetallic pseudocapacitive material. By using this strategy, NiCo2O4 nanowires (NiCo2O4NW) arrayed randomly to form a porous shell via in-situ epitaxial growth fully enclosing a MnO2 tube core, forming multiple transport channels and nano-heterojunctions between MnO2 and NiCo2O4NW, which facilitates electron transfer, i.e. exhibiting high electronic conductivity than any single component. As a result of the self-sacrifice-template epitaxial growth method, special hollow tectorum-like 3D hierarchical structure with considerable inter-nanowire space and hollow interior space enables easy access of electrolyte to NiCo2O4NW surface and MnO2 core, thereby resulting in highly exposed redox active sites of MnO2 core and NiCo2O4NW shell for energy storage. Comprehensive evaluations confirmed MnO2@NiCo2O4NW was a supercapacitor electrode candidate, delivering a superior energy density of 106.37 Wh kg−1. Such performance can be ascribed to the synergistic coupling effect of 3D hierarchical tube and nano-heterojunction structures. The proposed self-sacrifice-template epitaxial growth strategy provides important guidance for designing high-performance energy storage materials.