Axial Strength Research Articles

The Evolution and Performance of Cold-Formed Steel Built-Up Battened Columns

The cold-formed steel (CFS) built-up battened column represents a transformative and innovative solution in the construction industry due to its versatility, cost-effectiveness, and superior strength-to-weight ratio. In design consideration, chord spacing and batten plates influence the structural performance and stability of the column. The emphasis lies in the design flexibility of built-up battened columns, in which the composite action of several chord members connected by batten plates can enhance axial compressive strength. The batten plate plays a crucial role in preventing buckling and increasing the stability of the column while distributing the load evenly. The batten plates need to be properly designed to ensure stability and reduce buckling failure in the built-up battened column. However, implementing CFS built-up battened columns presents several challenges, including design complexity, connection design, and limited standards and guidelines.

Reliability analysis of various modeling techniques for the prediction of axial strain of FRP-confined concrete

PurposeThe external confinement provided by the fiber-reinforced polymer (FRP) sheets leads to an improvement in the axial compressive strength (CS) and strain of reinforced concrete structural members. Many studies have proposed analytical models to predict the axial CS of concrete structural members, but the predictions for the axial compressive strain still need more investigation because the previous strain models are not accurate enough. Moreover, the previous strain models were proposed using small and noisy databases using simple modeling techniques. Therefore, a rigorous approach is needed to propose a more accurate strain model and compare its predictions with the previous models.Design/methodology/approachThe present work has endeavored to propose strain models for FRP-confined concrete members using three different techniques: analytical modeling, artificial neural network (ANN) modeling and finite element analysis (FEA) modeling based on a large database consisting of 570 sample points.FindingsThe assessment of the previous models using some statistical parameters revealed that the estimates of the newly recommended models were more accurate than the previous models. The estimates of the new models were validated using the experimental outcomes of compressive members confined with carbon-fiber-reinforced polymer (CFRP) wraps. The nonlinear FEA of the tested samples was performed using ABAQUS, and its estimates were equated with the calculations of the analytical and ANN models. The relative investigation of the estimates solidly substantiates the accuracy and applicability of the recommended analytical, ANN and FEA models for predicting the axial strain of CFRP-confined concrete compression members.Originality/valueThe research introduces innovative methods for understanding FRP confinement in concrete, presenting new models to estimate axial compressive strains. Utilizing a database of 570 experimental samples, the study employs ANNs and regression analysis to develop these models. Existing models for FRP-confined concrete's axial strains are also assessed using this database. Validation involves testing 18 cylindrical specimens confined with CFRP wraps and FE simulations using a concrete-damaged plastic (CDP) model. A comprehensive comparative analysis compares experimental results with estimates from ANNs, analytical and finite element models (FEMs), offering valuable insights and predictive tools for FRP confinement in concrete.

A new hold-down device for seismic applications in CLT buildings: Design, testing, analytical and numerical assessment

An hold-down device was designed and tested experimentally for seismic applications (Seismic Hold-Down, SHD). The magnitude of axial strength as well as the up-lift displacement capacity is mainly oriented to cross-laminated-timber (CLT) buildings with medium-to-high ductility. There is consensus in the design practice of hold-down devices for promoting, as dissipative mechanism, flexural yielding of the dowel-type connectors (e.g. nails, screws) combined to timber’s embedment. Few are the applications aiming at hold-down’s optimization as it emerges from up-to-date literature review. In this framework, SHD was conceived such that tension break-out of steel was promoted at a reduced segment (fuse) of the vertical flange. In the context of capacity design, a convenient overstrength was assumed for other failure mechanisms, e.g. anchor’s pullout, laterally-loaded steel-to-timber connection, shear-plug of timber. The mechanical response under axial load was consistently predicted by an application of the component method, i.e. global stiffness and strength were analytically-derived using simplified series of non-linear mechanical springs. Three-dimensional finite elements model was employed to investigate buckling of the fuse which might occur, during cycles, when up-lift displacement is recovering. In practical circumstances, it is recommend to design SHD devices of a CLT wall similarly to diagonal elements of steel bracings, i.e. neglecting the contribution of the compressed element. Finally, SHD is compared to traditionally-designed hold-down, which mostly dissipates (and fails) at steel-to-timber connection. Overall hysteretic response is somehow similar, although the inelastic mechanisms involved are different. For example, both the devices show pinching during cycles which for SHD is mainly caused by buckling of the fuse while, for traditional hold-down, is dominated by timber’s embedment.

Evaluation of filler activation for sustainable FRP composite by studying properties, mechanism, and stability

The aim is to develop new fiber-reinforced polymer (FRP) water pipe by activating fiber glass (FG) by vinyltriethoxysilane (VS) getting vinylsilane-activated FG (AFG) for filling vinylester (VE) via continuous winding to make a novel VE-AFG composite. The novelty of this work is the activation of fiber glass by vinylsilane as a single filler in vinylester and compounding them via a two-dimensional continuous winding process for the first time. The crosslinking occurred in the AFG/VE/curing agent system after activation. The activated composites increased thermal stability; 25% VE-AGF increased the degradation temperatures at 10%, 25%, and 50% weight loss by 73.3%, 10%, and 7.2%. With the activated 20% composite, values of axial strength, hoop strength, and hardness were developed by 6.3%, 2%, and 8.7%, respectively. The decay resistance to different microorganisms was increased with VE-AFG composites as a result of a sharp decrease in biodegradability percentages. The activated composites are stable toward water absorption; the least percentage was recorded by 25% VE-AFG, which minimized the water absorptivity by more than 62%. The reported characterization sentence approves enhancement of thermal, physical, and mechanical stability of sustainable vinylester-fiber glass composites manufactured by continuous winding; this is recommended for application in water pipe systems.

Upper and Lower Bounds to Pull-Out Loading of Inclined Hooked End Steel Fibres Embedded in Concrete

Steel fibre-reinforced concrete (SFRC) consists of short, hooked steel fibres that are randomly distributed and oriented within the cementitious matrix. This paper presents a new analytical load-bounding approach that captures the tensile response of misaligned fibres embedded in the matrix. The contribution of fibres in bridging cracks to provide the required stress transfer relies on the orientation of the fibres in the concrete. Bridging fibres aligned with a crack are less effective than those inclined to it. Therefore, understanding the pull-out behaviour of misaligned fibres is a key factor in quantifying and optimising the design of SFRC in structural applications. In the laboratory, a single-oriented fibre embedded in a solid cylinder of concrete was subjected to a pull-out test, where the axis of the tensile force is aligned with the axis of the cylinder. Based on the observed behaviour, this paper presents a new analytical bounding approach to capture the pull-out response of misaligned hooked-end steel fibres embedded in a concrete matrix. The analysis was based on a transversely isotropic failure criterion assumed for the plasticity that occurs in the cold-drawn fibre. Lower and upper bounds to the loading failure were derived from fibre pull-out and fibre fracture, respectively. The division between bounds depended upon the fibre orientation, fibre diameter and the combined strengths of the steel and concrete. Bounding predictions were drawn from ratios between a fibre’s shear strength and its transverse and axial uniaxial strengths, as found from a novel testing proposal. The two bounds were compared with new data and other experimental results published in the literature. The results showed that the region between the bounds captured the failure loads of embedded fibres with effective load-bearing orientations. A critical orientation was observed at maximum strength. The present interpretation of the plasticity occurring within off-axis, hooked-end steel fibres suggests that it is possible to optimise the strength of concrete using this method of reinforcement.

Hydrophobic and thermal insulation properties of modified wood based on ATRP polymerisation

Balsa wood, despite being a cost-effective insulation material, has limited applications due to its inherent hydrophilicity. This study introduces an innovative technique for the in-situ growth of low surface energy long alkyl chain segments on balsa wood using the atom transfer radical polymerization (ARGET-ATRP) method, which not only provides durable and stable hydrophobicity but also preserves its natural texture, mechanical strength, and thermal insulation. The resulting hydrophobic wood demonstrated exceptional hydrophobicity in diverse environments, with a water contact angle up to 141.3° and a contact angle decrease of no more than 10.47 % after 150 min, confirming its hydrophobic stability. Furthermore, axial thermal conductivity of the wood was as low as 0.1012 W/m·K, the axial compressive strength decreased by only 12.8 %, further evidencing the retention of its mechanical properties. This simple yet effective strategy of in-situ alkyl chain growth on balsa wood not only preserves its structure but also opens new avenues for the multifunctional development of biomaterials.

Experimental study on hybrid fiber reinforced high performance concrete properties: Investigatingcomprehensive energy consumption capacity

The brittleness of concrete in tension increases with higher compressive strength, necessitating the study of cementitious composites that combine high strength and ductility. This study investigated the fresh and mechanical properties of high-strength concrete (HPC) incorporating fibers: steel, basalt, and polyethylene (PE). Hybrid fiber reinforced high performance concrete (HyFHPC) was created by tailoring mix proportions, with eight series of specimens cast, each carrying different fiber combinations alongside plain HPC as a reference. Compressive, tensile, and flexural tests were conducted, and results were analyzed. The electron microscopy techniques were employed to observe the microstructural morphology and perform elemental analysis of the composites. Findings revealed a dense HPC matrix with 1.5 % total fiber content, exhibiting uniform dispersion and ideal bonding. Digital image correlation (DIC) technique was utilized to analyze strain distribution and crack development of specimens in tension and bending, proving effective in tracking the strain and crack evolution. Statistical analysis of five influencing elements—cubic compressive strength, axial compressive strength, tensile energy dissipation, tensile fracture energy, and energy release rate—revealed Series F9 (S0.5P1) as optimal for comprehensive energy consumption performance. HyFHPC demonstrated enhanced strength, ductility, and toughness compared to HPC with mono fiber or none. The hybridization achieved positive synergy and improved reinforcing efficiency while conserving resources.

Study on the stressing state features of basalt fibre concrete lining structure under sulphate erosion

Basalt fibre (BF) is an environmentally friendly material with excellent corrosion resistance. When tunnels cross gypsum rock strata, the gypsum rock will dissolve sulphate and erode the supporting structure, thus affecting the safe operation of the tunnels in the long term. Adding BF to the supporting structure of gypsum rock tunnels can improve its resistance to sulphate erosion. This paper took Wuzhishan Tunnel as a case, and first determined the sulphate concentration of the gypsum rock stratigraphic environment at the site; then, analysed the change of mechanical properties of basalt fibre concrete (BFC) before and after sulphate erosion by mechanical tests; finally, examined the deformation and force characteristics of the BFC secondary lining structure by numerical simulation. The results showed that the bridging effect of BF fibres and the stable spatial network structure formed inside the concrete enhanced the mechanical properties of BFC and its ability to resist sulphate erosion. However, due to the agglomeration effect of BF fibres, too much BF would reduce the mechanical properties and erosion resistance of BFC. At a BF content of 6 kg/m³, BFC had the strongest ability to resist sulphate erosion, and the cube compressive strength, axial compressive strength, and modulus of elasticity of BFC were the highest, with 47.8 MPa, 33.6 MPa, and 38.7 GPa, respectively. The dense calcium silicate hydrate (C-S-H) gel, generated near the BF, enhanced the connection between the cementitious and the aggregate, inhibited the development of microcracks within the concrete, and reduced the erosion channels for sulphate ions. The maximum displacement of the BFC secondary lining structure was reduced by 20.15 % compared to plain concrete (PC) after sulphate erosion. The secondary lining structures consisting of both BFC and PC were stressed the most at footing. The secondary lining structure composed of BFC had better deformation resistance and higher strength than PC.

Experimental investigation of an electronegative cylindrical capacitively coupled geometrically asymmetric plasma discharge with an axisymmetric magnetic field

In this study, we have investigated the production of negative ions by mixing electronegative oxygen gas with electropositive argon gas in a geometrically asymmetric cylindrical capacitively coupled radio frequency plasma discharge. The plasma parameters such as density (electron, positive, and negative ion), negative ion fraction, and electron temperature are investigated for fixed gas pressure and increasing axial magnetic field strength. The axisymmetric magnetic field creates an E × B drift in the azimuthal direction, leading to the confinement of high-energy electrons at the radial edge of the chamber, resulting in decreased species density and negative ion fraction in the plasma bulk. However, the electron temperature increases with the magnetic field. It is concluded that low magnetic fields are better suited for negative ion production in such devices. Furthermore, in addition to the percentage ratio of the two gases, the applied axial magnetic field also plays a vital role in controlling negative ion fraction.

Experiments and design of laminated bamboo and concrete-filled steel tube columns under axial compression

To reduce the large amount of carbon emissions generated during concrete production and increase the application of green and sustainable building materials in the engineering field, laminated bamboo is used to replace the core section of concrete-filled steel tubes. The effects of cross-sectional forms and core section types on the failure modes and axial compressive properties of column structures are evaluated. The axial compressive behaviors of 16 bamboo columns, bamboo-steel tube (BST) columns, and concrete-filled steel tube (CFST) columns were compared from the perspectives of strength-to-weight ratio, stiffness, and absorbed energy. The experimental results show that the failure modes of laminated bamboo and concrete-filled steel tube (BCFST) columns are end buckling failure and diagonal shear failure. The axial compressive strength of the BST column increased by 94.49 % due to the restraining effect of the steel tube on the bamboo. The key finding is that the cross-sectional area of the core bamboo is a critical factor affecting the axial compressive strength. The BCFST columns with circular cross-sections show excellent ductility, with higher ductility factors of 111.50 % and 30.24 % than BST and CFST columns, respectively. In addition, laminated bamboo is found to be an excellent energy-absorbing material compared to other materials. Based on the confinement effect of BST columns, a prediction model for the axial compressive strength of BCFST columns is proposed, by which the predicted value shows a good agreement (overall error is less than 10 %) with the experimental results.

Effect of repeated steam sterilizations on insertional torque, torque to failure, and axial pullout strength of 3.5-mm and 2.0-mm cortical bone screws.

The objective of this study was to determine the effects of repeated steam sterilization cycles on the biomechanical properties of surgical screws. 42 3.5-mm and 42 2.0-mm self-tapping, cortical screws were divided into 3 groups per size and underwent autoclave sterilization for 1 (G1), 50 (G50), or 100 (G100) cycles and testing from August 2018 through June 2021. Sixty screws were then inserted into canine cadaver femurs, and biomechanical properties were measured, including peak insertional torque, torque to failure, and pullout strength, each normalized to cortical thickness. Scanning electron micrographs were taken from 24 screws, and images were blindly analyzed by 5 trained examiners. The mean normalized insertion torque for 3.5-mm screws was significantly different between G1 and both G50 and G100. The mean normalized torque to failure for 3.5-mm screws was significantly different between G1 and both G50 and G100. Axial pullout testing was found to be significantly different for 2.0-mm screws between G1 and G100. Scanning electron micrographs surface scoring identified a significant difference in 3.5-mm screws at the screw tip. The results indicate that biomechanical changes occur with repeated steam sterilizations. Specifically, peak insertional torque and torque to failure are decreased with increased sterilizations for 3.5-mm screws, whereas 2.0-mm screws were altered in pullout testing after 100 sterilizations. It is suspected that numerous sterilizations negatively alter the physical-mechanical properties of certain screw sizes. The biomechanical properties of the bone-implant interface could negatively be affected by multiple steam sterilizations during clinical setting.

Improving geopolymer concrete performance with hazardous solid waste phosphogypsum

Recycling the hazardous solid waste phosphogypsum (PG) in concrete is a popular trend. However, the inherent properties of PG used alone in concrete tend to limit the strength of the concrete. In this study, PG was used as a precursor for the production of phosphogypsum-based geopolymer concrete (PGC), which effectively improved the performance of geopolymer concrete by utilising the synergistic effect of different solid wastes in geopolymer concrete. The effects of PG content (0, 10, and 20 %) and alkali modulus (0.8, 0.95, 1.1, and 1.25) on the axial compressive properties and resistance to chloride penetration of PGC were investigated. The results show that 10 % PG improved the properties of geopolymer concrete the most, with a maximum increase in axial compressive strength of 17 %. Due to the addition of SO42−, the PG content also affected the optimal alkaline modulus of PGCs. Chemical composition and microstructural analyses revealed that the promotion of the geopolymer reaction by PG is crucial for PGC performance enhancement. In addition, leaching tests and carbon emission assessment, confirmed that PGCs are an environmentally friendly option. Based on the analysis of axial compression behaviour, resistance to chloride ion permeability and environmental impact, PGC with 10 % PG content and 1.1 alkali modulus is an environmentally friendly alternative to conventional concrete. This study shows that hazardous solid waste PG can improve the performance of geopolymer concrete and create a new type of solid waste concrete.

Reliability analysis of normal strength CFST rectangular columns through multiple approaches

Concrete-filled steel tube (CFST) rectangular columns have several benefits for structural engineering and buildings. The advantages of both steel and concrete are combined in these columns, creating a composite structural element with improved strength, ductility, aesthetics, seismic performance, construction efficiency, and cost efficiency. The current study aims to evaluate the mechanical performance of CFST rectangular specimens using an analytical approach that combines 3D-finite element analysis (3D-FEA) and artificial neural network (ANN) modeling. This methodology relies on a comprehensive database comprising 1045 sampling points from experimental studies. To simulate the response of CFST rectangular columns, an improved plasticity model for confined concrete was utilized in the 3D-FEA. This modeling considered various geometrical parameters and material features to accurately simulate the behavior of confined concrete and steel tubes. Comparison statistics were used to validate the 3D-FEA models against the experimental dataset of CFST specimens, confirming their accuracy. Furthermore, a parametric analysis was conducted using the 3D-FEA model to observe the potential impact of varying geometric and material-related variables on CFST specimen behavior. In addition to the 3D-FEA, a novel ANN model was developed to predict the axial strength of CFST specimens based on the experimental database. The comparison of R2 values among the empirical model, ANN model, and 3D-FEA model indicated that the ANN estimates were 18% more accurate than the empirical model and 9% more accurate than the 3D-FEA model. When considering the sampling points from the established database, both the empirical technique and the 3D-FEA model showed a strong association, with an R2 value of 0.842. However, the empirical and ANN-derived estimates exhibited an even higher correlation, with an R2 value of 0.916, while the predictions of the 3D-FEA and ANN models showed a slightly lower but still significant correlation, with an R2 value of 0.868.

Compressive behavior of concrete-filled FRP tubes with FRP solid waste as recycled aggregates: Experimental study and analytical modelling

The disposal and recycling of FRP (Fiber-Reinforced Polymer) solid waste pose significant challenges globally, with a recycling rate of less than 10 %. Current methods of handling FRP solid waste (FSW), including landfill disposal, incineration, chemical treatment, and thermal cracking, face limitations in achieving large-scale recycling and resource utilization. In civil engineering, FRP is widely employed for retrofitting structures and holds promise for new constructions. A new approach has emerged for recycling FSW by using it as aggregates in concrete, offering lower costs and reduced environmental impact. Research on using FSW aggregates in plain concrete shows that optimizing replacement ratios and aggregate shapes can enhance split tensile strength and toughness without significantly lowering compressive strength. To further improve the mechanical performance, this study investigated concrete-filled filament-wound FRP tubes with FSW aggregates (FSW-CFFTs) under axial compression. 35 specimens were tested to evaluate the influence of granular FSW aggregates (i.e., replacement ratio = 0 %, 20 %, 40 %, 60 %, and 80 %) and FRP thickness (i.e., 0 mm, 3 mm, and 5 mm) on their axial compression behavior. The experimental study revealed that: incorporation of FSW aggregates in unconfined concrete cylinders led to a notable decrease in Young's modulus and compressive strength, while concurrently increasing the peak compressive strain; as the replacement ratio of FSW aggregates increased, there was a tendency for the peak stress of FSW-CFFTs to decrease, while their ultimate axial strain tended to increase; compared FSW-CFFTs with unconfined concrete cylinders, the FRP confinement helped to mitigate the reduction ratio in axial compressive strength induced by the inclusion of FSW aggregates in the concrete, particularly at higher FSW aggregate replacement ratios; specimens with a thicker FRP tube exhibited higher secondary stiffness, along with higher strength and larger ultimate compressive strain. The modeling work indicated that accurately predicting axial stress-strain curves requires consideration of the bi-axial stress state of filament-wound FRP tubes.

Structural implementation of recycled lump prepared from waste concrete after elevated temperatures: Mechanical and environmental performances

To find a sustainable treatment for construction and demolition waste, the utilization of recycled lump (RL) prepared from waste concrete after elevated temperatures as coarse aggregate in concrete was investigated. The mechanical and environmental properties of recycled lump concrete (RLC) and reinforced recycled lump concrete (RRLC) were discussed with three RL replacement ratios and five treatment temperatures. The results show that increasing the RL replacement ratio would reduce the slump, and axial compressive performance of RLC, resulting from the presence of old adhered mortar on RL. The treatment of elevated temperature for RLC would improve the adverse effect of increasing the RL replacement ratio, resulting from the decreasing amount of old adhered mortar and interfacial transition zone on RL. The prediction formulas for the mechanical model of RLC were proposed while the design method for the axial compressive strength for RRLC was modified against the existing standard to conduct the full-range parametric analysis. The environment assessment indicates that the sustainable utilization of RL as coarse aggregate could reduce the environmental impact and global warming from concrete production whilst the RL prepared from waste concrete after 400 °C treatment is an appreciated option for the production of RLC and RRLC products from a mechanical and environmental perspective. In addition, the increase in external diameter would remarkably dwindle the environmental impact caused by the utilization of RL in structural members.

Study on Mechanical Properties of Moso Bamboo in Jian'ou City, Fujian Province, China

The original bamboo material of 3 to 4-year-old moso bamboo in Jian'o City, Fujian Province, was used as the research object. Study the change of mechanical properties such as axial compressive strength, bending strength, tensile strength, shear strength, and hardness test. The main work and results of this paper include:Forty-five longitudinal compression specimens on moso bamboo tubes were tested to investigate the effects of different sizes and bamboo knots on the axial compressive strength of the moso bamboo tubes. The mean tensile strength of moso bamboo was found to be 165.13 N/㎟. A total of 27 shear specimens of 5cm moso bamboo tubes were tested, and their average shear strength was 2.61Mpa; he average flexural strength of moso bamboo was 172.48N/㎟. The hardness of moso bamboo specimens was tested using the Janka hardness method. The hardness of each part of Moso bamboo was significantly different.Comparing the mechanical properties of moso bamboo with other wood timber, moso bamboo showed better mechanical properties, the research hoped to provide a theoretical basis and scientific evidence for a comprehensive understanding of the complex mechanical properties of Fujian moso bamboo and the use of moso bamboo in high value-added applications.

Use of Slag from Steelworks (BSSF and BOF) in the Manufacture of Concrete as a Possible Environmental Solution: Case Study with Tailings from the CSP of the Port of Pecém in Ceará

The increased demand for raw materials by the construction and processing industries, in particular steel produced from iron ore, has caused negative environmental impacts on the communities located around the steel industries. Therefore, this study validated the hypothesis that it is possible to use the waste produced and disposed of in steel mills (steel mill slag) in the construction industry. In this context, concrete manufacturing experiments were carried out by replacing the aggregate material (sand and cement) with steel mill slag (BSFF and BOF) and technical tests (particle size analysis, magnetic field testing, expansivity and axial strength) to prove the quality of the material produced. The results obtained show that the use of iron ore tailings produced at the Companhia Siderúrgica do Pecém (CSP) in the state of Ceará has potential to produce concrete that can be used in small and large constructions (low-income housing, asphalt sheets, buildings, and viaducts) and that this can help mitigate the negative effects of environmental pollution in the communities surrounding this region, helping to reduce environmental impacts.

Experimental investigation on seismic performance of CHS T-joints in salt spray environment

This paper aims to investigate the seismic performances of circular hollow section (CHS) T-joints with different regions of corrosion damage. A total of seven CHS T-joint specimens with various corrosion degrees were applied to conduct the quasi-static tests of brace axial cyclic loading, and the effects of corrosion damage on the hysteresis behavior and failure mode were discussed. Experimental results indicated the brace corrosion only had a slight influence on the seismic performance of CHS joints, while the corrosion difference on two sides of the brace might cause an additional bending moment and damage accumulation to accelerate the plastic collapse of the connection zone. Compared with the corrosion on the brace, the resistance of CHS joints was more susceptible to the corrosion located in the chord wall, resulting in the axial cyclic carrying capacity and stiffness of CHS joints significantly decreasing with the increase of chord corrosion level. However, the increasing corrosion on the chord would affect the final fracture behavior and fracture position, so the total energy dissipation and deformation of CHS joints presented a complicated and nonlinear degradation trend. In addition, corrosion damage simultaneously had an impact on reducing the bending capacity of the chord, and this phenomenon not only caused the differences between the degradation rates of axial tensile and compressive strength of CHS joints but also affected the failure mechanism and local deformation of CHS joints under the brace axial cyclic loading.

Enhancing Carbon Nanotube Yarns via Infiltration Filling with Polyacrylonitrile in Supercritical Carbon Dioxide.

Carbon nanotube (CNT) fibers are renowned for their exceptional axial tensile strength and modulus. However, in yarn form, they frequently encounter transverse loading in practical applications, which exposes their suboptimal mechanical attributes rooted in inadequate inter-tube interactions and yarn surface defects. Efforts to mitigate micro-slippage among CNTs have encompassed gap-filling methodologies with varied materials, yet the outcomes have fallen short of expectations. This work aimed to enhance the mechanical properties of CNT yarns via infiltration with polyacrylonitrile (PAN) under supercritical carbon dioxide (sc-CO2) conditions. PAN was strategically chosen for its capability to undergo pre-oxidation and subsequent carbonization, leading to robust graphitic reinforcement. Leveraging sc-CO2's swelling and high permeability properties, the infiltration process effectively plugged interstitial spaces, elevating the yarn's tensile strength to 277.50 MPa and Young's modulus to 5094.05 MPa. Additional enhancements were realized after pre-oxidation, conferring a dense, reinforced shell structure that augmented tensile strength by 96.93% and Young's modulus by 298.80%. Scanning electron microscopy (SEM) analyses revealed a homogeneous PAN distribution within the yarn matrix, corroborated by X-ray photoelectron spectroscopy (XPS) evidence of C-N bonding, indicative of a successfully interlaced network. Consequently, this investigation introduces a novel strategy to tackle micro-slippage in CNT yarns, thereby achieving substantial improvements in their mechanical resilience.

Compressive behavior of sustainable rubberized concrete‐filled steel tube columns having various recycled tire rubber aggregate contents and developing a predictive design model

AbstractAs a sustainable solution, employing recycled tire rubber aggregates in the production of concrete is of considerable interest. However, the applicability of rubberized concretes in construction is restricted due to their relatively low mechanical performance. Using rubberized concrete as a filling material in a steel tube provides a suitable solution for overcoming this issue and for using it effectively as a load‐bearing element. The objective of this study is to examine the impact of the material characteristics of the sustainable rubberized concrete‐filled steel tube (Ru‐CFST) and develop a design model based on ultimate strength prediction for the axially loaded Ru‐CFST stub columns with varying contents of tire rubber aggregate. The model was developed through the gene expression programming (GEP) technique by employing the experimental test results to determine the ultimate compressive strength of Ru‐CFST columns. Based on the principal component analysis, the sectional properties of the load‐bearing element (such as outer diameter, thickness, and length), material strengths (such as rubberized concrete and steel tube strengths), and rubber content were determined as statistically significant parameters affecting the ultimate axial strength of Ru‐CFST stub columns and thus, they were considered in the stage of the model generation. Furthermore, the proposed model's performance was compared to that of available models suggested for traditional CFST columns by commonly employed design codes, namely, ACI, AIJ, AISC, CSA, EC4, and GB. Based on the statistical analysis of the results, it can be concluded that the existing formulations have a relatively acceptable randomness and scatter of observations within the distribution, while the proposed design model gives a more accurate prediction for the ultimate bearing capacity of axially loaded Ru‐CFST columns with the highest R‐squared value of about 0.99 and the comparatively lowest mean absolute percent error of 7.54. It can be stated that the proposed GEP‐based design model will encourage engineers to use such sustainable structural members in their designs and constructions.