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This paper presents an experimental study on the behavior of low-strength concrete columns confined with cold-formed steel under axial compression. The laboratory test specimens consist of four groups of rectangular concrete stub columns in the size of 130 × 200 mm cross section and 300 mm height; the first group composes of the unconfined specimens, while the other three contain the confined specimens under 0%, 25% and 50% sustained axial loads. The jackets are made of two G450-grade channel cold-formed steel sections of 2.4 mm thickness welded together. No bonding material is used between the core concrete and the steel jacket. From the results, it is found that the cold-formed steel jacketing can increase the axial strengths of the unconfined concrete specimens by approximately 40-65%. The strength increase comes mainly from the confinement action, as only small axial deformation is detected in the jacket. Based on the given amount of prescribed preloads in this study, the presence of preload in the column does not have a significant effect on the increase in strength of the confined concrete columns. The measured strength enhancement ratio and the confinement ratio of the tested specimens are compared using five existing strength predictive equations. The performance of the unbonded cold-formed steel jacketing technique adopted in the stub columns is observed to closely conform with the predictive confinement model of the concrete-filled tubes. [ABSTRACT FROM AUTHOR]

Thin-walled composite cylindrical shells are nowadays widely used as primary structures in the aerospace industry. The so-called variable stiffness (VS) composite cylindrical shells with flexible stiffness tailoring characteristics have been made possible by existing AFP techniques. Considering the inherent imperfection sensitivity property of axially compressed thin-walled cylindrical shells, the buckling behaviors of the axially compressed VS composite cylindrical shells with initial geometric imperfections and delamination imperfections are investigated respectively in this paper. The design buckling loads of the axially compressed VS composite cylindrical shells are first determined by the probing method, which is verified by comparing with the existing test data and numerical simulation results. Additionally, a parametric study is conducted to investigate the effects of delamination imperfections on the buckling loads. The constraint delamination sizes of the VS composite cylindrical shells based on the design buckling load in this paper are given. Furthermore, the effects of continuously variable fiber angles on the buckling loads are investigated considering the imperfection sensitivity. The specific VS composite cylindrical shells with both high- buckling loads and low-imperfection sensitivity are obtained. Results indicate that the effects of imperfection sensitivity need to be carefully considered in buckling design of the axially compressed VS composite cylindrical shells. [ABSTRACT FROM AUTHOR]

OBJECTIVE: In pediatric patients, femoral neck fracture is a relatively rare injury with a high complication rate despite proper diagnosis and treatment. Fixation of femoral neck fractures is usually performed with screws placed along the neck axis. In this study, we aim to compare two different implants and methods in terms of biomechanics. MATERIALS AND METHODS: Twenty-eight right-left fresh femur bones of 6-month-old male Ovis aries lambs grown on the same farm were used. Bones were randomly divided into 4 groups (n=7). In group 1, the Delbet type III femoral neck fracture model was fixed with two 4.5 mm cannu-lated screws, one screw crossing the physis. In group 2, two 4.5 mm cannulated screws, which did not cross the physis, were used. In group 3, Delbet type III femoral neck fracture model was fixed with a 3.5 mm proximal femoral anatomical plate and five screws, one screw crossing the physis. Finally, in group 4, Delbet type III femoral neck fracture model was fixed with one 3.5 mm proximal femoral anatomical plate and five screws that did not exceed the physis. RESULTS: Biomechanical tests were performed using a Zwick/Roell AllroundLine 100 kN device. While axial failure burden (F = 6.819, p<.05, d = .46) and axial stiffness (F = 3.576, p<.05, d = .30) have been found to be significantly different between the independent treatment groups, axial failure displacement (F = .622, p>.05) and axial failure energy (F = .727, p>.05) have been found not to be significant between the independent groups. The effect sizes of the axial failure load and axial stiffness variables were 0.46 and 0.30, respectively, suggesting a moderate clinical effect. The highest axial failure load was recorded in group 3, while the smallest load was recorded in group 2. Similarly, the axial stiffness level in group 3 was statistically higher than the axial stiffness measurement recorded in group 2, p<.05. CONCLUSIONS: Consequently, we found that the biomechanical fixation success was the highest with a 3.5 mm proximal femoral anatomical plate, a 3.5 mm locking screw crossing the physis, and five 3.5 mm screws. [ABSTRACT FROM AUTHOR]

In this work, the deformation behavior of porous ceramics ZrO2–5.5 wt.% Y2O3 with different morphology of the pore space under axial quasi-static compression is studied by the digital image correlation (DIC) method. Two stages of the deformation behavior of the ceramics have been identified, namely, the controlled accumulation of microcracks and the formation of block structures. It has been found that an increase in the average pore size leads to a decrease in the tensile strength, a decrease in the effective elasticity modulus, and an increase in the ultimate deformation, while the nature of the deformation macrolocalization changes from ordered to chaotic one. It is shown that the rate of accumulation of local deformations in the central part of the deformable sample with a pore size of 68 μm is several times higher than in the sample with a pore size of 29 μm. [ABSTRACT FROM AUTHOR]

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Characterized with thin and hollow walls, bamboo has very few connective tissues in the transverse direction, and can be easily divided into thin bamboo strips. It is convenient to weave bamboo strips and wind them into loaded components since bamboo possesses good elasticity, flexibility and flexural ductility,. In this paper, the tensile properties of bamboo strips in parallel to the fiber directions were tested, and the relationship between their properties and the number of layers was analyzed. Circular tubes were manufactured using bamboo veneers by varying the winding angle (the angle between the longitudinal axis and the winding direction) to be tested under compression. Seven groups of tubular specimens were manufactured by varying the winding angle between 0 and 90 degrees with 4 identical specimens in each group. The load-displacement and stress-strain responses of each winding angle were investigated and the relationship between the key mechanical properties of tubular sections and the winding angle was analyzed. Obtained results indicate that with increase in the winding angle, the elastic modulus decreases and the ultimate displacement increases. The ultimate stress reached its maximum at a winding angle of 15°. [ABSTRACT FROM AUTHOR]

The research presented in this article consisted of analysis of the ship structural accidents at low temperatures and the effect of carbon percentage in various classifications of carbon steel, compared to the high tensile strength steel materials. The objective of this research was to fill the knowledge gap by expanding the understanding of the influence of low temperature, material, and structure on the axial compression test of tubes. The simulations as idealization of the compression test were conducted with variations in temperature, material carbon percentage, and geometry shape, using Finite Element Analysis (FEA). The results showed that at -100 °C, the material had the best ability to resist compression energy; high carbon steel had the highest strength at various carbon percentages, and the square geometry showed the best ability to absorb energy before failure. [ABSTRACT FROM AUTHOR]

Significant advancements have been made in the area of composite structures. Aligned with an innovative design, the motivation behind this research is, first, to make efficient use of timber as an environmentally friendly material and, second, to employ steel alongside timber effectively to prevent buckling of the steel. This research aims to bridge this knowledge gap by exploring the integration of steel, carbon fiber–reinforced polymer (CFRP), and timber. The objective is to create innovative composite column structures that leverage the unique properties of each material to enhance structural performance and efficiency. The authors conducted tests on a set of 24 columns under compression conditions. The results of the structural tests demonstrated significant compression capacities relative to their mass, highlighting the significant advantages of material synergy within these elements. The study thoroughly quantifies these benefits, shedding light on the potentially transformative impact of these innovative composite columns in the field of structural engineering. A significant finding was the influence of the timber section's geometry on preventing column buckling. Furthermore, the positioning of steel within the sandwich columns played a vital role, with steel elements having a greater area with timber exhibiting enhanced structural performance and reduced likelihood of debonding. This paper introduces a new parameter, the inelastic transition area denoted as INT±70% peak , which characterizes the smoothness or abruptness of the transition once the inelastic region begins and the graph descends. This parameter bears significance in risk analysis for structures susceptible to progressive failure. All specimens displaying substantial energy absorption featured larger timber sections, highlighting the pivotal role of timber in absorbing higher levels of energy during structural loading. The findings contribute to the growing body of knowledge on composite materials and their applications in modern construction. [ABSTRACT FROM AUTHOR]

BACKGROUND: Critical energy release rate is a global fracture parameter that could be measured during the failing process, and its value may change under different failure modes even in the same structure. OBJECTIVE: To propose an approach to predict the critical energy release rate in the femoral cortical bone structure under different failure modes. METHODS: Three-point bending and axial compression experiments and the corresponding fracture simulations were performed on the rat femoral cortical bone structures. Different critical energy release rates were repeatedly assigned to the models to perform fracture simulation, and the predicted loaddisplacement curves in each simulation were compared with the experimental data to back-calculate the critical energy release rate. The successful fit was that the differences in the fracture parameters between the predicted and experimental results were less than 5%. RESULTS AND CONCLUSION: (1) The results showed that the cortical bone structure occurred tensile open failure under three-point bending load, and the predicted critical energy release rate was 0.16 N/mm. (2) The same cortical bone structure occurred shear open failure under axial compression load, and the predicted critical energy release rate was 0.12 N/mm, which indicates that the critical energy release rate of the same cortical bone structure under different failure modes was different. (3) A comprehensive analysis from the perspectives of material mechanical properties and damage mechanism was conducted to reveal the reasons for the differences in the critical energy release rate in the cortical bone structure under different failure modes, which provided a theoretical basis for the measurement of the energy release rate and the accurate fracture simulation. [ABSTRACT FROM AUTHOR]

Hybrid fiber-reinforced polymer (FRP)–concrete–steel hybrid double-skin tubular columns (DSTCs) consist of an outer FRP tube, an inner steel tube, and a layer of concrete filled between the two tubes. Previous studies have demonstrated their structural performance compared with conventional concrete columns. However, their durability performance, particularly in aggressive environments, is not well understood. Therefore, this study aims to investigate the durability of hybrid DSTCs subjected to a wet–dry cyclic environment for up to 2 years. The time-dependent behaviors, including axial load–strain (axial and hoop) curves, ultimate load, and ultimate axial and hoop strains, are tested and discussed with regard to the aging time. The test results indicate that the ultimate load of hybrid DSTCs with a 6-mm glass fiber–reinforced polymer (GFRP) tube continuously increased by 15.1% after 2 years of exposure primarily owing to the increase in concrete strength. By contrast, the ultimate load of hybrid DSTCs with a 3-mm GFRP tube increased by 15.2% after 1 year of exposure and increased by 11.6% after 2 years of exposure. The results indicate that the reductions can be attributed to the degradation of the GFRP tubes, especially for a thinner GFRP tube. In addition, a design-oriented stress–strain model for concrete in DSTCs is verified against the test results. [ABSTRACT FROM AUTHOR]

The purpose of the research was to analyze the experimental-numerical influence of the type of cross-section on the stability of thin-walled composite columns with closed (rectangular) cross-sections. The subject of the investigation was thin-walled composite structures made of CFRP composite (carbon fiber reinforced polimer), characterized by a closed rectangular cross-section shape of the profile and a identical ply configuration. In this study, experimental and numerical investigations of axially compressed columns were performed to determine the values of buckling loads and buckling forms. Experimental investigations were performed using a universal testing machine with an optical deformation measurement system. In parallel with the experimental tests, numerical simulations were made using the FEM (Finite Element Method). The numerical studies conducted using dedicated numerical models and the experimental studies made it possible to carry out a thorough analysis of the impact of the cross-sectional shape on the buckling phenomenon of the structure. The novelty of the present paper is the use of interdisciplinary testing methods to compare the effect of cross-sectional geometry on the stability of thin-walled composite columns.

3D woven tubular composites (3D‐WTC), known for their lightweight and high‐strength characteristics, are widely used in various energy‐absorbing components. To enhance the energy absorption capacity of 3D‐WTC, this study conducted a mechanical analysis of bamboo tube structures and proposed concentric circular nested biomimetic structures with "single tube + double ribs" and "double tubes + double ribs." 3D woven tubular composites with bamboo‐structures (3DWTC‐Bamboo) were fabricated using the vacuum‐assisted resin transfer molding (VARTM) process. Axial compression tests were conducted using a universal testing machine to reveal and discuss the energy absorption capacity and failure modes of 3DWTC‐Bamboo. The results showed that 3DWTC‐Bamboo with a "double tube + double ribs" concentric circular nested biomimetic structures performed exceptionally, with a peak load of 28.93KN and specific energy absorption of 7.74 J·g−1. The failure mode was a hybrid of "rib folding + tube wall buckling." Finally, finite element analysis of the stress distribution during the compression of 3DWTC‐Bamboo was conducted using ABAQUS, which validated the experimental results. In summary, this work provides a reference for structural innovation in 3D‐WTC and further expands its application in the field of energy absorption. Highlights: Propose "single tube + double ribs" and "double tubes + double ribs" structures.Introducing the "rib" structures to enhance the local strength/stiffness.Test results show that 3DWTC‐Bamboo has great potential in energy absorption.The "ribs" can increase the local strength/stiffness of the tube structures. [ABSTRACT FROM AUTHOR]

To further expand the application range of cold-formed steel (CFS) members in practical engineering, a novel fold-fastened multi-cellular steel wall (FMSW) was introduced and investigated in detail. The FMSWs were mechanically connected by the hook-shaped and groove-shaped regions at both ends of the single limb members, by which the assembly efficiency was greatly improved. In this paper, a total of 10 slender FMSW specimens were subjected to axial compressive loadings, and the failure mode, load–vertical displacement curves, load–lateral displacement curves, and bearing capacity of the specimens were obtained. According to the experimental results, the development and failure modes of the local-global interactive buckling of FMSWs were revealed. All specimens experienced local buckling initially, followed by global buckling, and ultimately interactive buckling. The load–displacement curves exhibited similar trends, being characterized by three stages: the elastic stage, the elastic-plastic stage, and the descending stage. Furthermore, the nonlinear ascending segment was short, indicating that the failure was sudden. By comparing the bearing capacities among specimens, it was recognized that the ultimate resistance of FMSWs could be obtained by the superposition of the cells, and the bearing capacity was rarely affected by the height-to-thickness ratio. Based on the experimental results, refined finite element (FE) models were established and the accuracy and effectiveness of the modeling method were verified. Valuable reference could be provided by the research achievements of this paper for the subsequent research of CFS built-up members and their application in practical engineering. [ABSTRACT FROM AUTHOR]

The structural behavior of concrete columns reinforced with CFRP bars has been the focus of many researches over the past two decades. There is a dearth of comprehensive research concerning the axial compressive performance of retrofitted CFRP bars reinforced concrete (RC) columns. To fill this gap a thorough investigation was carried out to understand failure mode, load–displacement response, axial deflection, axial load-bearing strength, ductility index (DI), stiffness index (KI), and strength index (SI) of retrofitted CFRP bars RC columns. The experimental matrix comprised 14 short circular columns, seven reinforced with CFRP bars and hoops and the other seven with steel bars and hoops. Initial damage was induced through axial loading until a 35% reduction in peak axial strength was observed, after which damaged columns were repaired and retrofitted using CFRP sheets. The parameters of the study include concentric and eccentric compressions, transverse reinforcement spacing, CFRP wrapping, steel, and CFRP reinforcements. According to the findings, lowering transverse hoop spacing enhanced the utmost capacity and ductility of both types of retrofitted columns. The average peak strength and corresponding axial displacement of CFRP RC columns were 22.63% and 14.87%, and ductility (at a 20% load decrease) was 118% higher after CFRP retrofitting. The axial stiffness of damaged CFRP bars RC columns after strengthening with CFRP sheet were not fully rehabilitated and on average SI under concentric loading was 3.22% lower while DI under eccentric loading was 2.71% higher than steel RC columns. [ABSTRACT FROM AUTHOR]

Both bamboo scrimber and section steel are extensively employed in the construction industry however bamboo scrimber as a large composite member, easily experiences buckling and splitting under compression. To solve the problem of insufficient bearing capacity, a partially encased bamboo scrimber (PEBS) column was developed in this paper, and the PEBS column consisted of an H-shaped steel member with two rectangular bamboo scrimber members placed inside the web and flanges, forming a partial buckling restraint configuration. The aim of this arrangement was to enhance the axial compressive performance of the bamboo scrimber members through partial lateral confinement. To investigate the influences of the composite effect and specimen size, a total of 45 specimens were tested under axial compression to analyse the failure modes, load–displacement relationships, and mechanical properties. The results revealed that the composite specimens ultimately failed owing to buckling and wedged splitting in the bamboo scrimber members. The partial buckling restraint exhibited a substantial improvement in axial bearing capacity through delaying the buckling of the H-shaped steel and failure of the inner bamboo scrimber, leading to a further enhancement in the safety stock. Finally, a calculation method was proposed to predict the ultimate bearing capacity of the PEBS column. [ABSTRACT FROM AUTHOR]

With the increasing scarcity of natural gravel resources and increased production of construction and demolition waste, recycled aggregates offer prospects for concrete structures. However, the adhered loose and porous mortar and microcracks in recycled aggregates led to impaired mechanical behavior of recycled aggregate concrete (RAC) and reduced durability in harsh environments, significantly restricting its engineering application. Compression-casting can solve the problems of low strength and poor durability of RAC; however, it induces significant brittleness of concrete in compression. This study proposed an improvement in the ductility of compression-cast RAC through confinement using fiber-reinforced polymer (FRP) laminates. A total of 32 FRP-confined compression-cast cylinder specimens were tested under uniaxial compression, with variables including concrete mixture proportion, FRP thickness, and concrete casting method. The experimental results showed that the ultimate axial stresses of the unconfined RAC and FRP-confined RAC increased by up to 34.8% and 14.5%, respectively, and the ultimate axial strain decreased by up to 49.0% with compression-casting. Furthermore, the compression-casting method resulted in an 8.5% reduction in the measured average rupture strain of the FRP. The confinement efficiency was not significantly affected by compression-casting, as indicated by a slightly greater slope of the strength enhancement ratio with an increase in the confinement ratio for FRP-confined compression-cast RAC. Stress–strain models of FRP-confined compression-cast and normal RAC were proposed based on test data from this study and the literature. It was found that the proposed model improved the prediction accuracy of the stress–strain behavior compared with existing models. [ABSTRACT FROM AUTHOR]

Steel Circular Hollow Section (CHS) joints have been extensively utilized in construction. Current research mainly focuses on joints reinforced in unloaded states, reinforcement under load less commonly addressed. This study examines the mechanical behavior of CHS T-joints through an experimental analysis of six specimens, each featuring varying brace-to-chord diameter ratios (β), welded under different load factors. Identified primary failure modes of the joints are local buckling and out-of-plane inclination. Furthermore, a thermo-mechanical coupling finite element model, considering the material addition during the welding process, was developed to investigate the influence of the welding under load. The results indicate that welding under axial load has little effect on the ultimate loading capacity of the CHS T-joints. Notably, welding-induced residual deformation on the chord surpasses that on the brace, particularly when welding passes are proximal to the brace-chord intersection. Residual stress in welds is not significantly affected by the stress in the tubular; only the stiffeners near the welds are affected. Despite some joints exhibiting out-of-plane inclination, the enhancement in ultimate bearing capacity exceeds 24%. [ABSTRACT FROM AUTHOR]

The circular hollow steel-reinforced concrete (HSRC) column consists of an inner circular hollow steel tube and outer circular hollow reinforced concrete (RC). This design provides several advantages, including being lightweight, having a wide sectional profile, and having a high flexural stiffness. This paper aims to investigate the behavior of the circular HSRC columns under axial compression through testing and finite element (FE) modeling. An FE model was established to simulate the circular HSRC columns under axial compression, which was validated against the test data. Additionally, the load distribution and the interface stress between the outer hollow RC and inner steel tube were analyzed. Subsequently, a systematic parametric analysis was conducted on the diameter (d) and thickness (t) of the steel tube; slenderness ratio (λ); strength of concrete (fcu); yield strength of steel tube (fsy), longitudinal rebar (fly), and stirrup (fgy); as well as the stirrup spacing (s). The critical influencing factors of the circular HSRC columns under axial compression were identified. fcu, λ, d, fly, and fsy dramatically influence the bearing capacity, and the stiffness is notably affected by λ and fcu. Finally, three simplified design methods were summarized and evaluated for calculating the bearing capacity of the circular HSRC columns under axial compression. [ABSTRACT FROM AUTHOR]

Given their numerous functional and architectural benefits, such as improved bearing capacity and increased resistance to elastic instability modes, cold-formed steel (CFS) built-up sections have become increasingly developed and used in recent years, particularly in the construction industry. This paper presents an analytical and numerical study of assembled CFS two single channel-shaped columns with different slenderness and configurations (back-to-back, face-to-face, and box). These columns were joined by double-row rivets for the back-to-back and box configurations, whereas they were welded together for the face-to-face design. The built-up columns were filled with ordinary concrete of good strength. Finite element models were applied, using ABAQUS software, to assess mechanical performance and study the influence of assembly techniques on the behavior of cold-formed columns under axial compression. Analytical approaches based on Eurocode 3 and Eurocode 4 recommendations for un-filled and concrete-filled columns respectively were followed for the numerical analysis, and concrete confinement effects were also considered per American Concrete Institute (ACI) standards for face-to-face and box configurations. The obtained results indicated a good correlation between the numerical results and the proposed analytical methodology which did not exceed 8%. The failure modes showed that the columns failed due to instabilities such as local and global buckling. [ABSTRACT FROM AUTHOR]

Laser ablation damage has an important impact on the load-bearing capacity of the aircraft structure. This paper first uses ABAQUS ALE adaptive grid technology to establish and verify the numerical simulation analysis method of laser irradiation ablation of CFRP laminates. Then a finite element simulation analysis was conducted on the buckling process of the CFRP cylindrical shell under the combined loading conditions of laser irradiation and axial compression, and the critical buckling load and buckling mode of the cylindrical shell under different conditions were obtained. The effects of ablation damage and laser irradiation position on the critical buckling load are also discussed. When the laser irradiation position is between the end and the midpoint of the axis in the axial direction of the cylindrical, and is farthest from the axis in the radial direction, buckling failure is prone to occur. [ABSTRACT FROM AUTHOR]

Inspired by origami shape, two origami tubes are obtained through the arrangement of single-origami-cell structures (SOSs). Under quasi-static compression load, the specific energy absorption (SEA) value of same direction origami tube (SOT) is 13.46% higher than that of reverse origami tube (ROT). ROT shows the deformation mode of compression rotation, and SOT is layer by layer crushing. Various two-, three-, and four-layer origami structures are proposed through the combination of origami tubes and connecting plates, and their energy absorption efficiency is significantly higher than that of origami tubes. These origami structures exhibit stable deformation modes, mainly axial compression, torsion, and mixed deformation modes. The deformation mode of origami structures with four ROTs (4R) is similar to Fried Dough Twists. Regarding two-layer structures, origami structures consisting of reverse SOTs (RSOTs) and SOTs have significantly higher SEA values than those composed of ROTs and SOTs as well as ROTs and RSOTs. In addition, the compression performance of two-layer origami structures is significantly better than that of three- and four-layer origami structures. The SEA value of two-layer origami structure with two RSOTs and two SOTs (2RS2S) is higher than that of three-layer origami structure with four A cells (4A) and four-layer origami structure with one C cell and three D cells (1C3D) 68.05% and 64.48%, respectively. In summary, the origami structures show excellent mechanical properties and have broad application potential as energy absorbing structures. [ABSTRACT FROM AUTHOR]

This paper investigates the expansion of circular aluminium tubes using a rigid die under quasi-static loading conditions through experiments and finite element simulations. This study primarily focuses on the expansion of thin-walled tubes with a thickness ranging from 3.95 to 5 mm, and the finite element model is in good agreement with the experimental results. Additionally, the study emphasizes the impact of the coefficient of friction, energy dissipation properties and the diameter-to-thickness ratio on the energy expenditure associated with the expansion process of aluminium tubes using a rigid die. This study use Digital Image Correlation (DIC) technology to evaluate pictures obtained during experimental procedures, enabling accurate quantification of displacements, stresses, and rotations of major planes. The findings indicate that the energy absorption resulting from friction plays a significant role, with the coefficient of friction serving as a important parameter throughout the expansion process. The energy absorbed by the friction between tube-die contact surfaces was significantly higher than that absorbed by the plastic bending of the aluminium tube. For specimen AT-5.0-1, the energy absorbed by friction and bending is 3352 and 570 J, respectively. Result shows that a notable increase in the ultimate load, rising from 46.03 to 61.54 kN, is required for expanding the aluminium tube with a thickness of 3.95 to 5.0 mm. The local strain patterns seen on the surface of the tube offer useful insights, therefore enhancing researchers' ability to examine particular points on the specimen's surface without the need for fixed reference points prior to conducting experiments. [ABSTRACT FROM AUTHOR]

The purpose of the research was to analyze the experimental-numerical influence of the type of cross-section on the stability of thin-walled composite columns with closed (rectangular) cross-sections. The subject of the investigation was thin-walled composite structures made of CFRP composite (carbon fiber reinforced polymer), characterized by a closed rectangular cross-section shape of the profile and a identical ply configuration. In this study, experimental and numerical investigations of axially compressed columns were performed to determine the values of buckling loads and buckling forms. Experimental investigations were performed using a universal testing machine with an optical deformation measurement system. In parallel with the experimental tests, numerical simulations were made using the Finite Element Method (FEM). The numerical studies conducted using dedicated numerical models and the experimental studies made it possible to carry out a thorough analysis of the impact of the cross-sectional shape on the buckling phenomenon of the structure. The novelty of the present paper is the use of interdisciplinary testing methods to compare the effect of cross-sectional geometry on the stability of thin-walled composite columns. [ABSTRACT FROM AUTHOR]

The ductility of FRP-reinforced concrete structures is reduced by the brittleness of FRP bars. To address this issue, this study employs the hybrid reinforcement of stainless steel (SS) and GFRP bars to enhance the ductility of concrete columns. A total of 21 axially compressed seawater and sea sand concrete (SWSSC) circular columns are fabricated, including 15 hybrid GFRP and SS bar-reinforced SWSSC (GFRP-SS-SWSSC) columns, 3 GFRP bar-reinforced SWSSC (GFRP-SWSSC) columns, and 3 SS bar-reinforced SWSSC (SS-SWSSC) columns. The test results are analyzed in terms of failure mode, load–axial displacement curve, bearing capacity, and ductility. Results show that GFRP-SWSSC columns suffer brittle failure, while GFRP-SS-SWSSC columns and SS-SWSSC columns demonstrate ductile failure characteristics. Furthermore, the hybrid reinforcement contributes to an improvement in the bearing capacity of the columns. A calculation equation for the bearing capacity of axially compressed columns was established, providing reasonable predictions of bearing capacities, with a design compressive strain of 2000 με for GFRP bars. It was found that hybrid reinforcement enhanced the ductility of GFRP-SWSSC columns. In addition, when the percentage of the SS reinforcement ratio reaches 50%, the ductility indexes of the GFRP-SS-SWSSC columns closely approach those of the SS-SWSSC columns. [ABSTRACT FROM AUTHOR]

The aim of the current study was to determine the load capacity of composite columns subjected to axial compressive load. The subjects of the study were two types of columns with a rectangular cross-section, with different edge lengths. The tested columns had a closed cross-section. Four different fiber arrangements were analyzed for both cross-sections studied. The research was realized using interdisciplinary methods to determine the mechanism of damage to the composite material, with particular emphasis on damage initiation and propagation. Experimental tests were realized on a testing machine, the analysis was carried out with an acoustic emission system, and image analysis using visual assessment system of deflections of the walls of the structure. In addition, a number of numerical analyses were realized based on advanced modeling techniques for fiber-reinforced composites. A comparative analysis of both quantitative and qualitative results is presented for both analyses. The innovation of the presented research lies in the development of a custom method for modeling structures made of composite material with special emphasis on the failure phase. This will allow to accurately reflect the modeling of thin-walled structures with closed cross-section subjected to loading in a complex stress state. [ABSTRACT FROM AUTHOR]

An eco-friendly self-compacting geopolymer concrete made of ground granulated blast furnace slag was used as a confinement material in glass fibre-reinforced polymer columns to test its efficiency relating to load carrying capacity toward axial compression and cyclic lateral loads. Steel reinforcements were incorporated to improve the mechanical performance of the proposed composite specimens. Two significant parameters of the GFRP tubular columns viz., diameter to thickness (D/t ratio) and fibre winding angles were varied to examine their effects through experiments on mechanical, ductility, and rigidity characteristics. Two variations of D/t ratio viz., 30 and 50 and three different variations of fibre orientations viz., 0°, 30°, and 45° were considered for parametric analysis. Irrespective of the parameters considered, all the columns showed a two-segmented axial load-deformation pattern with a gradual increase in load carrying capacity post-yielding stage upon axial compression and closed hysteresis loop upon lateral cyclic loading. Stepping up the D/t ratio from 30 to 50 mm retarded the axial load carrying capacity up to 20% and 50% of that of the lateral load carrying capacity, as well as increasing the ductility of the composite columns. 0° fibre orientation showed significant efficiency of 6.67–46.78% relating to axial and lateral load carrying capacity compared to other orientations. The effect of the difference in 30° and 45° orientations was almost negligible, i.e., less than 10% concerning axial and lateral loading characteristics. [ABSTRACT FROM AUTHOR]

Waste tires pose an environmental issue that causes health problems when discarded by either land burial or burning. The current study investigated the properties and characteristics of different-length hybrid layered columns of Recycled Steel Fibers (RSF) at a fixed ratio (0.6%) of the volume fraction with utilized fixed content (15%) of Crumb Rubber (CR). Nine square column specimens were prepared and tested under axial compression load to reveal the effect of RSF and CR content on hybrid layered reinforcement columns. The results revealed that as the RSF content increased concrete's properties were enhanced. However, the inclusion of CR at the top layer resulted in performance reduction. Additionally, the layered structure with CR and RSF has higher characteristic properties, including higher load capacity and displacement. Moreover, adding 0.6% RSF to both layers and CR at the top led to a 120% increase in the toughness of the concrete loading capacity. This was followed by a reasonable improvement in displacement and ductility. [ABSTRACT FROM AUTHOR]

With the research and development of fiber composite winding tubes, this paper proposed an idea of using bamboo skin materials to prepare hollow tubes by hand lay-up process based on fiber winding tube technology, in order to solve the problem of existing bamboo hollow components in the field of civil engineering like radial bending, irregular section, bamboo joints and other problems. In view of the characteristics of brittle failure of bamboo winding tubes, this paper reinforced the outside of the bamboo winding tubes parallel to grain with bamboo skins perpendicular to grain, and studied the influence of different transversely reinforced layers on the overall bearing capacity of bamboo winding tubes. The test results showed that by adding transverse reinforcement to the outside of the bamboo winding tube, its bearing capacity can be effectively improved, making it an ideal column member. In addition, a prediction formula for the compressive strength of transversely reinforced bamboo winding tubes was proposed, and the calculation results of the formula are in good agreement with the test results. [ABSTRACT FROM AUTHOR]

Tubular structures are common in vehicles in the form of crash energy absorbers. Inevitably, these tubes contain holes for assembling fasteners and heating sources. Though the introduction of holes in the surface of the tube minimizes the initial peak crushing force (IPF), their structural stability also gets affected, which leads to a reduction in energy absorption capacity (EA). Therefore, the shape, dimension, and patterns of the holes in the tubular structure are to be scrutinized to minimize its unstable response during the crash event. This paper addresses the hole's position, shape, and dimensional effects on the performance characteristics of aluminum square tubes subjected to axial quasi-static compression experimentally. Numerical models were initially created using ABAQUS/CAE® code for simulating the quasi-static structural response of square tubes (without holes) and validated against experiments. Further, numerical analysis was explored to investigate the hole's position, shape, and dimensional effects on IPF and EA. The performance characteristics of all the examined specimens were quantified based on the best performance with the help of the TOPSIS method. Finally, Response Surface Methodology (RSM) was carried out to determine the best optimal square tube with holes. It was observed that, with an increase in the hole size, the IPF gets minimized. Among all the specimens, the diamond-shaped hole exhibits the best performance characteristics. The study also reveals that the EA varied greatly with the arrangement of holes (patterns). The research findings can provide ample guidance when designing crash tubes in the automotive protective system. [ABSTRACT FROM AUTHOR]

Purpose: The present study has described the axial deformation behaviour of mild steel and 7075 -T651 aluminium against 350 kg drop weight falling from different heights (0.67-4.78 m). Three different cross-sections of the circular (55, 70- and 85-mm diameter) and the square tubes (43.41, 55.19- and 66.97-mm edge length) have been considered to ascertain their effect on the axial compression, deformation mode and energy absorption. In addition, the experiments have been performed on a circular (82 mm diameter) mild steel tubes subjected to 350 kg drop weight impact falling from different heights (0.25-1.76 m). Methods: Numerical simulations have been carried out using ABAQUS/Explicit finite element code. The Johnson-Cook material model has been used to simulate the material behaviour of 7075 -T651 aluminium and mild steel tubes. Besides, numerical simulations have also been carried out for reproducing the experimental findings. Results: The predicted results of axial compression are found to have a deviation from the actual results in the range of 4-10%, showing the accuracy of the numerical approach. For both the metallic tubes, the axial compression of the circular and square tubes has been found to be decreased with an increase in the cross-sectional size of the tube, while the energy absorption has been found to be increased with an increase in the cross-sectional size of the tubes. For a given drop weight impact, the axial compression in square tubes has been found to be higher than the circular tubes of equivalent cross-sections. For both the metallic tubes, the energy absorption in the circular tube has been found to be higher than the square tubes of equivalent cross-sections. In addition, the axial compression in 7075-T651 aluminium tubes has been found to be higher than the mild steel tubes while the energy absorption in mild steel tubes have been found to be higher than the 7075-T651 aluminium tubes. Conclusions: Based on the findings, the mild steel tube has been found to be a better energy absorber than the 7075-T651 aluminium tubes and the circular tube describes higher crashworthiness than the square tube. Besides, the higher cross-sectional area tubes illustrate better energy absorption characteristics. [ABSTRACT FROM AUTHOR]

This paper aims to study the experimental and analytical behaviour of cold-formed steel (CFS) T-joint members with or without external ring stiffeners under combined axial compression and bending. The parameters varied in the study include the type of T-joints (with and without ring stiffeners), spacing of the stiffeners (100 mm and 200 mm from the central axis of the T-Joint), and thickness of the ring stiffeners (4 mm and 6 mm). The load–deflection and load-strain behaviour were studied by measuring the overall deflection of the T-joints and strain using dial gauges and strain indicators, respectively. The load-carrying capacity of the T-joints with external ring stiffeners was compared, and the results of a numerical investigation showed good agreement. An extensive parametric study was carried out for different geometric parameters of the ring stiffener, chord, and brace member using the FE model to obtain the ultimate strength of the stiffened T-joints, and strength was also compared and obtained using the published equation. From the results of this investigation, it was found that the T-joints with external ring stiffeners can resist more strength and deformation when compared to the T-joints without external ring stiffeners. [ABSTRACT FROM AUTHOR]

The spring system functions as a pivotal element of the check valve, with its compression performance significantly influencing the valve's time, flow stability, and other characteristics. Taking cues from conventional springs, a refined rectangular helical spring with integrated support features was thoroughly evaluated for its compression performance. The design approach for this spring was elucidated, encompassing the utilization of the Finite Element Method (FEM) to model its compression behavior. Additionally, a laboratory configuration was implemented to authenticate the findings derived from the FEM simulation. Subsequently, a comparative investigation was carried out between an engineered spring and a conventional spring subjected to analogous processing. The comparative analysis unveiled that the support-featured spring exhibited a diminished lateral offset of 2.84 mm (equivalent to a reduction of 10.1 %) and a force-displacement curve with narrower vibration intervals and smaller amplitudes. Moreover, it exhibited an enhanced force feedback of 17.5 % under identical compression displacement conditions.

The research presented in this article consisted of analysis of the ship structural accidents at low temperatures and the effect of carbon percentage in various classifications of carbon steel, compared to the high tensile strength steel materials. The objective of this research was to fill the knowledge gap by expanding the understanding of the influence of low temperature, material, and structure on the axial compression test of tubes. The simulations as idealization of the compression test were conducted with variations in temperature, material carbon percentage, and geometry shape, using Finite Element Analysis (FEA). The results showed that at -100 °C, the material had the best ability to resist compression energy; high carbon steel had the highest strength at various carbon percentages, and the square geometry showed the best ability to absorb energy before failure.

Self-compacting concrete has the advantages of high fluidity, high uniform density, and low porosity. To promote the engineering application of self-compacting concrete, this article studies the axial compression test of ten square steel tube self-compacting concrete columns. The effects of design parameters such as different grades of concrete strength and internal structures of circular steel tubes, square steel tubes, and H-shaped steel on the mechanical properties of self-compacting fly ash concrete filled square steel tube columns are studied. The failure mode, characteristic load and characteristic displacement, ductility, and energy dissipation capacity of each specimen are analyzed. On the basis of the test, the finite element analysis model of steel tube self-compacting concrete column is established, and the test results and simulation results are compared and analyzed. The results show that: the failure mode of the square steel tube specimen is the multilayer middle and upper ring buckling failure. Internal structural measures of square steel tube and H-shaped steel can improve the bearing capacity, ductility, and energy dissipation capacity of the specimen. It is not recommended to use the specimen with an outer square and an inner circle design. The results of the finite element simulation have a high degree of matching with the test results, which intuitively reflects the changes in force of each component.

The un-plasticized polyvinyl chloride (UPVC) is increasingly used in the construction industry because of its superior properties, particularly in greenhouses with UPVC as the skeleton. This study investigated the bearing capacities of UPVC pipes under axial compression. Eighteen UPVC pipe specimens with length-to-diameter ratios ranging from 24 to 45 were tested under axial compression. The failure modes and buckling resistances of the specimens were analysed. A finite element (FE) model was established to simulate the compressive behaviour of UPVC pipes, and the FE predictions were verified against the experimental results. Subsequently, extensive parametric studies were performed to analyse the effects of the diameter-to-thickness ratio, yield strength, and geometric imperfections on the overall stability of UPVC pipes under axial compression. The experimental and FE results were compared with the buckling curves obtained from the design codes for metallic material columns. Based on the test data and parametric analysis, a formulation of the buckling curves for UPVC pipes was proposed to predict the buckling performance of UPVC pipes better. These findings provide a basis for studying the mechanical performance of UPVC pipes subjected to axial compressive loading.

Concrete filled steel tube columns (CFSTCs) are commonly used in large-span bridges and high-rise buildings. As the shrinkage of concrete may lead to significant degradation in the mechanical performance of CFSTCs, expansive concrete or fibre reinforced concrete is usually employed to improve the mechanical performance of CFSTCs. This study presents an experimental study on the combined effects of expansive agents and steel fibres on the axial compressive behaviour of circular CFSTCs. 13 CFSTCs were designed and manufactured using concrete mixes with varying expansive agent rates and steel fibre contents. The time-dependent expansive behaviours of the specimens were monitored during the concrete curing period. Then, the 13 specimens were tested under axial compression load. The failure modes, compression load-axial strain relationship, hoop strain and axial strain relationship, and ductility were investigated. The results demonstrated that the combined addition of expansive agents and steel fibres would substantially improve the compressive strength and ductile behaviour of CFSTCs.

Hollow hybrid structural tubes were evaluated using commercial-grade Diamond Micro Expanded Mesh (DMEM) thin mesh of aluminum (Al) as structural reinforcement. Axial, transverse (flexural), and radial compression tests were performed on four different layered hybrid structures using bamboo (Bm) and basalt (B). With a maximum force of 34.7 kN, compressive ultimate strength of 238 MPa, and strain of 12.6%, AlBmB (with layers labeled from inside to outside) was the best performer in the axial compression test. AlBmB’s adaptability was demonstrated by the flexural test, showing a maximum bending force of 4.7 kN, a flexural strength of 97.7 MPa, and a decreased deflection of 13.2 mm. Radial compression test results underscored the superior energy absorption characteristics of AlBmB. The varying material interfaces in the hybrid tubes yielded distinctive performances. AlBmB, incorporating bamboo and basalt layers, stood out with superior energy absorption and crush force characteristics, indicating enhanced crashworthiness. The other hybrids AlBm, AlB, and BmB also exhibited commendable performances, emphasizing the adaptability of different material combinations. The meticulous selection of DMEM and innovative roll wrapping method for fabrication reliably influenced the tubes’ mechanical properties. The study contributes to advancing the design of lightweight, durable, and high-strength components.

Axial, flexure, and shear loads are the most common loads that could impact any structure. For instance, wall panels and columns majorly carry axial loads from the beam and slabs; they are also susceptible to flexure and shear loads from the wind or earthquake loads. Insulated concrete form (ICF) is a portable component of interconnected expanded polystyrene (EPS) panels filled with concrete. EPS remains in place and becomes part of the wall to enhance thermal resistance and structural performance. This paper focuses on an experiment that investigated the performance of ICF wall panels under axial compression and flexure. EPS with a higher density of 20 and 40 kg/m3 and a higher thickness of 50 and 100 mm was selected to prepare ICF wall panels for this experimental investigation. In addition, the plain concrete panel was cast for reference. Axial, flexure, and shear load-carrying capacity, load displacement, load–deflection profiles, crack propagation patterns, failure nature, and strain energy are analyzed and reported in this paper. It was observed that ICF panels were superior to plain concrete panels in terms of axial, flexure, and shear load-carrying capacity, failure nature, and absorbed strain energy.

Axial, flexure, and shear loads are the most common loads that could impact any structure. For instance, wall panels and columns majorly carry axial loads from the beam and slabs; they are also susceptible to flexure and shear loads from the wind or earthquake loads. Insulated concrete form (ICF) is a portable component of interconnected expanded polystyrene (EPS) panels filled with concrete. EPS remains in place and becomes part of the wall to enhance thermal resistance and structural performance. This paper focuses on an experiment that investigated the performance of ICF wall panels under axial compression and flexure. EPS with a higher density of 20 and 40 kg/m3 and a higher thickness of 50 and 100 mm was selected to prepare ICF wall panels for this experimental investigation. In addition, the plain concrete panel was cast for reference. Axial, flexure, and shear load-carrying capacity, load displacement, load–deflection profiles, crack propagation patterns, failure nature, and strain energy are analyzed and reported in this paper. It was observed that ICF panels were superior to plain concrete panels in terms of axial, flexure, and shear load-carrying capacity, failure nature, and absorbed strain energy. [ABSTRACT FROM AUTHOR]

These days, fiber-reinforced polymers (FRP) are being widely accepted in reinforced concrete structures because of their efficient structural performance and corrosion resistance. Efficient lateral confinement to the FRP-reinforced concrete compressive members is essential for their better performance due to the lower modulus of elasticity of basalt-FRP (BFRP) rebars. The combined usage of BFRP helices as transverse reinforcement in FRP-reinforced concrete members is not well examined in the body of literature currently in publication, especially in a variety of configurations. To better understand different transverse reinforcement configurations in FRP-reinforced concrete compressive members, this study is now underway. A combination of internal and external BFRP ties for dual restraints, an internal BFRP helix, external BFRP ties, and single BFRP ties are some of these designs. The investigation explores several aspects of the manufactured components, including the diameter of the longitudinal reinforcement, the type of material used for the transverse reinforcement, the vertical tie spacing, and various tie arrangements. In addition, a unique theoretical model that considers the contributions of both longitudinal and transverse BFRP rebars is put out to forecast the axial strength of the members that are created. When compared to the other two configurations, the results show that the application of BFRP combined helix-ties transverse reinforcement in FRP-reinforced concrete elements is the most effective in terms of core confinement and axial strength. Members with double BFRP ties and internal BFRP helix, as well as those with external BFRP ties, show enhanced axial strengths by 23% and 7%, respectively, in comparison to members with single BFRP ties. Secondary peaks in the load-deformation curves also show that members' ductility increases when the vertical distance between transverse reinforcement is reduced. The inclusion of FRP rebars in the study accounts for the notable higher accuracy of the proposed theoretical model as compared to earlier models, with only a 4% deviation from experimental results. [ABSTRACT FROM AUTHOR]

Concrete-filled steel tubular (CFST) columns are frequently used as the main load-bearing components in engineering structures due to their excellent load-bearing capacity. However, the presence of steel tube makes it impossible to accurately detect the damage characteristics of concrete by only relying on traditional mechanical measurement methods. This article quantitatively investigates the concrete damage of circular CFST column during axial compression based on the acoustic emission (AE) technique. Through the cumulative AE parameters including amplitude, count, and energy, the axial compression process of the CFST column can be divided into five main stages (Stage I is divided into two substages) to represent the different damage degree. The damage characteristics of concrete at each stage were explained by combining AE results and mechanical phenomena. A sensitivity analysis of the axial compression process was carried out using the Historic Index (HI) and Severity (Sr) and found that the sudden rise in HI and Sr corresponded to the changes in the different loading stages. The Improved b (Ib) value analysis calculated from the AE amplitudes reflects the evolution mechanism of the crack and can be used for the identification of the final failure moment of the specimen. Finally, a new method for processing and analyzing AE parameters was proposed, which effectively enhanced the dimensionality of real-time monitoring information on the damage of concrete filled in the steel tube. [ABSTRACT FROM AUTHOR]

An ordinary double steel plate–concrete composite wall (ODSC wall) is composed of core concrete, the faceplates, and shear connectors such as studs, etc. Based on an ODSC wall, a new type of stiffened double steel plate–concrete composite wall (SDSC wall) is conceived by incorporating additional stiffeners and tie plates on the internal surface, which aims to improve the local stability of the faceplates. In the authors' previous study, a series of axial compression tests were conducted on the SDSC walls. The SDSC walls in the test showed better mechanical performance, as the presence of stiffeners changed the buckling deformation mode and significantly improved the corresponding local buckling stress and ultimate strength. In this paper, a comprehensive summary of the prior research on SDSC walls is provided, and the effect of the constructive parameters on the local stability is discussed. The results reveal that the modified formula of the critical stress can degrade to the Euler formula when the stiffener-to-stud spacing ratio (i.e., a/B ratio) approaches infinity. What is more, the analysis model is also applicable for DSC walls with enclosed side plates, and the proposed formula can predict the buckling stress of the SDSC walls with different a/B ratios. In addition, according to the analysis of the numerical simulation, a design approach for SDSC walls to prevent local buckling is provided, which is applicable in practical engineering applications. [ABSTRACT FROM AUTHOR]

With the advancement in the concrete technology, the application of precast concrete elements in the buildings and road infrastructures is increasing very rapidly. One of such applications is the use of precast hollow concrete elements in the bridge construction. As the conventional steel reinforcement is highly susceptible to corrosion, the use of non‐corrosive reinforcement in precast hollow concrete piers and piles of bridges could be a good option for the durability of bridge structures., In this regard, hollow concrete columns reinforced with fiber‐reinforced polymer (FRP) have been considered as a potential solution to overcome the structural deterioration due to corrosion. In the past, limited studies have been carried out on hollow concrete columns reinforced with FRP, consequently, the behavior of such columns is not fully understood. Therefore, to comprehensively evaluate the behavior of hollow concrete columns for various design parameters, a finite element model (FEM) was developed in this study using the commercial tool "Abaqus". The model was developed and verified based on the experimental results of studies conducted by two independent research groups on circular concrete columns. The proposed model well predicted the peak loads with an error less than 10% and the failure modes of the tested columns. The verified constitutive relation and establishing method were further employed to conduct parametric evaluations to observe the influence of different parameters, such as inner‐to‐outer diameter ratio, longitudinal reinforcement ratio, lateral reinforcement ratio, and concrete strength, on the behavior of hollow concrete columns. Parametric analyses show that reduced inner‐to‐outer diameter ratio and larger longitudinal or lateral reinforcement may lead to higher peak load and confined concrete strength. Finally, based on the experimental and FEM evaluations, the strength prediction equations were developed for the analysis and design of hollow concrete columns reinforced with GFRP bars. [ABSTRACT FROM AUTHOR]

To investigate the confining effect and axial compressive behavior of rubberized concrete (RuC) confined by steel tube, axial compression tests were carried out on 12 circular RuC cylinders confined by steel tube. The cylinders considered parameters such as steel tube thicknesses (2 mm, 3 mm, 4 mm) and rubber volume replacement ratios of the fine aggregates (0%, 10%, 20%, and 30%). It was observed that the compressive strength of RuC decreases as the rubber volume replacement ratio increases. However, an increase in steel tube thickness enhances the confining effect of the core RuC, leading to an increase in its compressive strength and the corresponding strain, similar to that of conventional concrete. Moreover, post-peak curves are more likely to exhibit a strengthening part in confined concrete with more rubber content. Furthermore, a model was developed to determine the compressive strength of RuC confined by steel tube. Finally, an axial stress-strain model of steel tube confined RuC was proposed, which was validated against test results. [ABSTRACT FROM AUTHOR]