Cross-sectional Aspect Ratio Research Articles

Strength of Cold-Formed Stainless-Steel Corrugated Rectangular Sections under Compression

Provision of intermediate stiffening is an effective method to improve the strength of cold-formed steel compression members without having to increase the outer dimensions of the section. As cold-formed sections can be easily produced in various cross-section profiles, the effect of intermediate stiffening on ultimate load carrying capacity and behavior of structural elements need to be determined. In this study columns with Cold-Formed Stainless-Steel and Corrugated Rectangular Hollow Sections are studied numerically using Finite Element analysis. The column simulation is conducted using ABAQUS software including material nonlinearity and performed with the Static Riks procedure. The objective is to study how providing stiffening in the form of corrugations influences the buckling behavior of these columns. Columns for a range of slenderness ratio with varying cross-section parameters were modelled and compared to identify the influencing parameters. The study showed that buckling strength of columns can be significantly increased by providing corrugations. Corrugations effectively resisted local buckling in columns even with low slenderness ratio. The parameters influencing the buckling behavior are identified as cross-section aspect ratio, corrugation height, corrugation width and minimum radius of gyration of the cross-section. Buckling curves are placed for the corrugated sections based on the numerical analysis, and in relation to the buckling curves provided in design standards. On comparing them with the predictions by Euro Code (EN 1993-1-4 (2006)), it was observed that Euro Code predictions are conservative, which is also seen from the buckling curves shown for the corrugated sections.

Axial compression behaviour of round-ended recycled aggregate concrete-filled steel tube stub columns (RE-RACFST): Experiment, numerical modeling and design

Round-ended recycled aggregate concrete-filled steel tube (RE-RACFST) column is an innovative composite member, which holds the advantage of round-ended concrete-filled steel tube (RE-CFST) and expands the application of RAC in structural members. This paper presents the testing and numerical investigation on the axial compression behaviour of RE-RACFSTs. A total of 18 stub columns were tested to determine the failure mode, axial load versus strain response, vertical and circumferential strains of the round-ended steel tube, and the confinement effect from external steel tube in different positions. The effects of cross-sectional aspect ratio, coarse recycled aggregate (CRA) replacement and steel ratio were analyzed. In general, the ductile behaviour of the specimens reduced with increasing aspect ratio and decreasing steel ratio. The confinement effect during the entire compression process was investigated based on the vertical and circumferential strains. Finite element (FE) models were then developed, and a constitutive model suitable for core RAC in RE-RACFST columns was proposed. Parametric analysis was then carried out to evaluate the effects of the aspect ratio, steel ratio, CRA replacement level, and material strength on the axial compression response. Finally, several existing design provisions for rectangular CFST and RAC-FST members were assessed the feasibility of their application in RE-RACFSTs by using the equivalent method.

Thermal Behavior in the Inclined Space Connected to Fire Room

In this study, a model experiment was conducted to understand the effects of the parameters of the inclined space (cross-sectional aspect ratio and angle of incline) connected to the fire room on the hot gas flow in it. The trend of dimensionless temperature (<i>T*</i>) decrease in the vertical direction of hot gas flow in the inclined space was found to not be related to the width of inclined space in the range of <i>T*</i> > 0.3. Additionally, the trend of temperature decrease in the direction of hot gas flow in the inclined space was found to not be related to the width of the inclined space. Furthermore, a certain temperature decrease trend was observed under each tilt angle.

Aluminium alloy channel columns: Testing, numerical modelling and design

Aluminium alloys can be employed in a wide range of structural applications offering high strength-to-weight ratio, whilst they can easily be extruded in various shapes. Channel (C-) sections have been increasingly employed as compression members, such as wall studs and chord members of roof trusses in framed residential and commercial buildings. However, relevant studies on their compressive behaviour are quite limited and thus a greater emphasis should be placed on providing a deeper understanding. Towards this direction, this paper examines the structural performance of C-sections under axial compression. An experimental and numerical investigation was performed on 6082-T6 heat-treated aluminium alloy C-section columns. In total, 6 fix-ended stub column tests were executed to examine the cross-sectional compressive behaviour, whilst 8 pin-ended column tests were conducted to study their minor-axis flexural buckling behaviour. The obtained experimental results were utilised to validate the developed finite element models. Subsequently, extensive parametric studies were carried out to generate additional performance data over a broad range of cross-sectional aspect ratios, and cross-sectional and member slendernesses. Both the experimentally and numerically obtained ultimate strengths are utilised to assess the accuracy of Eurocode 9 design provisions, including the flexural buckling curve. On the basis of the experimental and numerical results, a new flexural buckling curve is proposed improving the design accuracy. The applicability of the Direct Strength Method on the design of aluminium alloy C-sections subjected to axial compression is also evaluated resulting in the most accurate and consistent design strength predictions.

Two- and three-dimensional simulations of flow and heat transfer around rectangular cylinders

This numerical study investigates the forced convection heat transfer from and flow topology around isothermal rectangular cylinders. The effects of various cross-sectional aspect ratios (AR = 0.25–4), Reynolds numbers (Re = 30–200), and Prandtl numbers (Pr = 0.7, 5) are examined on the results. Two or three-dimensional simulations are conducted depending on the Re and AR employed. The results show that the near primary vortices (Kármán wake) undergo a downstream transition to the two-layered vortices, followed by a transition from the two-layered vortices to the secondary vortices for AR ≤ 1. For smaller aspect ratios, the prevailing of the secondary vortices is further accelerated, i.e., they emerge at a lower Re and a shorter downstream distance from the cylinder. Three types of secondary vortices distinguished based on their shape, strength, and generation mechanism were observed. A geometric criterion (spacing ratio) for the onset of evolution of the two-layer structure is proposed for each AR. It is observed that the sensitiveness of the Nusselt number to AR and Re can be ascribed to the change in the scenarios of the flow separation and reattachment (flow regimes), vortex strength, and wake-recirculation size (Lr). The Nusselt number grows with increasing Re and Pr but diminishes with AR. The relationship between the average Nusselt number and Lr is direct in the steady flow, while they are inversely linked in the two- and three-dimensional unsteady flow. Reducing AR from 4 to 0.25, depending on Re and Pr, leads to a 90%–170% enhancement in the Nusselt number, whereas increasing AR amplifies the total heat transfer due to an enlargement in the heat transfer surfaces. The second law of thermodynamics analysis reveals that cylinders with smaller AR generate lower entropy (destroy lower exergy); therefore, they are more efficient.

A multi-institutional study of association of sonographic characteristics with cervical lymph node metastasis in unifocal papillary thyroid carcinoma.

ObjectivePapillary thyroid carcinoma (PTC) is the most common pathological type of thyroid carcinoma, and is prone to cervical lymph node metastases (CLNM). We aim to evaluate the association between sonographic characteristics of PTC and CLNM before the initial surgery.MethodsClinical information as well as ultrasonographic measurements and characteristics for 2376 patients from three hospitals were acquired in this retrospective cohort study. Univariate and multivariate logistic analysis were performed to predict CLNM in unifocal PTC patients. Receiver operating characteristic (ROC) curve was created to evaluate diagnostic performance.ResultsUnivariate analysis showed that gender, age, maximum tumor diameter and volume, cross-sectional and longitudinal aspect ratio, location, echogenicity, margin, and echogenic foci were independently associated with CLNM metastatic status (P < 0.05). Multivariate logistic analysis showed that gender, age, maximum tumor diameter and volume, cross-sectional aspect ratio (CSAR), location, echogenicity, margin, and echogenic foci were independent correlative factors; CSAR showed a significant difference for PTC2 to predict CLNM. The area under the curve (AUC) of the maximum tumor diameter, tumor volume, margin, and echogenic foci was 0.70, 0.69, 0.65, and 0.70, respectively. The multiple-variable linear regression model was constructed with an AUC of 0.77, a specificity of 73.4%, and a sensitivity of 72.3%. Kruskal-Wallis analysis for positive subgroups, maximum tumor diameter and volume, cross-sectional and longitudinal aspect ratio, margin, and echogenic foci showed statistical significance (P < 0.05).ConclusionsYounger age (< 55 years), male, larger tumor, and echogenic foci were high risk factors for CLNM in patients with unifocal PTC. CSAR had a more effective predictive value for CLNM in patients with larger thyroid tumors. A larger tumor with irregular and punctate echogenic foci was also more prone to the lateral neck, and both central and lateral neck metastasis.

Actuation performance of machined helical springs from NiTi shape memory alloy

Machined helical springs were designed and fabricated from NiTi shape memory alloy tube stock by cutting helical slots to make the coils, which provided them with high design flexibility and actuation potential. The springs were then subjected to isothermal tensile testing at temperatures of 20°C and 80°C, the experimental data showed that they could generate more than 50% actuation stroke at the applied force of 300 N. A material model was introduced to describe the thermally-induced actuation behavior of the machined NiTi spring. Finite element simulation of the springs was carried out to investigate the effects of geometries and applied loads on the actuation performance. With increasing applied load, the actuation stroke and transformation temperature increased as well, indicating more actuation potential at high loads. The actuation stroke was positively correlated to the outer diameter and the cross-sectional aspect ratio, negatively correlated to the cross-sectional area, and independent of the coil pitch. A variable-sweep wing actuated by two antagonistic machined springs was designed and numerically analyzed, the actuator could generate a steady cyclic motion up to 40 mm and allowed the swept-back angle of the wings to be continuously varied from zero to 90 degrees.

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

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

A stochastic study of the deformation and failure strain of Au bi-crystalline nanowires with a longitudinal twin boundary

Molecular dynamics (MD) simulations have been performed to understand the deformation mechanisms and ductility (failure strain) dependence on nanowire cross-sectional size for Au bi-crystalline nanowires with a longitudinal twin boundary (LTB). Different cross-sectional aspect ratios and volume ratios of grain sizes have been constructed in the MD simulations and tensile loaded. The simulation results indicate that all nanowires exhibit a similar elastic regime till peak yield stress and yielding occurs through nucleation of 1/6<112> Shockley partial dislocations from nanowire edges. Once interacting with the LTB, there are different paths of plasticity, mainly leading to two types of mechanisms: detwinning of the LTB with reorientation of the crystal and dislocation slip. For a given shape of nanowire, we found that the competition between these two operating mechanisms is stochastic and results in a distribution of detwinned volume fractions and strain to failures. Based on the simulation results we found that the average extent of detwinning is in correlation with the volume ratio of the grains. Also, it is in a linear correlation with the average strain to failure, which suggests that the LTB affects the ductility of the nanowire. We concluded from the results that the more symmetric are the grains that composes the nanowires, the smaller is the ductility.

Exfoliation of hexagonal boron nitride nanosheets assisted with covalent organic frameworks by ball-milling

Boron nitride nanosheets have superior chemical and physical properties. However, there are many problems in the preparation of hexagonal boron nitride nanosheets, and an effective exfoliation method is still lacking. To solve this problem, this paper intends to obtain boron nitride nanosheets by ball milling using TpPa from COFs material as a ball milling aid, and to investigate various factors affecting the ball milling effect. The h-BN obtained by using some other polymer materials such as starch and pvp as ball milling aids were compared with the h-BN peeled by using COFs materials as ball milling aids, and the results showed that the peeling effect of using TpPa as ball milling aids was not satisfactory because the structure of COFs materials was too stable. This paper also further conducted ball milling experiments on a variety of dry auxiliaries and compared them according to the ball milling effect The strength, friction, softening point and hardness were analyzed by machine learning. The analysis revealed that these aspects affect the cross-sectional area, thickness and aspect ratio of h-BN nanosheets. To obtain good h-BN nanosheets, the main conclusions of this paper are as follows: For the cross-sectional area of h-BNNS: the bond strength, friction, hardness and softening point of the ball milling agents have a strong influence on it and are positively correlated with it, while the friction and softening point of the ball milling agents are negatively correlated with it. For the thickness of h-BNNS: the bond strength and decomposition point of ball abrasives have influence on it, but not much, while hardness, softening point and contact angle have more influence on it, and hardness and contact angle are positively correlated with it, and softening point is negatively correlated with it. For the aspect ratio of h-BNNS: the hardness, softening point and contact angle of the ball abrasive have a greater effect on it, while the softening point has the greatest effect on it with a positive trend and the hardness and contact angle with a negative trend.

Analytical study and design approach of the axial and flexural response of reinforced masonry columns confined with FRP jackets

Using fiber-reinforced polymer (FRP) wraps has proven to be an effective and optimized confinement technique to upgrade the axial and flexural capacity of reinforced concrete (RC) and reinforced masonry (RM) columns. The axial capacity of FRP-confined masonry depends on both the compressive strength of masonry before strengthening and the confinement pressure provided by the FRP jacket. This study proposes a simplified methodology to design and analyze prismatic fully grouted reinforced masonry columns (RMCs) strengthened with FRP Jackets. The proposed design methodology included an analytical confinement model to predict the compressive strength gain in RMCs due to the effective confinement pressure provided by FRP jackets. The proposed procedure was also designed to predict the nominal capacity of RMCs for practical design applications, with columns subjected to both axial loading and bending moment. The essential parameters to perform detailed section analysis were established, and suggested expressions were proposed to obtain the parameter values. Practical values for the equivalent rectangular stress block parameters were proposed. The theoretical axial force-moment interaction diagrams obtained by the proposed procedure were compared with available experimental data. The experimental test results were in good agreement with the analytical predictions by a reasonable marginal error. Furthermore, the effect of five design variables on the axial-flexural interaction of FRP-wrapped RMCs was investigated. The variables considered in the parametric study were the number of FRP layers, radius of the corners, stiffness of the FRP composite, cross-sectional aspect ratio, and masonry compressive strength. The results showed that increasing the FRP layers, corner radius, and FRP jacket stiffness significantly enhanced the axial capacity of the FRP-confined RMCs. However, the increase in the masonry compressive strength and cross-sectional aspect ratio negatively affected the axial capacity gain ratio of FRP-strengthened RMCs.

Cold-formed ferritic stainless steel closed-section built-up beams: Tests and flexural response

This article presents the first experimental study reported on the flexural behaviour of cold-formed ferritic stainless steel (CFFSS) closed-section built-up beams. Each closed-section built-up beam has been formed by connecting two lipped channels in the face-to-face arrangement and spot welded at intermediate locations along the beam span. Sixteen specimens have been fabricated and tested till failure under three-point bending and four-point bending. Cross-sectional aspect ratio, plate slenderness of the compression flange and moment gradient were the critical parameters varied for investigating their influence through tests. The CFFSS chemical, material properties, geometric imperfections, ultimate moment capacity, failure modes and deflection responses were recorded for bringing out meaningful interpretation of the test results. The ultimate moment values obtained from the tests have been compared with the nominal design moment capacity predicted by the current Australian Standard (AS/NZS), American Specification (SEI/ASCE-8-02), European Code (EN 1993-1-4) and Direct Strength Method (DSM) in North American Specification (AISI-S100:2016) and Continuous Strength Method (CSM). The test results of the current study compensated for the important reliable data on the flexural behaviour of CFFSS closed-section built-up beams, missing from the literature.

Experimental and theoretical studies on neck thinning dynamics of droplets in cross junction microchannels

Necking processes of the droplet generation in the cross junction microchannels are experimentally and theoretically investigated, in which deionized water and hexadecane with the surfactant span 80 are used as the dispersed and continuous phases, respectively. Dynamic mechanisms of the neck thinning in two different regimes are revealed in three different microchannels with width ratios of 1, 1/2, and 1/3. Characteristics of the internal flow field are discussed and force estimations are carried out using the velocity information by Micro-PIV to compare the varied roles of the shear force between the two regimes. According to evolutions of the minimum neck width and the thinning rate, the necking process is further divided into different stages and the governing driving force during each stage is confirmed. Effects of the flow rates and the cross-sectional aspect ratio on the necking process as well as the neck profile at different stages are provided in detail. The distinct features of the two regimes in the squeezing stage are well captured by the theoretical estimations of the effective flow rate and the variations of the actual flow rates in different channels are reasonably reflected by the channel width ratio. In the collapsing stage, the quantitative relation between the minimum neck width and the remaining time is constructed to identify the physical mechanism and the self-similar profile is compared to cases in the open environment to reveal the influence of the confinement in microchannels.

Seismic behavior of concrete-filled wide rectangular steel tubular (CFWRST) stub columns

The concrete-filled wide rectangular steel tube (CFWRST) columns, with the aspect ratio of cross-section greater than 2.0, have attracted much attention in practice. Existing studies on the concrete-filled rectangular steel tube (CFRST) members have shown that the aspect ratio of cross-section is a main parameter controlling their behaviors under various loads, which means that the behaviors of CFWRST columns may be different from the common CFST members (the aspect ratio of cross-section not greater than 2.0) considered in existing studies. The behaviors of CFWRST columns under the combined constant axial compression and cyclic lateral loadings were investigated in this paper. Six full-scale columns were tested, with which the failure modes, hysteresis curve, skeleton curve, ductility, lateral stiffness and energy dissipation capacity of the specimens were analyzed and discussed in detail. For all tested specimens, the ductility indexes are between 2.028 and 3.433, and the equivalent damping ratios usually exceed 0.3 at the last of loading cycle. The finite element model was also developed and validated using the test results, and the parametric analyses were carried out with the influences of main parameters discussed. Furthermore, comparisons between the predictions of the solution of EC4 for CFST beam-columns and test results show that the solution of EC4 can provide safe predictions for the CFWRST columns under constant axial compression and cyclic lateral loading.

Influence of cross-sectional aspect ratio on biochar segregation in a bubbling fluidized bed

In this study, computational particle fluid dynamics was applied to investigate the segregation characteristics of biochar in a bubbling fluidized bed. The aspect ratio of the bubbling fluidized bed was changed and the effects of the aspect ratio on the segregation characteristics were investigated. The segregation characteristics of a mixture of biochar and sand particles were analyzed in terms of bubble size distribution, pressure fluctuations, and mixing index. As the aspect ratio increased, the bubble size decreased, leading to a clearer segregation of biochar and sand particles. The mixing index of the biochar and sand particles decreased as the aspect ratio increased.

Effects of cross-sectional area and aspect ratio coupled with orientation on mechanical properties and deformation behavior of Cu nanowires

Metal nanomaterials exhibit excellent mechanical properties compared with corresponding bulk materials and have potential applications in various areas. Despite a number of studies of the size effect on Cu nanowires mechanical properties with square cross-sectional, investigations of them in rectangular cross-sectional with various sizes at constant volume are rare, and lack of multifactor coupling effect on mechanical properties and quantitative investigation. In this work, the dependence of mechanical properties and deformation mechanisms of Cu nanowires/nanoplates under tension on cross-sessional area, aspect ratio of cross-sectional coupled with orientation were investigated using molecular dynamics simulations and the semi-empirical expressions related to mechanical properties were proposed. The simulation results show that the Young’s modulus and the yield stress sharply increase with the aspect ratio except for the 〈110〉{110}{001} Cu nanowires/nanoplates at the same cross-sectional area. And the Young’s modulus increases while the yield stress decreases with the cross-sectional area of Cu nanowires. However, both of them increase with the cross-sectional area of Cu nanoplates. Besides, the Young’s modulus increases with the cross-sectional area at all the orientations. The yield stress shows a mildly downward trend except for the 〈111〉 Cu nanowires with increased cross-sectional area. For the Cu nanowires with a small cross-sectional area, the surface force increases with the aspect ratio. In contrast, it decreases with the aspect ratio increase at a large cross-sectional area. At the cross-sectional area of 13.068 nm2, the surface force decreases with the aspect ratio of the 〈110〉 Cu nanowires while it increases at other orientations. The surface force is a linearly decreasing function of the cross-sectional area at different orientations. Quantitative studies show that Young’s modulus and yield stress to the aspect ratio of the Cu nanowires satisfy exponent relationship. In addition, the main deformation mechanism of Cu nanowires is the nucleation and propagation of partial dislocations while it is the twinning-dominated reorientation for Cu nanoplates.

Cross-Section Stability and Design of Normal Strength and High Strength Steel I-Sections in Fire

The structural response and design of normal strength and high strength steel I-sections at elevated temperatures are investigated in this paper. The shell finite element models of steel I-section elements capable of replicating their behavior in fire are developed and validated against experimental results from the literature. The validated shell finite element models are then utilized to generate extensive structural performance data for steel I-sections, considering a broad range of plate slenderness values for cross-section elements, elevated temperature levels, cross-section aspect ratios as well as different loading conditions and normal strength and high strength steel grades. The accuracy of the existing methods provided in the European structural steel fire design standard EN 1993-1-2 and its upcoming version prEN 1993-1-2 for the ultimate strength predictions of normal strength and high strength steel cross-sections in fire is assessed. Scope for improvement is observed. Considering this, a new method for the ultimate strength predictions of normal strength and high strength steel sections at elevated temperatures is put forward. It is shown that the proposed method leads to more accurate ultimate strength predictions for normal strength and high strength steel I-sections in fire with a higher level of reliability relative to the existing design methods provided in EN 1993-1-2 and prEN 1993-1-2.

Correlation Analysis of Nodular Sonographic Parameters with Cervical Lymph Node Metastases in Papillary Thyroid Carcinoma.

Background Papillary thyroid carcinoma (PTC) is the most common thyroid carcinoma and is prone to cervical lymph node metastases (CLNM). We aim to analyze the correlation between clinical information, ultrasonic parameters of PTC, and CLNM. Methods 1335 patients who had pathologically confirmed unifocal PTC were enrolled in this retrospective cohort study. Univariate and multivariate logistic analyses were performed to predict CLNM in PTC patients. The receiver operating characteristic (ROC) curve was used to evaluate the diagnostic performance. Results Univariate analysis showed that gender, age, maximum tumor diameter and volume, and cross-sectional and longitudinal aspect ratio were related to CLNM (P < 0.05). Multivariate logistic analysis showed that gender, age, maximum tumor diameter, and volume were independent correlative factors, and the cross-sectional aspect ratio had significant difference for PTC2 to predict CLNM. The area under the curve (AUC) of the maximum tumor diameter and volume was 0.738 and 0.733, respectively. Maximum tumor diameter and volume and the cross-sectional and longitudinal aspect ratio were statistically significant following analysis of variance (P < 0.05). Conclusions Younger age, male, and larger tumor were high risk factors for CLNM in patients with unifocal PTC. The cross-sectional aspect ratio had a more effective predictive value for CLNM in patients with larger thyroid tumors.

New strength–strain model and stress–strain relationship for square and rectangular concrete columns confined with CFRP wraps

The aim of this paper is to develop new models for the prediction of the ultimate strength, the ultimate strain, as well as the axial stress–strain relationship of square and rectangular concrete columns confined with carbon fiber reinforced polymer (CFRP) wraps. An experimental database covering 360 specimens with an unconfined compressive strength ranging from 11 to 94 MPa was collected from previous studies. In addition, the performance of eight existing strength and strain models was evaluated using the collected data. In this study, new strength–strain model considering the cross-sectional aspect ratio and the shape coefficient as a function of the depth of the rectangular cross-section was proposed using linear regression analysis. The proposed model provides a better correlation and a good fit with the experimental data compared to the other existing models. On the other hand, a new stress–strain relationship describing the axial behavior of square and rectangular columns confined with CFRP wraps was proposed, in which the parameters of confinement, such as the corner radius and the depth of the rectangular section were considered. The proposed relationship was validated with a set of experimental stress–strain curves and compared with four other existing models. The results showed that the proposed relationship provides good accuracy and better predictions over the existing models.

Axial compressive behavior and modeling of fiber-reinforced polymer-concrete-steel double-skin tubular stub columns with a rectangular outer tube and an elliptical inner tube

This paper presents the experimental results of monotonic axial compression tests on eighteen glass fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular stub columns (DSTCs) with a rectangular outer glass FRP tube and an elliptical/rectangular inner steel tube, as well as eight rectangular glass FRP-confined hollow stub columns (FCHCs) with an elliptical inner void. The effects of cross-sectional aspect ratio, FRP thickness, void area ratio and the shape of inner steel tube (i.e., elliptical and rectangular) on the axial compressive behavior of confined concrete core in rectangular DSTCs are considered and analyzed. The test results demonstrate that rectangular DSTCs possess excellent bearing capacity and ductility. Additionally, the axial stress-strain curves of confined concrete core in rectangular DSTCs are approximately trilinear and show obvious post-peak softening phenomenon because of the non-uniform and insufficient confinement. Furthermore, the larger aspect ratio, the thicker FRP tube, the higher void area ratio, as well as elliptical inner steel tube (compared with rectangular) have positive confinement effect on the axial compressive behavior of confined concrete core in rectangular DSTCs. Based on the analysis of experimental data, a design-oriented three-stage stress-strain model (considering post-peak softening behavior) of confined concrete in rectangular DSTCs with elliptical inner steel tube is proposed. Through the comparison, it is found that the predictions calculated by the proposed model accord well with the experimental results.