Outer Square Research Articles

Numerical analysis of square concrete‐filled double‐skin tubular columns with outer stainless‐steel tube

AbstractStainless steel has increasingly been utilized in concrete‐filled composite columns because of its high corrosion resistance and aesthetic appearance. However, there is little published information on the structural behavior of concrete‐filled double‐skin steel tubular (CFDST) columns made of square outer stainless‐steel skin and circular inner carbon steel tubes. The present study focuses on the nonlinear analysis of axially loaded CFDST short columns with outer square stainless steel tube and inner circular carbon steel tube. The explicit analysis methodology is adopted to develop the finite element model of CFDST columns. The verified model is employed to undertake a parametric study on the geometric and material effects on the performance of CFDST columns. The findings indicate that the outer tube diameter‐to‐thickness should be maintained <40 to ensure the required plastic resistance of CFDST columns with hollow ratio in range from 0.34 to 0.42. The design equation for calculating the ultimate axial strength of CFDST columns with outer stainless steel is proposed.

Experimental research and finite element analysis on seismic behavior of square reinforced concrete columns with four interlocking spirals

The seismic performance of square reinforced concrete columns confined by an innovative transverse reinforcement configuration composed of four interlocking spirals and outer square stirrups were investigated experimentally and numerically. Five composite specimens were tested under quasi-static reverse cyclic loading. The experimental results indicated that compared with conventional single spiral reinforced square composite column (SSRSCC) the newly developed interlocking multi-spiral reinforced square composite column (IMSRSCC) even with a slightly lower volumetric confinement ratio exhibited superior seismic performance in ultimate bearing capacity, energy dissipation and delaying the degradation of strength and stiffness. Moreover, a detailed three-dimensional finite element model considering the bond-slip behavior between concrete and steel reinforcement was developed and validated through a comparison with experimental results. The stress development and confining mechanism of transverse reinforcement of IMSRSCC was explored and the effects of the main design parameters on the seismic performance of IMSRSCC were also discussed through parametric studies.

Structural performance and design of stainless steel SHS-concrete‑carbon steel CHS double-skin stub columns

Concrete-filled double-skin steel tube (CFDST) with outer stainless steel square hollow section (SHS) and inner carbon steel circular hollow section (CHS) is introduced in this paper. The square-shaped section provides easier connection with other structural elements and the utilization of the three different materials (stainless steel, concrete and carbon steel) contributes to the advantages of their combined strength, corrosion resistance and economy. This paper reports a finite element (FE) analysis and the FE models are developed with consideration of geometric imperfection and stainless steel's non-linear material property. To validate the models, a comparison of the results of FE models and experiments is performed on the basis of ultimate section capacities, load deformation histories and failure modes. Parametric study is then carried out for the analysis of structural performance of CFDST stub columns, especially on interaction stresses between concrete and steel tubes, load deformation histories and stress distribution of each component. The failure modes and their corresponding ultimate limit states have been thoroughly discussed for the four typical types of CFDST stub column. In addition, the current international design codes including Eurocode 4, AISC and AIC are assessed with the generated ultimate section capacities from FE models. It is observed that ACI provides better predictions as compared to other codes. At last, the new design equation is proposed to predict the ultimate section capacity of the CFDST stub column which shows very good agreement with the FE analysis results.

Mechanical behavior of square composite columns with four interlocking spirals under compression

The compressive capacity of square composite columns confined by four interlocking spirals and outer square stirrups are experimentally and analytically investigated. The proposed innovative transverse reinforcement configuration used for square columns can improve the non-uniform confinement of outer square stirrup and thus enhance the confinement effect for the core concrete. Eight square composite columns for axial compression and ten eccentric compression specimens were tested. The study demonstrated that the newly developed interlocking multi-spiral reinforced square composite column (IMSRSCC) with the same volumetric confinement ratio outperformed conventional single-spiral reinforced square composite columns (SSRSCC) both in terms of ultimate load, bending stiffness and ductility under eccentric compression, while in axial compression test, the proposed new square composite column obtained similar ultimate load and deformation capacity. In addition, a comprehensive parametric study is presented using finite element analysis to explore the confinement working mechanism and key design parameters of IMSRSCC. Moreover, an analytical model is developed considering the composite confinement due to outer square stirrups and interlocking spirals and the formulas for calculating the bearing capacity of IMSRSCC are proposed. The analytical results are found consistent with experimental and numerical data.

SIW-based enhanced gain self-diplexing antenna using higher order modes

A self-diplexing antenna using slot-loaded cavity-backed Substrate Integrated Waveguide (CB-SIW) is presented with the enhanced gain. Higher-order modes (TE130 and TE310) in a square-shaped SIW cavity are utilized to emit linear and orthogonally polarized radiation with gain enhancement. Two concentric square ring slots are etched on the top conducting layer of the cavity to achieve broadside radiation. The asymmetric width of the outer square ring slot helps in achieving two different resonant frequencies at TE130 and TE310 modes. The proposed antenna is verified by observing a good match between the simulated and measured results. An excellent self-diplexing characteristic is achieved by getting isolation better than 28.0 dB between the two ports for a large tuning range. The proposed antenna radiates unidirectionally at two close frequencies 11.4 GHz and 12.2 GHz exhibiting gain of 9.8 dBi and 9.15dBi, respectively. In addition, the proposed design is single-layered, easy to fabricate as compared to traditional diplexing antennas.

Layout optimization analysis of zero Point system under extre-me conditions based on Workbench

In this article, Ansys workbench is used to perform mechanical simulation on the undetermined layout of the zero point system, and the difference between the layout and quantity of the different points of the connecting pins is analyzed, and the best layout is selected as the outer ring square (side length is 760). The inner circle is distributed in an equilateral triangle (side length is 250).

Modified double dumbbell-shaped split-ring resonator-based negative permittivity metamaterial for satellite communications with high effective medium ratio

Metamaterial with negative permittivity demonstrate excellent performance in cutting-edge technology. Thus, this study modified the double dumbbell-shaped split-ring resonator (MDD-SRR) based negative permittivity for satellite communications. The proposed MDD-SRR unit cell comprises a square-shaped split-ring resonator and two dumbbell-shaped rings. Some parts of the outer square ring were extended to enlarge the electrical length which altered the inductance of the metamaterial unit cell. The dimension of the proposed unit cell is 9 × 9 × 1.524 mm3, fabricated on a Rogers RT6002 (lossy) substrate material. Based on the results, five resonances for the transmission coefficient were achieved at frequencies of 2.896 GHz, 8.11 GHz, 9.76 GHz, 12.48 GHz and 13.49 GHz, including the S, X and Ku band satellite communication frequency bands through numerical simulation in a high-frequency electromagnetic simulator Computer Simulation Technology (CST) microwave studio. Negative permittivity at frequencies ranging from 2.896–3.76 GHz, 8.11–8.592 GHz, 9.76–10.784 GHz, 12.496–12.768 GHz, 13.504–14.4 GHz, were observed and extracted using the Robust and Nicolson–Ross–Weir (NRW) methods. Meanwhile, an effective medium ratio (EMR) measured at 11.51 to 2.896 GHz specified the goodness of the metamaterial unit cell for satellite communication with higher bandwidth and gain. The simulated, circuit model and measured results that were compared for validation purposes indicated that the simulation results, the equivalent circuit model results and measured results occupied each other. Moreover, the numerical simulation of the double dumbbell-shaped metamaterial unit cell was performed using a High-Frequency Structure Simulator (HFSS) to confirm the results. To evaluate the parametric study, the proposed unit cell was subjected to change different substrate types, change of split gap of rings, change of direction of electromagnetic field propagation, and structural optimization. In conclusion, the S, X and Ku-bands in the proposed metamaterial are competent for satellite communications as they are also investigated using an array of a unit cell.

Compression responses of composite corrugated sandwich square tube: Experimental and numerical investigation

By means of re-bonding inner square tube, corrugated core and outer square tube produced by hot pressing molding method, the composite corrugated sandwich square tubes (CCSSTs) were manufactured. Axial and lateral compression experiments were carried out on CCSSTs with length of 50 mm and 25 mm respectively, and the mechanical responses such as load, displacement and mid-height strain during the loading process were measured. The composite progressive damage finite element models were used to simulate the compression failure processes of CCSSTs. The simulated failure modes and load–displacement curves were in good agreement with experimental results. An analytical model based on homogenization theory was provided to evaluate the regularity of axial and lateral compression stiffnesses of CCSSTs. The research showed that the CCSST mainly underwent face crushing, face debonding and local buckling under axial compression. The lateral compression bearing capacity of CCSST reduced mainly caused by the outer face debonding. Increasing the height of the core could improve the axial compression stiffness and specific axial compression stiffness. The lateral compression stiffness performance and light weight benefit were both satisfying when the corrugation angle reaches 90°.

Numerical Thermal Analysis of a Hot Noncircular Rotating Cylinder in the Presence of a Magnetic Field

Abstract In this paper for the first time, a Lattice Boltzmann Simulation is performed to analyze the simultaneous effects of a hot rotating elliptic cylinder and the magnetic field on the mixed convection flow in a square enclosure. Complicated flow patterns and isotherm plots are found and analyzed in the concentric annulus between the internal elliptic cylinder and the outer square enclosure. Results indicate that increasing the Reynolds number, instantaneous averaged Nusselt number of the enclosure and its oscillation amplitude increase, while decrease with increasing the Hartmann number especially at its lower values. Furthermore, response surface method is adopted to find the optimal location of the elliptic cylinder. Response surface optimization results reveal that the average Nusselt number shows a decreasing–increasing trend with increasing both nondimensional parameters of cylinder center (Xc, Yc). Finally, the optimal location of the elliptic cylinder for the maximum heat transfer rate is obtained as Xc = 0.65 and Yc = 0.35. Moreover, a comparative study is performed to evaluate the heat transfer effects of the elliptical cylinder rotation as compared to circular cylinder. It was found that the elliptical cylinder rotation has a significant effect on the heat transfer enhancement, especially at high values of Re and Ha. As an example, the heat transfer rate for the elliptical cylinder at Re = 200 is increased by 13% and 34% as compared to the circular cylinder at Ha = 50 and 100, respectively.

Impact behavior of concrete-filled steel tube with cruciform reinforcing steel under lateral impact load

The objectives of this research are to investigate the behavior of cruciform steel-reinforced concrete-filled steel columns under impact load through experimental and numerical studies. The effects of impact velocity/height, axial pressure, thickness of steel tube and boundary conditions on the impact resistance of composite columns are studied through the tests of 16 specimens. The detailed progressive responses were recorded, including deformation mode, impact force-time history, deflection-time history and axial force-time history. Based on the test results, the impact resistances of steel-reinforced concrete-filled steel tubular columns and concrete-filled square steel tubular (CFST) columns are compared. In addition, FE models of the composite column are established using ABAQUS and validated based on experimental data. The strain rate effect of steel and concrete is considered in the model. The results show that the outer square steel tube effectively protects the internal steel-reinforced concrete. In the impact energy range of 17.02–51.08 kJ, the specimens only suffer minor bending deformation, which shows their excellent impact resistance. The ultimate plastic strain energy of square steel tube (EPT), cruciform steel section (EPS) and concrete (EPC) accounts for 56.4%, 18.2% and 25.4% of the total energy dissipation, which suggests that the steel tube (EPT) is the main energy dissipation mechanism of concrete-filled square steel tube columns.

Compression behaviour and bearing capacity calculation of concrete filled double skin square steel columns

In this paper, the mechanical behavior of concrete-filled double square steel tubular(CFDSST) columns under axial compression loading was studied by experiment and finite element (FE) analysis. The diagonal angle between inner and outer square steel tubes is 45°. In the experimental work, eight columns of 300 mm outer side length were tested. The variables considered were the wall thickness of inner and outer steel tube, side length of inner steel tube and aspect ratio. The 3D FE simulation of CFDSST is carried out by using the FE program ABAQUS, which was verified by the experimental results. The validated FE model was used to build models with different variables. The experimental and numerical results show that the ultimate strength and ductility of CFDSST columns were effectively improved by using inner steel tubes. Finally, the ultimate strength calculation method was proposed, which provides accurate prediction compared with experimental results and FE results.

Penta band single negative meta-atom absorber designed on square enclosed star-shaped modified split ring resonator for S-, C-, X- and Ku- bands microwave applications

This paper represents a penta band square enclosed star-shaped modified split ring resonator (SRR) based single negative meta-atom absorber (MAA) for multi-band microwave regime applications. FR-4 low-cost material has been used as a substrate to make the MAA unit cell with 0.101λ0 × 0.101λ0 of electrical size, where λ0 is the wavelength calculated at the lower resonance frequency of 3.80 GHz. There are two outer square split ring and one inner star ring shape resonator of 0.035 mm thickness of copper placed on the one side, and another side of the substrate has full copper to construct the desired unit cell. The MAA unit cell provides five absorption peaks of 97.87%, 93.65%, 92.66%, 99.95%, and 99.86% at the frequencies of 3.80, 5.65, 8.45, 10.82, and 15.92 GHz, respectively, which covers S-, C-, X-, and Ku- bands. The properties of MAA have been investigated and analyzed in the E-, H-fields and surface current. The EMR and highest Q factor of the designed MAA is 9.87 and 30.41, respectively, and it shows a single negative (SNG) property. Different types of parametric analysis have been done to show the better performance of absorption. Advanced Designed System (ADS) software has been used for equivalent circuit to verify the simulated S11 result obtained from the CST-2019 software. Experimental outcomes of the MAA unit cell have a good deal with the simulated result and measured result of the 24 × 20 array of unit cells also shown. Since the unit cell provides superior EMR, excellent Q-factor, and highest absorption so the recommended MAA can be effectively used as a penta band absorber in microwave applications, like notch filtering, sensing, reducing the unintended noise generated with the copper component of the satellite and radar antennas.

Double-Diffusive of a Nanofluid in a Rectangle-Shape Mounted on a Cavity Saturated by Heterogeneous Porous Media

This study presents numerical simulations on double-diffusive flow of a nanofluid in two cavities connected with four vertical gates. Novel shape of an outer square shape mounted on a square cavity by four gates was used. Heterogeneous porous media and Al 2 O 3 -water nanofluid are filled in an inner cavity. Outer rectangle shape is filled with a nanofluid only, and its left walls carry high temperature T h and high concentration C h . The right walls of a rectangle shape carry low temperature T c and low concentration C c and the other walls are adiabatic. An incompressible smoothed particle hydrodynamics (ISPH) method is applied for solving the governing equations of velocities, temperature, and concentration. Results are introduced for the effects of a buoyancy ratio − 2 ≤ N ≤ 2 , Darcy parameter 10 − 3 ≤ Da ≤ 10 − 5 , solid volume fraction 0 ≤ ϕ ≤ 0.05 , and porous levels. Main results are indicated in which the buoyancy ratio parameter adjusts the directions of double-diffusive convection flow in an outer shape and inner cavity. Adding more concentration of nanoparticles reduces the flow speed and maximum of the velocity field. Due to the presence of a porous medium layer in an inner cavity, the Darcy parameter has slight changes inside the rectangle shape.

Mechanical behavior of outer square inner circular concrete-filled dual steel tubular stub columns

The mechanical behavior of the outer square inner circular concrete-filled dual steel tubular (SCCFT) stub columns under axial compression is investigated by means of experimental research, numerical analysis and theoretical investigation. Parameters such as diameter ratio, concrete strength and steel ratio were discussed to identify their influence on the mechanical properties of SCCFT short columns on the basis of the experimental investigation of seven SCCFT short columns. By establishing a finite element model, nonlinear analysis was performed to discuss the longitudinal and transverse stress of the dual steel tubes. The longitudinal stress characteristics of the core and sandwich concrete were also analyzed. Furthermore, the failure sequence was illustrated and the reasonable cross-section composition of SCCFT stub column was proposed. A formula to predict the axial load capacity of SCCFT stub column was advanced and verified by the results from experiment and the finite element.

Concrete filled double skin square tubular stub columns subjected to compression load

Concrete filled double skin tubular members (CFDST) consist of double concentric circular or square steel tubes with concrete filled between the two steel tubes. The CFDST members, having a hollow section inside the internal tube, are generally lighter than ordinary concrete filled steel tubular members (CFT) which have a solid cross-section. Therefore, when the CFDST members are applied to bridge piers, reduction of seismic action can be expected. The present study aims to investigate, experimentally, the behavior of CFDST stub columns with double concentric square steel tubes filled with concrete (SS-CFDST) when working under centric compression. Two test parameters, namely, inner-to-outer width ratio and outer square steel tube's width-to-thickness were selected and outer steel tube's width-to-thickness ratio ranging from 70 to 160 were considered. In the results, shear failure of the concrete fill and local buckling of the double skin tubes having largest inner-toouter width ratio were observed. A method to predict axial loading capacity of SS-CFDST is also proposed. In addition, the load capacity in the axial direction of stub column test on SS-CFDST is compared with that of double circular CFDST. Finally, the biaxial stress behavior of both steel tubes under plane stress is discussed.

Simulation of Natural Convection around an Inclined Heating Triangular Cylinder Using Lattice Boltzmann Method: On the Stabilization of the Oscillatory Regime by Using Nanoparticles

Natural convection heat transfer in an inclined outer square cylinder confining a heated triangular cylinder is studied numerically using the Lattice Boltzmann method. The working fluid (pure water or Al2O3-water nanofluid) is confined in the space between the heated triangular body and an outer square cylinder. The cooling process of the system is ensured through two opposite isothermal cold walls of the external cylinder. The parameters governing the present problem are the Rayleigh number (103 ≤ Ra ≤ 106), the inclination of the configuration (0° ≤ θ ≤ 180°), and the volume fraction of nanoparticles (0 ≤ φ ≤ 0.04). The results obtained are presented in terms of streamlines, isothermes, intensities of the flow cells, and Nusselt numbers. This study shows that the inclination of the studied configuration has an important effect on the flow structure, the flow cells’ intensities, the amount of heat evacuated through each of the two cold walls and on the steadiness of the final state of the flow (steady or unsteady). It is shown that the inclination of the system has a moderate effect on the global quantity of heat leaving the block ( undergoes a maximum variation of 12.2% when the inclination is varied in its range). In addition, we show that it is possible to eliminate the Hopf’s instabilities and bring the flow to the steady regime by adding Al2O3 nanoparticles with certain volume fraction in the base fluid.

Square enclosed circle split ring resonator enabled epsilon negative (ENG) near zero index (NZI) metamaterial for gain enhancement of multiband satellite and radar antenna applications

In this article, a square enclosed circle split ring resonator (SEC-SRR) based metamaterial is described that shows negative permittivity (ENG) with near-zero-index (NZI) of refraction. The unit cell of this metamaterial is formed with two SRR rings, one with square in shape and another circular shaped. The inner circular SRR has related to the outer square SRR by the metal strip. The analyzed design is very simple, but the outcome of this recommended unit cell is high i.e., it covers the multiband S-, C-, and X- bands. Rogers is used as a substrate to design the proposed SEC-SRR that has a thickness of 1.524 mm. The unit cell has a dimension (electrical) of 0.070λ × 0.070λ. The simulation software CST microwave studio-2019 is used to identify transmission (S21) and reflection (S11) coefficient and from this knowledge relative permittivity, permeability and refractive index is obtained by using MATLAB code based on Nicolson-Ross-Wier (NRW) method. The simulated resonance frequencies are 2.61, 6.32 and 9.29 GHz with well-matched to the measured ones. The negative permittivity regions are obtained in 2.63–2.87 GHz, 6.39–7.45 GHz, and 9.37–9.52 GHz covering S-, C-and X-bands, respectively. The equivalent circuit is modeled in Advanced Design Software (ADS) and verified by comparing obtained S21 with CST output. The designed unit cell also exhibits NZI property, and high effective medium ratio (EMR) of 14.37 at lower resonance frequency. The applicability of NZI property of this ENG metamaterial has been investigated by applying for gain enhancement of LPDA antenna. Due to its near zero refractive index, negative permittivity, high EMR and simpler design, the proposed metamaterial can be utilized for S-, C-, and X-bands applications, especially for improving the gain of satellite and radar antennas with special features.

Cross coupled interlinked split ring resonator based epsilon negative metamaterial with high effective medium ratio for multiband satellite and radar communications

In this paper, a cross coupled interlinked split ring resonator based (CCI-SRR) based metamaterial has been presented. Epsilon negative (ENG) with a highly effective medium ratio (EMR) is attained in this metamaterial. The metamaterial unit cell consists of one square shaped split ring resonator and two rectangular rings. The rectangular rings reside within the outer square split ring. Two internal rings are coupled together by using a cross-shaped metal segment. These inner rings are also interlinked to the outer ring by using metal strips. Coupling causes to increase the electrical length and modifies the inductance of the unit cell. Multiple resonances covering C, X and Ku-band are achieved due to the interconnection of rings. The symmetric nature of the CCI-SRR unit cell exhibits unique quality to minimize noise and harmonics effect. The unit cell is designed on FR4 substrate with a thickness of 1.6 mm. The overall dimension of the unit cell is 0.124λ × 0.124λ, where λ is the wavelength calculated at a lower resonance frequency of 4.15 GHz. Three resonances are obtained for |S21| at frequencies of 4.15 GHz, 10.38 GHz and 14.93 GHz performing numerical simulation in CST microwave studio. Permittivity, permeability, refractive index and impedance are explored by using the Newton-Ross-Weir (NRW) method. ENG performance is observed in frequencies ranging from 3.95 to 5.65 GHz, 9.57–11.46 GHz, 13.68–16 GHz. Near-zero refractive index is attained within the frequency ranges, 4.16–5.75 GHz, 10.16–11.58 GHz, 14.46–16 GHz. An LC equivalent circuit is designed, and component values are achieved by Advanced Design Software (ADS) justifying |S21| with CST result. The study of electromagnetic wave interaction between the unit cell and the double positive medium reveals that the unit cell exhibits evanescent wave properties. The compact nature of the unit cell is confirmed by calculating EMR with a value of 8.03. The electromagnetic coupling effect is examined for 2 × 2 array in various orientations. The |S21| performance of 2 × 2, 4 × 4 and 8 × 8 is matched with the unit cell. Due to symmetric patterns, near-zero refractive index, negative permittivity and high EMR, the proposed unit cell can be used to enhance the performance of microwave devices used for C, X and Ku-bands, especially Satellite and Radar communications.

Unsteady characteristics of laminar free convection in an enclosure in the presence of power law fluid at Ra = 107

The present study deals with an unsteady laminar free convection inside the annuli confined between an outer square enclosure and an inner circular cylinder. The annuli are filled with non-Newtonian power law fluids. The inner cylinder is located at three positions along the vertical center line. The unsteadiness arising due to bifurcation of flow from steady state is also reported in this study. The flow characteristics were found to be steady in nature in case of shear thickening fluid. However, most of the cases in the shear thinning fluid regime are found to be unsteady in nature with periodic and non-periodic fluctuations. The bifurcation of the flow from steady to unsteady state is mainly governed by the location of the cylinder as well as the characteristics of non-Newtonian fluid. The Bernard cells arising due to very high convective flow at Ra = 107 are also observed in the flow fields.

Concrete Confinement Effect in Circular Concrete Sandwiched Double Steel Tubular Stub-Columns

Concrete sandwiched double steel tubular (CSDST) columns have improved ductility under cyclic loads. Two CSDST columns are investigated in this paper (1) CSDST-CS with Circular outer tube and Square inner tube and (2) CSDST-CC with Circular outer tube and Circular inner tube. The confinement of concrete between the annular spaces of the inner and outer tubes is very important for their behaviour. To the authors’ knowledge, the literature is scarce on a validated concrete confinement model for CSDST. In this paper, the concrete confinement mechanism in CSDST columns is explained based on thick-walled cylinder theory and a semi-analytical equation is developed. Hollowness ratio of the cross-section, width to thickness ratio of the outer steel tube, strength of the outer steel tube and sandwiched concrete strength are identified as the main parameters influencing the confinement effect in CSDST. The proposed equation is extended to CSDST-CS with inner square tube approximated as an equivalent circular tube. This assumption is validated by conducting tests on short column specimens under axial compression. With outer tubes being the same, concrete confinement effect in CSDST-CS, CSDST-CC and concrete filled steel tubular column (CFST) are 18%, 20% and 30%, respectively. This study has demonstrated that the presence of double steel tubes does not improve the concrete confinement in CSDST compared to CFST. Further, this study presents a modification to the design equations of EN 1994-1-2 2005-1-1 (Eurocode 4: Design of composite steel and concrete structures Part 1–1: General rules and rules for buildings. European Committee for Standardization, Brussels, 2004) for CFST columns to CSDST stub columns by incorporating the effect of hollowness.