Effect Of Thickness Research Articles

Fire resistance of square double-skin concrete-filled steel tubular columns and concrete-filled double steel tubular columns

Square double-skin concrete-filled steel tubular (DSCFST) columns and concrete-filled double steel (CFDST) columns possess excellent load-carrying capacity and ductility. However, there has been limited research on the responses of DSCFST and square CFDST columns exposed to fire. This paper presents a series of tests on such columns loaded concentrically to determine the effects of the steel tube thickness, the strength of materials, load ratio, and boundary conditions on their fire resistance. Additionally, finite element (FE) models are established using ABAQUS, in which the concrete’s transient creep strain is considered through the development of the user-subroutine UEXPAN. A parametric study is undertaken by simulating 156 FE models to further study the behavior of DSCFST and CFDST columns under fire exposure. The fire test and numerical results suggest that both the load ratio and strengths of the internal tube and concrete core play significant roles in determining the fire resistance of DSCFST and CFDST columns. The developed FE models are demonstrated to capture well the fire behavior of loaded DSCFST and CFDST columns. The proposed design model predicts the ultimate loads of DSCFST columns with good accuracy; therefore, it can be employed in the practical design of DSCFST columns.

Numerical Modeling of Uniaxial Corroded Reinforced Concrete Columns Exposed to Fire

Corroded concrete structures remain at risk of fire damage throughout their lifespan. This study explores the fire resistance of reinforced concrete columns, considering the simultaneous impact of corrosion and high temperatures. Thermal–structural models of the corroded concrete columns are developed using SAFIR software (2022). The numerical results are compared with published test data on temperature distributions and axial displacement–time curves. Then, parametric analyses are conducted to investigate the influence of various factors, such as corrosion degree, concrete compressive strength, cover thickness, and fire exposure models, on the fire performance of the concrete columns. The findings reveal that corrosion significantly undermines fire resistance: notably, columns with severe corrosion exhibited a 47% reduction in fire resistance. Conversely, increased concrete strength can bolster the fire resistance of intact columns, particularly when the concrete cover is minimal. Enhancing the cover thickness proves to be an effective strategy to mitigate the thermal degradation of steel reinforcements, thereby extending the columns’ fire resistance by as much as 23%. The study introduces coefficients to quantify the effects of corrosion, fire exposure, material strength, and cover thickness, culminating in a practical formula to calculate the fire endurance of corroded reinforced concrete columns. This formula could complement existing fire safety regulations.

Temperature monitoring test and thermal analysis during construction of deep orifice of arch dam

In the low-temperature season of Southwest China, concrete of orifice is easy to crack during pouring, and the superficial heat preservation of dam is needed. In this paper, the temperature gradient monitoring test of deep orifice of Baihetan Dam is carried out to obtain measured temperature data based on the distributed optical fiber sensing technique. Based on monitoring data, a finite element model of deep orifice of pouring blocks considering thermal insulation materials is established. By comparing calculated temperature with measured temperature, accuracy of the simulation model is verified. The temperature and stress of deep orifice with or without thermal insulation measures are analyzed, considering the thermal insulation effects of different thicknesses and different types of thermal insulation materials. The results show that when the insulation measures are not covered, the average temperature difference between day and night exceeds 2 °C, and the average temperature difference between day and night is within 1 °C after coverage. Using 3 cm or 5 cm polyethylene coil at the top surface and the transverse joint surface of pouring blocks, and spraying 3 cm or 5 cm polyurethane at the upstream surface of pouring blocks for thermal insulation can effectively prevent the temperature cracks.

Experimental study on the technology optimization of clear ice thickness detection on horizontal cold plate surface by using microwave resonance

The accumulation of snow and ice has the potential to have a negative impact on numerous industries if it is not accurately detected and processed in real-time. Microwave resonators have gained interest as durable and reliable ice detectors. To detect the thickness of clear ice slices on a horizontal cold plate surface, a capacitively coupled split-ring resonant sensor was experimentally investigated. To ascertain the efficacy of the sensor, plexiglass with similar relative permittivity to ice was firstly tested. The effect of the plexiglass plate thickness on the resonance amplitude of the transmission scatter parameter was found to be monotonic in the range of 16.8 mm thickness, thereby demonstrating the ability of the sensor to accurately measure plate thickness. Then, the effect of different thicknesses of clear ice slices within 17.0 mm on the resonance parameters was tested under constant temperature. The resonant amplitude decreased by 46.55% from −4.13 dB to −6.05 dB, as the thickness of the clear ice slice gradually increased from 2.5 mm to 17.0 mm. A model for the detection of ice thickness based on the analysis of theoretical principles and experimental data was developed. The ice thickness could be detected accurately within a range of 17.0 mm at temperatures between −3 and −20 °C, with a maximum deviation of 5.66% in the detection of ice thickness. This study validates the application of the sensor to detect ice thickness, such as on ships, roads and aircraft.

Effects of oxygen volume fraction, temperature and diffusion layer thickness on the sensing characteristics of limiting current oxygen sensor

Oxygen sensors are prepared by Pt paddle bonding method with dense diffusion barrier of short-circuited yttria-stabilized zirconia (YSZ) solid electrolyte. Different from the previous normal diffusion and Knudsen diffusion mechanisms, the limiting current equation of this type oxygen sensor is derived based on the diffusion of oxygen ions in the dense diffusion barrier. The effects of oxygen volume fraction, temperature and diffusion layer thickness on the limiting current density are investigated. The relationship between the physical quantities in the experiment is consistent with the derived equation.

Design of metal foam baffle to enhance the thermal-hydraulic performance of shell and tube heat exchanger

Solid baffles are widely used in shell and tube heat exchanger (STHX), while the highly increased flow resistance and dead zones remain serious drawbacks in the applications. To address this issue, metal foam baffle is proposed in this study to replace solid baffle. The numerical model with considering the thermal non-equilibrium between fluid and foam baffles was established. Laminar flow is assumed in the foam baffles region and the realizable k-ε turbulence model is assumed in the open region. Effects of porosity, pore density, thickness and number of foam baffle (N) on the performance were examined. Results show the foam baffles always lead to lower pressure drop of STHX compared to the solid baffles. Compared to five 2 mm thick solid baffles, five 6 mm thick metal baffles with the porosity of 0.80, 0.85 and 0.90 results higher outlet temperature at the pore density greater than 80, 120 and 160 PPI, respectively. The metal foam baffle leads to higher outlet water temperature compared with solid baffles at the baffle number N ≤ 7. The foam baffles with optimum pore parameters reduced the pressure drop by 12.9 % and increase the outlet and inlet temperature difference by 31.0 % compared to the solid baffles.

Experimental and numerical investigation in to the axial load behaviour of profiled composite walls reinforced by embedded tubes with comprehensive parametric study

This paper presents experimental and numerical investigation on the axial load behaviour of profiled composite wall (PCW) consisted of two profiled steel sheet (PSS) in-filled with concrete and reinforced with/without embedded cold formed steel tubes (CFSTs). This type of composite walls was designed to resist the in-plan axial loading (bearing wall) in buildings designed with shear walls system. The results of three different FE models, namely, NCW-FE, Oct-FE and OCT-L-FE were accurately verified with the results of three experimental specimens, namely, NCW-Exp, Oct- Exp and OCT-L- Exp. Then, after the verification study for the FE models a comprehensive parametric study was presented to show detailed information about the positive effect of the internal CFSTs thickness, number and cross sectional shapes with and without stiffeners on the axial load behaviour of the PCW. The effect of the PSSs thickness and the concrete compressive strength on the axial load resisting behaviour of the PCW was studied as well. The results of this study proved that the effects of the embedded CFSTs reduced the local buckling of the PSS and increased the ductility with the axial load resistance of the PCW.

The Effect of the Wall Thickness of the Material Loaded Cavity On the RCS Reduction

In this paper, the effect of a parallel plate waveguide's wall thickness on radar cross-section reduction (RCS) is rigorously analyzed for H-polarization by using the Wiener-Hopf Technique, when the waveguide region is loaded with dielectric material and terminated with a perfect electric conductor (PEC) plate. Transfer matrices are incorporated into the analysis to account for the effect of different material layers through continuity relations. The Fourier transforms of the diffracted field and the boundary conditions yield a modified scalar Wiener-Hopf equation of the second kind (MWHE-2). The classical procedure to solve the MWHE-2 is applied and the approximate expression of the diffracted far field is obtained. Numerical results are given by comparing with the results available in the literature for the case of the wall thickness of the cavity not being considered.

Numerical study of gas crossover effect on hydrogen-oxygen proton exchange membrane fuel cell

Hydrogen-oxygen proton exchange membrane fuel cell (H2/O2 PEMFC) is a typical fuel cell for the applications of air-free environments, such as aerospace and underwater. Gas crossover has an adverse effect on the cell performance especially on open-circuit voltage (OCV), and this phenomenon would be severe for H2/O2 PEMFC. In this study, we develop a H2/O2 PEMFC model considering hydrogen and oxygen crossover, and investigate the gas crossover effect on H2/O2 PEMFC, and effects of temperature, relative humidity, inlet pressure and membrane thickness. The numerical results show that the gas crossover effect on the cell performance is obvious in the low current density region, and this effect becomes weak with current density. Although the crossover flux rate of hydrogen is generally greater than that of oxygen, the crossover current density of oxygen could be greater than that of hydrogen. Increasing temperature and relative humidity will decrease the OCV, and increase hydrogen and oxygen crossover current density. The temperature effect on OCV is more obvious at high relative humidity conditions. Increasing inlet pressure only slightly increases the OCV with considering the gas crossover effect. The OCV increases with increasing membrane thickness, and this positive effect becomes weak when the membrane thickness is greater than 75 μm in the investigated range. The work illustrates the basic influence rules and some quantified results of the critical parameters on the gas crossover effect and OCV of H2/O2 PEMFC.

Effects of Sintering Aids and Thickness on Densification and Properties of Magnesia-Aluminum Spinel Transparent Ceramics in the Aluminum Electrolysis Cells

Effects of Sintering Aids and Thickness on Densification and Properties of Magnesia-Aluminum Spinel Transparent Ceramics in the Aluminum Electrolysis Cells

Dynamic Performance Analysis of Precast Segment Column Reinforced with CFRP Subject to Vehicle Collision

With the extensive use of a precast segment column in the field of engineering, impact resistance performance has gradually attracted attention, as many accidents have caused huge economic losses and casualties. This study explored the dynamic response and failure modes of a prefabricated segment column both with and without Carbon Fiber-Reinforced Polymers (CFRPs). Firstly, numerical models of a precast segment column and CFRP-wrapped steel column under impact loads were developed, and the modeling method’s accuracy was fully verified. Then, numerical models of a bridge precast segment column with and without CFRPs under vehicle collision were established, and the differences in the dynamic performances between the precast segment column with and without CFRPs are explored. Finally, the effects of impact velocity, concrete strength, and CFRP thickness on the dynamic performance of a precast segment column are considered. The results indicate that in the case of a vehicle collision, multiple cross-sectional positions form highly complex stress states. At 100 km/h, the differences in bending moment and shear force values between reinforced and unreinforced precast segment columns at the impact section are 7.6% and 7.1%, respectively. At this velocity, the peak impact force also increases by 15.8% as the local stiffness of the precast segment column increases after reinforcement with a CFRP. The bottom segment of the precast segment column with a CFRP is crushed, and the precast segment column experiences shear failure under vehicle collision.

Predicting the compressive strength of CFRP-confined concrete using deep learning

The application of externally bonded fiber-reinforced polymers (FRP) has revolutionized structural rehabilitation, offering cost-effective and rapid solutions for damaged structures. This study presents a novel deep learning approach for predicting the compressive strength of circular carbon-FRP-confined concrete columns. Leveraging an extensive database of 664 experimental results, the model incorporates monotonicity and smoothness constraints, with hyperparameters optimization using the OPTUNA framework. The proposed model demonstrates exceptional accuracy, achieving R² = 0.93, a20-index = 0.95, and MAPE = 7.89 % on unseen test data, consistently outperforming nine benchmark models including established design guidelines. Scenario-based analysis confirms the model's ability to capture known physical behaviors, such as the effects of concrete strength, column diameter, and FRP thickness on confinement effectiveness. The integration of physical constraints enhances the model's reliability and interpretability, bridging the gap between data-driven and physics-based approaches. This research contributes to the advancement of more accurate, economical, and reliable design guidelines for FRP-strengthened structures, while also demonstrating the potential of constrained deep learning in structural engineering applications.

Hierarchical nanoarchitectonics of hollow hexanitrostilbene (HNS) microspheres to improve safety and combustion performance

Hollow structures have great potential in the field of energetic materials due to their excellent properties. In this study, nitrocellulose (NC) was used as a binder, and hollow-structured HNS/NC microspheres were prepared in the form of a suspension using the microjet droplet technology. The effects of spray velocity, suspension concentration, and receiving liquid temperature on the morphology, particle size, cavity structure, and pore size of the microspheres were systematically investigated. Subsequently, the effects of shell thickness and pore size on the dispersibility, specific surface area, crystal structure, thermal performance, mechanical sensitivity, and combustion performance of the microspheres were further studied. The results show that compared with the raw HNS, the hollow HNS/NC microspheres have good dispersibility, while retaining the crystal structure and chemical structure of the raw HNS, and have a lower activation energy, which is expected to achieve a rapid energy release reaction. In addition, compared with the solid HNS/NC microspheres, the hollow HNS/NC microspheres have a higher specific surface area (19.658 m2·g−1 vs 31.335 m2·g−1) and better safety performance (6 J vs 50 J). The ignition experiment results show that the hollow structure significantly enhances the combustion performance of HNS (305 ms vs 92 ms), improving the energy release efficiency. This preparation method is simple, efficient, and easy to scale up, providing a more universal and environmentally-friendly technical approach for the multi-structural design of energetic microspheres.

Continuous Nanofiber Bundle Production Using Helical Spinnerets with Different Configurations in Needleless Electrospinning

This study investigates the production of continuous nanofiber bundles using needleless electrospinning with a focus on helical spinneret configurations. It delves into the effects of spinneret diameter, pitch length, and thickness on nanofiber bundle characteristics, employing polyacrylonitrile as the polymer. The research highlights the significant impact of these parameters on the nanofiber morphology, bundle width, productivity, and deposition properties of nanofiber bundles. Scanning electron microscopy imaging, bundle depositions analyses, and electric field modeling with COMSOL Multiphysics are applied for the nanofiber bundles electrospun by helical spinnerets. As the diameter of the spinneret increases, productivity, bundle width, deposition ratio, deposition intensity, and deposition homogeneity are increased significantly. Additionally, an increase in spinneret thickness leads to a decrease in average nanofiber diameter. Specifically, increasing the spinneret diameter from 30 to 50 mm, pitch length from 20 to 40 mm, and reducing thickness from 3 to 1 mm increases productivity by 170%, 72%, and 32%, respectively. As a result of practical and modeling studies on helical spinnerets, the optimized parameters are determined as 1 mm thickness, 40 mm pitch length, and 50 mm diameter.

Numerical Investigation of the Axial Load Capacity of Cold-Formed Steel Channel Sections: Effects of Eccentricity, Section Thickness, and Column Length

Cold-formed steel channel (CFSC) sections have gained widespread adoption in building construction due to their advantageous properties, including superior energy efficiency, expedited construction timelines, environmental sustainability, material efficiency, and ease of transportation. This study presents a numerical investigation into the axial compressive behavior of CFSC section columns. A rigorously developed finite element model for CFSC sections was validated against existing experimental data from the literature. Upon validation, the model was employed for an extensive parametric analysis encompassing a dataset of 208 CFSC members. Furthermore, the efficacy of the design methodologies outlined in the AISI Specification and AS/NZS Standard were evaluated by comparing the axial load capacities obtained from the numerically generated data with the results of four previously conducted experimental tests. The findings reveal that the codified design equations, based on nominal compressive resistances determined using the current direct strength method, exhibit a conservative bias. On average, these equations underestimate the actual load capacities of CFSC section columns by approximately 11.5%. Additionally, this investigation explores the influence of eccentricity, cross-sectional dimensions, and the point-of-load application on the axial load capacity of CFSC columns. The results demonstrate that a decrease in section thickness, an increase in column length, and a higher degree of eccentricity significantly reduce the axial capacity of CFSC columns.

Consensus Report by the Italian Academy of Osseointegration on the Importance of Peri-Implant Soft Tissues.

Background and Objectives: The influence of the quantity and quality of peri-implant soft tissue on implant health and long-term maintenance is controversial. This consensus aimed to assess the importance of peri-implant soft tissue by analyzing four aspects: the role of keratinized mucosa (KM), the efficacy of specific collagen matrix, the influence of abutment material, and soft-tissue thickness. Materials and Methods: Active members of the Italian Academy of Osseointegration (IAO) participated in the consensus. Four systematic reviews were conducted, and their results were discussed to provide guidelines on the importance of soft tissue around implants. The first review evaluated the effect of KM on soft-tissue health, peri-implant bone loss, and patient-related variables. The second one analyzed if there was a specific type of matrix that provided better results in terms of peri-implant buccal soft-tissue thickness and keratinized mucosa width compared to autogenous soft-tissue graft. The third review evaluated the influence of different abutment materials on the soft tissues, and the fourth assessed the effect of soft-tissue thickness on peri-implant marginal bone loss (MBL). Results and Conclusions: The agreements reached by the assembly were as follows: the presence of supra-periosteal keratinized tissue is considered to favorably influence peri-implant health and aesthetics but had no relation to preventing bone crest resorption unrelated to infection. It facilitates patient cleaning around implants and reduces patient-reported pain. The free gingival graft (FGG) is considered the best in terms of supra-periosteal KM increase. Connective tissue grafts (CTG) perform better than volume-stable collagen matrices to increase soft-tissue thickness. Collagen matrices reduce surgical time and patient morbidity and can give better camouflaging. The influence of abutment material (titanium or zirconia) on MBL remains controversial, and no conclusion could be reached on this issue. Peri-implant soft-tissue health and recession seem not to be influenced by abutment material, but data are limited to zirconia and titanium. Although this systematic review highlighted the absence of a correlation between soft-tissue thickness and MBL, the assembly failed to find a consensus on this issue.

The Effect of Jacket Area on The Behaviour of Repaired/Strengthened Reinforced Concrete Columns

acketing is the most popular method for strengthening reinforced concrete columns under axial loading. This repair and strengthening technique is widely used not only in Türkiye but also in other technologically developed countries. In this study, the effectiveness of this method is investigated by experimentally testing two parameters: column section geometry and jacket thickness. The specimens were enlarged on all four sides to understand how the thickness of the jacket layer affects the behavior of the column. Using the experimental data, load versus deformation curves were plotted for each specimen. The parameters (strength, rigidity, ductility, and energy dissipation capacity) that determine the behaviour of the reinforced column were then analysed. At the end of this study, the effects of column section geometry and jacket thickness on the jacketing method are discussed, providing valuable preliminary data for future experimental studies.

Radio Frequency Vacuum Drying Study on the Drying Characteristics and Quality of Cistanche Slices and Analysis of Heating Uniformity.

To fully leverage the advantages of both hot air drying and radio frequency vacuum drying, a segmented combination drying technique was applied to post-harvest Cistanche. This new drying method involves using hot air drying in the initial stage to remove the majority of free water, followed by radio frequency vacuum drying in the later stage to remove the remaining small amount of free water and bound water. During the radio frequency vacuum drying (RFV) phase, the effects of temperature (45, 55, and 65 °C), vacuum pressure (0.020, 0.030, and 0.040 MPa), plate spacing (65, 75, and 85 mm), and slice thickness (4, 5, and 6 mm) on the drying characteristics, quality, and microstructure of Cistanche slices were investigated. Additionally, infrared thermal imaging technology was used to examine the surface temperature distribution of the material during the drying process. The results showed that compared to radio frequency vacuum drying alone, the hot air-radio frequency combined drying significantly shortened the drying time. Under conditions of lower vacuum pressure (0.020 MPa), plate spacing (65 mm), and higher temperature (65 °C), the drying time was reduced and the drying rate increased. Infrared thermal imaging revealed that in the early stages of hot air-radio frequency vacuum combined drying, the center temperature of Cistanche was higher than the edge temperature. As drying progressed, the internal moisture of the material diffused from the inside out, resulting in higher edge temperatures compared to the center and the formation of overheating zones. Compared to natural air drying, the hot air-radio frequency vacuum combined drying effectively preserved the content of active components such as polysaccharides (275.56 mg/g), total phenols (38.62 mg/g), total flavonoids (70.35 mg/g), phenylethanoid glycosides, and iridoids. Scanning electron microscopy observed that this combined drying method reduced surface collapse and cracking of the material. This study provides theoretical references for future drying processes of Cistanche.

Performance degradation evaluation of square steel tubes with local penetration damage

Steel tubular structures are susceptible to welding defects, cracking defects and environmental corrosion, which can negatively affect the stability and reliability of structure. This study tested the axial compression performance of twenty-six square steel tubular stubs with localized penetration damage simulated by artificial notch, considering the influence of notch length, orientation, and position. The test results showed that the failure mode of the specimens was dominated by the local buckling along the direction of the notch axis. The failure mode of the specimen with vertical notch showed notch opening, while those with horizontal notch showed notch closing, resulting in the secondary peak value in the load-displacement curve. The existence of local penetration damage reduced the ultimate strength and ductility of the tubular stubs. Compared to the ultimate strength of the specimens with middle notch, those with corner notch were weakened more, up to 27 %. Furthermore, the effects of notch dimension, position, orientation, and tube wall thickness on the axial bearing capacity of square steel tubular stubs are discussed by using a validated finite element model. Owing to the analysis, the ultimate strength of the stubs is reduced by increasing notch length, width and depth, whereas the reduction effect tends to be weakened as the notch orientation angle increases. The notch located in the corner is the most unfavorable for the axial compression performance of the square steel tubular stubs. A semi-empirical formula for evaluating the ultimate strength of square steel tubular stubs with local penetration damage is proposed by introducing the strength reduction factor. An artificial neural network-based ultimate strength prediction model is developed that can consider the effects of wide-range parameters, achieving high accuracy.

Flexural capacity design model of reinforced concrete beams strengthened with hybrid bonded CFRP

In order to improve the calculation methodology for the flexural capacity of RC (Reinforced Concrete) beams strengthened with HB-CFRP (Hybrid Bonded-Carbon Fiber Reinforced Polymer), three-point bending tests were conducted in this study. The experimental setup involved 9 HB-CFRP strengthened T-shaped beams and 1 unstrengthened beam for comparison. The effects of anchor spacing, anchor pressure, CFRP thickness, and anchor distribution pattern on the flexural performance of strengthened beams were investigated. Additionally, the development of the full range load-deflection curves of the HB-CFRP strengthened specimens was analyzed. Two bond strength models (the Wu model and Liu model) were modified. Six parameters were considered in the modified model, namely, the CFRP elastic modulus, CFRP thickness, number of mechanical fasteners in the shear span, CFRP-concrete width ratio, concrete cylinder compressive strength and normal pressure applied to the mechanical fasteners. The accuracy of the modified models was compared on the basis of three specifications. Results indicated a notable enhancement in the flexural capacity of the strengthened beams, ranging from 61.1 % to 158.1 % compared to the unstrengthened beam. Taking the ACI specification as an example, the mean value and coefficient of variation (COV) of the flexural capacity obtained by directly using the Wu model were 1.187 and 0.169, respectively; the results obtained by using the modified Wu model based on the measured FRP strain were 1.038 and 0.125, respectively; and the results obtained by using the modified Wu model based on the ACI reversed-calculated strain were 1.012 and 0.106, respectively. After the strengthened beam reached the peak load, the load then decreased abruptly to the vicinity of the moment mid-span deflection curve of the reference beam. As the loading continued, the resistance improved by 27.4 %∼79.3 % due to the increase in interface friction in the mechanical fasteners and concrete.