Positive Bending Research Articles

Direct View for the Deformation Evolution of Sulfur Electrode during Li-S Battery Cycling

An experimental set-up was developed which can observe electrode deformation and electrochemical reaction in-situ during the charge-discharge cycling of lithium-sulfur battery. The positive bending deformation during charge and discharge was monitored at real time. It was found that the positive curvature increased during discharge and reduced during open circuit. The curvature would recover the original state during charge period. As electrochemical reaction proceeds, the electrolyte near positive electrode gradually become yellow and deepened due to polysulfide dissolution of discharge products. Results of surface and section morphology observation on sulfur electrode before and after cycle using scanning electron microscope (SEM) were consistent with curvature changes during cycling and verified the volumetric expansion of sulfur electrode.

Investigation of composite action on seismic performance of weak-axis column bending connections

This paper presents a developed beam-to-column connection which is suitable for weak axis of I-section column and H-shaped beam. Ten cruciform joint specimens, including five bare steel joint specimens (SJ) and five composite joint specimens (CJ) reinforced with partial shear connection, were tested under reversal of loads to evaluate the effect of composite action on the developed weak-axis connections. The beam ends were designed with standard, RBS, cover-plate, taper flange, and welded haunch respectively. The experimental results are analyzed and the composite action is discussed based on the test data. Overall, most joints failed due to welding fracture at the conjunction of diaphragm, skin plate and beam-end flange. But relatively speaking, the composite specimens performed well and achieved the story drift ratios of 0.04rad before experiencing 20% strength degradation because only slight strength degradation occurred in the composite joints compared to bare steel joints, thus the composite joints have a more stable bearing capacity. The test data clearly illustrate that the neutral axis shifted upward significantly under positive bending, resulting in larger strains on beam bottom flange. The reinforcing bars in concrete slab did not work well, but remained in elastic state. The slab slippage was negligible even in 50% degree partial shear connection. The welding quality is an important guarantee to avoid the brittle failure of the connections, and lamellar tearing resistant steel is suggested to be used in skin plate.

Mechanical performance of concrete pavement reinforced by CFRP grids for bridge deck applications

Abstract In this paper we develop and investigate a novel composite bridge deck (CPCG deck) formed by a steel fibre reinforced concrete (SFRC) pavement reinforced by carbon fibre reinforced polymer (CFRP) grids. This approach may mitigate damage in traditional asphalt pavement systems and in cracking of steel deck plates as observed in existing orthotropic steel bridges. An experimental study of CPCG decks subjected to four-point bending is presented considering different locations of CFRP grids in the depth direction. Two groups of CPCG decks are fabricated and tested to investigate their mechanical performance under positive and negative bending moments. A simplified theoretical model based on Timoshenko beam theory is proposed to predict the load deflection behaviour of the CPCG decks, and the section transformation method is used to calculate the stress distribution along the depth of the composite decks. The calculated results demonstrate good agreement with the experimental results. The results from parametric analysis further show that the best location of CFRP grids is in the horizontal direction of the pavement within the upper depth of the pavement. CFRP grids formed by SFRC can effectively increase the stiffness of steel deck plates. The effect has also been confirmed by Finite Element Analysis (FEA) using three-dimensional models.

Flexible transparent memory cell: bipolar resistive switching via indium–tin oxide nanowire networks on a poly(dimethylsiloxane) substrate

This report describes the fabrication and resistive switching (RS) characteristics of a novel flexible transparent (FT) resistive random access memory (ReRAM) device with a Ag/indium–tin oxide (ITO) nanowire network/ITO capacitor deposited on a PDMS substrate. The transmittance of the device is ∼70% in the visible region, and it exhibits a stable high-resistance state (HRS) to low-resistance state (LRS) ratio (HRS/LRS ratio) in different bending states. The RS characteristics are attributed to the congregate state of oxygen vacancies at different voltages, and the difference between positive and negative bending is mainly contributed by the effect of stress on the conductive layer. The FT-ReRAM can be used as nonvolatile memory element in future flexible transparent devices.

Bidirectional Soft Silicone Curvature Sensor Based on Off-Centered Embedded Fiber Bragg Grating

A compact bidirectional soft curvature sensor is achieved by embedding a fiber Bragg grating (FBG) off-centered in a silicone sheet. The proposed approach is capable to distinguish both the bending curvatures and bending directions through wavelength shift measurement of the FBG. Based on the pure bending model, the relationship between the FBG embedded position and the sensor sensitivity is studied and verified experimentally. Real-time curvature measurement of both positive and negative bending directions is experimentally achieved. The curvature sensor has a consistent performance and the results are highly repeatable with small variances. A linear relationship between applied curvature and FBG wavelength shift is obtained, with a large measurement range of up to $\pm 80~\text{m}^{-1}$ curvature.

Numerical Analysis on the Influence of the Twisted Blade on the Aerodynamic Performance of Turbine

Abstract With the gradual increase of the thermal power unit capacity, the inlet steam parameters and flow of the turbine also increase gradually, which causes considerable secondary flow loss. Therefore, studying the causes and distribution of secondary flow loss within the level is of great significance to effectively improve the stage internal efficiency of turbine. Take high-pressure stage moving blade of a turbine as the research object, and adopt the k-ωSST model, the SIMPLEC algorithm to numerically simulate the formation and development process of leakage vortex between the tip clearance of the positive bending twisted blade and its effect on the secondary flow of cascade passage. Results show that relative to the conventional twisted blade, the scope of influence of leakage vortex which the steam flow formed near the suction surface of positive bending twisted blade and the disturbance to passage mainstream become smaller, and the increase of tip clearance has weakened the „C“ type pressure gradient of suction surface of the positive bending twisted blade, increased the thickness of the boundary layer at both ends of blades and the loss of the blade end.

Rotation capacity of composite beam connected to RHS column, experimental test results

Commonly in steel frames, steel beam and concrete slab are connected together by shear keys to work as a unit member which is called beam. When a beam is subjected to positive bending, flexural strength and stiffness of the beam can be increased due to composite action. At the same time despite these advantages, action increases the strain at the beam bottom flange and it might affect beam plastic rotation capacity. This paper presents results of study on the rotation capacity of beam connected to Rectangular Hollow Section (RHS) column in the steel moment resisting frame buildings. Due to out-of-plane deformation of column flange, moment transfer efficiency of web connection is reduced and this results in reduction of beam plastic rotation capacity. In order to investigate the effects of width-to-thickness ratio (B/t) of RHS column on the rotation capacity of beam, cyclic loading tests were conducted on three full scale beam-to-column subassemblies. Detailed study on the different steel beam damages and concrete slab damages are presented. Experimental data showed the importance of this parameter of RHS column on the seismic behavior of beams. It is found that occurrence of severe concrete bearing crush at the face of RHS column of specimen with smaller width-to-thickness ratio resulted in considerable reduction on the rate of strain increase in the bottom flange. This behavior resulted in considerable improvement of rotation capacity of this specimen compared with and even bare steel beam connected to the RHS column with larger width-to-thickness ratio.

Properties of Fiber Reinforced High Performance Cement Based Overlays for Orthotropic Bridge Decks

An increasing number of steel orthotropic bridge deck require repair due to fatigue cracking. For the rib to deckplate joint, a possible solution is to reinforce the fatigue prone deck plate by replacing the asphalt wearing surface with a reinforced high strength concrete overlay. However, this process has been proven very difficult to execute and consequently has some issues regarding durability. This paper reports on high performance fiber reinforced cement based overlay solutions with gritted epoxy interlayer for a typical orthotropic deck with inadequate plate dimensions. Material characterization of three mix designs includes determination of compressive and tensile strength, and post crack behavior by CMOD registration from 3PBT. Furthermore, the steel-concrete composite action in the positive and negative bending moment zone is investigated experimentally. The test results give insight into the concrete behavior, the steel-epoxy-concrete interaction, and are used as input for a 3D finite element model of the reinforced deck under fatigue loading. The results indicate that fiber reinforced cement based overlay solutions may be a viable option for orthotropic decks with inadequate deck plate thicknesses

Experimental Investigation of the Shear Response of Precast Steel–Concrete Trussed Beams

AbstractThe results of an experimental campaign of three-point bending tests on precast composite beams, named hybrid steel–trussed concrete beams (HSTCBs), are provided. HSTCBs are typically constituted by a precast steel truss embedded in a block of concrete cast in place. Two series of specimens were manufactured, designed such that shear failure would occur, and tested under positive and negative bending moment. The experimental results obtained showed that fragile shear failure occurred in almost all cases, evidencing the crisis of the compressed concrete strut involved in the collapse mechanism. Yielding of the steel members provided ductility to the system, especially in those cases in which the mechanical properties of the concrete were adequate and allowed the failure of the strut to be delayed. Some of the more accredited expressions for prediction of shear resistance available in the literature were used to assess the shear capacity and compared against those experimentally obtained for all spe...

Study on flexural capacity of simply supported steel-concrete composite beam

This paper investigates the flexural capacity of simply supported steel-concrete composite I beam and box beam under positive bending moment through combined experimental and finite element (FE) modeling. 24 composite beams are included into the experiments and parameters including shear connection degree, transverse reinforcement ratio, section form of girder, diameter of stud and loading way are also considered and investigated. ABAQUS is employed to establish FE models to simulate the behavior of composite beams. The influences of a few key parameters, such as the shear connection degree, stud arrangement, stud diameter, beam length and loading way, on flexural capacity are discussed. In addition, three methods including GB standard, Eurocode 4, and Nie method are also used to estimate the flexural capacity of composite beams and also for comparison with experimental and numerical results. The results indicate that Nie method may provide a better estimation in comparison to other two standards.

Elastic-plastic secondary indeterminate problem for thin-walled pipe through the inner-wall loading by three-point bending

ABSTRACTThe inner-wall loading by three-point bending about thin-walled pipe is an elastic-plastic secondary indeterminate problem in the symmetrical three-roller setting round process. In this study, the shifting of the tangent point between the pipe and lower roller is ignored. The bilinear hardening material model is adopted, and the static equilibrium condition, physical relationship of elastic-plastic deformation, and deformation compatibility condition are taken into account. Based on the geometrical discrete idea, a semi-circular pipe is meshed equably into N micro-pipe-wall elements with same geometric parameters along the circumferential direction. Deformation characteristics of each element are calculated, and then the deformation history response of the whole pipe is resolved by the load increment method. The finite element model of static bending in three-roller setting round process is established by using the software package ABAQUS. The theoretical and simulated results show that the cross section of pipe has two positive bending regions and two reverse bending regions; the maximum bending curvature appears in the bottom section of pipe, the minimum bending curvature appears in the section corresponding to the tangent point of the pipe and lower roller. The quantitative relationships between the upper roller load, maximum(minimum) bending curvature and reduction are given. Finally, the reliability of theoretical calculation is proved by numerical simulation.

In-site experiments on the swelling characteristics of a shield tunnel in expansive clay: A case study

Expansive soil swells, softens, and disintegrates when absorbing water, whereas it shrinks when losing water. Understanding the swelling characteristics of a shield tunnel in expansive soil is important. However, most in-site experiences on the swelling characteristics of a tunnel are obtained from the NATM tunnels constructed in swelling rock using drill and blast method; most laboratory experiments or theoretical analyses on the swelling characteristics of a shield tunnel in expansive soil are under certain hypotheses which have not been verified in actual situation. To solve the problems, the Slender West Lake tunnel was selected as the background, laboratory and in-site experiments were performed to understand the swelling characteristics of a shield tunnel in expansive clay. Four experimental sections were constructed in the actual tunnel. The measuring gauges were pre-installed in the segments in factory and the segments were installed in-site to observe the actual earth pressure and temperature during construction. The influences of expansive soil to the distributions and variations of earth pressure, bending moment, and temperature were analyzed. The increasing earth pressure was divided into three stages. Large earth pressure was detected at the top, bottom, left, and right sides of the tunnel. The earth pressure at the left and right sides was larger than that at the top and bottom. Large negative bending moment was detected at the top and bottom of the tunnel, whereas large positive bending moment was detected at the left and right sides of the tunnel. The minimum bending moment appeared at 45° oblique. The largest negative bending moment was larger than the largest positive bending moment. Based on the observations, a load mode of swelling pressure for a beam-spring model was suggested. It can be referred by the similar tunnels.

A New Simple Design Method for the Plate Foundation of a Transmission Tower in Subsidence Area

In this article, we present a simple design method for the plate foundation of a transmission tower in a mining area, which is based on the theory of beam rested on an elastic foundation. The corresponding theoretical model has been developed with the synergistic reaction of a composite protection plate by considering the mining subsidence of ground. On the basis of this model, the function of flexural deformation and the distribution function of bending moment of the protection plate and their corresponding base counterforce have been deduced. The analysis of selected example shows that the control bending moment of the protection plate is the maximum positive bending moment at the center of the cross section during the moving process of pelvic floor. The tilt deformation is minimum, when the tower is either at the bottom or at the verge of pelvic floor. The tilt deformation is maximum at one-fourth times of the length of pelvic floor and is away from the bottom and the verge of pelvic floor. The contact pressure between the plate foundation and the soil is similar to a U-shaped distribution, when the protection plate is in pelvic floor area of a positive (curvature) deformation, and it is a M-shaped distribution, when the protection plate is in pelvic floor area of a negative (curvature) deformation. We do not observe any change of the contact pressure at the midpoint of the protection plate during the moving process of the basin.

Flexural stiffness of steel-concrete composite beam under positive moment

This paper investigates the flexural stiffness of simply supported steel-concrete composite I-beams under positive bending moment through combined experimental, numerical, and different standard methods. 14 composite beams are tested for experimental study and parameters including shear connection degree, transverse and longitudinal reinforcement ratios, loading way are also investigated. ABAQUS is employed to establish finite element (FE) models to simulate the flexural behavior of composite beams. The influences of a few key parameters, such as the shear connection degree, stud arrangement, stud diameter, beam length, loading way, on the flexural stiffness is also studied by parametric study. In addition, three widely used standard methods including GB, AISC, and British standards are used to estimate the flexural stiffness of the composite beams. The results are compared with the experimental and numerical results. The findings have provided comprehensive understanding of the flexural stiffness and the modelling of the composite beams. The results also indicate that GB 50017-2003 could provide better results in comparison to the other standards.

Soil-Structure Interaction of Space Frame Supported on Pile Foundation Embedded in Cohesionless Soil

The study deals with numerical modeling of space frame- pile foundation and cohesionless soil system using finite element models. The elements of the superstructure frame and that of pile foundation including soil mass are descretized using 20 node isoparametric continuum elements. The interface between pile and pile cap is idealized using 16 node isoparametric surface element. The complete three dimensional analysis is carried out to attempt a parametric study using sub-structure approach. The total stress analysis is carried out and immediate behaviour of the soil is considered. The effect of various parameters of the pile foundation such as spacing in a group and configuration of the pile group is evaluated on the response of superstructure. The response included the displacement at the top of the frame and bending moment in columns. Incorporation of the aspect of soil- structure interaction is found to increase the displacement in the range of 67–98 % and the maximum absolute positive and negative bending moment in superstructure columns is observed to increase in the range of 13–15 and 25–27 %. The effect of the soil-structure interaction is observed to be significant for the type of foundation and soil considered in the present study.

A mechanical model of symmetrical three-roller setting round process: The static bending stage

The static bending deformation of three-roller setting round process is an elastic–plastic secondary indeterminate problem, and belongs to the plane bending deformation. This paper adopts a bilinear material model. In consideration of shifting of the tangent points between the pipe and the lower rollers, the static equilibrium conditions, the physical relationships of elastic–plastic deformation, the deformation compatibility conditions, and the constraint conditions are analyzed comprehensively. By applying the discrete method, a semi-circular pipe is meshed equably into N micro-pipe-wall elements with the same geometric parameters. Deformation characteristics of each micro-pipe-wall element are calculated, and then the deformation history responses of the whole pipe are resolved by applying the load increment method, based on the variable step size, and the experimental apparatus is further designed to verify the theoretical model. Finally, the effects of various process parameters on the upper roller load and bending curvature are studied. The results show that the static bending deformation can be assumed to be a pure bending process; the cross section of the pipe has two positive bending regions and two reverse bending regions; the upper roller diameter and the lower rollers spacing are the major factors for the upper roller load and the bending curvature; the dynamic roll bending process can be simplified into a static to-and-fro bending process.

Moment Contribution Capacity of Tendon Prestressed Partial on Concrete Beam-column Joint Interior According to Provisions ACI 318-2008 Chapter 21.5.2.5(c) Due to Cyclic Lateral Loads

This research designed a partial prestressed concrete beam-column with reinforced concrete interior joint, using square columns of 400/400 mm, reinforcement 6 D16 + 4D13, section beam 250/400 mm, tensile reinforcement 5 D13, compression reinforcement 3 D13 + 2 strand tendon D12,7 mm , and joint without plastic hinge, then tested in laboratory with lateral cyclic loads on peak column, static axial load 1120 kN on the centre column, to get the tendon capacity to assume positive and negative bending moments due to lateral load, according to provisions of ACI 318-2008 part 21.5.2.5 (c). Test results showed that the moment tendon contribution on beam section, in the tensile area, the positive and negative moment both on the left side or the right side column are all qualified ( 25 %). As for the negative moment, either left or right side column are all qualified ( 4.0). Although the contribution of positive moment capacity tendon in compression areas does not qualify, in overall, the reliability and ductility of the structure qualify.

A Study of Thickening Phenomenon in Laser Bending Zone of a Metal Laminated Plate

A metal laminated plate, taking stainless steel/carbon steel laminated plate (SCLP) for example, is being increasingly used in the aircraft, ship, car and automotive industries. Based on the temperature gradient and thickening mechanisms, the thickening phenomenon was investigated for the SCLP forming and application widely. The bending zone thickness increases after laser bending of the SCLP. Then, an IPP image processing software was used to evaluate the grain size and thickness changes in laser bending zone. There are three areas they are stainless steel squeezed layer on the top, carbon steel extended layer at the middle and the bottom layer of stainless steel. The research results show that the grain size increases bigger in laser bending process which means thermal expansion thickening (TET) on one hand. In the positive bending process, grains extended by laser heating are squeezed through the bending stress and extrusion thickening (ET) on the other hand. The sizes of both stainless steel at upper layer and carbon steel layer at middle get thicker, but the bottom stainless layer changed little. The research outcomes also show the thickening size consists of TET and ET, where TET effect accounts for great proportion in the range of bending angle 5-20 degree. While ET effect increases in the range of bending angle 30-60 degree, the thickening ratio of TET and ET reaches 2 to 3 at bigger angles. The researches of the thickening phenomenon provide a deeper understand on laser bending theory and technology.

Study on the bending mechanical model of segmental joint in shield tunnel with large cross-section

With the consideration of the influence of the detailed structure of joint surface, the non-linear mechanical property of concrete and transferring cushion, the load transmission distinction with joint surface and the impact of pre-tightened joint bolt, the bending mechanical model of segmental joint, which could characterize the crack and crush of concrete, the yield of bolt and the damage of segmental joint, is established for the segment joint with complex joint surface in large cross-section shield tunnel. Then the flexural behavior of segmental joint in shield tunnel with large cross-section is analyzed using full-scale test of segmental joint bending. The results show that the maximum opening of joint surface grows slowly under small moment, while it increases significantly when the bending moment exceeds a certain value. After the joint opening becomes wide enough and the bolt is in tension, the growth rate of joint opening height gradually decreases and approaches a stable value. The time of joint surface opening and the bolt becoming loaded under the action of negative curvature is later than positive bending state. Meanwhile, with the axial force increasing, the time of joint surface opening is later and the opening height is smaller than that under the same moment. The bending stiffness of segmental joint shows nonlinear descent with the moment growing, while the higher axial force is more favorable to maintaining the bending stiffness stability. A larger the axial force results in a longer flexural capacity of joint surface. The results can provide guidance and reference for segmental joint design for large cross-section shield tunnel.

Dynamic Load Allowances Corresponding to Different Responses in Various Sections of Highway Bridges to Moving Vehicular Loads

Dynamic load allowance (DLA) is an important index used in design and evaluation of dynamic performance of highway bridges to moving vehicular loads. In many codes, DLAs of different responses in various sections are not distinguished. To facilitate a rational design and objective evaluation, the quantitative relationships of DLAs corresponding to different responses in various sections are systematically studied using both theoretical derivation and numerical simulation. According to results of theoretical derivation, for simply supported girder bridges, DLA of deflection is almost 20% higher than that of bending moment in the mid-span section. According to results of numerical simulation, for continuous girder bridges, DLA of negative (upward) deflection is 20% higher than that of positive deflection, and DLA of negative bending moment is 40% higher than that of positive bending moment in critical cases. These significant differences cannot be ignored. Finally, the contributions of high modes to different dynamic responses in various sections are investigated. Based on the recommended approach to considering these differences, the dynamic performance of bridge can be designed and evaluated in a simple yet rotational way.