Neutral Axis Research Articles

Flexural strength and stiffness of circular double-skin and double-tube concrete-filled steel tubes

Circular double-skin and double-tube concrete-filled steel tubes (CFST) have become increasingly attractive especially in marine structures due to their favourable mechanical behaviour. With the development of (ultra) high strength materials, thin-walled and thick-walled steel structures, it is urgent to propose a design method suitable for a wider range of parameters. This paper develops fibre beam element (FBE) models for the circular double-skin and double-tube CFST members under pure bending. The FBE models are verified by the collected experimental results. Numerical data including 435 double-tube and 213 double-skin CFST beams are generated to cover extensive parameters. Based on the plastic-stress distribution method, the design formulae are deduced to calculate the flexural strength of circular double-skin and double-tube CFST members considering the different positions of neutral axis inside and outside the inner tube. The predicted results agree well with the FBE results and test results. Finally, the curvature from half-sine wave calculation is modified and the design method for flexural stiffness is proposed.

Assessment of surface crack growth of composite girders with concrete-filled tubular flanges and corrugated webs through substructure-based numerical modelling

This paper presents an analytical assessment of surface crack growth behaviour of composite girders with concrete filled tubular flanges and corrugated webs (CGCTFCWs) with the aid of substructure-based numerical modelling. Distinctive features of crack propagation on the tubular flanges with considerable stress gradient from lower to upper cracked tube surface interacted with the weld toes along the corrugated webs are replicated in the substructure modelling and discussed in details. Based on a favourable verification of stress intensity factors (SIFs) with reported model with semi-elliptical surface crack in plates and rectangular hollow section tube, an analytically derived substructure model of critical corrugated web-flange welded details coupled to the rest of the structure is developed. Such a model is distinguished itself from that based on original Newman and Raju equation by an amendatory of the stress gradient induced by the shifting of the neutral axis and the geometry as crack penetrated through the tube wall. Based on a parametric analysis, the SIFs significantly influenced by the corrugation depth ratio, the tube thickness-to-width ratio and the tube thickness-to-depth ratio in relation with the dimensionless crack length are demonstrated and taken into account in the derivation of a new geometry amendatory coefficient. An experimental investigation was also implemented to further examine and validate the modelling crack propagation response. The resultant fatigue fracture manner and the stress concentration of the hot spot are virtually in good correlation with the modelling results. Moreover, the relations between the crack growth increment and fatigue endurances from experimental measurement match well with these predicted by the NASGRO equation using amended SIFs, indicating that the proposed model is able to trace the distinct geometry effects of the corrugated web and the tubular flange on the crack propagation response of CGCTFCWs.

Experimental study on the behaviour of steel fibre when used as a secondary reinforcement in reinforced concrete beam

There are many researches has been done to replace the constituent materials in the concrete to meet out the scarcity of the available raw materials and also, they have proven a successful one up to a certain level. But in this study, we are focused on to improve the structural behaviour by adding steel fibres in concrete without replacing any constituent materials. The scope of this project is to study experimentally the strength properties of the beam on inclusion of steel fibres. It also aims to investigate the structural behaviour of conventional concrete beams and steel fibre reinforced beam when steel fibre is used as a secondary reinforcement in beams. To overcome the deficiency of the conventional concrete, fibres have been added as secondary reinforcement. Steel fibres are added below the neutral axis of the RC beam in order to overcome the development of micro cracks under applied stress in the RC beam. The addition of steel fibres to the concrete has many advantages and the most notable among them is the improvement in the mechanical characteristics of the concrete. In our project steel fibres and modified steel fibres (adding fibres below the neutral axis) are added in the proportion of 1 % to the concrete. The tests for the fresh concrete and hardened concrete are carried out and their results are compared. The project is further extended to check the performance of the steel fibres in the reinforced concrete beams when they are added below the neutral axis. Two-point loading is applied to the structural members and the corresponding deflections are noted down. The performance of the SFRC beam and the modified steel fibre reinforced concrete (MFRC) beam is compared with the conventional RC beam. The discussions and conclusion are arrived based on the test results.

Experimental and numerical investigation on the lateral force resistance of modular steel sub-frames with laminated double beam

Modular construction was widely applied since higher integrity, faster speed and less emission. Especially for COVID-19, several modular steel hospitals were urgently built for treatment and successfully contributed to epidemic control. It has been known that laminated double beam has the capability of significantly strengthening the cooperation between adjacent floor and ceiling beams in modular steel buildings. However, the effect of the superposition of laminated double beam on the lateral force resistance of modular steel structure has not been fully understood. In present study, a series of full-scale lateral experimental tests and finite element analysis were conducted to comprehensively investigate the lateral response of modular steel sub-frames with laminated double beam. Moreover, a simple validated analytical procedure was developed to support the design and assessment of modular steel buildings in engineering practice. The results show that the application of corner plug-in junction could significantly strengthen the connection of critical components of a modular steel sub-frame. The superimposed bending action of the laminated beam was demonstrated by that the strain neutral axes of the layered beams are relatively close to the interface of the beams resulting from interfacial bolt connections. It shows that the superimposition of adjacent double beams could obviously reinforce the structural integrity and lateral force resistance of a modular steel sub-frame. Furthermore, the developed analytical procedure provides an accurate and efficient method for estimating the initial lateral stiffness of modular steel sub-frames.

Robotic arm-assisted total knee arthroplasty improves preoperative planning and intraoperative decision-making

BackgroundThe reliability of robotic arm-assisted total knee arthroplasty (RA-TKA) has been previously reported. In this study, we evaluated the predictive accuracy of the RA-TKA system in determining the required bone resection and implant size preoperatively and its effect on intraoperative decision-making.MethodsData on the outcomes of RA-TKA procedures performed in our department were prospectively collected. A three-dimensional model of the femur, tibia, and fibula was reconstructed using standard computed tomography (CT) images. The model was used preoperatively to predict bone required resection for the femur and tibia and implant size. Intraoperatively, the images were registered to the local anatomy to create a patient-specific model for decision-making, including real-time measurement of the medial-to-lateral difference in the extension/flexion gap and TKA component alignment. Differences between predicted and real bone resections and implant size were evaluated, and the post-TKA mechanical axis of the lower limb and difference in medial-to-lateral flexion/extension gap were measured.ResultsThe analysis was based on the data of 28 patients who underwent TKA to treat severe osteoarthritis. The RA-TKA system successfully predicted the femoral and tibial component within one implant size in 28/28 cases (100%). For the 168 bone resections performed, including both femoral and tibial cuts, the resection was within 1 mm of the predicted value in 120/168 (71%) of the cuts. The actual versus predicted bone resection was statistically different only for the lateral tibial plateau (p = 0.018). The medial-to-lateral gap difference was between − 1 and 1 mm, except in one case. The achieved lower limb alignment was accurate overall, with the alignment being within < 1.0° of the neutral mechanical axis in 13/28 cases (46%) and within < 3.0° in 28/28 cases (100%).ConclusionsThe RA-TKA system provided considerable pre- and intraoperative surgical assistance to achieve accurate bone resection, appropriate component sizing, and postoperative alignment after RA-TKA.

Static and dynamic modeling of functionally graded Euler–Bernoulli microbeams based on reformulated strain gradient elasticity theory using isogeometric analysis

Strain Gradient Theories (SGTs) are often considered to capture the intrinsic microstructural behaviors of the microbeams. In the present work, the recent Reformulated Strain Gradient Theory (RSGT), which accounts the effect of the strain gradient, couple stress (rotation gradients) and velocity gradients collectively, is extended for the static and dynamic modeling of Functionally Graded (FG) Euler–Bernoulli microbeams to account for the effect of the strain gradient, couple stress (rotation gradients) and velocity gradients collectively. The present formulation also considers the shift of neutral axis due to material inhomogeneity in the FG microbeam. The problems of static deflection and free vibrations with different boundary conditions are addressed. Numerical solutions are obtained using isogeometric analysis. Analytical solutions of the present formulation for simply supported FG microbeam for static deflection and free vibration problems are also obtained and employed to validate the numerical results. The influence of the material index, different length scale parameters on the static deflection and free vibration responses of the FG microbeams are discussed. The present FG RSGT microbeam shows the prominent size scale effect in thin beams and predicts stiffer response than the FG microbeam based on modified couple stress theory.

Accelerometer-based, hand-held navigation for improved knee alignment in total knee arthroplasty: An observational study

BackgroundMalalignment in total knee arthroplasty has been associated with poor implant longevity and clinical outcomes. The aim of this study was to investigate the accuracy of accelerometer-based navigation in restoring the mechanical axis. Methods106 primary total knee arthroplasties performed during February 2016 to September 2017 at a tertiary care centre in India were enrolled in this observational study. We noted the intra-op tourniquet time. Two separate blinded observers measured the preoperative mechanical axis and the post operative radiological results (mechanical axis, coronal and sagittal alignment of femoral and tibial components) and the mean value was taken as final data. Interclass correlation was done to look for variability between the two observers. ResultsThe mean pre operative mechanical axis was 13.74 ± 10.44. The mean tourniquet time was 53.14 ± 7.42 min 91.5% (96/106) knees were within ±3° of neutral mechanical axis with a mean of 1.00° ± 2.68°. The femoral and tibial components with coronal alignment within ±3° perpendicular to the mechanical axis were 93.39% (99/106) and 89.62% (95/106) respectively. In the sagittal plane 89.62% of the femoral components and 87.73% of the tibial components were within ±3° perpendicular to the axis of tibia. ConclusionThe Accelerometer based portable navigation system effectively reduces the coronal and sagittal alignment outliers in total knee arthroplasty and has no role in rotational alignment of components.

Design Method for End-Plate Bolted Connections

The design of buildings envelopes is more elaborate than it has ever been. Starting from the design method of nodal space frames made of one layer of structure and covered in glass, this paper presents e new type of end-plate beam to beam connection. Specific to this is the fact that both end-plates are welded inside of the tubes, having a minimum gap between them of 2 mm. This will reduce considerably the in-surface and welding-induced end plates tolerances which appear at classical end-plate connections. Through the pre-tensioning of the bolts, a continuous contact surface is assured along the cross-sections of the hollow profiles. Several tests were run with the software Gas Win in order to establish the maximum capacity of the connection. This condition is achieved when the neutral axis goes out of the crosssection and the entire cross-section is compressed. Installation hand-holes were also considered. In order to get a better understanding about the force flow, an FEM analysis was run using the Abaqus software. A comparison between the results followed.

Flexural Strength and Behavioral Study of High-Performance Concrete Beams using Stress-Block Parameters

Most of the existing codes are using stress block parameters which were derived for normal strength concrete. Rectangular stress-block parameters used for normal strength concrete cannot be used safely for higher grade concrete like HPC, hence new stress-block parameters are established from the experimental investigations. Theses parameters can be made very much useful in the design of HPC members. Present research aims at behaviour study of HPC using stress block parameters. High performance concrete single span beams were tested under monotonic four-point bending. Considering the experimental stress-strain curves of HPC for grade 60, 80 and 100 MPa, an idealized stress block curve is established and the stress block parameters are derived. Based on the idealized stress block curve, the equations for ultimate moment of resistance, depth of neutral axis, limiting moment of resistance and maximum depth of neutral axis are proposed. Based on the observation of experimental load deformation curves, an ideal load deformation curve is proposed, which follows four significant events identified as, first cracking, yielding of reinforced steel, crushing of concrete with spalling of cover and ultimate failure. The predicted values compare well with the experimental values. The average location of the first crack observed was at 0.535 times the span of the beam from the left support of the observer in the tension zone.

Influence of the electromagnetic field pressure on the free bending of the straight side

Bending is the operation of forming or changing the angles between the parts of the workpiece or giving it a curved shape and in the mean time is the most difficult and timeconsuming operation of the technological process of manufacturing parts from profiles. Aircraft bending parts of the following nomenclature are obtained as profiles: frames, ribs, stringers, linings and brackets. Profile parts are responsible for their intended purpose; therefore, high requirements are placed on the accuracy of their dimensions and the preservation of the crosssection shape. The process of bending profiles has its own characteristics, which are due to the shape of the profile section; the first feature is the presence of vertical shelves, significantly loaded and deformed due to large distances from the neutral axis of the bent section, the second is the mismatch of the bending plane with the main axes of inertia of the section, which causes oblique bending and twisting of the part. When analyzing the bending process of extruded profiles, it should be borne in mind that the neutral layer of the workpiece coincides with the line that passes through the centers of gravity of the sections. When using the hypothesis of planar sections of the plot of deformations and stresses in the stretched and compressed zones do not have a mutually reflected form. It is very important how the profile is oriented in the bending plane. Different orientation of the profile, even the simplest cross-section (for example, angular), gives a qualitatively different picture of the deformed state.

Experimental Correlations Nu vs Gr.Pr at Varying Widths for Convective Heat Flow Through a Large Aperture in a Full Scale Enclosed Space

Convective heat transfer through a large aperture has been studied theoretically and experimentally using reduced scale models for many years. This paper describes the effect of the width of a large opening on the convective heat flow in an enclosure for 5.6×108&lt; Rayleigh number (Ra)&lt;2.8×1010. In our case a full scale realistic calorimetric chamber (5.5m x 2.5m x 2.5m) was used in this study. This chamber contains two zones connected by a large aperture of height H. A hot and cold wall on each side of the aperture will create a temperature difference between the two zones. Empirical equations are expressed in terms of varying door aspect ratio ADS, i.e.: NuPr=(α+βWH)∗Grb, at various temperature differences between the two zones. It was clearly found that as the width decreases the convective flux increases substantially. The instability of the air flow due to the apparition of a small turbulence increased when the opening width gets larger. It was also noticed that the neutral axis (air velocity = 0) goes up when the width of the opening decreases resulting in an acceleration of the air flow above the neutral axis. The liability of these experimental results could be useful for the validation of simulation models.

Degree of coronal alignment correction can\u2019t predict knee function in total knee replacement

BackgroundWhether neutral alignment brings better clinical outcomes is controversial. Consideration of the preoperative knee condition of patients and some limitations of previous studies, we suggested that other index may be more important than a generic target of 0° ± 3° of a neutral axis to reflect changes in coronal alignment after total knee replacement (TKR). The purpose of this study was to explore the relationship between alignment and functional outcome with a new grouping method and the concept of correction rate.MethodsThe study included 358 knees, the mean follow-up period was 3.62 years. A new grouping method was adopted to divide patients into three groups based on the degree of correction of mechanical femoral—tibial angle (MFTA): under-correction (n = 128), neutral (n = 209) and over-correction (n = 21). Hospital for Special Surgery (HSS) score were compared among the 3 groups (ANOVA with or without LSD t-test). In addition, we also attempt to further explore whether the concept of correction rate can predict postoperative functional score (Simple linear correlation analysis).ResultsHSS score showed significant improvement in all groups. There was no difference in HSS score (88.27 vs 88 vs 85.62) (p = 0.88) or incremental scores (26.23 vs 25.22 vs 22.88) (p = 0.25) based on the postoperative alignment category for the degree of correction of MFTA at the last follow-up. The correlational analyses also didn’t show any positive results (r = -0.01 p = 0.95, r = -0.01 p = 0.97, r = 0.11 p = 0.15, r = 0.01 p = 0.90).ConclusionCategorization of optimal coronal alignment after TKR may be impractical. But we still believe that the concept of correction rate and new grouping method are worthy of research which can reflects the preoperative knee condition and the change of coronal alignment. Perhaps it can be better used in TKR in the future.Level of evidence: III.

Modal reduction-based finite element method for nonlinear FG piezoelectric energy harvesters

In this study, harvesting energy from a nonlinear functionally graded (FG) piezoelectric cantilever beam under harmonic excitation is investigated. The material properties of the piezoelectric are assumed to be a combination of piezo-ceramic and piezo-polymer materials for high performance and flexibility. The neutral axis is obtained in order to eliminate bending–stretching coupling. The geometrical nonlinearity and electromechanical coupling are incorporated in the coupled nonlinear equations that are derived using the generalized Hamilton’s principle and solved using the combination of modal reduction and finite element methods. The shooting method is employed to obtain steady-state periodic response of an FG nonlinear harvester with appropriate initial conditions. Also it is shown that at least two-mode approximation is required for accurate estimation of nonlinear response and harvested power. Using the method of nonlinear modal reduction, the unstable branches for frequency domain solution are estimated and the computational time is reduced considerably compared to full finite element method. A case study is also accomplished in detail to analyze the effects of base amplitude values and material distribution on harvested power and bandwidth.

Longitudinal Equivalent Flexural Stiffness of Rectangular Pipe-jacking Tunnel in Integrated Pipe Gallery

The rectangular pipe-jacking tunnel (RPJT) has a high section utilization ratio and is one of the primary forms of urban integrated pipe gallery (IPG) at present. This kind of tunnel will produce uneven longitudinal displacement under adjacent construction. Longitudinal bending stiffness is the crucial parameter to analyse its longitudinal stress characteristics. Combined with the structural elements of RPJT, the calculation models of the longitudinal bending stiffness of RPJT with round corners was put forward. The influence of longitudinal bolt number, ring width, and segment thickness on the neutral axis position and the longitudinal equivalent stiffness (LES) efficiency was further analysed. The influence of bending moment on the opening angle of the inter-ring joint was also analysed. The results show that increasing the number of longitudinal bolts, width of segment ring, and thickness of segment are beneficial to enhancing the LES efficiency and promoting the upward shift of the neutral axis. In addition, an increase of bending moment leads to the increase in the opening of the inter-ring joint, which is not conducive to structure safety. The research results can provide theoretical support for the structural design and longitudinal safety analysis of RPJT.

Improved barrier and mechanical properties of Al2O3/acrylic laminates using rugged fluorocarbon layers for flexible encapsulation

Thin film encapsulation (TFE) with high barrier performance and mechanical reliability is essential and challenging for flexible organic light-emitting diodes (OLEDs). In this work, SF 6 plasma treatments were introduced for surface modifications of acrylic in Al 2 O 3 /acrylic laminates fabricated by atomic layer deposition (ALD) and ink-jet printing (IJP). It was found that micro-/nano-structures and surface fluoridation appeared on the surface of acrylic, and could be modulated by the discharge power and irradiation of plasma treatment. The water vapor transmission rates (WVTR) of Al 2 O 3 /acrylic multi-layers decreased evidently because of reducing surface polarity and strong cross-link of acrylic after plasma treatments. Furthermore, the rugged surface and relieved residual stress resulted from etching and heating of acrylic could enhance the mechanical property remarkably. The plasma treated Al 2 O 3 /acrylic multi-layers with only 3 dyads exhibited a low WVTR value of 1.02 × 10 −6 g/m 2 /day and more stable mechanical property under 200 iterations blending test by comparative measurements, proving that the introduction of SF 6 plasma surface modifications could improve simultaneously the barrier performance and mechanical reliability prominently of the inorganic/organic multi-layers with no need of extra neutral axis design. • SF 6 plasma treatment was introduced for the interface modification of Al 2 O 3 /acrylic multilayers. • Micro-/nano-structures and surface fluoridation appeared on acrylic surface after SF 6 plasma treatment. • The barrier performance of Al 2 O 3 /acrylic multilayers can be improved remarkably by SF 6 plasma treatment. • The mechanical reliability of Al 2 O 3 /acrylic multilayers can be enhanced evidently by SF 6 plasma treatment.

The Threshold for Under-Reinforced Concrete Sections Proposed by ACI 318, EC 2 and BS 8110

The ductile behavior of reinforced concrete (RC) cross-sections has always been desirable for building codes and standards. However, the threshold to distinguish ductile and brittle behavior of RC cross-sections proposed by building codes has yet to be evaluated [1-4]. This behavior mainly depends on the type of RC cross-section whether it is under- or over-reinforced. While there is not much research conducted on general comparison of the three codes of ACI 318-19, BS 8110 and Eurocode 2 (EC2) regarding design and analysis of RC structural elements, the specific detailed investigation on the threshold for under- and over-reinforced RC cross-sections has yet to be conducted. This article aims to determine the most accurate threshold used to distinguish under- and over-reinforced RC cross-sections amongst the three aforesaid codes by scrutinizing fundamentals and assumptions. A RC cross-section with strain distribution diagram over the section for the three statuses of under-reinforced, balanced, and over-reinforced cross-section is discussed in this research. A theoretical approach is adopted to compare the threshold through the depth of neutral axis of balanced steel concrete cross-sections. The method of calculation is associated with the maximum tensile strain of longitudinal steel bars at the cross-section. The depth of neutral axis is considered to be equal to effective depth of the cross-section multiple by a coefficient. This coefficient is the focus of the comparison. The coefficient is directly given as a number by BS 8110 and EC2. In ACI 318-19 there is no direct value given for the threshold, which leaves no choice other than the accurate calculation of depth of neutral axis for the balanced reinforcement which is in form of an equation. The article concludes that ACI 318-19 provides the most accurate threshold to classify under- and over-reinforced RC cross-sections while EC2 provides the least accurate threshold. The accuracy of threshold proposed by BS 8110 is between those of ACI318-19 and EC2. The scope of this research is confined to singly- and doubly-reinforced concrete cross-sections with any shape using ordinary concrete.

Maintaining the Neutral Axis in the Treatment of Distal Femur Fractures Via Dual Plate or Nail Plate Combination Technique: When and How?

Distal femur fractures in the elderly have been historically treated with locked plating or retrograde intramedullary nailing with good, reliable results. However, in certain more complex fracture patterns (native or periprosthetic), increased density of fixation via dual-plate or nail plate combination can help achieve immediate weight-bearing. It can also potentially increase rates of union by shifting and maintaining the neutral axis, distributing forces more evenly across the fracture site. Here, we discuss the indications, pros and cons of both dual-plate and nail plate combination techniques in a concise case-based format.

Feasibility assessment of bulk density property of carbon nano tube as a viable alternative to reinforcement steel in construction projects

Carbon nanotubes are fibrous and porous materials prepared using standard test procedures of concrete. This research paper investigates the effect of three different bulk densities of multi-walled carbon nanotubes (MWCNTs) used in concrete. The results show that the specimens with lower range bulk density (0.04–0.06 g/cc) have better dispersion, mechanical and durability properties than higher range bulk densities. It is noteworthy that, during flexural beam test, MWCNTs are placed only at the bottom one-third of the specimen below the neutral axis, where most of the tensile region exists, without any joints. Flexural beam test results show that higher strength up to 9.62 MPa is obtained. The compression test reveals that higher strength possibly due to the reduced surface area of addition of bigger size coarse aggregates. A comparative of cost analysis with conventional steel rods is presented. Improvement in the ratio of flexural strength to compressive strength in respect of concrete is not as substantial as in mortar.

Clamped-end effect on static detection signals of DNA-microcantilever

Boundary constraint induced inhomogeneous effects are important for mechanical responses of nano/micro-devices. For microcantilever sensors, the clamped-end constraint induced inhomogeneous effect of static deformation, so called the clamped-end effect, has great influence on the detection signals. This paper is devoted to developing an alternative mechanical model to characterize the clamped-end effect on the static detection signals of the DNA-microcantilever. Different from the previous concentrated load models, the DNA adsorption is taken as an equivalent uniformly distributed tangential load on the substrate upper surface, which exactly satisfies the zero force boundary condition at the free-end. Thereout, a variable coefficient differential governing equation describing the non-uniform deformation of the DNA-microcantilever induced by the clamped-end constraint is established by using the principle of minimum potential energy. By reducing the order of the governing equation, the analytical solutions of the curvature distribution and static bending deflection are obtained. By comparing with the previous approximate surface stress models, the clamped-end effect on the static deflection signals is discussed, and the importance of the neutral axis shift effect is also illustrated for the asymmetric laminated microcantilever.

Flexible PDMS/Al2O3 Nanolaminates for the Encapsulation of Blue OLEDs

AbstractIn this work, the polydimethylsiloxane (PDMS)/Al2O3 nanolaminates with optimized sublayer thickness and interfaces have been developed to protect the organic light‐emitting didoes (OLEDs) from the erosion of the moisture in the ambient. The O2 plasma pretreatment is used to tune the wettability of the ultrathin PDMS sublayers with nanoscale thickness, and the distinct interfaces between the Al2O3 and PDMS sublayers are obtained. The electrical calcium test is exploited to evaluate the barrier properties of the encapsulation nanolayers, and the water vapor transmission rate (WVTR) value of the 2.5 PDMS/Al2O3 dyads can reach the range of ≈10−5 g m−2 day−1. The mechanical stability of the nanolaminates is further improved by introducing the top epoxy layer, which helps move the neutral axis (NA) to the center of the barrier, and the applied external strain decreases significantly. Compared with the sample without the epoxy layer, a slighter increase of the WVTR value of the multilayered encapsulation films with optimized NA position is obtained. Furthermore, the operational lifetime of blue OLEDs encapsulated with the multilayered encapsulation films improves from 6 to more than 370 h, which shows significantly improved stability and reliability.