Transverse Rigidity Research Articles

Successful Tracheal Replacement in Humans Using Autologous Tissues: An 8-Year Experience

Fifty years of surgical research using synthetic materials and heterologous tissues failed tofind a good, durable replacement for the trachea. We investigated autologous tracheal substitution (ATS) without synthetic material or immunosuppression. For ATS, we used a single-stage operation to construct a tube from a forearm free fasciocutaneous flap vascularized by radial vessels that was reanastomosed to internal mammary vessels and reinforced by rib cartilages interposed transversally in the subcutaneous tissue. Tracheal resections 7 to 12 cm long (mean, 11 cm) were done to treat 8 primary tracheal neoplasms, including 5adenoid cystic carcinomas (ACC) and 3 squamous cell carcinomas (SCC); 3secondary tracheal neoplasms, including 1 thyroid carcinomas and 2 lymphomas; and 1postintubation tracheal destruction after a long history of stenting. Transitory tracheotomy was associated to the absence of mucociliary clearance. ATS has been performed in 12 patients since 2004, with additional resections in 4 patients, comprising 1 carinal resection alone, 1 associated with lobectomy, and 2 pharyngolaryngectomies. All patients were extubated on postoperative day 1. Eight patients are alive at a mean of 36 months (range, 2 to 94 months) postoperatively, with no respiratory distress. The 2 patients with ATS and carinal resections died of pulmonary infection. No airway collapse has been detected by endoscopy, dynamic computed tomography scan, or spirometry. Two patients still have a tracheotomy because the procedure was performed too low at the level of the proximal anastomosis. One patient with a chronic severe respiratory insufficiency recently required a distal, short stent. ATS is a good, durable, tracheal substitutionthat resists respiratory pressure variationsbecause of transverse rigidity, without any immunosuppression.

Autologous tracheal replacement: From research to clinical practice

Despite numerous attempts, synthetic materials and heterologous tissues failed to replace durably the trachea. Autologous tracheal substitution (ATS) without synthetic material or immunosuppression was investigated to replace extended tracheal defect. We present our experience regards to this innovative challenge. After a previous research study, we developed a novel reconstruction technique for extended tracheal defects on animals. Through a single stage operation, a tube from a forearm free fascio-cutaneous flap vascularized by radial vessels is re-anastomosed to cervical vessels. This flap is reinforced by rib cartilages interposed transversally in the subcutaneous tissue. It provides also a reliable ATS. Twelve patients benefits from an extended tracheal resections, 7-12 centimeter (mean 11 cm) long. Indications were eight Primary tracheal Neoplasms (including 5 adenoid cystic carcinoma [ACC] and 3 squamous cell carcinoma [SCC]), three secondary tracheal neoplasms (including 1 thyroid carcinoma and 2 lymphoma) and one post-intubation tracheal destruction after long history of stenting. Daily bronchoscopy and transitory tracheotomy was associated due to absence of mucociliary clearance. The research work leads to present the first described animal model for tracheal resection and replacement with an autologous conduit. It was constructed from costal cartilages and a pediculed cervical skin flap. From 2004 to 2012, 12 patients have had ATS with associated resections in four cases. All patients were extubated on the first postoperative days; eight patients are alive at 2 to 94 months (mean=36) postoperatively, with no respiratory distress. The two patients with ATS after resection extended to the carina died due to pulmonary infection. No airway collapse has been detectable, either by endoscopy, dynamic CT scan or spirometry. Two patients still have a tracheotomy because performed too low at the level of the proximal anastomosis. One patient with a chronic severe respiratory insufficiency required recently a distal and short stent. ATS is actually a good, durable tracheal substitute that can resist respiratory pressure variations because of their transverse rigidity without any immunosuppression. The limits of this technique are probably, chronic respiratory insufficiency and cartilage calcifications. Research to develop a method for lining the neo-trachea with ciliated respiratory epithelium is needed.

Love waves in the fiber-reinforced layer over a gravitating porous half-space

This paper aims to study the propagation of Love waves in fiber-reinforced layer lying over a gravitating anisotropic porous half-space. The closed form of dispersion equation has been derived for the Love waves in terms of Whittaker function and its derivative, which are further expanded asymptotically, retaining the terms up to second degree. The frequency equation shows that the transverse and longitudinal rigidity of reinforced material, as well as gravity and porosity of the porous halfspace have significant effect on the propagation of Love waves. The study reveals that the increment in width of reinforced layer decreases the phase velocity. For a particular width of the reinforced layer, it is also observed that the phase velocity increases with increasing porosity of the half-space, but it decreases with increasing gravity.

OVERVIEW OF RECENT STUDIES AT IPST ON CORRUGATED BOARD EDGE COMPRESSION STRENGTH: TESTING METHODS AND EFFECTS OF INTERFLUTE BUCKLING

Several recent series of investigations were conducted on corrugated board performance in the areas of: loaded container endurance in cyclic humidity, predictive models for edge compression strength (ECT), effects of lightweight facings, measurement of transverse shear rigidity, effects of adhesive level, and out-of-plane crushing on ECT. The course of this program prompted exploration and review of several aspects of ECT testing methods: specimen height, test duration, and fixture-clamping effects. In this review, ECT values are shown to be influenced by the combination of the selected testing technique with the specific structural and strength characteristics of the board being tested. The effect of specimen height on selected single wall C-, E-, F-, and N-flute boards is measured and rationalized using a simplified beam-theory approach. Apparent loss of ECT in a C-flute crushed board is explored to determine whether mitigation is possible by selection or modification of testing method. Investigations of platen speed effects on C-flute substantiate previous work. Lightweight facings on A- and C-flute corrugated boards are observed to display localized buckling, which affects the ECT value. An analytical model that combines the measured bending stiffness of the facings and the compression strengths of the fluting and facings provides an improved predictive accuracy and is applied to a series of laboratory and commercial corrugated boards.

Cell wall structure and formation of maturing fibres of moso bamboo (Phyllostachys pubescens) increase buckling resistance.

The mechanical stability of the culms of monocotyledonous bamboos is highly attributed to the proper embedding of the stiff fibre caps of the vascular bundles into the soft parenchymatous matrix. Owing to lack of a vascular cambium, bamboos show no secondary thickening growth that impedes geometrical adaptations to mechanical loads and increases the necessity of structural optimization at the material level. Here, we investigate the fine structure and mechanical properties of fibres within a maturing vascular bundle of moso bamboo, Phyllostachys pubescens, with a high spatial resolution. The fibre cell walls were found to show almost axially oriented cellulose fibrils, and the stiffness and hardness of the central part of the cell wall remained basically consistent for the fibres at different regions across the fibre cap. A stiffness gradient across the fibre cap is developed by differential cell wall thickening which affects tissue density and thereby axial tissue stiffness in the different regions of the cap. The almost axially oriented cellulose fibrils in the fibre walls maximize the longitudinal elastic modulus of the fibres and their lignification increases the transverse rigidity. This is interpreted as a structural and mechanical optimization that contributes to the high buckling resistance of the slender bamboo culms.

Dynamic analysis of a bridge repaired by CFRP: Experimental and numerical modelling

A significant number of existing reinforced-concrete bridges all over the world require maintenance and repair. Hence, the need for a rapid evaluation procedure for the diagnosis of existing bridges. This paper presents the application of a dynamic analysis methodology for structural evaluation of reinforced-concrete bridges. The methodology is based on the application of ambient vibrations non-destructive testing method and the identification of the structure total response using finite element method. A case study of a three span reinforced concrete bridge in a strong seismic activity area in the north of Algeria is analysed. The ambient vibration testing was carried out on the bridge, before and after its repair by the application of carbon fibre composites. The tests were conducted using an acquisition system made up of four accelerometers with three components placed at specific locations on the bridge. The finite element model gave comparable results to the experimental ambient vibrations tests. The modal parameters of the bridge before and after repair were identified by this in situ testing. The application of composite material to strengthen the structure increases the transverse rigidity of the structure and thus its modal frequency.

The peacock's train (Pavo cristatus and Pavo cristatus mut. alba) I. structure, mechanics, and chemistry of the tail feather coverts

The feathers in the train of the peacock serve not for flying but for sexual display. They are long, slender beams loaded in bending by their own weight. An outer circular conical shell, the cortex, is filled by a closed foam of 7.6% relative density, the medulla, both of feather keratin. Outer diameter and thickness of the cortex decrease linearly from the body toward the tip. This self-similar geometry leads to a division of labor. The cortex (longitudinal Young's modulus 3.3 GPa, transverse modulus 1 GPa) provides 96% of the longitudinal strength and bending rigidity of the feather. The medulla (Young's modulus 10 MPa) provides 96% of the transverse compressive rigidity. Fracture stress of the cortex, both longitudinal and transverse, is 120 MPa.

Comfort and handle related properties of P/V blended air-jet textured yarn fabrics

The effect of blend percentage on comfort and handle related properties of fabrics made from polyester/viscose blended air-jet textured yarn weft were studied and the results were compared with fabrics made from polyester/viscose ring-spun yarn wefts of similar linear densities. It is observed that with increase in polyester content in the blend, the air permeability and water vapour permeability reduces whereas thermal resistance, transverse wicking and shear rigidity increases both in ring-spun yarn and textured yarn fabrics and bending rigidity increases in textured yarn fabrics. Textured yarn fabrics exhibit lower air permeability and extensibility, higher thermal resistance, relative water vapour permeability, transverse wicking values and bending rigidity as compared to the ring-spun yarn fabrics.

On transverse rigidity for singular foliations in (ℂ2,0)

On transverse rigidity for singular foliations in (ℂ2,0)

MECHANISM AND ENERGY RANDOM ANALYSIS OF TRAIN DERAILMENT ON RAILWAY BRIDGES

In this paper, the mechanism of train derailment on bridge is developed by applying the system dynamics stability concepts. The theory of energy random analysis for train derailment on bridge is put forward. The contents of the theory are as follows: (1) establishing vibration equation set for the train–bridge system; (2) determining exciting source of transverse vibration of the system; (3) method of energy random analysis of transverse vibration of the system; (4) geometric rules of derailment; (5) calculation of the whole process of train derailment on bridge; (6) criteria of energy increment for judging train derailment on bridge. Finally, three cases concerning train derailment on bridges are treated that coincide with actual conditions. Some main conclusions obtained are: (1) insufficient transversal rigidity of bridge is the reason causing train derailment on bridge and (2) enhancing transversal rigidity of bridge is the main preventive measure against train derailment on bridge.

Evaluation of the Structural Properties of Single-Walled Carbon Nanotubes Using a Dynamic Continuum Modeling Method

The structural properties of single-walled carbon nanotubes (SWCNTs) are evaluated by a new continuum modeling method, called the dynamic continuum modeling method (DCMM). In the DCMM, a repeating cell unit isolated from a SWCNT is represented as an equivalent continuum beam element by using the energy equivalence principle. The method may allow us to accomplish the static or dynamic analysis for SWCNTs without needing to assume their wall thickness. The structural rigidities of armchair SWCNTs evaluated by using the DCMM are within the range predicted by using the Young's moduli reported in existing references. It is also found that SWCNTs have quite high transverse shear rigidity, but with negligible coupling rigidities.

General method of analysis for composite beams with longitudinal and transverse partial interaction

This paper presents an analytical formulation for the analysis of two-layered composite beams with longitudinal and vertical partial interaction. The particularity of this model is its ability to incorporate an interface connection deforming both longitudinally, i.e., along the beam length, and vertically, i.e., transverse to the connection interface, which is modelled by means of a uniformly distributed spring. The novel formulation is based on the principle of virtual work expressed in terms of the displacement field consisting of the vertical and axial displacements of the two layers; for completeness, the proposed model is presented in both its weak and strong forms. The partial interaction problem is then solved by means of the finite element method. A parametric study is presented to investigate the effects of different combinations of longitudinal and transverse connection rigidities on the overall structural response. For the purpose of these simulations, a bi-linear constitutive model has been specified for the transverse interface connection to reflect the more realistic case in which two different responses are observed in the transverse interaction, one in which one layer is bearing against the other one, one when the two layers are separating. An iterative procedure has been proposed to obtain the convergence to the final solution.

Effects of the diaphragm at midspan on static and dynamic behaviour of composite railway bridge: A case study

This study focuses on composite multi-girder railway bridges of moderate span for high-speed trains. In this type of bridge the concrete deck is the primary element of transverse rigidity, so the real impact of cross beams is unknown. These cross beams increase the cost of this type of bridge, because they require handling and welding on site. This research studies the impact of a diaphragm in a typical multi-girder railway bridge used in France. The first objective is to develop appropriate modelling techniques that can be used to evaluate the function and effectiveness of a diaphragm in the transverse distribution of traffic loads. The second objective is to know if a diaphragm is really necessary. To answer this question, a three-dimensional model and nonlinear material constitutive equations are considered. Different static loading conditions (self-weight, UIC load, and TGV) are studied and the bridge deck responses to them with and without transverse diaphragm are analyzed. The TGV is modelled with moving loads in order to take into account the dynamic behaviour of the bridge deck. Several critical speeds of train corresponding to natural frequencies are then studied in dynamic analysis. Our static and dynamic analyses concluded that the diaphragm does not seem to be necessary, except for an accidental lateral load. Therefore, it may be possible to not install diaphragms on these bridges.

Análise não-linear inelástica de edifícios

Esse trabalho apresenta uma investigação original, ao estudar o comportamento estrutural de edifícios de múltiplos andares, através de um modelo de análise não-linear inelástica. Emprega-se a teoria geometricamente exata para cascas inicialmente planas em regime elástico não-linear e para barras no espaço tridimensional em regime elasto-plástico em carregamento monotônico modelado por elasticidade não-linear. Considera-se a influência da rigidez transversal da laje de concreto fundido no local como material homogêneo.Diferentes estruturas de edifícios são analisadas e com o auxílio do GID, versão 7, o comportamento estrutural dos edifícios pode ser observado através de diversas figuras. Os exemplos numéricos demonstram a robustez, precisão e eficiência do método e do programa computacional empregados.

Buckling Texturing Technology for Increase in Stability of Thin Sheet Metal Structures – Simulation and Application

Embossing is a well known method to improve the transverse rigidity of thin sheet metal plates. This paper deals with a special embossing method where bulges get embossed into the surface of a cranked workpiece by hydrostatic pressure. The base for describing the production process is the elementary bulge structuring process at which a bionic bulge pattern gets embossed into the surface of a cylindrical shell. This structure enables highest amount of stiffness. By FEMsimulations the main process parameters and the optimal dimensions of the bulges are ascertained. The identified bulge geometry is the base for the design of the structuring tool. In industrial applications the structuring process will be a rolling process with an elastomere coated pressure roll, followed by a rebending operation. The simulation of this complex process demands an analogous model based on a half shell, which is virtually straightened. Then the bending resistance of a so achieved bulge structured plate is calculated under a three-point-bending load. Using the same computing procedure a realistic automotive body part is investigated. The whole process combines CAD & FEM techniques in a new and efficient way.

Vibration analysis of a stepped laminated composite Timoshenko beam

The goal of this study is to investigate the vibration characteristics of a stepped laminated composite Timoshenko beam. Based on the first order shear deformation theory, flexural rigidity and transverse shearing rigidity of a laminated beam are determined. In order to account for the effect of shear deformation and rotary inertia of the stepped beam, Timoshenko beam theory is then used to deduce the frequency function. Graphs of the natural frequencies and mode shapes of a T300/970 laminated stepped beam are given, in order to illustrate the influence of step location parameter exerts on the dynamic behavior of the beam.

Dipole–Dipole Interactions in Microtubules

Dimers in microtubules possess a dipole moment with components along three axes. The interaction energy among all dipole components in a microtubule was calculated for an un-deformed and an elliptically deformed microtubule in a "dry" condition. The interaction energy was found to increase with deformation. The total interaction energy among all dipoles is positive, which implies that the un-deformed cylindrical shape of a microtubule represents a condition of minimum energy. This suggests that the cylindrical shape of microtubules is a consequence of dipole-dipole interactions. There may be other causes as well but these are not discussed in this paper. From these results, the contributions of the dipole-dipole interaction energy to the microtubule longitudinal and transverse flexural rigidities were calculated. It is shown that the longitudinal contribution to the elastic modulus is approximately 50-60% of the total measured value while the calculated transverse contribution is smaller than the longitudinal contribution by a factor of approximately 3. The ratio of the measured axial to the measured transverse flexural rigidity is approximately 125, in agreement with recent observations. However, these values are uncertain for reasons discussed in the text.

Influence of geometrical parameters on the flexural rigidity of the LHC dipole cold mass assembly

In order to predict the mechanical behavior of the LHC dipole cold mass in situations such as handling, transport and cool down, a number of important structural parameters are required. The dipole's flexural rigidity determines entirely the mechanical elastic behavior of the cold mass. Therefore, models of a bent cold mass were created to calculate its rigidity. This paper presents a simplified parametric finite element model, created to study the deflection of the cold mass in different situations and supporting conditions. The sensitivity of the models to the supporting conditions is computed. To provide the finite element and the analytical models with input, the deflection of the cold mass under discrete loads in normal condition and then 90-degrees rotated were measured with a laser tracker. By comparing models with measurements, the vertical and transversal rigidity of the cold mass assembly are determined. Additionally, the paper reports on the plastic behavior of the cold mass assembly in the range of the deformations that are needed to correct cold masses that result, after final welding of the outer skin, with unacceptable sagitta.

Flexural and Torsional Properties of Pultruded Fiber Reinforced Plastic I-Profiles

Experimental determination of the full section flexural and torsional properties of pultruded fiber reinforced plastic I-profiles is described. Based on beam theory approximations, test configurations for determining the various section properties are established. Tests were conducted on three different I-profiles with a range of span-to-depth ratios. Major and minor axis flexural rigidities and flexural moduli, determined from three- and four-point bending tests, show close correlation. Major and minor axis transverse shear rigidities and shear moduli show significant variation, due to differing effective areas of the cross section resisting transverse shear and differing fiber content and orientation in the web and flanges. St. Venant torsional shear moduli, determined from uniform torsion tests, are consistent but significantly greater than the transverse shear moduli, which may be due to variations in fiber content, orientation, and lay up. Warping torsional rigidities, determined from nonuniform tors...

High-Order Analysis of Unidirectional Sandwich Panels with Flat and Generally Curved Faces and a “Soft” Core

The bending behavior of a unidirectional sandwich panel with flat and generally curved faces and a flexible core in the vertical direction is investigated. The studied panels consist of an upper flat face sheet, a core of variable thickness, and a lower face sheet that can take any geometrical layout described by an analytical function. The core is assumed a two-dimensional elastic medium with shear and transverse vertical rigidities only, and the face sheets are considered as membrane and bending members made of metallic or composite materials. The term unidirectional refers here either to a beam (narrow panel) or to a wide beam (panel) undergoing a cylindrical bending. The field equations and the boundary conditions are derived via the variational principle of the virtual work and transformed from the local polar coordinate system of the curved face into the global Cartesian one. Higher order effects due to flexibility of the core in the form of nonlinear deformation fields are incorporated in the proposed analysis as a result of the closed-form solution of the field equations and are not postulated a priori. Numerical results in terms of deformations, stresses, and stress resultants are presented for some typical cases of flat-curved panels. The effect of a wide range of layouts, various boundary conditions, and the influence of manufacturing imperfections in the form of initially wrinkled face are investigated. The results demonstrate the capabilities and generality of the proposed model and present its ability to predict the high-order localized effects that characterize such panels.