Strip Model Research Articles

Finite strip large deflection and post-overall-buckling analysis of diaphragm-supported plate structures

A semi-analytical finite strip method is described for the analysis of the overall, geometrically non-linear, elastic behaviour of diaphragm-supported prismatic plate structures which may be made of composite laminated material and may have initial geometric imperfections. Both the large-deflection problem and the post-overall-buckling (under progressive end shortening) problem are considered. Enhanced strain-displacement relationships are used in the development of the properties of a range of finite strip models, and particular attention is paid to the appropriate representation of the longitudinal displacement. The development is made in the contexts of both first-order shear deformation and classical plate theories. A description is given of a small number of applications, most of which concern blade-stiffened panels. A comparison is made between the predictions of the developed finite strip method and those of a commercial finite element package, and such comparison is shown to be close.

Forces and stresses in seam welded overlap joints derived from outer surface deformation

The forces and stresses at keyhole seam welds of overlap joints can be derived from the outer surface deformations of the joined plates. The theoretical procedure is based on the definition of the jointing face forces and eigenforces in the seam weld, on the relations between these forces, and the structural stresses in the plates and on a plate strip model for connecting the measured surface deformations with the structural stress state. Relations between forces and stresses are also given which avoid the measurement of curvature. Unequal thickness of the plates and dissimilar materials are taken into account. A finite gap width is included. The tensile shear specimen is treated as an example.

Elastic local buckling of steel plates in composite steel-concrete members

A finite strip model for elastic local buckling is used to study the behaviour of steel plates in composite steel-concrete members. The accuracy of the numerical method is demonstrated by a comparison with solutions in the literature. Buckling of the steel skin is then considered, and width-to-thickness ratios suitable for design are suggested. The method is shown to be applicable to profiled composite slabs, profiled composite beams, profiled composite walls, composite steel-concrete columns and composite steel-concrete girders. A design example is given to show the applicability of the method.

Micellar‐Enhanced Ultrafiltration and Air Stripping for Surfactant‐Contaminant Separation and Surfactant Reuse

AbstractMicellar‐enhanced ultrafiltration (MELT) and air stripping were evaluated for surfactant‐contaminant separation and surfactant recovery. Two linear alkyl diphenyloxide disulfonate (DPDS) surfactants were evaluated with the contaminants naphthalene and trichloroethylene. A separation model developed from micellar partitioning principles showed a good correlation to batch MEUF studies, whereas flux analysis highlighted concentration polarization effects in relation to hydrophobe length. MEUF effectively concentrated the surfactant‐contaminant system (93 to 99 percent retention); however, this did not result in surfactant‐contaminant separation. Batch and continuous flow air stripping models were developed based upon air/water ratio, surfactant concentration, and Micellar partitioning; model predictions were validated by experimental data. Sensitivity analyses illustrated the decline in contaminant‐surfactant separation with increasing surfactant concentration (e.g., TCE removal efficiency declines from 83 percent to 37 percent as C‐16 DPDS concentration increases from 0 to 55 mM). This effect is greater for more hydrophobic contaminants (naphthalene vs. TCE) and surfactants with greater solubilization potential (C16‐DPDS vs. C‐12 DPDS). The resulting design equations can account for this effect and thus properly size air strippers to achieve the desired removal efficiency in the presence of surfactant micelles. Proper selection and design of surfactant‐contaminant separation and surfactant recovery systems are integral to optimizing surfactant‐enhanced subsurface remediation.

A Study on the Improvement of Prediction Accuracy for Rolling Force in Continuous Cold Rolling Mill

In the cold rolling mill, it is very important that a constrained static flow stress of rolled strip and rolling force calculation model be exactly considered to improve an prediction accuracy for rolling forces. Therefore, in this study, the values of the constrained static flow stress are used by deriving the regression equation which is a function of rolling conditions(FDT, CT) and chemical compositions(C, Si, Mn), previously applied by making the tables of yield strength for hot coils with size. And with the consideration that an elastic deformation part of an rolled strip appears at the entry and delivery side of the contacting area between the work roll and rolled strip is calculated. By applying these methods, the more accurate prediction for rolling force is obtained. As a results, the deviation of thickness is significantly reduced in the rolling direction.

Application of nonlinear finite strip technique to concrete deep beams

The salient features of an alternative version of the nonlinear finite strip method for analysing reinforced concrete elements is presented. Unlike the conventional finite strip models which can only handle structures whose geometry does not change in one direction, the newly developed finite strip model can analyse certain structures whose geometry (although still fairly simple) can change along their length such as deep beams with local changes of crosssection along their span(s). Moreover, unlike the conventional finite strip models, the new alternative model has the desirable feature of being able to incorporate any desired boundary conditions and different number of harmonics in various strips with minimal effort. Although the proposed model may, in certain cases, suffer when compared with the conventional alternatives, from the potential drawback of an increased number of strips with associated increases in computer storage, the present model needs many less displacement parameters at each nodal line because of the often substantially shorter lengths of the finite strips (cf. conventional strips) and, hence, needs a much narrower half-bandwidth (HBW) in the stiffness matrix with obvious savings in the subsequent computer running time. Very encouraging correlations have been found between predictions based on the present model and some recently reported test data on deep beams: these include continuous RC deep beams with changes of cross-sections over the supports and also simply supported RC deep beams covering a wide range of design parameters. In addition, the present method has been used to analyse data from a series of tests on RC deep beams with fixed-fixed boundary conditions. The numerical results for deep beams with fixed-fixed boundary conditions based on the present model provide a desirable double check on the validity of a recently reported, largely hand-based, method and should be valuable in identifying the areas in which further work may be required.

Refined three-dimensional finite strip model for analysis of thick composite sandwich plates

A refined three-dimensional finite strip model for stress analysis of thick hybrid composite sandwich plates is presented in the present article. The new model is based on a combination of two different strip elements: quadratic linear skin strip (QLSS), and modified quadratic cubic core strip (MQCCS). The applications of the proposed model for sandwich plates containing a local damage under membrane or bending loading are illustrated. Numerical results are compared to independent solutions and measured data and found to be in excellent agreement. A comprehensive discussion of the numerical aspects of the method is conducted to test the strips' characteristics regarding the spectral accuracy, finite element convergence and accuracy of numerical integrations.

AC losses in high T/sub c/ superconductors

The losses in high T/sub c/ superconductors do not differ in principle from those in low T/sub c/ materials, and the same calculations can be used. However it is necessary to allow for the granularity of the materials and the high aspect ratio of the conductors. This paper derives simple, if approximate, expressions for calculating the losses in the most important cases for practical purposes. These are the use of BSCCO tapes in magnets and cables at power frequencies. The predictions of elliptical and thin strip models are compared and it is found that an elliptical geometry agrees best with the experimental results. It is also found that the voltage measured in a transport measurement depends on the position of the contacts and that if an unambiguous loss measurement is required it is necessary to include the flux outside the sample in the voltage measurement loop.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Geometrically nonlinear behaviour or spot welded joints in tensile and compressive shear loading

The geometrically nonlinear behaviour of spot welded joints including buckling and gap closure and its influence on local stress parameters at the weld spot edge (structural stresses, notch stress or fatigue notch factor, stress intensity factors) are determined by a large displacement analysis of the tensile shear specimen subjected to tensile and compressive loading. The local parameters mentioned are considered decisive for fatigue crack initiation. A continuous beam model and a plate strip model are used within a simplified procedure. A more sophisticated finite element model is applied on the specimens thereafter. The nonlinear effect is small for steel plates more than 1 mm thick in the medium and high cycle fatigue range of tensile loading. It may be stronger for compressive loading but is at least partially compensated for in this case by the gap closure effect.

Fracture initiation outside the slit tip

Fracture initiation outside the slit tip is predicted using the Erdogan-Sih tangential stress criterion in the case of the double strip model subjected to counter-bending moments, whereas the Neuber hypothesis fails in the considered case.

Vibration of annular sector mindlin plates by the spline strip method

This paper presents the vibration of annular sectorial plates with two opposite radial edges simply supported using the spline strip method based on the Mindlin plate theory. To demonstrate the convergence and accuracy of the present method, several examples are solved, and the results are compared with those obtained by other numerical methods. Stable convergence and good accuracy are obtained using the high-order spline strip models. Accurate frequencies of annular sector Mindlin plates with different sector angles, radii ratios and boundary conditions along the circumferential edges are shown in tabular form.

Repeated tape stripping of normal skin: a histological assessment and comparison with events seen in psoriasis.

The aim of the present study was to investigate the response of normal human skin to repeated courses of Sellotape stripping. The skin of healthy volunteers was stripped five times at 24-h intervals. Skin biopsies were taken before stripping (day 0) and on days 2, 4, 7 and 10. The responses were studied using H & E staining and an immunohistochemical analysis of several aspects of epidermal proliferation and keratinization. Although increased proliferation (nuclear binding to Ki-67 binding), acanthosis and parakeratosis were observed, the overall histological picture did not resemble psoriatic histology completely: no micropustules of Kogoj and no thinning of the suprapapillary plate were observed. Involucrin staining followed the recruitment of cycling epidermal cells showing a statistically significant elevation of positive cell layers from day 2 onwards. Filaggrin expression showed an increase from day 2 onwards, which was statistically significant on day 7 and day 10. Using the anti-keratin antibodies KS8.12 (K13 and K16) and RKSE60 (K10) we observed a fast induction of K13/K16 expression, while the staining of keratin 10 showed the same overall intensity at different time intervals. In conclusion, the response to repeated courses of tape stripping provides an adequate model for studies on epidermal proliferation, hypergranulosis and hyperkeratosis. This approach causes a more prolonged induction of these phenomena than a single course of stripping. In contrast to the situation following a single course of stripping, repeated tape stripping induced the expression of filagrin. Therefore the repeated tape stripping model is less compatible with psoriasis than a single course of stripping.

Destructive Testing of Decommissioned Concrete Slab Bridge

A destructive test was conducted on a decommissioned skew RC slab bridge. This bridge had severely deteriorated shoulder regions, where the top mat reinforcing bars were exposed. The test bridge was loaded using hydraulic cylinders arranged so as to simulate an HS‐20‐44 truck entering the bridge in one lane. The results indicate that the boundary conditions and the geometry of the bridge significantly influence bridge behavior. During the test, changes in the boundary conditions and yielding of the reinforcing bars caused the load path to shift twice. Failure of the slab occurred due to punching shear at a load of 3,200 kN (720 kips), equivalent to the axle load of 22 HS‐20‐44 trucks. Although the deterioration did not appear to affect flexural behavior, it did greatly reduce the punching‐shear capacity. Analysis indicates that simple modeling methods, such as strip models, overestimate structural demand and underestimate structural supply because they do not properly account for additional load‐carrying ...

On slip and memory rules in elastic, friction contact problems

An elastic strip model resting on a frictional plane is first considered in order to illustrate slip and memory rules in the uniaxial case. Next, the axisymmetric slip rules are discussed and referred to the case of slip of two spheres acted on by normal and tangential forces. Close connection to the multisurface hardening plasticity rules is indicated. Slip rules are derived for both proportional and non-proportional loading cases.

Unstiffened Strip Approach for Perforated Wall Studs

Local buckling behavior of cold‐formed steel wall studs with rectangular web perforations is investigated experimentally and analytically. Stub column tests on short sections not subject to overall buckling are examined. The unified effective width approach to local buckling presented in the 1986 Specification for the Design of Cold‐Formed Steel Structural Members of the American Iron and Steel Institute (AISI) is modified to model the perforated section. The web is idealized as two unstiffened elements extending the length of the member. In addition, the current AISI stub column‐based empirical approach and a “simplified” method used by some designers are examined. In the simplified approach, perforation effects are ignored unless the perforation is located in a portion of the web that is at least partially effective. Comparisons made between predictions of post‐buckling strengths using the unstiffened strip approach and the stub column test results show the unstiffened strip model to be a useful design methodology.

Transient response of plates to travelling loads with application to slamming damage

There is a considerable range of slamming loads on hull plating which cause either elastic response or elastic-plastic response where the plastic deformation is of the same order as the elastic deformation. Failure criteria for plate design can likely be from pulses causing this range of deformation. This paper summarizes the author's Master's thesis which gives a detailed analysis of the elastic response of hull plating to slamming pulses. A finite difference model of a plate strip is developed which accounts for membrane effects. The analysis shows detailed stress and deflection response to various pulses. The results of the elastic analysis give the combinations of typical pulses of 207–1380 K Pa peak pressures and decay times of 0.001–0.5 s leading to, but not exceeding, incipient yield at 276 and 414 MPa (40 000 and 60 000 psi) in various plate sizes. The plate strip concept is then extended to the elastic-plastic range. The model is made of two rigid sections with deformable hinges at the center and ends. These hinges are comprised of layers of bar elements with elastic—plastic characteristics. The results of this analysis give the permanent deflections from pulses of two—six times those which cause incipient yield. Unexpected resonances of 5–30% occur in the elastic—plastic range, not noted in the elastic range. While the slamming load is a pressure wave which propagates across a plate at some finite velocity, it is common in the analysis of hull plate slamming response to assume a spatially constant load. This paper gives justification for the approximation by analyzing the response to a travelling pressure front and specifies the criterion for which the approximation remains valid.

Contractility of the guinea pig bladder measured in situ and in vitro.

To study the relative importance of neurogenic factors in detrusor contractility and to relate a total bladder in vitro contractility model to a previously described bladder wall strip model, active intravesical pressure values were compared in situ and in vitro in eight male guinea pigs. In situ, the active pressure was measured in spontaneous isometric and non-isometric micturition contractions. In vitro, the active pressure was measured in isometric contractions of the same bladders, developed in response to optimal electrical stimulation. The volume dependence of the active pressure generated by the bladder was measured in vitro in order to relate bladder capacity to the volume where the generated force is maximal and to determine the optimal volume at which to study detrusor contractility. The results indicated that in normal micturition the detrusor muscle was not fully stimulated: active pressure in isometric contractions in vivo was about 60% of the pressure values attained in vitro at the same bladder volume. Most micturitions occurred at a volume where the active pressure generated in vitro was about 80% of the maximal pressure. The active pressure-bladder volume relationship complied with the sliding filament-cross bridge theory. In whole bladder preparations active stress was about twice as high as in strips.

Effect of Yaw Angle on the Vortex Induced Oscillation of a Rectangular Cylinder

The yaw angle effects of wind on the vortex induced oscillation of a rectangular cylinder (the width/depth ratio.B/D=2.5) was investigated by wind tunnel tests with two dimensional rigid model and taut strip model. Strong oscillations were observed under various yaw angles.The end conditions had little effect on the response and the Karman vortex in the wake seemed to have a different roll on the responses of models in normal incidence and in yaw angle.

Heuristic softening strip model in the prediction of crack trajectories

Materials such as concrete rocks and fiber-reinforced composites when extended exhibit strain-softening behavior. The softening is assumed to be localized in a narrow band, outside of which the material behaves linearly. Such a strip region is regarded as a process zone or an extended portion of the actual crack; it is damaged but can still transfer load. Assumed is a linear variation of the stress in this zone with the crack opening displacement. Presented will be the theoretical development and numerical analysis of this henceforth referred to “fictitious crack model”. Results will be obtained to examine the directional stability of crack trajectories developed in a mixed mode load environment and they are compared with experiments.

Analysis of curved reinforced concrete slab bridges by the spline finite strip method

A layered spline finite strip model for the analysis of reinforced concrete slab bridges is presented in this paper. The natural coordinates ξ–η are adopted to make the method suitable for arbitrary curved slab bridges. A material model based on orthotropic nonlinear elasticity is employed to represent the property of plain concrete. Reinforcement is modeled as an elastoplastic strain-hardening material. The Newton–Raphson method and relaxation techniques are used to solve the nonlinear stiffness equation. Numerical examples are provided to demonstrate the efficiency and accuracy of the model. Key words: spline finite strip method, curved slab bridges, reinforced concrete, nonlinear analysis.