Bearing capacity of square footings on geosynthetic reinforced sand

The results from laboratory model tests and numerical simulations on square footings resting on sand are presented. Bearing capacity of footings on geosynthetic reinforced sand is evaluated and the effect of various reinforcement parameters like the type and tensile strength of geosynthetic material, amount of reinforcement, layout and configuration of geosynthetic layers below the footing on the bearing capacity improvement of the footings is studied through systemati model studies. A steel tank of size 900 x 900 x 600 mm is used for conducting model tests. Four types of grids, namely strong biaxial geogrid, weak biaxial geogrid, uniaxial geogrid and a geonet, each with different tensile strength, are used in the tests. Geosynthetic reinforcement is provided in the form of planar layers, varying the depth of reinforced zone below the footing, number of geosynthetic layers within the reinforced zone and the width of geosynthetic layers in different tests. Influence of all these parameters on the bearing capacity improvement of square footing and its settlement is studied by comparing with the test on unreinforced sand. Results show that the effective depth of reinforcement is twice the width of the footing and optimum spacing of geosynthetic layers is half the width of the footing. It is observed that the layout and configuration of reinforcement play a vital role in bearing capacity improvement rather than the tensile strength of the geosynthetic material. Experimental observations are supported by the findings from numerical analyses.

Transversely isotropic infinite cylindrical shell subjected to a radial axisymmetric line load

The problem of an infinite transversely isotropic circular cylindrical shell subjected to an axisymmetric radial external line load is investigated using elasticity theory, classical shell theory and shear deformation theory. The results obtained by these methods are compared for two ratios of inner to outer shell radius and for varying degrees of anisotropy. Some typical results are given here to show the effect of anisotropy and the thickness of the shell on the distribution of stresses and displacements.

Multilevel load frequency control (a perturbational approach)

A two-level control scheme for the load frequency control of a multi-area power system utilizing certain possible beneficial aspects of interconnections is described in this paper. The problem is identified as the determination of the necessary equivalent perturbation on the control distribution matrix to provide the corrective control.

Elasticity solution for a long circular sandwich cylindrical shell subjected to axisymmetric load

An elasticity solution has been obtained for a long circular sandwich cylindrical shell subjected to axisymmetric radial ring load using Love's stress function approach. Numerical results are presented for different ratios of modulus of elasticity of the layers. The results obtained from this analysis have been compared with those obtained from sandwich shell theory due to Fulton.

Load Transfer from a Smooth Elastic Pin to a Large Sheet

The plane problem of load transfer from an elastic interference or clearance fit pin to a large elastic sheet with a perfectly smooth interface is solved. As the load on the pin is monotonically increased, the pin-hole interface is in partial contact above certain critical load in interference fit and throughout the loading range in clearance fit.Such situations result in mixed boundary-value problems with moving boundaries and the arc of contact varies nonlinearly with applied load. These problems are analyzed by an inverse technique in which the arcs of contact/separation are prescribed and the causative loads are evaluated. A direct method of analysis is adopted using biharmonic polar trigonometric stress functions and a simple collocation method for satisfying the boundary conditions. A unified analytical formulation is achieved for interference and clearance fits. The solutions for the linear problem of push fits are inherent in the unified analysis. Numerical results highlighting the effects of pin and sheet elasticity parameters are presented.

Critical Evaluation of Determining Swelling Pressure by Swell-Load Method and Constant Volume Method

For any construction activity in expansive soils, determination of swelling pressure/heave is an essential step. Though many attempts have been made to develop laboratory procedures by using the laboratory one-dimensional oedometer to determine swelling pressure of expansive soils, they are reported to yield varying results. The main reason for these variations could be heterogeneous moisture distribution of the sample over its thickness. To overcome this variation the experimental procedure should be such that the soil gets fully saturated. Attempts were made to introduce vertical sand drains in addition to the top and bottom drains. In this study five and nine vertical sand drains were introduced to experimentally find out the variations in the swell and swelling pressure. The variations in the moisture content at middle, top, and bottom of the sample in the oedometer test are also reported. It is found that swell-load method is better as compared to zero-swell method. Further, five number of vertical sand drains are found to be sufficient to obtain uniform moisture content distribution.

Analysis of an orthotropic cylindrical shell having a transversely isotropic core subjected to axisymmetric load

A long two-layered circular cylinder having a thin orthotropic outer shell and a thick transversely isotropic core subjected to an axisymmetric radialv line load has been analysed. For analysis of the outer shell the classical thin shell theory was adopted and for analysis of the inner core the elasticity theory was used. The continuity of stresses and deformations at the interface has been satisfied by assumming perfect adhesion between the layers. Numerical results have been presented for two different ratios of outer shell thickness to inner radius and for three different ratios of modulus of elasticity in the radial direction of outer shell to inner core. The results have been compared with the elasticity solution of the same problem to bring out the reliability of this hybrid method. References

Some aspects of multilevel load-frequency control of a power system

The application of multilevel control strategies for load-frequency control of interconnected power systems is assuming importance. A large multiarea power system may be viewed as an interconnection of several lower-order subsystems, with possible change of interconnection pattern during operation. The solution of the control problem involves the design of a set of local optimal controllers for the individual areas, in a completely decentralised environment, plus a global controller to provide the corrective signal to account for interconnection effects. A global controller, based on the least-square-error principle suggested by Siljak and Sundareshan, has been applied for the LFC problem. A more recent work utilises certain possible beneficial aspects of interconnection to permit more desirable system performances. The paper reports the application of the latter strategy to LFC of a two-area power system. The power-system model studied includes the effects of excitation system and governor controls. A comparison of the two strategies is also made.

Wear characteristics and bearing performance of aluminium-mica particulate composite material

Some tribological properties of a mica-dispersed Al-4%Cu-1.5%Mg alloy cast by a conventional foundry technique are reported. The effect of mica dispersion on the wear rate and journal bearing performance of the matrix alloy was studied under different pressures and under different interface friction conditions. The dispersion of mica was found (a) to increase the wear rate of the base alloy, (b) to decrease the temperature rise during wear and (c) to improve the ability of the alloy to resist seizure.

Size optimization of a cantilever beam under deformation-dependent loads with application to wheat stalks

In this paper, we consider the optimization of the cross-section profile of a cantilever beam under deformation-dependent loads. Such loads are encountered in plants and trees, cereal crop plants such as wheat and corn in particular. The wind loads acting on the grain-bearing spike of a wheat stalk vary with the orientation of the spike as the stalk bends; this bending and the ensuing change in orientation depend on the deformation of the plant under the same load.The uprooting of the wheat stalks under wind loads is an unresolved problem in genetically modified dwarf wheat stalks. Although it was thought that the dwarf varieties would acquire increased resistance to uprooting, it was found that the dwarf wheat plants selectively decreased the Young's modulus in order to be compliant. The motivation of this study is to investigate why wheat plants prefer compliant stems. We analyze this by seeking an optimal shape of the wheat plant's stem, which is modeled as a cantilever beam, by taking the large deflection of the stem into account with the help of co-rotational finite element beam modeling. The criteria considered here include minimum moment at the fixed ground support, adequate stiffness and strength, and the volume of material. The result reported here is an example of flexibility, rather than stiffness, leading to increased strength.

On the unsteady flow of a fairly concentrated suspension due to contracting or expanding walls of a tube

Consummating our earlier work [1], the unsteady flow of a fairly concentrated suspension due to a single contraction or expansion of the walls of a tube is studied. A comparison of the results obtained by using two different formulae for the additional drag terms in the governing equations has been made. A region of circulation in the flow field is observed when the volume fraction Z greater-or-equal, slanted 0.3, the Schmidt number Sc < 1 and the density ratio (density of the particulate phase/density of the fluid phase) > 1.

Pulsatile blood flow in a rigid pulmonary alveolar sheet with porous walls

This paper deals with the pulsatile blood flow in the lung alveolar sheets by idealizing each of them as a channel covered by porous media. As the blood flow in the lung is of low Reynolds number, a creeping flow is assumed in the channel. The analytical and numerical results for the velocity and pressure distribution in the porous medium are presented. The effect of an imposed slip condition is also studied. Comparisons with the corresponding results for the steady-state case are made at the end.

Biaxial-load effects on isopachics for a crack at the interface of dissimilar media

The plane problem of two dissimilar materials, bonded together and containing a crack along their common interface, which were subjected to a biaxial load at infinity, is examined by giving a closed-form expression for the first stress invariant of the normal stresses, which is equally valid everywhere, near to, and far from, the crack-tip region. This exact expression for the first-stress invariant is compared by constructing the respective isopachic-fringe patterns, to the approximate expression with non-singular terms, due to the biaxiality factor, for the same quantity. Significant differences between respective isopachic-patterns were found and their dependence on the elastic properties of both materials and the applied loads was demonstrated. The relative errors between the computedK I - andK II -components by using the approximate expression for the first stress-invariant and the accurate one, derived from closed-form solution along either isopachic-fringes or along circles and radii from the crack-tip have been given, indicating in some cases large discrepancies between exact and approximate solutions.

Transversely isotropic infinite cylindrical shell subjected to a radial axisymmetric line load

The problem of an infinite transversely isotropic circular cylindrical shell subjected to an axisymmetric radial external line load is investigated using elasticity theory, classical shell theory and shear deformation theory. The results obtained by these methods are compared for two ratios of inner to outer shell radius and for varying degrees of anisotropy. Some typical results are given here to show the effect of anisotropy and the thickness of the shell on the distribution of stresses and displacements.