K. Chandrashekhara

A numerical method for separation of stresses in photo-orthotropic elasticity

A numerical method is suggested for separation of stresses in photo-orthotropic elasticity using the numerical solution of compatibility equation for orthotropic case. The compatibility equation is written in terms of a stress parameter S analogous to the sum of principal stresses in two-dimensional isotropic case. The solution of this equation provides a relation between the normal stresses. The photoelastic data give the shear stress and another relation between the two normal stresses. The accuracy of the numerical method and its application to practical problems are illustrated with examples.

Elastic Analysis of an Annular Slab-Soil Interaction Problem Using a Hybrid Method

An elastic interaction analysis of annular slab with soil has been made in which the soil has been modelled as either (i) homogeneous and isotropic half-space or (ii) multilayered half-space. The interaction problem has been solved by using a combined approach (hybrid method) in which the finite element method (FEA4) has been used to obtain the stiffness matrix for the annular slab while for the elastic half-space soil models, the stiffness matrix has been obtained using an analytical solution. In the analysis, the interface between the annular slab and the elastic half-space has been assumed to be frictionless. Later the combined stiffness matrix of the annular slab-elastic half-space has been obtained using the displacement continuity condition at the interface. Results of the contact pressure distribution, displacement (settlement) profile and bending moment variation in an annular slab have been presented for different half-space soil models. It is shown that the hybrid method presented here is easy to apply and computationally efficient.

Towards stress freezing in birefringent orthotropic composite models

Birefringent composite models are fabricated using epoxy resin reinforced with unidirectionally oriented glass fibers. The mechanical and photoelastic properties of the material at room temperature are determined. To explore the possibility of application of stress-freezing technique to birefringent composite models, the behavior and properties of this material are studied at elevated temperature (at stress-freezing temperature of the resin). The properties of the material at room and at elevated temperatures are reported. The feasibility of stress freezing glass-fiber-reinforced epoxy composites with low-fiber-volume fraction is discussed.

Ring plate on a transversely isotropic elastic halfspace

In this paper, a combined finite element method (FEM)-analytical approach has been used to study the elastic interaction of an axisymmetrically loaded ring plate with a transversely isotropic medium. Two cases of transversely isotropic medium have been considered viz., (i) homogeneous transversely isotropic halfspace and (ii) multilayered transversely isotropic halfspace. The stiffness matrix for the ring plate has been obtained using ring elements (FEM) in an explicit form and the stiffness matrix for the transversely isotropic halfspace models considered here have been obtained using a general analytical solution. The interface of ring plate and halfspace has been considered as smooth. The present approach automatically takes care of the semi-infinite nature of the transversely isotropic medium unlike the total finite element procedure where the halfspace is represented by a large size solid (discretised in to a large number of finite elements, especially in treating a multilayered halfspace) with certain imposed constraints. Results have been presented for the contact pressure distribution, displacement profile and bending moment variation in the ring plate. It is observed that the present approach is computationally efficient, more general and can be applied to different elastic contact problems.

Semi-analytical finite element analysis of a strip footing on an elastic reinforced soil

Abstract A plane strain elastic interaction analysis of a strip footing resting on a reinforced soil bed has been made by using a combined analytical and finite element method (FEM). In this approach the stiffness matrix for the footing has been obtained using the FEM. For the reinforced soil bed (halfplane) the stiffness matrix has been obtained using an analytical solution. For the latter, the reinforced zone has been idealised as (i) an equivalent orthotropic infinite strip (composite approach) and (ii) a multilayered system (discrete approach). In the analysis, the interface between the strip footing and reinforced halfplane has been assumed as (i) frictionless and (ii) fully bonded. The contact pressure distribution and the settlement reduction have been given for different depths of footing and scheme of reinforcement in soil. The load–deformation behaviour of the reinforced soil obtained using the above modelling has been compared with some available analytical and model test results. The equivalent orthotropic approach proposed in this paper is easy to program and is shown to predict the reinforcing effects reasonably well.

Photoelastic analysis of composite action of walls supported on beams

Abstract The paper deals with the two-dimensional photoelastic analysis of deep walls acting in conjunction with the supporting beams. The photoelastic composite model is constructed of two different materials which give the required ratios of elastic constant of wall and beam at elevated temperature (115°C). It is shown that the interface stresses could be obtained directly using the photoelastic data along with the continuity conditions at the interface. The stresses in the interior of wall portion are obtained using a recently developed numerical technique which requires the boundary stresses only to be known. Results are presented for walls, with and without opening, supported on beams.

An experimental investigation into pile group-layered soil interaction

Abstract An interaction analysis of an axially loaded single pile and pile group with and without a pile cap in a layered soil medium has been investigated using the two-dimensional photoelastic method. A study of the pile or pile group behaviour has been made, varying the pile cap thickness as well as the embedded length of the pile in the hard stratum. The shear stress distribution along the pile-soil interface, non-dimensionalized settlement values of the single pile and the interaction factor for the pile group have been presented. Wherever possible, the results of the present analysis have been compared with available numerical solutions.