P.C. Upadhyay

Non-axisymmetric dynamic response of buried orthotropic cylindrical shells

This paper deals with the non-axisymmetric dynamic behaviour of buried orthotropic cylindrical shells excited by a combination of P-, SV- and SH-waves. Numerical results have been presented for the case of an incident plane longitudinal wave (P-wave) only. The flexural mode response has been compared with that of the axisymmetric mode. It has been found that, depending upon soil condition and apparent wave speed, shell deformations in the flexural mode may be even greater than in the axisymmetric mode. Also, the shell response is found to be significantly influenced by variations in the shell orthotropy parameters and by the soil condition around the shell.

On the dynamic response of buried orthotropic cylindrical shells

This paper deals with the dynamic response of an orthotopic cylindrical shell, a pipe, buried underground and subjected to seismic excitation. A thick-shell model of the pipe including shear deformation and rotatory inertia has been used. The shell is assumed to be perfectly bonded to the surrounding medium (soil), of infinite extent. Only the axisym-metric response due to an incident compressional wave has been investigated. Effects of the shell orthotropy on its response characteristics have been illustrated by changing the non-dimensional orthotropy parameters of the shell over a wide range. Results have been obtained for different soil conditions—hard (rocky), medium and soft. It is found that the orthotropy parameters do not influence the shell response equally. Even the degree of their influence is found to be highly dependent on the rigidity of the surrounding soil.

Torsional springback in square section bars of nonlinear work-hardening materials

Abstract This paper deals with the torsional springback problems of bars of strain-hardening material with arbitrary cross-section. Using the deformation theory of plasticity, a numerical scheme with a Ramberg-Osgood type stress-strain relationship has been prepared which determines the elastic-plastic boundary in addition to springback in the bars. The results have been verified experimentally with mild-steel bars having square cross-section and the experimental results have been found to agree well with the theoretical results obtained numerically.

Springback analysis of torsion of L-sectioned bars of work-hardening materials

Abstract This paper deals with the torsional springback problems of L-sectioned bars of non-linear work-hardening materials, the properties of which can be modelled by a deformation theory constitutive equation of the Ramberg-Osgood type. The results have been verified experimentally with mild steel bars. It was found that the experimental results agree well with theoretical results obtained numerically.

Parametric assessment of torsional springback in members of work-hardening materials

Abstract The paper deals with the torsional springback problem of bars of strain-hardening materials with arbitrary cross-sections. Using the deformation theory of plasticity, a numerical scheme based on the finite difference approximation has been proposed. The growth of the elastic-plastic boundary and the resulting stresses while loading, and the torsional springback and the residual stresses after unloading, are calculated. The results are verified experimentally with mild steel bars having a square cross-section. The experimental results are found to agree well with the theoretical predictions obtained numerically.

Effect of imperfect bonding on the axisymmetric dynamic response of buried orthotropic cylindrical shells

Abstract This paper deals with the dynamic response of an imperfectly bonded buried orthotropic pipeline subjected to p-wave excitation. An infinite cylindrical shell model, including the rotary inertia and shear deformation effects, has been used for the pipeline. Only the axisymmetric response due to an incident compressional wave has been investigated. Effects of imperfect bond between the pipe and the soil have been included by considering a layer of infinitesimally small thickness between the pipe and the soil. The layer possesse stiffness and damping properties against any axial or radial movement. The ddgree of imperfection or the looseness of the bond is incorporated by varying the stiffness and the damping parameters of the layer. Effects of the imperfect bond on the radial and the axial displacement of the shell have been studied in different soil conditions. These effects have been compared with the effects due to changes in the orthotropic parameters of the pipe.

A comparison of thick and thin shell theory results for buried orthotropic cylindrical shells

Abstract This paper is concerned with the comparison of results of thick and thin shell theories for buried orthotropic cylindrical shell subjected to seismic excitation. The shell is assumed to be perfectly bonded to the surrounding medium of infinite extent. Only axisymmetric response due to an incident compressional wave has been investigated. The nature of variation of differences between the results of the two theories has been studied for varying ground conditions (rigidity) and wave velocity. Changes in results due to variation in the orthotropy parameters have been compared with the differences in the results of thin and thick shell theories.

Springback analysis of thin rectangular bars of non-linear work-hardening materials under torsional loading

A theoretical analysis of the springback of narrow rectangular strips of non-linear work-hardening material under torsional loading has been carried out. This theoretical analysis is supported by experimental results for rectangular mild steel strips of different thicknesses and lengths. Finally an analytical generalized expression relating angle of twist to twisting moment and residual angle of twist per unit length for rectangular strips under plastic torsion is obtained in non-dimensionalized form. A comparison between the results obtained for bars of non- linear and linear work-hardening materials loaded under torsion is also made.

Non-axisymmetric dynamic response of a buried orthotropic cylindrical shell due to incident shear waves

Abstract This paper deals with the non-axisymmetric dynamic response of buried orthotropic cylindrical shells excited by shear waves travelling in the surrounding infinite medium. Numerical results have been presented for the cases of incident SV- and SH-waves. For the case of an SV-wave, the flexural and axisymmetric modes have been compared. It has been found that the shell deformations in the flexural mode may be even higher than those in the axisymmetric mode. For SH-waves, only the flexural mode response has been presented as the axisymmetric response does not exist for this case. Shell response for both SV- and SH-waves is found to be significantly influenced by the shell orthotropy parameters, the ground conditions around the shell and the wave speed along the shell axis.

On the dynamic response of fluid-filled buried pipelines

Abstract This paper presents a theoretical analysis of the axisymmetric steady state dynamic response of buried fluid-filled pipelines excited by seismic waves travelling in the surrounding infinite medium (soil). An infinite cylindrical shell model including the rotary inertia and shear deformation effects, has been used for the pipeline. Comparisons of the numerical results for a fluid-filled shell with those for an empty shell show that the presence of the fluid suppresses the response at some wavelengths but augments it at others. The overall response of the fluid-filled shell is observed to be quite different from that of the empty shell, and this difference is found to be more pronounced in softer soil conditions.