ELASTIC AND KINEMATIC HARDENING PLASTIC BLAST INDUCED DEFORMATIONS OF UNDERGROUND TUNNELS B)I THE FINITE ELEMENT METHOD

This research deals with the stress analysis of typical underground tunnels using isoparametric finite elements. Enhanced soflware is used for predicting and analyzing this behavior by using a single phase formulation. This software was developed from an original Computer code namea MXOYN The finite element method is used to solve the dynamic equiiibrium equation with step-by-step tirre integration schemes. A selected type of dynamic load was chosen which is blast loading. Frictional and paniculate materials, i.e., concrete and soil, are considered. The soil and concrele structures arc analyzed where a dynamic elastic model for concrete and a linear elastic one for soil are used. The soil is further analyzed by a bounding surface plasticity model. Tlie stress wavcs havel and the reflection effects especially in the no tension materials, i.e., soil are investigated. The effects of blast loading are then analyzed hypothetically placing the explosion at the grourd surface. The stresses and displacements are computed at different sections. The nonlinear analysis utilizing the bounding surface plasticity characterization gave better predictions over the linear elastic model. The linear elastic model is proposed to be used as a first prediction of the problems encountered, but it is incapable of realizing the actual behavior under dynamic loads

Stress and the pituitary-adrenal axis

The hypothalamo-pituitary-adrenal axis is controlled by complex regulatory mechanisms. Numerous factors such as CRF, vasopressin, oxytocin, angiotensin II and conceivably other hormones--all controlled by various substances acting on central locations--stimulate the release of the stress hormone ACTH. On the other hand, glucocorticoids inhibit the secretion of ACTH by acting at the hypothalamic and/or pituitary level. The release of ACTH is therefore the final outcome of the interactions between the hypothalamus, the adrenal gland and possibly other organs. The multimolecular nature of the factors responsible for the control of the pituitary-adrenal axis is an attractive hypothesis because of the great variety of stress stimuli. The various factors could have specific roles in various stress situations. They provide a highly sensitive mechanism regulating very finely the stress hormone in response to a whole variety of endogenous and exogenous stimuli. Depending on the type of stress, they may therefore singly or in combination affect the amount and duration of ACTH and steroid secretion. The released glucocorticoids may then produce their numerous effects on inflammatory and immunological processes, carbohydrate metabolism, shock and water balance. It has been postulated that these effects may be important in order to prevent host responses from over-reacting to stress and threatening homeostasis. However, proof of the necessity of the glucocorticoid hypersecretion in response to stress remains elusive