GEO-MECHANICS AND GEO-TECHNICAL ENGINEERING

► Stress is the internal resistance, or counterforce, of a material to the distortion effects of an external force or load.

► These counter forces tend to return at their normal positions. The total resistance developed is equal to the external. This resistance is known as stress.► Stress (s) can be equated load per unit area, or the force (F) applied per cross-sectional area (A) perpendicular to the force as shown in the Equation below

Concepts of Stress

Concepts of Strain► When a metal/rock body is subjected to a load (force), it is normally distorted or deformed. If the load is small, the distortion will probably disappear when the load is removed.

► The intensity, or degree, of distortion is known as strain.

► If the distortion disappears and the metal returns to its ordimensions upon removal of the load, the strain is called elastic strain.

► If the distortion disappears and the metal remains distorted, the strain type is called plastic strain.

NORMAL STRESS

► A normal stress results when a member is subjected to an axial load applied through the centroid of the cross section.

► It is symbolized by the Greek letter sigma σ,

► The average normal stress in the member is obtained by dividing the magnitude of the resultant internal force F by the cross sectional area A. Normal stress is-

•Normal stress•Shearing stress•Bearing stress

► Stress σ acts in a direction perpendicular to the cut surface, it is referred to as a NORMAL stress.

► Thus, normal stressed may be either tensile orcompressive. Here sign convention for normal stresses is:Tensile stresses are positive (+)Compressive stresses are negative (-)

SHEAR STRESS (Simple or Direct Shear)

► A shear stress results when a member is subjected to a force that is parallel or tangent to the surface.

► It is symbolized by the Greek letter tau τ,

► The average shear stress in the member is obtained by dividing the magnitude of the resultant shear force V by the cross sectional area A. Shear stress is:

BEARING STRESS► A bearing stress is a compressive normal stress that occurs on the surface of contact between two interacting members.

► It is symbolized by the Greek letter sigma σb,

► The average normal stress in the member is obtained by dividing the magnitude of the bearing force F by the area of interest. Bearing stress is

As previously mentioned, we generally assume the normal stress distribution in an axially loaded member is uniform, except near the vicinity of the applied load.

STRESS DISTRIBUTION UNDER AXIAL LOADING