Direct Stress

By Aina Parasher|Updated : August 26th, 2022

Direct stress is the stress which is induced due to the applied load when it is perpendicular to the body or structure. When the load is directly applied by tangential force, then shear force is developed in the body or structure. Depending upon the type of loading and cross-section of structure and position of load, the direct stress is divided into several types.

This article elaborates on direct stress, the type of load with respect to variation of stress when it acts on the center of gravity, and the occurrence of eccentricity when the load is not acting upon the center of gravity. The method of finding minimum stress and maximum stress using an example of a column. Let us understand direct stress.

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What is Direct Stress?

The Stresses which are acting normal in the plane of the body are called normal or direct stresses. Stresses are called normal when acting perpendicular to the plane of the body.

Direct stress is the stress developed due to force applied which is parallel or collinear to the axis of the component. Examples of this type of stress are tensile stress, compressive stress, shear stress, and thermal stress.

Differentiate Between Direct Stress and Bending Stress

Direct tensile and compressive stress is set up due to load applied parallel to the length of the object and direct shear stress is set up in the section which is parallel to the line of action of the shear load. But bending stress is set up due to load at right angles to the length of the object subjected to bending. So simple stress is subdivided into 3 types of stress.

types of stress

Shear Stress

When shear force is applied along the surface, in opposition to an offset force acting in the opposite direction. Shear stress occurs when a shear force is acting on a body. Each of these stresses affects an object in different ways and is caused by the internal forces acting on the object. The direct stress is produced by bending moments or by the bending action of shear loads, while the shear stresses are due to shear and/or torsion of a closed section beam or shear of an open section beam.

Stress due to Concentric Loading

Let us consider a column in which is one end fixed and another end having when the load acts at the center of gravity of the cross-section. In simple terms, we can say that a column is subjected to compressive load. So, direct compressive stress developed only in the body, and the intensity of this direct compressive stress will be uniform across the cross-section of the column in the below figure.

concentric

Direct compressive stress developed in the column,

σd= (Axial applied compressive load/ Area of cross-section) of the given column

σd = P/A

σd = P/(b.d)

Where,

P= Direct compressive load

A= Area of cross section = b.d ( for rectangular cross-section)

Unit of Direct compressive stress (σd ) = N/mm2

Stress due to Eccentric Loading

When an eccentric load is acting on a column, it produces direct stress as well as bending stress on one side of the neutral axis there is maximum stress and on another side, there is minimum stress. When the bending stress is less than direct stress, the resultant stress will be compressive. If bending stress is equal to the direct stress, there will be tensile stress on one side.

eccentric

Bending stress, σb=M/(I/y)

M= Bending moment

I= moment of inertia in mm

y = vertical distance of a point away from the neutral axis

I/y = Z = section modulus

Maximum Stress and Minimum Stress

When a column is subjected to eccentric loading, the edge of the column towards the eccentricity is subjected to maximum stress at one end and another end is subjected to minimum stress. Hence, the Maximum stress will be,

σmax= Direct stress + Bending stress

σmaxdb

σmax= P/A + M/Z

Minimum stress,

σmin= Direct stress + Bending stress

σmind- σb

σmin= P/A - M/Z

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FAQs on Direct Stress

  • The stresses which are acting normal to the plane of the body are called normal or direct stresses. Direct stress (σd) is produced when applied load acts on a body. Mathematically,

    σd= Axial applied compressive or tensile load/Area of cross section = P / A

  • Direct stress is divided into some categories depending upon the action of force along the surface. The type of stress is tensile stress, compressive stress, shear stress, and thermal stress.

  • The direct stress is called normal when it is acting perpendicular to the plane of the body. Stress is said to be normal stress when the direction of the deforming force is right angle to the cross-sectional area of the body.

  • The direct stress is produced in a body when it is subjected to an axial tensile or compressive load only, and Bending stress is produced in the body when it is subjected to a bending moment (when eccentric loading acts on a body).

    Direct tensile and compressive stress is set up due to load applied parallel to the length of the object and bending stress is set up due to load at right angles to the length of the object subjected to bending.

  • The column will be subjected to compressive load and as the load is applied axially, there will be developed direct compressive stress only in the body and the intensity of this direct compressive stress will be uniform across the cross-section of the column.

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