AHSANULLAH UNIVERSITY OF SCIENCE & TECHNOLOGY

Department of Civil Engineering

Prestress Concrete Design Sessional CE 416

PRESENTED BYMD. SHARIFUL ISLAMSTUDENT NO: 10.01.03.008

COURSE TEACHERSMr. Munshi Galib MuktadirMs. Sabreena Nasrin

PRESENTATION TOPIC : AXIAL FORCE

PRESENTATION OUTLINE

-Definition -Unit -Scope -Description -Conclusion

Definition :

A force applied parallel to the centerline of an object.

Axial force evaluates the internal forces that exist in a structure, often presented by the characteristics of its dimensions.

COLUMN UNDER AXIAL FORCE F

Force F

Center line

* Axial forces are forces corresponding to the centerline that are functional in an object.

* Typically, in an axial-force, the stresses as well as strains are consistently distributed over the cross section. The term is normally applied in engineering.

UNIT:

Axial force is determined by width, effective length, and load and is measured in kilo pounds or kips (1,000 pounds of force).

At any cross-section of the member, it is the algebraic sum of all forces acting parallel to the longitudinal axis on either side of the section. A tensile force is assumed to be positive while compressive as negative as shown in figure:

SCOPE:

Compressive axial force (-ve)

Tensile axial force (+ve)

Compression members, such as columns, are mainly subjected to axial forces. The principal stress in a compression member is therefore the normal stress,

The failure of a short compression member resulting from the compression axial force looks like,

DESCRIPTION

An axial force is any force that directly acts on the center axis of an object. These forces are typically stretching force or compression force, depending on direction.

A prime example of these forces can be seen on columns within buildings. The column has an axis that runs through the entire form from top to bottom. The column is constantly compressed as it supports the roof of the structure.

One of the most important parts of examining axial forces is the idea of a geometric center.

Geometric center:This is a point within the boundaries of a solid object that is the perfect center of the entire mass. It is basically the point at which the mass of the object is the same in any opposing direction.

Factors such as density and protruding arms could cause the geometric center to exist on the surface or even outside of the form.

Concentric: when the force load is even across the form’s geometric center, it is concentric.Eccentric:when the force load is uneven across the form’s geometric center, it is eccentric.

In the column example, the axial force runs through the geometric center of the form; this makes the force concentric. A concentric force is stable at rest. When the axis doesn’t pass through the geometric center, the shape isn’t stable and the force is eccentric. This typically means that the form is unable to withstand axial forces while at rest.

The compressed beam under axial force F stores energy U of a value according to the formula

Now, the figure below shows a small segment along a beam element subjected to simplified 2D forces ( axial force P, shearing force V, and bending moment M):

In a general case 3 forces and 3 moments act on the segment.

Uniform axial stress = P/A (similar to truss elements)Uniform shearing stress = V/AThe bending moment M causes a bending stress that varies linearly with the vertical distance y from the neutral axis.Bending stress (bending in y direction)  = My/I

where I is the moment of inertia about the neutral axis.The bending stress is the largest at the extreme fibers.

In this example, the largest compression occurs at the top fiber and the largest tension occurs at the extreme bottom fibers.

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