Laterally Supported Beam

– In general, a beam that does not move nor rotate laterally is termed as “Laterally Supported Beams”. This lateral restraint can be possibly obtained

by several means. Few of them are,

Compression flange of

the element embedded inside the slab

Compression flange

connected to the slab by means of shear connector

Lateral braces

provided in the beam

Determining the

bending strength of the laterally supported beam is quite straight forward, before

moving into it, let’s get ourselves clear about the failure modes for the

laterally supported beams, from which we can understand which factor governs

the bending strength of the beam.

A typical laterally

supported beam could fail by anyone of the following failure modes:

·

Shear failure of the

section

·

Flexural failure of

the section (bending failure)

·

Web crippling/web

buckling (local failures)

·

Deflection

Of the above-mentioned

failure modes, Flexural failure of the section is a bending failure, occurs

when the applied load produces an internal bending moment, which is pretty much

higher than the bending strength or moment capacity of the beam.

If we look into the

above statement, there are two important terms,

1. The internal bending moment generated because

of the applied load.

2. Bending or Moment capacity of the beam.

The first one can be

determined by simple mechanics. For example, if we have a laterally supported

pinned beam of length L and which supports a uniform load of W kN/m. Then the

bending moment produced will be WL*L/8.

Our main interest is

the Moment capacity of the section. It depends upon the cross-section of the

beam as well as material grade.

In general, the Moment capacity of the section equals the product of Section Modulus and Yield

strength of the material.

M = Z * fy * (factor of safety as per the specified code)

Thus, we have our

required bending capacity or strength of the section.