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Laterally Supported Beams - Lesson Summary

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Introduction to Flexural Members: Beams
 
Beam is basically a structural member that is subjected to transverse loading. The different types of beams are: 

Joist
Purlin
lintels
Floor beam
Girt
Rafter
Girder
Stringer
Spandrel beam

The primary modes of failure in beams are bending failure, the shear failure, and deflection failure.
 
The types of steel section that are often used for beams are:


Channel section
I - section
Box section
Compound section




Composite section
Encased beam
Tapered section
Castellated beam

Failure Modes of Flexural Members
 
The I-section is the most efficient and economical section and therefore, is the most commonly used section as a beam member.
 
Primarily, the design criteria of beams are based on deflection, stress due to bending, and shear.
 
The design procedure of the beam can be divided into three parts: Structural, secondary effects, and practical limitations.
 
Introduction to Laterally Supported Beams
 
Beams can be designed on the basis of laterally supported or laterally unsupported. In the case of a laterally supported beam, it is assumed that torsional buckling may be prevented. 
 
For laterally supported beams:
 
When the factored design shear force is less than 0.6 * Design shear strength of the cross-section, it can be called low shear.
 
When the factored design shear force is greater than 0.6 * Design shear strength of the cross-section, it can be called high shear.
 
The steps in designing a laterally supported beam are:
 


Calculate the load acting on the beam
Determine the distribution of bending moment and shear force along the length of the beam
Calculate the trial plastic section for the beam
Select a suitable section which has plastic section modulus slightly greater than the calculated value in step 3
Classify the section as plastic, compact or semi-compact
Calculate the design shear strength of the beam
Check whether the beam is high shear or low shear
Check the trial section for design bending strength
If the design bending strength is less than actual moments, increase section size and repeat from step 5
If the design shear strength from step 6 is less than the maximum factored shear force, redesign the section by increasing the section size
Check beam for deflection as per the codal provisions
Check beam for web buckling
Check beam for web crippling