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Module 1: Compression Members

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Introduction to Compression Members
 
A compression member is a structural member that is straight and subjected to compressive forces along its axis.
 
The modes of failure that can occur in compressive members are: 

Squashing
Overall flexural buckling
Flexural-torsional buckling
Local bucking
Torsional buckling

The factors that affect the strength of a compressive member are:

Material Property of the member
Cross-sectional configuration
Imperfections
Length of the member
Support conditions
Residual stresses

Compressive Strength fo Members
 
The three main parameters that affect the compressive strength of a member are the material strength of the member, slenderness ratio, and local buckling.

 
The four basic approaches adopted to establish a column design formula are:
 


Formula based on maximum strength
Formula based on tangent modulus theory
Perry Robertson formula
Empirical formula

Compressive Strength of Single Angle Struts
 
Struts, basically, take a light load and has less effective length. An angle section is used to take care of the compressive load. 
 
The compression in single angle struts may be transferred either concentrically to its centroid through end gusset or eccentrically by one of its legs to a gusset or adjacent member.
 
When a single angle strut transfers a compressive load through one of its legs, an eccentricity occurs. This eccentricity results in Flexural – Torsional buckling, flexural buckling, and torsional buckling.
 
Compressive Strength of Double Angle Struts

 

Double angle sections have higher design strength than single angle sections. To find the design strength of a double angle section, the effective length of the double angles must be known.