Introducing
Your new presentation assistant.
Refine, enhance, and tailor your content, source relevant images, and edit visuals quicker than ever before.
Trending searches
Compression of Steel Structures
2
Compression of
Steel Structures
Ana García Durán
METAL STRUCTURES
Compression members in trusses
Introduction
Stress in the column cross-section
f = P/ A
Structural elements subjected to axial compressive forces
Design governed by strength and buckling
Columns are subjected to axial loads through the centroid
Tension VS Compression
· Compression beside compression forces causes buckling of member
· Tension in members causes lengthening of them
· Presence of holes in bolted connection reduce Gross area in tension members
Compression Member
Vs
Tension Member
· The bending of tension members probably will not be serious as the tensile loads tends to straighten those members, but bending of compression members is serious because compressive loads will tend to magnify the bending in those members
Compression Member Failure
A compressive material failure
A buckling failure
A combination of both compressive and buckling failures
Compression Member Failure
Torsional Buckling
these columns fail by twisting (torsion) or combined effect of torsional and flexural buckling
Torsional Buckling
Local Buckling
This occurs when some part or parts of x-section of a column are so thin that they buckle locally in compression before other modes of buckling can occur
Local Buckling
Flexural Buckling
(Euler Buckling)
Is the primary type of buckling members are subjected to bending or flexure when they become unstable
Flexural Buckling
(Euler Buckling)
Section used for Compression Member
Numerous shapes can be used for columns to resist given loads.
However, from practical point of view, the number of possible solutions is severely limited by section availability, connection problems and type of structure in which the section is to be used
Buckling
Buckling occurs when a straight column subjected to axial compression suddenly undergoes bending.
Buckling is identified as a failre limit-state for columns.
Stable Equilibrium
The column will go back to its original straight position.
In columns elasticity of column itself acts as a restoring force.
This action contributes stable equilibrium
Stable Equilibrium
Precarious Equilibrium
· The amount of deflection depends on amount of force F
· The column can be in equillibrium in an infinite number of bent position
Precarious Equilibrium
Unstable Equilibrium
· The elastic restoring force was not enough to prevent small disturbance growing into an excessively large deflection
· Depending on magnitude of load P, column either remain in bent position, or will completely collapse or fracture.
Unstable Equilibrium
Compression member buckling
· Buckling occurs when a straight, homogeneous, centrally loaded column subjected to axial compression suddenly undergoes bending
· Buckling is identified as a failure limit-state for columns
Critical load
· The value of P at which a straight column becomes unstable is called the Critical Load
· When column bands at critical load, it is said to have buckled
· Therefore, critical load is also called the buckling load
Elastic Buckling of Columns
· The critical buckling load Pcr for columns is theoretically given by
Elastic Buckling of Columns
· Tendency of compression members to buckling is governed by L/r
Effective lenght in different direcctions
Euler slenderness
· The intersection point P, of the two curves represents the maximum theorical value of slenderness of a column compressed to the yield strength. This maximum slenderness (sometimes called Euler slenderness)
Inelastic Buckling
· In elastic buckling it was assumed that a column made of a metal whose stress-strain curve is linear until a yield plateau reached
· For a column with intermediate length, when buckling occurs after the stress in the column exceeds the proportional limit of the column material and before the stress reached the ultimate stregth. This kind of situation is called inelastic buckling.
Inelastic Buckling
Load Buckling
· If local buckling of the individual plate elements occurs, then the column may not be able to develop its buckling strength
· Therefore, the local buckling limit state must be prevented from controlling the column stregth