Bending of Structural Hollow Sections
• Structural Hollow Sections can bend in either hot or cold condition.
• During this process folds may occur in the inner zone and decrease of
thickness takes place at outer zone.
Hot Bending
1. To avoid folds fill the section with sand and heat up to 850 Degree Celsius.
2. By Induction heating locally.
Hot Bending by Induction heating Locally
Different Methods of Cold Bending
1. By Pressing
2. Using a winding system
3. By means of forming box
4. Roller Bending
5. By means of Mitre Cuts and “V” notches.
Cold Bending of Hollow Sections
1. By Pressing
In this process Hollow Section will be
set between two fixed rollers and
bending them by displacement of a
central former.
Usually this central former is
connected to a hydraulic actuator
Cold Bending of Hollow Sections
2. Winding System
The Hollow Section is held by a shoe or
clamp, firmly connected to a circular former
“b” . A corresponding fixed gliding shoe “c”
is then rotated and force the tube in to the
recess of the former “b”
Cold Bending of Hollow Sections
3. Forming Box
In this process Hollow Section will be
forced in to a pre-shaped forming box.
This method is economical if many
bends of the same size are required.
Cold Bending of Hollow Sections
4. Roller Bender
• Bending is obtained by pressing the
hollow section through three rollers.
• All three may be driven , but the
central one which determines the
radius of the bend, can be idle.
• This process is generally preferred by
the steel constructors.
Cold Bending of Hollow Sections
5. Mitre cuts or “V” Notches
• An approximate curve is obtained by
joining the straight sections end to end
by welding.
• By making “V” notches in the webs
and bottom flange and bend the top
flange to the required bend.
Cold Bending of Hollow Sections
Commonly used Methods.
Cold Bending using Three Roller Machine
Hot Bending using Induction heating with a radial arm controlling
the radius
Mitre Cutting and welding.
Bending of RHS/SHS
Bending of RHS/SHS
• In general when bending a RHS the inside face will compress, the outside wall will
stretch and the side wall will exhibit both.
• If bending is severe on a section of high width to wall thickness ratio, convexity in
the two side walls and concavity in the inner face may develop.
Problems facing for bending of 180x180x6
• Side Wall buckling
• Concavity in inner face
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