Bending of Structural Hollow Sections Structural Hollow Sections

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 heat up to 850 Degree Celsius. 2. By Induction heating locally.

Hot Bending by Induction heating Locally

Cold Bending of Hollow Sections 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.

Bending of RHS/SHS Commonly used Methods. v Cold Bending using Three Roller Machine v Hot Bending using Induction heating with a radial arm controlling the radius v Mitre Cutting and welding.

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 180 x 6 • Side Wall buckling • Concavity in inner face

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