CAMBER

 

Cold cambering is the most common method used in fabrication shops to induce camber in a steel member, as it is a simpler and more cost-effective method than heat cambering.  This method uses a mechanically induced force to achieve the desired curvature. The member (I – beam) is placed in a device called a cambering machine that is often built by the fabricator but is also commercially available. The cambering machine consists of two restrained pivots, one near each end of the beam and one or two hydraulic jacks near the middle of the beam.  The jacks apply a force to induce camber into the member.

After placing the member at the restrained end pivots, the rams of the hydraulic jack or jacks are advanced to apply stress into the member past it’s yield point to produce a permanent deflection. When the rams are retracted, the residual deformation remains.  The beam may need to be moved back and forth to actuate the jacking forces at different locations along the length of the beam to produce a uniform camber.

Depending on the capacity of the machine and the amount of camber required, this process may need to be repeated until the required deformation (camber) is attained. During this process adequate precautions should be taken to prevent over-stressing the beam and exceeding the yield strength of the member, which may result in buckling, excessive thinning of the convex flange, and cracks or tears in the member. 

Correction of over-camber: It is important to never attempt to reduce the amount of camber in a member that has been over-cambered by immediately applying force to the beam in the opposite direction.  If this action is taken, strain weakening may occur, and the steel strength may be affected.  To correct over-camber in a cold cambered member, mild heat usually between 200°F and 550°F may be applied for a few minutes to accelerate molecular relaxation.  The heat should be applied as evenly as possible in the most stretched and compressed areas of the beam.  If the beam still exhibits an over- camber condition after mild heating, the application of heat in wedge-shaped segments can be used at the convex of the flange to provide the necessary adjustments. 

There are limitations to the use of the cold cambering method.  AASHTO/AWS D1.5 and owner specifications must be adhered to when proposing the method of bending.

Va= $49,500.00 DLLS   (500  TON)

Vr=0.15*49500=$ 7425.00 DLLS

Ve=10000 HRS

Ha=200 HRS/WEEK

Ka=.04

Q=.10

Sa=37.40 $/HR