Camber - need clarification
Camber - need clarification
(OP)
I read another thread on pre-cambering steel beams, but Im not clear.
Does cambering a 40'+ beam to the equivalent of the dead load deflection override the total load deflection requirement, ie L/240 floors or l/600 with masonry? Or is it in addition to meeting the total load deflection requirements?
Does cambering a 40'+ beam to the equivalent of the dead load deflection override the total load deflection requirement, ie L/240 floors or l/600 with masonry? Or is it in addition to meeting the total load deflection requirements?






RE: Camber - need clarification
There are 2 conditions: composite construction and non-composite construction.
Non-Composite:
If your deflection due to total load is say 3", then cambering the beam 2" will cause a final deflection of 1" (L/480). Cambering does not override the deflection checks, it only helps in keeping it within the code requirements.
Composite:
Your camber is controlled mostly by the pre-composite deflection (self weight of beam + construction load + wet weight of concrete). The idea is to camber the beam enough such that it does not deflect (sag) due to the wet weight of concrete. It is important because if the beam sags under the wet weight of concrete, then you will need to add more concrete to keep the floor level, and it is a vicious cycle. Typically, beams are cambered to around L/360 before bumping up the member size.
Cambering a 40' beam to equate the dead load deflection does not void the L/240 requirement. It only means that you don't have to include the dead load deflection (which will now be ZERO) in computing total deflection. The total deflection will now be only due to the live and superimposed loads.
RE: Camber - need clarification
RE: Camber - need clarification
RE: Camber - need clarification
All this depends on the order of installation, so use your judgment.
That being typed, the usual recommendation is to not camber spandrel beams supporting cladding. I do not understand this recommendation and have violated it many times without a problem. Still, some people who've been around a long time recommend against it.
RE: Camber - need clarification
A total deflection limit is a visual deflection limit and it is affected by precamber.
If there is also a live load deflection limit, it would not be affected.