camber tolerance

By SWN1158 (***)

Date 07-20-2018 19:43 Edited 07-20-2018 19:46

We have a W24 x 55 x 59-3 that is designed to have a 1/2" camber in it. I checked the natural camber in it and it has 1/4". The latest COSP states the following......

6.4.4. For beams that are specified in the contract documents with camber, beams received by the fabricator with 75% of the specified camber shall require no further cambering. Otherwise, the variation in camber shall be as follows:

(a) For beams that are equal to or less than 50 ft (15 000 mm) in length, the variation shall be equal to or less than minus zero / plus 1/2 in. (13 mm).

(b) For beams that are greater than 50 ft (15 000 mm) in length, the variation shall be equal to or less than minus zero / plus 1/2 in. plus 1/8 in. for each 10 ft or fraction thereof (13 mm plus 3 mm for each 3 000 mm or fraction thereof) in excess of 50 ft (15 000 mm) in length.

For the purpose of inspection, camber shall be measured in the fabricator’s shop in the unstressed condition.

Commentary:

There is no known way to inspect beam camber after the beam is received in the field because of factors that include:
(a) The release of stresses in members over time and in varying applications.
(b) The effects of the dead weight of the member.
(c) The restraint caused by the end connections in the erected state.
(d) The effects of additional dead load that may ultimately be intended to be applied, if any.

Therefore, inspection of the fabricator’s work on beam camber must be done in the fabrication shop in the unstressed condition.

The 1/2" camber was not specified by us when the material was purchased, so I don't think that 6.4.4 would apply. The 1/4" camber that exists is natural, and not induced. This W24 x 55 has secondary (detail) pcs. welded to it, so I think that D1.1 camber tolerances would apply. The top flange of this beam is also supporting field bolted joists, but I'm having a little trouble trying to decide which "beam and girder camber" paragraph, with regard to tolerance, I need to apply to my situation. Right now I'm more confused than a homeless man on house arrest.

By welderbrent (*****)

Date 07-21-2018 03:54

Good Day Scott,

Nice to see you around on occasion again.

So, First, the "For beams that are specified in the contract documents with camber" does not indicate those members ordered by you from your steel supplier. That refers to what the engineer has specified for the condition of the member when shipped by the fabricator to the job site. As such, if it came from the mill and steel supply with 75% of the specified camber it is okay as received by you.

Thus, Your member could have arrived with a 3/8" camber and you would not have to add any camber to it. Since it is only 50% or 1/4" camber you need to add more camber. The allowable tolerances would now be -0, +5/8" (1/2" over for the first 50' and 1/8" for the additional 9'-3"). So it can be camber from the specified 1/2" to a total of 1 1/8".

Now, having looked at AISC COSP, note that as the applicable working code, D1.1 would rule. So, as you didn't say anything about it being embedded in concrete, I would be looking at Clause 5.22.3. You have specified camber but not with concrete haunch. So, for your beam length, -0, +3/4". Since your specified camber is 1/2", now you can be between 1/2"-1 1/4".

The COSP is a reading of STANDARD PRACTICE. It does not necessarily dictate the final conditions to be adhered to. But, the applicable code, in your case D1.1, does give us just a slight bit more latitude in camber but pretty close to the standard practice from COSP.

Hope this helps.

He Is In Control, Have a Great Day, Brent