Quick Survey -- Beam dimension for RTU support
Quick Survey -- Beam dimension for RTU support
(OP)
I get this RFI on just about every project:
"Please provide the dimension off line 'x' for the W12x19..." supporting the RTU curb. Fabricators get insolent because they can't "finalize" shop drawings without these dimensions. We'll get the cut sheet from the MEP for a TRANE unit with dimensions and weights of the unit, and we provide support. Then we call out the weight on plan and show a beam adequate for support. We never dimension it. I guess the argument is that too many times the contractor will say "I can save $4000 by buying the unit from Mom n' Pop RTU," the mech. eng. gives the ok, but the unit is 8 inches narrower. No one bothers to tell us, so we have a beam in the 'wrong' place, and it's our fault. So, we tend to punt when this question comes up. We tell the GC to coordinate with his fabricator and provide the dimension based on the unit he buys. Is this fairly typical in the industy? Does anyone actually provide that dimension? And if not, why does every contractor ask this question?
As always... I appreciate your input.
"Please provide the dimension off line 'x' for the W12x19..." supporting the RTU curb. Fabricators get insolent because they can't "finalize" shop drawings without these dimensions. We'll get the cut sheet from the MEP for a TRANE unit with dimensions and weights of the unit, and we provide support. Then we call out the weight on plan and show a beam adequate for support. We never dimension it. I guess the argument is that too many times the contractor will say "I can save $4000 by buying the unit from Mom n' Pop RTU," the mech. eng. gives the ok, but the unit is 8 inches narrower. No one bothers to tell us, so we have a beam in the 'wrong' place, and it's our fault. So, we tend to punt when this question comes up. We tell the GC to coordinate with his fabricator and provide the dimension based on the unit he buys. Is this fairly typical in the industy? Does anyone actually provide that dimension? And if not, why does every contractor ask this question?
As always... I appreciate your input.






RE: Quick Survey -- Beam dimension for RTU support
RE: Quick Survey -- Beam dimension for RTU support
RE: Quick Survey -- Beam dimension for RTU support
DaveAtkins
RE: Quick Survey -- Beam dimension for RTU support
RE: Quick Survey -- Beam dimension for RTU support
RE: Quick Survey -- Beam dimension for RTU support
RE: Quick Survey -- Beam dimension for RTU support
RE: Quick Survey -- Beam dimension for RTU support
For what its worth, when sizing the RTU support beams, I generrally size them for a unit 50% (for larger RTU's) to 100% ( for small RTU's) heavier than what the mechanical engineer tells me they are going to weight.
I got tired of getting a call from the mechanical engineer, after the steel is all erected of course, to the effect of 'We orginally thought RTU-1 was going to weigh 5000 lbs, but we have had to modify our system and now RTU-1 weighs 10,000 lbs. Is this OK? '
RE: Quick Survey -- Beam dimension for RTU support
More generally, I only indicate "structurally significant" dimensions on the structural drawings. Dimensions that actually matter for the structural design (column grids and so on). Floating dimensions affecting architectural, mechanical units and so on MUST be "fixed" on the drawings by SOMEONE (definitely not structural) and my opinion is that it should be the discipline that warrants the piece to be located. It is unacceptable and unfair to the contractor to figure this out regardless whether they are competent enough to figure out themselves.