EOR Design Drawings for Pre-Engineered Roof Trusses
EOR Design Drawings for Pre-Engineered Roof Trusses
(OP)
Hi Everyone!
As the EOR for a new building with pre-engineered roof trusses (wood or cold-formed steel), do you show a roof plan with C&C pressures and zones for the truss designer/fabricator? Or, do you just state the required wind design parameters on the notes (Kzt, Kd, V, exposure, etc.) and let the truss fabricators calculate wind loads themselves? Will fabricators even calc wind loads on their own if you show them on your drawings as an independent back check, since they typically will stamp their own shop drawings, or do they just take the EOR's word for it? Is it a regional thing like with steel connection details? What the "right" thing for the EOR to do when putting together design drawings for bidding purposes?
As the EOR for a new building with pre-engineered roof trusses (wood or cold-formed steel), do you show a roof plan with C&C pressures and zones for the truss designer/fabricator? Or, do you just state the required wind design parameters on the notes (Kzt, Kd, V, exposure, etc.) and let the truss fabricators calculate wind loads themselves? Will fabricators even calc wind loads on their own if you show them on your drawings as an independent back check, since they typically will stamp their own shop drawings, or do they just take the EOR's word for it? Is it a regional thing like with steel connection details? What the "right" thing for the EOR to do when putting together design drawings for bidding purposes?






RE: EOR Design Drawings for Pre-Engineered Roof Trusses
RE: EOR Design Drawings for Pre-Engineered Roof Trusses
Mike McCann
MMC Engineering
RE: EOR Design Drawings for Pre-Engineered Roof Trusses
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: EOR Design Drawings for Pre-Engineered Roof Trusses
Calculating the loads is not much effort, and you have the opportunity to add loads for likely (but not certain) future mechanical loads that the truss engineer will not add. 3 psf extra can provide a lot of extra capacity for a minor cost increase.
If the truss engineer calculates loads (wind, seismic, dead ... for vertical up and down, and lateral at the wall...) that are different than what you expect, all of the engineering effort (including your review and coordination time) after that is wasted.
In addition, I would be explicit about the connection of their component to your superstructure, since the coupling and rigidity ("fixity") of the connection can load your structure in ways you do not intent.
Even for reasons of pure self-interest, the more you give the "downstream" engineer, the less back-and-forth there will be.
RE: EOR Design Drawings for Pre-Engineered Roof Trusses
RE: EOR Design Drawings for Pre-Engineered Roof Trusses
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: EOR Design Drawings for Pre-Engineered Roof Trusses
Just to clarify, I always show the truss diagrams with dead and live load requirements. I also always calculate the reactions, both lateral and vertical (uplift) based on my own wind calculations, mostly for comparison with the truss designers reactions as woodman88 pointed out.
I was just curious how others handle the C&C wind uplift when dealing with delegated truss designers, as I have seen both ways (defining only wind parameters on the drawings and showing roof plans with C&C pressures and Zones).
RE: EOR Design Drawings for Pre-Engineered Roof Trusses
There are days when I wake up feeling like the dumbest man on the planet, then there are days when I confirm it.
RE: EOR Design Drawings for Pre-Engineered Roof Trusses
We design all the connections conservatively up front for the assumed truss layout. But we gave up a long time ago trying to get the truss manufacturer to lay out the framing plan a specific way, and also gave up guessing. Also I have come to the conclusion that they know trusses and have the programs to quickly come up with the most efficient design. So for CYA, we put a large note on the roof framing plan indicating the truss connections are preliminary, and final design will be based on the final truss layout and reactions provided on the truss shop dwgs. We also reserve the right to modify the truss connections as needed. The cost implications of connection modifications should be minimal anyway.
Finally, remember to design the connections for all forces you are imparting on them, not just uplift, but possibly out-of-plane lateral forces from the walls, and shear forces from the diaphragm if you do not use blocking. Simpson provides all of these allowable reactions in their catalogs with diagrams so it is pretty clear, and then you just use their interaction equations.
RE: EOR Design Drawings for Pre-Engineered Roof Trusses
Simple loading on a component can be described in paragraph form, but for typical load conditions with mechanical equipment on the top chord, hanging loads on the bottom chord, wind uplift, and chord axial loads from wind/seismic, and so on, a picture is worth a thousand words.
RE: EOR Design Drawings for Pre-Engineered Roof Trusses
What are the requirements in your stare?
Mike McCann
MMC Engineering
RE: EOR Design Drawings for Pre-Engineered Roof Trusses
RE: EOR Design Drawings for Pre-Engineered Roof Trusses
RE: EOR Design Drawings for Pre-Engineered Roof Trusses
Wouldn't it be great if all posters from the United Stares could proofread their posts... :)
tg