Pre-engineered Metal Building Design Loads
Pre-engineered Metal Building Design Loads
(OP)
I have a question about the gravity loading to use for pre-engineered metal buildings.
I don't have a copy of the MBMA manual. Does anyone know if it allows different loading and related structural criteria than the governing building code (Florida Building Code in this case)?
What are the typical superimposed/collateral gravity loads that would be used for a church?
I don't have a copy of the MBMA manual. Does anyone know if it allows different loading and related structural criteria than the governing building code (Florida Building Code in this case)?
What are the typical superimposed/collateral gravity loads that would be used for a church?






RE: Pre-engineered Metal Building Design Loads
Alexander Newman discusses this in his book "Metal Building Systems - Design and Specifications." He concludes that with the real-world behavior of purlins loaded with concentrated loads, such as from sprinkler mains, not being fully understood, that it's best to err on the side of caution and go with a higher collateral load.
RE: Pre-engineered Metal Building Design Loads
And this is not to mention the temporary construction load.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Pre-engineered Metal Building Design Loads
They have responded that they use 5 psf for offices/churches, etc. and 3 psf for warehouse type structures.
I am curious if the MBMA manual has a reference for recommended loads.
Also ASCE7 has a minimum allowance of 4 psf for mechanical ducts. Do you guys read this as a requiremnt or a recommendation?
RE: Pre-engineered Metal Building Design Loads
"Minimum Design Loads for Buildings and Other Structures"
I take the key word to be "Minimum".
RE: Pre-engineered Metal Building Design Loads
If you are using ASCE 7 as your criteria base, then all of its provisions apply, and as TJ stated...they are "Minimum".
Regarding another issue with purlins in PEMB's, when you apply a concentrated gravity load such as to hang sprinklers or mechanical equipment, you risk taking the purlin out of plane for its design properties. For wind loads on the gable end, this can create a buckling problem for the purlins...Check it.
Also, keep in mind that if you have large doors on the building, such as a hangar, you should design as partially enclosed rather than enclosed, because of the gaps at the doors (see ASCE 7 Commentary C6.5.11.1)
RE: Pre-engineered Metal Building Design Loads
There is a table of various building components/materials and their weights. That is where this 4 psf comes from. This table is located in the Commentary, which is not part of the ASCE Standard Minimum Design Loads for Buildings and Other Structures. It is provided for information purposes only.
So, 4 psf may be a good value to use, but it is not mandated that you use at least that.
RE: Pre-engineered Metal Building Design Loads
RE: Pre-engineered Metal Building Design Loads
They, and others, obviously need to up the anty here and apply the actual dead loads that are going to be seen by that particular structure, not what they feel is normal in the industry for that type of structure.
You need to DEMAND the 16 psf, and document the loads seen by the structure that totaled to that amount. As the supplier, they MUST comply to your specs.
Possible additional problem: Did they already submit a bid based on the 3 to 5 psf value to design, fabricate and erect the structure?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Pre-engineered Metal Building Design Loads
I have to disagree with some of what you said. It is the EOR who has to determine the building loads to be addressed by the metal building manufacturer; they don't know the details of the building the way the EOR does. If you give them the loads to design for, they will do it.
Secondly, the Metal Bldg. industry differentiates between dead load (the weight of the building componets) and collateral load (the weight of attached items in the building treated as dead load).
On a recent job, one method of handling this for a light industrial building was to call out a DL = 4 psf over the entire roof area (the weight of the actual building components), plus 4 psf collateral on purlins and 10 psf collateral on main frames. The result was that purlins were designed for a total "dead load" of 8 psf and main frames 14 psf; realistic values for this particular structure.
RE: Pre-engineered Metal Building Design Loads
Ceiling..............1 psf
Sprinklers...........3 psf
Ductwork.............3 psf
Lights...............1 psf
Misc.................2 psf
I guess I am starting to get to the point that I am an old fart but this business that is my chosen profession is not so much fun anymore.
RE: Pre-engineered Metal Building Design Loads
If you look on the calcs and add their dead load value to the collateral load value, what is the total? If it is 16 psf or greater, I think you may be OK if the loads are correctly applied with the proper load combinations.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Pre-engineered Metal Building Design Loads
Got an email from the supplier with their standard dead loads:
Suspended ceiling....1 psf
Lighting.............0.1-1 psf
HVAC ducts...........1 psf
Sprinklers...........1.5 psf (dry)
3.0 psf (wet)
So that is how they arrive at 5 psf. Only 1 psf for HVAC. If the owner wants to add anything in the future they would have to add framing.
RE: Pre-engineered Metal Building Design Loads
Their dead loads are a bit light, but then they will argue that they are only supplying a building shell with a minimal allowance for anything.
I am also of the opinion that these buildings typically have way too many air leaks to be considered enclosed (if large doors of any type, particularly rolling doors). I did a check on one just before going to trial on it about 6 months ago....windward gaps exceeded 4sf allowable around doors (for a 12x12 door, you only need a 1-3/8" gap all around to exceed, assuming a seal on the bottom)
RE: Pre-engineered Metal Building Design Loads
This implies that there are exceptions. The manual also states that the local BO can alter these load values if he or she sees fit. This includes you as the approving engineer of record.
For the record, collateral loads are all those dead load weights of materials that are not supplied by the metal building manufacturer, such as mechanical, electrical, suspended ceiling, sprinklers, etc. The decking does not see these loads, but the purlins might, and the mainframes will.
Section 1.1 Introduction, at the end of the first paragraph, an interesting statement is made. After referring to the IBC and ASCE7 as the source documents, it states that "The user should refer to the source documents for a complete presentation of the loading requirements and only use this Manual as a review and commentary."
Sounds pretty explicit to me. Stick to your guns.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Pre-engineered Metal Building Design Loads
Roof top HVAC units should have supplemental framing to carry the load to main framing members. I think this is one reason a dual load system is good, every purlin is not going to see an RTU but any main framing member may.
RE: Pre-engineered Metal Building Design Loads
RE: Pre-engineered Metal Building Design Loads
Regarding up lift, I suppose everyone has their own way of looking at it, but I think collateral loading should be added with DL for the uplift calculation. If they are supposed to be real loads, they should be included. And, they still would get factored down, .6(DL+CL).
Just my two cents.
RE: Pre-engineered Metal Building Design Loads
RE: Pre-engineered Metal Building Design Loads