Delegation of Wind Load Calculations? 6

271828 · Mar 15, 2023

Greetings everyone. One of my clients is a steel fabricator. They are working on a project with open-web steel joists. I think the joist manufacturer is a sub to the fabricator. I haven't been involved in the project up to this point.

It's a small retail building in a high wind zone. The structural design information is on the architectural drawings, so the architect is apparently acting as the registered design professional for structural. The construction drawings do not include any wind load design criteria for delegated design. The joist manufacturer sent an RFI to the fabricator asking for the wind uplift pressures.

Clarification: this is only about roof uplift components and cladding, not about main wind force resisting system design.

I'm told that an RFI was sent to the architect about this, and the answer was the joist manufacturer is to calculate the uplifts. They're obviously violating the IBC Ch. 16 with this, but they probably don't know that. To get the project unstuck, my client contacted me to see if I can provide the wind uplifts for the joist design.

I have a license in the project state and can easily provide these. I could clearly state that my scope is limited to the pressures for steel joist design. I could also request that the calculations be sent for approval by the registered design professional, but I'm not sure they would be.

The fact that the IBC says this info must be on the construction docs implies that this should not be delegated. Should I contact the building official to make sure they're OK with this?

I feel like I might be missing something here.

Any advice would be appreciated!

skeletron · Mar 15, 2023

I think contacting the Building Official would be a reasonable first step.
Can you contact the Architect, since they are the registered design professional? Or is that crossing the client/consultant line?

Gut feel is that, yeah, you can probably do the calculation from a numbers-on-paper point of view. But, ultimately it's a liability issue because who is owning the building design. In my experience, you can't (or shouldn't) really delineate the Vertical System design from the Lateral System design because they should coordinate.

I don't practice in the States, so only providing an opinion based on how it's generally presented here.

271828 · Mar 15, 2023

Thanks skeletron.

A clarification: this is only for roof joist uplift design, so it's components and cladding, not main wind force resisting system

driftLimiter · Mar 15, 2023

Way I see it, the original construction documents are in violation of IBC 2018 1603.1.3 the Registered Design Professional is required to indicate the Design Pressures to be used for exterior C&C materials that are not specifically designed by the EOR.

The most proper mechanism I can think of would be for the Architect (EOR) to contract with you to determine C&C pressures and MWFRS pressures for the Joist MFG to design (delegated).

This brings up the dubious point that I am sure you don't want to tread into. Should the Architect really be stamping design load data if they cannot produce it themselves? Any competent engineer should be able to determine these pressures and indicate them properly. The arch have already shown their hand that they don't really understand the structural provisions (even the most basic CDs requirements) by calling for delegated design without indicating the proper wind design data.

If you don't get the Arch to indicate this properly on the design drawings, and you instead submit your calcs and your statement limiting scope, well now all you have done is become the most competent engineer on a project that is not conformant to the IBC.

phamENG · Mar 15, 2023

Who designed everything else? Beams? Columns? Walls? MWFRS? If they can't figure out what the uplift should be, how did they design whatever bracing or shear walls were required?

I think driftLimiter is mistaken - you won't be the most competent engineer on the project; you'll be the only engineer on the project.

dik · Mar 15, 2023

I'd spec the roof design load and have it confirmed by the Architect... I wouldn't likely go the AHJ route...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

271828 · Mar 16, 2023

Thanks driftLimiter, phamENG, and dik.

Spurred on by some of your comments, I've requested that a more strongly worded RFI be sent, pointing out the IBC and SJI Specification sections that say this info must be in the construction drawings.

If the architect refuses, I'll probably provide the calc with a lot of CYA and scope limiting language, and push for it to go through approval.

MotorCity · Mar 16, 2023

You can delegate any part of the design you want to. Ultimately, all parts of the design whether delegated or not are under the responsibility of the EOR (or RDP in this case??). The concept of delegated design is just another form of a subcontract arrangement, it does not relieve the EOR of responsibility. However, the wind loads, if delegated, should have been done so prior to issuing the drawings. It is not in compliance with IBC to issue drawings without the proper loading noted. To place the burden of calculating wind load on the joist manufacturer (or any third party supplier) is not appropriate. They are not in the business of calculating YOUR wind loads, they make joists based on loads they are given.

JedClampett · Mar 16, 2023

Maybe I'm mistaken but, when I've got wood truss submittals, the engineer used his own winds loads, no matter what I provided. He put the wind speed, height, etc., in his software, pushed enter, and got a wood truss package. Granted, the calculations were pretty much incomprehensible, but he (or she) sealed them, so I considered them all right.
What is the difference between the supplier doing their own wind loads and delegating them?

I went to a seminar on deferred design a few months ago and was shocked on what was being deferred:

PhamENG said:
Beams? Columns? Walls? MWFRS? If they can't figure out what the uplift should be, how did they design whatever bracing or shear walls were required?

Pretty much all those things and more. It seems that the EOR is more of a clearing house for deferred designs, hopefully assembling them into some kind of structure. The only saving grace is that, on these type projects, the EOR is still legally responsible for the total building. But the responsibility will get diluted with all these engineering entities involved.

phamENG · Mar 16, 2023

So the section of the code being referenced (IBC 1603.1.4) lists the wind design information required on the "Construction Documents."

Construction Documents are defined as "Written, graphic and pictorial documents prepared or assembled for describing the design, location and physical characteristics of the elements of a project necessary for obtaining a building permit."

To be fair, it doesn't say who needs to put that information on the Construction Documents. Yes, it is typically the Designer(s) of Record. But in the case of trusses, as Jed pointed out, it's often "shown" in the truss profile sheets (which most jurisdictions require for permitting and are required to be kept on site at least until the framing inspection is complete).

Joists are a little different as you get into the Code of Standard Practice. You can deviate from it, but it should be made very clear that you are deviating and make sure that the contractor catches it. Doesn't sound like that was done here. And, unless I'm mistaken, the SJI COSP takes it a step further than the IBC and requires you to list net uplift on the joist, not just a generic C&C wind load schedule.

JedClampett said:
I went to a seminar on deferred design a few months ago and was shocked on what was being deferred:

I hear you, and even had a client at my last firm ask me why he even hired us when he saw the list of things my boss decided we would defer on one of his jobs. But that's not my concern here. OP said that structural requirements were listed on the A sheets. That's fine if you're looking at a ladder or some little miscellaneous fabrication. But the roof joists? It sounds to me like there is no EOR to properly specify and manage those deferrals.

271828 · Mar 16, 2023

Thanks again everybody. It's great to have all of your input. When something atypical comes up, it seems perilous to have only the ideas rattling around in my head.

phamENG said:
Joists are a little different as you get into the Code of Standard Practice. You can deviate from it, but it should be made very clear that you are deviating and make sure that the contractor catches it. Doesn't sound like that was done here. And, unless I'm mistaken, the SJI COSP takes it a step further than the IBC and requires you to list net uplift on the joist, not just a generic C&C wind load schedule.

This is a great chance to ask a question. SJI 200 Section 5.12 states "Where uplift forces due to wind are a design requirement, these force shall be indicated on the structural drawings in terms of net uplift in pounds per square foot."

I'm not completely sure I know what they mean by "net." My first interpretation was that they need the result of 0.6D+0.6W. So I was starting to try and figure out a dead load to use. However, "net" could also mean only the wind part: exterior suction plus interior pressures. Any of you have a thought on that, or better yet a reference with an example?

driftLimiter · Mar 16, 2023

We had always interpreted net to mean 0.6D+0.6W. I kind of find this clunky and a potential for error though so whenever I use the Net, I also provide on the same tables the D and W values used to derive each net pressure.

phamENG · Mar 16, 2023

I've always understood net uplift to be 0.6D+0.6W or 0.9D+1.0W, depending on the EOR's specified analysis procedure/philosophy.

271828 · Mar 16, 2023

One weird thing about this job is there are parapets over 3 ft tall, so the downward pressure in zones 2 and 3 are pretty high. D + 0.75(0.6W) + 0.75Lr might control over D + Lr. Thus, I need to break these things out and not only give 0.6D+0.6W.

I guess I'll have to do some explaining!

Thanks again everybody!

driftLimiter · Mar 16, 2023

Check your zone 3 pressure against footnote 5 of Figure 30.3-2A if it applies to this situation it could afford you some reduction in the corners.

271828 · Mar 16, 2023

Yep, that's what I was looking at. The Zones 2 and 3 suctions are close enough that I consolidated those anyway. The positive values of (GCp) being set to Zones 4 and 5 are causing the pressures to be higher.

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