Vult and Vasd on Construction Documents 1

[P1ENG]

I recently had the privilege of doing a project for MD (2015 IBC). One of my deviations was that I must list both Vult and Vasd on the drawings. I did it to please the state, but I don't know why I had to do it. They referenced section 1609.3.1 as the requirement for listing both, but I still disagree. I was told that if I think there is a conflict with the IBC that I should contact ICC for an opinion, but I am not a member and there is no conflict in my interpretation. Also, opinions are not official positions of ICC and the state could still ignore it. I wrote them the following.

Please follow the progression through the code below.

1.) 1603.1.4(1): Ultimate design wind speed, Vult, (3-second gust), miles per hour (km/hr) and nominal design wind speed, Vasd, as determined in accordance with Section 1609.3.1.
2.) Go to 1609.3.1 to find out how to be "in accordance"
3.) 1609.3.1: When required, the ultimate design wind speeds of Figures 1609.3(1), 1609.3(2), and 1609.3(3) shall be converted to nominal design wind speeds, Vasd, using Table 1609.3.1 or Equation 16-33.
4.) When is it required? In this very same section (1609.3.1) Vasd is defined as "Nominal design wind speed applicable to methods specified in Exceptions 4 and 5 of Section 1609.1.1.
5.) Go to 1609.1.1 to find out Exceptions 4 and 5 are:

* Designs using NAAMM FP 1001​

* Designs using TIA-222 for antenna-supporting structures and antennas, provided the horizontal extent of Topographic Category 2 escarpments in Section 2.6.6.2 of TIA-222 shall be 16 times the height of the escarpment.​

6.) Notice ASCE 7 is not part of exceptions 4 and 5 so there is no need to list Vasd on construction documents.

I have provided an actual argument above, but my logical argument: Vasd provides no relevant information to the building department unless it is to cross reference wind speeds used in the standards of Exceptions 4 and 5 (NAAMM FP 1001 and TIA-222) which relate to flagpoles and antenna structures. So why require it for all structures? I don't want to ruffle any feathers, but at the same time I don't like having to do something that isn't necessary.

A Vasd of 93 mph with risk category I or IV are both equal to a Vult of 120 mph? Vasd has to be limited to risk category II structures (importance factor 1) anyway (my structure is overdesigned as RC=IV) or the conversion falls apart:

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[ash060]

Alot of times this has to do with openings. Authorities will require that openings (windows and doors) can resist the applicable wind loads. The window and door manufacturer will have tested assemblies that meet certain wind pressures. The wind pressures used for testing are ASD based, so when the opening is purchased the rating will be compared to what is specified.

 

[P1ENG]

Finally! An actual reason for requiring it. The building department gave me no such reasoning. They have no idea why they require it other than they think the IBC says so. But still, per my comment at the end, the Vasd does not consider importance factor. This is moot point if all windows and door reports are based on a RC=II.

So the building department can require it for such a reason (an amendment), but not because they base it off of any authority of the IBC.

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[spieng89]

This is good info, currently doing a project in IBC 2015 and this would apply

 

[UcfSE]

A structure in category 3 or 4 does not have the same wind speed as a structure from category 1, or category 2. When you convert to V[sub]asd[/sub], you get a higher number for cat 3 or 4 vs 1 and 2. There is no need to account for an importance factor. The calculation is only meant to go one way from ult to asd, not from asd to ult. V[sub]asd[/sub]=V[sub]ult[/sub]*√0.6

 

[wannabeSE]

See 2015 IBC section 1603.1 for information required on construction documents. Vase and Vult are required.

 

[sandman21]

Not just openings, but cladding systems, roofing material are still in ASD.

 

[P1ENG]

ucf, OK, say I have a hospital in Indiana (RC=IV, so 120 mph). That means I have a hospital with Vasd equal to 93 mph but it is still a risk category IV building. What do I do with this information of 93 mph? Find a door that is rated for 93 mph? What components list approval based on design wind speed? Don't you rather find components rated for pressure, not wind speed? If not, what did you do prior to 2012? Say a door is rated for 90 mph but wouldn't it also have to include the risk category (and end/interior zone, exposure, etc) since it affects the pressure? Or can any 90 mph door be used on anything from interior zones of sheds in the city to end zones of prisons on the coast as long as it is in a 90 mph zone?

wannabe, care to read the OP? You are directing me to code I quoted.

sandman, I thought windows/doors, cladding, roofing, etc. are rated for pressures not speed. So, putting the required C&C pressures on the design documents is sufficient in choosing rated components and cladding. If their documentation is based on ASD pressures, multiply the pressures by 0.6.

I don't think I will ever be convinced that putting both on will ever help anybody. I am surprised no one has agreed with me though. If anyone does have an ICC membership, perhaps you wouldn't mind passing on my original post (specifically the quoted part progressing through the code) to get an ICC opinion?

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[wannabeSE]

P1ENG.
Well 1603.1 is pretty clear I thought you missed is because you keep referencing 1609 and said "They referenced section 1609.3.1 as the requirement for listing both".

Why do you think it is not required to list ASD and Ult wind speeds on the construction documents? Or, do you think it should not be required? Or are you upset because you got a trivial plan check comment?

The requirement to put the wind speed on construction documents has been around for quite a while (2000 IBC?). When ASCE 7 switched wind speeds, having both on the construction documents seemed like a good idea so it is very clear. I have even included strength and ASD CC wind pressures on the construction documents.In a couple years, I can see changing back to having one wind speed on construction documents.

 

[P1ENG]

Wannabe, To be clear, I think the IBC does not require both to be listed unless the structure is an antenna, antenna support structure, or flagpole. I also personally think it shouldn't be listed. I don't mind the plan check comment, but I do mind being forced to do something illogical regardless of how trivial or easy it is to comply. Please follow the numbered list in the quoted text of my OP to understand why I think it shouldn't be there. I have been as clear with my thought process as I can. Your last paragraph has some merit, but it has been 7 years since the new wind speeds came out. If I am designing to the 2012 or 2015 IBC, ASD wind speeds are of the past. If they still want ASD wind speeds, why bother adopting the ASCE 7-10. I have also put the nominal and ASD PRESSURES on the design document, and I agree that helps clarify when a jurisdiction recently adopts the new wind speeds, but I stand by the fact that the Vasd provides no realistic benefit. Section 1603.1 directs you to go to 1609.3.

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[sandman21]

I have seen them different ways from different companies, one day everyone will be on the same page and you wont have to include it. ICC is simply going to refer you to 1603.1, the when required in 1609.3.1 does not change the requirements of 1603.1. Your explanation to them is far more energy than I would ever expect to spend on such a minor issue.

 

[P1ENG]

Sandman, I don't disagree it is minor. This discussion could lead to more knowledge though.

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[P1ENG]

Sandman, sorry I would edit my post but you are active right now so I don't know if you would get the notification of a new post.

If you have time, humor me and go to 1603.1. Find this text within that section and then tell me if you still think 1609.3 has no influence on 1603.1: "1603.1.4(1): Ultimate design wind speed, Vult, (3-second gust), miles per hour (km/hr) and nominal design wind speed, Vasd, as determined in accordance with Section 1609.3.1".

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[kmart30]

They are for windows, doors, roofing, cladding, ect ,ect. Here in Florida contractors as required to include the product approvals for these materials when they submit for a building permit. Plan reviewers and inspectors can cross check your design pressures on the plans with the product approvals testing data. I include both ultimate and nominal when I do a project in Miami-dade or in a HVHZ area; all other areas I just include ult.

 

[UcfSE]

Ideally the manufacturer would go by the pressures, because pressures will include exposure effects, topography effects and others that a simple indication of wind speed will not. Not all of the manufacturers have a test report that indicates pressure; instead it indicates a wind speed rating and they tend to be blissfully ignorant of the difference. So in your example, someone would look for a door with a wind speed rating of better than 93 mph. To be clear, I only include the V[sub]asd[/sub] because the building code indicates it. I'm not typically involved with those who are choosing these components based on this information or how useful it ends up being. I also place a note under my wind pressure tables indicating the values are at strength level, and that service-level wind pressures can be obtained by multiplying the wind pressure table by 0.6 to help out where I can.

 

[wannabeSE]

P1ENG,

Maybe I am missing something. I assume that the IBC requires both because it says ( with bold added for emphasis):

1603.1.4 Wind design data
The following information related to wind loads shall be shown, regardless of whether wind loads govern the design of the lateral force-resisting system of the structure:
1. Ultimate design wind speed, V[sub]ult[/sub], (3-second gust), miles per hour (km/hr) and nominal design wind speed, V[sub]asd[/sub], as determined in accordance with section 1609.3.1.
2 Risk category . . .

 

[P1ENG]

1603.1.4 Wind design data
The following information related to wind loads shall be shown, regardless of whether wind loads govern the design of the lateral force-resisting system of the structure:
1. Ultimate design wind speed, Vult, (3-second gust), miles per hour (km/hr) and nominal design wind speed, Vasd, as determined in accordance with section 1609.3.1.
2 Risk category . . .

Bold added for emphasis. I feel like no one is reading my original post.


Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[wannabeSE]

1609.3.1 says when required this is the procedure
1603.1.4 says it is required to be on construction documents

 

[P1ENG]

Ok, I think we have read the same thing but now we just disagree. That's fine, I wanted others' opinions. As I read the code, I can say that Vasd does not exist per 1609.3 because I am not designing to those standards in the exceptions. So "in accordance" with 1609.3, Vasd doesn't exist.

I'm still curious what ICC would say in an opinion request.

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[Once20036]

I`m with wannabeSe.
1603.1.4 says it is required
1609.3.1 says how to calculate it

The reference to exception 4 and 5 of 1609.1.1 are definitely odd, but those exceptions are referred to simply for the definition of what Vasd is.