Vult and Vasd on Construction Documents
Vult and Vasd on Construction Documents
(OP)
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.
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
Quote (Juston)
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






RE: Vult and Vasd on Construction Documents
RE: Vult and Vasd on Construction Documents
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
RE: Vult and Vasd on Construction Documents
RE: Vult and Vasd on Construction Documents
RE: Vult and Vasd on Construction Documents
RE: Vult and Vasd on Construction Documents
RE: Vult and Vasd on Construction Documents
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
RE: Vult and Vasd on Construction Documents
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.
RE: Vult and Vasd on Construction Documents
Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant
RE: Vult and Vasd on Construction Documents
RE: Vult and Vasd on Construction Documents
Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant
RE: Vult and Vasd on Construction Documents
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
RE: Vult and Vasd on Construction Documents
RE: Vult and Vasd on Construction Documents
RE: Vult and Vasd on Construction Documents
Maybe I am missing something. I assume that the IBC requires both because it says ( with bold added for emphasis):
RE: Vult and Vasd on Construction Documents
Bold added for emphasis. I feel like no one is reading my original post.
Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant
RE: Vult and Vasd on Construction Documents
1603.1.4 says it is required to be on construction documents
RE: Vult and Vasd on Construction Documents
I'm still curious what ICC would say in an opinion request.
Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant
RE: Vult and Vasd on Construction Documents
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.
RE: Vult and Vasd on Construction Documents
There is nothing "odd" about the definition. You want to ignore the definition because you think it is odd, but that definition is the basis of my argument.
By definition, Vasd only exists to be used in the referenced standards of those exceptions (for antenna and flagpoles). If you are not using those standards, then there is no need for Vasd. Those standards obviously have their own pressure calculations (not equal to ASCE) and have not been updated to use the new wind speeds. If you use ASCE, there is no need for Vasd because no equation in the ASCE uses the term Vasd.
Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant
RE: Vult and Vasd on Construction Documents
RE: Vult and Vasd on Construction Documents
Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant
RE: Vult and Vasd on Construction Documents
I think a better argument for your position is in 1603.1 where it states
It can be argued that Vasd is not pertinent, therefore it is not required to be listed. The problem with this argument is that the exception to 1603.1 for conventional light frame construction still requires Vult and Vasd on the construction documents for this type of construction.
RE: Vult and Vasd on Construction Documents
My take on 1603.1 is also that Vasd is only required on the Structural Drawings when it is applicable to the project(i.e. when the exceptions listed under 1609.1.1 are applicable). I would go as far as to say Vasd is not only not required to be listed, but shouldn't be. It seems that if Vasd is listed, designers of wall components, roof components, etc. could be easily mislead into thinking that the Vasd value provided on the drawings is the wind speed to be used in calculating the design wind load that are used in the load combinations. Using the reduced value of Vasd (sqrt0.6xVult) would result in significantly lower values, since wind values are further and additional 0.6 factor is applied in the updated ASD load combinations.