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

 

[P1ENG]

You mean this definition that I provided in #4 of my original post: Vasd = Nominal design wind speed applicable to methods specified in Exceptions 4 and 5 of Section 1609.1.1

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

 

[sandman21]

And? We use ASCE as a referenced standard from the building code, the building code will always govern over a reference standard. So what does the building code say is required to be shown on the contract documents? 1603.1.4 says both are required to be shown, no exceptions are given. What does 1609.3.1 say is required to be shown? The section says nothing on the matter as it is only the determination of the speed. While you may not be designing anything that would require ASD speeds, I am sure you are not the only person working on the project and the possibility exists that you have an item that would. Just to make it more unclear Table 1609.3.1 footnote b wind speed applicable in Exceptions 1 to 5 of section 1609.1.1. As an example AISI 230 still uses ASCE7-98 as the standard.

 

[P1ENG]

This deviation came from the state modular office. Modular buildings more often than not only have one engineer. So your assumption of other engineer involvement is incorrect. I do see the footnote listing exceptions 1-5 while the definition limits it to exceptions 4 and 5. So there is a discrepancy, but it is only on which exceptions are required, none of which are ASCE 7, except wind tunnel testing. I have yet to be convinced contrary to my original position. It seems we just won't agree. We will both be listing Vasd on our construction documents; you doing it happily and me begrudgingly.

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[wannabeSE]

P1ENG,

I think a better argument for your position is in 1603.1 where it states

The design loads and other information pertinent to the structural design required by Sections 1603.1.1 through 1603.1.8 shall be indicated on the construction documents.

It can be argued that V[sub]asd[/sub] 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 V[sub]ult[/sub] and V[sub]asd[/sub] on the construction documents for this type of construction.

 

[ckohl17]

P1ENg,
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.

 

[swearingen]

Researching something else and came across this thread. FWIW, I'm in P1ENG's camp. His argument is logical. The code goes most of the way to saying it's not required to put Vasd on the drawings without actually stating it specifically.


-5^2 = -25 ;-)

http://www.eng-tips.com/supportus.cfm

 

[Mjkkb2]

Interesting discussion, however what’s the problem with providing both numbers, it doesn’t take but a second to do it????