ASCE 7-05 Effective Wind Area
ASCE 7-05 Effective Wind Area
(OP)
Hi, I am new to ASCE 7-05, Eng Tips, and my internship as a structural engineer. I am trying to understand the effective wind area. I am given to understand that it is the area of, say, a wall in which a window is located. So, it is the area of the wall and not the window?
Thanks for helping a beginning structural engineer!
Thanks for helping a beginning structural engineer!






RE: ASCE 7-05 Effective Wind Area
For the design of the wall, if you are designing wall studs, I usually use the height of the wall squared divided by 3 as my area. If I am designing a concrete tilt wall panel than I will design using the area of the panel.
I hope that helps!
RE: ASCE 7-05 Effective Wind Area
One more question... Why are there no leeward pressures for walls given in the simplified version
(table 6-2 (method I) of ASCE 7-05?
Thanks!!!
RE: ASCE 7-05 Effective Wind Area
I don't use the simplified method much if at all in figure 6-2, but my assumption is that they are assuming that both the windward and leeward wall are the same height and have combined the pressures together for the one side. So if your walls are different heights, you will most likely have to use a different method to calculate the pressures.I usually use Method 2 in Figure 6-6
RE: ASCE 7-05 Effective Wind Area
Also, I'm curious to know where you got the wall^2/3 for the MWFRS tributary area.
Thanks again, I am getting a lot out of this dialogue.
RE: ASCE 7-05 Effective Wind Area
RE: ASCE 7-05 Effective Wind Area
RE: ASCE 7-05 Effective Wind Area
RE: ASCE 7-05 Effective Wind Area
For smaller areas, we take the so-called "lesser time average".Let me explain.
The wind velocity to be taken is a function of height( well understood by all) and time t(not so well understood.
Let me illustrate with an example.
Given :- Wind velocity Vbasic of 35 m/s at 10m above ground averaged over tbasic of 1 hour.
Design the following :-
1) Design a structure at height of 50m and time average of 3 sec.For structures with small areas averaging time is less.
2)Design a structure at height of 45m and time average of 3 minutes.For structures with large areas averaging time is greater.
So WindVel(Vbasic,tbasic,10m,50m,3sec)= say 47 m/s for case 1.(The expression to calculate the functionis given in API RP-2A.
Similarly
WindVel(Vbasic,tbasic,10m,45m,3 minutes)= say 44 m/s.
Rgds
RE: ASCE 7-05 Effective Wind Area
I don't disagree with the difference in wind pressures based on time, however in the US all wind calculations are based on a 3-second gust regardless of the size of the structure. The effective area does modify the pressure but I don't know that it is specifically because of time. I don't know of any provision in the code that says if the structure is larger you use a corresponding averaging time.
As for your question Heck83, if you are designing the rafters then the effective area for each one would be different based on the span and the tributary width as we have discussed earlier. You also have to pay attention to what zone the rafter falls in (zone 1, zone 2, and zone 3) as the pressures vary greatly between the zones. You can see how these zones are defined in figure 6-3 of the ASCE 7-05
RE: ASCE 7-05 Effective Wind Area
Stenbrook, do you think it is not acceptable to consider a plane of a roof to be a system, and therefore use the total area of the plane? Of course, this is paying proper attention to which zone(s) lie in the plane.
RE: ASCE 7-05 Effective Wind Area
RE: ASCE 7-05 Effective Wind Area
RE: ASCE 7-05 Effective Wind Area
RE: ASCE 7-05 Effective Wind Area