ASCE 7-05 Simplified wind procedure

[canwesteng]

I'm looking for someone older and wiser to help me with an issue with ASCE 7-05. Unfortunately, this is a bit before my time, but it is technically the code in force in a jurisdiction I'm working in, and the old 3 second gusts don't play well with the new limit state gusts in modern ASCE 7. The simplified MWFS procedure gives a load on one wall only - no problem for the lateral load resisting elements... but the columns that take this load up to the diaphragm now see the sum of the windward and leeward pressure. I'm sure how to approach this - basically I've got bending moments in my columns that are 50% too high. How was this tackled when 7-05 was in force in the US?

 

[XR250]

I always thought they work out roughly the same if the newer code is converted to ASD.

 

[canwesteng]

I think it's pretty close, even actually a little lower for MWFRS in 7-16, but ultimately this needs to be reviewed by a local AHJ equivalent, so I prefer sticking within the bounds of the code. My though is to divy up the wind load by windward/leeward side using the analytical method.

 

[RWW0002]

The All Heights Method and Envelope Procedures do not vary much between ASC7 05 thru ASCE7 16 to my knowledge (although their names may have changed). Obviously there is the ultimate vs nominal wind speed difference, but that's pretty easily accounted for. Some of the simplified methods over the years have not always meshed real well, but the methods that have been around for a while have not undergone super significant changes in a long time.

I agree that for the case you're describing above some simplified methods may be too conservative, and you may need to pull out Windward and Leeward pressures (and pay attention to components and cladding pressures as well), but I'm not aware of any significant code change from '05 to current that would affect this.

By the way it blows my mind that Engineers that practiced with ASE 7-05 are suddenly the old guys.. this makes me feel really old

 

[canwesteng]

Old guys, just a bit older than me haha... If I was stateside I think I would have missed 7-05 by just a year or two depending on the jurisdiction, but most of my formative work was with NBC.

I think I found it in the commentary now... wall elements designed for 0.85/-0.7 if in the windward or leeward face.

 

[lexpatrie]

I need a diagram or something, how's the column seeing wind load exactly?

115 ultimate is roughly 90 ASD, a slight bit less, usually, but it's in the third or second decimal.

If I recall some of the newer (newset?) codes this is down to 112 or so, so the newer (newest?) Loads are slightly less than slightly less than 90 ASD.

You can parse the loads into windward leeward, but the two procedures don't really mix. One is pseudo tap pressures, the other is more math derived, so if you do the more math oriented one it produces higher loads, from what I remember. That would be conservative, so it's more or less fine. I've broken the loads up when I have difficulty justifying load transfer (meaning a goofy wall, goofy toph chord, goofy floor diaphragm). Then each side gets justified for the higher load case (leeward, usually).

 

[XR250]

I have not graduated from 7-10 yet and started on 7-93
Honestly, I usually just throw 13 PSF on everything for MWFRS in my 90 MPH ASD zone (which used to be 80 in 7-93).

 

[canwesteng]

The wind is applied to the columns to take the wind to the diaphragm and then into the MWFRS... this is a 135 mph ASD zone, so 13 psf may not quite cut it.

 

[lexpatrie]

That 80 value is fastest mile. 90 is 3 second gust, 115 is "ultimate" 3 second gust, just to clarify. They all math out in a similar range.