Wood Building Seismic Design - who does it?

[jvvse]

I'm curious who does wood building seismic design.

Also, the real reason I'm asking, is how do you do it? Do you do it by hand or with a program?

 

[msquared48]

By hand.

Mike McCann
MMC Engineering

 

[LonnieP]

By spreadsheets written 20 years ago and updated as code changes.

The sooner you write your own, the longer you can use them. Mine do wind/seismic at the same time.

LonnieP

 

[a2mfk]

this can't be a real question...

 

[jvvse]

It's real. This isn't asking for advice, it's more of a survey.

 

[msquared48]

I'm sure I will be the odd man out here...

Mike McCann
MMC Engineering

 

[Jerehmy]

I get the loads from spreadsheets and look the diaphragm up in the NDS table. I never check seismic though, wind governs where I live.

 

[asixth]

I don't because wood floors and roofs are usually very light, maybe only 1/10th of a concrete floor. So when the numbers crunch out wind is normally the governing criteria.

This is my experience.

 

[rowingengineer]

Could we assume asixth that your location is in a non seismic area.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[XR250]

I do mine by hand, but do not have to check seismic very often.

 

[jvvse]

I guess I should modify the question then. I am in a high seismic area so that tends to be all I think of, but wind or seismic makes no difference to me. For lateral design of wood diaphragms and wood shear walls, do you use a program, a spreadsheet, or do calcs by hand?

 

[msquared48]

I do it by hand for each case, wind or seismic, and I have to do both for each structure where I am.

However, I do have formatted hand fill-in sheets for both wind and seismic that I use with the equations and code references listed for the plans checker. Works for me.

Mike McCann
MMC Engineering

 

[KootK]

I use a combination of WoodWorks, spreadsheets, and hand calculations.

I think that the "who does it" question has some merit as a discussion point. I've worked for some prominent firms in the past and have never seen anyone do what I would consider to be a complete seismic design on any but the simplest light frame wood buildings. I think that this is because:

1) Light frame wood buildings are often rather complex with regard to the lateral load path.
2) The fee just isn't ever there to support the effort. Ethics would lead us to believe this is irrelevant, of course.

On the sketchy side of things, I've seen designers sum up the applied shear loads, compare then to the lengths of plywood / gypsum walls available, and call it a day. No tie downs, no explicit chords, no transfer diaphragms...

At the other end of the spectrum is the material that I've been reading in a book called "The Analysis of Irregular Shaped Structures: Diaphragms and Shear Walls". It's excellent, tedious, and all about wood lateral. It gives me hope in that the methods prescribed are very detailed and rigorous. I just truly don't know how I could ever squeeze enough fee out of a light frame wood project to make a go of it. And, even if I could, the guy down the street would probably just undercut me by $2K and buy a new boat with all of the fee he didn't spend looking into light frame wood lateral.

Yes, I'm jaded on this particular topic.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[BUGGAR]

Here in seismic SoCal, on light frame construction I at least compute the seismic base shear to verify that wind controls. If wind controls, no further seismic is done. Except you still have to do seismic detailing as required by the seismic Category. The local building departments get whiney when you don't show some reference to seismic.

I love that USGS site that figures out the basics for you!

Distributing seismic forces up and down and back and forth (to the LFRS) is a pain.

 

[jvvse]

How do you do it buggar? By hand, spreadsheet, or with a program?

 

[msquared48]

I assume you are referring to the seismic forces?

Mike McCann
MMC Engineering

 

[jvvse]

Argh my brain. I meant to ask how do you design the LFRS, whether it's wind or seismic?

 

[BUGGAR]

JVVSE
I generally do seismic by hand. Most of my structures are unusual and when I write a spreadsheet, it's not adaptable to other seismic problems.

I used to program all my seismic and wind calcs in Basic since that emulated my hand methods. Is Basic still around?

 

[Archie264]

>>>Here in seismic SoCal, on light frame construction I at least compute the seismic base shear to verify that wind controls<<<

Wow, Buggar, that's a surprise to me. Are you saying that in Southern California wind controls most of your designs?

 

[jvvse]

ASCE 7 wind loads are ridiculously high (IMHO) and for light-frame structures it can sometimes govern. If he's doing unusual structures then wind can get even higher. Also don't forget So Cal is a big area. Seismic base shear can be as low as 0.1W in the rural/desert areas or as high as 0.4W in LA/SF.