UBC - braced wall support

[mayflug]

Can anyone explain what clause 2320.5.6 of the UBC/CBC actually means? It refers to continuous foundations under braced walls and then cites an exception which allows cripple walls. I do not class cripple walls, founded on individual pier blocks as continuous.
Also, to what does the "50 foot intervals" refer?

All comments gratefully received.

David

 

[JAE]

Assuming you are talking about UBC 1997 -

Check out section 2320.11.5 where it defines cripple walls. I don't think they intend, in section 2320.5.6 to allow cripple walls to "span" from isolated footing to isolated footing. They require a continuous footing below the cripple wall.

So I would envision a continous concrete footing, supporting a wood framed cripple wall (no higher than 4 feet) which then supports a main, first floor.

The intervals talked about relate to the whole concept of "light framed construction" in the UBC which is a special kind of wood framing where a full engineered system is not required...i.e. apartment buildings and such.

The light framed construction requires that certain walls be identified as braced wall lines (see 2320.4.1, 2320.4.2 and 2320.5.1 for some info on wall lines). Also see 2320.11.3 which lays out the requirements of construction.

The 50 feet is the spacing between lines of walls (i.e. shear walls) that you need to provide to meet the definition of "light framed construction" which Chapter 23, Div. IV covers.

Its a weird chapter and you really should read it over a couple of times, outlining the provisions by hand as you go.

Good luck.

 

[mayflug]

Thanks for your input.

The project is a two story apartment block and I'm using Light Frame Construction to avoid having to do a lateral design on the diaphragms and shear walls.

I'm left with an overall stability check and anchor design but that's a lot less work. I think I'm going to use a stem wall perimeter then split the plan area (70'x30')in half with another stem wall. The remaining shear walls can sit on cripple walls.

I agree with you that the whole division is weird. I find the tables particularly confusing!

Thanks again.