Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: wood framing - commercial structures

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Jen,

I agree with everything Jason wrote. You may have to have an embarrassing
conversation with the owner and contractor that not only will you have to
use 2x6 studs every where but you'll need twice as many hurricane clips,
twice as many nails in the sheathing, etc, etc., that is once you actually
engineer the structure as opposed to using the prescriptive construction
guidelines. The guidelines are IMO there to provide laypeople a design for
when an Engineer is not required not for Engineers to use as engineering.
Your predecessor left you with quite the quagmire.

HTH,
Rand



----- Original Message ----- From: "Jason W. Kilgore" <jkilgore(--nospam--at)leok.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Friday, October 22, 2004 10:05 AM
Subject: RE: wood framing - commercial structures


Oooooohhh.. I HATE inherited projects.  The "time is of the essence"
inherited projects are even worse.

First, wood structures CAN be "built to last".  In the long run, however,
the maintenance requirements for wood are typically more extensive and
problematic.  You'll never have problems with termites in concrete, for
example.

Second, and probably most important, it looks like the original engineer
(designer?) used the "Conventional Light-Frame Construction" rules.  Just
in
your brief description, I see several reasons why you CANNOT use
conventional rules in designing this structure:

2308.2.1. Buildings shall be limited to a maximum of three stories above
grade.
 - You have 5 stories above grade.

2308.2.3. Loads as determined in Chapter 16 shall not exceed the
following:
  3.2. Live loads shall not exceed 40 psf for floors.
 - Corridors, exits, and public spaces for condominiums have higher loads.

2308.2.4. Wind speeds shall not exceed 100 mph (110 in exp cat. A or B)
 - You have 130 mph

2308.12.1. Structures of conventional light-frame construction shall not
exceed one story in height in Seismic Design Category D or E.
 - you have 4 or 5, depending on how you look at it.


Now, on to your questions:
1. You CANNOT use "Conventional Light-Frame Construction" rules and
methods
as specified in section 2308.  But yes, you CAN use wood.  You have to use
the specific engineering requirements in sections 2304, 2305, 2306, and
2307.  This means that Table 2308.9.1 is useless to you.  Also, you'll
need
to get your hands on the AF&PA NDS for wood construction.

2. Yes, you can extend concrete or CMU up.  However, you need to design
significant drag strut connections to transfer the force from the floor
diaphragms into the walls.

3. I don't see any way 10'-0" 2x4's will work in exterior load bearing
walls
in 130 mph wind, even for the top 2 floors.  MAYBE for roof-support only,
because there will be no downward gravity load because of uplift.

Basically, instead of looking up "2x4 will support one floor, roof, and
ceiling" in a table, you'll need to calculate the gravity and C&C wind
loads
on a stud and figure out what you'll need as far as size and material
properties.  I'd guess that 2x6 is the MINIMUM, and you might even require
double 2x6 studs on the lower level.

There are about a gazillion other code issues to consider.  Good luck, and
I
hope you didn't need any sleep until this project is resolved.

---
Jason Kilgore
Leigh & O'Kane, LLC
Kansas City, Missouri
________________________________________
From: Jen Wadsworth [mailto:JWadsworth(--nospam--at)TricoEngineering.com]
Sent: Friday, October 22, 2004 8:03 AM
To: 'seaint(--nospam--at)seaint.org'
Subject: wood framing - commercial structures

My experience with this subject is limited. in my opinion if it's going to
last, you should be using conc. and steel. However, in changing of jobs
you
inevitably inherit some projects of the past, and this is the predicament
I'm in:  we've got a 4-story condominium structure on top of a parking
level- so essentially, it's 5 stories. The roof will be a terrace area
with
jacuzzi's and separation walls.  The design is concrete walls around the
bottom level and load bearing stud walls the rest of the way up to the
roof.
There are two cmu stairwells and one cmu elevator shaft, continuous to the
roof level.  We're using IBC 2000, seismic cat. D, wind speed 130
(Charleston, SC).
The original question raised by the contractor was - can we use 2x4 stud
walls instead of 2x6 for the load bearing walls? Investigating this led me
to several other questions:

1 -- can we use wood framing for a structure this high? The floor-to-floor
heights are 10'.  In sect. 2308.12.1 (seismic cat D requirements) it
specifies conventional light framing is not to exceed one story for this
category. what is defined as conventional light framing?? Can we get
around
this and if so.

2 - sect 2308.12.2 says conc or masonry walls cannot extend above the
basement.  Any way around this and if so.

3 - the contractor and owner want 2x4 stud walls all around. Our walls
(load
bearing) are currently 2x6 stud walls for the first two levels, and 2x4
for
the top two. This was decided from Table 2308.9.1 from IBC 2000.  Is there
something I'm missing here, or am I correct in saying we need 2x6 walls to
support 3 floors and a roof?

I've just done a brief scanning of IBC2000 so if there are additional code
(or other) issues we need to consider, please let me know.  The drawings
have already been submitted for construction once, and revised once. We're
on the second revision, and the project has been delayed about a year, so
time is of the essence.

TIA,

Jen





******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
*
*   This email was sent to you via Structural Engineers
*   Association of Southern California (SEAOSC) server. To
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
*   send to the list is public domain and may be re-posted
*   without your permission. Make sure you visit our web
*   site at: http://www.seaint.org
******* ****** ****** ****** ******* ****** ****** ********



******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
* * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
* Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********