Need a book? Engineering books recommendations...

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

RE: Residential Design Discussions

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Gerard-

I agree with 99% of your position.

The only thing I take exception to is 10/lw. The "author" of this provision
is Phil Richter. Shortly after the adoption of the 1997 UBC, I was in a
seminar (I believe it was a SEAOSC Seminar on the 1997 UBC Seismic
Provisions in Commerce, CA). At the break, I spoke with Phil who clarified
this point with me. He said that his intent was to use 10/lw as an aid, not
a penalty but, somehow, in the wordsmithing process, the "<=1" got left out.

Yes, you are right, the Code does not say "10/lw<=1", but we ALL know that's
what it means, don't we? Aren't we ALL (when I say ALL, I am including plan
checkers and "expert" witnesses) reasonably sensible and keep ourselves up
to date by reading and following interpretive discussions on the Code in
order to come up with a rational interpretation of an antiquated body of
instruction (1997 UBC), enforced by an organization which has, for the first
time in it's history (ICBO) abandoned the off year amendment cycle? The only
avenue we are left with is an organization like the Structural Engineers of
California (SEAoC) to write "position papers" on things like Rho, rigid vs.
flexible diaphragms, 10/lw<=1, et. al., so that we designers have rational
tools with which to use for design.

In my (sometimes not so humble) opinion, when SEAOC does not respond to such
issues, absent the presence of new codes or off year Code amendments, it not
only misses a wonderful opportunity to serve the design community for which
it purports to represent but also provides fodder for (expletive deleted)
attorneys.

We designers should be able to have at our disposal proper ammunition to
present a defensible position, backed by a recognized authority on seismic
design (who better than SEAoC?) in a court of law or any other venue issues
that the 1997 UBC Code left vague and ambiguous. I am certain even the
authors of the particular code sections would agree.

Remarkably, I can't believe (well, I guess I can) believe these issues are
STILL alive after all these years.

Sheesh!

Bill Allen, S.E. (CA #2607)


||-----Original Message-----
||From: Gerard Madden, PE [mailto:gmadden(--nospam--at)attbi.com]
||Sent: Wednesday, September 25, 2002 2:53 AM
||To: seaint(--nospam--at)seaint.org
||Subject: RE: Residential Design Discussions
||
||
||Dennis,
||
||You know my position as we have discussed privately, but I
||will share it
||here to hopefully bring a fresh voice. It's long winded of course ...
||
||Most of my career has been structural design of commercial buildings.
||For the past year now I have been doing almost exclusively residential
||design. The reason is two fold, One is that I find the projects
||challenging/interesting and the second is that commercial construction
||is dead in California.
||
||Here is what I have come to realize...
||
||The 97 UBC is in desperate need of revision as it pertains to
||residential light frame construction. There are two key areas
||that need
||to be addressed. One is the RHO factor calculation and the
||other is the
||rigid diaphragm distribution.
||
||I'll start with RHO...Ron Hamburger is I believe the brains behind the
||RHO factor. He used to be on this list up until about 2 years
||ago. When
||he did post on this topic, he stated the theory behind the
||10/lw clause
||for shearwalls in the RHO calculation. The INTENT was to give the
||engineer a break when he/she had a 40 foot long shearwall.
||The engineer
||could count the wall as 4 separate elements when determining rmax (or
||3.4 walls if you had a 34 foot shearwall). The reasoning was that this
||big long wall is obviously a different animal than say a braced frame.
||The 10 factor was based on an average story height of 10 feet for a
||building and concrete cracks on a 45 degree plane. So it made
||sense that
||each ten foot segment could be treated as and individual
||element in this
||calculation for redundancy check.
||
||At this point in my career, I was doing mostly tilt-ups. On
||the front of
||a modern tilt up building, you are lucky to get 4 feet of solid panel
||and even less when you consider the panel joints. When you do
||the 10/lw
||calc you get a number greater than 1.0 for anything shorter than a 10
||foot segment. So I had to treat say my 9.75 foot wall segment as less
||than a single resisting element and this increased my RHO value. But
||this was not the intent. The intent was to help when you had a long
||wall, not punish when you had a short wall. There is no
||exemption or cap
||that 10/lw need not be taken grater than 1.0 - this is a problem when
||one tries to follow the letter of the code. The same thing applies to
||wood/residential construction where shearwalls are not usually 10 feet
||long. Gary Searer destroyed the whole concept of RHO. Everyone should
||spend the 30 minutes and educate themselves on this joke code
||requirement. Gary looked at more than wood frame construction
||and did a
||fine job punching holes in it. I think it can be downloaded
||on Dennis's
||structuralist web site. The seismology committee has reviewed it, but
||doesn't seem to want to commit to anything concrete.
||
||On the rigid diaphragm requirement, I have come to realize that it is
||virtually impossible to prove a wood diaphragm is flexible - It just
||doesn't occur in most house configurations. Now I will say that I feel
||that the diaphragm will most likely distribute loads in a semi-rigid
||manner, more rigid than flexible. The problem lies in calculating the
||rigidities of walls and diaphragms. The equations used to determine
||these values are largely based on tests in a controlled environment.
||Wall rigidities take into account nailing, nail slip, shear
||thickness of
||sheathing, hold-down deflections, and shrinkage. Diaphragm deflections
||are based on similar equations for BLOCKED conditions. Due to the
||limitations on shear capacity for walls and spans for wood floor
||members, shearwalls are too close together to ever come out as having
||the proper deflection ratios to diaphragms considered flexible.
||
||Now, your million dollar house is framed by some clown like me sitting
||in front of Home Depot every morning sipping a 7 Eleven decaf
||waiting to
||get pick up by you local California Licensed contractor. I can't read
||blue prints so I proceed to make swiss cheese of the OSB left
||out in the
||rain the night before as I shoot nails into the wall framings to the
||beat of Metallica in my headphones, because more is always better.
||
||So after all my sophisticated analysis, I have a shearwall in
||the field
||that has twice as many nails as calculated, and the OSB has swelled up
||and been shot to hell. Since I have built 2000 houses with
||the same set
||of drawings, and I also sat there all day and watched the framer drive
||each nail flush and I measured the nail spacing on each
||panel, is all my
||sophisticated rigid analysis going to predict the behavior during the
||next 7.4 earthquake? Of course it is, because like nailing, more
||calculation is always better.
||
||Now, what do those of us who do this type of engineering need
||to do? Do
||we ask those who write the codes to listen to us. Yes we do. But will
||they take these concerns seriously and try to re-analyze why these
||things came into the code to begin with and the impact it has if
||followed to the letter? Are code writers taking into account the
||uncertainties of construction, code interpretation by building
||officials, the rationale of equations based on controlled tests, and
||past performance of buildings that may have had other causes
||to create a
||concern (i.e. weak/soft stories, or concrete topping slab on plywood)?
||What is the goal, save lives or save re-straightening of
||picture frames?
||Some want to dumb the code down ... I don't think this is necessary,
||just make it realistic. We have enough codes and I think much of the
||1997 UBC is good. But the code cycle in California has made things too
||risky as we sit in limbo.
||
||Can we be legally protected when we refuse to follow irrational code
||requirements ? Can we (small firms who do 90% of residential
||work) just
||call it performance based design and call it a day? Can we be expected
||to participate in committees that seem to be largely tools for
||self-promotion of firms and building departments who have the
||resources
||to pay someone to travel and spend time in this process. Are we at the
||mercy of those who wish to complicate the code to keep business for
||themselves by making it difficult for other to catch up with new
||methods? E&O Insurance continues to rise for structural
||engineers, there
||is big money in expert witness testimony. When I get sued, Is Ron
||Hamburger going to cancel his Performance Based Design seminar to come
||to my trial and say, "Gerard is correct in his interpretation of the
||intent", or is the hired gun going to simply say - "Gerard has stated
||publicly that he understood the code and knowingly ignored the
||requirements. The code is clear on this and is not open for
||interpretation. If Gerard is allowed to go unpunished, what's to stop
||him from using a live load of 35 psf on a residential floor instead of
||40 psf? Send a message to Gerard and other rogue engineers
||ignoring the
||code as they see fit". 5 Years after the 97UBC was published,
||and maybe
||another 5 years before another code is adopted in California, we are
||left hanging out to dry by our code developed by our PEERS on the 21st
||floor overlooking San Francisco Bay and spending the week at the SEAOC
||convention sipping Margaritas.
||
||I await your barrage.
||
||-gerard
||Santa Clara, CA
||


******* ****** ******* ******** ******* ******* ******* ***
*   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 
******* ****** ****** ****** ******* ****** ****** ********