Need a book? Engineering books recommendations...

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

Re: Effects of the New Code on Wood structures - good or bad?????

[Subject Prev][Subject Next][Thread Prev][Thread Next]
chuckuc wrote:

> The fact of the matter is that many the wood framed structures did not 
perform
> acceptably during the Northridge earthquake.  As a consequence, some very
> knowledgeable and experienced engineers have proposed changes in the Code in
> order to improve the performance of wood frame construction.  Design loads 
have
> been increased and we are now being asked to evaluate our structures a 
little
> more carefully.  That is going to include an evaluation of rigid and 
flexible
> diaphragm performance, like it or not.

Lynn Howard wrote:

"Really!!  And just where do you get your information from on this?  I
would be VERY interested in getting ANY data on low rise residential
type structures that had plywood diaphragms and plywood shear walls that
did not perform up to a life-safety level of performance during the
Northridge earthquake."


(Ben Yousefi)	:	Right on Lynn!

I think it is exactly the type of assumption stated above that has led to 
this hoopla about the wood diaphragm rigidity calculations. Some engineers 
have bought into the idea that just because some reputable people (with 
possibly good intentions) are banging their drums about this issue, they must 
be right and the rest of us are wrong and should follow.  Instead, I, like to 
you, and many others who have asked this question before would like to ask 
the proponents of this methodology:	

Where is the proof? (or should I say where is the pudding)!

Show me any documentation that because of the erroneous assumption of 
diaphragm rigidity, the performance of a wood light frame building was 
adversely affected in a recent quake, and I will forever hold my peace on 
this subject. And please don't tell me that these building haven't been 
tested yet. Thousands of these types of structures have been built with this 
assumption and have been subjected to several good sized shakings such as 
Whittier, Loma Prieta and the Northridge.

I was a member of the ICBO lateral design committee for the entire duration 
of 97 UBC code hearings and never ever was any argument made, nor evidence 
presented about the poor performance of diaphragm or shear walls because of 
the flexible assumption and no attempt was made to correct this phantom 
problem either.

I do, however, want to clarify that I am not claiming that no wood framed 
building suffered serious damage in Northridge. I, along with many others, 
witnessed considerable damage (may be not life safety) to wood buildings. 
However, the 97 UBC, in my opinion, tried to address many of these issues 
properly. The Reduced H/W ratio of 2:1 for shear wall was an excellent 
change. Other requirements such as increased bolt size and 3x framing members 
at certain locations were good steps. And some general requirements for all 
buildings, such as the inclusion of redundancy coefficients were major 
accomplishments. But all those are being overshadowed by this puny of an 
issue on diaphragms, and the 97 UBC is not getting the credit it needs for at 
least trying to address many real issues.



Ben Yousefi, SE
San Jose, CA