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]
     To those who are frustrated with the 1997 UBC wood design provisions.
     It is productive to discuss the deficiencies, ambiguities, and 
     possible interpretations of the code.  Discussion leads to knowledge 
     and innovations.
     It is counterproductive to badmouth the SEAOC seismology committee 
     VOLUNTEERS who have provided the input to the code.
     It is productive to make constructive code input to the VOLUNTEER 
     SEAOC seismology membership, both local and state level.  This input 
     should include a detailed thought process of the problems with the 
     current wording, and suggestions to improve the situation.  Actual 
     design examples and proposed code wording would be a big help to the 
     VOLUNTEER committee members.  From a practical standpoint, proposals 
     should be as revisions to the 2000 IBC, although proposed revisions to 
     the 1997 UBC would still be useful.
     To those of us who are SEAOC members, the FASTEST way to effect code 
     changes has always been to work through your local seismology 
     committee members.  Contrary to the stated opinion of several on the 
     list server, the committee members do work for a living, and they do 
     listen to input from those not on the committees.
     To those of us who are SEAOC members, the SLOWEST way to effect code 
     changes has always been to gripe, complain, and badmouth the authors.
     If it's broken, let's fix it, the fastest way possible.
     Rick Drake, SE
     Fluor Daniel, Aliso Viejo

______________________________ Reply Separator _________________________________
Subject: Effects of the New Code on Wood structures - good or bad????
Author:  Seaintonln(--nospam--at) at fdinet
Date:    7/22/99 1:57 AM

It appears from working through the design examples that under ideal 
conditions the goal is to design the struture so that all walls deflect with 
the same relative stiffness. The code does not suggest what should be done to 
"tweak out" the walls nor does it explain what to do when stiffness differes 
from grid line to grid line or between walls in each grid line. 
It does not seem practical in wood framing to tweak out walls to 
specifically. You may be able to reduce your liablity, but will have a great 
deal of trouble controling the quality of construction in the field. If the 
Building Industry does not take some responsiblity to require those who build 
these structural systems to be certified and educated with special knowledge 
of the code, there can be no quality control that will be be effective and 
you, as the engineer of record, still remains liable under the Strutural 
Observation guidelines. 
There have been many discussions both public and private on the SEAINT 
Listservice regarding these topics and most engineers supporting the code 
feel that we need to design both ways and to identify the effects of torson 
on our structures. However, arbitrarily adding stiffness will change the 
distribution of torsion and may not yeild ideal results.
The code requires the design of wind, and in most cases, wind will still 
govern in wood design. Wind is a uniform load that will not be affected by 
the geometry of the structure as in seismic design. With uniform loading, the 
rotational differences do not appear to be as great as when seismic controls. 
Therefore, one of the underlying questions is "If wind controls, can torsion 
be ignored and the resisting walls designed by rigidity to keep the same 
stiffness in each line of shear?"
Now that the aspect ratio of the walls are greatly impacted by the new code, 
I suspect that we will start to see more proprietary shearwall systems like 
the Hardy Frames or Simpson Strongwalls. How are these frames suppose to be 
modeled in this program? You can not simply substitute these propriatary 
frames for wood walls without knowing their stiffness factors. Yet I suspect 
that engineers will want to substitute one Hardy frame for four various 
shearwalls in one gridline so as to simplify the analysis. Does this force us 
back into manual calculations to readjust the shear?
How do we treat field changes when the owner decides he wants to add walls or 
remove walls - or wants to enlarge walls during the course of construction. 
Any minor change such as this will require rebalancing the entire structure 
and a change in one area may affect the torsional shear in another area. How 
do we explain this to our clients?
There are a great number of problems with the new code as it applies to 
residential construction that needs to be addressed and quickly. I am 
interested in any comments from my peers.
Dennis S. Wish PE.