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Re: Effects of the New Code on Wood structures - good or bad[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: Effects of the New Code on Wood structures - good or bad
- From: Rick.Drake(--nospam--at)fluordaniel.com
- Date: Thu, 22 Jul 1999 08:06:40 -0400
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)aol.com at fdinet Date: 7/22/99 1:57 AM ****** IMPORTANT CODE CONCERNS WHICH NEED TO BE RESOLVED********** 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.
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