Need a book? Engineering books recommendations...
Blue Book Revisions for Wood Framing[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: Seaint(--nospam--at)seaint.org
- Subject: Blue Book Revisions for Wood Framing
- From: Seaintonln(--nospam--at)aol.com
- Date: Mon, 9 Aug 1999 16:53:48 EDT
I sent this last night and wondered why there was no response. I looked at the post that I received and it stated that the email was too large for posting on the list. Therefore, I will summarize the revised 2000 Blue Book Wood section that I received yesterday from Saif Hussein, SE who is the current Chair of the Seismology Committee: Please don't write me for a copy of the draft. I sent it to Shafat and asked him to post it on the Website for those who are interested. This is a summary and it is not my intent to misrepresent the text by taking sections out of context. It seem approriate to summarize the highlights of the document. Embedded Columns R values - this was the most heated of the controversy's: "The relative flexibility of cantilevered columns compared to parallel shear walls is thought to have been one factor contributing to the poor performance of buildings with tuck-under parking in the Northridge Earthquake..........Although damage resulting from the of relative flexibility of vertical elements should theoretically occur to varying extents in many other types of wood buildings, it has not yet been reported as a major cause of damage." "Modification of Section 105.4.4 in this edition of the Blue Book now recommends the application of the lower R factor just to those elements that are along the same line of resistance as the cantilevered columns." Rigid Diaphragm Analysis (Torsion): "Earthquake damage observed to date suggests that the Life-Safe Performance Level, as defined in Vision 2000 Part 1, has generally been achieved where structures with wood structural panel diaphragms designed using flexible diaphragm assumptions have a fairly regular configuration and redundancy." "Consideration of rigid diaphragm behavior is recommended where the diaphragms can be judged by observation to be stiff compared to the vertical lateral-force-resisting elements, and particularly where one or more lines of resistance are substantially less stiff than the rest." "For small, substantially regular buildings that have a good distribution of lateral resistance and are well tied together, earthquake performance to date suggests that design using flexible diaphragm assumptions is adequate for Life-Safe Performance. It has been suggested that one and two-family residences be given blanket exemption from consideration of the applicability of rigid diaphragm analysis. Such a blanket exemption does not, however, make sense from an engineering standpoint because many one and two-family residences now being designed have highly irregular configurations with low redundancy and significant discontinuities in the structural system." Shearwall distribution by rigidity: ""As a result of aspects like these, the creation of fine-tuned calculations of shear wall relative stiffness for purposes of lateral force distribution does not make a lot of sense. It is necessary to apply engineering judgment to the information available. Approximate methods of evaluating relative stiffness may be appropriate, and a simplified evaluation of stiffness used with engineering judgment may well lead to more realistic results than a numerically rigorous method. " Legal Liability for non-code compliance in past: "Past and present design practice in California and other areas has almost exclusively used flexible diaphragm assumptions for distribution of seismic forces in structures with wood diaphragms. While design using structural materials other than wood had considered rigid and occasionally semi-rigid diaphragm behavior prior to the 1988 UBC, design of wood structures had been based on the assumption that all wood diaphragms behave in a flexible manner." "Although damage resulting from the of relative flexibility of vertical elements should theoretically occur to varying extents in many other types of wood buildings, it has not yet been reported as a major cause of damage. Earthquake damage observed to date suggests that the Life-Safe Performance Level, as defined in Vision 2000 Part 1, has generally been achieved where structures with wood structural panel diaphragms designed using flexible diaphragm assumptions have a fairly regular configuration and redundancy. "
- Prev by Subject: Re: Blue book and commentary
- Next by Subject: Board diciplinary actions
- Previous by thread: RE: Progressive Collapse Design
- Next by thread: 1997 UBC Equation 32-2