Need a book? Engineering books recommendations...

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

RE: Log Strucutres - IS-LOG document

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Log structures are like any other building, you have to design each part in a chain of connections to get the loads where they are supposed to go.  The way I've seen the interconnection between logs done is with single shear between each log with threaded rod connections using yield limit equations and overturning being checked with full height threaded rods in tension.  The walls have to be held at the top and bottom by floors, foundation, roof or girts or from side to side with side walls - and they seem to be working.  I know log home kit manufacturer who has a bunch of structures that made it through the 7.9 Mentasta earthquake without an issue.
 
I don't have the draft standard at work but I thought I remember there are prescriptive limits on the layout but it does not get into any detail on connections etc...  Also I thought I remember there being limits on where engineering is not required like Seismic Design Category C or lower.  If it has to be designed in seismic design category D then it would be useful  to have a response modification factor so you can determine the seismic forces.


From: Jordan Truesdell, PE [mailto:seaint1(--nospam--at)truesdellengineering.com]
Sent: Wednesday, June 28, 2006 5:35 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Log Strucutres - IS-LOG document

Okay, just checked and apparently the only "intact" version is from May of 2005 - the first draft. No updates have been made to the full document (which is available for download). The 2nd and 3rd drafts - which look just like the standard, and are not identified as changed sections only, are just the changed sections. I'm sorry, but in an era of digital documentation why would you not publish the 3rd draft as the entire document, instead of as a compilation of changed sections? (sorry, rant off)

It's interesting that there are no prescriptive provisions. None. Nada. Okay, technically it's "shall be permitted to use prescriptive provisions as approved by the building official." I assume that's because the IRC says "if the building official feels like it, he or she may approve any 'prescriptive design' document which is not part of the building code, regardless of source". Except, of course, it doesn't. The standard provides limits beyond which prescriptive design is not applicable, but provides no enforceable prescriptive design. Practically everything in the engineered design sections come right out of mechanics textbooks; there are 5 pages of requirements which boil down to "the engineer should follow engineering practice in the design of a log structure".

Maybe you have some insight on this, Scott, as I'm unfamiliar with the development process, but this looks like a waste of 65 pages. I've read some of the comments, and they are well intentioned, but seem to be missing that fact that there is no useful construction data contained in the pages. I'm sure that there must have been discussion on this (I would hope at least), but is seems like a glaring omission. I'm sure someone will suggest that I write the 30-40 page section that should go in section 402, and submit it as a comment, but quite frankly I'm not qualified. Log homes are, to use a poor analogy, like Spanish to me. I can read it, and I can use a dictionary and textbook to make sure the grammar is correct, given a document to start with, but I can't present a speech in front of a native speaking audience and make them believe that it's my first language.
Jordan


Haan, Scott M POA wrote:
I've made comments on it.  There were lots of log homes located in the Fairbanks area that performed better than light frame timber buildings in the 7.9 magnitude Mentasta earthquake in November 2002. There is currently no R response modification factor for log homes in the building codes that I could find.   I ordered the 2006 IBC and ASCE 7 to see if they have an R for stacked log walls with drift pins / threaded rods.  My comment was that they should have an R=6.
 
 The prescriptive stuff in that draft standard is limited to low seismic zones, low wind.
 
 

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