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- Subject: [SEAOC] Re: [SEAOC] simpson strength values
- From: ERIC BROWN <73537.2542(--nospam--at)CompuServe.COM>
- Date: 30 Jun 96 15:09:22 EDT
> The Simpson catalog specifies all values are based on dry lumber ( >moisture content under 19% ) on page 6 item e of the 1-1-96 catalog. > The local lumber yard ( Hagle lumber , Somis, CA ) says all lumber 4 X >and larger is only available S- Green ( moisture content over 19 % ). 2 X is >available S-dry at a 10 to 15 % premium . Visits to jobsites confirm the >lumber is S-green and even wet when pulled from a stack. Very few days pass >from the time the lumber is dropped at the site untill hangers and straps are >nailed. > 94' UBC sec 2335.5.3 and table 23 III B on page 2-991 specify Cm of .75 >for nails installed in lumber partially seasoned ( moisture content over 19% >), even when the lumber dries later. > I called Bob Greg at Simpsons S. CA office and he confirmed they assume >dry conditions. They do not test the nailed portion of connections but >calculate the nails and values from the code. > Therfore, it appears correct to reduce all simpson nailed connector >values 25% for typical wood framing, in this area at least. > In the past i have not been using this reduction in design and as a plan >check engineer, i do not see others using this reduction. Am i missing >something ? I would value you comments. I thought that I'd put in my two cents. Section 2312.4.1 ('94 UBC) States that: Allowable stress values for dry conditions of use shall be applicable for normal loading when the moisture content in service is less than 16 percent, as in most covered structures. (also see Sec. 2335.5.3) The code reductions are for moisture content in service. The problem you state is in regards to the installation of green lumber which will shrink when the wood dries. The installation of green wood will result splitting parallel to the grain (checking). Bolted connections are especially vulnerable because the holes cause a weakened plane and a crack will likely develop through the bolt holes. The only mention I could find in the code for installation moisture content was in Section 23188.8.131.52 for light metal plate connected wood truss design: All lumber should have a moisture content of less than or equal to 19 percent at the time of fabrication, unless engineering design specifically states that the moisture content may be higher. This section might also be applicable to nailed connections but I don't think that any design or detailing would prevent the problems at bolted connections. Eric Brown ...
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