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Re: Moments in wood structures

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Acie-
I see the bolted type of post bases often used in this area for 6' high fences in spite of Simpson's cautions. They usually start leaning pretty quickly.
 
One observation I've made is that the bolt holes are usually over drilled causing a sloppiness in the connection (since the distance between the bolt holes is only 3" and the distance from center of rotation (halfway between the bolt holes) and the top of the post is about 7.5', the deflection at the top of an 8 foot post with a hole 1/16" over the bolt size would be plus or minus 3.7 inches under little if any load (ignoring the initial friction from tightening the bolts which goes away with shrinkage). The holes are usually over drilled by more than 1/16" making it even worse). That would probably not set well with the homeowner.
 
The CBQ type would be less sloppy since there is no oversize to the SDS screw holes but it would probably be difficult to get them to figure either. 
 
Regards,
Bill Cain
 
In a message dated 5/8/2006 4:10:10 P.M. Pacific Daylight Time, njineer(--nospam--at)att.net writes:

Acie,

 

You could calculate moment capacities based on connector shear values.  I don’t believe Sampson publishes moment capacity values.  I would orient the vertical straps at the base at right angles to the vertical straps at the cap, and figure the straps as transferring vertical shear into the posts, rather than figuring the vertical straps as acting in torsion.  It would probably be easier to figure a moment capacity using the CBQ base and CCQ cap since the SDS connectors on opposite sides of the wood member act independently; it’s may not be clear how to figure shear capacities and resultant moment capacities for a bolt for which the force is upward on one side of the wood member and downward on the other side.   

 

Nels Roselund, SE

South San Gabriel, CA

njineer(--nospam--at)att.net


From: Chance, Acie [mailto:AChance(--nospam--at)lacsd.org]
Sent: Monday, May 08, 2006 1:41 PM
To: seaint(--nospam--at)seaint.org
Subject: Moments in wood structures

 

List

     A city engineer told a client that he would sign off on a patio with Simpson CB at the bottom and Simpson CC at the top of six wood columns.  Patio is 20' X 40' with two rows of three columns. Wood beams connect the six columns.   As there are no shear walls or braces at least one of these connections, top or bottom must be moment resistant.  I have not been able to find any EER or other data showing these connections will take moment.  If any one know of any information this hardware making moment connections in wood share it with me.

Thanks
Acie P. Chance

 
Regards,
Bill Cain, S.E.
Berkeley CA