Need a book? Engineering books recommendations...

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

Re: Tie Downs

[Subject Prev][Subject Next][Thread Prev][Thread Next]
I have *not* performed 300, or even one, such test, but as a practicing S.E. specializing in residential seismic upgrades in the Bay Area I have to ask:  How much practical difference does 3/8" or even 1/2" deflection make when the objective is collapse prevention?  

I realize that expectations may differ for the performance of new, and probably expensive, construction.

Ralph Hueston Kratz, S.E.
Richmond CA USA
www.rhkse.com 

Sent from my iPhone 3G

On Jun 12, 2009, at 7:20 AM, "Al Commins" <al(--nospam--at)comminsmfg.com> wrote:

In response to your posting on the SEA site.

 

In performing well over 300 full size shear wall tests I have developed some strong opinions.

 

Tie-downs connected head to tail will introduce excessive deflection.  (See attached flyer example #1).

Deflection through three hd's will be well over 3/8" and may be 1/2" or more-without considering shrinkage/settling.

 

I suggest a threaded rod connect the shear wall directly to the foundation with the rod passing through the cripple wall.

If shrinkage/settling is a consideration (over 1/8") a screw type shrinkage compensator should be used.

 

 

IBC (Section 2305.2) and the CBC (Section 2305.2) place deflection limitations on the design of wood Diaphragms. As outlined in the SEAOC Seismology AC155 commentary, hold down deflection can contribute 83% of the allowable drift from the hold-down deformation alone. This is with a single hold-down.  Three HD's will triple the movement

 

Comments on my analysis and the video clip (linked in the Shrinkage-Backlash flyer) are welcome.

 

Best Regards.

 

Al Commins

 

360 378-9484

<Al Commins.vcf>
<Shrinkage Compensators-Shrinkage-Backlash 1.pdf>
<080517 - SEAOC Seismology AC155 Final (2).pdf>