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RE: Kneebraced Post Design

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Knee braces are present ALL the time in timber framing.  Regardless, I NEVER
make use of them for resisting seismic loading as it is rather difficult to
get any ductility out of a wood knee brace system, especially with timber
framing connections (i.e. mortise and tenon type stuff).  I will rarely (and
reluctantly) use knee braces to resist wind loads.  Thus, the R=1.5 makes
perfect sense to me (one could argue for R=1.0).

Now, that does not help you specifically, but just thought I would
comment...

Regards,

Scott
Adrian, MI

-----Original Message-----
From: chris.slater(--nospam--at)gmail.com [mailto:chris.slater(--nospam--at)gmail.com] On Behalf Of
Chris Slater
Sent: Friday, May 09, 2008 5:47 PM
To: seaint(--nospam--at)seaint.org
Subject: Kneebraced Post Design


Tried sending this earlier, and it never made it.  I'm assuming the list
doesn't like attachments.  Instead, I've included a link to the file on my
web server.

--

A lot of our firm's work is residential, and of that, a moderate percentage
is small additions and remodels.

One thing that we see very often (and more frequently as jurisdictions start
getting tougher about requirements) is small covered patio additions.

Engineering the lateral support for these is tricky.  The favored solution
for owners and contractors is to kneebrace the support posts. We've done
this in the past, and made it work for small patios, using NDS combined
lateral and pullout values for Lag Screws, and an R value of 4.5 (UBC).

In the new code, we have to use R=1.5, which means that even for a small
patio, the seismic load is fairly high, and it is very difficult to make
this work.  However, in an effort to not have to specify steel columms for
every little patio we engineer, we've tried to look at other options, such
as 1/4" steel side plates with either lag screws or through bolts.

I developed a spreadsheet, using the NDS equations, that gives options based
on what we put into it.  I've attached the spreadsheet to this e-mail
(actually, it's here:  examplecalcs.com/Kneebraced%20Post%20Design.xls)
and would appreciate it if any of you had time to review it and offer
feedback.  If you find it useful, please feel free to keep a copy.

So the request for feedback is my first request.  But I also am interested
in what others are doing with regard to small patios and knee braced posts.
I know that this type of thing falls way below the radar of many on this
list, but it is something we run into very often in our practice.

Thanks,

Chris Slater

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