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RE: TILT UP RETROFITS

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Jeff,
It has been a long time since working with these retrofit changes, but some
of the issues you bring up are similar to those I had in Los Angeles City
about five years ago. I've included in your message some of the comments I
have and the problems I ran into. Mind you, I was retrofitting a reinforced
Brick building which was not under the same mandatory constraints as the
tilt-up but had the same problems. Because of the lack of a mandatory
ordinance, the owner chose not to do the work. See below:

-----Original Message-----
From: Jeff Coronado [mailto:"jcse(--nospam--at)flash.net"@flash.net]
Sent: Thursday, May 04, 2000 7:16 AM
To: SEAINT(--nospam--at)SEAINT.ORG
Subject: TILT UP RETROFITS


For those of you who do a fair amount of LA City Division 91 and LA
County Chapter 95 work:

1.  We have typically doubled up the existing subpurlins that are to be
anchored with new full length 2x subpurlins.  The 2-2x subpurlins are
supported at each end with a new hanger.  The new 2-2x is attached to
the diaphragm with A35 clips.  I would be curious to know what some
other offices are doing.

<DSW> The capacity of the connection determined the number and spacing of
anchors. At the time, I was allowed to use one subpurlin but only allowed to
use the tension capacity that resulted in the wood as governing with two
holddowns attached. Furthermore, very little credit was given for an A35
connection to the sheathing. If I recall, Los Angeles only allowed a maximum
of 50-pounds per connector when the A35 was screwed directly to the
sheathing (assumed 1/2" at the time). Therefore, the development length was
dependent upon the most likely component to fail. Remember too that where 1x
or 2x sheathing occurred, the capacity of the connection was based on 2
nails per joist per board.

2.  Do you carry the building continuity ties through the full length of
the building or do you stop them by nesting subdiaphragms until a full
width subdiaphragm can be justified?

<DSW> We were only required to develop the capacity needed for the weight of
the wall (lateral) tributary to the anchorage. The contractor at the time
complained about the development length through the diaphragm which was not
the full depth of the diaphragm, but considerably longer than what was
required in URM retrofit a few years prior (1800 lbs based on 100-plf at the
roof (times two for each side of the diaphragm) or 500-600 plf at the
floors).

3.  Do you specify an arbitrary minimum end distance between the holdown
and the end of the wood member even though the holdown is self-jigging?

<DSW> At the time we were using HD's or HDA's and the installation position
was based, if I recall, on 7 times the tension rod diameter. This needs to
be verified. If using a PDH (Pre-Deflected Holddown) with screwed
connections that need 2-2x joists for a connection, I would say that the
default distance from ledger or wall to holddown is valid.

4.  A contractor has told me that what he sees some engineers do to
reduce or eliminate subpurlin continuity ties is to reduce the depth of
the subdiaphragm by increasing the subpurlin nailing at the time of the
next reroof.  Is this common practice?

<DSW> I can't answer this one. I doubt that the building official will allow
a credit to be issued if and when the owner gets around to re-roofing. There
is no enforcement to assure that the work will be done. But then again, this
depends on the local agency and what they are able to enforce.

Thanks for the assistance,

Jeff Coronado, S.E.
West Covina, CA