Re: Anchoring roof diaphragm to concrete wall[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "SEAOC List" <seaint(--nospam--at)seaint.org>
- Subject: Re: Anchoring roof diaphragm to concrete wall
- From: "Paul Feather" <pfeather(--nospam--at)san.rr.com>
- Date: Tue, 14 Aug 2001 18:09:17 -0700
The 420 plf is a strength level minimum. How you apply this will depend on
the load cases / methodology you have chosen to work with.
Item 4 of the same section requires a 1.4 factor for strength design of the
steel elements of the wall anchorage. If you were to design steel
connectors you would either be using 1.4(420plf) for LRFD or 420 plf for
Item 5 allows .85(420plf) for strength design of the wood elements, or
.85(420/1.4) for ASD.
Use of manufactured ties like Simpson hardware basically blows all the
carefully thought out force per material provisions out the window. Most if
not all of these types of products have published values based on tested
failures and a factor of safety somewhere between 2 and 6. Was the limiting
factor pull-out, wood failure, or steel failure? This is information is not
quickly and easily obtainable.
You could try and calculate the capacity of these products relative to the
appropriate material force factors, as recommended in the SEAOC Blue Book,
but for most of us I think I am safe in stating that this is simply not
practical. The simple solution for wood framed construction is to simply
apply the unreduced 420plf and compare this directly to the Simpson tables.
It is conservative, but the cost impact on typical projects is not too
severe. Larger projects may warrant the additional effort to reduce the tie
requirements and justify the numbers.
With regard to your original question, I assume you have a wood nailer on
the top of the wall and 3x minimum joists framing over the wall?
One solution is to create a custom beam seat consisting of two side plates
with through bolts at the beam tie welded to a couple of perpendicular angle
segments (vertical leg down) that slip over the wall plate. Leave enough
gap for anchor bolts to project through the wall plate. Either way it goes,
one or the other angle is in bearing and the anchor bolt design is the same
as a ledger. A couple of pilot holes and wood screws will prevent the seat
from lifting off the wall plate.
Another alternative is to use ledgers each side of the wall with through
bolts for the typical framing to bear on (may only need one side depending
on load) and use bent plate or angles with through bolts to the tie element
and anchor bolts directly to the top of the wall.
Just some thoughts,
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