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Northridge EQ and Wood

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AF&PA's American Wood Council published a report on observations of multi-family
structures, single-family dwellings, manufactured housing units, and
commercial/industrial/warehouse structures. fax or photocopies are available by
emailing your request to awcinfo(--nospam--at)afandpa.org.

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From: Drew Morris <drew(--nospam--at)Alaska.NET>
To: "seaoc(--nospam--at)seaoc.org" <seaoc(--nospam--at)seaoc.org>
Subject: Wood

I recently sat through a seminar on the 1997 UBC and the speaker
mentioned the problems that occurred after the Northridge EQ.  Are there
referances and publications that deal mostly with the problems noticed
with conventional wood framing? I am interested in getting references to
the problems that occurred with sill plate anchor bolts and tiedowns.

Also, did the homes engineered for lateral forces handle the earthquake
better than  the homes designed by the prescriptive design chapter in
the UBC?

*************


From: Tim McCormick <TMCCORMI(--nospam--at)BAS.CI.LA.CA.US>
To: seaoc(--nospam--at)seaoc.org
Subject: Northridge EQ and Wood

Drew,

The 11/94 SEAOSC seminar on the joint COLA/SEAOSC Task Force for
the Northridge EQ has some of the information you seek. Contact Don
Gilbert @ 562-908-6131 for a copy. 

The City did not study the difference between prescriptive and
engineered designs. Whether or not engineered structures do better has
a lot to do with the quality of construction. We accept that engineered
structures will do better when properly designed and constructed.

Problems that occurred with sill plate anchor bolts were:

1. Lack of proper embedment due to use of the two-pour foundation
system  (footings first, then slab).
2. Horizontal misplacement causing improper edge distance in the wood 
usually at interior walls.
3.  Vertical misplacement  (out of plumb) causing oversized holes in the
sill plate.

Tie-down (holdown) connectors had the following problems:

1. Oversized bolt holes in the end stud(s) / post.
2. Excessive elongation of the connector causing cross-grain failure of
the sill plate and panel buckling.
3. Loosening of the connection due to wood shrinkage.
4.Horizontal misalignment of the tension bolt causing improper edge
distance in the end stud(s) / post.
5. Insufficient embedment/ edge distance for the tension anchor bolt.

Also, long shear walls with little to no overturning had split sill plates.

Hope this helps,

Tim McCormick, P.E.
City of Los Angeles
Department of Building & Safety