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Fw: 3x sil's

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I posted this over on the residential list, I thought that I would send it
here to see what you folks think.

-----Original Message-----
From: Randy Vogelgesang
Date: Saturday, July 29, 2000 9:11 AM
Subject: 3x sil's

+AD4-I have a question about the use of 3X sil+IBk-s.
+AD4-I engineer quite a few single family houses in a high wind area (85 mph,
+AD4-C), seismic zone 3 (northern Nevada).  Quite often the seismic load on a
+AD4-wall is very low while the wind load is above 350 plf.  Table 23-II-I-1
+AD4-requires the use of a 3X sil but doesn+IBk-t distinguish between wind and
+AD4-seismic loads.  In reading the SEAOC blue book commentary (both the 96 and
+AD4-99 editions), the reason for the 350+ACM- trigger was +ACI-in response to damage
+AD4-observed in the 1994 Northridge earthquake+ACI-.  The commentary goes on to
+AD4-describe the seismic failure mode of the sil+IBk-s.
+AD4-It seems to me that the 3x sil need only to be used when the seismic load
+AD4-greater than 350, not wind.   The reason that I say this is because the
+AD4-shear walls for wind loads are usually in the elastic range, not cyclic,
+AD4-do not under go the large deflections associated with the described
+AD4-If they did, we would have to re-sheetrock the houses after each large wind
+AD4-event.  While it is true that the shear wall doesn+IBk-t know when it will be
+AD4-asked to resist a seismic load, if this house were located in a 70 mph,
+AD4-B area it would not have a 3x sil.
+AD4-Does any body know if this was a code oversight or am I way of base?
+AD4-Randy Vogelgesang S.E.

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