In regard to Michael's comments here is my 2 cents:
1. The simplified procedure is already in the 97 UBC (section 1630.2.3)
and actually based on ICBO structural committee's suggestion, the 2000 IBC
incorporated a simplified procedure (and god knows it needs it!) in the
2. The only item that is not currently addressed in the simplified
procedure is the horizontal distribution for plywood diaphragms (rigid vs.
flexible). And that is where an ICBO/SEAOC opinion would be useful now.
3. As to checking plywood shear wall deflection, I think the intent of
the code has always been that if you comply with the prescribed aspect
ratios for shear walls, you do not need to check deflection for these types
of buildings. And I do not think we need to change that now, especially with
the stricter 2:1 ratio in the 97 UBC and 2000 IBC.
4. As to plywood diaphragm acting rigid because of 1 ½ gypcrete, I
believe much research needs to be done to prove this claim. Keep in mind
that the gypcrete is usually not continuous over the entire area and is
often interrupted by interior wall sill plates.
From: Mlcse(--nospam--at)aol.com [SMTP:Mlcse(--nospam--at)aol.com]
Sent: Wednesday, May 12, 1999 11:29 AM
To: seaint(--nospam--at)seaint.org; SaifH(--nospam--at)aol.com
Subject: Re: Seismic Upgrade ..... Appeal to those who
created the code
In a message dated 5/12/99 8:49:20 AM EST, ROH(--nospam--at)eqe.com writes:
As a further note, to Ali's excellent explanation below-
The Building Seismic Safety Council's Technical Subcommittee 2 is
process of reviewing an introduction into the 2000 NEHRP Provisions
Simplified Design Procedure. This will be somewhat similar to that
contained in the 1997 UBC. Major points are:
1- Base shear is determined by a somewhat simpler, but a little bit
2- Vertical shear distribution is rectangular rather than inverse
3- Deflections need not be checked
4- (most of interest) Structural use panel diaphragms may be
flexible, for purposes of analysis.
These provisions will be applicable to nearly all residential
While they will not "officially" take effect for a few years, it
the "Standard of Care" issue to be able to point out that it was
specfically included in the resource document recommended for
editions of the IBC. Also - the note Ali suggested on the design
should help as well.
Do you anticipate that there might be a cut off point for when to
structure for flexible or rigid depending upon the type of building.
Single story Family Residence: flexible, no deflection check
Two story Family Residence: flexible only, with shear wall
of first floor walls.
Apartment buildings: plywood floor: flexible, shear wall
Apartment buildings: plywood floor w/ 1-1/2" gypcrete: flexible and
checks plus shear wall deflection check.