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RE: Seismic design of block fences

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The basic formula 30-1 in the 1994 UBC was intended to determine values for
nonstructural components supported by a building.  The 2/3 factor in the 94
UBC Sec 1630.2 was an attempt to remove the amplification effect of the
building on the nonstructural component.  

The 1997 UBC was obviously a rewrite as opposed to just tweaking the old
formula.  The 1997 methodology more directly takes into account the effect
of the building itself with the h sub x and h sub r ratio.  And as you
pointed out, the 1997 value is in fact less than the 1994 value.

	Fworking = .14W (1997 UBC)
	F = .20W         (1994 UBC)

Leaving in the 2/3 factor in the 1997 UBC would have been unconservative.

Harold Sprague
The Neenan Company

-----Original Message-----
From: Parkerres(--nospam--at) [mailto:Parkerres(--nospam--at)]
Sent: Tuesday, August 17, 1999 11:08 PM
To: seaint(--nospam--at)
Subject: Re: Seismic design of block fences

Harold and Bill - 

Thanks for the site wall clarification.  We had been using hx = hr = 1 
giving, F = .54 W based on ap=1, Rp=3, Ca=.44x1.3 and dividing it all by 1.4

for working stress.

At hx=0, eq 32-2 goes to Fworking = .14W.  This is less than eq 32-3 where 
Fwrkg = .29W which is almost the same as the .30 W of the 1994 Code.

Unfortunately, we seem to have lost the 2/3 reduction for ground supported 
walls that we used in the 1994 Code so F = .20 for site walls.  Where did it

go?  And why?

Bruce Resnick, SE
Parker Resnick Str. Eng.

In a message dated 8/17/99 1:49:26 PM Pacific Daylight Time, 
harold.sprague(--nospam--at) writes:

<< Currently you are in the right spot (32-2).  The h sub x and h sub r is
 intended to reflect the effect of elevated floors for nonstructural
 components.  The intent is that when you are on grade, the h sub x over h
 sub r term goes to 0. >>