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Re: UBC shearwall reinf.

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The definitions of rho(v) and rho(n) have been unnecessarily 
confusing for a number of years.  The problem arose when the 
codewriters tried to generalize the definitions to cover 
reinforcement that was placed at an angle (not vertical or 
horizontal).  The resulting definitions are very difficult to 
interpret at they confuse what is perpendicular (the reinforcement or 
the plane).

The definitions in ACI 318-99 are finally clear.  Here they are:

rho(n): ratio of area of distributed reinforcement parallel to the 
plane of Acv to gross concrete area perpendicular to that 

rho(v): ratio of area of distributed reinforcement perpendicular to 
the plane of Acv to gross concrete area Acv.


> Date:          Mon, 18 Oct 1999 08:23:30 -0700
> From:          Panos Trochalakis <panost(--nospam--at)>
> Subject:       UBC shearwall reinf.
> In UBC 1921.6.5.2 the shear capacity of a wall is based on rho(n). In
> the beginning of section 1921, rho(n) is defined as the shear
> reinforcement PERPENDICULAR to plane of Acv. In this same section Acv is
> defined as the net area bounded by the web thickness and length of
> section in direction of shear force considered. I would interpret Acv as
> a section through the wall in plan. Therefore, rho(n) would be defined
> as the vertical reinforcement? (perpendicular to Acv plane) The
> horizontal reinforcement is typically designed as the shear
> reinforcement and this is specifically called out in numerous texts
> including PCA's seismic design book. Am I reading the UBC definition of
> rho(n) incorrectly?
> thank you,
> Panos

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Michael Valley                                   E-mail: mtv(--nospam--at)
Skilling Ward Magnusson Barkshire Inc.                  Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699          Fax:        -1201