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Re: ACI 530 R=1.5

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The exception in ACI 530 states that if you reduce the response modi. factor to 1.5 or less, then you can use masonry wall piers to resist lateral loads.  What type of structure are you designing?

On Thu, Feb 5, 2009 at 8:42 AM, Rick <mohr2circle(--nospam--at)> wrote:
Look at ACI 530 it limits the R to 1.5, but only in the strength section.  City of LA code references 530 to answer the other section.
I saw, and thought thats what they were origianlly referring to, but is pretty clear. But nothing in ASD

--- On Thu, 2/5/09, Paul Feather <PFeather(--nospam--at)> wrote:
From: Paul Feather <PFeather(--nospam--at)>

Subject: RE: ACI 530 R=1.5
To: seaint(--nospam--at)
Date: Thursday, February 5, 2009, 8:35 AM

ACI 530 does not set or establish R factors.  There are only two possible explanations that I am aware of: first if using strength design there is a provision for maximum area of flexural tensile reinforcement ( where M/Vd greater or less than 1 and IF the design used an R of less than or greater than 1.5 is a trigger for additional design requirements.  This is not an R factor limitation, just a trigger for other provisions.  Second would be if they are somehow mis-interpreting the shear force required of 1.5V in ASD design, but this is an IBC requirement and not in ACI 530 either.
I would ask the Plan reviewer to specify which code provision he / she is referencing with his comment.
Paul Feather PE, SE

From: Rick [mailto:mohr2circle(--nospam--at)]
Sent: Thursday, February 05, 2009 7:58 AM
To: seaint(--nospam--at)
Subject: RE: ACI 530 R=1.5

I have a City of LA Plan check comemnt that R = 1.5 "must" be used for masonry walls piers per ACI  530.
Can someone point me to the specific reference.

David Topete, SE