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# Re: 'R' Values

• To: <seaint(--nospam--at)seaint.org>
• Subject: Re: 'R' Values
• From: Scott Maxwell <smaxwell(--nospam--at)umich.edu>
• Date: Mon, 05 Oct 2009 20:04:25 -0400

```Thor:

And my point was that there likely is no "rational" equivalence since the
current IBC/ASCE 7 R values are more based upon "political"/backroom
agreements than pure rational engineering.  Your best bet is to compare the
various values from the IBC/ASCE 7 to the Canadian values and see if there
is some sort of rational "static" factor that could be applied to one to get
the other...but I kind of doubt that there is such a single multiplication
factor.

My only reason for blathering on about the concept was to illustrate that in
theory there SHOULD be a rational engineering method, even though there is
not.  In other words, there is no engineering reason that current R values
should largely be "hocus pocus"...the current R values are driven largely by
one material group wanting to get a competitive advantage over the competing
materials.

Regards,

Scott

On 10/5/09 7:24 PM, "Thor Tandy" <vicpeng(--nospam--at)telus.net> wrote:

> Hi Scott.
>
> I'm familiar with the 'R' concept but was trying to see the equivalence of
> our Rd*Ro to the US 'R'.
>
> Thanks
>
> Thor
>
> -----Original Message-----
> From: Scott Maxwell [mailto:smaxwell(--nospam--at)umich.edu]
> Sent: Monday, October 05, 2009 2:58 PM
> To: <seaint(--nospam--at)seaint.org>
> Subject: Re: 'R' Values
>
> Hocus pocus.
>
> If I try engage my serious mode...
>
> R vlaues, in theory, are to represent the amount of ductility relative
> to a purely elastic system.  The idea is a purely elastic response
> would have an R of 1.0.  The higher the R value, the more ductile the
> system will behave.
>
> Now, in theory, you can think of this a relative measure of the energy
> of the system response or the area under the curve of plot load vs
> deflection for a system.  Nominally, in theory, a system with an R of
> 5 will be able to dissipate 5 times the energy than that of a system
> with a pure elastic response.
>
> In reality, R values have never really been done purely based upon a
> rational method.  The have more been a function of "politics" (i.e.
> Kind smoke-filled backroom agreements).  While they are not complete
> BS, they can not currently be determined from a rational engineering
> method.
>
> In theory, this is potentially going to change.  There is an effort to
> make R values be more rational.  This part of the reason why Appendix
> A of the SIP ICC-ES acceptance requirements was killed (this assumes
> you read my long dissertation post on SIPs for lateral loads).
> Personally, I have lost track of where this effort stands.
>
> HTH,
>
> Scott
>
> On Oct 5, 2009, at 4:47 PM, "Thor Tandy" <vicpeng(--nospam--at)telus.net> wrote:
>
>> Showing my ignorance of IBC/UBC through little use thereof.
>>
>>
>>
>> What makes up the 'R' value?  I'm trying to align some Hardy Frame
>> table
>> values (quoting 'R'= 5.5 & 4.4) with the local 'R' for loads I'm
>> using here
>> in BC.
>>
>>
>>
>> No doubt apples & oranges .  :^)
>>
>>
>>
>> Thanks
>>
>>
>>
>> Thor A. Tandy P.Eng, C.Eng, Struct.Eng, MIStructE
>> Victoria, BC
>>
>>
>>
>>
>>
>>
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```