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# Re: 'R' Values

• To: "<seaint(--nospam--at)seaint.org>" <seaint(--nospam--at)seaint.org>
• Subject: Re: 'R' Values
• From: Scott Maxwell <smaxwell(--nospam--at)umich.edu>
• Date: Mon, 5 Oct 2009 17:58:03 -0400

```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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