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RE: 1.7 allowable increase gone? 2003 IBC

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Chad:

See comments below...


On Tue, 7 Oct 2003, Chad Druffel wrote:

> This is a follow up from a topic I brought up a few weeks ago:
>
>
> RESPONSES TO CHARLIE:
>
> A)
> I appreciate your detailed description of the 1.7 factor, this helps to
> clarify the intent of the code provisions.  I DO think that this should
> be described within the commentary to AISC 341-02, so that everyone can
> understand the intent (while on the subject, wouldn't it be nice to have
> a commentary for the IBC and ASCE-7 published along side each of the
> sections like the ACI does?  Although these resources would probably
> then triple in size).

ASCE 7 does have a commentary (which you might be aware of)...they, of
course, do not print the commentary side-by-side with the code provisions.
The ACI "only" codes are the only ones that do this.  The MSJC (masonry
code...which is joint through ACI, TMS, and ASCE) does not print the
commentary side by side.  After working at ACI, I learned that some people
really like the side-by-side format, while others don't.

>
> MY OWN GENERAL VENTING:
>
> In general, I am disappointed with the IBC 2003 / ASCE 7-02
> relationship.  IBC creates confusion by throwing you into and out of
> ASCE-7.  ASCE-7 should have been more in-line with the IBC so that it
> could have been fully adopted with only minor modifications.

Some (including myself) would argue that you have it backwards...the IBC
should be more in-line with ASCE 7...in otherwords, DON'T make minor
modifications but rather fully adopt the ASCE 7.  ASCE 7 is done within a
consensus process while the IBC is not.  This potentially means that the
IBC is more susceptible to special interest "tweaks".  Many times there
are those who cannot get the support for a change within the consensus
process (i.e. not enough people by the rationale), but then do an "end
run" by going to the IBC/ICC hearings and trying to get it in there.
Sometimes it is justified, but most times not.

>
> I am also disillusioned with ASD Steel Design.  ASD is essentially being
> made more and more difficult and confusing, in part due to the issues I
> previously discussed.  With the inclusion of variable phi factors with
> the allowable stress increase, they have basically permitted you to
> continue to use stress based design, but both the load and resistance
> sides of the equation are going to be factored.  This creates a new
> level of difficulty when using design programs such as RISA, that do not
> take into account a phi factor when performing ASD; thus you have to
> increase the load side of the equation instead, and create new load
> combinations, and these load combinations will vary with the phi factor
> depending on what portion of the braced frame you are designing.  One
> way to get around this complexity is to use the most conservative phi
> factor everywhere, but what a waste.
>
> The ASD "exceptions" that are interlaced throughout the code and other
> references have created too much confusion and I find myself getting
> "lost in the numbers" more and more.  So I have reluctantly decided to
> make the switch to LRFD for steel design.  I feel that I might as well
> make the switch now because that is the direction we will continuously
> be "nudged".
>

Use LRFD and the confusion goes away!!! <grin>

To be less annoying, AISC is planning on making the edition of the
specification a joint LRFD/ASD spec (in 2005).  In otherwords, they have
heard the message that people like their good ol' ASD, thus AISC will
resurrect it.  But be careful what you wish for...ASD has not been updated
since '89 while LRFD has is in it third iteration since then.  There is a
lot of new steel knowledge that is not included in ASD that will be when
it gets updated.  Thus, your good ol' ASD will no longer look like what
you are used to.  But that highlights the problem that you have
encountered...the current seismic provisions are "aimed" at LRFD which has
this "new stuff" in it...ASD does not...so getting the seismic provisions
to work with ASD is kind of like translating from one language into
another that does not really translate well (if that makes sense).

HTH,

Scott
Ypsilanti, MI


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