FW: Techinal clarification for application of UBC 1997 and UG-23(d)

[kc445]

In using the compress ,we need some clarificatioin as below.
please check and let me know your opinion.

1. Application of UBC-1997 in compress

1.1 We have commented from our cliient for application of using load combination in UBC-1997.
[please refer the attachment # 1]
the comment do not allow for increase in allowable stress by Para 1612.3.1 In UBC-1997
but there is two cases for load combination in para 1612.3 UBC-1997.
One is basic load combinations and another one is alternate basic load combinations.

So, please let us know what load combination is basically applied in compress.
and how can apply these load combinations[Para 1612.3.1 & 1612.3.2 UBC-1997] one form the other in compress

1.2 And if we apply para 1612.3.1 basic load combination UBC-1997, with relation to para 1612.3.1,
there is no warning to use UG-23 increase stress factor 1.2 in compress even though not allowed to apply increase stress.
So, we would like to know your opinion for application of UBC-1997 in compress totally.
And we also would like to know that stress increase[factor =1.2 ] as per UG-23 can be applied with basic load
combination 1612.3.1 in UBC-1997[see commented page - attachment #1]

 

[TomBarsh]

There are several different, unrelated issues obtaining.

1- The factor 1.4 is indicated as a combined load reduction factor for cases in which seismic load is combined with certain other loads. The factor does not represent an allowable stress increase factor. This issue is discussed further in this document:

http://www.codeware.com/support/faq/1020.html

2- COMPRESS provides two inputs for allowable stress increase factors:

a- An increase in allowable stress for pressure components is permitted by ASME Code and is indicated as 1.2 in paragraph UG-23(d). COMPRESS provides an input where the designer may change this factor to any value between 1.0 to 1.2, inclusive. See the ASME Codes dialog for the "UG-23(d) Stress Increase" input; by default this value is 1.2.

b- Increase in allowable stress for structural components is not addressed by ASME Code. COMPRESS provides an input for allowable stress increase for structural supports such as skirt, legs, saddle, etc. This factor may be any value between 1.0 and 1.333, inclusive. See the Set Mode Options dialog, Calculation tab for the "Skirt/Legs/Saddles Stress Increase".

The building code for wind and seismic will generally dictate the permissible increase in allowable stress for structural components. Older building codes permitted a 1/3 increase in allowable stress; newer building codes generally do not permit such an increase. This issue is discussed further in this document:

http://www.codeware.com/support/faq/1150.html.

Please refer to the important information in this document, and to the links to articles at AISC website (AISC = American Institure of Steel Construction).



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Tom Barsh
Codeware Technical Support

http://www.codeware.com