1/3 stress increase 1

[PSF]

Does the allowable stress increase of 1/3 for wind loads apply to a steel structure built in 1930?? We only have a steel manual as far back as 1950, and the 1/3 increase is permitted then.

 

[haynewp]

If you are trying to determine if the building is safe, or are adding to an old building, then I would use current code provisions. I wouldn't mix new and old nor try to determine if a building is safe based on a 75 year old building code.

This may help for your specific question:

http://www.aisc.org/template.cfm?template=/ContentManagement/ContentDisplay.cfm&ContentID=26812

 

[JAE]

I don't think it matters (today) whether an old code permitted the 1/3 stress increase. All designs, design checks, and load capacity determinations should be based upon the current applicable code.

That said, this doesn't mean that an old structure designed under an old code must, in all circumstances, be brought up to the current code. Most jurisdictions I've worked with (in the US) allow for a grandfather provision where you don't have to upgrade anything unless you perform 20% or more renovation work on the building (cost of renovation = 20% or more of the value of the building).

I think the concept of the 1/3 stress increase is quite old though, to answer your question. 1930 wouldn't surprise me if it used it.

 

[archeng59]

I recommend using current code provisions, no 1/3 stress increase. However, the various load combinations in ASCE 7, chapter 2, provide some relief for wind loads that is similar to the 1/3 allowable stress increase.

 

[haynewp]

I think the grandfather provision is also in the IBC under existing buildings and being able to use it is based on amount of new force added to an element, if I remember correctly. But I would always document to the client when a building doesn't meet current codes if I were analyzing it, even when the grandfather provision applied.

 

[Taro]

You might also want to look into a code that explicitly deals with existing buildings such as the International Existing Building Code.

 

[PSF]

We are checking our model with the original loads that were provided from 1930, and 1/3 increase would help the members pass the code check. We are also analyzing for today's loads under IBC.

 

[haynewp]

The 1/3 increase should be in the 1923 specification according to the link I gave.