assessment of existing stuctures - code variance

[oneintheeye]

if your assesing an old structure for a given loading (which may or not be higher than original, you don't know) do you assess to the current code, or the code at time of design or a hydbrid method. Particuraly when the code approach is different i.e. designed to permissible stress but current code is limit state (factored loads).

 

[asixth]

If you are doing any changes to the structure then it must be rated to current design standards. This includes increasing the design load, if it were designed for 3kPa (60psf) in 1970 and you want to increase the design load to 5kPa (100psf). The load and load combinations must be checked to current standards.

Living in Australia, seismic codes were non-existant pre-Newcastle Earthquake in 1989. Since then there are more stringent requirements for the lateral design of structures and I have found some designs of older-type structures that I have dealt with to be 'undercooked' if there were to be designed to todays standards.

How do I insert hyperlinks into the main body of my reply??

 

[Ron]

You make the assessment based on the code at the time of construction, or if the structure has been modified since, in accordance with the code under which it was modified.

If your assessment results in remediation, the level of remediation might bring current code into play.

Some areas have codes for existing buildings and those typically interject levels of remediation and to which code those must be done.

 

[oneintheeye]

two conflicting views there! The issue I have I suppose is that we don't know the initial load. The allowable steel stress for instance is based on working loads. i.e. use loads and derive the strees < allowable. Current codes say factor the loads and check capacity on grades of material. There is an obvious chance of missing something either way;

1) If I use current code to what material strength do I use as the old codes is permissible stress (i.e. factored to some degree). I don;t know the actual material strengths.

2)If I use old code is there something inherently 'weak' or missing that has been picked up in new codes that the old code wouldn't take into account.

 

[JAE]

I think asixth and Ron both said essentially the same thing. asixth said, "If you are doing any changes to the structure..." then the current code. Ron said the same thing. It's when you do renovation work, changes, etc. to the structure that you use the new applicable code. Some areas say work totalling more than 20% of the building's value require the new code.

Whether you use ASD or factored design doesn't matter that much as both provide similar safties against probability of failure. If you don't have the original strengths, then it is on you to find them out by sampling, testing, etc.

 

[msquared48]

What JAE said in the first paragraph is what we do in the Puget Sound area, in general. It really depends on the specs of the local building jurisdiction.

Mike McCann
MMC Engineering

 

[BAretired]

asixth,

I don't think anyone has answered your hyperlink question. You simply copy and paste the link as follows:

http://en.wikipedia.org/wiki/Newcastle_earthquake

It appears as ordinary text in your message, but when you Preview Post, it appears in bold, hyperlink text.

BA

 

[paddingtongreen]

Best bet here is to assume a loading and check the member to working stress methods. Unless the structure is very old, it was probably 36ksi steel. You should be able to find, fairly quickly, the the largest uniform load that it could have been designed for. If your load exceeds it you must then analyze to the current code.

If the structure is very old, use 33ksi steel, but you should be able to tell from the shapes, the time frame for it's original design. I assume you do have drawings.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[Ron]

As JAE and Michael noted, check to working/allowable stress. Current codes in the US do not preclude the used of allowable stress methods for steel.

If you don't know the allowable stress levels or the age of the material, then you'll have to do a little detective work. Assuming you can't get other information, do some testing on the steel. You can remove enough of a specimen to get a tensile strength of the steel without compromising the structure. If you can't or are not allowed to do so, check the hardness of the steel and use correlations. That's not the better of the two approaches, but it will get you in the ballpark. Make sure that whomever does the portable hardness testing knows how to prepare the surface and understands the localized surface conditions of hot rolled steel materials.