Seismic Load Combinations

[monchie]

Hello,

I've seen a documents "Manual for the Analysis/Design using ETABS" by ATKINS(pls. see attached screenshots).
According to the documents the load combinations are based on UBC 97/ASCE-7.
Flicking the pages of UBC 97/ASCE-7-05, there's a discrepancy on the factors used.
Also, load combinations for serviceability conditions have seven(7) load combinations,
I am wondering where in the code I can find it?
Any ideas/sugeestions will be greatly appreciated.

 

[delagina]

you were able to find strength/lrfd combination but not serviceability/asd load combination in ubc or asce?
they should be on the same page or 1 page difference if i remember right.

 

[monchie]

@delagina, pls. see my previous attachment. I already attached strength combination for both
UBC 97 and ASCE 7-05 but I cannot notice any similarity between ATKINS documents and UBC 97/ASCE 7-05 regarding their "factors".

Also, where ATKINS derived the "serviceability" load combinations as per UBC 97/ASCE 7-05?

 

[JAE]

You should never mix UBC 97 and ASCE 7-05 as they are completely separate documents with different load basis and sometimes different approach.

UBC 97, only references back to ASCE 7-95, Chapter 6 for Wind Design.



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[monchie]

@JAE, what I've meant is that, comparing it to UBC 97, the factors used in the "Atkins Manual" is quite different. Compared it again to ASCE 7-05, the ~"factors" used is quite different.

Especially, the 7 serviceability load combinations shown on the "Atkins Manual". I've searched for both UBC 97 and ASCE 7-05 to find clues/similarities but to no avail. Did I miss something?

I really believe that the published maual by ATKINS is correct(no doubt) but I am looking for clause/reference where these load combinations originates.

 

[JAE]

I really believe that the published maual by ATKINS is correct(no doubt) but I am looking for clause/reference where these load combinations originates.

The "correct" load combinations are those required by the applicable building code which governs your building or structure.

I'm not familiar with Atkins - but I wouldn't use a list of load combinations from a software product - only use the applicable code combinations.

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[delagina]

Monchie, I already told you UBC also has allowable load combination, that's where atkins serviceability load combination was based from.
You only posted UBC strength load combination.
If you have UBC, it should not be difficult to find UBC allowable load combination.

Now, whether Atkins followed UBC97 or ASCE-05 load combination factors is another thing.

Just looking at atkins 1st strength load combination
1.4DL + 1.6Mech + 1.6LL

should have been
1.2DL + 1.6Mech + 1.6LL (assuming mech is a live load also)

btw who still uses UBC...

 

[JAE]

UBC 97 - Section 1612.3 has Service-level load combinations.

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[monchie]

Thanks Delagina/JAE,

It is sometimes really a pain when you find a reference material claiming it is based on reference codes (whether it is UBC 97 or ASCE 7-05), and then you started reading it, and you will end up confused rather than informed when you realized that something is not right(load factors, coefficient etc.).

I am hoping that somebody from ATKINS(Dubai) will settle this issue or made some clarification since their documents are all over the internet.

 

[monchie]

@Delagina,

In the Philippines, we still uses UBC 97 as the main code for Earthquake analysis(NSCP-2010) and ASCE 7-10 for wind loads.