# AISC seismic design manual - load combinations



## civildong (Aug 29, 2013)

I am really get confused of the seismic load combinations when there are redundancy factor &amp; overstrength factor.

Based on my understanding, only one of them need to be considered in calculations. Am I right? then my question is about how to determine which one need to be included in the combinations when both are given.

In the AISC seismic design manual Part 3 for R&gt;3

Example 3.1, 3.2, 3.3: both PHO and Omega are given, but only PHO was used in the analysis

Example 3.4: both PHO and Omega are given, while Omega is included in the calculation

anyone can explain why? I am really not a steel person. Anyone can help me out for the load combinations? Thanks in advance.


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## kevo_55 (Aug 30, 2013)

Well, the best way to explain this is that "the devil is in the details."

When looking at steel design for seismic applications you'll find that the load could come from "standard" load combinations, "omega" type load combinations, and even a load based on the member's "maximum" strength itself. This all really happens to be related to what type of seismic system is chosen.

I would take a look at AISC 341 section 14. This is for OCBF type systems. The different types of connections &amp; members calculated pretty much have the required load combination type spelled out for you.

I hope this helps.


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## civildong (Aug 30, 2013)

Kevo, thank you so much for the explaination. I really need to read the code.......Too much to be remembered in the provisions.


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