Progressive Collapse Loading

[GBMRAO]

HI Friends,

I am currently analyzing a building for progressive collapse. The m factors and an increased load is suggested to be placed on the floors. I was wondering if the first option "a" satisfies then is it ok or do we have to check both of them both a and b lines. why is there "c other" interpolation of web slenderness will still result in a higher value from flange slenderness. so it's obvious to use flange slenderness. unless i am missing or misunderstood.

IF i have three floor and the first-floor column is removed. we calculate the M value for all three-floor beams. But do we have to use the least m value out of all 3-floor beams or each floor has its own m value and corresponding GLF has to be applied to each floor with its respective increased loads. some times each floor may have different live loads.

 

[JAE]

You might get a few answers if you add more information - which design document are you referring to for one.

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[MrHershey]

As a preface, if you’ve never used ASCE 41 before (or have only done tier 1/2 stuff) then please take the time to sit down with someone who has or take the time to watch a webinar or similar to get acquainted. I’m normally someone who prefers to just pick things up and dive right in, but ASCE 41 is so different from normal design that it really merits taking some time to get acquainted.

To your actual question, I wouldn’t really call these ‘options’ as that implies you have a choice on which one to use. The screenshot you’ve provided from ASCE 41 contains different performance criteria based on a bunch of different factors. You’ll need to determine what applies to your situation based on member properties, yield stress (adjusted for slenderness), target performance level, and then whether member you’re looking at is primary or secondary.

You’d only need to satisfy the one(s) that actually applies to you, don’t need to check both lines if only one applies. But you don’t get to pick your favorite, you have to figure out which one applies to you. It’s not ‘choose a or b’, it’s ‘if a, do this; if b, do this; if between a and b, do this’.

And m-factors are usually assigned individually to each component/action, so no issue using unique ones for each beam. That’s actually what is intended.

 

[GBMRAO]

Thanks for the response.

Thanks for your response.
I agree with you. I jumped on it and started reading the code ASCE 41 along with GSA and FEMA P-2006 guides. As you have said I don’t have any one here who has that experience to take a shoulder help and guide. That’s why reaching to our fellow engineers. Searching for good webinars and seminars online too.
I am using ASCE 41 code. I have calculated the m factors for the increased loads but the confusion I am having is whether to apply the fully loads to model on only beams?

1. After calculating the increased load factors should I apply the load to the primary members and the infill joists ( secondary members).
2. If dead load is already a default on my model how I can delete and apply (risa software)? I am little confused as to how to apply two load combinations to the same floor?
3. Should the m factor be only calculated for the beam and apply increased load or should it be the least of beams, columns above the removed column?
4. IF I only calculate for the beams its coming to 8 and if I multiply 0.9m+1.1 its going to be 8.3. If I multiply this with the 1.2DL +0.5LL then increased loads are too high.

 

[structSU10]

I recommend you download UFC 4-023-03 - it is the military standard for progressive collapse, but it uses ASCE 41 and modifies it. The nice thing about it is that there are design examples in the appendix that should help clarify some of the basic points of the analysis.