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Live load reduction

Live load reduction

Live load reduction

I searched through the threads and the only thing I could find close to my question was in the following topic: https://www.eng-tips.com/viewthread.cfm?qid=425321

Under the design options, I see there is an option to define the live load reduction factor for a member. I assumed that it would take the design forces from the analysis and scale the live load component of it based on the value specified to perform the design check, but it doesn't appear to do anything. Does this feature not do anything?
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RE: Live load reduction

I investigated this feature a few years ago and it seemed to not do anything. I couldn't figure out what it's used for.

RE: Live load reduction

Ok, glad to see it's not just me. That's unfortunate, I'm pretty sure other structural analysis packages have implemented a feature like that. Thanks!

RE: Live load reduction

I'll see if I can research it a bit. I have to admit that I've never done used LL Reduction in SAP2000, only ETABS.

RE: Live load reduction

Ok, I wanted to circle back on this because I think I found the reason why it didn't work. Thanks JoshPlumSE for volunteering to look into it.

It was because I was trying to apply it to non-linear load combinations. When it's applied to linear load combinations, it's able to apply it. Makes sense since the linear combinations are just superposition of the load cases, so the program should be able to easily apply the llrf directly to the live load contribution to the forces, whereas for non-linear load combinations it must run the entire set of loads for each combination.

RE: Live load reduction

Ahhhh, that makes perfect sense. Theoretically, in order to get "load pattern" reductions you need to have a an analysis where load superposition works. It works great in a linear analysis, of course. But, non-linear load combinations are a different story. I have some ideas about how it could be approximated for non-linear load combinations. But, those ideas would probably work better for building models (like ETABS) than for a general analysis program like SAP2000.

Sorry, it's taken me so long. All the documentation that I looked up implied that it should work. But, then I couldn't find any documentation of the methodology for reduction like we have in ETABS.

My next step (which I'll probably still do) is to build a simple example for myself to see how well it works (or doesn't work). But, I just haven't had any time.

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