seismic resistance

seismic resistance

Postby arbitect » Tue Apr 10, 2018 8:54 pm

"Of the three basic types of lateral load resisting systems, shear walls are generally the most rigid, that is, they deflect the least when subject to a given lateral load. Braced frames are usually less rigid, followed by moment-resisting frames, which are the least rigid. The more rigid the lateral load resisting system, the more seismic load it tends to attract."

Does this mean that shear walls are better at resisting seismic loads than the other two or worse?
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Re: seismic resistance

Postby vrcat25 » Wed Apr 11, 2018 1:20 pm

Not sure what you mean by "better" or best in terms of the systems. Yes, shear is most rigid, braced is in between and moment is least rigid, but this doesn't mean that shear is beter for seismic. In fact, rigid isn't usually good for seismic, the opposite is true..FEMA 454 chapter 5 discusses mixing systems, but i don't see anywhere where one system is "BEST". It doesn't work like that in the real world. There are probably 10 or more systems and most of the time shear, braced, moment are mixed unless you have a metal building...
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Re: seismic resistance

Postby arbitect » Wed Apr 11, 2018 1:33 pm

Thanks....that's kind of what I thought. But there was a question in Brightwood about which is better and the answer was moment resisting frames because they are ductile. Anyway, it's all a little confusing still.
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Re: seismic resistance

Postby arbitect » Wed Apr 11, 2018 1:34 pm

And I think the term that throws me off is "the more seismic load it tend to attract." What exactly does that mean?
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Re: seismic resistance

Postby vrcat25 » Fri Apr 13, 2018 5:45 am

arbitect wrote:And I think the term that throws me off is "the more seismic load it tend to attract." What exactly does that mean?


You may be overthinking it...by it's very nature a shear wall is rigid. It stabilizes other walls it intersects. Braced frames and Moment frames are also rigid...In fact, a moment frame is also called a "rigid frame". It's ironic and confusing that it's the least rigid of the 3 though. I can see why you are confused. Many practice test questions have "best guess" type questions that are just plain stupid. You can tell that the people who make questions like that have no idea what they're talking about. Maybe you can find in one of the referenced text books which system is "best", but I highly doubt it since a structural system can be assembled in over 10 different ways. Take a look at "structures illustrated" by Ching and you will see that even skyscrapers use a variety of sytems and NONE of them are "best"...
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