Moment resisting frame or Braced frame w/ chevron bracing?

Structural Layout Vignette and Multiple Choice

Moment resisting frame or Braced frame w/ chevron bracing?

Postby vrcat25 » Wed May 24, 2017 8:03 am

In the ARE sample problems, question #79 says that for a lateral load resisting system, a braced frame with an eccentric chevron bracing is the most flexible between the given choices, while shear wall is the most rigid.

Question #103 says that a "moment resisting frame" is the most flexible system.

Is chevron bracing a type of moment resisting frame or are they two separate systems?
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Re: Moment resisting frame or Braced frame w/ chevron bracin

Postby gbalaka » Thu May 25, 2017 9:00 am

I took this exam about a year ago, but I actually remember this information.

The reason the eccentric chevron bracing system is flexible is because the braces do not meet at a common point. Instead of "I\/I", it's more like "I\_/I" (mirror the V, so it's upside down). The little portion of the beam that is "unbraced" in the middle allows for that portion to bend, so it it a braced frame that allows for some bending.

And yes, a moment resisting frame is the most flexible system if you're talking about the 3 main choices (shear wall, braced frame and moment resisting frame).

You can most certainly have a combination of these systems.

That's my understanding of this.......
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Re: Moment resisting frame or Braced frame w/ chevron bracin

Postby corbismyhomeboy » Fri May 26, 2017 6:44 am

The eccentrically braced frame is a part of the braced frame "family".

So in terms of flexibility (from most to least):
1.) Moment Frame
2.) Eccentrically Braced Frame
3.) Concentrically Braced Frame
4.) Shear Wall

There are so many variations (Concentrically can be 'ordinary' or 'special', etc.,) and dual systems (combining a moment frame and a shear wall for example) that it was easier for me to think in these kind of simplistic terms for the exam.
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