Comparing Brace Configurations 4

[GearsNsparks]

I'm looking at two brace configurations and I don't think one has greater capacity than the other. See the attachment:

Is there a reason why someone would design for style A instead of B? Does it come down to fabrication or preference?

 

[canwesteng]

Are loads uni or bi directional? It's more efficient to carry only tension in diagonals if possible.

 

[P205]

Have you considered a chevron |/\| instead?

 

[JoshPlumSE]

Either of these configurations would be penalized if it were an SCBF which requires that at least 30%, but no more than 70% of the total horizontal force be resisted by braces in tension.

 

[JAE]

Josh, isn't that a requirement for the total of braces in line?
So it is POSSIBLE that a brace with 100% compression would be fine as long as there was another brace, in line with it, working in tension?

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[KootK]

I'm drawn towards "A" aesthetically but there might be a slight economic advantage with "B". With trusses, a disproportionate amount of the connection costs are associated with the joints where two or more webs meet at the chord. Option "A" has four such joints and option "B" has two.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[WARose]

Is there a reason why someone would design for style A instead of B? Does it come down to fabrication or preference?

I think comparing those two it would come down to aesthetics. You may want to bounce it off the client if they are exposed.

 

[SlideRuleEra]

If all other factors are equal, I prefer the geometry that creates to most "triangles" (for redundancy).
In this case, assuming both structures are on firm foundations, style "A" creates 6 triangles; style "B", 8 triangles.
I would select "B".

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[JoshPlumSE]

JAE -

Yes, that's what I was thinking of. That his picture would be the only braced bay in that line of framing. Though I should have been more clear.

Re-reading his original post, I merely assumed that's what the OP was getting at. But, he never actually said it. Therefore, I may have assumed too much.

 

[GearsNsparks]

Sorry for the late response; this board posts quickly.

The lateral loading is bidirectional.

They are normal concentric brace frames.

The customer is fine with the looks of either configuration. I'm leaning towards B.

 

[EngineerEIT]

The beams in configuration A will have to be designed for the accumulating axial load as the horizontal component from the brace above will have to travel through the beam to the brace on the opposite side. Configuration B has a more direct load path and the beams would only need to be designed for any drag load.

 

[StrP88]

My opinion is simplicity is the best Fig A due to lateral loads in one direction puts all bracings at a same time in compression or tension. Fig B instead creates inconsistency in the nature on bracings, two will be in one nature (Tension, or Compression)and middle story bracing will act opposite(Compression, or Tension.

Other point is in Fig B you have more connection and possibly load on the left column at 2nd floor and fist floor right column.
I will go with Fig A

Also, I didn't catch how the numbers of triangles in Fig B came to 8 ??? Seems to me both Figs create same number of triangles !!!

 

[SlideRuleEra]

I didn't catch how the numbers of triangles in Fig B came to 8?

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[sticksandtriangles]

The beams in configuration A will have to be designed for the accumulating axial load as the horizontal component from the brace above will have to travel through the beam to the brace on the opposite side.

I used to think this as well, until I was in my seismic design class I took.

My professor brought up an interesting point in that higher levels of modes, where adjacent floors are moving in opposite directions of each other, the beams in configuration A B will actually need to be designed for axial load due to the higher level mode shape. I have honestly not put much thought to this comment, but what my professor said seems to make sense. Probably not a big factor in a low seismic region, but I always like to be alerted to items that go counter to my intuition. I should make a quick model and verify this statement.

 

[sticksandtriangles]

Sorry I meant to say configuration B in my note above.

 

[haynewp]

Option B has 4 connections to be addressed where A has 6. B also has more direct transfer to braces. I prefer B.

 

[cliff234]

I did not read all the responses, so I apologize if I’m repeating anything that was previously mentioned.

I like “B”. The load path for B is more direct. With A, the loads must travel through the floor beams at every level (requiring the beams to be designed for a potentially significant axial load). With B, the loads just go from brace to brace. No such axial loads in the beams with B. With A you may need to use bigger beams (depending on the forces in the braced frame).

 

[amec2004]

In terms of Structural optimization:

1) Get braces as all tension brace if possible

2) Get hor load transfer to foundation in the shortest path

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