Intercepting vertical bracing with beam?

[StructureMan44]

On a project we need to extend a floor to the end of a bay. At the end of the bay are two W14 vertical bracing members (see attachment). This vertical bracing is mirrored at levels above and below forming Xs as you move up and down the large structure. I’d like to directly connect to the W14 braces with the proposed W18 but do not want to create an overly stiff “story”. (Maybe a stiff story is created already because the W14s are braced by the W27x94?) Is there any published guidance on whether this is acceptable or rules of thumb on relative stiffness? I looked in AISC 327 and 325 and didn’t find anything.

 

[structSU10]

could you provide a section through this elevation? How does the W27 and proposed W14 connect to these braces? This puts awkward forces into the vertical bracing. I would frame off the columns (out of the page) and then put a spandrel beam between the beams, with a pour stop to extend the floor over, that way I don't have to mess with the braces.

 

[KootK]

I'm fine with this. I don't think that it does create a stiff story to any significant degree.

Diagrid buildings do this kind of thing in spades. Check out the John Hancock building.

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.

 

[StructureMan44]

structSU10: Attached is a plan at this elevation (at 181’-0” and the (+7’-0”) is elevation 188’-0”) and the connection between the W27x94 and vertical bracing W14s. The floor is steel grating (75psf allowable load) so a pour stop isn't necessary. As you can see in the plan that out of the page is open space and there is only one beam framing into the center of the W27x94 at elevation 181'-0". Are you suggesting to add a beam to the columns outside of the braces and frame to it with floor beams and completely bypass the vertical braces?

KootK: Thank you for your feedback, the Hancock is near me and I always wondered if and to what extent the floors provide bracing for the large vertical X braces.

 

[StructureMan44]

Sorry, the plan at elevation 181’-0” and 188’-0” (+7’-0”) did not attach.

 

[jayrod12]

Your attachment didn't work,

If I remember correctly you can't have punctuation in the file name.

 

[KootK]

I guess the one exception that I'd note is if your brace is meant to be a high ductility "special" braced frame for seismic. Then, delaying buckling in your braces might overload other parts of the system.

I would have just used simple shear/axial framing connections rather that all of the welding.

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.

 

[msquared48]

I strongly exercise caution here per KootK's first comment in the post above. Could be a deal breaker...

Mike McCann, PE, SE (WA)

 

[StructureMan44]

jayrod12: I have reattached the pdf with punctuation removed from the file name.

KootK: This is an ordinary concentrically braced frame. I would attach the proposed W14x68 to the vertical bracing W14s with bolted angles on both sides of the web. The angles would have to be cut at a skew on the leg attaching to the W14x68 web.

 

[KootK]

I was originally thinking that your floor beams would be attached to a diaphragm that would restrain the beams laterally. With grating, that's probably not the case and I would share StructSU10's concern regarding the "awkward" forces.

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.

 

[StructureMan44]

KootK: By "awkward" forces I assume you mean if the proposed W14x68 buckles in the weak axis direction it might create a torsional load on the W14 brace. As you can see in the attached pdf the proposed W14 is laterally braced.

 

[KootK]

I just meant that the floor beams will induce reaction loads in the braces that will be transverse to the braces. Your braces are pretty beefy and may be okay with that.

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.

 

[jike]

Why don't you connect the new beam to the flange of the existing column rather than to the brace? The beam would then be parallel to the brace but it a different plane.

 

[StructureMan44]

KootK: thank you for your feedback

jike: If I understand your suggestion, the columns and the braces are in the same vertical plane.