Relocating Bracings in a frame

[SKJ25POL]

I have a project that requires cutting few opennings in different floors and that results interrupting the diagonal in the particular bay that is going to be cut for openinig. I am thinking to place a diagonal same direction in the adjacent bay. Is it sufficient to do without reanalyzing the whole thing again?

Any directions will be appreciated.

Thank you

 

[RHTPE]

A sketch would vastly improve the responses so that we do not have to guess at what the bracing was intended to accomplish (in the original design).

Ralph
Structures Consulting
Northeast USA

 

[Once20036]

With the little information we have, I`ll cast a vote for reanalyzing the whole thing again.
The only way you could "just move" a structural member without worrying about it is if there was zero force in the member.

 

[Wallache]

No, you can't remove braces and move them elsewhere in the building without at least doing some analysis.

 

[JedClampett]

You might be putting horizontal members in tension or compression that weren't designed for it. Sometimes there are special connections in the horizontal members (also part of the bracing) required to transmit bracing forces.

 

[BISIS]

Dont forget to check the footing and anchor bolts if the brace is going to connect to a different column base.

 

[msquared48]

Move the hole to avoid the diagonal or shoot the Architect.

Mike McCann, PE, SE (WA)

 

[SKJ25POL]

The sketch.
msquared48 (Structural), well thank you for ur comment but this is not a joke and if I could move the the location of the openings I would.

 

[RHTPE]

My initial thought would be to reanalyze the bracing after replacing the "X" bracing with "K" bracing and make the Architect adjust some of the opening locations slightly to accommodate.


Ralph
Structures Consulting
Northeast USA

 

[SKJ25POL]

RHTPE (Structural),

Thank you for your response.
You mention K bracings I was thinking to beef up the adjacent bracing that runs the same direction that the "to be removed" is running or Running a bracing from middle of the adjacent bracing to a corner.

Do know other options?

How does K bracing work? is one in tension and the other in compression?

Thank you

 

[RHTPE]

"K" bracing is a configuration that looks like a capital "K" rotated 90 degrees clockwise. The braces run from the bottom of one column at floor level to the mid-point of the beam on the floor above, then back down to the bottom of the other column. Depending on the direction of the lateral load, one will be in tension, the other in compression. It will require analysis of the beam to insure it has the required strength, or can be strengthened to accommodate the forces.


Ralph
Structures Consulting
Northeast USA

 

[canwesteng]

I'd call that chevron bracing. When I hear k bracing, I think of an actual K brace, which isn't permitted in seismic applications generally. Probably requires more analysis than just X bracing the adjacent bay, and I think X bracing is a better solution. You first floor ?Y? brace looks pretty questionable to me though.

 

[RHTPE]

canwesteng You are correct - mia culpa on my part. My description was as intended but my terminology was incorrect.

Simply removing a portion of the bracing because of an architect's whim is usually never a trivial matter.


Ralph
Structures Consulting
Northeast USA

 

[JAE]

It would potentially be very difficult to "move" a brace. By moving it you are relocating the load path for all the lateral loads.
This would possibly negatively affect the following:
1. The floor or roof diaphragm (longer diaphragm span would possibly exceed the diaphragm strength)
2. The diaphragm to collector connections may not be adequate.
3. There may not be a collector to use.
4. The columns now associated with the new brace may not be strong enough.
5. The beam at the diaphragm may not be adequate - or the beam-to-column connection may not be adequate.
6. The new load path through a different bay now will load columns below differently - may be an issue.
7. The new load path through a different bay now will load footings below differently - may be an issue.
8. An offset or change in the brace may create an irregular structure designation (for seismic design) and create all sorts of problems.
9. etc.

When you ask a question like: [blue]How does K bracing work? is one in tension and the other in compression?[/blue] it suggests to me that you don't quite understand structural engineering fully. Perhaps you need to find someone who can directly help you rather than here. Such as an experienced structural engineer perhaps? I would second msquared's advice above.


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[msquared48]

Talk dollars to the Architect here, and especially the owner, who will eventually be paying for this. This will be a very expensive door, necessary or not. Outside of the humor, find another way to do this without removing the brace. There just has to be another way...

Mike McCann, PE, SE (WA)

 

[msquared48]

Another thought:

Removing or modifying that braced frame will affect each and every other shear element, vertical or horizontal, plus connections, in the entire structure whether you like it or not. And the entire structure may have to be brought to current code depending on the extent of the modifications. Is the owner willing to pay for that structural investigation, let alone the ripple of potential modifications?

Mike McCann, PE, SE (WA)

 

[TehMightyEngineer]

I highly second what msquared48 is saying. I did a project where bracing was moved up 12 inches off of the working point to accommodate a door. This involved an entire analysis of all the bracing on each floor for the entire column line, replacing the bracing with stronger 50 ksi steel, strengthening the columns, verifying the baseplate and existing steel wasn't overloaded by the shift in loads (every frame was affected), verifying new deflections weren't overloading columns for P-delta effects, and strengthening columns 3 bays over because we had changed how the lateral overturning load was distributed. We only got away with this being anything less than extremely costly because the original facility was over-designed and a fairly new building with very detailed original drawings.

Maine Professional and Structural Engineer.

http://www.fepc.us

 

[SKJ25POL]

msquared48 (Structural),
You mentioned, "And the entire structure may have to be brought to current code depending on the extent of the modifications."

I like to learn that cutting those bracings and beefing the other existing bracing does it make me to bring it to the current code?

As a matter of fact I am placing platforms/catwalks infront of the doors.

Where can I learn about the requirements due to retrofit or modification to existing buildings?
What is the amount of modification that does not trigger brings the structures to current code?

Thank you

 

[TehMightyEngineer]

Depends on the building codes adopted by your jurisdiction. Under the if it's under the 2012 International Existing Building Code then any alterations that decrease the capacity of the LFRS, increase the load, or introduce irregularities require an update of the LFRS to the current code. There's also probably a clause that requires updates to other areas depending on the amount of structure modified.

Maine Professional and Structural Engineer.

http://www.fepc.us

 

[msquared48]

This trigger has been discussed at length in the past here. Do a search.

Mike McCann, PE, SE (WA)