Building divided into 4 quadrants by Exp. Jts.

[jike]

We are adding load to a square building with expansion joints running down the middle in both directions. It has wall bracing in both direction at the exterior wall only.

It seems to me that the because there is only bracing in 2 directions for each quadrant and chords are discontinuous at exp. jts. that in theory building quadrants are not adequately braced. This assumes that there is no frame action, etc. A building unit, normally, needs at least 3 sides braced.

Any comments? Am I missing something here?

 

[BAretired]

I'm with you. Bracing on only two adjacent sides of a quadrant does not seem enough.


BA

 

[haynewp]

It is not stable and I would never do it. Each segment may be standing because of drywall partitions or the building as a whole may have some type of cantilever action from the ground with the weight of the structure resisting rotation about the concurrent corner (thinking in 3d like a cantilevered angle on pin supports).

 

[kslee1000]

What a crazy house it is! Do you know why its need such arrangement? And, I don't understand if the chords are discountined at the joints, how could the trusses functioning properly without side effects? A square puzzle.

 

[JAE]

I agree with the others, jike. Sounds like someone didn't know what they were doing.

 

[enginerding]

Do these expansion joints allow shear transfer across the joint while preventing tension/compression?

 

[BAretired]

What is the size of the square building? Could you connect the quadrants together and make it one structure?


BA

 

[jike]

The steel framed upper story is a penthouse about 300 square feet with exp. jts. subdividing it into 4 quadrants. The lower story is slightly larger, CIP cols and inverted tee girders/Precast DT's with exp jts in the same locations. I believe the lower story is stable with the girder lines and perimeter precast walls resisting lateral load. It is the upper story that I have concerns about.

Thanks for the confirmation!

We will have to do something to fix it!

 

[JAE]

The CIP columns might be cantilever columns providing the lateral resistance...you might check for that.

 

[BAretired]

A penthouse of 300 SF? Should that read 3000 SF?


BA

 

[JLNJ]

Seems so small that it doesn't need joints at all. Maybe the joints are needed in the roofing material only and not the whole structure.

 

[kslee1000]

jike:

Is that what you are going to do - expend the 300 SF penthouse over the entire building?

 

[jike]

JAE: We have already looked at that.

BA: The 2nd story contains mech. equip and is about
300' x 300'.

JNLJ: Agree, but this is an existing condition, built in 1970.

kslee1000: we are not extending the building, we are adding equipment, but am concerned about the existing stability

 

[kslee1000]

Study the original design if you can find it. Althought sounds odd, there must be a reason for that building to stand such long period of time. Looks like you did miss something, but I don't mean the design was good, nor say it (stability after addition) isn't a concern. Also check out, do you need to bring it up to the latest code.

 

[jike]

kslee1000:

I believe it has stood because the columns are short and there is probably some frame action, even though base plates and cap plates are not much larger than columns.

Our concern is that it is a Seismic Category D.

 

[kslee1000]

Has that area has been hit by earthquake event(s)? Guess it hasn't, at least to the magnitude suggested by the seismic regulatory authorities. Otherwise you may not have the chance to work on it (may have already fell to ground).

Anyway, besides the side talks, can you post simple sketches to continue this conversation? I believe many of us here are quite curious about, and interested in, it

 

[OzEng80]

Jike - can you confirm that the expansion joint extends through the roofing as well - there is no roof level bracing/diaphragm connecting the walls?

 

[jike]

OzEng80:

The diaphragm is completely broken across the expansion joints. Diaphragm does connect to outside walls but is broken at expansion joints. No bracing in the plane of the roof. Expansion joint in roofing also.