roof diaphragm and building expansion joints

[fne]

We have a large building that will require an expansion joint. There are also plans to add on in the future, creating another expansion joint perpendicular to the first. If everything is built we would have a building split into four quadrants by the expansion joints. Has anyone done a roof diaphragm only supported on two perpendicular sides?

Client is resistant to bracing and contractor does not like the cost of moment frames. Looking at ways of making both happy.

 

[KootK]

With just the two orthogonal walls braced, you wouldn't satisfy equilibrium. There's gotta be something else introduced.

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.

 

[JAE]

Are the joints necessary? How large is the building?

With the joints you have to include additional braces or brace systems.

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[fne]

bldg is approximately 400' x 765' now, with future adding similar.

 

[EngineeringEric]

How is it only supported on two sides? possible plan?

Can't you brace the expansion joint and tie the diap. into the lateral system along that joint?

 

[fne]

Thanks to all for the quick responses. As KootK noted we need to check equilibrium so we either need some bracing or we would have to make the two walls act like an angle resisting the torsion created by the eccentricity of the lateral loads. Walls are precast so a bunch of segements, don't want to go there.

We will provide bracing or a frame. Problem is a design-build client that will want to keep things as open as possible for the owner and a design-build builder who will resist the cost of a frame and associated foundations.

 

[JAE]

I've done buildings about that size where it was divided into two segments (i.e. the 400 ft. are OK without an EJ).

At the expansion joint, we used a Chevron brace (upside down "V") to minimize the braces interruption of space usage below. You might also look at eccentric braces of some kind to keep the diagonal braces as vertical as possible to further minimize its effect on the spaces.



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[KootK]

One system that might be made to work is this:

1) joist girder moment frames on some or all framing lines in one direction.

2) A single braced line perpendicular to the moment frames (shear wall or braced frame).

Fundamentally, this is a permutation of the three sided building concept which many engineers despise and some will reject out of hand. It would have the following advantages however:

1) open space is preserved.

2) minimal impact on foundations etc because overturning resistance is distributed.

While this may not ultimately be the best path to take, sometimes it's good to have an innovative solutiion in your bank pocket just to show that you're willing to play ball. Optics.

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.

 

[MotorCity]

For large industrial or manufacturing plants, it is common to use joist girder or truss moment frames in both directions. This eliminates obstructions from vertical bracing, which owners often require to keep the floor space open and allow for frequent changing of equipment and processes. For REALLY large plants, you can have "modules" separated by expansion joints in both directions for as far as the eye can see.