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Huge hip roof concerns

Huge hip roof concerns

Huge hip roof concerns

(OP)
I am working on the support frame for a commercial building light gage truss hip roof.  The building is 148' x 160' and will have a full hip roof with a 3:12 or 4:12 roof pitch.  The roof could triple the height of an existing 13' tall flat roof building.

To support the new trusses, steel support beams will be added where necessary.  There will also be an interior space 8' to 10' tall starting one column bay in from the exterior walls.  The trusses over this space will be supported on a new elevated steel frame.

I have conceptualized the truss layout for the most part, but would like to throw out some ideas for consideration.

The outermost column bay will be framed with mono trusses bearing on the outside wall and the first column line inboard of that.  The hip corners will be framed with step-down mono trusses and jack trusses.  The step-down mono truss supporting the jack trusses will be around the middle of the corner column bays.

To support the mono trusses, I could support the bottom chord at both ends, as is typical.  Or I could save a layer of support steel by supporting the high end on a layer of raised steel.  This sounds like a good cost savings, but maybe it changes the design of the truss too much to be worth while?

The inner 83' x 104' area will then be framed with the bearings 8'-10' higher supported on the raised steel frame.  These trusses can be full span with interior supports as the bottom chord elevation will be consistent.

Does it sound like I am on the right track for framing such a large area?

Also, should I be concerned with expansion and/or contraction with such a large roof area?  The surface will be standing seam metal roof over metal deck or plywood, TBD.  The entire enclosed roof area will be vented, but not temperature controlled.

Thanks,
Miscmetals

RE: Huge hip roof concerns

It appears that you have some good concepts to work with.  I would check the reactions due to thermal growth on the outside bearing walls, what amount of flexibility do they have etc, depending on the lentgh of your mono trusses. If the building is in northeast PA then expansion will probably not be a major concern.  (Lower central PA the temps can get fairly high on a summers day.) Thermal considerations should not be a problem with the Standing Seam Metal Roof (SSMR) as they are now built with moveable clips that easily allow them to move for expansion and contraction.  The major problem with SSMR is if they are contained by a parapet wall at one or both ends - then problems due to inadequate details because of thermal expansion come into play.

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