scissor truss support
scissor truss support
(OP)
Anyone ever had pre-fab wood scissor trusses supported by wood columns or bundled studs? I know the concerns about lateral kick-out of scissor trusses and this concerns me being that they would be supported by columns.






RE: scissor truss support
BA
RE: scissor truss support
1) The kick out should be evaluated in terms of deformation compatibility with surrounding construction.
2) The trusses should be positively attached to the top of the columns in most cases. No slip bearing nonsense.
3) The top of the column would need to be braced in the plane perpendicular to the trusses, particularly if a high truss heel is employed.
Other than that, I'm fine with it.
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.
RE: scissor truss support
RE: scissor truss support
RE: scissor truss support
I don't have a framing plan yet - just went over the concept that the arch was planning today. It's going to be a nice building once all said and done. It's not a pole barn, but I see where you are coming from on that. I don't think there is any way to allow one end to slide free with it bearing on a column. I would think you have to make a connection that is rigid enough to not slip and design the column for that horizontal force at the top of the column. You would need to analyze it to see how much it moved and look at what that would do to the structure. I'm thinking we'd need to drop in steel columns. Maybe even fix them at the base.
RE: scissor truss support
The truss will not be permitted to "slide free" on the column but the flexibility of the columns supporting the scissors truss will be equivalent to a hinge-roller support for the truss from an analysis point of view. The reactions of the truss will be vertical with little or no horizontal component.
Steel, glulam or Parallam columns would be a better choice than bundled studs. Dimension lumber is not easily obtained in 24' lengths.
BA
RE: scissor truss support
RE: scissor truss support
Based on your feedback, the column will move no matter what type of connection you have because of the flexibility of the column. This was my thought exactly. These are the checks that I believe I would need to make:
- check the horizontal deflection at the top of the column against recommended allowable out of plane movement
- check the column for p-delta effects from that movement - combined stresses on column
- check the connection to make sure it can take the force into the column - determine the force needed to move the top of the column by the amount of horizontal deflection and check for this load
- check the column base to make sure that it is anchored properly to the foundation - steel would be easy because it is bolted - wood not as simple
- check the horizontal reaction as XR250 recommended for effects on truss - coordinate with truss designer
any other checks anyone can think of?
Thanks for the feedback!
RE: scissor truss support
RE: scissor truss support
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.
RE: scissor truss support
kootk - with steel, we'll have the possibility of modeling either fixed or pinned bases. I will probably check both just to make me sleep better at night.
thanks
RE: scissor truss support
RE: scissor truss support
RE: scissor truss support
Yes, the roof diaphragm distributes the lateral forces to shear walls. The footprint is 60'x100' roughly. The scissor trusses will have framing running over the top of the scissor trusses. This will be decked with structural sheathing. Roughly 60% of the building is 2 story and 40% is full height to bottom of scissor trusses. We will have 3 sides of shear walls on the 2 story portion and 1 side of shear wall on the full height portion. Of course I need to check aspect ratio at the full height because those walls are 24' tall.
RE: scissor truss support
RE: scissor truss support
Are you saying this because you you believe the roof decking will help keep the scissor trusses from deflecting horizontally?
RE: scissor truss support
RE: scissor truss support
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.
RE: scissor truss support
RE: scissor truss support
They CAN be aesthetic!
RE: scissor truss support
RE: scissor truss support
RE: scissor truss support
I'm thinking the less I mess with the scissor trusses, the better, so trying to get the truss designer to analyze a fixed condition or partially fixed condition would be tough
Framing the scissor truss to the side of a steel column on a seat may be a good idea - I'm going to spend some time on it tonight and will post my findings/sketches
RE: scissor truss support
RE: scissor truss support
BA