Ways to improve stiffness of wood frame roof diaphragm. Smart ideas
Ways to improve stiffness of wood frame roof diaphragm. Smart ideas
(OP)
We are still working out some details on a personal building. This is a post frame building, trusses on 12ft centers, and recessed roof purlins on 3ft centers, in joist hangers.
The stiffness values coming from this setup is not ideal and is loading too much into our columns. I need to obtain a higher stiffness for better load transfer.
In looking at a few studies, it appears the stiffness may be lower for hangers. I am not sure if this is due to tension issues at the interface. I am looking for some ideas to correct this? obviously we can throw more and more lumber at this but right now, I really cannot pinpoint the stiffness issue. the Strength is not an issue, just need to get deflections down.
The stiffness values coming from this setup is not ideal and is loading too much into our columns. I need to obtain a higher stiffness for better load transfer.
In looking at a few studies, it appears the stiffness may be lower for hangers. I am not sure if this is due to tension issues at the interface. I am looking for some ideas to correct this? obviously we can throw more and more lumber at this but right now, I really cannot pinpoint the stiffness issue. the Strength is not an issue, just need to get deflections down.






RE: Ways to improve stiffness of wood frame roof diaphragm. Smart ideas
Can you post a diagram of your building?
Mike McCann, PE, SE (WA)
RE: Ways to improve stiffness of wood frame roof diaphragm. Smart ideas
RE: Ways to improve stiffness of wood frame roof diaphragm. Smart ideas
RE: Ways to improve stiffness of wood frame roof diaphragm. Smart ideas
RE: Ways to improve stiffness of wood frame roof diaphragm. Smart ideas
I am just not yet sure where the extra 'play' is coming from.
RE: Ways to improve stiffness of wood frame roof diaphragm. Smart ideas
Are those 25' tall wood columns?
RE: Ways to improve stiffness of wood frame roof diaphragm. Smart ideas
RE: Ways to improve stiffness of wood frame roof diaphragm. Smart ideas
1) What exact movement is it that concerns you? Middle of diaphragm? Top of columns? Lateral movement? Vertical movement?
2) What are your vertical lateral load resisting elements for the two axes of the building? Braced frames in the walls? Cantilevered columns?
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: Ways to improve stiffness of wood frame roof diaphragm. Smart ideas
Are the end walls exhibiting high displacement under lateral forces? If they are not moving much (by code or by your SE's judgement), then you can investigate the diaphragm. If the end walls are moving significantly, then focus on the lateral design for the end walls first.
What kind of fixity do you have/expect at the base of the 25' tall end poles? Are foundations embedded to a depth sufficient to handle the moment on each pole?
The building may/may not "stiffen up" when the diaphragm is installed, and the wall sheathing is installed - depends on the use of proper load path & quality of detailing.
For the safety of you and others, strongly recommend hiring a structural engineer to review your personal building before you begin construction.
RE: Ways to improve stiffness of wood frame roof diaphragm. Smart ideas
Due to the pitch and size of the roof, vertical forces are negative (uplift), and we are way over built for that. No problems.
The building is not currently under construction.
The columns will be embedded, then encased in concrete, then a concrete floor will be poured which will help support lateral forces applied to the base of the columns.
The end walls are looking fine at this point in shear but as I mention, the roof system needs the appropriate stiffness to efficiently transfer the load to them.
The shear strength in the roof system works well within margins but without enough stiffness, this is putting to much lateral load at the top of the columns.
The roof system is 26ga corrugated steel roof paneling, applied directly to the framing.
RE: Ways to improve stiffness of wood frame roof diaphragm. Smart ideas
Also, just thinking out loud- Does the bottom chord of a scissors truss need bracing to remain stable under gravity loads? Inquiring minds want to know!
RE: Ways to improve stiffness of wood frame roof diaphragm. Smart ideas