Once in a while PF buildings come up on the board but it seems a lot of engineers avoid them. My previous experience working on a PF building was a structure that was fully clad with 1/2" plywood (walls & roof), which made analysis easier since I am familiar with WSP diaphragms and shearwalls. I based a lot of my analysis methodology on the paper by Don Bender "Simplified Lateral Design of Post-Fram Buildings", which I found to be quite good and easier to use than the more rigorous method found in the ANSI/ASAE EP484.2.
With this next PF building I have a very simple structure, 21'x40' rectangle with posts at 8' o/c, 4:12 pitch roof. 2-ply truss @ 8' o/c that sandwiches 6x6 PT posts. Post height is 8' tall, with trusses resting on 2-2x6 ledgers attached to posts. The roof sheathing is 2x6 purlins @ 24" o/c with polycarb panels (26"x12').
There is no wall sheathing, the structure is completely open on all sides.
Based on this description you can see there are no shear walls, so the rigid roof design method used in the paper above is not applicable. My thinking on this analysis is that each "bent" or post-truss-post frame will pick up a tributary lateral wind load from the roof, essentially treating the roof diaphragm as flexible. Does this assumption or methodology seem reasonable or am I missing something here.
The lateral wind loads in the longitudinal direction should be comparatively negligible since there is no gable end cladding or gable walls, only a certain amount of cross sectional area of the truss and posts. I've always worried about wind drag on a structure but I don't have a good way to quantify this. Since the structure is very light seismic lateral loads will not govern but I'm always curious to run the numbers regardless just to see how it compares to the wind loads.
Another thing that comes to mind is how to check the loads on the polycarb panels. The panels are only spanning 24" between purlins, but a quick check of the allowable bending is prudent given a certain amount of snow load (25 psf). Does anyone have any reference design values for typical polycarb panels or could point me in the right direction?
A confused student is a good student.
Nathaniel P. Wilkerson, PE
With this next PF building I have a very simple structure, 21'x40' rectangle with posts at 8' o/c, 4:12 pitch roof. 2-ply truss @ 8' o/c that sandwiches 6x6 PT posts. Post height is 8' tall, with trusses resting on 2-2x6 ledgers attached to posts. The roof sheathing is 2x6 purlins @ 24" o/c with polycarb panels (26"x12').
There is no wall sheathing, the structure is completely open on all sides.
Based on this description you can see there are no shear walls, so the rigid roof design method used in the paper above is not applicable. My thinking on this analysis is that each "bent" or post-truss-post frame will pick up a tributary lateral wind load from the roof, essentially treating the roof diaphragm as flexible. Does this assumption or methodology seem reasonable or am I missing something here.
The lateral wind loads in the longitudinal direction should be comparatively negligible since there is no gable end cladding or gable walls, only a certain amount of cross sectional area of the truss and posts. I've always worried about wind drag on a structure but I don't have a good way to quantify this. Since the structure is very light seismic lateral loads will not govern but I'm always curious to run the numbers regardless just to see how it compares to the wind loads.
Another thing that comes to mind is how to check the loads on the polycarb panels. The panels are only spanning 24" between purlins, but a quick check of the allowable bending is prudent given a certain amount of snow load (25 psf). Does anyone have any reference design values for typical polycarb panels or could point me in the right direction?
A confused student is a good student.
Nathaniel P. Wilkerson, PE
