Sawmill Shed truss construction question

[mart]

I am getting ready to pour the mono slab for my sawmill shed and will be constructing my trusses for the shed. It will be 20x40 with the 40 foot side being open on the front for loading logs on the mill, so the gable will be on the long side. I'll eventually add two more sections to my LT 15 so I can do up to 36 foot beams if needed. It will have a 4/12 pitch and the trusses will be a double Howe type truss. I already have the building diagram for the trusses but it only specifies a 40 foot bottom chord, My question is, where would you make the joint in joining the two boards to make the full 40 foot chord. In the middle under the king post? In between the uprights and the struts? Under where a strut or secondary upright connects with the chord? Thanks guys for any advice.

[Don P]

This isn't a design but should give you some ideas about where the forces are lowest, notice the center section of the bottom chord. A truss shop would probably splice in between panel points in that area but a true truss would do it at the node, where everything, and I mean everything, is coming together, that is a busy location. Notice the sense and relative magnitude of the forces at work. You'll need to get the actual magnitude of the forces to develop your connections but hopefully this helps start thinking about it.



 

Its been awhile since I played with it but I think the Medeek truss designer in sketchup puts out those forces.

Don't forget to beef under the truss supports in the pour.

[mart]

Thanks. The slab will be 4 inches with a 12 inch footer all the way around. 6x6 posts and a 6x12 beam on each end to support the trusses. The 6x6 posts will be four feet apart except for an eight or ten foot opening on each end for a rolling door. May add in some knee braces in the door ways. 

[scsmith42]

Don, are there any online calculators for parallel chord trusses?  The links that you shared with me before no longer seem to work.

Thx.

Scott

[sealark37]

It really makes no difference where you join the members on the bottom. If you use plywood nail plates, make them large enough with properly sized nails.

[Don P]

Scott, that was what took me so long to respond on Dana Stanley's thread. I downloaded half a dozen programs. They were either too limited in their free version, over my head, poorly documented or metric. I finally messed around with my old standby and figured out how to make an exception that allowed its outdated unsecured java to run. That's it above, try it and see if its enough for your purposes;
http--pages.jh.edu-~virtlab-bridge-truss.htm
It may not be granular enough for your long slender span. Skyciv looks like its paid version would be good, but I balked  :D. There are a number of youtube and online tutorials on the method of joints, one way to figure a truss longhand. I've got that in a few texts I can scan as well. It's kind of frustrating work but is what is behind most of these calcs.

[scsmith42]

Don, when I click on the Calculate button at the bottom of the linked page, it opens up a blank page and nothing happens.  

The problem might be on my end.... I have flash player disabled due to hacking concerns.  I'll try it from a different computer.

Thanks much.

Scott

[scsmith42]

I'm having the same result with Firefox.  When I click on "Time to build a bridge truss", it opens a new, blank window with only wallpaper in the background. >:(

[Don P]

I'll keep looking for another simple one, the java is so old on that I'm guessing most browsers are blocking it from loading.