Timber frame truss design help please!!!

[Talman144]

Aloha! I'm currently trying to design the most simple timber frame truss design that will span between two shipping containers...

The container layout is actually four 10'x20' containers Laid out in a U shape. Thus creating a floor area of about 40'x30'.

I'm looking for the simplistic method using home milled lumber 6"x6" post & beam (hoping to use container frame as post)

Will be milling blue gum eucalyptus lumber using Alaskan mill

This is my first time 🙏

See sketch and picture ideas for general concept



 



 

 

[Ianab]

Posts in the middle change the load a LOT. The picture shows no posts, but braces to support the span. The floor plan indicates posts?

Rather than a 6x6 for the roof truss, a 3x12 is the same amount of wood, but is MUCH stronger in that use case. 6x6 for vertical load bearing is fine, but spanning a gap, you want depth.

100% for sure it can be done, especially with a strong wood like blue gum. But I'm not a structural engineer, so I'd just build it stronger than needed.

[scsmith42]

If each one of the four containers is 8.5 x 20 (standard container size), by my math your "floor" area appears to be 20x20 (excluding container footprint).  The upper corner of each container that is adjacent to the open area can be load bearing - vastly simplifying your trusses and reducing sizing.

I would design the trusses to be attached to the inside roof corners of the containers, with a vertical member in the truss above the container wall.  Extending the top chord to the outside of the containers can be done via rafter - no need for a truss.

There is no need to install intermediate supports inside a 20' span in the open area.

[Talman144]

If each one of the four containers is 8.5 x 20 (standard container size), by my math your "floor" area appears to be 20x20 (excluding container footprint).  The upper corner of each container that is adjacent to the open area can be load bearing - vastly simplifying your trusses and reducing sizing.

I would design the trusses to be attached to the inside roof corners of the containers, with a vertical member in the truss above the container wall.  Extending the top chord to the outside of the containers can be done via rafter - no need for a truss.

There is no need to install intermediate supports inside a 20' span in the open area.

Yes this is what I was trying to go for🙏 Can someone show me what this would look like?

[Don P]

That would take Scott.
These are rough sketches that were running in my head;


 

 

 

[Stephen1]

Jim Rogers on the FF does TF design services and might be the worth talking to him. What you're doing looks pretty simple.

[scsmith42]

Don, what I'm envisioning above the gap in-between the containers is a quasi Pratt style truss.  It could be constructed entirely from 2x12's (16' max length) with diagonal members glued and nailed on each side of the top and bottom chords at the splice points as well as intermediate locations.

They would be load bearing onto the walls of the containers that formed the inside of the covered area.

The top chord could be extended across the container with a common rafter spliced onto the end of the truss.

These could be made from a combination of 2x12x16' and 2x6's. 

In-between the trusses could be 2x6 purloins nailed on edge - ala chicken house roof style.

Concept drawing below.  I haven't done any math on this concept, but it should have plenty of safety margin for his application.  The top and bottom chords could probably be made from 2x6 or 2x8 for cost/weight savings, but I still like the 2x12 inner members for splice strength.



 

[Don P]

I like it.
What happens if you turn it basswards, trusses on the ends, rafters up top, the sea cans are essentially non flying big fat buttresses. They are the thrust restraint, screw them down or make sure they are heavy;



 

[Talman144]

 Thank you for the suggestions everyone 🙏 to clarify I need a design using 6x6 timber as I will be milling my own wood on site.
I tried to start an idea with sketch up, I'm still learning the program but wondering if this is close to what you mean by using a vertical support?

*I will extend the rafters later to cover to edge of container

I might take your suggestions and contact someone you says dies this type of design

Mahalo 🤙🏽🤙🏽🤙🏽



 

 

[Ianab]

I think you are on the right track. Rule of thumb is that everything needs to be a triangle. You can adjust the angles of those triangles to suit, but if it's not a triangle it's weaker and you have to rely more on the strength of the material and fasteners.

So in that last sketch, you say you are going to extend the rafters down to the outside of the container, that's good (essential?) because you then brace the upright posts with a triangle. There is also a 4 sided box in the design, probably needs another brace to split that into 2 triangles? See SC's sketch, every element is a triangle.

Being limited to 6x6 isn't really a problem, you could build trusses for this job out of 4x2s if you had to. Just it would need more of them, and more braces. Deeper members in the truss just give more weight bearing for the same volume / weight of wood, but you can change designs to use the material you have, within reason.  A structural engineer can then basically tell you how many trusses you need / spacing between them.

[Stephen1]

Talman, the next thing you need to do is fill out some of your details so we know where you are from. I get the feeling you are in the pacific, no snow load so the design is a lot different than in the Rockies with a snow load of 75 lbs per sq ft.

[Talman144]

Ok so I think this is more inline with what I'm hearing to do....

I'm In Hawaii no snow issues but possible wind
I want the 4:12 pitch to accommodate my solar panels



 

 

[Ianab]

That's basically Don P's first sketch, and once the rafters are extended down to the outside edges it's a sensible design. I'm guessing tropical storm winds are a major design consideration for you. How the roof is held down is going to matter, especially if the front is open to catch the wind.  This design would also use a bit less material, and allow more headroom in the centre of the structure. Parking taller vehicles etc?