Open gable porch roof

[JStructsteel]

Ask for advice or how you would go about designing this deck roof. No cross ties, so ridge beam a must, but the open end is where I am hung up. Steel frame? Cantilevered columns?

I dont see wood being an option, but wanted input on how to resolve those end forces

Thanks
[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1692188786/tips/Document1_troz9g.pdf[/url]

 

[phamENG]

If you can cantilever the column it could work. Another option is to use XR250's gable flitch solution.

 

[JStructsteel]

Thanks phamENG, were you thinking the flitch would be at the end beam and extend all the way down the column, with some sort of moment connection at the joint?

 

[phamENG]

No moment connection needed. The angled flitch - if it can be made to work in this situation - creates a moment connection at the peak of the roof and prevents spreading while supporting the ridge beam. Assuming you're attaching to a building, design the roof as a cantilevered diaphragm.

If yours will be similar in size to the picture you may need to go with a pair of steel tube rafters welded at the peak rather than the flitch plates, but wood could still work for the columns, beams, and other rafters.

 

[XR250]

That's a pretty big roof for a flitch.
I generally use dogleg I-beams in this case.
If you use tube steel, make sure you have a plate at the peak or otherwise provide a way to stiffen the "flange" at the kink.

 

[DoubleStud]

Bent steel beam. I do this all of the time. You really have to detail it and think about how everything goes. Sometimes the architects dont think about these things. For example, the lookout for this roof, how are you framing it? Ladder framing over the bent steel? If you ladder frame it, typically you cant expose the rafters (look ugly) and the bent steel goes below the rafters. Sometimes the architect shows 2 shoulder beams that pick up the rafters. But then these 2 beams will interfere with the bent steel because they are both at same elevation. It can get complicated sometimes because the architect just draw things to make it pretty without thinking about the structural part and how it will have to be built.

 

[JStructsteel]

Thanks all.
This is exactly whats happened. Architect has come up with this. No input yet from engineer. I bid the job, added about 10 hours just for this part.

Maybe I dont want the job, lol.

 

[Eng16080]

I'm not sure if this is a reasonable solution, but you could create a truss in the shape of a tetrahedron.

The tension and compression forces back at the building wall would need to be resisted somehow. Perhaps the compression forces could be resisted by the interior floor and the tension force resisted by a roof diaphragm beyond. The truss would be designed accounting for an acceptable amount of vertical deflection at the end of the ridge at the open end.

 

[DoubleStud]

Eng16080, interesting concept. May be too complicated for framers and need extra careful on the tension and compression. Bent steel seems to be the easiest and safest.

 

[Eng16080]

I agree this would have a good chance of getting screwed up without a lot of oversight. Probably the bent steel is the way to go. Maybe a cantilevered column as mentioned above, although I doubt that works unless it's also steel and fairly large.