I recently saw a "tie" that was two different sticks (king post). I thought that the rafter thrust on the connections below would create tension on the "tie". How do you have a tie that is two different pieces withstand tension?

Simple... shouldered and pegged. Or two half dovetails... Steve Chappell does it quite often I believe. This is the Library loft at Fox Maple. I can't remember if this is half dovetailed or not, but you can see the shoulders and pegs.

That looks like a posted ridge -- so there wouldn't be any tension in the "tie". If you are clear spanning with a truss, the situation is different.

It takes an extremely serious scarf to join a tie beam for a truss of any size. We built some 36' kingpost trusses recently (with a continuous tie) and under design loads there is 15,200 lbs of tension in the bottom chord. And we don't have any snow loading to speak of here.

One way you could do it is a really long (maybe 4 feet or longer) tabled scarf with shear blocks or split rings. But to deal with 15.2 kips you will need 3 or 4 shear blocks and enough of a shear plane between them to develop enough capacity. It takes through bolts or steel bands to keep the pieces clamped together tightly.

Maybe some of the bridge guys can dig up a photo of a bottom chord scarf (Will - are you out there?).

Not exactly sure what a posted ridge is, but Carlos picture shows a kingpost with split tie beam. The very bottom of the king has a pendant (not a post) which is just out of range of the picture shot. I was there when he took the pic. The kingpost truss spans the width of the library. What you also see in the pic is a small partial perimeter loft framed by a couple floor joists. The center of the building is left open to the ceiling.
Steve showed us how this was possible so that you didn't need really long tie beam timbers. Of course you always have to work out all the loading and stresses, like on any design to be sure it is strong enough with enough margin of safety.

That roof of the library building is thatched and is something like a 14/12 pitch.
I have photographed that king post also....

As brad stated that is a clear span with a pendant. Sorry it is the only picture I had available. I don't understand why you would state that there is no tension as it is a post!! There would still be tension as the rafter feet push outwards even if it is on a post.

A post holding a king post would be rather redundant(depending on sizes of timbers and loads) as the king post actually pulls/holds the tie beam upward.

Carlos

I thought the kingpost was a ridge post, running from the floor to the peak and holding the ridge up since that is what it looks like in the picture. If that were true then the rafters would not be pushing outwards. If the top is held up, the only load at the feet is vertical.

What is the span of that building?

Sorry I'm not great at estmating distances... somewhere between 20 and 30 feet...

Yes I agree a ridge post would eliminate a lot of the horizontal thrust... somehow that skipped by....

Carlos

Mo,

Here is an awesome tension scarf in a bottom chord of a bridge. Photo by Will Truax -- Will, I hope you don't mind my posting this again.

Gabel - don't mind at all, I posted it for folks to see.

I missed this initial call to arms. I must admit, sometimes I don't wade through all the chatter.

And as you suggest snowload is a huge factor in these calcs, I live about an exact hour southwest of Fox Maple Land and the GSL in my town (assigned town by town here - highly variable with differences in proximity to the coast and elevation - This years huge accumulation may have the powers that be re-accessing those assignments as was done after the last such winter which saw collapses) is 95 lbs psf

Brad - you suggest "Steve showed us how this was possible so that you didn't need really long tie beam timbers"

Would you elaborate please.

I'm asking for two reasons - I'm curious to learn as to how...

But perhaps foremost, I'm also concerned that someone could view this thread, and attempt to build a clear span King Post in the configuration pictured and that IMO, holds the potential for disaster.