Timber Frame Truss - Combining Connection Capacities
Timber Frame Truss - Combining Connection Capacities
(OP)
Hey everyone,
I am designing a timber frame truss to resist uplift due to wind loading, and this question comes from looking at the Rafter/Ridge Beam/King Post connection. I have two ways to consider load distribution (load is applied from an end reaction on the ridge beam): either the load is distributed through the whole frame like a truss, or the king post resists all of the load through a pegged tenon & mortise connection. (see attachment for connection details/options)
The pegged connection does not have enough capacity to act on its own, so I will probably design as a truss and most of the load will be carried by the wood screws (of which I'll have to specify more than the 2 screws shown).
However, I am wondering if anyone knows of a good way to consider the capacities of both the wood screws (through truss action) AND peg connection (at king post) simultaneously. This way the pegs would be more than just decorative and I could probably get away with just the 2 screws indicated.
Thanks in advance!
Truss layout:
I am designing a timber frame truss to resist uplift due to wind loading, and this question comes from looking at the Rafter/Ridge Beam/King Post connection. I have two ways to consider load distribution (load is applied from an end reaction on the ridge beam): either the load is distributed through the whole frame like a truss, or the king post resists all of the load through a pegged tenon & mortise connection. (see attachment for connection details/options)
The pegged connection does not have enough capacity to act on its own, so I will probably design as a truss and most of the load will be carried by the wood screws (of which I'll have to specify more than the 2 screws shown).
However, I am wondering if anyone knows of a good way to consider the capacities of both the wood screws (through truss action) AND peg connection (at king post) simultaneously. This way the pegs would be more than just decorative and I could probably get away with just the 2 screws indicated.
Thanks in advance!
Truss layout:






RE: Timber Frame Truss - Combining Connection Capacities
RE: Timber Frame Truss - Combining Connection Capacities
The second drawing is not a truss layout. It is a truss elevation. Why not carry the uplift on the truss and forget about a ridge beam?
BA
RE: Timber Frame Truss - Combining Connection Capacities
And yes, ridge beam is 8" x 12". Drawings given to me show the tenon & mortise oriented the wrong direction, they would be rotated 90 deg. around y-axis in order to work.
The ridge beam spans about 15' between two of these timber frame trusses and picks up roof load from typical sawn lumber rafters, so the ridge beam cannot be removed.
RE: Timber Frame Truss - Combining Connection Capacities
If you don't need trusses, why not simply use sawn rafters throughout and suspend the ceiling members from the ridge beam?
BA
RE: Timber Frame Truss - Combining Connection Capacities
In this arrangement, I suspect that the M&T load path will be much stiffer than the truss load path. As such, I would not recommend combining capacities, I worry that your pegs would give out before the truss mechanism really kicked in.
Can you perhaps add another row of pegs above the one proposed?
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Timber Frame Truss - Combining Connection Capacities
The two screws tend to pull out of the top chord members parallel to the grain and apply tension across the grain of the beam, a questionable connection. The chords should be tied together with a steel strap to prevent them from separating.
BA
RE: Timber Frame Truss - Combining Connection Capacities
RE: Timber Frame Truss - Combining Connection Capacities
BA