Timber Truss Connection

[Galambos]

I have a timber truss connection that I am trying to wrap my brain around (see attached pic).

When i use the NDS to calculate the capacity, i come across a problem. When i look at the left compression member, i need to specify the side member properties. How does this work with three members intersecting at one point? Also, do i have to consider the compression against the grain from the left member into the right member in the side failure modes?

This seems like a very simple statics problem that i just cant see. Would someone with experience in timber connections give me a hand?

 

[BAretired]

I have not designed a "carpenter's truss" for about fifty years. We did something like your sketch shows, but we used shear plates or split ring connectors, not just plain bolts.

I don't think anyone is building those now, but I could be mistaken. I think I would use a steel plate at the top of the king post. The top chords and king post are each composed of two members, so place one each side of the steel plate. Use as many bolts into the king post and top chord members as you need to carry the load. I assume you are familiar with the Hankinson formula for loads at an angle to the grain. If you cannot carry it with bolts alone, use shear plates.

The attached sketch shows the arrangement.

Nowadays, most people are using prefabricated trusses with steel truss plates. In your case, it would likely be a two or three ply girder truss.

BA

 

[Galambos]

BA,

thanks for the reply. This is a pro-bono job for a non-profit and the architect has requested us to eliminate steel connector plates.

 

[BAretired]

The truss should be symmetric if possible. I think you should abut the top chord members rather than overlapping them. That way the compression is largely transferred by bearing and the connectors have to be able to carry the tension in the kingpin.

If you can manage with a single ply kingpin, and insert it between the chords, the overall thickness of truss is 3 plies instead of 6.

BA