Dibs-h
Established Member
Simon - much appreciate the reply and links. Ive downloaded Jack Soben's book and will be going thru that.
Wish I'd come across it sooner. When I'd "designed" the truss - almost all the stuff I across was by Nicholas Tredgold, or referred to his work and made extensive use of his "Tables of Scantling Sizes", which gave sizes for the members in Queen and King post trusses for various spans at 10' apart.
The sizes I used were adequate for 20' spans - so mine at around 16' should be more than ok. The sizes of the tennons resulted from the resultant angles in Cad. The tennons you see for the Kingpost connections were done so that the mortises on both sides did not meet in the middle, but were separated by around 1.5". At the longest part the tennon is around 2.5" - I'm hoping a single pin of around 18mm should fit and not be too close to the shoulder - yet leave enough relish. The tennons are around 35mm thick - so I'm hoping that offsetting the holes by around 3mm and draw-boring them should destroy the tennon\relish.
The timber is softwood. The tennons shown in the 1st example would require the kingpost, in my case, to be cut from something like 12" wide - as opposed to the current 7" wide.
The kingpost tennon at the base is about 4.5" deep and my thinking was that the joint at the base of the kingpost is the one in signifcantly more tension than the rest - the others at the top of the kingpost due to the angled shoulders and tennon - should resist the forces (better) trying to pull the tennon out. Might be a load of cobblers - but abit too far gone to do anything else - at least with the current truss.
The timber analysis software - showed that for the relavant wind\snow loads the timbers themselves should cope with the strains\deflections.
If it starts to go weird - plan B might be to use steel straps and bolts to reinforce the connections. I'm in the process of going thru Jack Sobens book so will digest it overnight and then formulate a plan. Having said that - it's only a workshop roof - in a very sheltered spot (I appreciate that the direct wind load may not be huge but other things like suction, etc. can't be ignored). Even if the roof is built - i could fit the straps afterwoods.
An alternative plan could be to cut a slot in the end of the members with tennons (I suspect those that are at the top of the Kingpost) running thru and epoxy a 5mm steel plate - effectively turn it into a mini flitch beam type connection, and perhaps use metal pins\bolts instead of wooden pegs.
As an aside I did wonder whether one should use a strong glue in the joints as well. Or is that a big no no?
Cheers for the PM - may well give you a ring later on (or tomorrow).
Wish I'd come across it sooner. When I'd "designed" the truss - almost all the stuff I across was by Nicholas Tredgold, or referred to his work and made extensive use of his "Tables of Scantling Sizes", which gave sizes for the members in Queen and King post trusses for various spans at 10' apart.
The sizes I used were adequate for 20' spans - so mine at around 16' should be more than ok. The sizes of the tennons resulted from the resultant angles in Cad. The tennons you see for the Kingpost connections were done so that the mortises on both sides did not meet in the middle, but were separated by around 1.5". At the longest part the tennon is around 2.5" - I'm hoping a single pin of around 18mm should fit and not be too close to the shoulder - yet leave enough relish. The tennons are around 35mm thick - so I'm hoping that offsetting the holes by around 3mm and draw-boring them should destroy the tennon\relish.
The timber is softwood. The tennons shown in the 1st example would require the kingpost, in my case, to be cut from something like 12" wide - as opposed to the current 7" wide.
The kingpost tennon at the base is about 4.5" deep and my thinking was that the joint at the base of the kingpost is the one in signifcantly more tension than the rest - the others at the top of the kingpost due to the angled shoulders and tennon - should resist the forces (better) trying to pull the tennon out. Might be a load of cobblers - but abit too far gone to do anything else - at least with the current truss.
The timber analysis software - showed that for the relavant wind\snow loads the timbers themselves should cope with the strains\deflections.
If it starts to go weird - plan B might be to use steel straps and bolts to reinforce the connections. I'm in the process of going thru Jack Sobens book so will digest it overnight and then formulate a plan. Having said that - it's only a workshop roof - in a very sheltered spot (I appreciate that the direct wind load may not be huge but other things like suction, etc. can't be ignored). Even if the roof is built - i could fit the straps afterwoods.
An alternative plan could be to cut a slot in the end of the members with tennons (I suspect those that are at the top of the Kingpost) running thru and epoxy a 5mm steel plate - effectively turn it into a mini flitch beam type connection, and perhaps use metal pins\bolts instead of wooden pegs.
As an aside I did wonder whether one should use a strong glue in the joints as well. Or is that a big no no?
Cheers for the PM - may well give you a ring later on (or tomorrow).
for ideas and information, I have a few questions re: your kingpost trusses.
