huangyhg

wood "moment connection"
im not sure if this is possible or not. my gut reaction was that it wasnt but after thinking about it, maybe it is, but i need to find a good reference. i have a existing paralam structural ridge that is going to be extended approx. 10'. the client wants no posts, support, etc. under the splice so essentially if this is going to work it needs to be a wood version of a full penetration welded splice. any guidelines/references for using steel plates and bolts to splice wood/engineered lumber in this manner?
true moment connections in wood are elusive, at best. but maybe it is possible, see the paper "moment resisting connections in glulam beams" - free .pdf at this link
i have designed splices for floor joists in the past, using a "sister joist" next to the joist with the splice, and running the sister joist a long distance each way beyond the splice, while using a lot of nails.
my point is that a moment splice in wood is possible, as long as you design the steel plates and the bolts for the moment each side of the splice. i would be a little nervous about bolt slippage allowing the splice to "hinge" a bit, but i don't think the splice would fail.
daveatkins
not sure of overall dimensions, but maybe you can run a new ridge under existing which will allow you to have cantilever without any weird connections. will need some extra details for cutting into and using existing supports, but you get to have a clean cantilever and don't need to cut away and resecure rafters.
either way lack of column will make extension tricky.
thanks fss, thats a good idea. when i get into the project i will consider that option and see if it works. i have a call into the paralam company engineer to see if they have any guidance. i will post any relavant info i get from them.
i came across a similar situation. my solution was to provide a steel "sleeve" constructed of plate field welded in place. i extended the sleeve beyond the splice location such that the hinge effect mentioned by daveatkins above would be minimized. i used plate instead of a steel tube for the sleeve to achieve a tighter fit with the wood. i also called for bolts to secure the sleeve to the wood beam. if you decide to do this, be sure to specify a fire retardant fabric or other material between the steel and wood beam so that you will not risk the beam catching fire when welding the plate. the client was quite pleased with this detail because not only was it relatively inexpensive, it was also aesthetically pleasing in that it looked like a beefy steel connection to a wood beam. it worked quite well.
i remember seeing in the eurocode 'timber design' a significant section on moment connections for timber construction. it was elegant in that the the connections were bolted, with the bolt pattern being circular ... as is the moment ... don't have a code handy and this was a number of years ago. i suspect you would need large surface areas to accomplish though.

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