Truss Reactions 2

[Sparkes1992]

Hi Guys,

I've been modelling a simple truss in the program spacegass with a dead and live loading on the top chord. I seem to be getting large horizontal reaction forces. Shouldn't the bottom chord of the truss be acting in tension hence stopping the top chord from opening up? How do i ensure that the perimeter beam that the trusses are sitting on recieve no lateral force? Any help would be much appreciated.

Jack

 

[bowlingdanish]

I'm really not a fan of those whacky cantilevered columns, are the deflections OK? Even if it works on paper it just doesn't feel right.

What's driving the truss locations? Why don't you align the trusses with the 'whacky columns' and design it as a fully welded fixed frame. Then you can have pin-pin supports at the base. Much cleaner.

 

[Sparkes1992]

Thanks for the responses all. Nice sketch by you kootk. So let's say the bottom cord is twice as stiff as the perimeter beam in the minor sxis, am I right to assume it will take twice the load?

Bowling danish, good idea mate, that's pretty much what I went with.

 

[Teguci]

Who's doing the waterproofing detail for the roof to roof valley? That looks like it'll be pretty tricky and could be the cause for a future call back when they keep getting leaks. The dogleg column will want to deflect down and the eave, when the existing truss is loaded will deflect up. If you can lap the trusses, you stand to reduce these deflections and simplify the structure. You just need accurate information on the location of the existing trusses and how they are tied in. If you design for a 0.3 m play in truss location, you can defer the final locations to the contractor and have the trusses fabricated while he installs the new footings.

 

[rb1957]

isn't the original gutter still there (in the valley) ?

another day in paradise, or is paradise one day closer ?

 

[KootK]

So let's say the bottom cord is twice as stiff as the perimeter beam in the minor sxis, am I right to assume it will take twice the load?

Correct.

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.

 

[Tahoebrian5]

If I was designing this I would probably recommend to the client to remove the fascia and tails at the existing structure so the new trusses can bear either on or adjacent to the existing wall. Less wasted coffee will likely result