scissor truss
scissor truss
(OP)
I need to check the capacity of an existing scissor truss roof. It is home made with plywood gussets. I have the measurements of all members, span (35 ft) spacing, pitches, etc. Does anyone know of a text which will give me a graphical or mathmatical method of analysis. NOT using a computer program
Thanks loads
J
Thanks loads
J






RE: scissor truss
DaveAtkins
RE: scissor truss
RE: scissor truss
RE: scissor truss
RE: scissor truss
In the old days (for wood trusses) that is exactly what we did. To simplify - we used to:
Convert distributed loads on truss to point loads at panel points.
Solve for axial forces.
Apply distributed loads to each member and using NDS check each member using Interaction Equation.
Deflection of truss as a whole can be checked with Virtual Work. Not too hard - but time consuming.
And the answers (which took quite awhile) were not that much different than today's answers using high powered computers.
But with more exacting analysis - they now wring out every inch of span available which saves money.
RE: scissor truss
RE: scissor truss
Very good question and you might want to pose that on the "Truss Engineering Design" forum. Things have changed over the years. They may have a different solution.
My thoughts - you cannot resist the horizontal reaction with a plain wood stud wall - just no way. There was a posting a couple of weeks ago where someone wanted to make some sort of frame (maybe even outlining the plate line) to try to contain these forces. And these forces are large even for small trusses.
Therefore - we used to use an anchorage clip that allows horizontal movement - Simpson and others have them. And let the trusses slide around a bit.
Years ago, I was an expert witness where an architect had modified a truss (making it a collar tied truss) and had not taken into account this scenario. The walls moved like 2'' and ruined the room. He lost. A collar tied truss is not exactly the same - but close enough.
RE: scissor truss
Under PC Software checkout the program WinWood. You can download a Demo or buy the program for $40.00.
http://www.archoneng.com/
RE: scissor truss