cantilever lengths max - need back-up
cantilever lengths max - need back-up
(OP)
OK, we got rid of the thirteen foot conical cantilever over the garage with the slate roof that took the two steel beams weighing 3800 pounds apiece (I may be exaggerating slightly, but not much) due to expense. I have managed to find criteria for trusses stating that the maximum cantilever using a strut is .25L, L being the span. And I know about the rule of thumb of twice the back span...but I cannot seem to get through to this guy... is there anything else anyone knows of that gives a more solid...reason than common sense not to use a cantilever with say, oh .44L? I mean, I CAN make it work, I suppose, uplift at the opposite end, bracing of the compression chord, check the stresses check the deflections and make it stout, but it is SO stupid. Any help anyone can give me would be appreciated.






RE: cantilever lengths max - need back-up
RE: cantilever lengths max - need back-up
Without seeing the actual detail it is difficult to judge but if you have reservations over your design, go with your gut feeling. If it looks right it usually is right but if it looks wrong that's because it is wrong!
RE: cantilever lengths max - need back-up
I assume by "this guy" you mean your client? If you feel uncomfortable using a cantilever that isn't 1/3 - 2/3 just tell him it's "not economically feasible". Clients understand $$$, not stresses, moments, & uplift reactions.
RE: cantilever lengths max - need back-up
RE: cantilever lengths max - need back-up
While I agree that clients don't understand shears and moments, they sure can see deflection. Most lay people are surprised when they find out the deflections we deal with and allow in a structure. Show him the 1 1/2" deflection and see what his reaction is.