External Reaction of Truss
External Reaction of Truss
(OP)
Hey guys,
I'm new here and sorry for this newbie question, I would to ask how to I obtain the reaction of the pinned connection of A, B, and C (See attachment)? Do I really have to use Force-Method? I actually attempted to use Moment at different places and do simultaneously (Idk if it's the right thing to do) but apparently I got Ay = 38.07kN, By = 37.39kN and Cy = 0, which I think it is wrong, can anybody help? After getting this, then I can proceed to calculate the internal force and pick the type of section to use.
Thanks.
-TR
I'm new here and sorry for this newbie question, I would to ask how to I obtain the reaction of the pinned connection of A, B, and C (See attachment)? Do I really have to use Force-Method? I actually attempted to use Moment at different places and do simultaneously (Idk if it's the right thing to do) but apparently I got Ay = 38.07kN, By = 37.39kN and Cy = 0, which I think it is wrong, can anybody help? After getting this, then I can proceed to calculate the internal force and pick the type of section to use.
Thanks.
-TR






RE: External Reaction of Truss
For what it's worth, this feels like homework.
RE: External Reaction of Truss
-TR
RE: External Reaction of Truss
RE: External Reaction of Truss
-TR
RE: External Reaction of Truss
After completing my degree I spent 18 months doing highway work then moved to site supervision on a viaduct project. I still remember the struggle I had trying to remember reinforced concrete basics when a senior engineer asked me to check the reinforcement in a small retaining wall.
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: External Reaction of Truss
Alternately, you could look at the actual support connections and see if you can't rationalize it into a determinate structure. Perhaps at the low end of the truss on the left and the high connection on the right they become rollers. Do you actually have two connections on the right side of the truss? That seems odd. Generally we would bear the truss at the bottom only, and perhaps connect the top of the truss for out of plane loads only.
RE: External Reaction of Truss
then I thought Ay, Bx, Cx; or Bx, By, Cx and add Ay (as a propped cantilever, unit force method).
as I see it there are several members (well 2) with zero load (including the member BC).
this is (I think) triply redundant, I'd use FEA (maybe play with different react sets to see the changes).
Maybe too instead of hard constraints support the truss on springs (ie finite stiffness constraints)
another day in paradise, or is paradise one day closer ?
RE: External Reaction of Truss
RE: External Reaction of Truss
No, that would still be indeterminate.
You could make A or B a horizontal roller and remove C to make it determinate. Or you could remove A and make B a vertical roller (or any direction other than horizontal). Or you could remove B and make C a vertical or horizontal roller (or any direction other than normal to AC).
Most would likely choose the first option.
BA
RE: External Reaction of Truss
RE: External Reaction of Truss
If B remains hinged and C becomes a vertical roller, the structure is stable and determinate. Making A a horizontal roller adds a redundant reaction.
Alternatively, if B remains hinged and A becomes a horizontal roller, the structure is stable and determinate. Making C a vertical roller adds a redundant reaction.
M(a) and M(b) are not independent equations. For equilibrium, the sum of moments about any point must be zero. If that is so, the moment about any other point must also be zero.
BA
RE: External Reaction of Truss
in 2-D you have 3 Equilibrium equations
Sum X =0
Sum Y = 0
Sum M = 0
that's it.... no more
So 4 unknown is one too much
Maybe it would help to read one on the basic text books on mechanics :)
best regards
Klaus
RE: External Reaction of Truss
RE: External Reaction of Truss
Perhaps, but an equal and opposite horizontal reaction at B and C will reduce the vertical reaction at A and increase the vertical reaction at B as the truss attempts to act as fixed ended at BC.
BA
RE: External Reaction of Truss
interestingly I think you can solve Bx, By, Cx, and Cy (because of the relationship between Cx and Cy); I thought the problem triply redundant but maybe it is doubly redundant ?
Cx and Cy can be determined from sum moments about B (> Cx) which defines the load in the truss member going into C (member BC sees no load, as both B and C are constrained) and so Cy can be determined. Then you can determine Bx and By (from sum forces). Then you could plot the deflection of point A, and probably see Ay is the significant reaction here.
another day in paradise, or is paradise one day closer ?
RE: External Reaction of Truss
BA