Weld stress in joint
Weld stress in joint
(OP)
Suppose I have a weldment with a tri-pod design (see attachment). The load is 36,000 lbs, so each leg is supporting 1/3 of that weight. What would the stress be in the weld that secures the leg to the center tube? My attempt: the reaction (Rby) at each foot at the base is 12,000 lbs, the opposite reaction in the vertical direction on the tube-to-leg weld group (Rcy) would also be 12,000 lbs. The tube, cut at an angle at the point of attachment, has dimensions of 1 x 4.73 and is welded all the way around. Following the information in Shigley's, this grouping has a total throat area of 1.414h(b + d). In this case, b = 1" and d = 4.73". With a 1/8 fillet weld, the total throat area is calculated to be 1.414*(.125)*(1+4.73) = 1.012" Shear = F/A, so 12,0000/1.012 = 11,857 psi. According to this I can get away with an 1/8 weld, but that just seems small given 18 tons being applied? Is this methodology correct or am I missing something?






RE: Weld stress in joint
Check the wall thickness of the circular vertical tube for concentrated loads from the legs. If the extended centerline of each leg does not meet precisely at the midpoint of the circular tube, a torsional moment will exist which must be resisted by the three legs, but also by the wall of the circular tube. Thus the legs must be positioned rather accurately.
The stability of the assembly is dependent on the thickness of the wall of the vertical tube. If the attachment of each leg to the central tube allows free rotation about a vertical axis, the assembly is unstable.
BA
RE: Weld stress in joint
RE: Weld stress in joint
What is value of the estimated maximum transverse force at the top of the tripod (Rax?).
How Are the tripod legs oriented in the top/plan view?
120 degrees?
http://g-ecx.images-amazon.com/images/G/01/aplusau...
or inline?
Regardless, if the interfaces to the "ground" and I-beam are not very secure, and slip free, A few ties lower on the legs might provide some nice redundancy.
http://g-ecx.images-amazon.com/images/G/01/aplusau...
RE: Weld stress in joint
RE: Weld stress in joint
BA
RE: Weld stress in joint
RE: Weld stress in joint
RE: Weld stress in joint
With only 0.12" wall thickness, you are correct when you say that by code, you cannot exceed a 1/8" fillet weld.
I don't believe you are overthinking it at all. You should be satisfied that the computer results pass a sanity check.
BA