Tie-Down Welding Load

[hungrydinosaur]

Hi All,

I did an analysis on a equipment. The equipment is welded to the ground plate at 16 points/Nodes (N1, N2...N16). The analysis under 3 different loading scenarios give 3 outputs as attached. I am doing some hand calculations for welding at these nodes. The TOTAL LOAD (highlighted in yellow) in any one direction differs in the 3 load scenarios. Any advice which one of the 3 loading scenario (worst case) should I pick for doing my hand calculations?

Thanks in advance.

Regards,

HD

 

[canwesteng]

Without any better information, I would say design all the nodes for the worst case nodal loading (root sum of squares of your x and z component).

 

[JGard1985]

Agreed, pick greatest X Load from 3 cases, Greatest Y-load from 3 cases and greatest Z load from 3 cases. Remember it may be the greatest absolute load (depending on what your negative signs indicate). I'd bump loads up a little bit to cover any minor changes and go from there. When designing multiple weld groups, I try to give myself a nice envelope of design margin. Stops re-work

Jeff
Pipe Stress Analysis Engineer

http://www.xceed-eng.com

 

[dhengr]

Hungrydinosaur:
Is this a large size, high C.G., piece of equip. being lashed down to the steel deck of a ship? What are the actual load conditions that you analyzed to get your listed results? Those force direction and magnitude listings are really not very meaningful without some plans and elevations of the piece of equip. Show important dimensions, sizes, C.G. location, you tie-down node locations, etc., etc. We can’t see what you are looking at from here, and we can’t read your mind either. How did you arrive at the node load listings? How did you account for the relative stiffness of the ship’s deck and the piece of equip? Are all of these tie-down nodes on the base of the equip. and then welded directly to the deck? What does your tie-down hardware look like, show sketches of this hardware. How this hardware is oriented w.r.t. the x, y & z axes will dictate what the welding should be or can be. Do you have any ‘plane old’ shear blocks welded to the deck at important equip. base locations, to just take out lateral loads at those locations? Normally, I would do those tie-down weld calcs. by hand once you have the load components at each node. But, I’d also have to understand what gross loading condition caused each of these lists. I’m not sure I understand what the listed total load components mean, except that they might relate back to the equip. weight at the C.G. for the given loading condition, as a check of the loads in each direction. That is sum of the Fx = zero, etc.

 

[hungrydinosaur]

Hi Canwesteng/JGard1985/Dhengr,

Thanks for your replies. Dhengr, this is a Winch which is welded down to the ship with tie-down plates on all four sides of the winch. The plates are bolted with a single bolt to the winch. The plate is then welded to the deck of the ship. See attached file. The total loading conditions mean the total check of loads in each direction, for a particular load case (here there are 3 load cases). Thanks in advance.

Regards,

HD

 

[IFRs]

I would design the weldment to be stronger than the attachment to the frame.

 

[dhengr]

Hungrydinosaur:
Did you talk to the winch manuf’er. about how to tie their system down to a ship’s deck? What did they give you in the way of the tie-down loads, methods and locations? You say you have 16 tie-down nodes, and your photo shows 4 on each side, generally under the winch drum bearings, and 2 at each corner on the front and the back, 4 in front and 4 in back, that adds up to 16 nodes, assuming symmetry. Is this a correct interpretation of the photo? Again, you show no dimensions, x, y, or z axes, member sizes, node locations, tie-down plate or bolt sizes, loads or the three different load conditions which you claim to have evaluated. You must elaborate, in detail, if you want meaningful answers. When you did your analysis for the various load conditions, how did you determine the load paths down to the winch base, and how did you determine the relative stiffness’ of the winch structure and its base and the ship’s deck structure, the various member section properties, etc? What happens with the tie-down loads when the wire rope is coming off one side of the drum or the other. What direction does the wire rope take when it leaves the top of the winch structure? Those 16 - 2 or 2.5" wide weld plates do not appear, to me, to be properly located w.r.t. the winch frame and load paths, although I’m not sure I fully understand the winch structure or how it works. I don’t like the idea that the loads go through 16 short welds and weld plates, with all their starts and stops and potential for weld defects in short welds, in a number of different ways.

 

[hungrydinosaur]

Dhengr,

The winch manufacturer has given the same tie-down loads which I had sent earlier. You are correct on the 16 nodes and interpretation of the photo, with Y axis as the vertical axis. The loads are worst case loads with the wire rope angle in the worst case. The stiffness of winch structure and the deck structure is something not clearly the winch manufacturer has given us.

Regards,

HD