Shipping Saddle Base Plates

[ChrisF90]

I am currently designing shipping saddles and was wondering if there were circumstances where the baseplate thickness would not need to be calculated with the shipping loadings. The vessel will be tied down directly over each saddle such that the longitudinal and lateral loads will be translated into additional vertical loads. The saddles themselves will not be secured to the transport.

I would think that the baseplate would only need to be thick enough to support the weight of the vessel (without shipping loadings considered), if the vessel is tied down as I described above during shipping.

Thanks,

Chris

 

[dhengr]

PVEngineerCF:
Well... you can’t ignore or neglect the thickness of the base plates, they are part of the design of the whole saddle. The idea of the saddles is to get all the loads (various loads and load paths) from the vessel down into the transporter or the permanent foundation, without hurting the vessel. I would think you should have a top flange plate, conforming to the general shape of the vessel, maybe cushioned on top by wood or some such to protect the vessel, a crushing surface. You should have a main web member or members, perpendicular to the vessel axis, and likely some web stiffeners, properly located; all to take the vessel loads down to the base plate and then into the transporter deck. Then, you have the base plate which distributes these compressive loads (column loads, bearing loads) into the transporter deck or permanent conc. foundation. Thickening the base plate might reduce the bearing stresses on the conc. found. (or whatever) under the webs and stiffeners. As likely as not these saddles might be used for lifting the vessel onto the transporter or into its final position. This all has to be taken into account when you design the saddle.

You say that the transport loads (lateral and longitudinal impacts/impulses, etc., plus added tie down loads) are converted to vert. loads on the saddle, and this is basically true. But, you can’t ignore the fact that some longitudinal or lateral loads will be applied at top of the saddle, while cables or chains actually pick up their bracing/tie down loads. These loads have to be taken down through the saddle to ground. That entire saddle has to take this kind of loading without crumpling under this loading action. You also need to know much more about the transport means than you have revealed; is it by ship, railcar, 4 mph transporter, or what. That base plate is pretty cheap in the whole scheme of things, if it adds to the integrity of the saddle. At the same time, I would not assume that the saddle. bolted down to the deck, would take all of the lateral loads, under all conditions.

 

[ChrisF90]

dhengr,

I appreciate the response. I am quite familiar with how to go about designing support saddles and my questions is only regarding the design of the base plate.

I disagree that if the vessel is tied down above each saddle that the saddle will see lateral and long. loads. These loads would be transferred through the tie down cables and translated into additional vertical loads in the saddle. To clarify this will be shipping on a truck flat bed and the saddles themselves will not be secured to the truck. With this said I believe there should be no bending moment resulting in the base plate from the shipping loadings. Since the cables are only meant to translate the lat. and long. loadings during shipment, this would lead me to believe the only consideration for base plate thickness would be the weight of the vessel.

The vessel will be tied down with (2) trunnion-like attachments above each saddle which will have a cable wrapped around it and secured to the bed of the truck at around 45 deg on each end. Keep in mind the truck bed would be treated as rigid.

I hope that clears it up. Let me know your thoughts. I may be able to sketch something to help better illustrate if need be.

Thanks,

Chris