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Reaction of Horizontal Vessel
2

Reaction of Horizontal Vessel

Reaction of Horizontal Vessel

(OP)
I am a young civil engineer and recently I begin to learn to design foundation of horizontal vessel.
But I have some confusion.

The title is reaction, but for civil, we focus on load applied to top of foundation from vessel.
My confusion is:
1. Usually, vendors specify that horizontal force in longitudinal direction is applied only to fixed end. In Wind or Seismic load case, so it is. But in these load cases, the vessel doesn't move, so it is balanced. There must be a force of the same value and the opposite direction with the load applied to fix end. applied on the sliding end.
Is this idea right or not?

RE: Reaction of Horizontal Vessel

(OP)
2. I am also confused that
When expansion or shrinkage happens, the vessel slides, there is a friction force between one saddle with slotted holes and sliding end of foundation.
In this case, is there horizontal load applied to fixed end of foundation?

RE: Reaction of Horizontal Vessel

Don't triple post.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Reaction of Horizontal Vessel

I'm not a structural engineer but I'm guessing one end of the vessel is secured tightly to the floor and the other end should be able to float horizontally. If so then a horizontal force through the fixed end/floor/bolts would be reacted by a sliding force (friction) on the floating end and by inertia of the accelerating tank.

Just a guess.

RE: Reaction of Horizontal Vessel

1. Usually, vendors specify that horizontal force in longitudinal direction is applied only to fixed end. In Wind or Seismic load case, so it is. But in these load cases, the vessel doesn't move, so it is balanced. There must be a force of the same value and the opposite direction with the load applied to fix end. applied on the sliding end. Is this idea right or not?

In the longitudinal direction only, only the fixed end can resist loads since in the longitudinal direction the sliding end cannot resist a load since it slides. However in any other direction both the fixed end and sliding end can resist loads. In other directions the sliding end is restricted from moving too. The sliding end bolts are in contact with the edges of the slots so the vessel is restricted from moving horizontally sideways including from wind and earthquake loads. The sliding end bolts should also be arrange so that they can take the resulting sideways overturning moment.

For any longitudinal loads the fixed end will need to take all applied loads and moments. The only resistance to loads of the sliding end in the logitudinal direction is friction of the sliding support plate on the foundation. So all loads in the longitudinal direction are transfered to the fixed end only and only frictional load exists at sliding end.

I am also confused that
When expansion or shrinkage happens, the vessel slides, there is a friction force between one saddle with slotted holes and sliding end of foundation. In this case, is there horizontal load applied to fixed end of foundation?

Yes the frictional sliding load on the sliding support is transfered back to the fixed support through the vessel wall.

RE: Reaction of Horizontal Vessel

(OP)

Quote (Snickster)

Yes the frictional sliding load on the sliding support is transfered back to the fixed support through the vessel wall.
When vessel slides, are the forces applied on it balanced or not?

RE: Reaction of Horizontal Vessel

As long as the vessel is not accelerating then all external forces acting on it are balanced by the reaction forces and moments at the supports.

The force of sliding friction is also balanced. When the vessel slides the sliding support bottom plate experiences a friction force equal to the weight of the vessel on the sliding support times the coefficient of friction = 0.3 for steel on steel. This forces acts on the sliding support in a direction opposite to the thermal motion. This force acts on the sliding support through the saddle into the vessel and to the fixed support via compression in the vessel wall. The force then is resisted by an equal force in the fixed support.

Imagine that both supports were free to slide without fixing and that the weight shared by each sliding support were equal and hence the frictional force was equal. In this case if the vessel expands by one inch thermally then the movement at each support will be 1/2". But since one side if fixed all of the thermal expansion is forced to the sliding end side of the total 1" and this motion is brought about by the friction force acting on the fixed support pushing the vessel expansion towards the sliding support as described above.

RE: Reaction of Horizontal Vessel

(OP)

Quote (Snickster)

In the longitudinal direction only, only the fixed end can resist loads since in the longitudinal direction the sliding end cannot resist a load since it slides. However in any other direction both the fixed end and sliding end can resist loads. In other directions the sliding end is restricted from moving too. The sliding end bolts are in contact with the edges of the slots so the vessel is restricted from moving horizontally sideways including from wind and earthquake loads. The sliding end bolts should also be arrange so that they can take the resulting sideways overturning moment.

For any longitudinal loads the fixed end will need to take all applied loads and moments. The only resistance to loads of the sliding end in the logitudinal direction is friction of the sliding support plate on the foundation. So all loads in the longitudinal direction are transfered to the fixed end only and only frictional load exists at sliding end.
How is horizontal force applied on fixed end in longitudinal balanced?
Why isn't there static friction on sliding end?

RE: Reaction of Horizontal Vessel

The frictionn force is on the sliding end as it is the moving end. This force is transfered to the fixed end through the vessel as I have described. The force of friction on the sliding end is then balanced by the reaction force on the fixed end.

RE: Reaction of Horizontal Vessel

(OP)

Quote (Snickster)

The frictionn force is on the sliding end as it is the moving end. This force is transfered to the fixed end through the vessel as I have described. The force of friction on the sliding end is then balanced by the reaction force on the fixed end.
These are not the same load cases.
One is thermal load case, the vessel expands or shrinks, and the vessel moves. In this case, both fix and sliding ends burdens horizontal force. This is what you describe.
Before this load case, you also describe "horizontal force in longitudinal direction is applied only on fixed end", which is seismic or wind load case.
My question is in seismic and wind load case, there isn't horizontal fore on sliding end, then how is horizontal force on fixed end balanced?
It is balanced with external force?

RE: Reaction of Horizontal Vessel

The horizontal force on the fixed end is balanced by the seismically induced inertial loads or wind loads applied to the tank.

RE: Reaction of Horizontal Vessel

You need to look at it as a free body diagram with the vessel as the free body. External loads will act on the vessel body pushing on the vessel and these loads are balance by equal but opposite forces pushing back on the vessel at the support points. For loads acting longitudinally on the ends of the vessel inline with its axis, the loads that act on the vessel can only be resisted by the fixed support reaction forces acting back on the vessel at the fixed support. So the answer is any horizontal longitudinal force on the vessel is balanced by the fixed support only so the fixed support will need to be designed for the entire longitudinal seismic and wind loads.

RE: Reaction of Horizontal Vessel

Also in the thermal expansion case and the free body concept, the external load acting on the vessel body is the friction force on the sliding support and the balancing force acting on the free body is the equal but opposite reaction force at the fixed support.

RE: Reaction of Horizontal Vessel

(OP)
Friction force differs from static friction force and sliding ones.
In case we push an object on a rough surface, when the force is small ,the object doesn't move, the friction force is a static type. When push force is increased, and the object moves, the friction force is a sliding friction.
So here, when seismic or wind load pushes a vessel, the vessel does not move, but is there static friction on sliding support?
If not, vessel should not have a tendancy to move, the anchor bolt at the fixed support is strong. Is this understanding correct ot not?

RE: Reaction of Horizontal Vessel

Friction force differs from static friction force and sliding ones.
In case we push an object on a rough surface, when the force is small ,the object doesn't move, the friction force is a static type. When push force is increased, and the object moves, the friction force is a sliding friction.

I understand that but I wanted to keep the discussion simple so I did not get into detailed explanation of static and dynamic friction. The maximum resisting force though is the static force which the fixed support needs to be designed to.

So here, when seismic or wind load pushes a vessel, the vessel does not move, but is there static friction on sliding support?
If not, vessel should not have a tendancy to move, the anchor bolt at the fixed support is strong. Is this understanding correct ot not?

Correct. The wind or seismic load is partially resisted by the frictional force of the sliding support of weight at support times the coefficient of static friction. Therefore the net resisting longitudinal force at the fixed support is the external horizontal load minus the friction force at the sliding support. But I would personally design the fixed support for the entire external seismic or wind load without considering the frictional force at the sliding support. In fact it may be that the frictional force at the sliding support is enough to resist the wind and seismic load without having any load on th fixed support but it is an engineering judgement as to whether you consider this friction force sufficient to resist the horizontal wind and earthquake load even though by calculationn it really does. Personnally I would design the fixed support to take the entire load and not consider the opposing friction force. What happens if the seismic load causes the vessel to lift up off the foundation at the location of the sliding support? Then the entire seismic load then really will be transfered to the fixed support without any contribution to the resisting force coming fiom the friction force at the sliding support.

RE: Reaction of Horizontal Vessel

Remember that anything you design that don't work will cause you to look incompetent. Therefore always design things so that nothing could ever go wrong in any freak way and that it is totally idiot proof. I designed things for 40 years with just two or three minor mistakes (at least those that were brought to my attention. lol) by being conservative in my design philosophy but not too overconservative to where critics would be able to attack me for overdesigning things.

RE: Reaction of Horizontal Vessel

(OP)

Quote (LittleInch)

Don't triple post.
OK.But experts in different fields have different advantages. They may have different ideas to the same question.Please understand me.

RE: Reaction of Horizontal Vessel

Like I said - Don't triple post. It's against the forum rules and you've been around E-T long enough to know that. Your other two posts will likely vanish. You might be correct, but that's not how it works here as otherwise you get a scatter gun effect and what one person says in one thread, may be countered by something said in another, plus most people inhabit a number of forums so to answer the same question three times isn't going to happen and makes people annoyed.

Your query is fairly simple and I think has been addressed above.

So yes, the longitudinal force if you like along the axis of a vessel will be higher at the fixed end as it needs to take all the loads of the vessel, seismic, wind and other forces from pipework connections. The sliding end axially only see static friction and sliding friction forces caused by thermal expansion or other forces so is max vessel weight / 2 x coeff of friction. Now what you take that to be can vary depending on steel on steel or teflon pads. It can easily be quite significant.

Sideways force though is the same at both ends as is any uplift forces.

Easiest is just to make them both the same then no one will get it wrong in the field or if the vessel designer decided to shift the fixed and sliding end... (It has happened)

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

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