Overhead crane tractive forces

[CDLD]

Hi,

I'm working on an existing industrial building, and adding loads to existing crane columns.
How does everyone stand on equally distributing the tractive forces (parallel to rail) to all columns (7 bays).

You can see below that the bracket to crane girder connection is slotted.
I assume the rail is held to the crane girder by clamps.
Is the friction from the clamps enough to distribute the tractive force to all columns?

 

[X4vier]

I usually assign those loads the pair of diagonal angles to the nearest column. I don't see that kind of angle diagonal bracing in your details.

 

[CDLD]

These details are from an existing crane.
I'm not sure I understand what you mean by "a pair of diagonal angles to the nearest column".

 

[EngDM]

See the two attached photos. This is typical.

 

[CDLD]

The existing details do not call for those braces.
Additionally, the strut/girt is not tied into a vertically braced bay.

For tractive loads the columns will twist and bend about the weak-axis.
Basically, my question is whether all columns will share the twist and weak-axis bending.

For this to happen, the tractive load would have to pass through all the crane girders to load up the columns equally.
I am hesitant to run with this given that the crane W310 brackets have slotted holes in the direction of the tractive force.

 

[PMR06]

Are the bolts in those slotted holes fully pre-tensioned, slip critical? If so, that could be justification of the load path and load sharing all along the crane runway.

 

[FLCraneBuilder]

See the two attached photos. This is typical.

If the building col is stiff enough to resist the rotation, then diagonals not needed.Their necessity is also a function of the actual longitudinal load

is the long load 500 lbs or 5000? (2 ton crane or 25 ton or ?)

 

[FLCraneBuilder]

Hi,

I'm working on an existing industrial building, and adding loads to existing crane columns.
How does everyone stand on equally distributing the tractive forces (parallel to rail) to all columns (7 bays).

You can see below that the bracket to crane girder connection is slotted.
I assume the rail is held to the crane girder by clamps.
Is the friction from the clamps enough to distribute the tractive force to all columns?


View attachment 9793

We have run a number of models on this topic...
the columns near the crane share the load (crane) somewhat equally (assumes good tie backs)
as you get further form the crane, the load seen by columns diminishes. We suspect this is due to the runway beam deforming (it is like a horizontal column - but very long)..,, even thought the runway beams is tied back, the building is not completely rigid either.

BTW - the tiebacks shown on the detail have been known to cause problems. The top flange should be tied back , not the web. If a heavy duty application, the top flange will rock back & forth eventually causing cracks where web & top flange intersect (K area)

Noet that much of this conversation is altered by the actual longitudinal force your are working with. I see 40# rail, so this might be a light load?

 

[EngDM]

If the building col is stiff enough to resist the rotation, then diagonals not needed.Their necessity is also a function of the actual longitudinal load

is the long load 500 lbs or 5000? (2 ton crane or 25 ton or ?)

My response was solely to give photos for @X4vier 's post.

 

[CDLD]

Are the bolts in those slotted holes fully pre-tensioned, slip critical? If so, that could be justification of the load path and load sharing all along the crane runway.

I assume they are not slip critical.

 

[CDLD]

If the building col is stiff enough to resist the rotation, then diagonals not needed.Their necessity is also a function of the actual longitudinal load

is the long load 500 lbs or 5000? (2 ton crane or 25 ton or ?)

The crane is 15T and I assume the bridge/trolley weight is about 15T.
Longitudinal load is 10% of wheel load, which is approximately (30k lifted load + 30k/2 bridge weight)*0.1 = 4.5kips

We have run a number of models on this topic...
the columns near the crane share the load (crane) somewhat equally (assumes good tie backs)
as you get further form the crane, the load seen by columns diminishes. We suspect this is due to the runway beam deforming (it is like a horizontal column - but very long)..,, even thought the runway beams is tied back, the building is not completely rigid either.

BTW - the tiebacks shown on the detail have been known to cause problems. The top flange should be tied back , not the web. If a heavy duty application, the top flange will rock back & forth eventually causing cracks where web & top flange intersect (K area)

Noet that much of this conversation is altered by the actual longitudinal force your are working with. I see 40# rail, so this might be a light load?

Thanks for this. Crane is rarely used and has been in service for 40 years. What do the tie backs have to do with transferring longitudinal loads? Aren't they only used for resisting side-thrust?

 

[CDLD]

My response was solely to give photos for @X4vier 's post.

Thanks for that.
I am considering adding bracing to resist the longitudinal load.
I cannot run with your detail since the strut is not at the same elevation as the crane beam, however I can brace the brackets back to the strut which will take care of the torsion.