Bridge Crane Side Thrust

[n8engr]

I am designing some new bridge crane runways for a client. When determining the side thrust load to the columns, is that load split between each side (50%) or applied 100% to each column.

For example: Side Thrust load= 60k. Is that 30k to each side or 60k to each side.

 

[Gumpmaster]

I deliver the full thrust to one side. There's some play in the trucks and I don't think you can really count on them to deliver the thrust equally.

 

[MiketheEngineer]

That is probably a bit conservative - but surely will be OK

 

[JAE]

100% to one side for me. The crane wheels sometimes are one-sided flanged wheels (like a RR train) where load is imparted in only one direction. Some wheels are dual flanged so that may not be an issue.

 

[Stillerz]

I use 100% to one side also & for the same reasons already mentioned.

 

[MikeHalloran]

The bridge crane wheels I've seen up close are one-side flanged, _and_ tapered, just like train wheels.

Additionally, the rails are crowned.

Tapered wheels on crowned rail tend to center the trucks on a train, or the bridge on a crane. When it's done right, the flanges hardly ever touch the rail.



Mike Halloran
Pembroke Pines, FL, USA

 

[apsix]

Rails could be crowned, the cranes I work with usually don't have crowned rails.

As above, I design for 100% each side.

 

[MikeHalloran]

They're not crowned much, maybe .012" across 2".
Just enough to get a CAD drawing all screwed up if you don't snap to the center of the arc.

Ask your rail supplier for a drawing, or zoom in on a section in your CAD file.



Mike Halloran
Pembroke Pines, FL, USA

 

[apsix]

Mike
The rail I'm dealing with;

http://www.emrails.com.au/images/products/86kg crane rail.pdf

It's also common to use 50 x 25mm Flat bar as 'rail' here for light cranes.

 

[weab]

My 2 cents. I agree with MikeHalloran. Given wheels with 1 sided flanges, 100% each side would seem correct. That's what I do.

 

[MikeHalloran]

Yep, that's flat rail.

It's also amazingly heavy.



Mike Halloran
Pembroke Pines, FL, USA

 

[ishvaaag]

MikeHalloran, that's what some of you taught to me: what for some is a barbarity, for others is just enough. There are different appreciations of what it is safe, different levels themselves, and requirements of, and different abilities to afford some level of safety.

 

[Stillerz]

There might be one point that is missing here.
Though you may assign 100% of the side thrust load to act at one end of the bridge (as I would) this does not necessarily mean that 100% of that load goes to one crane column.
Straight from AISE Tech. Report No. 13:
"...The recommended total side thrust shall be distributed with due regard for the lateral stiffness of the structures supporting the rails...."

If in a building with roof trusses and bottom chord bracing (or any other build for that matter) the side thrust loading will be distributed to several columns to either side of a given column, even if the crane is directly in line with one column.
This is why it is important to design bottom chord bracing in such structures properly.

 

[racookpe1978]

OK, well figure he's picking up his max lift load at the left side of the crane bay, then accelerating that load sideways towards the right side. All the sideways forces are pushed to left as he accelerates, neutral in the middle as it runs along, then pushed to the right as he de-accelerates at the right.

So at best, the sideways loads would be concentrated at one column or between two columns on both sides, but at the full sideways load each time. The crane is not going to "pull" equally on one rail while it pushes equally on the other rail during these acceleration times - friction neglected.

 

[KurtSauer]

A couple comments: most new EOT crane bridge wheels for cranes made/installed in US are double-flanged, turned flat; however, a few are made with a tapered running surface, to "center" the crane on the runway rails. The rails in US have a very slight crown, with eased edges; however that crown wears with use. There is a clearance between the inner edges of the flanges and the edge of the rail of (total) 3/4" min. larger than the rail head, ideally split equally on each side of the rail. Thus the design allows the crane to move slghtly perpendicular to the rail--typically min. of 3/8".

I do not suggest, Stillerz, that one arbitrarily assumes that the lateral load is distributed. Much depends on the integrity and design of the rail-to-bridge girder connection, and the location and treatment of rail splices in relation ot eh column locaitons. A signifidcant portion of the lateral load applied to the rop of the crane rail can be imparted directly to the nearest column--at least initially, until deflection/movement in connections and bracing is terminated, both within the runway girder-to-crane/building column connection and within the buidling bracing system itself. While these loads are not usually severe or of significant magnitude, given the proper circumstances, they can be problematic.

Finally, the sidethrust load imparted by an overhead crane trolley is dependent on trolley speed, trolley and load weight, decelration/acceleration rates, and type and properties of the trolley endtruck bumpers. the lod values will reflect both normal operating conditions and "crash" values, obtained by trolley strking the endstops at full speed, with full load, closely coupled (raised). More information can be found in the Crane Manufacturers Association of America (CMAA) Specificaton No. 70.

 

[cntw1953]

Cab driving (heavy duty) crane rarely stay in straight line after a while of use, single flange wheel is still heavy in use, and needs to be replaced quite frequently due to wear, tear, and damage (broken) by side pull (one side usually).

Do not distribute lateral thrust without looking/understand entire structure system. Often times the building columns are simply stub out from the runway columns, it is more like pinned/hinged support at just below the runway level. Furthermore, these building columns could be another 20'-30' above the runway so the highest point of the crane can clear the bottom chord with M.J. or Y.M. standing on the trolley do the dumps.

Just some noise to draw attentions.

 

[Stillerz]

I dont really see how I was suggesting that one "arbitrarily assumes that the lateral load is distributed".

One could assume that the crane is lined-up directly with the column and impart the full load into that column. It would just be slightly conservative and would also be ignoring the relative stiffness of the bracing system as one function of the bottom chord bracing is to distribute the lateral loading to adjacent columns. With a proper 3-d model, this would be achieved nearly by default.

It could be the case that the overwhelming majority of the load is imparted to one column, that does not make any "arbitrary" assumption. It is not as if I suggested that you only impart 50% of the load to the column, I was merely suggesting that you follow the suggestions of a widely used and highly regarded design guide in order to achieve an efficient design. If you are doing a simple hand calculation, then you might be stuck using the full side thrust load at the column.

I work for a man who was a committee member for AISE Tech. Report 13 up thru the 1997 publication. I am not trying to name drop, just stating that I have had lengthy discussions on this very topic.

Part of the reason for load factors and allowable stresses is that we recognize that an veritable armageddon of combinations of loads is not likely to happen and should it happen, we still have not overstressed our members.