Free standind Crane runway girder. 1

[Alves21]

Hello fellow Engineers.
I was asked to review a free standing crane runway girder for a 20t crane. Due to space limitations the project was made with beam span of 14m and column height is 9m.
I did check the runway beam (simply supported) and the columns according to design guide 7 and in terms of resistance it goes ok with a welded beam of aprox. 100cm height.
My concerns are with the beam being unbraced on the flanges and possible torsion problems that may result. As far as I know for a runway beam with that span on a industrial building I would have to lateral brace it but this case being a free standing crane this is not possible.
Also concerned with deflection of column on the crane plane since there is no brace in that direction. Right now the solution is to use very robust columns and set strongest inertia (xx) to work on that plane. I am attaching a picture that shows the geometry.
Any tips for this type of structure is appreciated.
Kind Regards

 

[SlideRuleEra]

http://www.SlideRuleEra.net

 

[Alves21]

I would like to add one more question. Since this is a free standing and is not connected to a building column etc, is it ok not to deal with Tie Back Links?

 

[jayrod12]

How are you dealing with the lateral load applied by the crane? I see the moment frame in the one direction, are you counting on 9m tall cantilevered columns? That's a fair ask.

 

[Alves21]

How are you dealing with the lateral load applied by the crane? I see the moment frame in the one direction, are you counting on 9m tall cantilevered columns? That's a fair ask.

That's why I brougth this here, from my point of view this structure is unsafe due to only counting on this columns in order to deal with lateral loads, even those beeing relatively bulk columns...

 

[jayrod12]

It's certainly possible. But we don't have all of the information to run the numbers, nor would we be willing to.

What size of column are we discussing?

What rating and class of crane?

What type of foundation are they supported by?

There's a bunch of information we would need to make educated responses.

From the information so far, it's possible, but would require some fairly substantial members.

 

[MegaStructures]

I think you are going to have more problem with detailing a fixed connection at the base of the column than the columns themselves, no? It's fairly easy to confirm the stiffness of steel columns, less straightforward to determine fixity of the connection to the foundation. Do you have room to add small outriggers to the columns out of plane of the frame?

 

[Alves21]

Couple more informations.
That would be a 20t Class A - Standby or Infrequent Service Crane.
The column was specified as a 650x600mm welded I shape. Flanges and webs are 3/4" width.
As far as foundation, I am afraid I wont be able to give much information since that's not my department. In fact, just to explain better, I am not used to work with that type of structure but when I saw it over here it called my attention and I am trying to help.

 

[jayrod12]

As MegaStructures indicated, the column and beam analysis is fairly straight forward. The base connection and the foundations are where things are going to work or not.

I'm not going to run the numbers specifically, but I would say you're cutting it a bit tight on the column, but not so much that it doesn't work. As I said I haven't ran the numbers to check it. 2L/d = 30 which is a bit higher than I'd generally want to go, but might be doable. Deflection will be tough.

But all that is a moot point if the connection at the base of the column can't provide the strength and rotational stiffness required for the column to perform. Same thing for the foundation.

 

[Alves21]

I did ran a deflection analisys of the column

Top deflection is 15mm. According to regulations It should remain lower then H/400 wich would be 22,5mm.
But there's something I am not conviced. From what I've studied, top flange is the one receiving the lateral loads from the crane. Since there is no brace or anything and that part is free, how would it transfer this load to the column and not actually tumble over it.

 

[jayrod12]

If you look at SlideRule's post, generally there's a cap channel that is intended on resisting the lateral loads. In extreme cases I've seen a wide flange shape used as a cap to resist the lateral.

 

[HTURKAK]

I would like to remind the picture at the cover of AISC Design Guide 7_ Industrial Buildings Roofs to Anchor Rods and other applicable detail , Fig. 17.2.1 .

In past, I have designed similar case, ( the OH crane in the hall was extending out of the bldg to open yard) I have provided portal bracing for longitudinal and designed the columns as cantilever for transversal direction..

 

[HTURKAK]

https://res.cloudinary.com/engineering-com/image/upload/v1599230891/tips/yard_crane_gvcfyq.png[/img]7]

 

[Alves21]

Thanks for everyone contributing. I think on the Steel Structure department this is serving its proposal. My understandment is that it's not the most eficient structure but given the situation it was conceived, as far as strength and service checks it's doing the job. Now the ones designing the fundation will have to handle this.

 

[r13]

It is not the best choice, but for light duty bridge crane, double flanges wheel can be used to provide some stability - on lateral movement, the frame deflects, but the rotation of the runway beam/girder is prevented by the crane bridge. The crane wheel may need frequent replacement though.

 

[MegaStructures]

Alves if I was the owner I would love to see knee braces out of plane to provide a more efficient load path to the foundation. Not sure if that’s possible with your space requirements, but I personally enjoy redundancy and don’t like counting on a connection to the foundation as fixed.

 

[JLNJ]

Don’t forget PDelta. Very important for cantilevered columns.