Jib crane connection to Existing Stack Wall

[StrucPEng]

Hey Everyone,

I am attempting to design the connections of a new Jib crane to an existing stack wall for an industrial application, i have attached a sketch and detail of the brackets.

- The Jib crane will be a bought out item but the connection to existing will need to be designed.
- I will be going with a welded connection as there is no access tot he interior of the wall to bolt the brackets.
- Loads are provided by the manufacturer for pull and thrust.
- Currently we have no information on the thickness of the stack we are connecting to (not too happy about this). But I want to design the connections under the assumption the stack is of sufficient thickness and at the same time calculate the thickness of the stack that would make this design feasible. That way we can outline for the client the required stack thickness to proceed with the installation.

I am not really sure where to start with this or how to analyze it by hand (I do not have access to FEA software). My ideas are as follows:

1. Design similar to a base plate for a column (The column is the bracket and the base plate is the stack) using AISC Design Guide #1.
2. Design similar to a Jib to HSS connection Outlined in the Engineering Journal Q2 (2002) "Design Concepts for Jib Cranes.

Not sure if this is the right way to look at this. I would appreciate any help getting me on the right track. Let me know if I can provide anything else i missed that would help facilitate a more complete answer.

Thanks for the help!

Matt

 

[WARose]

You can do it by hand....at least as far as the stack goes. If you have 'Pressure Vessel Design Handbook' (by: Henry H. Bednar), it has examples of thrust loads coming into cylindrical walls. IIRC, it also design examples where reinforcement pads are used where the thickness isn't sufficient.

EDIT: This assumes we are talking about a decent sized cylinder here (for your "stack").....not sure what your diameter is.

 

[JStephen]

That's a lot of thrust. If your stack is pretty heavy-walled, it may work.
I'd try to arrange a thickness test with an ultrasonic tester first, should be fairly quick and easy.
The pressure vessel books have some guidance, WRC 107 and 297 and related have some guidance. If you have or can get access to vessel software, some of this is automated and included in that.
Also, in Bednar's book, there is a section on line loads that may help (although it seems overly conservative).
For a thinner-wall stack, you may be looking at stiffeners on the stack or including both lugs into one large repad.

 

[StrucPEng]

Thanks for the replies, I will take a look at those books and references and see if I can work through it. I will reply if I come across any problems.

The stack is approximately 9ft - 10ft in diameter and about 200 ft high just for clarification sake.

JStephen - We will definitely be recommending testing be done on the stack prior to any commencement of construction.

Thanks again for your help!

 

[robyengIT]

Loads are not only the ones you showed, but when the jib is rotating left or right there are two other loads (tangential to the stack). You should follow the last sentence of JStephen

 

[StrucPEng]

robyeng - So are you saying when the jib swings it will create a force that would be cause a sort of torsion in the stack around its center? I might be thinking of that wrong.

 

[JAE]

If there is an unknown stack thickness that is that essential to the structural system, I'd either verify the thickness or use some other means to avoid overstressing the wall.

First - I assume this is a steel stack? You didn't state that (vs. concrete or masonry).

For thickness verification, I've used a testing lab to come out with an ultrasonic non-destructive testing equipment which measured approximate wall thicknesses of some 48" diameter steel force mains.
(looking for verification of a 3/8" thickness). They used an Olympus Ultrasonic 38DL Plus Thickness Gauge.

To avoid the overstress, you could look at adding a vertical jib column in front of the stack wall, extended down to the floor below and fastened to the stack wall.
This vertical element could provide additional stiffness to reduce or relocate forces applied to the stack wall.


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[robyengIT]

NO ! . When the loads are like you showed the direction of the loads is radial. When the jib is rotated 90° the loads are tangential to the wall (with a partial component radial). I don't mind (because impossible) of overturning of the stack itself.

 

[StrucPEng]

JAE - Yes it is a steel stack. We have a few options for companies to come out and test thickness of the stack and I agree it will need to be done. Looking at the references mentioned above the equations allow for a thickness of additional plate in the location of the loads and the more i go through it the more likely that looks. As for the column idea, I like it but I also left out this is about 100 ft up the stack. with that said, there is a platform that they would be working the jib from, it is not substantial enough to directly take the crane loading but it may be able to take some through a design similar to what you suggested. I will look at that. Thanks!

robyeng - I think I see what you mean. In that case it would not be a thrust and pull radially but a tangential moment at the bracket location?

 

[robyengIT]

correct !

 

[TimSchrader2]

Hello ....Most of the reply's are related to the stack. Not sure if the question involves the brackets also. If so you can analyze by hand with some conservative assumptions. The leg on the bottom supporting the crane will take tension and bending. Or torsion and bending at 90 degrees. The stress in the lower leg of bracket will need to checked for combined stresses to the reduced allowables (one method)

All or most of the vertical 2400lb load will be on one leg as noted in the drawing, bending the lower leg. A conservative assumption would be to design as if the lower leg takes 75% of the 14.4KIPS for the tension on each leg.

The pull out capacity of the Top bracket bolts will need to be checked. Noting that the top two bolts will have more tension from the 2400lbs @ 4".

 

[StrucPEng]

Tim - thanks for your response. In this case though the brackets are part of the bought out crane and are per-engineered so we are alright on that front. Although I will keep that in mind when and if I have to design some similar brackets on my own.

Just to close this out for everyone who is interested, the existing stack was determined to be 1/2" thick A36 plate cladding with a reinforced 7/16" A516-Grade 70 inner wall. Using the references noted above I was able to achieve some acceptable stresses in the wall by adding a backing plate and moving down to a 1 ton jib crane.

Thanks everyone for the help, it is much appreciated!