Jib Crane Column Design, Base Plate

[Aj Mech]

Hello Forum,

I hope you all are doing good. I am currently working on a column design for tie-rod jib crane/suspended jib crane (1000lbs capacity). As I have never done this before, I need some guidance on solving this problem. You can find the drawing of jib crane attached (image 1). From the crane supplier general arrangement diagram, I can see the thrust and pull as 4.2kip. Using Fisher and Thomas report (Image 2) on jib crane design, I calculated the horizontal and vertical forces that act on column. My question at this point is, is the horizontal force = pull/thrust mentioned in the supplier diagram, vertical force = axial load acting on column.

The column is a hollow square, of 7in x 7in outer, 6.25inx6.25in inside, length 187.25in. End conditions: bottom is fixed (welded to base plate and anchored to concrete floor, top :free). I calculated moment of inertia, critical axial load, radius of gyration. To evaluate column classification, I also calculated slenderness ratio which came out to be long column. I believe since the vertical load that I calculated above is well below the critical axial load in this step, I believe the column can withstand the jib crane at full load capacity. (25% design factor = 1250lbs).

I tried researching on circular base plate calculation, but I couldn't find any. If anybody could direct me towards the design on circular base plate (min thickness, bolt distance), it would be greatly appreciated. My potential failure mode calculation would be, steel strength tension on anchor, concrete breakout strength in tension, pullout strength tension of anchor and bolt thread pullout. Any directions to solve this problem would be helpful.

Concrete is 2500PSI and 6in thick.

 

[ProgrammingPE]

The column and baseplate need to be designed for an axial load of 1800 lbs (250 lbs hoist + 450 lbs jib crane + 1000 lbs capacity * 1.1 vertical impact factor) using a column K value of 2.0. The column strength will be controlled mostly by flexure due to the horizontal forces, though. (I get 4.6 kip when you account for the distance to the center of the column and the vertical impact factor.)

In addition to the combined axial and flexure strength, there's two more things you need to check. You will need to check the column for torsion which will occur when the jib is rotated 90 degrees. You will also need to check the vertical deflection at the end of the jib due to the column rotation which should be limited to the jib boom length divided by 225 as recommended by AISC's Design Guide 3.

As for the baseplate design, it's more common to have square base plates with square columns. If you still want to use a circular plate, you can always design it as a square plate following AISC's Design Guide 1, and then use a diameter that matches the square's diagonal dimension so that your circular plate circumscribes it.

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[dik]

...and moment from the load at the tip... many jib cranes have circular or hexagonal (or octagonal) base plates with stiffeners. An existing building column framing from roof to floor... then only added shear from moment with the column taking the jib crane moment. My oversight...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[JoelTXCive]

For the baseplate, definitely get ahold of of AISC's Design Guide 1. There are older versions online for free.

Also, you can use Hilti's free anchor design software "Profis Engineering" for the anchor bolts.

For the first 30 days, it also has a feature that will run a finite element model of your baseplate.

 

[JLNJ]

If the jib is column-mounted rather than floor-mounted, you need to check the building column for all the load combinations it might see PLUS the moment created by use of the jib. And, as said above, the column needs to be checked for the jib in any possible orientation. Often the controlling factor is when the jib is loading the column on its weak axis.

You may need to reinforce the building column for the jib load. Sometimes the most pragmatic approach is to provide the steel required for the jib loads and not try to figure out what's happening with the existing column.