Jib Crane Mounting Base 1

[blacksix]

I have a jib crane that I need to mount on a portable base. By portable, I mean made of steel and concrete and not fastened to the floor. The boom is 10 ft long and the clearence is 11 ft. The capacity is 1/4 ton. How big does this base need to be, and are there any tools that can help me determine the overturn moment and how big my base needs to be. I have read in several other posts that the base must be 3-5 ft deep. I would like to have the base be no more than 1 ft deep. Please advise. Thank you.

 

[RockEngineer]

You need to have a factor of safety of at least 1.5 against overturning when you consider the lifted loads, weight of the jib and impacts. Using standard impact of 1.15 on the hoisted load and 1.1 on the the weight of the boom and hoist. From there just use the centers of all your weights and do an overturning calculation. The weight of your foundation if above ground and not attached must counteract all the other loads throughout the working range of your equipment.

 

[dirtsqueezer]

Not to put the nut on before the washer, but I've worked with a ringer crane crew, and I believe their base was wood. 12" square studs layed out in a mat they called a 'dance floor'. You can imagine the configuration. I don't know of the FS or engineering, but the loads we lifted exceeded 50 kips totalling, including the weight of the crane, over a million pounds. I remember that being a really cool concept at the time. Best of luck. Remember, your loads will not be static, and will also be dependent on load distance from the crane. I would bet you are looking for tables of some sort. Yeah, on second thought, I would maybe even sub out a specialist if you were worried at all about topple. There are moments to consider that may present to you something of a white whale, and you may be able to use the data for this project yourself if you have steady work with this crew. Again, best of luck.

 

[kevlar1]

It sounds like you have what the crane guys call a pillar jib crane. That is, a vertical support capped with a rotating horizontal beam that supports a load. The overturning moment is, conservatively, the total of horizontal beam weight, the weight of any load supporting hoist or harware, and the maximum load capacity, multiplied by the travel length (10 feet assuming full length travel of the beam you describe). Multiply by the appropriate factor of safety, 1.5 minimum, but 2.0 is often used, especially around concrete. The result is the design overturning moment. Your base needs produce a resisting moment of at least the same value. A 3-5 foot thick concrete base, 4 feet on a side, is sufficient for use in a fixed foundation, assuming support from surrounding soils. For your "portable design", a 1 foot thick concrete slab will need to be around 10 feet on a side to give you the necessary resisting moment. A possible alternative would be to mount outriggers to the base of the vertical column. Outriggers should be at least the same length as the load beam. A good example of outrigger design is a standard engine hoist. Remember to consider the rigidity of the vertical post and any resulting stiffening required before finalizing the design.