Jib Crane Support

[dik]

I'm looking for a 'generic' solution for a jib crane support. The actual jib crane has a maximum reach of about 20' and a maximum service load of 2000 pounds. The existing concrete floor slab is sawcut away, a small pit is excavated and a 'blob' foundation is cast into the void. The top of the foundation is cast flush with the top of the slab and the jib crane bolted to the foundation. Soil is generally dense, non-cohesive. I've designed a few of these, but an wondering if there's a generic solution out there (nice to have a reference).

The gravity loads are resisted by the soil and the overturning is resisted by the soil at the base, active soil pressure on one side and the concrete slab at the top. The effects of any soil friction on the sides has been neglected, but the generic solution could include this (although I wouldn't include this component in the final design).

Can anyone suggest a website, spreadsheet or a text that has a generic solution for this?

 

[JedClampett]

I just had to do one of those (1000 lb. at 10 ft) and I was surprised how big the foundation got (4 ft. cube). But I found out the same thing you did, there's no easy way to do it. Got out the big foundation book and cranked out the foundation with axial load and moment formulae. I even tried Enercalc, but it wouldn't check the moment.
The jib crane manufacturer's will do the design for you (assuming a 2500 psf soil allowable), but they'd rather wait until you order the equipment.

 

[jheidt2543]

Somewhat along the same line, I see many shops where the maintenence crew attaches a jib hoist to a building column without any engineering at all! The comment is usually, it is only 250 lbs at 8' or a 500 lbs at 6'. Then looking at the hoist arm it is on a swivel that allows the load to rotate around the column from strong side to weak side. It gets pretty scary out here sometimes, it is a wonder that there arn't more "accidents"!

 

[chicopee]

FROM YOUR DESIGN CRITERIA, I THINK YOU WOULD BE BEST TO SECURE THE TOP PORTION OF YOUR JIB CRANE W/ A MEMBER SO AS TO PREVENT OVERTURNING OF THE BASE. EVEN IF THE BASE IS BIG ENOUGH TO RESIST OVERTURNING, THERE WILL BE SETTLEMENT AND OVERTIME THE JIB CRANE WILL LEAN. ALSO INHERENT IN YOUR DESIGN IS AN ECCENTRICTY OF THE MAST, SO BE PRUDENT.

 

[dik]

Thanks Chicopee... the preliminary base size is 7'x7' and 5' deep... braced by the slab at the top. The loading will not be sustained and the location of the load will be approximately 180 degrees apart for the most part; it may be years before they have to shim the base... I've considered the mass of the boom and the load of the hoisting equipment in the preliminary design. I hadn't considered the use of a counterweight on the opposite side of the boom... wouldn't hurt.