The new generation of ‘super cranes’ offers amazing possibilities, such as the 5,000t capacity ALE SK 350, the 3,500USt capacity PCT 140 by Mammoet and Terex Demag’s, 3,520USt capacity CC 8800-1 Twin.

In addition, Liebherr recently came out with the 3,300USt capacity LR13000 crawler.

With capacities ranging from 1,500 to 5,000USt, they can place larger, heavier loads at long radii and extreme heights. These capabilities promote modular construction designs that reduce the hazard to employees working in high places and shorten construction time.

One reason companies choose large cranes is that the cost savings of shorter turnaround schedule offsets the high cost of a large crane.

However ‘super cranes’ produce extreme ground pressures: even raising one of the massive booms creates immense ground pressures.

We rarely if ever find soil or concrete already on site that’s substantial enough to mitigate those pressures.

Regardless of location, we need to build crane foundations to withstand the pressures.

A typical foundation system would be a pile-supported concrete slab.

Becht Engineering works with major heavy lift contractors, mechanical contractors, major engineering companies and refinery owners all over the world to design or review lift packages.

A lift study may be done many months or years before the lift starts.

The first step in a large crane foundation design is to determine the type and capacity of the natural soil at the location using a soil analysis.

We contract a subcontractor to do this as there are many reputable specialist companies to choose from locally where we’re working.

What happens during a soil analysis is specialist companies will do borings and record the different types and densities of soils in the various layers with different load bearing capacities. Sometimes we’ll find a combination of soil and rock and sand and that needs to be investigated.

Secondly, radar sounding is commonly done to see if there are underground structures, cavities or voids that would cause loss of the crane’s stability.

Considering the maximum track or outrigger pressure produced by the crane, a load distribution system is custom designed to reduce those pressures.

Computer programs are utilized followed by hand calculation to assure the foundation will not only support the crane dead load, but will also withstand the dynamic loads imposed while the crane is working.

‘Super cranes’ produce high ground pressures and have to be on a stable foundation to work and lift safely. Unlike foundations for some smaller cranes, construction of a ‘super crane’ foundation system will usually be concrete with piles. It will include excavation of the existing soil and back filling with suitable compacted base.

Ground bearing support for cranes with capacities less than 1,500USt require different ground bearing load distribution systems.

Those ground pressures are usually significantly less, therefore the load distribution system doesn’t have to be as complex.

Very often we determine we can use just timber mats or a combination of steel mats and plates. Other times we have to do an excavation of some very soft soil and replace it with compacted base material or rock.

In our opinion failures occur with smaller cranes more often than is commonly understood, and with today’s technology there’s no excuse for that.

Ground conditions, soil type and capacity have to be considered for every case and reviewed at every new work location.

At a recent refinery project near the Mississippi River in Memphis, Tennessee, lifting a fluid catalytic cracker regenerator head and a series of heavy scrubber modules required a 2,500USt crawler crane. The natural soil capacity at the site was less than 700psf (pound force per square foot).

The foundation had to support over 4,000psf and consisted of over 100 65ft-long pieces of piling, a three-foot thick concrete slab with four layers of one-foot thick timber crane mats on top.

The concrete slab was built below grade so it could be buried after the crane was removed and used again at a later date if the same crane was needed.

This is often the case in refineries where major components of the plant have to be replaced or refurbished every few years. We also serve industrial gas, fossil and nuclear power, as well as offering specialized support for innovative technologies, such as pressure vessel and vibration issues in the petrochemical industry.