ABC’s Of Foundation

Loadings Under

Cranes by Ron Kohner, PE

CRANE

FOUNDATION

LOADINGS

“Allowable Bearing Capacity of the soil at a

given site is a loading intensity which is so

limited that it provides an adequate factor of

safety against soil rupture and also insures

that settlement due to static loading will not

exceed the tolerable value.”

Basic Soil Engineering

by

B.K. Hough

250 TON CRAWLER CRANE – GROSS WEIGHT

Counterweight 140000 lbs.

Machinery Deck 83000 lbs.

Carbody 48000 lbs.

Crawler Sideframes 94000 lbs.

Boom 25000 lbs.

Hook Load 110000 lbs.

TOTAL 500000 lbs.

250 TON CRAWLER CRANE – BEARING FOOTPRINT

Bearing Length (First-Last Track Roller ) 22.2 ft.

Track Shoe Width 50 in.

Average (Minimum) Bearing Pressure

500000 lbs. = 19 psi (2736 psf)

22.2 ft. x 12 in./ft. x 50 in. x 2

Contact

Gap

Cross-bolting

Hardwood Crane

Mats on

Compacted Fill

Mats under outriggers to

reduce point pressures on

ground

Outrigger Pad

Steel Float

Hardwood Crane Mats

No Cribbing Needed Under Outrigger

Pads on Deeply Frozen Ground

How Much Mat Width Is

Effective In Distributing

Load To The Soil?

It Depends On What Type Of Soil The

Mats Are Placed On

Theoretical Effective Mat

Width

High Crawler

Track Loads

Minimum

Effective Width

Maximum Effective Width

45o

Strong, Hard Soil Does Not Yield to

Distribute Load Under A Mat

High Soil Pressures

Limited Soil Contact

– No Settlement

High Crawler

Track Loads

Mat Stronger Than Soft Soil

High Crawler

Track Loads Crawler Track Settles This

Amount Under Load

(Crane Out Of Level?)

Soil Compresses - Full Mat Width In

Contact With Soil

(Uniform Pressure Distribution)

Depth of Mat Settlement

Over Gas Line

Gas Burning

From Cracked

Underground Line

Crane

Mat Stronger Than Soil

High Crawler

Track Loads

Full Mat Width In Contact With Soil -

Bearing Pressure Less Than Allowable For Soil (Uniform Pressure Distribution)

Mats & Crane

Leveled

Proper Mat

Use Track Centered On Mat

Ski lift headgear

Embankment edge

Soil Stronger Than Mat

Crawler Track Has

Settled This Amount

(Crane Out Of Level?)

High Crawler

Track Loads

Weak Mat Bends

Under Load

Soil Compresses - Full Mat Width In

Contact With Soil

(Uneven Soil Pressure Distribution)

Mat Timbers Too Weak

High Crawler

Track Loads

Weak Timbers Bend - Soil Pressures Concentrate In

The Center Until Soil Yields - Timbers Break!

Undersized Timbers

Concrete

Slab

Broken

Cribbing

Outrigger

Beam

Cribbing/Matting Can Fail By:

•Bearing (Crushing at the surface)

•Bending

•Horizontal Shear (Splitting Longitudinally)

Crawler Track Off Center On Mat

High Crawler

Track Loads

Soil Compresses Under High End Bearing Pressure

Mat Tilts Up Reducing Soil

Contact And Further

Increasing Bearing Pressure

THE CRANE

THE RIGGING

THE LOAD

THE FOUNDATION

What Could Fail ?

A Lift Plan Must Consider

•The Foundation

•The Crane

•The Load

•The Rigging

The WORK Plan

&

A comprehensive lift plan covers:

•Soil – How will the crane be supported?

Soil – Key Questions

•What loads will the tires/outriggers/crawler tracks

put on the soil?

•Can the soil withstand the tire/outrigger/crawler

track loadings?

•Will matting or cribbing be necessary?

•Has the surface been properly prepared and

leveled?

•Are there underground cavities or utilities?

• Manitowoc Ground Pressure Estimator

• Grove CompuCrane

• Liebherr LICCON

• Link Belt Internet Website

• 3D Lift Plan

Ground penetrating radar

used by a skilled operator can detect

subsurface discontinuities

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