abc's of foundation loadings under cranes.pdf
TRANSCRIPT
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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