As they say, the devil is in the details and it’s no different when prepping and planning for a crane delivery or set-up. In this presentation, Mr. Koberg covers the three factors affecting the size of the crane mat or outrigger pad and provides necessary evaluation tools for sizing mats or pads. Speaker: Kris Koberg, DICA Outrigger Pads

1. Outrigger Pads for Mobile Cranes
Rules – Standards
Rules of Thumb
Sizing Recommendations
Setting Up For Success

2. Objectives
 Disclaimer
 Share information to assist you in making better decisions
 Agree on Basic Definitions
 Identify the Rules & Standards that apply to:
 Ground Conditions
 Blocking Cribbing & Pads
 Identify & evaluate different industry “Rules of Thumb”
 Sizing Advice
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3. Focus on Outrigger Enabled Equipment
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4. Float, Foot, Pontoon, Pad
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5. Pad, Mat, Blocking, Cribbing,
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6. Mobile Crane
Applicable Rules & Standards
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OSHA
• 1926 Subpart CC Section1402 • Definitions
ASME B30.5 Mobile & Locomotive Cranes
• 3.2.1.5 • Moving the Load
• 3.4.6 • Footing

7. What's Important to Note About OSHA Regulations
BASIC RULE: You must not assemble or use a crane unless ground conditions
are firm, drained, and graded to a sufficient extent so that, in conjunction
(if necessary) with the use of supporting materials (such as blocking, mats, cribbing,
or marsh buggies), the equipment manufacturer's specifications for adequate
support and degree of level of the equipment are met.
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8. What's Important to Note About OSHA Regulations
OSHA does not have a rule regulating the construction, design, or materials
used as foundation support. (pads, mats, blocking or cribbing)
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9. 9
Abbreviated Inspection Checklist
1. Determine the adequacy of ground conditions beneath the
equipment set up area such as the support/foundation matting,
cribbing, blocking, etc.
https://www.osha.gov/OshDoc/Directive_pdf/CPL_02-01-057.pdf

10. OSHA 1402 Ground Conditions “Summarized”
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 Equipment must stay within manufactures specifications for
support and level.
 Use supporting materials (blocking, mats, cribbing) to accomplish this
 Controlling entity is responsible for ground conditions.
 Including underground hazards
 If there is not a controlling entity, then the responsibility shifts to
the employer.
 Crane company & operator are responsible for evaluating the
ground conditions. They must notify others of inadequate ground
conditions before beginning or continuing operations.

11. ASME B30.5-2011
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3.2.1.5 Moving the Load
(i) When outrigger floats are used, they shall be attached to the
outriggers. Blocking under outrigger floats, when required, shall
meet the following requirements:
(1) sufficient strength to prevent crushing, bending, or shear
failure.
(2) such thickness, width, and length, as to completely
support the float, transmit the load to the supporting surface,
and prevent shifting, toppling, or excessive settlement under
load.

12. Not Sufficient Strength (Physical Failure)
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13. Not sufficient rigidity (Functional Failure)
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14. 14
ASME B30.5-2011
3.2.1.5 Moving the Load
Blocking under outrigger floats, when required, shall meet the
following requirements:
(3) Use of blocking only under the outer bearing surface of
the extended outrigger beam

15. 15
http://www.elcosh.org/document/1488/748/d000104/selection.html
(3) use of blocking only under the outer bearing surface of
the extended outrigger beam

16. 5-3.1.3.3 Responsibilities of Crane Operators.
(b) knowing what types of site conditions could adversely affect the
operation of the crane and consulting with the lift director
concerning the possible presence of those conditions.
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ASME B30.5-2011

17. 17
Know Your Ground Conditions
(Waikato)

18. Industry Rules of Thumb
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19. Industry Rules of Thumb
• Estimating Outrigger Reaction Force
• Estimating Ground Strength
• Estimating Pad Sizing
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20. Outrigger Reaction Force = Pressure
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PRESSURE
(PSF)

21. Common Outrigger Load Rules of Thumb
Capacity x 85%
Rated Capacity (lbs.) of the Crane x 85% = Outrigger Reaction Force
International - (Referenced in European and Australian standards)
(Total Crane Mass (lbs.) + Load(lbs.)) x 65% = Outrigger Reaction Force
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22. Outrigger Load Rules of Thumb Example
Grove RT890E
Capacity x 85%
180,000 x 85% = 153,000 Lbs
International
(Mass + Load) x 65% = Outrigger Reaction Force
(117,235 + 180,000) = 297,235 x 65% = 193,200 Lbs
Difference = 40,200 Lbs
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23. Outrigger Load Rules of Thumb Example
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24. Outrigger Load Rules of Thumb Example
Grove GMK 5276
• Rated Capacity = 220 Tons, 440,000 Lbs
• Total crane mass = 150,000 Lbs
Capacity x 85% Example –
• 440,000 lbs. x 85% = 374,000 lbs.
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25. Outrigger Load Rules of Thumb Example
Grove GMK 5276
• Rated Capacity = 220 Tons, 440,000 Lbs
• Total crane mass = 150,000 Lbs
International Example –
• (Total Crane Mass + Load) x 65%
• 150,000 Lbs + 440,000 Lbs = 590,000 Lbs
• 590,000 Lbs x 65% = 383,500 Lbs
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26. Outrigger Load Rules of Thumb Example
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27. Outrigger Load Rules of Thumb Example
What is the Maximum Outrigger Reaction Force (MORF) for
your crane?
 Crane manufactures provide this information
 Newer software solutions from manufacturers & others
 Manitowoc - Compu-Crane
 Liebherr - Liccon Software
 Link Belt – Technical specifications
 Tadano – Online request tool?
 3-D Lift Plan
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28. 28
Grove GMK5275 220 Ton Crane Full Cwt

29. Outrigger Load Rules of Thumb Example
Grove GMK 5275 220 Ton Crane
Compu-Crane Output
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30. Know What Lifts Generate the Highest
Pressures Picks=126k (126psi) vs. 875 (104psi)
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31. Outrigger Load Rules of Thumb
DICA Advice –
Don’t use a rule of thumb to determine the maximum outrigger reaction force.
Know the Maximum Outrigger Reaction Force of your crane.
Why – MORF drives the Strength Requirements of your Pad
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32. Ground Strength Rules of Thumb
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33. Bearing Capacity of Soils
Determining the bearing strength of the ground and soils is an
extremely complex combination of science, engineering and art.
Seek the advice of a geotechnical engineer.
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34. Bearing Capacity of Soils
Ultimate bearing capacity (UGBC) is the theoretical maximum
pressure which can be supported without failure.
Allowable bearing capacity (AGBC) is what is used in
geotechnical design, and is the ultimate bearing capacity divided
by a factor of safety.
 In the case of temporary structures the typical FOS = 1.5 - 2
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35. Ground Bearing Capacity –
Shear Failure
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36. How To Prevent Shear Failure
Improve the Ground
 Compaction
 Bring in rock or other dense inorganic materials to increase ground bearing capacity
 Remove un-compacted surface layers
 If wet, allow time for moisture to evaporate
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37. How To Prevent Shear Failure
Reduce the Pressures Imposed into the Ground
Increasing the contact area to the ground using load spreading tools such as
Pads, Mats, Blocking, Cribbing
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38. How To Prevent Shear Failure
“It might make sense to do some of both…”
 Keith Anderson. Rigging Engineering Basics, 1st edition
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39. Ground Strength Rules of Thumb
Visual Analysis –
• Reference a generally accepted Ground Bearing Pressure Chart based
on the soil type and condition
Roll Tests
• Know the Pressure exerted by the tires of your crane.
• Measure the compaction of the ground under the tires
• Develop a plan to identify the ground strength based on ground
compaction
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40. Generally Accepted
Ground Bearing Pressures
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Shapiro Cranes & Derricks, fourth edition

41. Know Your Ground Conditions
Dynamic Cone Penetrometer
The DCP procedure is currently standardized by ASTM D 6951-03.
(Good for depths up to 6’)
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42. Ground Strength Rules of Thumb - Dangers
Little Jack Horner Sat in a corner, eating his Christmas pie, he put in his thumb, & pulled out a
plumb, & said, what a good lad am I!‘
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43. Ground Strength Rules of Thumb
DICA Advice –
• Use Caution at All Times
• Understand Specific Site Information from the Controlling Entity
• Reference Geotechnical Information Whenever Possible
• Monitor the Ground During All Operations
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44. Ground Strength Rules of Thumb
DICA Advice –
Know what Ground Strength Your Pads are Designed For
Why – Ground Strength is Key to Determining Pad Area
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45. Pad Sizing Rules of Thumb
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46. Pad Sizing Rules of Thumb
3x The Area
Area of the Float x 3 = Area of Matting
Shapiro Method
Capacity of the crane in Tons / 5 = Area of Matting
Duerr - Simple Mat Sizing
(Capacity x 1,100) / Soil Bearing Capacity = Area of Matting
Square Root Method
√ capacity / 4 = Area of Matting
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47. Other Pad Sizing Methods
Equalization Method (soil bearing capacity method)
Outrigger Load/ ASBC = Area of Matting
Duerr – Effective Bearing Length of Crane Mats
Evaluation of the material being used to meet the matting objective.
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48. Sizing Methods Evaluated
• 3x The Area
• Shapiro Method
• Duerr - Simple Mat Sizing (SMS)
• Square Root Method
• Equalization (Soil Bearing Capacity) Method
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49. Crane Specific
Rule of Thumb Evaluation Assumptions
• Crane MORF is the Load to be fit for
• Weight of the mat is not included in the calculations.
• Steel pads generally add 50 – 100 Psf
• Pad size results are rounded up to the nearest foot.
• Allowable Ground Bearing Capacity of 5,000 Psf is used, when
applicable.
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50. Generally Accepted Ground Bearing Pressures
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Shapiro Cranes & Derricks, fourth edition

51. Grove RT650 E 50 Ton Crane
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52. Link-Belt 3140 140 Ton Crane
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53. Grove GMK6350 350 Ton Crane
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54. Confused, Don’t Use Any Pads
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55. Outrigger Pad Sizing Rules of Thumb Analysis
54 Total Cranes Evaluated
 Not every crane was evaluated in every method due to
unconfirmed data.
3 Different Crane Manufactures
 Grove, Link-Belt, Tadano
Range in Lifting Capacity from 8.5 Tons – 300 Tons (Defined Bands)
 < 50 Ton Cranes = 11
 > 50 and < 100 Ton Cranes = 16
 > 100 and < 200 Ton Cranes = 12
 > 200 Ton Cranes = 6
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56. Outrigger Pad Sizing Rules of Thumb
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57. Outrigger Pad Sizing Rules of Thumb
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58. ROT Analysis – Soft Ground (2,500 Psf)
Avoid using a ROT in Soft Ground Conditions
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59. Outrigger Pad Sizing Rules of Thumb
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60. Outrigger Pad Sizing Rules of Thumb
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61. 3x The Area –
– Cranes < 100 tons, where ASBC > 5,000 Psf
– Small Cranes on Stable, Strong Ground
Shapiro Method
– Cranes up to 200 Tons, where the ASBC ~ 5,000 Psf
– +/- Changes in actual ASBC Significantly Alter the Results
Square Root Method
– Cranes up to 200 Tons, where the ASBC ~ 5,000 Psf
– +/- Changes in actual ASBC Significantly Alter the Results
Duerr - Simple Mat Sizing (SMS)
– Cranes from 50 – 200 Tons in All ASBC
– By Far the Most Accurate Rule of Thumb – Takes the ASBC into account
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Rule of Thumb Sweet Spots?

62.  Rule of thumb conclusions vary significantly from method to
method.
 Most rules of thumb do not take ground conditions into account.
 Rules of thumb Do Not address pad and mat material, design or
construction.
 Rules of thumb assume pads and mats are designed and
constructed in a way that meets or exceeds the bearing, flex and
shear strength needed.
 They only output estimated pad area.
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Rule of Thumb Evaluation Conclusions

63. DICA Advice –
Avoid use a pad sizing method that does not take defined
ground conditions and actual outrigger loads into account.
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Rule of Thumb Evaluation Conclusions

64. Sizing Advice
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65. What Outrigger Pads and Crane Mats Must Do:
• “The must spread the load from the float/pontoon over a large enough
area that the bearing pressure to the ground surface is acceptable.”
• “Provide support to the crane that is stiff enough that the crane will not go
out of level as the loads from the crane change during lifting operations.”
David Duerr P.E., 2DM and Associates Inc.
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Sizing Advice

66. 66
Simple Sizing:
“To keep things simple, you may decide for your fleet of outrigger based cranes
that, knowing the ground capacity and the max loadings each crane could put
down, each crane must always use a particular size mat. That would guarantee
keeping within the permissibles at all times and avoid having to recalculate every
time.”
Keith Anderson P.E., Bechtel
Sizing Advice

67. Sizing Advice
1. Know the Maximum Outrigger Reaction Forces for your
Equipment.
2. Size the Area Your Pads Based On Defined Ground Conditions.
3. Ensure the Pad You Choose has the Strength and Rigidity you
need to Not Fail, and to Distribute the Load.
4. Consult with your Outrigger Pad or Crane Mat Manufacturer
 Specifically for proprietary materials and construction
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68. DICA 3 Step Fitting Process
1. Identify the Equipment Data Points
 Crane capacity
 Outrigger Float dimensions
 Maximum Outrigger Reaction Force
2. Determine the Pad Strength & Stiffness (thickness)
necessary to Support & Spread the load.
3. Determine the Mat Area Needed Based On:
 Outrigger Reaction Force to be FIT for
 Soil Bearing Capacity to be FIT for
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69. 69
Example:
• MORF= 428,000 Lbs. Outrigger floats 2’ x 2’ = 4 sq. ft. Pressure = 743 Psi
• Allowable Ground Bearing Capacity = 5,500 Psf
• Mat Area Needed = 78 sq. ft. (428,000 / 5,500 = 78 sq. ft.)
• Crush Rating 1,000 Psi > 743 Psi
• 10.5’ x 7.5’ = 78 sq. ft. mat with proper material, strength, bending and rigidity
properties
Sizing Advice - Example
Liebherr LTM 1350-6.1 350 Ton Crane

70. Know your limitations:
Know what Outrigger Load and Ground Bearing Pressure the mats are
designed for.
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Sizing Advice

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72. Larger Areas, Require More Rigidity
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73. Recommended Resources
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David Duerr, P.E. - 2DM Associates
 Book – Mobile Crane Support Handbook
 Paper – Effective Bearing Length of Crane Mats
 Presentation - Crane Mats & Ground Bearing Issues
Lawrence & Jay Shapiro
 Book - Cranes & Derricks, Fourth Edition
J. Keith Anderson, P.E. - Bechtel
 Book – Rigging Engineering Basics, First Edition
Ron Kohner, P.E. - Landmark Engineering Services, LTD
 ABC’s of Foundation Loading Under Cranes

74. This is 100% Preventable
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75. Thank You
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