Outrigger Pads for Mobile CranesRules – StandardsRules of ThumbSizing Recommendations

Setting Up For Success

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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Focus on Outrigger Enabled Equipment

Float, Foot, Pontoon, Pad

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Pad, Mat, Blocking, Cribbing,

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Mobile CraneApplicable 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

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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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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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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

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.

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.

Not Sufficient Strength (Physical Failure)

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Not sufficient rigidity (Functional Failure)

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ASME B30.5-20113.2.1.5 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

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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

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

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Know Your Ground Conditions (Waikato)

Industry Rules of Thumb

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Industry Rules of Thumb

• Estimating Outrigger Reaction Force • Estimating Ground Strength

• Estimating Pad Sizing

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Outrigger Reaction Force = Pressure

PRESSURE(PSF)

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Common Outrigger Load Rules of ThumbCapacity 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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Outrigger Load Rules of Thumb ExampleGrove 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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Outrigger Load Rules of Thumb Example

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Outrigger Load Rules of Thumb ExampleGrove 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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Outrigger Load Rules of Thumb ExampleGrove 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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Outrigger Load Rules of Thumb Example

Outrigger Load Rules of Thumb ExampleWhat 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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Grove GMK5275 220 Ton Crane Full Cwt

Outrigger Load Rules of Thumb ExampleGrove GMK 5275 220 Ton CraneCompu-Crane Output

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Know What Lifts Generate the Highest Pressures Picks=126k (126psi) vs. 875 (104psi)

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Outrigger Load Rules of ThumbDICA 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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Ground Strength Rules of Thumb

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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Bearing Capacity of SoilsUltimate 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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Ground Bearing Capacity – Shear Failure

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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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How To Prevent Shear FailureReduce 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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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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Ground Strength Rules of ThumbVisual 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

Generally AcceptedGround Bearing Pressures

40Shapiro Cranes & Derricks, fourth edition

Know Your Ground ConditionsDynamic Cone Penetrometer The DCP procedure is currently standardized by ASTM D 6951-03. (Good for depths up to 6’)

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Ground Strength Rules of Thumb - DangersLittle 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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Ground Strength Rules of ThumbDICA 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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Ground Strength Rules of ThumbDICA Advice –

Know what Ground Strength Your Pads are Designed For

Why – Ground Strength is Key to Determining Pad Area

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Pad Sizing Rules of Thumb

Pad Sizing Rules of Thumb3x The AreaArea of the Float x 3 = Area of Matting

Shapiro MethodCapacity 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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Other Pad Sizing MethodsEqualization 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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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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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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Generally Accepted Ground Bearing Pressures

50Shapiro Cranes & Derricks, fourth edition

Grove RT650 E 50 Ton Crane

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Link-Belt 3140 140 Ton Crane

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Grove GMK6350 350 Ton Crane

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Confused, Don’t Use Any Pads

Outrigger Pad Sizing Rules of Thumb Analysis54 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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Outrigger Pad Sizing Rules of Thumb

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Outrigger Pad Sizing Rules of Thumb

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ROT Analysis – Soft Ground (2,500 Psf)

Avoid using a ROT in Soft Ground Conditions

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Outrigger Pad Sizing Rules of Thumb

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Outrigger Pad Sizing Rules of Thumb

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?

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

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

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Sizing Advice

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

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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

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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DICA 3 Step Fitting Process1. 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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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

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Sizing Advice - ExampleLiebherr LTM 1350-6.1 350 Ton Crane

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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Larger Areas, Require More Rigidity

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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

This is 100% Preventable

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Thank You

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