Support documents for mobile crane operation

The SC&RA Guide to Outrigger Pad Materials, Selection and Usage was produced for members of the Specialized Carriers & Rigging Association. It is geared toward outrigger supported cranes.

This year sees the publication of two new guides for the planning of supports for mobile cranes. The first is the SC&RA Guide to Outrigger Pad Materials, Selection and Usage from the Specialized Carriers & Rigging Association. As the title suggests, this guide is directed toward outrigger-supported cranes. The second is a new Appendix D titled “Planning for LHE Foundation and Support” in ASME P30.1-2024 Planning for Load Handling Activities. This appendix is somewhat more general than the SC&RA guide in that it addresses both outrigger-supported and crawler-supported cranes.

It is worth noting that there is a fair amount of membership overlap between the ASME P30 Committee and the SC&RA Task Force. Five of the 14 members of the SC&RA Task Force also serve on the ASME P30 Committee. Thus, the industry will see that these two publications complement each other, rather than conflict. This article provides a brief discussion of both publications.

SC&RA Guide to Outrigger Pad Materials, Selection and Usage

In 2022, the Specialized Carriers & Rigging Association (SC&RA) convened the Outrigger Mat Resource Task Force as part of the SC&RA Safety & Education Committee. This group was charged with writing a best practices guide for the selection and use of outrigger pads and mats under mobile cranes and other outrigger-supported load handling equipment. The SC&RA Guide was released this past September in conjunction with the 2024 Crane & Rigging Workshop.

The seven chapters of the SC&RA Guide address the range of topics one must understand to select and use outrigger pads safely. These topics include the applicable aspects of lift planning, descriptions of the various types of pads available, job site considerations that may affect equipment location and setup, and guidelines for outrigger pad setup and use. The final chapters provide a list of definitions of terms used throughout the SC&RA Guide and a list of outside references for those situations where more in-depth information is needed.

While intended to be a set of guidelines and recommendations for users of outrigger-supported equipment, the SC&RA Guide to Outrigger Pad Materials, Selection and Usage goes far beyond this goal in terms of its usefulness. The depth of discussion of the products, how they are used, and the planning considerations that go into selection and use of outrigger pads also make this booklet an excellent training and education tool. Further, in addition to standing on its own, the SC&RA Guide can serve as an outline for a much more detailed discussion of the covered subjects for the training of lift planners and lifting operation managers.

The new Appendix D titled “Planning for LHE Foundation and Support” in ASME P30.1-2024 Planning for Load Handling Activities. This appendix addresses both outrigger supported and crawler supported cranes.

It is also appropriate to note what this Guide is not. This Guide is not an engineering textbook. There is some technical information, such as presumptive bearing pressures for various types of soil, and simple calculation examples for the determination of outrigger mat bearing area. However, more complex applications of load handling equipment support design that require technical rigor will call for the use of outside assistance, particularly in the area of geotechnical engineering, or reference to one or more of the resources listed in Chapter 7.

ASME P30.1-2024 Nonmandatory Appendix D “Planning for LHE Foundation and Support”

Whereas the SC&RA Guide to Outrigger Pad Materials, Selection and Usage is focused on outrigger-supported lifting equipment, the new Nonmandatory Appendix D in ASME P30.1-2024 offers a much broader scope. Further, Appendix D provides a greater level of technical information and guidance for the selection and sizing of outrigger pads, conventional timber crane mats, steel crane mats, and the like. This all starts with a detailed flow chart that organizes the process necessary to design and specify a safe support system for load handling equipment.

The section of Appendix D that addresses determination of the loads imposed by the equipment includes illustrations that show how outrigger loads or crawler track bearing pressures vary based on the orientation of a crane’s upper. A discussion is also provided to address methods by which these loads to the supports may be reduced when necessary. As with the SC&RA Guide, reliance on software provided by the load handling equipment manufacturer is emphasized.

A lengthy section addresses the very important requirement to determine the allowable ground bearing pressure for the site. Appendix D Section D-5 discusses the use of existing information, such as previously performed geotechnical investigations, the value of physical observations of surface conditions, and the performance of project-specific soil testing. Like the SC&RA Guide, Appendix D also includes a table of presumptive ground bearing pressures for various soil types and consistencies. Last, methods by which soil bearing properties can be improved are discussed.

And now we get to the good part. The actual evaluation of conventional crane mats, whether made of large timbers or of structural steel beams, often presents a challenge to the lift planner who does not have a strong engineering background. Appendix D includes not only a detailed discussion of how mats perform to distribute the support loads to the ground, but also includes graphs by which the load spreading ability of timber and steel mats can be determined. The timber mat curves are based on the species of wood commonly used for mat construction in the United States and Canada. The steel mat curves are based on a range of section properties (that is, the section modulus of the beams), as noted on the graphs. The calculation method used to generate these graphs are as developed in the Mobile Crane Support Handbook. Example problems illustrate the use of these graphs.

ASME P30.1-2024 Planning for Load Handling Activities has completed the required ANSI Public Review process and is now being prepared for publication. This new edition should be available in late 2024 or early 2025.

And that’s it. The industry now has (or soon will have) two new tools for the evaluation of support for load handling equipment for those engaged in lift planning and lift management. The SC&RA Guide to Outrigger Pad Materials, Selection and Usage and ASME P30.1-2024 Planning for Load Handling Activities, Appendix D “Planning for LHE Foundation and Support” provide complementary guidance and recommendations for equipment support and should be in the libraries of all those working with mobile load handling equipment.

ABOUT THE AUTHOR

David Duerr, P.E. (ret.), president of 2DM Associates, Inc., entered the rigging industry on November 8, 1974 (50 years ago this month) in the employ of Hoffman International and has since worked for VSL Corporation, Williams Crane & Rigging, and McDermott International. He founded 2DM Associates in 1986. Duerr is the author of the Mobile Crane Support Handbook, a definitive guide to the engineering of support systems for mobile cranes, and Telescopic Hydraulic Gantry Systems, the only comprehensive text on the use of hydraulic gantry systems. He currently serves as a Contributing Member on the ASME P30 Committee and provided an independent review of the SC&RA Guide to Outrigger Pad Materials, Selection and Usage.