True Steel Crane and Rigging offers all terrain, crawler crane and rough terrain machines with a wide range of capabilities to handle your project needs, in Oklahoma City and surrounding areas. Our largest fleet is in the all terrain category, however, we now offer the Liebherr LR 1500 crawler crane from our immediate fleet and have the resources to acquire other cranes as needed . Contact True Steel today for any questions you may have and we'll work with you to match the correct crane for your requirements.
How important is rigging in crane operations?
There are many variables that contribute to a successful lift involving crane operation. The process of rigging is among the most important of these tasks. At the most basic level, the rigger is responsible for using ropes and cables for attaching to the load. Depending on the type of load, an assessment will be made to determine what type of rigging method should be used. This method is based upon slings used in a certain hitch or configuration for lifting a specific type of load. As with any skill or occupation, the riggers ability to perform all the required tasks depends upon the level of training they’ve received and the extent of their knowledge. Of further importance are the skills they’ve acquired through experience and education, overall ability to utilize the proper rigging equipment and to perform the necessary inspections.
Basic skills consist of identifying the components of the rigging system to ensure clear and effective communication takes place between personnel. A rigger must be able to perform inspection of slings and hardware components to confirm there is no visible damage that could interfere with the lift or pull. Knowledge in attaching the rigging and associated hardware with a foundational knowledge of hitch configurations, specifications, capacities and basic knots is also necessary. A rigger must also be familiar with and able to utilize applicable signal operations to communicate with the crane operator and other involved personnel. Finally, a rigger will be aware of the surroundings, recognize potential hazards that could impact the crane operation and be able to confidently communicate concerns with the crew and agree upon a safe way to advance.
Advanced Rigging Skills
More highly experienced riggers have other skills as well. Inspection of lift points where the rigging hardware and slings will attach are important to determine that there is no visible damage and confirm to be a viable option for a lifting point. They will be able to estimate the weight of a given load and determine the center of gravity of a load and therefore be able to determine lift points and rigging configurations. An advanced rigger will be able to understand dynamic loads, namely, how a load will respond when it begins to move during the hoisting and lifting process and what it may do given certain conditions. They will also be able to attach rigging with the correct hitch configurations based upon load angle factors, rigging capacities, overall specifications and load integrity. Finally, advanced level riggers will have a high working knowledge of all hoisting equipment including winches, jacks, turnbuckles, shackles, master links, lifting bags and similar rigging components.
Rigging System Components
*All sling types will have a sticker or tag with the rated sling capacity under various rigging configurations. The lifting capacity is based upon the sling diameter, the type of material and how it is attached to the load being hoisted. Materials being lifted often have sharp edges and corners that can cause damage to synthetic slings. A chain or wire rope sling may alternately cause damage to a fragile load. In either situation, the rigger must be aware of these circumstances and use protective sleeves or pads for protection from damage.
The basket hitch utilizes 2 slings, in either a single or dual sling configuration, and the resulting load balance is equally distributed between the 2 legs of the same sling. A basket hitch has twice the lifting capacity of a basic vertical hitch when the vertical legs are within a 5 degree variance of a 90 degree vertical angle. Wire and chain material slings must meet a load diameter to sling diameter ratio of 25/1 and 6/1 respectively for the 2x lifting capacity. The load diameter to sling diameter ratio is not applicable to synthetic slings.
Caution must be exercised when considering a single sling basket hitch. The load must be balanced and this is sometimes difficult to achieve unless using two or more slings, with a spreader bar, to achieve this proper hitch rigging configuration. Per the above diagram, as the sling vertical is reduced to less than 90 degrees the amount of lifting capacity is reduced as well.
As a general rule, 30 degrees reduces from 2x to 1.7x capacity, 45 degrees from 2x to 1.4x capacity and 60 degrees to 1x capacity making it equal to that of a basic vertical hitch. This is important in crane and rigging operations not only for safety but also for efficiency. A knowledgeable and highly skilled rigger will have a detailed understanding of these principles and be able to choose the rigging components and hitch configurations that will result in the safest lift while working at the highest efficiency possible.
Variations of the basket hitch include the double basket hitch and the double wrap basket hitch.
As touched on in the above paragraph, the double basket hitch with a spreader bar is a useful option for utilizing the basket hitch configuration while addressing load stability. The double wrap basket hitch, as shown in the diagram, is wrapped twice around the load. This increases surface contact, allows greater compression of material and overall is a suitable rigging method for loose materials and bundles of rod or pipe.
The vertical hitch is the most basic rigging configuration and utilizes the specified lifting capacity of the lift sling. As the image shows, one end of the sling is attached to the crane hook while the other end is attached to an anchored point on the load.
When lifting a load with a single sling vertical hitch it is important to have a tag line attached to provide additional control to the load to reduce any rotation or twisting while the object is in motion.
The choker hitch is often used when load control is a concern. The sling is used to snug the load tight. One end of the sling is wrapped around the load while the eye of the other end is threaded through the opposite eye and onto the crane hook per the above diagram. The place of concern is at the choke point and due to the stress occurred with this hitch the lifting capacity is reduced to approximately 75% of the slings capacity in a vertical hitch configuration. As the choke angle increases the lifting capacity continues to decrease and can reach as low as 40% of specified capacity. Choker hitches can be used in a double sling situation with a spreader bar and can also be double wrapped for greater surface contact and increased load control.
Planning a lift
Many factors must be considered prior to rigging a load and making a lift.
- Mapping the load path from the pick point to the final resting destination.
- Potential obstacles
- Identifying personnel and active work sites impacted by the pick
- Determining the weight of the load
- Ground conditions and capacity to support the crane weight and outriggers
- Weather conditions & lighting
- Knowing the radius of the lift
- Full communication between the crane operator, rigger and authorized personnel
- Keep tag lines clear of the body
- Ensure that a suspended load is always attended
- Stay required distance from all power lines
- Never standing or work underneath a suspended load
An experienced crane operator and skilled rigger make a safe and productive team that results in successful lifts and satisfied customers. We at True Steel genuinely value our employees and seek to provide a quality service to our customers. Building solid business relationships, offering fair pricing with quality equipment and proven, consistent dependability are the trademarks of our company. We look forward to answering your questions and offering solutions for all your crane, rigging, and equipment rental needs.