Mobiling

Find out how to position for a lift, communicate with crane operators and work on changing ground conditions and side slopes.

Preparing for a lift

Unlike slewing mobile cranes, articulated cranes do not have outriggers. Crane stability is from the crane tyres. Crane rated capacities on tyres depend on:

• tyre capacity
• condition of the tyres
• tyre air pressure
• ground condition.

All tyres must be checked and inflated to the recommended pressure before lifting.

Ground shall be examined to understand ground conditions. The crane shall be set up on a firm, level and uniform surface. The crane operator shall read and fully understand the manufacturer’s instructions for site conditions and lifting conditions before conducting the lift.

Positioning

As a dogger/rigger, your position can help keep you safe. You should consider the following:

• Always position yourself so you can be seen by the crane operator.
• Do not position yourself in the travel path of a crane tyre or track. This is to prevent risk of injury if you trip or fall down.
• Do not position yourself between the load and the crane. This is to prevent crush.
• If site conditions allow, you should always position yourself on the high side above the crane and the load. This is to avoid being crushed.

Example of working with tag lines

During a lift

During the lifting operation, slewing mobile cranes usually lift the load from a fixed location. Articulated cranes often travel on sites with their load.

When operating the crane to lift and carry a load, the crane operator shall follow the manufacturer’s instructions.

All operating conditions should be considered. These include:

• the supporting surface
• pendulum action of the load
• jerking or sudden stops of the load
• other factors affecting stability. Rated lifting capacities are based on freely suspended loads with the crane on a firm, level (maximum 1% slope / 0.6 degrees) and uniform surface.

Directing the crane operator

When mobiling with a load, the dogger/rigger should direct the crane operator in the most direct path. Consider the following:

• Load swing can occur due to inertia created by travelling or by sloping ground (up, down or sideways).
• Travel path should be on firm level ground, free from potholes and soft or rough ground. This is to avoid potential load swing.
• When travelling over potholes and soft or rough ground, the same precautions should be used as if the crane is travelling on side slope.
• Maintain enough clearance between the load and the ground. This is to account for vertical load movement due to uneven ground.

Changing ground conditions

Crane operators shall take into consideration changing ground conditions. Ground conditions can change when travelling while carrying load. Changing ground conditions (like uneven road surface or potholes) will cause a reduction in crane rated capacity.

Images below are examples of crane stability problems caused by changing ground conditions when travelling on road.

These conditions create a side slope condition. The rated capacity of the crane reduces to ensure the crane remains stable. Manufacturer’s instructions should be followed for operating on a side slope.

Crane stability example 1

Crane stability example 2

Crane stability problems

Side slope

Lifting a load on a side slope induces a side load as the load swings down the slope. This affects the tipping line of the crane.

Crane operators should follow the deration percentage specified on the deration load chart. This is provided by the crane manufacturer. Use this chart to calculate the appropriate crane rated capacity for the lifting job.

The combination of crane articulation and ground side slope can cause serious problems with crane stabilization and crane travelling path analysis.

Here are some ways to avoid these issues:

• de-rating calculation of the crane lifting capacity should be done during the work-planning phase
• crane side slope indicators should be correctly interpreted
• a crane side-slope chart should be used.

videocam 40:53

Operating on a side slope

Articulated cranes

Slewing mobile cranes can perform lifting operations with a slewing angle of 360°.

Articulated cranes’ operation is only permitted through the crane articulation range. This is typically up to 40°.

Most articulated cranes have a reduced rated capacity above 10° articulation. During crane articulation, the crane’s centre of gravity gets closer to the axis of rotation. This reduces the movement from the crane counterweight.

Here's an example of operating on a side slope in articulated configuration:

Operating on a side slope in articulated configuration

In the example above, the crane tipping line changed to the side wheel line. The distance between crane weight and tipping line was greatly reduced, while the distance between load and tipping line increased.

Travelling on a slope

Travelling forward down a slope increases the working radius of the crane. This is due to the load swinging. Once the load settles vertically to the boom tip, it will be at a greater radius than if on level ground.

The preferred method of travelling is to direct a crane operator to travel backwards down a slope.

Travelling backwards down a slope will have the same effect as travelling forwards up a slope. The load swings towards the crane and settles vertically to the boom tip at a radius less than if on level ground.

When travelling backwards make sure there is enough space between the crane and the load. This is to prevent contact.

Working radius example 1

Working radius example 2

Side loads on the boom

Operating a crane on a side slope creates side loading on the boom. The side loads on the boom caused by working on a slope can result in boom collapse.

Force

Effects of non-vertical lifting

Side slope of a boom due to operating with the outriggers out of level (from ground or hydraulic settling) has a similar effect on the side loading of the boom that travelling on a side slope has.

The side loads on the boom caused by swinging the load can be minimised with smooth slewing operation.

Side loads on the boom due to inertia

Never pull a load sideways. Lifting non-vertically can provide the same side loading on the boom as operating on a side slope.

Side load at the boom of jib head