What crane to use?
How to determine the right crane for your lift. Failure to calculate a cranes lifting capacity can result in disastrous and onerous consequences including damage to the crane, surrounding infrastructure or even death.
Lift Safety is Crane Hire SA’s top priority
How to determine the right
crane for your job
Crane size matters… On any project and for every lift, the crane capacity and suitability needs to be calculated. At Crane Hire SA we have a variety of cranes ranging from 8 tons to 220 tons for hire and to ensure the success of your project, we have the knowledge to ensure that every lift is a safe lift. With our experience the best crane that suits your type and size of work is a priority. Our priority is always completing your project safely and efficiently, on time at the best possible price point.
What size of crane do I need?
Different jobs require different sizes of cranes. With this in mind, one should always consider several factors before settling for the crane to hire. Some of these factors include the accessibility of the site, the weight of the load you need to lift and ground conditions, and the radius as well as the height required to lift. These steps are necessary to take before settling for the crane size:
- Confirm the total weight of the load. Considering an engineering profession in this is key since some loads which are oddly shaped or do not have hook attachments cannot be lifted by any crane and will require highly skilled and knowledagable riggers.
- Determine if the counterweight will be obstructed by any barriers when swinging.
- Calculating the approximate distance that the crane boom needs to reach-that is the distance from the middle of the slew ring to the point where the load needs to land.
- Addressing any clearance concern’s-which include determining if there are any height obstructions and the ceiling height if operating inside a building. If any obstructions always verify if the crane can work around those obstructions or if they need to be eliminated.
- Ensure the ground can balance the crane –this may require some specialist to do the testing.
- Determine how the crane will access and leave the site. This is important because some of the cranes are assembled on the site.
- Confirming the hook height required with lifting equipment.
Below are images of cranes that were not suitable for the job and resulted is serious damage to property, the crane and potentially Life.
DETERMINING THE CRANE LIFTING CAPACITY
Determining the crane lifting capacity is important before hiring a crane or crane truck. Projects may look similar but they all may require a different crane size with different lifting capacities.
Understanding the crane lifting capacity helps prevent site incidents, and downtime on the project, and contributes highly to ensuring a safe working environment for those on-site. Some of the factors that determine a crane’s lifting capacity are:
Ground conditions: The ground should be stable enough and have a good bearing capacity to support all the load being lifted by the crane. The pressure exerted by the crane depends on the operating conditions and the quadrants of operation. When operating on ground with newly constructed buildings with uncompacted backfill or where underground services like sewer pipes and water pipes proper care should be taken.
Crane configuration: Crane operators should always use the appropriate load chart and ensure the configuration of the crane is correct before commencing any work. This will include but is not limited to knowing the type and length of the boom, the counterweights which are being used, the type of the jib and how to erect it, the configuration of the host reeving, and the wire rope size and grade. For example a 100 Ton crane with additional counterweights can achieve the same maximum lift as a larger crane but experienced and knowledgable riggers would determine the best mobile crane for the job.
Weather conditions: working with cranes in cold temperatures affects crane operations negatively. This is because this weather reduces the crane’s precision and strength thus affecting the total lift capacity. It also affects visibility and maneuverability.
The height of the lift: when the weight is lifted in the air factors such as gravity and acceleration come to play. As the height of the lift is increased these factors get more complicated thus reducing the crane’s lifting capacity.
Other factors include the distance to the load to be lifted and the structural configuration.
Calculating the crane lifting capacity
Determining the crane lifting capacity helps in protecting the crane as well as preventing the load from dropping. At Crane Hire South Africa, we provide some of the best crane lifting services available in South Africa. Our Experience, red seal riggers and administration staff ensure that all cranes are certified and hold the necessary load test certificates. Some of the ways we use to determine the crane lifting capacity entail:
Consulting a professional: if the crane operator is not familiar with the load calculations irrespective of relying on the lifting guide they should consult a professional. This is because for a crane to lift a load several factors come to play and one single mistake can lead to serious site accidents and costly crane repair.
Use of load chart: All mobile cranes and cranes mounted on trucks cranes come with a convenient Crane load chart that allows one to estimate the crane’s lifting capacity without extensive calculations. It is the responsibility of every operator to check if the machine comes with a guide and refer to it before each job commences. Understanding your crane plays a big role in ensuring site safety and the success of the project.
Measuring geometric components: the crane lifting capacity is highly dependable on the geometry of the machine. Elements that need to be measured include the hoist, the boom, and the ground. When all these aspects are measured getting the crane lifting capacity become easy. The standard calculation of the maximum crane capacity is, (r)(hC)/100 where r is the radius between the ground and the load, and hc is the lifting height multiplied by the capacity.
Understanding the crane: before beginning any calculation understanding the type of crane and configuration is important. This is because these factors contribute highly when it comes to the machine’s lifting capacity as well as stability.
Below are the load chart and Dimensions for a 40 Ton Terex mobile crane These images indicate the load that can be lifted at different radius with and without a jib, as well as the space required for the crane to gain accessThe size of the footprint with outriggers deployed is shown in image 2.
Crane lifting capacity equation:
Crane outriggers are crucial when it comes to the lifting capacity of the crane. This is because they are responsible for providing a solid platform for the crane’s safe operation and efficient use. Most of the cranes’ hazards are associated with the outriggers not being properly set therefore the operators and workers should always be aware of how important placement and use of outriggers contribute highly to the crane performance. It is therefore important for every operator to have an outrigger safety checklist which should include:
Ground inspection: The condition of the ground the outrigger is to sit on should always be the first concern. Cranes exert hundreds of thousands of forces on the round hence if in any case, these forces exceed the strength of the ground the crane is likely to damage the surface, topple, or sink.
Maximum outrigger reaction force: manufacturers often provide outrigger force calculations which should always be compared to the ground bearing capacity to determine if the crane can lift the expected weight or if more outrigger pads need to be added.
Inspection and positioning of outrigger pads: The pads provide a firm surface for the lift to be performed safely. One should always ensure the pads sit solidly on the ground and that they are smooth and free from any debris. They should also not be smaller than the outriggers’ feet.
Surroundings inspection: where the triggers are set in a busy area to avoid any accident the flow of traffic should be redirected or the position of the crane should be adjusted.
Counterweights are one of the most essential components of a crane. They can either be built into the body of the crane or applied additionally. Most of the crane counterweights are made of cast iron, which because of its density provides enough weight to balance out even when the load to be lifted is very heavy. Some counterweights are made of concrete or lead. To prevent site accidents engineers design counterweights for a specific type of crane putting into consideration the weight, size, and shape of the weight to be lifted.
Importance of counterweights
A Counterweights main role is to ensure the crane remains stable and it does not fall over when lifting an item. Without the counterweights on a crane, it would not be able to lift its capacity. Designing it properly and ensuring it possesses the right shape prevents the crane from toppling over in the direction of the load.
Calculating the proper counterweight
Mathematical errors are the main causes of cranes toppling. To prevent this it is important to have the correct weight and size before manufacturing. A mathematical formula is applied to ensure the weight of the counterweight is as required. The weight is gotten by multiplying the volume of the material to be used, its density, and the gravitational constant.
Safety measures when using counterweights
To prevent the counterweights from falling out, they should always be reinforced in a way they will not fall at the load-bearing section. Their weight should also not be too heavy for the weight of the boom to avoid the crane from toppling backward. When in use regular inspections should be performed to detect potential accidents.