Introduction

Knowing the crane load capacity is critical for safely operating a crane without lowering the load or damaging the machine. This number must be recalculated each time a crane is used since it varies depending on the location of the hoist and the lift radius, among other factors. 

Crane load capacity is one of the essential considerations in any construction project. The crane load capacity is determined to ensure a healthy working environment and enable the project to move forward smoothly. For the load chart, you will need to locate the Crane Capacity index. When considering crane installation, one needs to also look for the capacity of the crane to avoid mishaps and risks related to the overloading of crane installation.

Physics of a crane

A crane is controlled from an outrigger foundation, a movable and rotating platform that can be several metres high. The boom arm stretches upward and outward at a set angle for the entirety of its length, with an apparatus at the end that raises and moves the load. There are no horizontal forces since the load (mass times gravity g, or 9.8 m/s2) is lifted vertically (windy days play havoc for crane operators).

Instead, when the crane's upward force precisely balances the weight of the load, a tension T (force per unit length) is preserved in the rope. The load moves upward when the motor drives T above this point, assuming the cable is strong enough to withstand the power.

The geometry of a crane

The crane boom, the field, and the vertical cable form a right triangle when viewed from one side. The boom arm is the hypotenuse, the distance r from the outrigger base to the load is the long arm of the triangle, and the vertical height h of the boom "tip" above the ground is the short arm of the hypotenuse. For calculating lifting power, the effective radius r must account for the outrigger base and is thus slightly shortened; that is, it does not begin at the motor, where the tip of this de facto right triangle lies.

Factors affecting the capacity of the crane installation

Before considering crane installation, it is important to determine the factors that affect the crane’s capacity.

1. When the main hoist line is reeved to one side of the boom tip, unbalanced rope reeving occurs. The crane's rated capacity is reduced as a result of this situation, as the boom twists. Only when the boom tip is symmetrically rigged can full chart ratings be applied. The boom twist is reduced in single-line reeving when the hoist line runs along with the centre sheave or the sheave beside the boom's centerline. The boom twist will be reduced on multi-part reeved systems if the line sections are equally distributed on either side of the boom centerline.
2. The ground surface must have sufficient stability and bearing power to accommodate all of the crane's loads. When lifting near houses, mainly those new and have uncompacted backfill, trenches, or areas where water mains, sewer pipes, or steam lines are buried, extreme caution should be used. Depending on the working conditions and the quadrant(s) of operation, a crane installation exerts varying pressures on its load-bearing surfaces. The machine's total weight is spread over the entire area of the drive tracks or all outrigger supports, resulting in the minimum bearing pressure.
3. Only openly suspended loads and loads picked up directly under the boom tip are subject to the load chart ratings. Sideloading happens when the load is on either side of the boom tip, reducing the crane's power. One of the most common causes of boom failure is side loading, which usually happens without notice. When a load is dragged or pulled sideways, when the load begins swinging rapidly, when the crane installation is not level or exposed to high wind speeds, side loading may occur.
4. High wind speeds reduce a mobile crane's capacity by increasing side loading on the boom and load radius and reducing tipping (both forward and backward) capacity. Furthermore, lifting in windy conditions makes it more difficult to control the load.
5. The crane installation load chart scores assume that it is completely level in all directions. Sideloading of the boom occurs when a crane is not level, lowering the rated power. Initial levelling should be done with the crane's target level; however, a carpenter's level should be used for vital lifts.

How to calculate the capacity of the crane?

Finding the crane's precise lifting capacity is not difficult; in fact, it is straightforward. 

1. Load chart- Each crane installation comes with a load chart detailing the crane's capabilities, including its features and how its lift ability varies depending on distance and angle. Failure to review a crane load chart before renting or hiring a crane for a particular job could leave you with too much or too little power for your job, similar to the adage "if you don't prepare, you plan to fail." The crane map must be consulted before a crane is leased, shipped, hired, or purchased. All must interpret a crane map, from the crane operator to the work managers and even the salesmen. The pointers to keep in mind on how to read the load chart.

• The measurements of the crane are depicted in the chart. It contains information about how to operate with the outriggers extended and transport weight and steering measurements. Since the lifting capacity varies depending on whether the outriggers are extended, knowing this information is particularly important if the crane operates in a confined space. The transport weight decides the trailer to use, load the crane onto the trailer, the path to take, and what permits are required to get it to the Jobsite.
• The crane installation unique lift is indicated by the legend on the chart. The feet on the left axis indicate the radius (or distance) from the centre pin to the centre of the load when graphing the lift. Often determine the crane's maximum capacity by the shortest lift, generally over the crane's back with the outriggers fully extended.
• Lift charts are often used in range diagrams to show how much boom length is needed to lift loads at any distance or height. When using a luffing or fixed crane jib, the lift angle refers to the highest lift. The crane's pick and carry referred to as "crane in motion." The load map depicts the total weight picked up while stationary at a 360-degree angle. Both the rolling load at a zero-degree angle and the total weight when moving can be supported by the total weight.

2. You will need to know the machine's geometry to get an accurate crane installation load estimate. The boom, hoist, and field, which form a triangle, are all elements that should be calculated. You can get an accurate crane load estimate by measuring the dimensions of this triangle.

(r)(hC)/100 is the standard formula for calculating maximum crane power. 

Where

R- radius between the load and the ground

hC = Capacity multiplied by lifting height

Conclusion

The secret to a secure and efficient construction job is to understand your equipment. And one of the most important things that need to be considered is the crane’s capacity and how it can be calculated to ensure efficient working of the crane installation. And if you are planning a crane installation in UAE, then these pointers might come in handy.