Crane Design Terminology: A Beginner's Guide to Essential Terms

Crane design terminology forms the basis for reading engineering drawings, performing design calculations, and communicating technical proposals. This guide introduces common terms covering crane parameters, duty classes, metal structures, loads, and performance indicators.

Key Crane Design Terminology: Parameters and Duty Classes

Crane mechanism parameters describe the operating performance of lifting machinery and provide a basis for design and equipment selection. A crane duty class considers the utilization of lifting capacity and time, as well as the number of working cycles.

1. Rated Lifting Capacity Gn

Rated lifting capacity is the total weight of the load or material that a crane can lift, together with detachable lifting attachments (excluding container spreaders) or accessories such as grabs, electromagnetic lifting devices, and lifting beams. For variable-radius cranes, such as tower cranes, truck cranes, and portal cranes, rated lifting capacity changes with the working radius. The nominal rated lifting capacity is the maximum rated capacity permitted under safe working conditions at the minimum radius.

In ordinary usage, “lifting capacity” generally means rated lifting capacity.

To support series production and standardization, a rated-capacity series standard has been established (Table 1-1). The source cites GB783-87 and gives the unit as t. For newly designed lifting machinery, the rated lifting capacity of the crane and auxiliary hoisting mechanism should conform to the standard series values. Equipment with special performance should also conform to, or remain as close as possible to, the standard series values.

2. Span S

For a bridge crane, span is the horizontal distance between the centerlines of the crane's bridge-travel rails. It is represented by S, although L was commonly used in the past, and is measured in metres (m). Electric bridge crane spans have a national standard series (source Table 1-2). Figure 1-1 illustrates crane span. The span of a bridge crane depends on the building span Sc; in the span series, the increment is generally 3 m.

Figure 1-1 includes (a) crane span and (b) the span of a crane with two rails.

3. Gauge K

Gauge, also called wheel track, is defined as follows:

• For a trolley, it is the distance between the centerlines of the trolley rails.
• For a jib-type crane, it is the distance between the rail centerlines or between the centerlines of the running-wheel treads.

4. Wheelbase B

Wheelbase, also called axle spacing, is the distance between the support centerlines of the crane or trolley along the longitudinal travel direction. The measurement of wheelbase B depends on the arrangement of the supporting wheels.

5. Lifting Height H, Lowering Depth h, and Lifting Range D

The source defines the relevant vertical distances using the highest and lowest working positions of the lifting attachment and gives:

D = H + h

Where there is no lowering depth, lifting range D equals lifting height H. Lifting height and lowering depth are measured using the centre of the hook bowl as the reference point. For other lifting attachments, such as grabs, the lowest point in the closed position is used as the reference.

6. Mechanism Operating Speeds

Mechanism operating speeds vary according to the crane mechanism:

• Lifting and lowering speed Vn: the vertical displacement speed of the rated load in a steady operating state, measured in m/min.
• Crane or bridge-travel speed VR': the travel speed of the crane carrying its rated load on a horizontal surface or rail in a steady operating state, measured in m/min.
• Trolley-travel speed Vt': the speed of a trolley carrying its rated load along a horizontal rail in a steady operating state, measured in m/min.

7. Wheel Load

Wheel load is the maximum vertical pressure exerted on the crane wheels by the bridge self-weight, together with the trolley self-weight and rated lifting capacity when the trolley is at its limiting position. It is an important basis for the design of the travel mechanism and rails.

8. Duty Class

Crane duty class is divided according to utilization class—the total number of working cycles over the design life—and load state. It indicates how demanding the crane's work is, including how busy it is over time and how often it handles full loads.

The source divides duty classes into A1–A8. Its approximate comparison is A1–A4 for light duty, A5–A6 for medium duty, A7 for heavy duty, and A8 for extra-heavy duty. Source Table 1-4 lists examples of crane duty classes.

Common Terms for Crane Metal Structures and Components

1. Crane Metal Structure

A crane metal structure, also called a crane steel structure, is a structure capable of carrying the various loads of a crane. It consists of steel plates and sections formed from metal materials and assembled in a defined structural arrangement using welding, riveting, bolting, and other connection methods.

Crane metal structures consist of load-bearing members, non-load-bearing members, and connection sections. Main girders, end girders, and legs are load-bearing members and require strength, stiffness, and stability calculations. Walkways, railings, and ladders are non-load-bearing members; the source states that they do not require strength, stiffness, and stability calculations, but that safety, ease of use, and ergonomics should be considered. Connections mainly use welding and bolting, while riveting is now rarely used.

2. Typical Metal-Structure Types

Typical types include bridge structures, gantries, towers, and jibs. Crane metal structures are made from members, plates, and sections that form basic members such as main girders, end girders, and legs. Different members form basic crane structures such as bridges, gantries, towers, and jibs.

3. Common Structural and Component Terms

• Main girder: The primary load-bearing member of an overhead or gantry crane, carrying the lifting load.
• Leg: A support member of a gantry crane or truck crane that helps maintain overall operating stability.
• Jib: A fixed or telescopic arm on a jib-type crane used for lifting loads and adjusting the working radius.
• Hoisting mechanism: The mechanism that raises and lowers loads vertically, consisting of a motor, gearbox, drum, brake, hook, and other components.
• Travel mechanism: The mechanism that moves the complete crane or trolley; it may be rail-mounted or non-rail-mounted.
• Slewing mechanism: The mechanism that rotates a jib around a vertical axis, commonly used on truck cranes, crawler cranes, and tower cranes.
• Brake: A braking device used for stopping, speed limiting, and safety holding.
• Limit switch: A safety device that limits lifting height, travel distance, or slewing angle to prevent overtravel.
• Overload limiter: A safety device that automatically cuts lifting power when the lifted load exceeds the rated value.

Load and Force Terms

1. Regular Loads

Regular loads occur frequently during normal crane operation. They include gravity loads, inertial loads produced when driving or braking accelerates or decelerates the crane, and loads caused by displacement or deformation of the crane steel structure. These loads should be considered when calculating and checking against strength failure, elastic instability, and fatigue failure.

Regular loads include:

• Self-weight load PG: The gravitational force of the crane's steel structure, mechanisms, electrical equipment, and other masses.
• Rated lifting load PQ: The gravitational force of the total lifted mass when lifting the rated capacity. When the lifting capacity is large, the weight of the lifting attachment and wire rope should be included.
• Horizontal travel inertial load PH: The horizontal inertial force produced by the crane's or trolley's own mass and lifted mass when travelling longitudinally or transversely and accelerating or braking in a horizontal plane.

2. Accidental Loads

Accidental loads are loads that do not occur frequently during normal operation but may arise occasionally. They mainly include the following types:

• Horizontal lateral load from skewing Ps: A load caused by the guiding reaction at a guiding device, such as a wheel flange or horizontal guide wheel, when the crane or trolley skews during longitudinal or transverse travel.
• Grade load Pp: The resistance experienced when the crane or trolley travels uphill along its running rail. The source wording “along s running rail” appears to contain a textual error and requires technical review.
• In-service wind load Pw: The maximum wind force that an outdoor crane should withstand while operating. The source also mentions ice, snow, and temperature loads.

3. Special Loads

Special loads are loads that occur under exceptional conditions when the crane is not operating normally or is out of service. They mainly include the following types:

• Collision load Pc: A load generated when two adjacent cranes on the same rail collide, or when a crane collides with a buffer stop at the end of the rail.
• Horizontal overturning load Psl: For example, in a stacker crane, an object or load-handling device moving inside a rigid lifting guide frame, or the lower end of the rigid guide frame, may collide with an obstacle and generate a horizontal force that tends to overturn the crane or trolley.
• Seismic load PE: A load caused by an earthquake and acting on a hoist-type crane.
• Out-of-service wind load: The maximum wind force that the crane can withstand while out of service, measured in N.

Other loads may occur in specific situations, such as process loads. Fatigue load is a cyclic alternating load experienced by the structure during repeated crane operation and affects equipment service life.

Performance-Indicator Terms

• Strength, including fatigue-strength verification: The ability of a member to avoid failure under external forces. Strength includes tensile and compressive strength, bending strength, shear strength, and bearing or crushing strength.
• Stiffness: The ability to limit member deformation under external forces. It includes static stiffness in the vertical and horizontal directions, as well as dynamic stiffness related to use.
• Stability: The ability to resist loss of stability under external forces. It includes overall anti-overturning capacity, global member stability, and local stability.
• Safety factor: The safety margin reserved in design, defined here as the ratio of structural load-bearing capacity to actual loading. It must meet applicable code requirements.
• Allowable stress: The maximum stress value that the applicable code permits the structural material to withstand.

Summary

These terms are basic and frequently used in crane design. They support drawing preparation, parameter calculations, technical proposal discussions, and further study of structural design and code application.

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