Tower Crane Terms and Definitions per ISO 4306

GB/T 6974.3-2008 is Part 3 of the GB/T 6974 crane terminology series, specifically standardizing the vocabulary used for tower cranes. A unified terminology system is fundamental to the design, manufacturing, operation, and management of tower cranes. This article provides a systematic review of the core terms defined in the standard.

Standard Scope and Tower Crane Terminology

GB/T 6974.3-2008 is the third part of the GB/T 6974 "Cranes — Vocabulary" series, dedicated to the standardization of tower crane terminology. Due to their distinctive structural configuration — tower mast, jib, balance arm, tower head, and slewing bearing — tower cranes have developed a specialized terminology system of their own. The standard covers approximately 150 crane-specific terms, organized in the following sequence: crane types → structural components → mechanism systems → safety devices → performance parameters → installation devices → operational terms. Standardized terminology is critical for accurate communication across design, manufacturing, erection, and operation. For example, precise definitions of "free-standing height" and "anchored height" directly influence foundation design and safe use.

Tower Crane Type Classifications

The standard clearly defines the terminology for each tower crane configuration. A tower crane is a jib crane with the jib mounted on the upper part of the tower mast, capable of a full 360° rotation via the slewing mechanism. By jib type, tower cranes are classified as: trolley luffing tower crane (commonly referred to as a "trolley tower crane") — where a trolley travels along a horizontal jib to change the working radius; and luffing jib tower crane (commonly referred to as a "luffing tower crane") — where the working radius is changed by altering the jib angle. By mounting type, the standard defines: fast-erecting tower crane — a crane that can be erected and folded quickly using its own mechanisms, typically transported on a trailer; anchored tower crane — a crane whose mast is connected to the building structure via tie-in struts, allowing it to reach construction height; and climbing tower crane — a crane installed inside an elevator shaft or dedicated hoistway within the building, climbing incrementally as the structure rises.

Structural Component Terminology

The standard defines the terms for the main structural components of a tower crane. The tower mast standard section is the basic modular unit of the mast, a welded lattice structure with a square cross-section, where the main chord members are angle steel or square steel tube; adjacent sections are joined with high-strength bolts or pins. The climbing section is a special mast section used during the climbing and adding sections process to increase tower height, equipped with internal climbing steps and pawl mechanisms. The rotating mast top is the portion of the mast above the slewing bearing that connects the jib and balance arm, rotating with the upper structure. The tower head is the tapered structural component at the top of the mast that anchors the jib tie bars and balance arm tie bars, bearing the tensile forces from both. The jib (boom) is the horizontal lattice structure of a trolley luffing tower crane, typically triangular or rectangular in cross-section, connected to the tower head via tie bars. The balance arm is a steel structure that carries the counterweights to balance the load moment; it is typically much shorter than the jib. Ballast refers to concrete or cast-iron blocks placed at the base of the mast to enhance the crane's overall stability.

Mechanism and Safety Device Terminology

The standard standardizes the terminology for tower crane mechanisms and safety devices. The hoisting mechanism is the lifting drive system mounted on the balance arm, comprising an electric motor, reducer, drum, and brake. The slewing mechanism drives the 360° rotation of the upper structure through the combination of a slewing drive unit (motor + reducer + pinion) and a large ring gear. The luffing mechanism is either a trolley luffing system (a winch pulls the trolley along the jib) or a luffing jib system (hydraulic cylinders or a winch change the jib angle). The climbing mechanism is a hydraulic-cylinder-driven system for adding mast sections to increase tower height. The load moment limiter (LML) is a safety device that integrates lifting capacity and radius signals to prevent the crane from exceeding its rated lifting moment. The height limit switch cuts power to the hoisting mechanism when the hook reaches its highest permitted position. The radius limit switch cuts power to the luffing mechanism when the trolley reaches the end of the jib or when the luffing jib reaches its limit angle. An anemometer measures real-time wind speed and triggers an alarm when the wind exceeds the safe threshold.

Performance Parameter Terminology

The standard provides precise definitions for key tower crane performance parameters. The rated lifting moment is the product of the lifting capacity and the corresponding working radius (expressed in kN·m) and is the primary specification parameter for a tower crane (e.g., QTZ80 indicates a rated lifting moment of 800 kN·m). Free-standing height is the maximum height a tower crane can reach without tie-in struts. Maximum anchored height is the maximum height achievable with tie-in struts installed (typically 5 to 10 times the free-standing height). Maximum radius is the greatest working radius the jib can reach (for a trolley luffing tower crane, this equals the overall jib length). Tip load is the rated lifting capacity at maximum radius. Maximum lifting capacity is the highest rated lifting capacity across the entire radius range. Free height (for fast-erecting tower cranes) is the maximum height at which the crane remains stable without any additional support. Kelude adopts the standard terminology specified in GB/T 6974.3 across its technical exchange, product documentation, and operator training to ensure seamless communication within the industry.

Tower Crane Terminology Comparison Table

The comparison table below outlines the core parameter configurations for tower crane terminology, serving as a reference for equipment selection and operational staff.

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