Interpretation of the GB/T 28757 Standard “Terminology and Definitions for Bridge and Gantry Cranes”
GB/T 28757, “Bridge and Gantry Cranes—Terminology,” is the foundational terminology standard for the crane industry and is administered by the National Technical Committee for Lifting Machinery Standardization (SAC/TC 227). This standard uniformly specifies the core terms and their definitions related to the design, manufacture, inspection, use, and maintenance of overhead and gantry cranes. It applies to general-purpose overhead and gantry cranes with a rated load capacity of 3.2 metric tons or more.
Consistent terminology is the foundation of technical communication in the crane industry. In actual projects, contract disputes, technical misalignments, and installation rework resulting from misunderstandings of terminology are all too common. GB/T 28757 establishes a comprehensive terminology system covering everything from complete machines to individual components, spanning the following six major categories.
I. Terminology for Classifying Complete Machines
| Terminology | Definition | English Equivalent |
|---|---|---|
| Overhead crane | A crane whose bridge is supported directly on elevated rails at both ends by a traveling mechanism | Overhead traveling crane |
| Gantry crane | A crane supported on ground rails or a foundation by legs on both sides | Gantry Crane |
| Electric single girder overhead crane | A bridge crane with an electric hoist as the lifting mechanism and a single main girder | Single-girder overhead crane |
| Electric Double-Girder Crane | A bridge crane with a trolley as the hoisting mechanism and two main girders | Double-girder overhead crane |
| Overhead Crane | Bridge cranes suspended from the roof truss or the lower chord of a load-bearing structure | Underslung crane |
| Metallurgical Cranes | Specialized Gantry Cranes for Metallurgical Processes | Metallurgical Crane |
II. Key Parameter Terminology
- Rated Lifting Capacity (Gn): The maximum allowable lifting capacity of a crane, measured in metric tons (t). This includes the weight of the lifting tackle but excludes the weight of the hook block.
- Span (S): The horizontal distance between the centerlines of the travel rails of a bridge crane, measured in meters (m).
- Lifting Height (H): The vertical distance between the lowest and highest working positions of the lifting device, measured in meters (m).
- Job Level: A classification parameter that comprehensively characterizes the operational characteristics of a crane, determined based on the utilization level (U0–U9) and load condition (Q1–Q4). General-purpose overhead cranes typically use classes A3–A7.
- Operating Speed: Including hoisting speed, trolley travel speed, and gantry travel speed, with units in m/min.
- Work Schedule (S1–S10): According to the motor operating modes specified in IEC 60034-1, hoisting mechanisms typically use S3 (intermittent duty) or S4 (intermittent duty including starting).
III. Terminology for Structural Components
| Terminology | Definition | Common Structural Configurations |
|---|---|---|
| Main Beam | The primary load-bearing members that support the hoisting load and their own weight | Box Girder, Truss Girder, Offset Box Girder |
| End Beam | A component that connects the two ends of the main girder and is linked to the crane travel mechanism | Box-type end beams, forged wheel end beams |
| Small Bike Frame | Frame Structure Supporting the Hoisting Mechanism and Trolley Travel Mechanism | Welded frames, cast trolley frames |
| Support Leg | A vertical or inclined support member in a gantry crane that connects the main girder to the ground track | Rigid legs, flexible legs |
| Driver's Cab | Enclosed or semi-enclosed work spaces for operating cranes | Fixed-type, mobile-type (moves with the cart) |
| Walkway/Railing | Platforms and Safety Barriers for Maintenance and Pedestrian Access | Designed in accordance with GB 4053.3 |
IV. Terminology for Mechanisms and Components
- Hoisting Mechanism: The mechanical assembly that enables the lifting and lowering motion of the lifting device, consisting of a motor, brake, gearbox, drum, wire rope, and hook assembly.
- Trolley Travel Mechanism: The mechanism that drives the trolley along the main girder track typically uses a separate drive system.
- Large Vehicle Travel Mechanism: The mechanism that drives the entire crane along the workshop tracks.
- Reel: A cylindrical component used to wind steel wire ropes for lifting and lowering lifting slings; its diameter is determined in accordance with GB/T 3811.
- Pulley: A wheel-shaped component used to change the direction of a steel wire rope or to form a pulley block.
- Hook Assembly: A lifting assembly consisting of a hook, a crossbeam, pulleys, bearings, and other components.
V. Terminology for Safety Devices
- Load Limiter: A safety device that automatically cuts off the hoisting power source when the load exceeds a preset value. Total error ≤ ±5%.
- Lifting Height Limit Switch: A limit device that prevents lifting gear from exceeding the designed lifting height; an essential safety device.
- Travel Limiter: A device that limits the maximum operating position of large or small vehicles.
- Buffer: A device that absorbs the energy generated when a crane or trolley collides with the end stop on the rail; these are classified as elastic buffers and hydraulic buffers.
- Wind-Resistant and Anti-Slip Device: A device designed to prevent outdoor cranes from sliding along the rails due to wind forces, consisting of rail clamps and anchoring devices.
- Interlock Protection: A safety device that automatically cuts off power to the hoisting mechanisms when the cab door or the access door to the crane is opened.
VI. Terminology for Inspection and Testing
- Type Testing: Comprehensive validation testing to verify whether a product’s design meets the requirements of the standard; this must be performed before a new product enters production or after a standard is updated.
- Factory Testing: Functional and performance verification is conducted on each unit before it leaves the factory.
- Static Load Test: Conducted at 1.25 times the rated load to verify the structural load-bearing capacity and the permanent deformation of the main beam (≤S/2000).
- Dynamic Load Test: Conducted at 1.1 times the rated load to verify the operational functionality of each mechanism and the effectiveness of the safety devices.
- Initial Inspection: Safety performance inspection of equipment after installation and prior to commissioning.
- Periodic Inspection: Safety performance inspections of in-service equipment, conducted in accordance with the intervals specified in TSG Q7015, are generally performed once every two years.
Frequently Asked Questions
Q: What is the difference between the scope of application of GB/T 28757 and that of GB/T 6974.1, “Cranes—Terminology”?
Answer: GB/T 6974.1 is the foundational standard for general terminology applicable to all types of cranes, covering definitions for all categories, including mobile, tower, bridge, and gantry cranes; GB/T 28757 specifically addresses overhead and gantry cranes, supplementing the standard with terminology unique to these types of cranes, such as off-track box girders, flexible legs, and C-type legs. In bridge and gantry crane projects, both standards should be used in conjunction—refer to GB/T 6974.1 for general terminology and GB/T 28757 for terminology specific to bridge and gantry cranes.
Q: What is the difference between operating classes A1–A8 in GB/T 28757 and motor duty types S1–S10?
Answer: The duty class (A1–A8) is a service life classification parameter for complete bridge and gantry cranes specified in GB/T 3811. It is determined comprehensively based on the utilization class (U0–U9) and load condition (Q1–Q4), and is used for selecting the complete crane model and performing structural fatigue calculations. Motor duty classes (S1–S10) are classified according to IEC 60034-1 and are used for verifying motor thermal capacity and matching operating modes. Motors for hoisting mechanisms are typically selected with duty classes S3-40% or S4-30%, while motors for traveling mechanisms are selected with the S1 continuous duty class. These two classification systems serve different purposes and must not be used interchangeably.
Q: How do the definitions of safety device terminology in GB/T 28757 align with the testing requirements in GB 6067.1?
Answer: GB/T 28757 provides standardized terminology (such as ”hoist height limiter” and ”load limiter”), while GB 6067.1, ”Safety Regulations for Lifting Machinery,” specifies the mandatory installation conditions, operational accuracy, and inspection requirements for these devices. For example, GB/T 28757 defines the classification of “buffers” (elastic/hydraulic), while GB 6067.1 stipulates that hydraulic buffers must be used when the impact velocity exceeds 0.7 m/s. Equipment inspections are governed by the safety regulations, while the preparation of technical documentation is based on the terminology standards.
Q: How does Krude Heavy Industry use GB/T 28757 to ensure consistency with international terminology in its export projects?
Answer: Krude Heavy Industry’s technical solutions and factory documentation all use GB/T 28757 as the terminology standard, and a Chinese-English terminology comparison table is prepared with reference to ISO 4306-1. Case Study: For the export project of the QD-type 32-metric-ton double-girder bridge crane, terms such as ”main girder camber,” ” ”trolley track gauge,” and ”end girder connection” are all annotated with both Chinese and English definitions. During reviews, foreign inspection agencies (SGS/TÜV) can directly cross-reference these terms with ISO standards to understand the technical requirements, thereby avoiding delays in technical clarifications caused by ambiguous terminology. This method has been established as a standardized delivery process for all export projects.
