• Feb 13, 2025
• News

Structure of Container Gantry Cranes

Container gantry cranes are structured primarily around a supporting frame, which is a large and robust framework that supports the capability.

Container gantry cranes are equipment used to load and unload containers in ports, terminals and other places around the world, enabling efficient transportation on ships, trucks and warehouses. Understanding the structure of the container helps to choose the right equipment for specific operational needs, this article focuses on the structure of the container crane.

Understanding the Structure of Container Gantry Cranes

Due to the frequent trade in ports and terminals, the demand for container loading and unloading is extremely high, thus requiring efficient handling solutions. Container gantry cranes are designed to prioritize the stability of the body, load carrying capacity and operational efficiency. The same applies to the individual components of the crane. Although cranes are a customized product with no standard items, and different manufacturers produce different cranes, the main components are still similar.

1. The Gantry Structure: The Foundation of Stability and Movement

The gantry itself forms the primary supporting framework of the crane, providing both vertical elevation and horizontal mobility. It is essentially the crane's legs and base, allowing it to straddle containers and move along designated pathways. The gantry structure is engineered to withstand substantial static and dynamic loads, ensuring stability during lifting operations and movement.

1. Legs (Columns): These are the vertical supports of the gantry crane, bearing the entire weight of the crane structure, the trolley, and the lifted container. Legs are typically constructed from heavy steel box sections or lattice structures, designed for high compressive strength and resistance to buckling. The design and spacing of the legs are critical for overall crane stability and load distribution.

    

2. Sill Beams (Tie Beams): Connecting the legs at the base are sill beams, also known as tie beams. These horizontal structural members provide rigidity to the gantry structure, preventing the legs from spreading apart under load. Sill beams contribute to the overall stability of the gantry and ensure that the legs act as a unified support system.

    

3. Gantry Girder (Main Girder or Bridge Girder): Spanning horizontally between the legs at the top is the gantry girder, sometimes referred to as the main girder or bridge girder. This is a primary load-bearing component, supporting the trolley and hoist mechanism and transmitting the load to the legs. Gantry girders are typically constructed as box girders or welded plate girders, designed for high bending strength and torsional stiffness. The span of the gantry girder determines the width of the area the crane can service.

    

4. Travel System (Wheels and Rails or Rubber Tyres): Depending on the container crane types, the gantry structure is equipped with a travel system that enables horizontal movement. Rail-mounted container gantry cranes utilize steel wheels running on rails embedded in the ground. This system provides precise and efficient movement along a fixed path, ideal for high-throughput container terminals. Rubber-tyred gantry cranes (RTGs), on the other hand, use large rubber tires, offering greater mobility and flexibility within the container yard. RTGs can maneuver in multiple directions and do not require fixed rails, making them suitable for dynamic yard layouts.

    

2. The Trolley: Horizontal Movement and Hoisting Mechanism Support

Positioned atop the gantry girder, the trolley is a wheeled structure that traverses horizontally along the girder's length. The trolley's primary functions are to support the hoisting mechanism and to provide horizontal movement for precise container positioning above the target location.

1. Trolley Frame: The trolley frame is the structural base of the trolley, supporting all trolley components. It is designed to be robust and lightweight to minimize inertia during trolley travel and to withstand the dynamic forces generated during hoisting and lowering operations.

    

2. Trolley Wheels and Drive System: The trolley moves along the gantry girder on wheels, driven by a motor and drive system. The trolley drive system must provide smooth and precise horizontal movement, allowing for accurate positioning of the container over the desired location. Variable frequency drives (VFDs) are often used to control trolley speed and acceleration/deceleration for optimized performance and reduced load swing.

    

3. Hoist Mechanism Support: The trolley frame provides the mounting platform for the hoist mechanism, which is responsible for the vertical lifting and lowering of containers. The trolley frame must be designed to transmit the hoisting loads effectively to the gantry girder.

    

3. The Hoist Mechanism: Vertical Lifting and Lowering of Containers

The hoist mechanism is the heart of the container gantry crane, responsible for the vertical movement of containers. This complex system comprises several critical components working in unison to lift and lower heavy loads safely and efficiently.

1. Hoist Drum and Wire Rope: The hoist drum is a large cylindrical component around which the wire rope is wound. As the drum rotates, it winds or unwinds the wire rope, causing the hook or spreader to move vertically. High-strength steel wire rope is used for its exceptional tensile strength and flexibility, capable of withstanding the repeated bending and loading cycles of hoisting operations. Multiple layers of wire rope are often wound on the drum to achieve the required lifting height.

    

2. Hoist Motor and Gearbox: A powerful electric motor drives the hoist drum through a gearbox, providing the torque and speed reduction necessary for lifting heavy containers. The hoist motor is typically a high-torque, heavy-duty motor designed for frequent start-stop cycles and demanding lifting operations. The gearbox reduces the motor's high-speed rotation to a slower, higher-torque rotation suitable for driving the hoist drum.

    

3. Braking System: A robust braking system is crucial for safety and load control. Hoist mechanisms are equipped with multiple brakes, including service brakes for normal stopping and holding, and emergency brakes that engage automatically in case of power failure or system malfunction. These brakes ensure that the load is securely held at any height and can be safely lowered in controlled manner.

    

4. Rope Reeving System: The wire rope is reeved through a system of sheaves (pulleys) to multiply the lifting force and increase the lifting speed. The reeving arrangement determines the hook speed and the load capacity of the hoist. Common reeving arrangements include single reeving, double reeving, and multiple reeving, depending on the crane's lifting requirements.

    

4. The Spreader

The spreader is the specialized attachment at the end of the hoist rope that directly engages and secures the container for lifting and movement. Spreaders are designed to automatically lock onto standard ISO containers and can often handle different container sizes and types.

1. Telescopic Frame: Most container spreaders are telescopic, meaning they can extend and retract to accommodate different container lengths (typically 20-foot, 40-foot, and 45-foot containers). This adjustability allows a single spreader to handle a range of standard container sizes, enhancing operational flexibility.

    

2. Twistlocks: Twistlocks are the critical interface between the spreader and the container. These are rotating locking mechanisms that engage with corner castings on the container. When activated, twistlocks securely grip the container, ensuring a safe and reliable connection for lifting. Spreaders are equipped with multiple twistlocks (typically four or eight) to distribute the lifting force evenly and securely.

    

3. Sensing and Control Systems: Modern spreaders are equipped with sensors and control systems that monitor twistlock engagement, container presence, and load distribution. These systems provide feedback to the crane operator and enhance safety by preventing accidental container drops or misaligned lifts. Automatic spreader systems can further streamline operations by automating the twistlock engagement and disengagement processes.

    

5. Operator Cabin and Control Systems

The operator cabin serves as the command center of the container gantry crane, providing the operator with a vantage point to oversee all crane operations and manipulate the controls. Advanced control systems are integral to safe and efficient crane operation.

1. Operator Cabin Structure: The operator cabin is typically located at an elevated position to provide a clear view of the working area, containers, and surrounding environment. Cabins are designed for operator comfort and visibility, often featuring ergonomic seating, climate control, and large windows.

    

2. Crane Control Consoles: Inside the cabin, control consoles house the levers, buttons, and displays that the operator uses to control crane movements – hoisting, trolley travel, gantry travel, and spreader functions. Modern consoles often incorporate joystick controls, touchscreens, and programmable logic controllers (PLCs) for precise and user-friendly operation.

    

3. Monitoring and Diagnostic Systems: Advanced control systems include monitoring displays that provide real-time information on crane status, load weight, wind speed, and diagnostic data. These systems enhance situational awareness for the operator and facilitate proactive maintenance by providing early warnings of potential issues.

    

4. Safety Control Systems: Safety control systems are integrated into the operator interface, including emergency stop buttons, overload alarms, and interlocks. These systems are designed to prevent unsafe operations and protect personnel and equipment.

    

6. Power Supply and Distribution System: Energizing the Crane

Container gantry cranes are electrically powered, requiring a robust power supply and distribution system to energize all crane functions.

1. Power Collection System: Quay-Side Container Cranes (Ship-to-Shore (STS) Cranes) typically receive power from the port's electrical grid via cable reels or conductor bars along the quayside. Rubber-tyred and rail-mounted gantry cranes in container yards may also be powered via cable reels or conductor rails, or in some cases, by diesel-electric generators for greater mobility.

    

2. Transformer and Switchgear: Onboard transformers and switchgear panels step down the incoming voltage and distribute power to various crane components, including motors, control systems, lighting, and auxiliary equipment.

    

3. Cable Management System: Cable reels or festoon systems manage the power and control cables, allowing for free movement of the crane along its travel path while maintaining a continuous power supply.

    

7. Additional Structural and Operational Elements

Beyond these core components, container gantry cranes may incorporate other elements that enhance their functionality and performance.

1. Storm Anchors and Tie-Downs: In regions prone to high winds, storm anchors or tie-down systems are essential for securing the crane against overturning during severe weather conditions. These systems anchor the crane to the ground or rails, preventing movement during storms.

    

2. Lighting Systems: Comprehensive lighting systems illuminate the working area, container handling zones, and walkways, enabling safe and efficient operations during nighttime or low-light conditions.

    

3. Maintenance Platforms and Access Systems: Integrated platforms, walkways, and ladders provide safe access for maintenance personnel to reach various crane components for inspection, lubrication, and repairs.

    

4. Anti-Collision Systems: In container yards with multiple cranes operating in proximity, anti-collision systems can be implemented to prevent crane-to-crane collisions. These systems use sensors and control logic to monitor crane positions and automatically prevent cranes from entering the same working zone simultaneously.

    

Conclusion

Container cranes are made up of a combination of components, the gantry frame determines the overall load carrying capacity and stability of the crane, the hoisting mechanism affects the hoisting speed of the crane, and each component has a specific role.