Double Girder Overhead Travelling Crane: Types, Differences, and Classifications

Overhead cranes are essential in many warehouses and industrial facilities for moving heavy materials efficiently. Double-girder bridge cranes are a popular choice for handling larger capacities and spans.

Unlike a single-girder crane, aDouble girder overhead travelling crane uses two parallel bridge beams (girders) across the span, giving it greater strength to lift heavier loads. 

The hoist and trolley run on rails atop these two girders, providing more lifting height (hook height) than a hoist suspended under a single beam.

Companies choose double-girder cranes for high-capacity, high-duty applications that require extra strength and lift height.

What is a Double Girder Crane?

Adouble-girder crane is an overhead bridge crane with two main horizontal girders forming the bridge, spanning between the crane's runways. Wheeled end trucks that travel along the runways support these girders at each end. The hoisting trolley typically runs on rails mounted on top of the two girders, which maximizes hook height by positioning the hoist above or between the beams.

Companies commonly use double girder overhead traveling crane to lift heavier loads (typically above ~20 tons) and cover wider spans than single-girder cranes. Their robust design also allows for adding features like maintenance walkways or operator cabs on the bridge, which single-girder cranes cannot easily support.

Top-running cranes are usually, if not always, double-girder cranes. This configuration, where the crane's bridge rides on rails mounted on top of the runway beams, means the crane's weight (and its load) is transferred directly downwards onto the building's primary support columns and foundation. Because the crane sits on top of these robust runway beams, it requires a strong building structure to support these downward forces. 

This design offers superior hook height, making it ideal for high-bay warehouses, steel mills, large fabrication shops, and other heavy industries where large, frequent loads are handled without wasting vertical space.

In summary, a top-running crane is the powerhouse for heavy loads and maximum lift height. In contrast, an under-running crane offers a space-saving solution for lighter loads and lower headroom situations. The choice depends on your building constraints and lifting needs – a plant with heavy products and ample headroom will favor a top-running crane, whereas a low-ceiling workshop might require an under-hung crane.

What is an Under-Hung Double Girder Crane?

An underhung double girder crane suspended from roof-mounted runways provides maximum headroom in a low-ceiling space.

Anunder-hung double girder crane is a double girder overhead crane that travels beneath its runway beams instead of on top. The two-girder bridge is supported by end trucks that ride along the bottom flanges of the runway beams. This design is used in facilities with low headroom that still require the strength of two girders.

They are generally limited to moderate capacities because the roof must carry the load. Under-hung double girder cranes fill a niche for medium-duty lifting where a top-running system won't fit, providing extra headroom beneath the runways. However, underhung double girder cranes become impractical or costly beyond a certain size.

"When you're regularly handling heavy loads or need maximum clearance, double girder cranes really shine. They're built for strength, reliability, and long-term efficiency, helping your warehouse operations run smoothly day after day."– Nathan Stout - HOJ Innovations Crane Engineer.

You may also be asking yourself. Why do double-girder underhung cranes exist? I could just use a single girder underhung crane and achieve up to a 20-ton capacity; why would I waste all that extra steel to make it a double girder? You're right that for capacities up to around 10-15 (or even 20) tons, a single-girder underhung crane isoften the more practical and cost-effective choice due to:

• Lower Cost: Less material and simpler fabrication.

• Lighter Weight: Reduced load on the building's existing roof structure.

• Easier Installation: Generally quicker and less complex to install.

• Suitable for Moderate Loads: Perfectly sufficient for many light to medium-duty applications.

But for some instances, a double girder wills be required. Here is why.

Low Headroom + Higher Capacity/Span (Beyond Single Girder Limits): This is the primary reason.

• If you need a crane in a facility withminimal headroom, but your lifting requirements occasionally exceed the practical capacity or span of a single-girder underhung (e.g., needing to lift15-20 tons consistently, or up to 30 tons in some cases, or wider spans), an underhung double-girder becomes a viable solution. The second girder provides the extra structural rigidity and load-bearing capacity needed for these heavier lifts or longer spans while still keeping the crane below the runway.

Increased Stability for Specific Loads: For certain types of wide loads that might require extra stability (e.g., when attaching specialized below-the-hook lifting devices, manipulators, or stackers), the two-girder configuration can offer better load control and rigidity, even in an underhung setup.

Another reasons one might choose a double girder underhung crane is that it has better Hook Height than Single-Girder Underhung (in some designs): In some double-girder underhung designs, the hoist trolley can be designed to sitbetween the two girders, similar to a top-running double girder. This can allow for a slightly better hook height than a typical single-girder underhung where the hoist usually hangs below the single beam.

Support for Additional Features: While not as common as on top-running double-girder cranes, the added stability of two girders in an underhung configuration could potentially supportsome more complex hoist setups or limited maintenance access compared to a single girder, though complete walkways or operator cabs are highly impractical.

Overhead cranes are also rated byservice class (duty cycle) from A through F, which indicates how much use and stress the crane is designed for. These classifications range from infrequent use to continuous severe service:

• Class A: Used only occasionally for light, infrequent lifts.

• Class B: Low usage and light loads in settings like repair shops or light warehousing.

• Class C: Moderate use in general manufacturing – handling average loads around 50% of capacity.

• Class D: Heavy use in industries like fabrication or foundries, with frequent lifts often near capacity.

• Class E: Very heavy continuous use (often 24/7) in harsh environments, lifting near full capacity much of the time.

• Class F: The toughest duty – essentially continuous full-capacity operation.

Knowing these ratings helps you select a crane that can handle your needs without excessive cost. Higher classes (D–F) endure more frequent heavy use (and cost more), whereas lower classes (A–C) are suited for occasional or light duty. Selecting the right class ensures you get sufficient performance without overpaying.

For your specific needs, HOJ Innovations offers a wide range ofoverhead cranes from Class A through Class D, capable of handling most general manufacturing, fabrication, and warehousing demands. However, if your operation requires the extremely heavy or continuous severe service of Class E or Class F cranes, you would need to consult with a specialized manufacturer for those higher-duty cycle requirements.