As much as 18 billion tons of freight moves around the country each year by truck, rail, and ship, most of which is met at the final destination by bridge girder cranes.
Moving large amounts of raw materials through a plant or product pallets through a warehouse is done more efficiently with an overhead crane. With lots of configurations, these lift solutions can be customized to meet your specific operational needs.
Understanding those needs is the first step toward choosing between single girder bridges or a more expensive double girder. They’re equally solid and durable choices and the biggest determining factor in the complexity and cost of your crane.
The choice ultimately comes down to your lifting requirements and environment. Let’s take a look at these two options to help you determine which best meets your needs.
Single Girder Overhead Crane
The most popular option for an overhead crane is the single girder because it’s simple and cost-effective.
Single girder cranes involve one girder beam running across and supported by end trucks. The trolley runs along the lower flange of the bridge girder so that it hangs down underneath.
This style of a bridge crane can give you maximum facility coverage with a quicker set-up time. It’s the right solution for a business that needs light-to-medium-duty crane help or for a building space where headroom or floor space is limited.
Whether a single girder crane is right for your operation depends greatly on the amount of work you need it to do. The span of the crane rarely goes wider than 60 feet, and the weight capacity is usually limited to 15 tons. That’s not to say you can’t customize a single girder crane to go beyond that, but these are common limitations. Common duty cycle ratings for single girder cranes are CMAA class C.
A single girder crane can run for up to six hours at a time. It can be run by a pushbutton station or wireless remote. Most of the time, you can choose from either electric chain hoists or wire ropes hoists to maximize the flexibility of your workspace.
This style of bridge crane does cost less thanks to the fact that it’s more compact and lightweight. You save through lower cost of material, freight, and installation. The crane can also accommodate lighter runway systems that tie into existing building support structures without adding too much extra strain.
Single girders are commonly used in workshops, warehouses, material yards, and manufacturing.
Pros of Single Girder
- Less expensive upfront due to less material and faster installation
- Most economical light-to-medium-duty crane choice
- Lower load on the building structure
- Better hook approach for trolley and bridge travel
- Easier to install, service, and maintain
- Good if the building has adequate headroom
Cons of Single Girder
- Hoist is usually under the girder so reduced hook height
- The under-running trolley can lead to premature wear on the beam
- Special features like service walks and lights can be expensive or hard to add
- Lower weight capacity
- Shorter crane span
Double Girder Overhead Crane
When span and capacity start to increase, it’s time to consider double girder bridge cranes as a heavy-duty lifting solution.
Double girder cranes use two parallel girder beams as the bridge with an end truck on each side. The trolley and hoist travel on a rail installed on top of the bridge, which increases your maximum hook height by as much as 36 inches. If you need more headroom under the runway, the trolley can be designed to run along the bottom flange of the girder instead of on top.
If your production needs call for lifting more than 20 tons at a time, you definitely need to consider a double girder. These overhead cranes can handle up to 600 tons of material in one go. It’s the simplest factor in choosing between single and double girder. Common duty cycle ratings for double girder cranes are CMAA class D and E.
Even if you lift small loads, a double girder might turn out to be your better choice. Special lift height requirements might call for a double option since it can pick up items higher than a single girder can. You also can move your load over greater distances since the span can be longer.
Double girders are also called for if you need to have a bridge crane set up to work outdoors. Doubles can also be run for eight hours or more at a stretch, an advantage over singles max of six hours.
Price is a factor here since double girder cranes have higher costs due to needing more materials to make them and the time and labor needed for set-up. You might also have added costs to ensure your building’s support structure can handle the extra weight of the beams and runway system.
Double girders are the common choice for use in mining, metal production, rail yards, and shipping ports.
Pros of Double Girder
- Larger to handle more weight
- Can span more distance
- Greater hook height
- No limits on how far it can span or capacity
- Can add features like catwalks, cabs, or lights
- Can be used indoors or outdoors
- Easy to maintain
Cons of Double Girder
- More expensive because of more material, added structural support, and more complex components
- Higher set-up cost
- Lessened hook approach for trolley or bridge travel
Choosing Girder Cranes
As you can see, the major factor in deciding which type of girder crane you should choose is the type of work you need to do. A double girder is the better choice if you’re moving heavy loads or need a high hook height, but you will pay more upfront. If you have relatively lighter loads or have space limitations, a single girder might meet your needs at a lower initial cost.
At Shannahan Crane & Hoist, we’ve been manufacturing and servicing overhead material handling equipment in the Midwest since 1961. If you’re looking for girder cranes in Saint Louis, contact us to talk about designing a solution for you.