Lifting Beams and Spreaders – Below the hook lifting
Spreader bars and lifting beams are very similar devices in common use in almost every industry. Both of these devices have very similar functions; they allow a single crane to lift loads from multiple locations, to spread out the load and provide balance to the lift. However, each of these devices have very different properties and uses. There are cases where one device is ideal and the other would be cumbersome and inefficient.
The Spreader Bar
Spreader bars (lifting spreaders) are a very simple device, and consist of a long bar that functions to hold a sling apart to the lifting distance. From a loading standpoint, they convert the lifting loads into compressive forces in the bar, and tensile forces in the slings. This results in a highly efficient use of material, which makes them lighter, easier to design, and cost less than their lifting beam counterparts. However, they require much more headroom to make the lift than lifting beams.
The Lifting Beam
Lifting beams, on the other hand, consist of a long beam that converts the lifting load into a bending moment through the beam. This is a much less efficient use of material, and as a result, lifting beams are in general heavier and more costly than spreader bars. The main benefit of lifting beams is the substantially reduced headroom required to perform the lift. These qualities make lifting beams well-suited to lighter, shorter span lifts that have a small headroom requirement, such as in smaller manufacturing shops or storage facilities.
Another advantage of spreader bars to lifting beams is a spreader bar is easily made adjustable in length to accommodate a range of lift spreads. Due to the axial nature of the load, the most efficient shape for spreader bars are square or round tubes. It then becomes easy to add a section that will slide overtop other sections. This allows telescopic spreader bars to double or triple in length (depending on the number of sections), giving spreader bars many more options for storage, transport, and handling.
In contrast, designing a lifting beam to be collapsible becomes a much bigger challenge, as the most efficient material shape is an I-beam. As well, because the load is lifted from a central location, and not from the ends, the beam must remain balanced. It becomes much more difficult to create a telescopic lifting beam. However, by adding multiple lifting points along the beam, a lifting beam can be made to handle different spreads. As well, this can also allow for more than 2 lifting points to be used for a single lift, something a spreader bar can never do.
The difference between the two devices can be described as similar to the difference between a suspension bridge and a cantilevered bridge. Suspension bridges are very similar to spreader bars, with cables supporting their length, turning any vertical load into a tensile force on the cables, and a compression force on the towers and deck. Cantilever bridges are like lifting beams, where the vertical loads are converted into bending moments. To further this analogy, the longest suspension bridge in the world is the Akashi Kaikyō in Japan, with a main span of 6,532 feet. The longest cantilever bridge in the world is the Pont de Quebec in Canada, with a main span of 1,800 feet. This is very similar to what you can expect when comparing lifting beams to spreader bars; the spreader bars will be much more effective at lifting loads at large spans.
How to Choose Between a Spreader Bar and Lifting Device
When choosing between a spreader bar or lifting device, the following questions can help in deciding what would work best for your lift:
1. What are you lifting, and,
2. How are you lifting it?
Consider the weight of the object you are lifting, as well as where the lifting points are located. For very wide spans, a spreader bar will be much more effective. However, if you need to support the lift throughout the length, then a spreader bar will be useless as it can’t support anywhere in the middle.
3. Where are you lifting it?
If you have height constraints that can’t be avoided, then a lifting beam is probably a better choice. Keep in mind though that even if your load is very light, a wide span will still require a pretty stout lifting beam.