Spreader Beams vs Lifting Beams
Thursday, 11 October 2018
Spreader and lifting beams are two popular pieces of lifting equipment. They go by many names and the terminology is useful, but names are trivial compared to the functional distinctions between beams themselves which can come in all shapes, styles and sizes.
As a broad distinction, in their purest forms:
- Spreader beams are mainly subject to compressive stress and are lifted using a two-legged sling at the top.
- Lifting beams are mainly subject to bending stresses and are lifted from a central lifting lug.
Correct slinging arrangements need to be understood prior to use. For example, it is easy to destroy a pure spreader beam by wrapping an additional sling around its middle to make it work like a lifting beam. The reality is that any beam can be damaged or cause unsafe conditions whenever unauthorised sling arrangements and loading conditions are applied.
Load ratings (working load limits) and loading configurations (sling angle limits etc.) go hand in hand. It is time for a new beam if:
- The conditions of use are not clearly marked or documented
- If the manufacturer is unknown or unable to confirm the verified ratings
- If you require a configuration which is not explicitly authorised.
What type of beam should you opt for and what aspects should you consider when planning a lift?
Here is where the broad distinctions can become important, these are the aspects to consider:
1. Spreader beam lifting arrangements require more headroom height.
This is because of the two-legged slings above them. Under tension, this sling acts as a rigid extension of the beam. This can create problems with headroom – i.e. when there is insufficient vertical space beneath the crane hook.
2. Spreader beams are more stable.
This is because the two-legged sling above the beam are rigid under tension. The head-ring for this sling becomes the pivot point for the whole beam and is well above the beam itself. This stability has the beneficial effect of granting stability to the beam itself, but also to the payload. This is extremely important if the payload is to be slung from its base. Lifting something from below its centre of gravity is an inherently unstable process – the payload wants to turn upside-down. When lifting something from below its centre of gravity it may be essential to use a spreader beam – if a lifting beam is used the payload might tip the moment it lifts off.
3. Spreader beams are (usually) lighter.
This is because spreader beams are designed so that sling forces generate compression rather than bending. If we take the simple example of a steel tube section, this will be able to take a higher load in compression than it will in bending. The same generally holds true for any section profile that might sensibly be used. This results in a beam which is generally lighter even with the added weight of the upper slings. However, for certain beam types, and particularly for beams which are very short relative to their capacity – a lifting beam may be the lightest option.
4. Spreader beams can be cheaper.
With careful design and clear user instructions it is possible to save money by using existing two-legged slings as the upper slings for a spreader beam. This can take full advantage of the spreader being made from smaller sections of steel and therefore being lighter and cheaper to build. This is not always the case however, and some spreader beams have very specific sling requirements. If the conditions of use are not clearly expressed in the markings or drawings, extra steps may be needed to ensure that the correct sling specifications are applied.
5. Lifting beams in certain circumstances can make good equalisers.
Many spreader beams have the advantage of accepting multiple upper sling configurations. This means that it is frequently possible to use a very tall set of slings, which can aid stability (see point 2 above). Unfortunately, if either of the upper slings are too close to vertical and the whole assembly is very tall, as a result, small load swings can throw the whole of the load weight upon one upper sling, or a disproportionate share upon one lower sling leg. This can be hazardous if not accommodated with rigging design and oversizing of components to suit, which defeats the purpose of load equalisation. Lifting beams by contrast have a central lug and low headroom. It takes an extreme load swing to defeat the load sharing.
IMPORTANT – Lifting beams and spreader beams only equalise lower sling loads if there is one pair of symmetrically placed lower slings in use. If there is more than one pair, then there is no definite load share that can be calculated. And if the pair isn’t symmetrical, then there is load sharing, but it is uneven and must be competently calculated.
There are of course many other considerations in determining which beams might be safely used or which beams are the optimum solution. It is important to consider the whole lift, including the available cranes and the range of payloads. By far the most common reasons for using spreader and lifting beams is to avoid slings and sling forces which could potentially risk damaging payloads. Therefore, it is impossible to safely specify rigging without considering the payloads as well.
If the slings beneath a beam are thoughtlessly applied, come off at the wrong angle or are just the wrong size or type then disaster may strike. A competent solutions-based approach to rigging selection and use is vital.
Our team here at Nobles is here to help. To speak to a lifting & rigging specialist please call Nobles on 1300 711 559 or email email@example.com.
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