# What the HECK is LAM or LAF mean? - Crane Rental Podcast Episode 6 - 4K

In the crane rental industry and heavy rigging industry we use what are called slings to attach a load to the crane hook. These slings can consist of synthetic materials, braided steel and other materials. The manufacturer of the sling rates the slings in a few standard situations and are as follows: vertical, choke and basket. The manufacture will rate the slings based on these three lifting situations. But the capacities of the slings are only rated for these three situations when the load is perpendicular to the sling.

When you start to lower the angle between the load and the sling, math and geometry is introduced into the equation. Your slings are no longer experiencing 5,000 lbs. like they would if the angle was 90 degrees.

In the above picture we have labeled all of the information required to get B squared, which is the hook height. It is worth noting again that you only need to know two out of three sides to get your LAM or LAF factor. In this case we know the lengths of the slings we are using and we know the length of the beam, which is where we derive A from. From here it is a simple math equation to find B, which is our unknown. If the equation is A2 + B2 = C2, then we will need to modify the equation to fit what know values we have.

Shown above is the process involved to modify the Pythagorean Theorem to suit our scenario. B2 is our unknown and the value that we are looking for. To find B2 we simply take the square of 20, which is 400 and subtract it from the square of 10, which is 100. So B2 is equal to 300. To find B now we will take the square root of 300, to reveal the height of our hook. The square root of 100 is 17.320. Which means that the height of our hook is 17.32 foot. The hook height is 17.32 ft. in relation to the load. Why does this matter? Let’s go back to what we were originally trying to find and that is our LAM or LAF. To get our LAM or LAF multiplier we need to divide the length of our sling reprinted by C and our hook height B. If you know these two values already then you don’t have to go through the above math. You can simply jump to this point and get your LAM or LAF by knowing those two values. In our example however, we didn’t know our B2. Now we have our C value and our B value. Now we simply divide our C value by our B value to reveal our LAM or LAF. In this case we divide 20 by 17.32 and we get a LAM or LAF of 1.1547. I took this number out to 4 decimal places for a reason. I like to take it that far so I can get a better sense of the true value of the number. In all cases I make it a point to round the LAM or LAF number up to the second decimal place. Instead of having a LAM or LAF of 1.15, I instead see that the value is 1.1547 and round the number up to 1.16. This helps add another layer of safety into this equation. Now that I have my LAM or LAF, I can simply multiply the known weight of the beam divided by two, because we are using two slings, with our LAM or LAF. When I multiple 5,000 by 1.16 I get 5,800 lbs. This means that the slings are now experiencing 5,800 lbs. of force and are in tension. Okay, so we have our sling tension loading. Now we are ready to make sure the slings that we are using can handle this type of force. Simply put, you need to be using slings that are capable of handling 5,800 lbs. But coming full circle you can never be to safe. You can always bump up the slings that you are using like 10,000 lb. or 8,000 lb. capacity slings and you know for sure that you are good to go.

What the heck is LAM or LAF? Well they are crane rental industry terms that mean load angle multipliers [LAM] or load angle factors [LAF]. Okay, so now you know what the words technically mean, but what do they practically mean in the crane rental industry?

In the crane rental industry and heavy rigging industry we use what are called slings to attach a load to the crane hook. These slings can consist of synthetic materials, braided steel and other materials. The manufacturer of the sling rates the slings in a few standard situations and are as follows: vertical, choke and basket. The manufacture will rate the slings based on these three lifting situations. But the capacities of the slings are only rated for these three situations when the load is perpendicular to the sling.

Meaning the sling angle in relation to the load is 90 degrees, or another way to look at it is the load is directly below the hook. You can clearly see this in the drawing above. This is an example of the load being directly below the slings. The angle between the load and the sling is 90 degrees. This is how the manufacture would rate the slings. Let’s say that the load here weighs 10,000 lbs. In the example above the load that each sling experiences is 5,000 lbs. In theory/on paper you could use 5,000 lb. slings for this lift and be “okay.” But in reality you would want to use slings that were rated higher than 5,000 lbs. This adds more play room, perhaps the load weighs more than when it was manufactured [i.e. build of material on the load could increase weight]. This is merely one example. Okay, so we have now established the basics of slings and how the manufactures rates slings capacities. What happens though when we introduce a lower angle to this scenario, i.e. the angle between the load and the slings decreases and goes below 90 degrees?

When you start to lower the angle between the load and the sling, math and geometry is introduced into the equation. Your slings are no longer experiencing 5,000 lbs. like they would if the angle was 90 degrees.

In the above picture we have labeled all of the information required to get B squared, which is the hook height. It is worth noting again that you only need to know two out of three sides to get your LAM or LAF factor. In this case we know the lengths of the slings we are using and we know the length of the beam, which is where we derive A from. From here it is a simple math equation to find B, which is our unknown. If the equation is A2 + B2 = C2, then we will need to modify the equation to fit what know values we have.

Shown above is the process involved to modify the Pythagorean Theorem to suit our scenario. B2 is our unknown and the value that we are looking for. To find B2 we simply take the square of 20, which is 400 and subtract it from the square of 10, which is 100. So B2 is equal to 300. To find B now we will take the square root of 300, to reveal the height of our hook. The square root of 100 is 17.320. Which means that the height of our hook is 17.32 foot. The hook height is 17.32 ft. in relation to the load. Why does this matter? Let’s go back to what we were originally trying to find and that is our LAM or LAF. To get our LAM or LAF multiplier we need to divide the length of our sling reprinted by C and our hook height B. If you know these two values already then you don’t have to go through the above math. You can simply jump to this point and get your LAM or LAF by knowing those two values. In our example however, we didn’t know our B2. Now we have our C value and our B value. Now we simply divide our C value by our B value to reveal our LAM or LAF. In this case we divide 20 by 17.32 and we get a LAM or LAF of 1.1547. I took this number out to 4 decimal places for a reason. I like to take it that far so I can get a better sense of the true value of the number. In all cases I make it a point to round the LAM or LAF number up to the second decimal place. Instead of having a LAM or LAF of 1.15, I instead see that the value is 1.1547 and round the number up to 1.16. This helps add another layer of safety into this equation. Now that I have my LAM or LAF, I can simply multiply the known weight of the beam divided by two, because we are using two slings, with our LAM or LAF. When I multiple 5,000 by 1.16 I get 5,800 lbs. This means that the slings are now experiencing 5,800 lbs. of force and are in tension. Okay, so we have our sling tension loading. Now we are ready to make sure the slings that we are using can handle this type of force. Simply put, you need to be using slings that are capable of handling 5,800 lbs. But coming full circle you can never be to safe. You can always bump up the slings that you are using like 10,000 lb. or 8,000 lb. capacity slings and you know for sure that you are good to go.