The placement of the screw eyes and the length of the chain are intended to replicate scenarios with the connections at 30°, 45°, and 60°.Īfter cutting the 2×6 to 3ft. The imperfect connections at the screw eyes and the variation in the spring scale as a load is applied make predicting the exact angle difficult. This increases the weight of the critical lift.īefore Class: Build and verify your model. These scales measure the weight of the lift and along each chain. These are used for quick connections of the chains to the screw eyes and the weight to the load screw eye. It also is used for the top spring scale to analyze the total weight of the lift.

This locks and holds the two spring scales along each chain. These are used for the rigging connection points on top and the load connection point on the bottom.

Once cut to size, this is the critical lift.

This is smaller than the straight chain and is used to connect the weight plate to the spring link on the lower screw eye. While increasing the connection angle of a two-point lift may be required to increase the stability of the lift, careful consideration must be taken in regards to the sling capacity and weight of the lift. This can be derived using the figure below. Students must comprehend that decreasing the angle creates a horizontal force component that in turn increases the tension in the rigging. The key engineering principle with this demonstration is related to an understanding of statics. The following chart shows the increased force applied to the rigging when the rigging angle is reduced. The forces in rigging (sling, chain, wire rope, webbing, shackles, etc.) increase substantially as the angle formed by the sling leg and the horizontal becomes smaller. The demonstration should take 15-20 minutes.Ī sling’s working load limit (WLL) is based on a crane lift performed at a straight (90°) angle. By varying the connection points and sling length, students will be able to calculate the predicted forces and analyze the best combination of connection points and sling lengths to successfully complete the critical lift.

Reducing rigging angles results in a significant amplification of forces in the rigging, potentially leading to failure. This demonstration depicts the importance of rigging angles during crane lift operations on a construction site.

Sling angle factor chart