Precast lifting and sling loads

It estimates the part weight, applies the stage multiplier (stripping, yard, transport) and works out the tension in each sling leg and insert, comparing them with the working load limits you enter. It also shows the pick point locations that give the part the least bending moment.

An inclined leg has to pull harder to hold the same share of weight: tension is the vertical share divided by the cosine of the angle. In the example, the 7,800 lb beam with a 1.2 multiplier gives 4,680 lb per vertical leg; at 30° from vertical it rises to 5,404 lb, and at 60° it would reach 9,360 lb.

From PCI Design Handbook Table 8.3.1: stripping 1.2 to 1.7 depending on product shape and form finish (suction), yard handling and erection 1.2, and transportation 1.5. Use your engineer of record’s factors if the project specifies others.

The 26 ft × 12 in × 24 in beam weighs 7,800 lb. With 2 legs at 30° from vertical and a 1.2 multiplier, each leg and insert sees 5,404 lb, 68% of the 8,000 lb WLL. Pick points 5.5 ft from each end keep the bending moment near 5.4 kip·ft, versus 30 kip·ft if lifted at the ends. The governing item is the 2-leg bridle rating (1.4 × 8,000 lb), used at 84%.

On a rigid part, small length differences make two opposite legs carry almost all the weight. Rated capacities of 3- and 4-leg bridles are therefore based on 3 legs at most, and a conservative check uses 2. Only a spreader beam, equalizing sheaves or reeved slings make all 4 legs share.

Insert capacity in the concrete (pullout, concrete cone, edge distance), concrete strength at stripping, cracking, lateral stability of the part, the crane and the ground. Those belong to the part design and the lift plan.

Whenever precast parts or heavy loads are lifted. OSHA 1910.184 and 1926.251 require slings to be inspected and used within their rated loads; the lift plan should be prepared by a qualified person, following the insert manufacturer’s instructions.