Referring to the rigger reference booklet, what is the coefficient of friction for moving a metal load on concrete?

• A. .45
• B. .50
• C. .70
• D. .60

Answer: (D)

Understanding friction resistance when moving a load is key in rigging. When a metal load is slid across concrete, the friction force resisting movement is determined by the kinetic (moving) coefficient of friction between the contact surfaces, multiplied by the load’s normal force (which is essentially the weight of the load on a horizontal surface). In the rigger reference booklet, the value used for moving a metal load on concrete is 0.60. This means the friction resisting motion is about 60% of the load’s weight, so the pulling force needed to start and continue movement is roughly weight × 0.60 (plus any additional system losses).

This value is specific to moving contact; static friction is typically higher (around 0.70) and would apply if the load isn’t yet in motion. The other options (0.45 and 0.50) would understate the resistance for metal on concrete when moving, which is why 0.60 is the best choice.