Crane Stability & Rotational Overturning

Objective
To investigate crane stability and rotational overturning.

Definition and Theory
One way a crane can fail is due to rotational overturning, resulting in the crane tipping over. When a load is lifted a distance from the edge of the crane it causes a rotation about that point called a moment. For this reason, most cranes need to be counter balanced. To calculate the overturning moment, the load P is multiplied by the horizontal distance H the load extends beyond the edge of the crane. To counter balance this moment, a load is applied to the other side of the crane a horizontal distance that equals the overturning moment.

 Variables: M = Moment (rotation about a point) P = Load d = Actual Distance from the rotation point to the counter balance weight D = Total Distance (1d, 2d or 3d) M = P x D SM = Sum of the Moments = 0 (about the rotation point the crane will not tip over) Example: SM = (P x 1d) - (.5P x 2d) = 0 (P x 1d) = (.5P x 2d)

Procedure

• Measure the distance from the rotation point to the counter balance weight, this is the (d) value.
• Calculate the Moment that the load on the crane arm generates. The Moment is equal to the load (P) multiplied by the distance (D). Enter the Moment in Data Table 1.
• Calculate the required counterweight load (P(calc.) = M / d)
• Place the counterweight load on the crane. Remove pennies from the load until the crane tips. Record the results in Data Table 1.
• Answer the questions in the lab.