1100 kg lift is suspended by a series of 24 steel cables of mean diameter 20mm. Cables are attached to the lift top and are arranged so torsional vibration is minimised.

Lift is accelerating upwards at a rate of 0.22m/s2 and is driven by a winding drum of diameter 1.0m, which has a radius of gyration of 0.45m.

The mass of the drum is 230kg.

1. What is the average tension per cable during this upwards acceleration?

2. If the lift moves upwards from a stationary position through a distance of 17m, how long does it take to climb this distance? How many revolutions has the drum made?

The secondary braking system fails and the lift freefalls through 5m before it kicks back in. The braking force is applied at a rate of 20kN/s for 0.8s. If the cable is manufactured from steel with an elastic modulii of 185GN/m2 and elastic constant of 200kN/m:

3. Explain the system dynamics after the brake is applied. Clearly state any assumptions that you have made.

4. What will be the total displacement of the cable 0.7 seconds after the lift comes to a halt?

5. What is the magnitude of the tangential impact force on the drum at the point of maximum braking?

6. What effect does this impact force have on the rotational axis of the drum? Detail

7.Calculate the maximum impact force that the cables can withstand before catastrophic failure occurs, assuming a safety factor of 3.3.