You are an engineering consultant hired to verify an elevator design. The elevat
ID: 1767487 • Letter: Y
Question
You are an engineering consultant hired to verify an elevator design. The elevator mass is 500kg and has a maximum occupant capacity of 800kg. Carbon steel cables with total cross sectional area of 64cm2 support the elevator. The maximum speed of the elevator is 2 meters per second. At the maximum speed, each cable extends at least 4 meters and cannot extend more than 22 meters unstretched. When the car is not moving and the cables are extended by 22 meters of (unstretched) cable, there is 3 meters of clearance between the bottom of the elevator and the concrete floor of the shaft. Carbon Steel Cable: Young's Modulus: 207 GPa Yield Strength: 131 MPa Ultimate Strength: 290 Mpa Requirements for the elevator include a factor of safety of 3 for cable failure and the occupants must not ever experience more than 5 times the acceleration of gravity. Make a sketch of the problem. Answer the following questions: 1.If the elevator is moving at maximum speed and the motor suddenly stops, what is the worst case for cable failure? 2.What is the value of the worst case stress in the cable (MPa)? 3.The design meets the cable failure factor of safety requirement.(T/F) 4.If the elevator is moving at maximum speed and the motor suddenly stops, what is the worst case for occupant acceleration? 5.Describe at least one chang performance relative to the requirements nt e to improve the design. Explain how your suggestion would improveExplanation / Answer
2. The ultimate strength is the stress value at which the material failures to fracture. So, the worst case value of the stress in the cable is equal to ultimate stress of cable i.e. 290/3=96.667 MPa.
Since ,3 is the factor of safety used in the cable failure. Therefore, the value of worst case stress will be ultimate stress divided by factor of safety i.e. 290 / 3 = 96.667 MPa
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