Question

Answer the following factor of safety(safety factor) and safety margin questions for each of the following designs

a) what is the safety factor and safety margin for a small rural bridge with an expected load of 17tons(1 ton = 200 Ibs) and a structural strength of 30 tons ?

b) The maximum force on the landing struts of a jet during an emergency landing is expected to be 125,000 Ibs.what safety margin and factor of safety would a structural strength of 175,000 Ibs yield ?

c) In the design for guide wires of a cellular tower,there is a required factor of safety of 1.6 what should the actual cable strength be in tension if the worst case tension load is expected to be 62,000 Ibs?

d) The manufacturer of a pressurized cylinder asked for a safety margin of 90% and the actual pressure the material can support is 6,000 PSI.what should be the design pressure limit published in the consumer manual for the cylinder?

Answer 1

Safety factor is the ratio of Absolute strength and applied for a material (or) structure (F O S = Fs/F_2) [Margin of safety = (- 1 + F O S)] a) strength of bridge = F_8 = 30 tons Expected load = F_2 = 17 tons implies Safety factor F O S = 30/17: safety margin = 30/17 - 1 = 13/17 b) Strength of struts F_5 = 175,000: Maximum force F_2 = 125,000 safety factor F O S = 175000/125000 = 7/5 safety margin = 7/5 - 1 = 2/5 c) Factor of safety F O S = 1.6: Maximum load F_d = 62000 lbs implies F_5/F_2 = 1.6 implies F_5 = 62000 (1.6) = 99,200 lbs should be actual cable strength d) safety margin = 90 % (or) 0.9 implies F O S = 1 + 0.9 = 1.9 Actual Preasure (P_3)