Factor of safety

A difference between tank cars and most pressure vessels is that tank cars are designed in terms of the theoretical ultimate or bursting strength of the tank. The test pressure is usually 40 percent of the bursting pressure (sometimes less). The safety valves are set at 75 percent of the test pressure. Thus, the maximum operating pressure is usually 30 percent of the bursting pressure. This gives a nominal factor of safety of 3.3, compared with 4.0 for Division 1 of the ASME Pressure Vessel Code. 

Concrete nuclear reactor vessels, of the order of magnitude of 15-m (50-ft) inside diameter and length, have inner linings of steel which confine the pressure. After fabrication of the liner, the tubes for the cables or wires are put in place and the concrete is poured. High-strength reinforcing steel is used. Because there are thousands of reinforcing tendons in the concrete vessel, there is a statistical factor of safety. The failure of 1 or even 10 tendons would have little effec t on the overall structure. 

Effect of Variables on Corrosion Tests It is advisable to apply a factor of safety to the results obtained, the factor varying with the degree of confidence in the applicabihty of the results. Ordinarily, a factor of from 3 to 10 might be considered normal. 

Total force they can withstand considering a factor of safety as 100%... 

As in Figure 28.36, although each phase will be supported on two insulators and each insulator mounted on 2 x M8 size of fasteners, it is possible that at the instant of fault, the forces are acting either upwards or downwards. Therefore, assuming forces to be acting only on two fasteners, at the instant of fault and assuming a factor of safety as 100%,... 

A = cross-sectional area of section a - a) Shared by Factor of safety... 

It is possible that during the fault only one ot the insulators is subject to the transitory first peak of the fault, as there may be slight misalignment between the insulators, asymmetry in the busbars, an imperfect bolt fixing and their fastening, or a combination of such factors. To be on the safe side it is advisable to consider each support and its fasteners to be suitable to withstand the forces by themselves. We have assumed a factor of safety of 100% in all the above calculations to account for this. 

One may consider a factor of safety of. id-100%, depending upon the criticality ttf the installation in all the forces that may arise on an actual fault to ensure a foolproof system. 

This stress is only a quarter of the yield stress of a typical structural steel, and the shaft therefore has an ample factor of safety against failure by plastic overload. 

Table 4.1 Factors of safety for ductile and brittle materials and various loading conditions (values shown in brackets from 1905, without brackets from 1965) (,S = ultimate tensile strength,, Sy = yield strength)...

The factor of safety had little scientific background, but had an underlying empirical and subjective nature. No one can dispute that at the time that stress analysis was in its infancy, this was the best knowledge available, but they are still being applied today Factors of safety that are recommended in recent literature range from 1.25 to 10 for various material types and loading conditions (Edwards and McKee, 1991 Haugen, 1980). 

Figure 4.54 Section depth, d, based on factor of safety...

Mischke, C. R. 1970 A Method of Relating Factor of Safety and Reliability. Journal of Engineering for Industry, August, 537-542. 

NASA Engineering Management Council (EMC) 1995 Preliminary NASA Standard, General Requirements for Structural Design and Test Factors of Safety. 1 August (http // amsd-www.larc.nasa.gov/amsd/refs/fac saf.html). 

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