Factors of safety for shoring design.

[geotis]

Consider shoring design basics as an example.

Passive pressure is a resisting force to which we apply a factor of safety to obtain a lower allowable passive pressure for design.

The active pressure is a driving force. Is a factor of safety applied to the active load to obtain a higher active pressure value for design?

 

[racookpe1978]

Usually, margins are only applied once. The load is assumed higher (like in rigging designs), or the load is left based on the original contract specifications and assumptions; and the "ability to resist loads) is reduced. If the contract requires a floor to carry a 42,000 truck, the owner has said he needs that capacity. You don't design for a 84,000 truck.

However, ...

For example, the steel in that platform will be assumed to be 36,000 yield, but the actual metal purchased to A36 specification may be 36 ksi to 44 ksi. A safety factor might be 1.25 or 1.5 or 2.0, so the assigned yield of 36,000 is reduced to a design maximum stress of 18,000 psi using that alloy at that location. Is the platform "over-designed sicne the metal might carry two times the 42,000 lb truck? No.

wire rope is specified to break at 120,000 lbs load, but might be limited to 1/4 that amount (30,000 lbs) when the rigging plan is worked.

You don't "increase the assumed load" arbitrarily unless a dynamic or impact scenario is being worked. Then, you make the appropriate assumptions and acceleration changes to find the design load.

Once you have a design load, work from there.