ultimate strength = norminal strength ? 2

[tipsabc]

In concrete structure member design, is the ultimate srtength equal to the norminal strength or the norminal strength times the strength reduction factor (phi)? For example, ultimate P = Pn or (phi)*Pn? ultimate M = Mn or (phi)*Pn? Thank you very much.

 

[Tomfh]

The ultimate strength is the unfactored value.

 

[JAE]

Applied Load must be less than available strength.

Applied Load
You apply loads to a structure and get an effect....say an axial load, P.

You mulitiply this load times a load factor to get a factored (ultimate) load, Pu (i.e. Pu = 1.6 x P)

Available Strength
You calculate the capacity of your member based upon derived formulae which are based upon tests, concepts, etc. to get Pn, which is the nominal strength of the member.

You multiply the nominal strength of the member times a strength reduction factor [φ](to account for variabilities in calculating the strength accurately) and this gives you the member design capacity [φ]Pn.

Compare
In strength design, therefore, you choose, size, or specify a member big enough SO THAT:

Pu <= [&phi;]Pn