计算基础Ncr = π²EI/Lcr²; λ̄ = √(Afy/Ncr); Φ = 0.5[1+α(λ̄−0.2)+λ̄²]; χ = 1/(Φ+√(Φ²−λ̄²)); Nb,Rd = χAfy/γM1.