Calculate the interaction diagram

Question

Solve the following problem:

Consider a non slender column with cross-section as in Figure  and d₁ = 40 mm, A_s1 = 803.8 mm², d₂ = 225 mm, A_s2 = 401.9 mm², d₃ = 375 mm, A_s3 = 401.9 mm², d₄ = 40 mm, A_s4 = 803.8 mm², h = b = 600 mm. The materials of the RC column are f’_c= 27.5 MPa, f_y = 413 MPa.

Calculate the interaction diagram for the following cases:

(1) unstrengthened member,

(2) strengthened member with n = 3 layers of carbon-epoxy FRP with properties f’_fu= 3, 800 MP a ,ε’_fu= 0.0161, tf = 0.5 mm.