[ A_g - 0.015 A_g = 0.985 A_g ] [ 0.85 \times 21 \times 0.985 A_g = 17.57 A_g ] [ 420 \times 0.015 A_g = 6.3 A_g ] Sum = (17.57 A_g + 6.3 A_g = 23.87 A_g)
[ A_g = 300 \times 300 = 90,000 , \text{mm}^2 ] [ A_{st} = 0.015 \times 90,000 = 1350 , \text{mm}^2 ] Use 4 #19 bars (4 × 284 mm² = 1136 mm²) – slightly less, adjust to 4 #22 (4 × 387 = 1548 mm²). diseno de columnas de concreto armado ejercicios resueltos
[ K_n = \frac{P_u}{\phi f'_c A_g} = \frac{1800 \times 10^3}{0.65 \times 28 \times 160000} = \frac{1.8 \times 10^6}{2.912 \times 10^6} \approx 0.62 ] [ R_n = \frac{M_u}{\phi f'_c A_g h} = \frac{120 \times 10^6}{0.65 \times 28 \times 160000 \times 400} = \frac{1.2 \times 10^8}{1.1648 \times 10^9} \approx 0.103 ] [ A_g - 0