Strip Footing Capacity

Output:

Definitions
• ϕ_c = Resistance factor for concrete
• ϕ_s = Resistance factor for reinforcing steel
• f_c = Specified concrete strength (psi)
• f_y = Specified reinforcing steel yield strength (ksi)
• λ = Concrete density modification factor; 1.0 for normal density concrete
• A_s = Area of reinforcing steel (in²)
• α₁ = Stress modification factor for equivalent stress block
• β = Cracked concrete shear factor
• d = Depth to primary reinforcing (in)
• B = Width of footing (in)
• L_f = Footing length (ft)
• t_w = Wall thickness (in)
• Cover = concrete cover to centroid of reinforcing (in)
• q_a = Allowable bearing resistance for service conditions (ksf)
• q_ult = Ultimate bearing resistance (ksf)
• q_s = Service bearing demand (ksf)
• q_u = Factored ultimate bearing demand (ksf)
• d_v = Shear depth, normally taken as 0.9d (in)
Calculate soil bearing stresses
DCR = 91%
• P_s = (D + L)/L_f = (4 + 3) / 1 = 7 kip/ft
• P_u = max[1.4D, 1.25D + 1.5L] / L_f = max[5.6, 9.5] / 1 = 9.5 kip/ft
• q_s = P_s / B = 7 / (30/12) = 2.8 ksf
• q_u = P_u / B = 9.5 / (30/12) = 3.8 ksf
Calculate shear capacity at critical section, located 'dv' away from the face of the wall
DCR = 25%
• d = h - cover = 12 - 3 = 8.6875 in
• d_v = max[0.9d, 0.72h] = 0.72 (12) = 8.64 in
• β = 0.21 if h < 14in or (B-t_w < 2d_v)). Else β = 230/(1000 + d_v*25.4). --> β = 0.21
• V_u,crit = q_u L_f (B - t_w - d_v) = (3.8) (1) (30 - 12 - 8.64)/12 = 2.96 kip
• V_c = ϕ_c λ β √f_c L_f d_v = (0.65) (1) (0.21) (0.852) (1) (8.64) = 12.05 kip
• V_u / V_r = 2.96 / 12.05 = 0.25 --> okay
Calculate the flexural capacity at the critical section, located at the face of the wall
DCR = 3%
• M_u = q_u L_f (B-t_w)² / 2 = (3.8) (1) ((30 - 12)/12)² / 2 = 51.36 kip-in = 4.28 kip-ft
• M_r = ϕ_s A_s f_y (d - a/2), where a = (ϕ_s A_s f_y) / (ϕ_c α₁ f_c L_f)
• Mr = (0.85) (5) (60) (8.6875 - 3.269/2)
• Mr = (255) (7.053)
• Mr = 1799 kip-in = 149.88 kip-ft
• M_u / M_r = 4.28 / 149.88 = 0.03 --> okay
User Notes:
User notes