NEC Civil Engineering cheat sheet
NEC Civil Engineering · Keep the key ideas within reach.
Civil Engineering
Structural load combinations (ASD): D; D+L; D+(L or S or R); D+0.75L+0.75(Lr or S or R)+0.75W; 0.6D+0.6W; 0.6D+0.7E - use the combination producing the largest effect.
LRFD basic combination: U = 1.2D + 1.6L + 0.5(Lr or S or R); wind combination U = 1.2D + 1.0W + 1.0L + 0.5(Lr or S or R).
Allowable soil bearing pressure q_allow = q_ult / FS, with FS typically 2.5–3.0 for shallow foundations; footing area A = P_total / q_allow (service loads).
Terzaghi bearing capacity (strip footing): q_ult = c·Nc + q·Nq + 0.5·γ·B·Nγ; N factors depend on friction angle φ.
One-way slab shear check: φVc = φ·0.17·λ·√f'c·b·d (SI, MPa, mm); beam shear capacity uses the same expression with bw instead of b.
Minimum reinforcement ratio for beams: As,min = max(0.25·√f'c/fy, 1.4/fy)·bw·d (SI, MPa).
Concrete modulus of elasticity: Ec = 4700·√f'c MPa (normal-weight concrete); steel Es = 200,000 MPa.
Manning's equation for open channels: Q = (1/n)·A·R^(2/3)·S^(1/2) (SI); hydraulic radius R = A/P.
Rational method peak flow: Q = C·i·A, where C is runoff coefficient, i is rainfall intensity, A is drainage area - units must be consistent.