NEC Civil Engineering flashcards
NEC Civil Engineering · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Allowable bearing capacity
- The maximum soil pressure a foundation may impose under service loads, equal to ultimate bearing capacity divided by a factor of safety, typically 2.5 to 3.0.
- Terzaghi bearing capacity equation
- q_ult = c·Nc + q·Nq + 0.5·γ·B·Nγ for a strip footing, where Nc, Nq, Nγ are functions of the soil friction angle.
- Factor of safety definition
- Ratio of ultimate resistance to applied service load; for foundations it is applied to bearing capacity, and for slopes to resisting versus driving shear forces.
- Effective stress principle
- Total vertical stress minus pore water pressure gives effective stress; soil strength and settlement depend on effective stress, not total stress.
- Consolidation settlement
- Time-dependent volume decrease of saturated clay under sustained load as pore water drains; magnitude depends on compression index, thickness, and stress increase.
- Standard penetration test
- In-situ test counting blows to drive a split sampler 300 mm; the N-value correlates with relative density and is corrected for overburden and energy.
- Atterberg limits
- Water contents marking clay soil consistency transitions: liquid limit, plastic limit, and shrinkage limit; plasticity index equals liquid minus plastic limit.
- Active earth pressure
- Lateral pressure when the wall moves away from the soil enough to mobilize full shear resistance; coefficient Ka = tan²(45° − φ/2) for level backfill.
- Passive earth pressure
- Lateral resistance developed when a wall pushes into the soil; coefficient Kp = tan²(45° + φ/2) for level backfill, much larger than active pressure.
- Manning equation
- Q = (1/n)·A·R^(2/3)·S^(1/2) in SI units; n is roughness, A flow area, R hydraulic radius (area/wetted perimeter), S channel slope.
- Rational method
- Peak runoff Q = C·i·A, where C is the runoff coefficient, i rainfall intensity for the time of concentration, and A drainage area.
- Time of concentration
- The time for runoff to travel from the hydraulically most distant point of a catchment to the outlet; used to select rainfall intensity in the rational method.
- Hydraulic jump
- Abrupt transition from supercritical to subcritical flow, dissipating energy; conjugate depths satisfy momentum conservation across the jump.
- Critical flow condition
- Flow at Froude number equal to 1, where specific energy is minimum for a given discharge; occurs at the control section of channels and weirs.
- ASD load combination
- Allowable stress design combines service loads, for example dead plus live, or dead plus wind, and compares resulting stresses to allowable values.
- LRFD load combination
- Strength design applies factored loads such as 1.2D + 1.6L and compares factored demand to factored resistance φRn, with resistance factor below one.
- Strength reduction factor
- φ in LRFD reduces nominal member strength to account for material variability and failure mode; tension-controlled flexure uses about 0.90, shear about 0.75.
- Balanced section
- Reinforced concrete section where concrete crushes and steel yields simultaneously; defines the limiting reinforcement ratio for tension-controlled behavior.
- Minimum beam reinforcement
- As,min = max(0.25·√f'c/fy, 1.4/fy)·bw·d in SI units, ensuring the section does not fail abruptly upon first cracking.
- Concrete modulus of elasticity
- Ec = 4700·√f'c MPa for normal-weight concrete, used to compute stiffness, deflections, and transformed section properties.
- Neutral axis depth
- Depth where strain is zero in a bending member; for cracked concrete sections it locates the centroid of the transformed cracked section.
- Shear capacity of concrete
- Nominal one-way shear strength Vc = 0.17·λ·√f'c·bw·d in SI units, reduced by φ to obtain design shear capacity.
- Development length
- Embedment length required to transfer bar force to concrete without pullout or splitting; depends on bar size, fy, f'c, cover, and spacing.
- Slenderness ratio
- Effective length divided by radius of gyration for columns; high values indicate buckling governs and second-order effects must be considered.
- Euler buckling load
- Critical axial load Pcr = π²EI/(KL)²; the effective length factor K depends on end restraint conditions of the compression member.
- Shear center
- Point through which a transverse load must act to produce no twisting of a thin-walled section; offset from centroid in unsymmetric sections.
- Plastic section modulus
- Z equals the sum of first moments of area about the equal-area axis; plastic moment Mp = Fy·Z exceeds the yield moment based on elastic modulus.
- Compaction versus consolidation
- Compaction removes air by mechanical densification at constant water content; consolidation removes water from saturated soil over time under sustained load.
- Darcy law
- Seepage velocity v = k·i, where k is hydraulic conductivity and i is hydraulic gradient; flow rate equals v times cross-sectional area.
- Liquefaction susceptibility
- Saturated loose sands below the water table can lose shear strength during earthquake shaking; risk rises with low density and high water table.
- Culvert hydraulic capacity
- Governed by either inlet control (entrance geometry and headwater) or outlet control (barrel friction and tailwater); the lower capacity governs.
- Detention storage routing
- Peak outflow is reduced and delayed relative to inflow by temporary storage; storage volume equals the area between inflow and outflow hydrographs.