IESL Part II Civil flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Target mean strength

The concrete strength used for mix design, set above the specified characteristic strength to account for variability: f'cr = f'c + 1.34S or f'c + 2.33S − 500 psi, whichever is greater.

Slump test purpose

A workability test (ASTM C143) measuring the vertical drop of a concrete cone; it indicates consistency but not strength, and is invalid if the sample shears or slumps asymmetrically.

Tension-controlled section

A reinforced concrete section with a net tensile strain at nominal strength of at least 0.005; it permits φ = 0.90 in flexure and exhibits ductile, gradual failure.

Balanced reinforcement ratio

The steel ratio at which concrete crushing and steel yielding occur simultaneously: ρb = 0.85β1(f'c/fy)(0.003/(0.003+fy/Es)); sections with less steel are tension-controlled.

Development length

The embedment length needed to develop the yield strength of a reinforcing bar in tension through bond; it depends on bar diameter, fy, f'c, cover, and transverse confinement.

Minimum flexural reinforcement

The least tension steel required in a beam to prevent brittle failure on cracking: As,min = max(0.25√f'c/fy, 1.4/fy)·bw·d for non-prestressed beams.

Nominal maximum aggregate size

The largest sieve through which most aggregate passes; limited to 1/5 of the narrowest form dimension, 1/3 of slab depth, or 3/4 of clear bar spacing.

Water-cement ratio

The mass of water divided by the mass of cementitious material; a lower ratio increases strength and reduces permeability, and durability exposure classes set maximum values.

Effective span

The span used in structural analysis: the clear span plus the lesser of the support depth or the bearing width at each end, not the centre-to-centre distance.

Section modulus

The ratio S = I/c, where I is the second moment of area and c is the distance to the extreme fibre; the maximum bending stress equals M/S.

Euler buckling load

The elastic critical load of a slender column: Pcr = π²EI/(KL)², where K is the effective length factor depending on end conditions.

Effective length factor K

A multiplier on the unbraced length of a column: 1.0 for pinned–pinned, 0.5 for fixed–fixed, 0.7 for fixed–pinned, and 2.0 for a cantilever.

Degree of indeterminacy

The number of redundant reactions or internal forces beyond those needed for equilibrium; indeterminate structures require compatibility of displacements for solution.

Terzaghi bearing capacity

The ultimate bearing pressure of a shallow strip footing: qult = c·Nc + q·Nq + 0.5·γ·B·Nγ, with N factors depending on the soil friction angle.

Effective stress

The stress carried by the soil skeleton: σ' = σ − u, where σ is total stress and u is pore water pressure; it controls shear strength and compressibility.

Plasticity index

The difference between the liquid limit and the plastic limit (PI = LL − PL); a high PI indicates a highly compressible clay, while a low PI indicates silt or sandy soil.

Consolidation settlement

The one-dimensional compression of a clay layer: Sc = Cc·H/(1+e0)·log10((σ'0+Δσ)/σ'0), where Cc is the compression index and σ'0 the initial effective stress.

Critical hydraulic gradient

The upward seepage gradient at which effective stress becomes zero, causing quick conditions: ic = (Gs − 1)/(1 + e), with Gs the specific gravity and e the void ratio.

Rankine active coefficient

The ratio of horizontal to vertical effective stress at failure in extension: Ka = tan²(45° − φ/2); the passive coefficient is Kp = tan²(45° + φ/2).

Rational method

A peak flow formula for small catchments: Q = C·i·A/360 (SI, i in mm/h and A in hectares), where C is the runoff coefficient and i the design intensity.

Manning equation

The open-channel velocity formula V = (1/n)·R^(2/3)·S^(1/2), where n is roughness, R the hydraulic radius (A/P), and S the channel slope.

Froude number

The ratio Fr = V/√(gD) classifying open-channel flow: Fr < 1 subcritical, Fr = 1 critical, Fr > 1 supercritical; hydraulic jumps occur when flow transitions to subcritical.

Time of concentration

The travel time of runoff from the most hydraulically remote point to the outlet; it sets the minimum design storm duration for the rational method.

Design truck HL-93

The AASHTO live load model with 35 kN, 145 kN, and 145 kN axles spaced 4.3 m apart, with the rear spacing variable from 4.3 m to 9.0 m.

Dynamic load allowance

The impact factor IM = 33% applied to the design truck or tandem axle loads in bridge design; it is not applied to the design lane load.

Stopping sight distance

The distance for a driver to perceive, react, and stop: SSD = 0.278·V·t + V²/(254·(f ± G)), with t the reaction time and f the friction factor.

Superelevation equation

The relationship V² = 127·R·(e + f) (SI, V in km/h, R in metres), where e is the superelevation rate and f the side friction factor.

Vertical curve K value

The ratio K = L/A, where L is the curve length and A the algebraic grade change in percent; a larger K gives a flatter curve and longer sight distance.

Critical path

The longest path through a project network; it has zero total float and determines the minimum project duration, and any delay on it delays the project.

Total float

The amount of time an activity can be delayed without delaying the project completion: TF = LS − ES = LF − EF; the critical path has zero total float.

Cost performance index

CPI = EV/AC, where EV is earned value and AC actual cost; a value below 1.0 indicates the project is over budget.

Live load reduction

A permitted reduction for members supporting large tributary areas: L = L0·(0.25 + 4.57/√(KLL·AT)) (SI, AT in m²), with a lower limit of 0.4L0 for one floor.