Free PE Civil Exam Flashcards

Bank volume is the in-place, undisturbed volume of soil before it is disturbed. Loose volume is that same soil after excavation, expanded by air voids introduced during digging. The swell factor (loose ÷ bank, always greater than 1) converts between the two.

LCY = BCY x swell factor = 10,000 x 1.25 = 12,500 LCY. Always multiply bank volume by the swell factor to size trucking, since excavated soil takes up more space than it did in place.

Shrinkage factor = compacted volume ÷ bank volume, and it is typically less than 1. Compaction closes air voids left by the natural in-place soil structure, so a given bank volume yields less volume once recompacted in a fill.

Total Float = LS - ES (equivalently LF - EF). It is the amount an activity can slip without delaying the overall project finish date.

Free Float = the successor activity's early start (ES) minus this activity's early finish (EF). It measures delay tolerance without pushing ANY downstream activity, whereas Total Float measures delay tolerance without pushing the PROJECT finish.

The longest path of activities from project start to finish. Every activity on it has zero total float, so any delay to a critical activity delays the entire project's completion date.

PV is the budgeted cost of work that was scheduled to be done by now. EV is the budgeted cost of work actually performed. AC is the real cost incurred to perform that work. All EVM performance indices are built from these three values.

CPI = EV / AC and SPI = EV / PV. CPI under 1.0 means the project is over budget (money spent exceeds the value of work earned); SPI under 1.0 means the project is behind schedule.

5 feet is OSHA's trigger depth requiring a protective system in trenches and excavations, with the required system depending on the soil's Type A (most stable), B, or C (least stable, e.g., saturated or previously disturbed) classification.

Formwork is the mold that shapes wet concrete. Falsework is the temporary structure supporting concrete placement or erection work (such as bridge segments) until it becomes self-supporting. Shoring is vertical or lateral support that prevents collapse of an excavation or an existing structure.

G = gravel and S = sand, the coarse-grained soils (more than 50% retained on the No. 200 sieve). M = silt and C = clay, the fine-grained soils. Secondary letters (W/P for gradation, H/L for plasticity) refine each group further.

PI = Liquid Limit (LL) minus Plastic Limit (PL). A high PI signals a highly plastic, compressible, moisture-sensitive clay (like CH) prone to significant volume change and reduced strength when wet.

qult = cNc + qNq + 0.5gammaBNgamma. Nc captures the contribution from soil cohesion, Nq from surcharge/overburden pressure, and Ngamma from the soil's unit weight and footing width (self-weight of the failure wedge).

qallow = qult / FS, where the factor of safety (commonly 2.5-3.0 for shallow foundations) accounts for uncertainty in soil parameters and keeps service loads well below the bearing failure threshold.

sigma' = sigma - u (total stress minus pore water pressure). Effective stress is the grain-to-grain contact stress that actually resists deformation, so it governs shear strength and consolidation - not the total stress, which includes the water's weight.

e = Vv / Vs, the volume of voids over the volume of solids. A high void ratio indicates a loose, more compressible soil with greater settlement potential than a dense, low-void-ratio soil.

Ka (active, wall moves away from the soil) < K0 (at-rest, no wall movement) < Kp (passive, wall pushes into the soil). Passive pressure is always largest because the soil is being compressed rather than allowed to expand.

Skin friction (shaft resistance) develops along the pile's embedded side length; end bearing develops at the pile tip on firm strata. Total pile capacity is the sum of both, with the dominant component depending on the soil profile and pile type.

Loose, saturated, cohesionless (sandy) soil subjected to rapid loading such as an earthquake. Pore pressure builds faster than it can dissipate, driving effective stress toward zero so the soil behaves like a fluid and loses bearing and shear strength.

Immediate settlement occurs quickly from elastic deformation. Consolidation settlement in saturated clays happens slowly over time as excess pore water is squeezed out under load, letting the soil skeleton compress - this time-dependent behavior is what geotechnical engineers must predict for clay-supported structures.

1.2D + 1.6L (plus other applicable factored loads such as 0.5Lr, S, or R) typically governs ordinary gravity design. The 1.2 factor reflects lower dead-load uncertainty and the 1.6 factor reflects the greater variability of live load.

D + L, using unfactored service-level loads. ASD compares those service loads against an allowable stress that already has one built-in safety factor, while LRFD factors loads up and resistance down as two separate steps.

Wood design. NCEES specifications require ASD for timber, while steel and concrete problems may be worked using either ASD or LRFD depending on the design standard referenced in the question.

The portion of floor or roof area that structurally drains its load to a specific supporting member (beam, column, or footing). Multiplying tributary area by the load per square foot gives that member's design load.

The moment diagram is the integral of the shear diagram (dM/dx = V); equivalently, the shear diagram is the slope of the moment diagram. Moment is maximum where the shear diagram crosses zero.

f = Mc/I, where M is bending moment, c is the distance from the neutral axis to the extreme fiber, and I is the section's moment of inertia. Equivalently f = M/S using section modulus S = I/c.

delta max = PL^3 / (48EI), occurring at midspan. Because deflection scales with the CUBE of span length, span is the dominant variable controlling deflection.

phi = 0.9, the highest reduction factor in the code. Tension-controlled sections yield in the reinforcing steel well before the concrete crushes, producing ductile, predictable failure with warning before collapse.

The embedment length of reinforcing bar needed to transfer force between the bar and surrounding concrete through bond stress, preventing the bar from pulling out before it reaches its design (yield) stress.

LRFD: phi*Rn >= sum(gamma_i * Q_i) - factored resistance must exceed factored load effects. ASD: Rn / Omega >= sum(Q_i) - nominal resistance divided by a safety factor must exceed unfactored service loads.

PC (Point of Curvature) is where the curve begins and the incoming tangent ends. PI (Point of Intersection) is where the two tangents would meet if extended. PT (Point of Tangency) is where the curve ends and the next tangent begins.

SSD = 1.47*V*t + V^2 / (30*(f +/- G)), combining (1) reaction/perception distance (1.47*V*t, V in mph, t about 2.5 seconds) and (2) braking distance, adjusted for friction f and grade G (uphill increases required distance, downhill decreases the braking term's demand).

e + f = V^2 / (15R). Superelevation and side friction together supply the centripetal force that keeps a vehicle on the curve at design speed.

On a crest, the road surface itself blocks the line of sight over the high point, so daytime SSD governs. On a sag there is no daytime obstruction, so at night the limiting factor is how far the vehicle's headlight beam reaches ahead.

LOS is a qualitative A-through-F grading (per the Highway Capacity Manual) of traffic flow quality, based on measures like density, speed, and delay - A is free flow and F is breakdown/gridlock.

v/c = actual traffic volume divided by the roadway's maximum capacity. A v/c ratio above 1.0 means demand exceeds capacity, producing oversaturated flow, queuing, and LOS F conditions.

PHF = hourly volume / (4 x peak 15-minute volume), measuring how uniformly traffic is distributed within the peak hour. A PHF near 1.0 means steady flow across the hour; a low PHF means traffic is concentrated in a short, intense burst.

The yellow (change) interval plus the all-red interval. Together they give a vehicle already in the intersection time to clear before conflicting traffic receives a green, preventing right-angle collisions.

ESAL converts mixed traffic (cars, trucks, and buses with varying axle loads) into an equivalent number of standard 18,000-lb single-axle load repetitions, which pavement design methods use to size pavement thickness for cumulative traffic damage over the design life.

A composite index of the overall structural capacity required from the pavement's combined layers (surface, base, subbase), built from each layer's thickness, layer coefficient, and drainage coefficient - a higher SN means a thicker or stronger pavement section.

Q = CiA, where Q is peak flow rate, C is the runoff coefficient (dimensionless), i is rainfall intensity (in/hr) at the time of concentration, and A is drainage area (acres). It is best suited to small watersheds, roughly under 200 acres.

C is the fraction of rainfall that becomes surface runoff rather than infiltrating or being stored. Impervious surfaces (pavement, rooftops) push C toward 1.0; permeable, vegetated, or sandy soils lower it.

Tc is the time for runoff to travel from the hydraulically most distant point in the watershed to the point of analysis. Design rainfall intensity is selected at a duration equal to Tc, since that produces the peak flow for the watershed's response time.

For larger or more complex watersheds, or when a full runoff hydrograph is needed rather than just a peak flow value - the SCS/NRCS method uses a soil- and land-cover-based curve number to generate a complete time-distributed hydrograph.

Q = (1.49/n) * A * R^(2/3) * S^(1/2) in US units, where A is flow area, R is hydraulic radius, and S is channel slope. The coefficient n describes channel surface friction - a higher n means a rougher channel and lower velocity.

Hazen-Williams estimates head loss and velocity in closed, pressurized pipe flow (such as water distribution mains) using a C-coefficient for pipe roughness, whereas Manning's equation applies to gravity-driven open-channel flow.

It calculates head loss due to friction in pipe flow: hf = f*(L/D)*(V^2/2g). The friction factor f depends on both pipe roughness and Reynolds number (flow regime), making Darcy-Weisbach more general than Hazen-Williams.

The sum of pressure head, velocity head, and elevation head is constant along a streamline (ignoring losses): p/gamma + V^2/2g + z = constant - an expression of conservation of energy in flowing fluid.

The Froude number distinguishes subcritical flow (Fr less than 1: slow, deep, gravity-dominated) from supercritical flow (Fr greater than 1: fast, shallow, inertia-dominated). Fr = 1 is critical flow, the boundary between the two regimes.

Coagulation, then flocculation, then sedimentation, then filtration, then disinfection. BOD (Biochemical Oxygen Demand) measures the oxygen consumed by microorganisms breaking down organic matter in water - a key indicator of wastewater's organic pollution strength.