Glossary
63 terms, defined so each one stands on its own
Construction Engineering
- CrashingShortening a project schedule by adding resources to critical activities, cheapest per day first.
- Critical PathThe longest chain of dependent activities through a schedule, which sets the project duration.
- Earned ValueThe budgeted cost of the work actually completed to date.
- Swell and ShrinkageThe change in volume of soil between its natural (bank), excavated (loose) and compacted states.
- Total FloatHow long an activity can be delayed without delaying the project, LS − ES.
Dynamics
- Coefficient of RestitutionThe ratio of the speed of separation to the speed of approach in an impact, from 0 to 1.
- ImpulseA force integrated over the time it acts, equal to the change in momentum it produces.
- Work-Energy PrincipleThe work done on a body between two positions equals its change in kinetic energy.
Engineering Economics
- Annual WorthA project’s cash flows expressed as an equivalent uniform amount per year at the interest rate.
- Benefit-Cost RatioThe equivalent worth of a public project’s benefits divided by its costs; 1.0 or more is acceptable.
- Cash Flow DiagramA timeline showing when each cost and benefit occurs, with direction indicated by arrow.
- Present WorthThe value today of a future cash flow, discounted at the interest rate.
- Sunk CostMoney already spent that cannot be recovered whichever alternative is chosen, and so is ignored in the decision.
Ethics and Professional Practice
- Public Safety ObligationAn engineer's paramount duty to protect public health, safety and welfare.
- Responsible ChargeDirect control and personal supervision of engineering work, which a licensee must hold before sealing it.
- Standard of CareThe level of skill a reasonably prudent engineer would exercise in the same circumstances, used to judge negligence.
Fluid Mechanics
- Bernoulli EquationA relation trading pressure head, velocity head and elevation head along a streamline.
- Centre of PressureThe point on a submerged surface where the resultant hydrostatic force acts — always below the centroid.
- Continuity EquationA statement that mass flow rate is conserved along a streamtube.
- Head LossEnergy lost per unit weight of fluid, usually to pipe friction and fittings.
- Reynolds NumberThe ratio of inertial to viscous forces in a flow, which decides whether it is laminar or turbulent.
Geotechnical Engineering
- ConsolidationThe slow settlement of a saturated clay as water is squeezed out of its pores under a new load.
- Effective StressTotal stress minus pore water pressure: the stress carried by the soil skeleton.
- Plasticity IndexThe range of water content over which a fine-grained soil is plastic: liquid limit minus plastic limit.
- Relative CompactionField dry unit weight as a percentage of the laboratory maximum dry unit weight from a Proctor test.
- Shear Strength (Soil)The largest shear stress a soil can sustain, τ = c′ + σ′·tan φ′ by the Mohr-Coulomb criterion.
- Void RatioThe volume of voids in a soil divided by the volume of its solids.
Materials
- Fineness ModulusAn index of how coarse a fine aggregate is: the sum of cumulative percentages retained on standard sieves, divided by 100.
- Modulus of ElasticityThe slope of the linear region of the stress-strain curve — a measure of stiffness, not strength.
- Proportional LimitThe greatest stress for which stress and strain remain directly proportional.
- Saturated Surface-Dry (SSD)The aggregate moisture state with pores full of water but no water on the surface — the basis of mix design.
- Water-Cement RatioThe weight of mixing water divided by the weight of cement — the main control on concrete strength.
- Yield StrengthThe stress at which a material begins to deform permanently.
Mathematics and Statistics
- Confidence IntervalA range, computed from a sample, that contains the true population value with a stated confidence.
- Definite IntegralThe signed area under a curve between two limits, found from an antiderivative or estimated numerically.
- Standard DeviationA measure of spread: the square root of the average squared distance of data from their mean.
Mechanics of Materials
- Neutral AxisThe line in a bent beam’s cross-section where bending stress and strain are zero.
- Polar Moment of InertiaThe section property that sets a round shaft’s resistance to twisting, J = πd⁴/32 for a solid shaft.
- Principal StressThe largest and smallest normal stresses at a point, which act on planes carrying no shear.
Statics
- CentroidThe geometric centre of an area: the point where its first moments about any axis balance.
- EquilibriumThe state in which all forces and all moments acting on a body sum to zero.
- Free-Body DiagramA sketch of one isolated body showing every external force and moment acting on it.
- Method of SectionsFinding truss member forces by cutting the truss and applying equilibrium to one side of the cut.
- Moment of Inertia (Area)The second moment of an area about an axis, which measures how strongly a cross-section resists bending.
- Zero-Force MemberA truss member carrying no load under a given loading condition.
Structural Engineering
- Effective LengthA column’s length multiplied by a factor K that accounts for how its ends are restrained.
- Influence LineA graph of one response — a reaction, shear or moment at a point — as a unit load moves across a structure.
- Load and Resistance Factor Design (LRFD)Strength design in which factored loads must not exceed the nominal strength multiplied by a resistance factor.
- Statically IndeterminateDescribes a structure with more unknown reactions or member forces than the equations of equilibrium can find.
Surveying
- Azimuth and BearingTwo ways of stating a line’s direction: azimuth clockwise from north, 0–360°; bearing as an angle from north or south.
- Backsight and ForesightLevel rod readings taken on a point of known elevation (backsight) and on a point to be found (foresight).
- BenchmarkA permanent, marked point of known elevation from which a leveling run starts or closes.
- Latitude and DepartureThe north-south and east-west components of a traverse line, L·cos(bearing) and L·sin(bearing).
Transportation Engineering
- Equivalent Single Axle Load (ESAL)The number of 18,000 lb single-axle passes that would do the same pavement damage as a mixed traffic stream.
- Peak Hour FactorThe hourly volume divided by four times the busiest 15-minute volume within that hour.
- Stopping Sight DistanceThe distance a driver needs to see ahead to perceive a hazard, react and brake to a stop.
- SuperelevationThe cross slope given to a roadway on a horizontal curve to counter the outward pull on vehicles.
Water Resources and Environmental Engineering
- Biochemical Oxygen Demand (BOD)The oxygen microorganisms consume while breaking down the organic matter in water, usually measured over five days.
- Critical DepthThe depth at which a given open-channel flow has the least specific energy and a Froude number of 1.
- DrawdownThe lowering of the water table or piezometric surface around a pumping well.
- Hydraulic JumpAn abrupt rise in water surface where supercritical flow turns subcritical, dissipating energy.
- Hydraulic RadiusFlow area divided by wetted perimeter, the size term in open-channel equations.
- Time of ConcentrationThe time runoff takes to travel from the hydraulically most distant point of a watershed to the outlet.