Junior Engineer flashcards

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

Hooke's Law

Within the elastic range, stress is proportional to strain: σ = E·ε. The constant E is Young's modulus, a material property measured in the same units as stress, such as MPa or ksi.

Section Modulus

S = I/c, where I is the moment of inertia about the neutral axis and c is the distance to the extreme fiber. Bending stress is then σ = M/S, so a larger S lowers stress.

Poisson's Ratio

The negative ratio of lateral strain to axial strain under uniaxial loading, ν = −ε_lateral/ε_axial. Typical values are about 0.3 for steel and 0.15–0.2 for concrete.

Thermal Stress

When thermal movement is fully restrained, stress equals E·α·ΔT, where α is the coefficient of thermal expansion and ΔT the temperature change. Free movement produces no stress.

Parallel Axis Theorem

The moment of inertia about any axis equals that about the parallel centroidal axis plus area times the square of the distance between axes: I = I_c + A·d².

Neutral Axis

The line through a bending cross-section where longitudinal strain and bending stress are zero. It passes through the centroid for elastic bending of a homogeneous section.

Resultant Vector

For perpendicular components, magnitude R = √(Fx² + Fy²) and direction θ = arctan(Fy/Fx). For non-perpendicular vectors, resolve into components, sum, then recombine.

Moment of a Force

The rotational effect about a point: M = F·d, where d is the perpendicular distance from the point to the line of action. Units are force times length, such as kN·m.

Continuity Equation

For steady incompressible flow, Q = A·v is constant along a pipe, so A₁v₁ = A₂v₂. Reducing the cross-sectional area increases velocity proportionally.

Centroid of a Triangle

The centroid lies one-third of the height above the base, measured along the median from the base, and at the average of the vertex coordinates.

Drawing Scale Ratio

A scale of 1:n means one drawing unit represents n real units. A 25 mm dimension on a 1:100 plan equals 2,500 mm, or 2.5 m, on site.

Rebar Mass per Meter

For a round steel bar of diameter d in millimeters, mass ≈ d²/162 kg/m. A 16 mm bar gives about 1.58 kg/m; a 20 mm bar about 2.47 kg/m.

Bill of Quantities

A measured schedule listing work items with descriptions, units, and quantities, used for pricing and progress payment. It is distinct from the schedule of values.

Cutting-Plane Line

A heavy chain line on a drawing marking where a section is taken, with arrows showing the viewing direction and letters matching the section drawing title.

Order of Precedence

The contract clause ranking documents when they conflict. Specifications commonly govern quality over drawings, and larger-scale details govern over smaller-scale plans.

Average End Area Method

Earthwork volume between two sections: V = L·(A₁ + A₂)/2, where L is the spacing and A₁, A₂ are cross-section areas. The prismoidal formula adds a mid-section term.

Formwork Stripping Strength

Soffit formwork for slabs and beams is removed only after concrete reaches a specified strength, commonly about 70% of f'c, confirmed by field-cured cylinders.

Crane Load Chart

A manufacturer table giving capacity at each combination of radius and boom length. Capacity falls as radius increases, and rigging and attachment weights must be deducted.

Wellpoint Dewatering

A line of small-diameter suction points installed around an excavation lowers the water table by roughly 4–6 m per stage, suitable for granular soils.

Height of Instrument

HI = known elevation + backsight. A new point's elevation is HI minus the foresight reading on that point. The run checks when ΣBS − ΣFS equals the elevation change.

Closed Traverse Angle Check

For a closed polygon with n sides, the sum of interior angles must equal (n − 2) × 180°. Any misclosure is distributed among the angles before coordinates are computed.

Latitude and Departure

Latitude = distance × cos(bearing) and departure = distance × sin(bearing). A closed traverse requires the sum of latitudes and the sum of departures each to equal zero.

Slope Correction

A measured slope distance is longer than the horizontal distance. The correction is C = −h²/(2L), where h is the elevation difference and L the slope distance.

Hierarchy of Controls

Effectiveness order from highest to lowest: elimination, substitution, engineering controls, administrative controls, then personal protective equipment. PPE is the last line of defense.

Excavation Protective System

Excavations 1.5 m or deeper require sloping, benching, shoring, or shielding unless entirely in stable rock. A competent person inspects daily and after rain.

Recordable Incident Rate

Incident rate = (recordable incidents × 200,000) / hours worked. The 200,000 constant represents 100 full-time workers at 40 hours for 50 weeks.

Total Float

The time an activity can be delayed without delaying project completion: LS − ES or LF − EF. Activities on the critical path have zero total float.

Critical Path

The longest-duration chain of dependent activities through the network. It sets the project duration, and any delay on it delays completion unless compressed.

Cost Performance Index

CPI = EV/AC, earned value divided by actual cost. A value below 1.0 indicates the work cost more than budgeted; above 1.0 indicates cost savings.

Estimate at Completion

EAC = BAC/CPI when current cost performance continues. If remaining work proceeds at the budgeted rate, EAC = AC + (BAC − EV).

Liquidated Damages

A contract-specified sum per day of delay that is a genuine pre-estimate of the owner's loss. Courts may reject it if it is an unenforceable penalty.

Substantial Completion

The stage when the work is sufficiently complete for its intended use. It typically starts the warranty period and allows partial release of retainage.

Concrete Slump Test

A workability test per ASTM C143: concrete is placed in a standard cone in three layers, the cone is lifted, and the drop of the sample is measured.

Standard vs Modified Proctor

Both find maximum dry density and optimum moisture content. Modified Proctor uses greater compaction energy, giving higher maximum dry density at lower optimum moisture content.