WBPSC AE Civil key terms

The internal turning effect produced at a section of a beam by external loads, measured as force multiplied by perpendicular distance and expressed in kN·m, causing bending stress across the section.

The ratio of a section's second moment of area to the distance from the neutral axis to the extreme fibre; it converts bending moment into maximum bending stress through the relation stress equals moment divided by section modulus.

The line within a beam cross-section where longitudinal bending stress is zero, passing through the centroid for homogeneous elastic sections and separating compressive and tensile zones during bending.

The internal transverse force at a beam section equal to the algebraic sum of all vertical loads and reactions on one side of that section, producing diagonal tension and shear stress in the material.

The maximum or minimum normal stress acting on a plane where shear stress is zero, found from the stress transformation equations and used to check failure criteria in combined loading problems.

A graphical construction plotting normal stress on the horizontal axis and shear stress on the vertical axis, from which principal stresses, maximum shear stress and plane orientations are read directly.

The number of unknown reaction and internal force components exceeding the available equilibrium equations; it governs which analysis method, such as force or displacement methods, can be applied to a structure.

A diagram showing how a particular response, such as reaction, shear or moment at a fixed point, varies as a unit load moves across the span; used to place moving loads for maximum effect.

A displacement-based iterative procedure for continuous beams and frames in which unbalanced fixed-end moments are distributed according to member stiffness and carried over to adjacent joints until residual moments become negligible.

A design philosophy checking that a structure resists collapse with partial safety factors on loads and materials, and that it performs acceptably in service without excessive deflection or cracking.

The value of material strength, such as concrete cube strength or steel yield stress, below which not more than five percent of test results are expected to fall; it forms the basis of design calculations.

A multiplier applied to loads or material strengths in limit state design to account for uncertainty, variability and the consequences of failure, ensuring adequate reliability of the designed member.

A reinforced concrete section proportioned so that concrete crushing and steel yielding occur simultaneously at ultimate load; it marks the boundary between under-reinforced and over-reinforced behaviour.

A dimensionless ratio of inertial to viscous forces in fluid flow; low values indicate laminar flow, high values turbulent flow, and it governs similarity in hydraulic model studies.

A dimensionless ratio of inertial to gravitational forces, equal to velocity divided by the square root of gravitational acceleration times depth; it classifies open channel flow as subcritical, critical or supercritical.

An abrupt rise in water surface when supercritical flow changes to subcritical flow, dissipating large amounts of kinetic energy through turbulence and commonly used below spillways as an energy dissipator.

The total energy head of flowing water measured relative to the channel bed, equal to depth plus velocity head; its minimum value defines critical flow at a given discharge.

The direct runoff hydrograph resulting from one unit depth of effective rainfall occurring uniformly over a catchment in a specified duration, used to derive flood hydrographs for other rainfall events.

The time taken for runoff from the most remote point of a catchment to reach the outlet; it determines the critical rainfall duration for peak discharge estimation.

A simple peak discharge formula multiplying runoff coefficient, rainfall intensity for the time of concentration and catchment area; suitable for small urban catchments where storage effects are minor.

The technique of separating the slowly varying groundwater contribution from the total stream hydrograph so that direct surface runoff attributable to a rainfall event can be isolated and analysed.

Biochemical oxygen demand: the dissolved oxygen consumed by microorganisms while oxidising organic matter in a water sample under specified conditions, commonly five days at 20 degrees Celsius, indicating pollution strength.

Chemical oxygen demand: the oxygen equivalent of organic matter oxidised by a strong chemical oxidising agent under acidic conditions, measured rapidly and including non-biodegradable matter that BOD does not capture.

The natural ability of a flowing water body to reduce pollution through dilution, sedimentation, oxidation and biological action as it travels downstream from a discharge point.

The volume in millilitres occupied by one gram of activated sludge after settling for a specified period; it indicates sludge settleability, with high values warning of bulking problems.

The water content at which soil changes from plastic to liquid behaviour, determined by the Casagrande apparatus or cone penetrometer, and used with the plastic limit to compute the plasticity index.

The numerical difference between liquid limit and plastic limit water contents; it measures the range over which a soil remains plastic and helps classify fine-grained soils for engineering use.

The time-dependent reduction in volume of a saturated soil due to expulsion of pore water under sustained loading, causing settlement that must be predicted for foundations on compressible clay.

An in-situ test in which a split spoon sampler is driven into the ground by a standard hammer fall, with the blow count for a specified penetration used to estimate soil density and bearing capacity.

California Bearing Ratio: the ratio of the load required to penetrate a compacted soil or pavement specimen to that required for a standard crushed stone, expressed as a percentage and used in flexible pavement thickness design.

A concrete mix proportioned by testing and calculation to achieve specified strength, durability and workability requirements, as opposed to a nominal mix fixed by volume ratios.

A simple field test in which freshly mixed concrete is placed in a standard cone that is then lifted, and the vertical drop of the concrete measures workability or consistency.

The process of determining the unit cost of a construction item by summing material, labour, plant, overhead and contractor profit components for a specified unit of work.

An itemised schedule listing measured quantities of work with descriptions and units, forming the basis for tendering, valuation of work done and progress payments.

A tabulated statement giving the bar mark, diameter, shape, cutting length and number of reinforcement bars in a member, used to estimate steel quantity and guide site fabrication.

The area of land irrigated by a unit discharge of water continuously throughout the crop season, usually expressed in hectares per cubic metre per second, and the reciprocal of delta.

The total depth of water required by a crop during its entire base period, expressed in centimetres or metres, used to compute the volume of irrigation water needed.

A simple surveying instrument with two perpendicular sights used to set out right angles at a chain line point, commonly employed in chain surveying for offsets.

A permanently established point whose reduced level is known with reference to a datum; it serves as the starting reference for levelling operations and for checking survey accuracy.