KPSC AE Civil key terms

The ratio of the elastic modulus of steel to that of concrete, used in working stress design to transform a reinforced section into an equivalent concrete section for stress calculation.

The perpendicular distance between the compressive force resultant in concrete and the tensile force resultant in steel at a section; its depth governs the resisting moment of a reinforced concrete beam.

A reinforced concrete section in which concrete and steel reach their permissible stresses simultaneously, giving the maximum steel percentage for a given grade combination in working stress design.

A design approach that keeps stresses under service loads below permissible values using linear elastic theory, with a factor of safety applied to material strength rather than to loads.

A design philosophy checking that a structure does not become unfit for use, using partial safety factors on loads and materials for collapse and serviceability conditions separately.

The ratio of the depth of the neutral axis to the effective depth of a reinforced concrete section, denoted xu/d, which determines whether the section is under-reinforced or over-reinforced.

The non-uniform distribution of bending stress across a wide flange, where stresses are higher near the web and lower at the flange tips, affecting effective width assumptions in design.

A diagram showing the variation of a particular response, such as shear, moment or reaction, at a fixed point as a unit load moves across the structure.

A theorem stating that the influence line for a response equals the deflected shape produced by releasing the corresponding restraint and applying a unit displacement there.

A structural analysis technique in which unknown joint displacements are the primary unknowns, related to applied loads through the structure's stiffness matrix and member end forces.

The number of redundant reactions and internal forces beyond those needed for equilibrium, computed from members, joints and reaction components for a given structure.

The negative ratio of lateral strain to longitudinal strain in a material subjected to uniaxial stress, typically about 0.3 for steel and 0.15 to 0.2 for concrete.

The normal stress acting on a plane where shear stress is zero; the two principal stresses at a point are found from the stress transformation equations or Mohr's circle.

The point in a cross-section through which a transverse load must act to produce bending without twisting; for unsymmetric sections it does not coincide with the centroid.

The slope of the linear portion of a stress-strain curve, expressing a material's stiffness in tension or compression within its elastic range.

A sudden transition from supercritical to subcritical flow in an open channel, accompanied by turbulence and energy loss, used as an energy dissipator below spillways.

A dimensionless ratio of inertial force to gravitational force in free-surface flow; values above one indicate supercritical and below one indicate subcritical flow.

The depth of flow in an open channel at which specific energy is minimum for a given discharge, marking the boundary between subcritical and supercritical regimes.

The direct runoff hydrograph resulting from one unit of effective rainfall occurring uniformly over a catchment in a specified duration.

A curve obtained by summing an infinite series of shifted unit hydrographs, used to derive unit hydrographs of shorter durations than the original.

The maximum rate at which soil can absorb rainfall under given conditions, decreasing with time during a storm and often modelled by Horton's exponential equation.

The average interval in years between occurrences of a hydrological event equalled or exceeded, equal to the reciprocal of the annual exceedance probability.

The gradual reduction in volume of a saturated soil under sustained load due to expulsion of pore water, governed by permeability and compressibility.

A soil parameter expressing the rate at which excess pore pressure dissipates and consolidation progresses, commonly determined from the log-time or square-root-time plot.

The intergranular stress carried by the soil skeleton, equal to total stress minus pore water pressure; it controls shear strength and volume change in saturated soils.

Loss of shear strength in loose saturated sands when cyclic loading raises pore pressure until effective stress approaches zero, causing the soil to behave like a fluid.

An in-situ test in which a split spoon sampler is driven by a 63.5 kg hammer falling 750 mm, with the blow count for 300 mm penetration giving the N value.

The discrepancy between the computed and known positions of the starting station in a traverse, distributed among the survey lines to adjust the traverse.

A traverse adjustment method distributing total closing error in proportion to the length of each line, commonly applied when angular and linear measurements are of comparable precision.

The horizontal distance between successive contour lines, which indicates ground slope: closely spaced contours mean steep ground and widely spaced contours mean gentle ground.

A curve of gradually varying radius introduced between a straight and a circular curve to allow gradual application of centrifugal force and superelevation.

The transverse slope provided on a horizontal curve to counter centrifugal force, raising the outer edge relative to the inner edge.

The transverse slope given to a road surface on straight sections to drain rainwater quickly to the sides.

The volume in millilitres occupied by one gram of activated sludge after settling for 30 minutes, used to judge sludge settleability and control the return sludge rate.

Biochemical oxygen demand, the oxygen consumed by microorganisms while decomposing organic matter in a water sample under specified conditions, usually five days at 20 degrees Celsius.

An attached-growth biological treatment unit in which wastewater trickles over a bed of media coated with a microbial film that absorbs and oxidises organic matter.

The increase in the bulk volume of moist sand caused by films of water pushing particles apart, which must be accounted for when measuring sand by volume.

The ability of hardened cement paste to retain its volume without excessive expansion, tested by the Le Chatelier apparatus to detect unsound lime or magnesia.

The mass of water divided by the mass of cement in a concrete mix; it chiefly controls strength and durability, with lower ratios giving stronger, less permeable concrete.