ISRO Scientist Civil key terms

A design condition in which a structure or member reaches its maximum load-carrying capacity through yielding, crushing, or buckling, and is checked using factored loads with partial safety factors applied to both loads and material strengths.

A multiplier applied separately to loads and to material strengths to account for uncertainty and variability, producing design values that ensure adequate safety against the specified limit state within a chosen probability of failure.

The value of material strength below which not more than five percent of test results are expected to fall, determined statistically from cube or cylinder tests and used as the base value before applying partial safety factors.

An iterative structural analysis technique that releases joints to find unbalanced moments, then distributes them in proportion to member stiffnesses and carries over fixed fractions to far ends until residual moments become negligible.

A diagram showing the variation of a specific response quantity, such as shear, bending moment, or deflection at a chosen section, as a unit load moves across the structure from one end to the other.

The ratio of a compression member's effective length to its least radius of gyration, indicating its susceptibility to buckling; larger values lower the permissible compressive stress in steel and concrete column design.

The equivalent pin-ended length of a compression member that would buckle at the same load as the actual member with its real end restraints, obtained by multiplying the actual length by a support-condition factor.

Sudden lateral instability of a slender member under compression when the applied load reaches a critical value, causing large deformation and possible collapse well before the material's yield strength is exhausted.

Loss of shear strength in saturated loose cohesionless soil during earthquake shaking, when cyclic loading raises pore water pressure until effective stress approaches zero and the soil behaves like a fluid.

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

Time-dependent volume reduction of a saturated soil caused by gradual expulsion of pore water under sustained load, described by a coefficient of consolidation and a compression index derived from an oedometer test.

The ratio of the volume of voids to the volume of solids in a soil mass, a fundamental phase parameter used to compute porosity, unit weight, and degree of saturation.

An in-situ test in which a split-spoon sampler is driven into the ground by a hammer and the blow count for a specified penetration is recorded, giving the N value used to estimate relative density and strength.

A dimensionless ratio of inertial forces to viscous forces in a flow, used to classify flow as laminar or turbulent and to predict transition and friction characteristics in pipes and channels.

A dimensionless ratio of inertial forces to gravitational forces in free-surface flow, whose value relative to unity distinguishes subcritical, critical, and supercritical flow in open channels.

An abrupt rise in water surface when a supercritical flow changes to subcritical flow, dissipating energy through turbulence and used in stilling basins below spillways and drop structures.

The total head of flowing water measured relative to the channel bed, equal to the sum of depth and velocity head, whose minimum value at a given discharge defines critical flow conditions.

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

The downward entry of water into the soil surface, expressed as a rate that typically starts high under dry conditions and decays toward a constant value as the soil profile wets up.

The average interval in years between occurrences of a hydrologic event equaled or exceeded, equal to the reciprocal of the annual exceedance probability and used to select design flood magnitudes.

The amount of dissolved oxygen consumed by microorganisms while decomposing organic matter in a water sample over a specified incubation period, commonly five days at twenty degrees Celsius, indicating organic pollution strength.

The oxygen equivalent of organic matter in a water sample oxidized by a strong chemical agent under acidic conditions, measured rapidly and including both biodegradable and non-biodegradable matter.

A secondary biological treatment in which sewage is aerated with a recycled microbial culture that oxidizes organic matter, followed by sedimentation; performance is controlled by solids retention time and food-to-microorganism ratio.

A water treatment sequence in which a chemical coagulant neutralizes particle charges and gentle mixing promotes collisions, forming larger settleable flocs that are removed in subsequent sedimentation.

Gravity settling of suspended particles in still or slowly moving water, designed using overflow rate and detention time so that particles with a given settling velocity are removed with known efficiency.

The California Bearing Ratio, a penetration test result expressed as a percentage of the load required to penetrate a standard crushed stone sample, used to characterize subgrade strength and design flexible pavement thickness.

A road structure in which load spreads gradually through successive granular and bound layers that deform elastically with the subgrade, designed by limiting vertical compressive strain and tensile strain at layer interfaces.

The chosen speed used to determine geometric features such as horizontal curve radius, superelevation, sight distance, and gradient, selected from terrain and road classification and generally exceeding the operating speed of most vehicles.

The transverse slope provided on a horizontal curve by raising the outer edge, which counteracts centrifugal force and is limited by friction between tyre and pavement and by comfort considerations.

The length of carriageway visible to a driver ahead, comprising stopping sight distance based on reaction time and braking distance and overtaking sight distance for two-lane roads.

A permanently established point whose reduced level is known with high accuracy and from which vertical differences to other points are measured during leveling surveys.

The elevation of a survey point expressed relative to a chosen datum, obtained by adding or subtracting successive level differences measured with a leveling instrument and staff.

The discrepancy between the computed and known values of a traverse or level run, such as a nonzero sum of internal angles or a mismatched final elevation, indicating measurement mistakes or accumulated random errors.

The distance on the ground represented by one pixel of a remotely sensed image, determined by sensor altitude, focal length, and detector size, and controlling the smallest feature that can be resolved.

The normalized difference vegetation index, computed from near-infrared and red reflectance as their difference divided by their sum, giving a value from minus one to plus one that indicates vegetation vigor and density.

In a project network, the longest sequence of dependent activities from start to finish, whose duration equals the project duration and where any delay directly extends the completion date.

The amount of time an activity can be delayed without delaying the project completion or violating a successor constraint, distinguishing total float from free float in network scheduling.

The process of determining the unit cost of a construction item by summing material, labour, plant, and overhead components per unit quantity, forming the basis of bill of quantities rates.

A tender document listing measured quantities of work items with descriptions, against which bidders quote unit rates and which forms the basis for interim payments and variations during construction.