BTSC JE Civil key terms

The mass of a material divided by its total volume including the voids inside it, used to judge aggregates and bricks. It is lower than true density whenever internal pores exist.

The quantity of water a porous building material takes up when soaked, expressed as a percentage of dry mass. High values signal porous, weaker bricks and aggregates that may need extra mixing water.

The property of hardened cement paste staying at constant volume rather than expanding and cracking. It is tested by Le Chatelier or autoclave methods and is harmed by free lime and magnesia.

The period from adding water to cement until the paste begins to lose plasticity, tested with the Vicat apparatus. Ordinary Portland cement must not start setting earlier than 30 minutes.

A simple field test where fresh concrete in a standard cone is allowed to settle after the cone is lifted, and the drop is measured. It indicates consistency and workability but not strength.

How easily fresh concrete can be mixed, transported, placed and compacted without segregation. It is judged by slump, compaction factor or Vee-Bee time and depends on water content, grading and admixtures.

The mass of water divided by the mass of cement in a concrete mix. Lowering it raises strength and durability but reduces workability, so it is the key parameter in mix design.

The strength value below which not more than a stated small percentage of test results are expected to fall, usually taken as the 28-day cube strength in design codes. It is the basis for mix design and safety factors.

A structural design philosophy checking that a structure remains safe against collapse and serviceable in normal use. It uses partial safety factors on loads and material strengths rather than a single global factor.

Steel, usually vertical stirrups or bent-up bars, placed in a beam to resist diagonal tension caused by shear forces. It prevents sudden brittle shear failure and confines the concrete.

The distance between the centres of supports, or the clear span plus effective depth, whichever is smaller, used when calculating bending moments and deflections. It differs from the clear span.

A geometric property of a cross-section measuring how its area is distributed about an axis, governing resistance to bending. A larger value means less curvature for the same bending moment.

The moment of inertia of a section divided by the distance from the neutral axis to the extreme fibre. It converts a bending moment directly into maximum bending stress.

The ratio of lateral strain to longitudinal strain when a material is stretched or compressed within its elastic range. Typical values are about 0.2 to 0.3 for concrete and steel.

The slope of the straight part of a stress-strain curve, expressing how stiff a material is in tension or compression. A stiffer material deforms less under the same stress.

The equivalent pin-ended length of a compression member that has the same buckling load as the actual member with its real end restraints. It depends on support conditions and bracing.

The effective length of a column divided by its least radius of gyration. Higher values mean greater susceptibility to buckling, so allowable compressive stress falls as it rises.

Systems of small connecting members that tie together the components of a built-up steel compression member so they act as one unit. They resist shear and prevent local buckling of individual parts.

A deep built-up steel beam made of a web plate and flanges joined by welds or rivets, used where rolled sections are too small. It needs stiffeners to prevent web buckling.

The water content at which a fine-grained soil changes from plastic to liquid behaviour, found with the Casagrande apparatus. It is one of the Atterberg limits used to classify clays.

The difference between the liquid limit and the plastic limit of a soil, showing the range of water content over which it stays plastic. A large value indicates a highly compressible clay.

A laboratory compaction test in which soil is compacted in a standard mould in layers with a standard hammer. The result gives the maximum dry density and the optimum moisture content.

The gradual squeezing out of water from saturated soil under sustained load, causing slow settlement. It is a time-dependent process distinct from immediate elastic settlement.

A dimensionless ratio of inertial forces to viscous forces in a flow. Low values indicate laminar flow and high values turbulent flow, with the transition depending on geometry.

A dimensionless ratio of inertial forces to gravity forces, used to classify open-channel flow as subcritical, critical or supercritical. It equals flow velocity divided by the square root of gravity times depth.

An abrupt rise in water surface when supercritical flow becomes subcritical, dissipating large amounts of energy. It is deliberately created below spillways and weirs to protect the bed.

Duty is the area of land irrigated per unit discharge, and delta is the total depth of water applied over a crop season. They are linked through the base period of the crop.

The total water taken from a field by crop transpiration and evaporation from the soil and plant surfaces. It excludes water returning to the source as runoff or deep percolation.

A factor applied to reference evapotranspiration to estimate the water use of a particular crop at a given growth stage. It varies through the season and with crop type.

The direct runoff hydrograph produced by one unit depth of effective rainfall falling uniformly over a catchment in a stated duration. It is used to predict floods from design storms.

The time taken for water to travel from the most remote point of a catchment to its outlet. Rainfall lasting longer than this can contribute fully to peak flow.

The average interval in years between events of a given size or larger, such as a flood peak. It is the reciprocal of annual exceedance probability, not a guaranteed waiting time.

California Bearing Ratio, the penetration resistance of a soil or pavement layer compared with a standard crushed stone, expressed as a percentage. It is used to design flexible pavement thickness.

The transverse slope given to a road curve, raising the outer edge, so that centrifugal force is balanced by gravity and friction. It is limited to avoid discomfort and slipping.

The slight cross slope provided on straight road sections to drain rainwater quickly to the sides. Its amount depends on surface type and rainfall intensity.

Biochemical oxygen demand measures oxygen consumed by microbes breaking down organic matter in a sample, while chemical oxygen demand measures oxidation by a strong chemical agent. Comparing them indicates biodegradability.

The cloudiness of water caused by suspended particles that scatter light. It is measured in nephelometric units and reduced by coagulation, flocculation, settling and filtration.

The average period water spends in a treatment tank, calculated as tank volume divided by flow rate. It governs settling efficiency and disinfection contact in design.

The gap between the computed end point of a survey traverse and its known starting point, expressed as a distance or angular misclosure. It is distributed over the lines by a traverse adjustment.

A fixed point of known reduced level used as a reference for levelling and setting out works. Permanent benchmarks are often embedded in masonry or rock.

The constant vertical distance between successive contour lines on a map. A small interval shows fine detail on flat ground, while a large one suits steep terrain.

The process of working out the unit cost of an item of work from labour, material, plant and overheads plus contractor profit. It supports preparation of estimates and bills of quantities.

A document listing measured quantities of each work item with descriptions, used for tendering and payment. Rates are filled against these quantities to form the contract price.

A reserve of money included in an estimate to cover unforeseen items and price changes during construction. It is usually a percentage of the estimated cost.

A form of deductive reasoning with two premises and a conclusion, tested by checking whether the conclusion necessarily follows. Standard techniques include Venn diagrams and the rules of valid inference.

A sequence of numbers following a hidden rule, where the candidate must find the next term or the odd one out. Common patterns use differences, ratios, squares and alternating operations.