Civil Engineering Glossary
62 terms from surveying, concrete and materials, structural engineering, highway design and quantity surveying — defined in plain language, with the distinctions that actually cause mistakes on site, and linked to the calculator or formula that uses each one.
A
Aggregate coarse and fine Concrete & materials
The inert granular material — sand, gravel or crushed stone — that makes up most of concrete's volume. Fine aggregate passes a 4.75 mm sieve and is what most people call sand; coarse aggregate is retained on it. Aggregate is not filler: its grading, shape and cleanliness control workability and strength as much as the cement does.
Azimuth Surveying & geospatial
A horizontal direction measured clockwise from a reference meridian, normally expressed 0°–360°. Which north it refers to matters: true azimuth is referenced to geographic north, grid azimuth to the grid north of a projection, and the two differ by the grid convergence.
B
Backsight BS Surveying & geospatial
The first staff reading taken after setting up a level, always onto a point whose reduced level is already known. It establishes the height of the line of sight, so every later reading from that setup can be converted into a level.
Bar bending schedule BBS Quantity surveying
A tabulated list of every reinforcement bar in a structure: mark, diameter, shape code, cutting length, number of bars and total mass. It is what the steel yard cuts from and what the quantity surveyor prices, so an error in a cutting length becomes both a site problem and a payment problem.
Bearing Surveying & geospatial
The direction of a line, stated as an angle from a reference meridian. In whole circle form it runs 0°–360° clockwise from north; in quadrantal form it is stated as an angle up to 90° measured from north or south towards east or west, such as S 37° 30′ E.
Benchmark BM Surveying & geospatial
A point of known and recorded reduced level, used as the datum for a levelling run. A permanent benchmark belongs to a national network; a temporary benchmark (TBM) is established for one project and should be on something that will neither move nor be demolished mid-contract.
Bending moment Structural
The internal moment at a section resisting the tendency of applied loads to rotate it. For a simply supported beam under uniform load it peaks at mid-span at wL²/8; for a cantilever it peaks at the support at wL²/2 — four times as large for the same span and load.
Bill of quantities BOQ Quantity surveying
A document listing every item of work with its measured quantity, so that tenderers price the same scope on the same basis. Because it fixes what is being priced, the measurement conventions behind it — which standard method applies, what is deducted, how items are grouped — matter as much as the arithmetic.
Bowditch rule compass rule Surveying & geospatial
A method of distributing traverse misclosure in proportion to the length of each line, assuming angles and distances are of comparable reliability. Each line's correction is the total misclosure multiplied by that line's length over the perimeter, applied with the opposite sign.
C
Camber crossfall Highway
The transverse slope given to a road surface so water drains to the edges. On a straight it falls both ways from the crown; through a superelevated curve it is replaced by a single crossfall towards the inside of the curve.
Cantilever Structural
A member supported at one end only. Bending moment and deflection are far larger than for a supported span of the same length, which is why deflection rules treat cantilevers separately rather than scaling the ordinary limits.
Chainage station Highway
Distance measured along the centre line of a road, railway or pipeline from a defined origin, used to locate every feature along the route. Written as 1+450 or 1450.000 depending on local convention — the first meaning one kilometre plus 450 metres.
Change point turning point Surveying & geospatial
A point that carries a levelling run across an instrument move: it takes a foresight from the old setup and a backsight from the new one. It must be firm and well defined, because any movement between the two readings is carried into every level that follows.
Characteristic strength fck Concrete & materials
The compressive strength below which no more than a defined small proportion of test results is expected to fall — a statistical basis, not an average. A grade such as M20 denotes a characteristic cube strength of 20 N/mm², so the mean strength of the mix must be appreciably higher.
Cover nominal cover Concrete & materials
The distance from the concrete surface to the nearest reinforcement, links included — not to the centre of the bar. It protects steel from corrosion and fire, and the required value rises with the severity of the exposure condition.
Curing Concrete & materials
Keeping concrete moist and at a reasonable temperature while it gains strength. It is the cheapest step in concrete work and the one most often cut short: concrete that dries out early can lose a substantial part of its potential strength and becomes far more permeable.
D
Dead load permanent action Structural
The self-weight of the structure and everything permanently attached to it — slab, beams, finishes, partitions, services. Kept separate from imposed load because it is known with far greater certainty and is therefore treated differently by load factors.
Deflection Structural
The displacement of a member under load. A serviceability concern rather than a strength one: a beam can be perfectly safe and still deflect enough to crack finishes or alarm occupants, which is why span-to-depth limits sit alongside strength checks.
Degree of curve D Highway
An alternative measure of how sharp a circular curve is: the central angle subtended by a standard arc. Two conventions exist — a 30 m arc in metric practice, a 100 ft arc in US practice — and they give different numbers for the same curve, so the convention must always be stated.
Departure Surveying & geospatial
The east–west component of a survey line: length multiplied by the sine of its whole circle bearing, positive east and negative west. Paired with latitude, it turns a bearing and distance into coordinate differences.
Development length anchorage length Structural
The length of bar needed beyond a section for bond with the concrete to develop the bar's design force. Too short and the bar pulls out before it yields, so the reinforcement never reaches the capacity the calculation assumed.
Dry volume bulking factor Concrete & materials
The combined loose volume of cement, sand and aggregate needed to produce a given volume of finished concrete — conventionally about 1.54 times the wet volume, because water and compaction close the voids between particles. Mortar and plaster use a smaller factor, roughly 1.27 to 1.33, having no coarse aggregate.
E
Effective depth d Structural
The distance from the extreme compression fibre of a section to the centroid of the tension reinforcement — not the overall depth. Most reinforced concrete expressions use effective depth, and substituting overall depth is a common and consequential error.
Effective span Structural
The span used in analysis, which is not simply the clear opening. Depending on the code and support condition it is the clear span plus the effective depth, or the distance between support centres, whichever is smaller.
F
Foresight FS Surveying & geospatial
The last staff reading taken from a levelling setup before the instrument moves. A reading taken between backsight and foresight with the instrument stationary is an intersight — booking one as the other corrupts the arithmetic checks.
G
Geoid geoid separation Surveying & geospatial
The equipotential surface of the earth's gravity field that best approximates mean sea level. GNSS measures height above the ellipsoid, a smooth mathematical figure; the difference between the two is typically tens of metres and varies across a region, which is why a GNSS height is not a level.
GNSS Global Navigation Satellite System Surveying & geospatial
The general term for satellite positioning systems, of which GPS is one. A modern receiver may track GPS, GLONASS, Galileo and BeiDou together, which improves availability among buildings and trees rather more than it improves absolute accuracy.
Grade of concrete M20, C25/30 Concrete & materials
A designation of concrete strength. In the M system the number is the characteristic cube strength in N/mm², so M20 is 20 N/mm². The European C system quotes cylinder and cube strength together, so C25/30 and M30 describe similar concrete by different measures.
Grid convergence γ Surveying & geospatial
The angle between grid north and true north at a point, caused by the map projection rather than by magnetism. It is zero on a zone's central meridian and grows with both latitude and distance from it; a bearing referenced to true north must be corrected by it before use on the grid.
H
Height of instrument HI, collimation Surveying & geospatial
The reduced level of a levelling instrument's line of sight, found by adding a backsight to the known level of the point it was read on. Despite the name it is a level — a value such as 101.425 m — not the height of the tripod.
I
Imposed load live load Structural
Load arising from the use of a structure — people, furniture, stored goods, vehicles — as distinct from its own weight. Values are taken from the loading code appropriate to the occupancy rather than calculated from first principles.
L
Lap length splice length Structural
The overlap given to two reinforcing bars so that force transfers from one to the other through the surrounding concrete. Laps are staggered rather than aligned, so that no single section contains every splice.
Latitude (traverse) Surveying & geospatial
The north–south component of a survey line: length multiplied by the cosine of its whole circle bearing, positive north and negative south. Not to be confused with geographic latitude, the angular coordinate on the earth.
M
Misclosure closing error Surveying & geospatial
The gap between where a survey computation says you finished and where you know you actually are. In a closed traverse it is the resultant of the summed latitudes and departures; expressed against the perimeter it gives the relative precision, the usual test of whether the work is acceptable.
Moment of inertia second moment of area, I Structural
A geometric property describing how a section's area is distributed about the bending axis, and therefore how stiff it is. For a rectangle it is bd³/12 — depth cubed, which is why a joist is far stiffer on edge than laid flat.
N
Nominal mix Concrete & materials
A concrete mix specified by fixed volumetric proportions such as 1 : 1.5 : 3 rather than designed from trial testing. Convenient for small works and lower grades, but it cannot guarantee a characteristic strength, which is why higher grades require a design mix.
P
PCC plain cement concrete Concrete & materials
Concrete without reinforcement, used for blinding layers, levelling courses and mass fill where only compressive capacity is needed. It has negligible tensile capacity, so it is not used where bending occurs.
PI, PC and PT IP, BC, EC Highway
The three points defining a circular horizontal curve: the point of intersection where the tangents meet, the point of curvature where the curve begins, and the point of tangency where it ends. PT is reached by adding the curve length to PC — never by adding the tangent length to PI.
Preliminaries prelims Quantity surveying
Items in a bill of quantities covering the cost of running the project rather than any measured permanent work — site establishment, supervision, scaffolding, insurances, temporary services. Often a substantial share of a tender, and a frequent source of dispute when scope or programme changes.
Provisional sum Quantity surveying
An allowance included in a contract for work that cannot yet be measured or specified. It is an estimate to be expended and adjusted against actual cost, not a fixed price; the final account replaces it with the real value.
Q
Quantity take-off taking off Quantity surveying
The process of measuring quantities of work from drawings and specifications to produce a bill or an estimate. Its accuracy depends less on arithmetic than on consistent application of a method of measurement and disciplined recording of what was and was not included.
R
Rate analysis Quantity surveying
Building up the unit rate for an item of work from its constituents — materials, labour, plant, overhead and profit — rather than adopting a market figure. It makes a rate defensible in negotiation and lets it be adjusted rationally when one component's price moves.
RCC reinforced cement concrete Concrete & materials
Concrete with steel reinforcement placed to carry tension, which concrete alone cannot. The combination works because the two materials expand at similar rates with temperature and because concrete protects the steel from corrosion — provided the cover is adequate.
Rebar reinforcement bar Concrete & materials
Steel bar cast into concrete to carry tensile and shear forces. Its mass per metre is d²/162.2 kilograms with the diameter in millimetres, a constant derived from the circular area formula and a steel density of 7850 kg/m³.
Reduced level RL Surveying & geospatial
The height of a point above the chosen datum — the end product of a levelling run. Reduced levels are compared against design levels to give the cut or fill at each point.
S
Scale factor point scale factor Surveying & geospatial
The ratio by which a map projection stretches or shrinks distance at a point. On UTM it is 0.9996 on the central meridian and exceeds one near the zone edges, so a distance computed from grid coordinates is not the distance you would tape on the ground.
Section modulus Z Structural
A section property equal to the second moment of area divided by the distance to the extreme fibre — bd²/6 for a rectangle. Bending stress is simply the moment divided by it, which makes it the quickest way to check a section by hand.
Shear force Structural
The internal force acting across a section, tending to slide one part of a member past the other. In a simply supported beam under uniform load it is greatest at the supports and zero at mid-span — the mirror image of the bending moment.
Sight distance SSD Highway
The length of road a driver can see ahead, and the criterion that usually governs vertical curve length. Stopping sight distance must cover both the reaction time before braking begins and the braking distance itself.
Slump Concrete & materials
A simple measure of the workability of fresh concrete: how far a cone of concrete settles when the mould is lifted. It indicates consistency, not strength — and adding water on site to raise the slump lowers the strength of the concrete being placed.
Superelevation banking, cant Highway
The transverse slope built into a road on a curve so that part of the centripetal force is carried by gravity rather than side friction. The design relation is e + f = V²/(127R) with speed in km/h and radius in metres; the maximum permitted e depends on climate and the governing standard.
T
Transit rule Surveying & geospatial
A traverse adjustment distributing misclosure in proportion to each line's latitude and departure rather than its length. Appropriate when angular measurements are appreciably more reliable than the distances — the opposite of the assumption behind the Bowditch rule.
Traverse Surveying & geospatial
A connected series of survey lines whose lengths and directions are measured, used to carry coordinates through a site. A closed traverse returns to its start or to another known point, so the work can be checked; an open traverse does not, and cannot be verified from within itself.
Tributary area Structural
The floor area whose load a particular column or beam carries — for an internal column, half the span to each neighbouring support in both directions. Using the full bay area instead is a common error that doubles the computed load.
U
UTM Universal Transverse Mercator Surveying & geospatial
A projected coordinate system dividing the world into sixty 6°-wide zones, each projected separately so distortion stays small within it. Coordinates are metres east and north, and are meaningless without their zone and hemisphere.
V
Variation change order Quantity surveying
An instructed change to the scope, quality or sequence of the contract works, valued and added to or deducted from the contract sum. Recording the instruction and its measured effect at the time is what makes it recoverable later.
Vertical curve K value Highway
A parabolic transition between two road gradients. Its length is usually expressed through the K value — metres of curve per one percent of grade change — with crest and sag curves governed by different sight distance criteria.
W
Wastage allowance Quantity surveying
A percentage added to a measured quantity to cover material lost in cutting, breakage, spillage and over-ordering. It belongs on the materials that actually suffer it — bricks and tiles typically — rather than being applied uniformly to every line of a take-off.
Water–cement ratio w/c Concrete & materials
The mass of water divided by the mass of cement in a mix, and the single strongest influence on hardened strength and permeability. Lower ratios give stronger, denser concrete but reduce workability — which is what plasticisers exist to resolve.
WGS 84 EPSG:4326 Surveying & geospatial
The global geodetic datum GPS broadcasts in and most mapping data uses, defined by an ellipsoid with a semi-major axis of 6 378 137 m and an inverse flattening of 298.257223563. A national grid may use a different datum, and the shift between the two can be hundreds of metres.
Whole circle bearing WCB Surveying & geospatial
A bearing expressed from 0° to 360° measured clockwise from north — the form used in traverse computation, because it feeds directly into the latitude and departure formulas without needing a quadrant rule.
Workability Concrete & materials
How easily fresh concrete can be placed, compacted and finished without segregating. It is a property of the mix as a whole — water content, aggregate grading and shape, admixtures — and is measured indirectly, most commonly by slump.
About this glossary
Definitions are written for people who already work in construction, so they concentrate on the distinctions that cause errors — effective depth against overall depth, grid north against true north, slump against strength — rather than restating the obvious.
Where a term has a formula behind it, the entry links to the formula reference, which gives the symbols, units, a worked example and the usual mistakes. Surveying terms link to the surveying reference for the fuller treatment.
Free to quote and link. If a definition is wrong, unclear, or uses a convention that differs where you work, tell us — corrections are published with the page's updated date.
