Note. The definitions and explanations below represent my understanding of certain terms. Some apply only to their usage on this website. It would be impossible to provide for every potential reader. I can only hope that I have achieved a reasonable balance. In civil engineering, building and architecture, terms are shared and applied loosely by people with a wide range of technical knowledge and by people working in different disciplines, to a certain extent isolated from each other. Practice and theory are constantly developing and terms are borrowed from previous practice or other fields and attached to objects that are similar in form or purpose to the original. One example is the modern structural engineer's definition of 'column', which is quite different from the one found in dictionaries of architecture. When the Monash & Anderson office made the switch from arch bridges to flat girder bridges it continued to use the term 'centres' for the temporary timber structures required during construction, even though the term derives from the semi-circular form of arches and domes. A.H.
|abutment||1. The substructure (wall, block of masonry, etc) against which the end of a bridge rests.|
2. Sometimes the natural rock or soil at this location.
See sketches of arch bridge and girder bridge.
|arch, Monier||A form of arch construction in which Monier concrete replaced traditional brick or stone masonry. Sketch.|
|arch, segmental||The profiles of the arch bridges included in this study were made up from 3 or 5 segments of circles of different radii, joined tangentially. Fords Ck Bridge was a 3-segment arch.|
|beam||A linear structural component whose length is usually much greater than its depth and width, supported at two or more discrete points, and loaded so that it bends. The typical beam is horizontal and subjected to gravity loads.|
Monash referred to the smaller 'beams' projecting below floor slabs in a building as 'ribs', and the larger ones as 'girders'. Where beams project below slabs, a situation that also occurs in bridge decks, the height of the 'beam' is thought of as the full height from bottom of projection to top of slab. A width of slab larger than the width of the projection may be considered an integral part of the beam, which then becomes a 'T-beam'.
|caisson||In its simplest form an open-ended vertical barrier, circular or rectangular in plan, established in a river so that the enclosed water can be pumped out to allow preparation of foundations in the river bed. Typical caissons are built by driving a ring of piles into the bed, or allowing a timber or metal box to sink at the desired location. Large diameter concrete pipes stood on end serve the same purpose.|
|cantilever||An end portion of a beam projecting into space, lacking support at its far end. (Also verb to cantilever.)|
|catenary bars||A true catenary is the shape adopted by a rope or cable when hung between two supports. Its shape is similar to that of a parabola. In the period we are studying the term was used loosely to describe reinforcement draped or bent in a vaguely similar fashion. In a reinforced concrete beam that is continuous over several supports, some of the bars that lie in the bottom at mid-span may be bent up so that they run along the top of the beam over the supports. (This is because the concrete in a continuous beam is subjected to tension at the bottom at mid-span, but at the top over the supports.) JM and his contemporaries referred to these 'bent-up' bars as 'catenary bars'. Some of the bars are run along the bottom for the full length, and these were referred to as 'tension bars', even though the 'catenary' bars were also subjected to tension.
Note. The term 'catenary bar' and its distinction from 'tension bar' would be unfamiliar to a modern engineer.
|cathodic protection||A method of controlling corrosion of an iron or steel object - in this study, reinforcing grids or cages. In the 'sacrificial' method the ferrous object is connected to a lump of less noble metal such as magnesium, aluminium or zinc, which becomes the anode of an electrical cell. Corrosion occurs in the anode rather than the reinforcement. In the 'impressed current' method, the object to be protected is connected to the cathode of a supply of electricity. Applied to protect the Anderson St Bridge.|
|cement||In modern civil engineering usage this term refers almost always to 'Portland' cement: a fine powder made by heating a mixture of clay and crushed limestone in a rotating furnace and grinding the resulting nodules. When this cement is mixed with water a chemical reaction takes place forming a brittle solid.|
|A temporary structure intended to support the weight of an arch or dome during construction, until it has sufficient integrity and strength to support itself. For Monash & Anderson's bridges, centring was composed of timber members and supported timber sheeting. On this surface was placed the steel reinforcing bars and eventually the wet concrete (compo). The centring was removed when the compo had hardened sufficiently to carry its own weight. (US spelling: centers, centering. In the UK centering is the most common spelling in this context.)|
|cold joint||A joint formed in a mass of concrete or mortar when work is suspended for an interval and this concrete has time to set before fresh concrete is placed against it when construction is resumed. Because of the uncertain bond between the older concrete and the new, a 'cold joint' forms a potential plane of weakness in the concrete mass.|
|column||In engineering terminology, a vertical, linear structural member (its length large in comparison with its cross-sectional dimensions) which carries vertical (gravity) load and is therefore compressed. A column is normally bent by the action of the beams and floors that it supports.|
|compo||The term used around the turn of the century to describe the coarse dry mortar used in Monier construction.|
|compression||When a material is squeezed it is said to be 'in compression'. Also, adjective 'compressive', as in 'compressive stress'.|
|concrete||A mixture of sand and stones bonded by a cementing material. In modern usage the term normally refers to cement concrete. At the end of the 19th century lime, being less expensive than Portland cement, was still used as a binder in mass concrete where high compressive strength was not required. Concrete is strong in compression (difficult to crush), but weak in tension (easily pulled apart).|
|concrete, reinforced||After some uncertainty, the engineering world finally settled on reinforced concrete as the generic term for concrete reinforced with bars placed at specific locations to carry the tension which plain concrete cannot resist, and sometimes to aid it in carrying compression.|
|concrete, rubble||Concrete containing small boulders or randomly shaped blocks of stone embedded in a matrix of lime or cement mortar, often used for foundations and abutments in Monash & Anderson bridges.|
|coping||The horizontal bed of stones or concrete forming the top layer of a wall and designed to shed rainwater.|
|corbel||In reinforced concrete construction: a bracket projecting from a column, usually to support a beam. The term may also be applied to a cantilever, particularly if it projects from the side of a bridge and has an ornamental shape. (Also verb: to corbel, corbelled.)|
|cover||The distance between the surface of a reinforcing rod and the nearest surface of the enclosing mortar or concrete. Strictly, this is measured from the surface of any reinforcement, but some codes allowed it to be measured from the 'main' reinforcement, neglecting elements such as 'ties' (or 'ligatures') in columns, and 'stirrups' in beams.|
|counterfort||A vertical rib or fin projecting usually from the back of a wall, similar in form and function to a buttress, but bonded to or integral with the wall. The term is applied to such fins on earth-retaining walls.|
|creep||A very gradual change in length which occurs over time when a material is subjected to sustained load. The rate of creep decreases with the passage of time but does not die out completely. In the context of this study, creep is produced mainly by the self-weight of bridges. It is appreciable only in concrete or mortar; insignificant in steel. In slabs and girders the effect is to increase the downward deflection. In arches, creep reduces the circumferential length of the arch ring. This leads to sagging of the crown, causing the arch profile to deviate from that chosen for optimum stability by the designers. Photo.|
|crosshead||In this study: a thickening of the top of a cross-wall (part of a pier) to provide seating for the ends of bridge girders. The crosshead has the appearance of a beam, but does not function as such because of the support it receives from the wall. See sketch.|
|cross-girder||A beam or girder running across the width of the bridge to support the ends of the main girders, itself supported on columns and forming part of a pier. See sketch.|
|crown||The highest point of an arch.|
|culvert (vs bridge)||In present usage: a pipe or box-like tube which penetrates an embankment to allow passage of water. The box culvert would normally have an integral floor or 'invert'. The Monash & Anderson office applied this term to small bridges.|
|curtain wall||See 'wall, curtain'.|
|deck, decking||This term applies to the reinforced concrete slab which provides the supporting surface for traffic and pedestrians in girder bridges, but may also include the beams and girders directly beneath it. In all extant Monash bridges the slab was cast in situ and is integral with the girders. Sketch.|
|design||In structural engineering English, the word 'design' includes not only conception of form but the calculation required to prove that the structure and its foundations will successfully resist the loadings and other influences to which they will be subjected. Generally, conception is the responsibility of a senior experienced engineer and the calculation is done by an assistant. Calculating the necessary dimensions of structural components may be called 'sizing', but this is not common.|
Some languages (e.g. French) have separate words for conception and sizing, while the word 'design' is applied to the modelling of the structure, especially from an 'aesthetic' point of view.
|elastic limit||See yield.|
|expanded metal (reinforcement)||See expanded metal controversy.|
|expansion joint||For the bridges in this study: a narrow gap formed across the width of a bridge to allow the girders to change in length, following changes in ambient temperature, without causing extra stress.|
|'extra'||Because of the uncertainty involved in civil engineering projects, especially in the excavation and construction of foundations, the contractor is usually recompensed for unforeseen work at a specified price per unit quantity e.g. per cubic metre of extra concrete poured. In building construction it is common for the client or architect to alter the design of the building after the contract has been signed. Recompense claimed by the contractor for an item under these headings is known as an 'extra'. (Extras are also known as 'variations', because they represent variations from the original contract, but this term was not used by M&A or RCMPC.)|
Extras are not payable in a 'bulk sum' contract where a contractor has tendered a fixed price for a specific task. The Supreme Court of Victoria ruled that M&A had entered into a bulk sum contract for construction of the Fyansford Bridge and they were unable to recoup a large amount of money they had spent, mainly on additional concrete in the foundations.
|factor of safety||A structure which is twice as 'strong' as the worst forces that can reasonably be expected to act upon it can be said to have a 'factor of safety' of 2. Engineers provide the extra strength to allow for uncertainties in the estimation of loads; inevitable variations in dimensions, in materials and in the quality of work; etc. It also provides a measure of safety against overloading by ignorant users. (The knowledge that structures are designed to a factor of safety tempts some builders to cut corners in construction and some users to overload them. This is one of the main reasons why structures sometimes fall down.)|
There are several schools of thought on defining the FoS. A simple approach is to calculate the load at which a structure will collapse under a certain load pattern, and divide it by the expected magnitude of that loading. In the period of our study the most common method was to determine the stress at which a material would 'fail' and divide it by the highest stress calculated to occur in that material due to the worst expected load. (The definition of 'failure' leaves further room for debate.)
The 1907 specification for the Commercial Bank in Launceston anticipated steel with an ultimate tensile strength in the range 26 to 30 tons per square inch, and the 'safe steel stress' was fixed at 7 tsi. Taking an average strength of 28, this was seen to give a FoS of 4. During the middle of the 20th Century, the calculated stress under expected loads was limited to a proportion of the yield stress.
|flange||The horizontal portion(s) of a beam - typically beams with I or T cross-sections. Flanges play an important part in resisting bending.|
|flexure||When structural components are bent by superimposed loading they are said to be subjected to 'flexure'.|
|force||Vertical forces on structures arise from gravity loads such as the weight of people, vehicles, building contents and conatined liquids (e.g. water in elevated tanks). Horizontal forces are applied by wind; by retained solids (e.g. earth behind bridge abutments and basement perimeter walls, wheat in silos); and by contained liquids (e.g. water behind dams and in tanks). The action of such forces generally results in compression, extension, flexure or other distortion of the structure, generally invisible to the naked eye. Forces may arise in structures due to change of temperature, if the structure (e.g. a bridge deck) is not completely free to expand and contract. Engineers identify forces within structural components - e.g. if a single-span beam sags under load the top of the beam is compressed and the bottom stretched, thus a compressive force can be said to exist in the top and a tensile force of equal magnitude in the bottom. See units for more.|
|footing|| A footing is a widening of the base of a column or wall to spread its weight and any load it may carry over a wider area of soil or rock. The area is calculated to ensure that the pressure on the soil or rock is within its carrying capacity. The footing also provides stability to the column, restricting rotation of its lower end and preventing overturning.|
Spread footing. A footing of a column, usually in the form of a slab, which is square or rectangular in plan. Sometimes the upper surface of the slab has the form of a very flat truncated pyramid. Sketch.
Strip footing A common footing serving a line of columns or a wall. Sketch.
|foundation||1. The base of a structure in contact with the soil or rock on which it rests.|
2. The soil or rock on which a structure rests.
|foundation, cylinder||In RCMPC work, a form of foundation in which lengths of (usually large diameter) Monier pipes placed vertically end-to-end were sunk through soft soil usually to reach bed rock.|
|frame||In this study: a portal formed by two columns joined at their tops by a beam.|
|gauging||The process of measuring sand, gravel, cement and water in specified proportions for mixing to form concrete. In M&A's early Monier work sand and gravel were measured in shallow boxes and mixed prior to addition of cement and water. Mechanical concrete mixers were adopted by RCMPC around 1910.|
|girder||In this study: a large beam. Monash referred to the main members of his building floors as 'girders' and the minor members as 'ribs'.|
|girder, T||These occur in bridge decks and in building floors. The deck of a bridge with four main girders appears as a TTTT form in cross-section, as can be seen in Sketch 1 and Sketch 2. Each T acts structurally as a beam, the bar (or 'flange') of the T sharing with the stem (or 'web') in resisting the bending caused by loads on the span. In the period covered by this study the webs were cast integrally with the deck or floor slab.|
|girder, trough||In this study: sheets of heavily troughed iron or steel placed across a gap to be bridged (the corrugations running in the direction of span) and covered with a thick layer of concrete. Bond between metal and concrete ensured composite action, similar to the principle of reinforced concrete.|
|haunch||In the Monash & Anderson office this term was applied to the ends of an arch close to the springing. The thickness of the arch at the springing was referred to as the 'haunch thickness'. Sketch. The term is also applied when the depth of a long girder is gradually increased towards its ends.|
|hundredweight (cwt)||See force.|
|in situ||Concrete poured wet into its final position is said to be cast 'in situ'. The alternative is to precast it and transport the solid component to its final location.|
|intrados||The inner surface of a vault or arch.|
|iron, cast||A ferrous metal containing a relatively large proportion of impurities and especially carbon. As it is brittle (weak in tension) its use in beams prior to the 20th Century caused some disasters, but it was used satisfactorily in parts of structures subjected to compression, such as columns.|
|iron, wrought||A ferrous metal with a low carbon content made by melting pig iron with mill scale (iron oxide), separating purified iron from the resulting slag, and hammering and rolling it when cool. It was the preferred material for metal construction in the 19th century for parts of structures subjected to tension or flexure, such as tie rods, chains and girders.|
|Jack arch||A common floor system that predated reinforced concrete floors consisted of shallow vaults resting on the bottom flanges of the floor joists between which they spanned. The vaults were sometimes of brick masonry covered with filling to obtain a flat floor surface. In the Dennett system shown below, the vault was of concrete with a level top surface. Such vaults are often referred to as 'jack arches'.|
|Joist||Generally applied to relatively small beams supporting a floor or ceiling.|
|lime||The burning of limestone produces calcium oxide or 'quicklime'. When water is added to quicklime a strong chemical reaction produces calcium hydroxide, commonly known as lime. When lime is used as a bonding agent in mortar the initial 'set' occurs simply as a result of drying. Over a long period the lime reacts with carbon dioxide in the atmosphere to form calcium carbonate (limestone). Some limestones contain clay, and when they are burnt the result includes some of the constituents of Portland cement. They thus gain some strength as a result of a chemical reaction with added water. These are known as 'hydraulic limes'. In the period considered in this report, good quality cement was still expensive and in short supply in Australia and lime was still considered a suitable substitute in structural engineering in locations where high strength was not required.|
|load, dead||In modern terms a load which is permanent or of long duration, such as a structure's own weight ('self weight'). However, the Monash office sometimes applied the term to the uniformly distributed load used in bridge design to represent the effect of a line of traffic or a crowd, perhaps because it was perceived to be less active than the steam roller, which applied heavy concentrated loads and caused vibrations.|
|load, live|| In bridge engineering the weight of traffic and pedestrians applied to a bridge. In the period covered by this study, this live load was considered to be adequately represented by a uniformly distributed load and/or the weight of a steam roller or traction engine. The magnitude of the distributed load was set at either 100 pounds per square foot of deck surface (4.79 kPa) or one hundredweight per square foot (5.36 kPa). It was assumed that it could be distributed over the whole or part of the bridge. In the case of arches, such a load applied to one half of the span produced a more severe stress condition than when applied over the full length. The steam roller was normally assumed to weigh 15 tons (149 kN).|
In building design, live load includes the weight of people, office furniture, goods stored in warehouses, etc. Again the effects of these loads on a structure are represented chiefly by the effect of a uniformly distributed load (UDL). In Monash's time this normally varied for office buildings from 80 to about 120 psf (3.83 to 5.75 kPa) depending on the form of occupancy, though it did go as high as 200 psf. In factories it could be much higher. For the Hide & Skin Store the figure was 896 psf or 8 cwt/ft² (42.9 kPa). Most codes of practice require floors to resist a concentrated, or 'point', load at any location. Also, known concentrated loads, such as those from machinery or high-density filing cabinets are are taken into account along with the general UDL.
In proof tests the distributed load was represented by a layer of bricks or sand placed on the deck.
|Monier||1. The surname of Joseph Monier.|
2. In the early part of the period covered by this study: a 'composite' material consisting of a layer of coarse mortar containing a grid of iron bars as used in the arch bridges. When the Monash office changed to girder bridges the term 'Monier' continued to be used for a time for what was more properly reinforced concrete.
|monolithic||Although reinforced concrete construction is normally interrupted at the end of a day's work and the concrete poured that day sets and hardens to some extent, when pouring is recommenced the following day a good bond can be ensured between the 'old' concrete and the new by removing the surface of the old concrete before the new is poured against it (see cold joint). Reinforcement can be made effectively continuous by 'lapping' (i.e. over-lapping) reinforcing bars. Where the bars overlap they are held together by thin wire ties. The force in one bar is transferred to the other through the bonding action of the concrete. Care is taken to ensure that cold joints are not formed where laps occur in the reinforcement. As a result the entire concrete structure: foundations, columns, girders and deck may become a single 'monolithic' unit.|
|monkey||English name for the heavy weight used to drive piles into the ground. The weight was lifted by a winch and allowed to fall. Monash noted that the weight is called in German "bär" (bear) and in French "mouton" (sheep).|
|mortar||A mixture of sand, cement and sometimes lime to which water has been added.|
|parapet||The low wall provided along each edge of the arch bridges to provide security to users. Sketch.|
|pier||In bridges: sub-structures providing intermediate support. In Monier arch bridges this consisted of a thick wall running across the width of the bridge, often perforated by arched openings. Photo. In Monash's girder bridges it consisted usually of a row of columns spaced across the width, supporting a cross-girder. Sketch. Sometimes the spaces between the columns were filled with a thin reinforced concrete wall (usually 4" to 6" thick). This was widened at the top to form a cross-head. Sketches.|
|pier, cylinder||In some bridges the columns forming the pier were constructed from large diameter reinforced concrete pipes placed vertically end-on-end and filled with concrete (containing a cylindrical cage of reinforcing bars).|
|pile (driven)||In soft ground a foundation can be obtained by driving long posts of timber, steel or reinforced concrete into the soil. If rock exists at a convenient depth, the pile may be driven to contact hard rock or penetrate soft rock. However, if rock cannot be reached, the friction of the soil against the sides of the pile can suffice to support a considerable load. If the toe of the pile is blunt, some additional load carrying capacity is provided by the toe bearing on the compressed soil beneath it.|
|pillar||This term has been used in our publications to describe the short columns seated on the arch ring of an open-spandrel arch bridge to support the deck (see e.g. Hurstbridge Bridge).|
|plate||In structural engineering: a thin, essentially rigid, sheet of material; especially a horizontal sheet subjected to vertical loading such as a floor in a building. In Monier construction thin slabs of reinforced concrete laid on steel bridge girders to form a deck were known as 'Monier plates'. They were also used as covers for drains and septic tanks.|
|precast concrete||Structural components of reinforced concrete are sometimes cast in a factory and transported to site. The Monier Pipe Co, merged in 1905 into RCMPC, had a factory which made precast pipes, drain covers, and small flat slabs or plates. Photos.|
|pressure||The force applied to a surface, per unit area of surface. Usually reserved for the pressure of footings on soil; and of soil, water and gas against surfaces which contain them.|
|Referees, Building.||As is well known, municipal and national authorities require that buildings be designed and constructed according to a set of rules, backed by law. Properly administered, this system simplifies the designer's work; simplifies communication between designers, suppliers, builders and regulators; and sets a basic standard for quality and safety. However, it makes it difficult to introduce innovative techniques that were unknown at the time the rules were written. Regulatory authorities therefore have a panel of experts to review innovative proposals. If they are satisfied on safety, they may issue a permit for a technique or for a specific project. Until Monash and others achieved changes to the Melbourne Building Regulations, RCMPC was obliged to appeal to the Referees on numerous occasions.|
|Requisition.||There is frequent reference in this JM website to 'the first requisition'. Orders for materials, chiefly steel reinforcing bars and cement, were issued by John Gibson. Part of his job as Managing Director was overseeing the day-to-day financial affairs of RCMPC. Monash was in charge of the engineering operations. When negotiations, planning and design for a project were complete, and construction work was about to commence, JM would send a requisition to Gibson for the first batch of materials required. The date of the first requisition is often the best indicator of commencement of operations.|
|ring, arch||The term 'arch ring' is used to emphasise that reference is made to the arch itself - the structural member which carries the load - and not to the entire assembly of abutments, spandrel walls, filling, etc. which might be thought to constitute the arch.|
|RSJ||Rolled steel joist. A standard steel beam of I shape in cross section, produced by repeatedly rolling a block of red hot steel between progressively narrowing rollers. Although the term 'joist' is normally used for minor floor beams, RSJs could be of considerable size. For the first hundred years or so, the flanges of rolled I sections had a characteristic taper. (This is still occurs in the smallest sections currently rolled.)|
|Royal prerogative.||In the context of this web site: the power of the Crown to use patented inventions. For instance, the UK Patent Act states: "Notwithstanding anything in this Act, any Government department, and any person authorised in writing by a Government department, may make, use and exercise any patented invention for the services of the Crown in accordance with the following provisions of this section". The provisions seem to mean that if the Crown gets in early, before the patent is fully registered, it may thereafter use it without payment. Otherwise, an attempt must be made to reach an agreement, failing which recourse is had to the courts. The NSW Government paid GF&Co a commission until at least 1905. To the best of our knowledge, the Victorian Government refrained from using M&A's or RCMPC's methods until 1908 when George Swinburne, as Minister for Water Supply, refused to recognise their patent as valid.|
(In general, the term refers to the power of the Crown to act without consulting Parliament. As far as patents are concerned it appears most often in connection with the power of the Crown to grant patents.)
|Excavation of the soil in a river bed by the flow of water, especially around the base of piers and walls. This can lead to undermining of foundations.|
|screed||Here: a layer of mortar laid on top of a concrete floor to provide a smooth finish, often with a gentle slope to allow water to drain off the surface.|
|set (of cement)||When mortar or concrete is first mixed it is in a plastic condition. The first stiffening, as perceived by a standard test, is known as set.|
|shear||A situation in which a portion of material or a structural member is subjected to an action similar to that caused by a pair of scissors or shears. In a bridge beam this is most evident when a wheel has just moved onto the span and is tending to shear the beam against the face of the support.|
However shearing action in general, conceived as the tendency of a particle of material to slide against the particle adjacent to it, may be present in all directions under many circumstances of loading. See also Monash's tests on shear in T-girders.
|skew||A bridge which does not span directly across a river or road at right angles is said to be 'skewed', or 'on the skew'. Photo. A bridge which spans directly across is said to be 'square' or 'on the square'. The angle of skew of a bridge is most commonly defined as the angle by which the centreline of the roadway it carries deviates from that of a square bridge. In a 'lightly skewed bridge' this angle will be small, while in a 'heavily skewed bridge' it will be large. However, Monash and his colleagues defined angle of skew in the other sense as the angle between the centreline of the roadway and the centreline of the creek. Professor Kernot, in making notes on the failure of the first King's Bridge at Bendigo, wrote "angle of skew 40° (a square arch being 90°)".|
|slab||In structural engineering, principally a structural member whose horizontal dimensions are greater than its depth, such as the flat portion of a building floor or bridge deck.|
|slab-and-girder bridge||1. Another way of envisaging a T-girder bridge (see below).|
2. Also used in this study to indicate a bridge formed by placing Monier plates (slabs) on iron girders.
|soffit||The lower surface of a arch, beam or [floor] plate.|
|spalling||In this study: the process in which rust formed from corrosion of reinforcing bars forces off the concrete or mortar which is intended to provide protection. (Rust occupies a larger volume than the iron or steel from which it is produced.) Photo|
|span||1. That part of a bridge between two adjacent supports.|
2. The distance between two adjacent supports.
The 'clear' span is the distance between the vertical faces of the supports. For descriptive purposes the distance between centres of supports of a multi-span bridge is usually quoted. The value used by engineers for computation depends on a number of technical factors.
|spandrel||When an arch bridge is viewed from the side, the spandrel is the area between the upper surface of the arch ring and the line of the deck. In the Monier arch bridges described in this study, this area was occupied by a 'spandrel wall' which retained the soil filling on which the road was built. Sketch. At the time, the spelling 'spandril' was used.|
|springing||The location at which an arch ring emerges from its support or abutment. Sketch.|
|'square'||As a measure of building floor area: 10 feet×10 feet.|
|standard||In this context: a vertical post in the balustrade of a bridge.|
|steel||Any ferrous metal (i.e. mainly iron) with a low level of impurities and low carbon content. Towards the end of the 19th Century steel was becoming available in large economic quantities and replacing iron for most structural engineering work.|
|stirrup||A reinforcing rod of small diameter bent into an elongated U shape, placed in a vertical position in beams, with its bottom end looped around one or more main reinforcing bars. Stirrups help resist failure of the beam due to diagonal cracking (conventionally attributed to shear force). See beam No.6 in Monash's tests of shear strength of T-beams.|
|strain||In modern engineering: the extension or contraction of a unit length of material due to applied force, foundation settlement, etc. (Normally expressed in 'dimensionless' form, but sometimes as a percentage and occasionally, alas, in mixed units such as "millimetres per metre".)|
At the start of our period, Monash and his associates used the word 'strain' where modern engineers would use 'stress'.
|stress||In engineering, the force transmitted through unit area of cross-section of a material. In structural engineering in the English-speaking world at Monash's time it was usually measured in pounds (force) per square inch (lb/in² or psi). Now generally expressed in Newtons per square millimetre (N/mm²) which are known as megapascals (MPa) in most countries.|
At the start of our period, Monash and his associates used the word 'stress' where modern engineers would use 'load'.
|strike (verb)||To lower and/or dismantle the temporary framing which has supported a structure during construction.|
|string course||In this study: the single layer of bricks or stones at the top of the spandrel wall of an arch. This line was normally accentuated by having it project from the face of the spandrel wall, and sometimes (as in most of the Bendigo bridges) by building it in bluestone to contrast with the brick face of the spandrel wall and parapet. The string course could also be made of concrete.|
|strip (of arch)||The arch rings of the wider and longer Monier arches were cast (turned) in a number of parallel strips, about 12 feet (3.66m) wide, so that one strip could be completed in a single day. The joins between the strips can be seen clearly in the underside of the larger arches, as at Morell Bridge, Melbourne.|
|T-girder||See Girder, T.|
|tension||When a material is being pulled apart (stretched) it is said to be 'in tension'. Also, adjective 'tensile', as in 'tensile stress'.|
|trough girder||See Girder, trough.|
|turn (verb)||To 'turn' an arch is to complete its construction from one abutment to the other. This expression was applied by Monash and his associates to Monier arches. Most engineers today would use the verb 'to cast' for a reinforced concrete arch.|
|vault||Used in this study as synonymous with 'arch ring' (see 'Ring, arch' above).|
|wall, wing||A wing wall in a bridge is a short wall continuing the face of an abutment, but usually angled back away from the stream or thoroughfare over which the bridge spans. Its purpose is to retain and protect the earth of a river bank or the embankment of an approach road. See sketch.|
|wall, curtain||This term has been used in our publications for a thin wall filling the spaces between a row of columns in a bridge pier. Sketch.|
Later in the 20th Century, the term was applied to the external surfaces of buildings in which all major loads were carried by a skeleton of beams and columns, leaving the 'envelope' with the task only of keeping out wind and weather. This contrasted with previous practice in which massive masonry walls carried the major loads, leading to extremely thick external walls.
|yield||When metal is subjected to a small tensile load (or 'pull') it stretches. If, when the load is removed, it returns to its original length, as a rubber band does, the metal is said to be 'elastic'. With steel, the change in length is initially proportional to the load and the material is said to be 'linearly elastic'. However, at a certain value of load this relationship breaks down. With the type of steel used for most structural purposes in the 20th Century (under normal conditions of temperature and stress) the metal becomes 'plastic' and stretches somewhat like plasticine. This is called 'yield'. In laboratory tests, the load is divided by the cross-sectional area of a test specimen to obtain the stress at which yield occurs. Manufacturers aim to produce steels with a specified 'yield stress'. In Monash's time, designers ensured that the stress imposed on the steel by the predicted loads (the 'working stress') was a specified fraction of the yield stress. They saw the 'factor of safety' as the yield stress divided by the working stress. Modern engineers see things differently, but that is beyond the scope of this website.|
Metals yield also in compression.
(After yield has occurred, there is considerable extension in 'mild' steels, then an increase in resistance until the point at which the metal finally breaks. This is known as the 'ultimate tensile stress' or 'ultimate strength'. Plastic behaviour is desirable because it permits the material to 'remold' itself, adapting to the stress situation and redistributing the burden to less highly stressed parts of the material or the structure. It can give early warning that a structure is being overloaded; and failure, when it occurs, should be less sudden. Cast iron and some high strength steels do not yield, but snap suddenly ('brittle' failure). Even 'mild' steel may fail in this manner if subjected to extreme cold and/or tensile stress acting in three directions.)