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EIILM UNIVERSITY, SIKKIMDIPLOMA CIVIL ENGINEERING, SEMESTER – III, YEAR-2nd 

BUILDING CONSTRUCTION

Duration -3 Hours Max Marks: 60

Note: 1. Attempt any FIVE questions.

2. All questions carry equal marks.

1. Differentiate between rock and soil?

1. Explain foundation and its purposes?

Ans1

A foundation (also a charitable foundation) is a legal categorization of nonprofit organizationsthat will typically either donate funds and support to other organizations, or provide the source of funding for its own charitable purposes.

This type of non-profit organization differs from a  private foundation which is typically endowed by an individual or family.

Foundations in civil law

The term "foundation," in general, is used to describe a distinct legal entity.

Foundations as legal structures (legal entities) and/or legal persons (legal personality), may havea diversity of forms and may follow diverse regulations depending on the jurisdiction where theyare created.

In some jurisdictions, a foundation may acquire its legal personality when it is entered in a publicregistry, while in other countries a foundation may acquire legal personality by the mere actionof creation through a required document. Unlike a company, foundations have no shareholders,though they may have a board, an assembly and voting members. A foundation may hold assetsin its own name for the purposes set out in its constitutive documents, and its administration andoperation are carried out in accordance with its statutes or articles of association rather thanfiduciary  principles. The foundation has a distinct patrimony independent of its founder .

Foundations are often set up for charitable purposes, family patrimony and collective purposes.

Finland

Foundations in Finland must have state approval and register at the National Board of Patentsand Registration within six months from its creation. A minimum capital of € 25,000 isobligatory. A foundation can be created with any legal purpose and may have economic activityif this is specified in its Bylaws and the business supports the foundation's purpose.

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France

There are not many Foundations in comparison to the rest of Europe. In practice publicadministration requires at least €1 million is considered necessary. States representatives have amandatory seat in the Board. [1]

Germany

German regulations allow the creation of any foundation for public or private purposes inkeeping with the concept of a gemeinwohlkonforme Allzweckstiftung ("general-purposefoundation compatible with the common good"). A foundation should not have commercialactivities as its main purpose, but they are permitted if they serve the main purpose of thefoundation. There is no minimum starting capital, although in practice at least €50,000 isconsidered necessary.

A German foundation can either be charitable or serve a private interest. Charitable foundationsenjoy tax exemptions. If they engage in commercial activities, only the commercially active part

of the entity is taxed. A family foundation serving private interests is taxed like any other legalentity. There is no central register for German foundations.

Only charitable foundations are subject to supervision by state authorities. Family foundationsare not supervised after establishment. All forms of foundations can be dissolved, however, if they pursue anti-constitutional aims. Foundations are supervised by local authorities within eachstate (Bundesland) because each state has exclusive legislative power over the laws governingfoundations.

In contrast to many other countries, German law allows a tax sheltered charitable foundation todistribute up to one third of its profit to the founder and his next of kin, if they are needy, or to

maintain the founder's grave. These benefits are subject to taxation.

As of 2008, there are about 15,000 foundations in Germany, about 85% of them charitablefoundations. More than 250 charitable German foundations have existed for more than 500years; the oldest dates back to 1509. There are also large German corporations owned byfoundations, including Bertelsmann, Carl Zeiss AG and Lidl.

Foundations are the main providers of private scholarships to German students.

Italy

In Italy, a foundation is a private non profit and autonomous organization, its assets must bededicated to a purpose established by the founder. The founder cannot receive any benefits fromthe foundation or have reverted the initial assets. The private foundations or civil codefoundations are under the section about non commercial entities of the first book (Libro Primo)of the Civil Code of Law (Codice Civile) from 1942. The Art. 16 CC establishes that the statutesof the foundation must contain its name, purpose, assets, domicile, administrative organs andregulations, and how the grants will be distributed. The founder must write a declaration of intention including a purpose and endow assets for such purpose. This document can be in theform of a notarised deed or a will. To obtain legal personality, the foundation must enroll in thelegal register of each Prefettura (local authority) or some cases the regional authority. There areseveral nuances in requirements according to each foundation's purpose and area of activity.

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Portugal

A foundation ( Fundação) in Portugal is normally credited by the Portuguese Foundation Centre(CPF - Centro Português de Fundações), that was founded in 1993 by the Eng. António deAlmeida Foundation, the Calouste Gulbenkian Foundation and the Oriente Foundation.[2]

Spain

Foundations in Spain are organizations founded with the purpose of not seeking profit andserving the general needs of the public. Such foundation may be founded by private individualsor by the public. These foundations have an independent legal personality separate from their founders. Foundations serve the general needs of the public with a patrimony that funds publicservices and which may not be distributed to the founders' benefit.

2. Give various uses of stones in construction?

Ans2

Crushed stone or angular rock is a form of construction aggregate, typically produced

 by mining a suitable rock deposit and breaking the removed rock down to the desired size

using crushers. It is distinct from gravel which is produced by natural processes of 

weathering and erosion, and typically has a more rounded shape.

Uses

Angular crushed stone is the key material for macadam road construction which depends on the

interlocking of the individual stones' angular faces for its strength.

[1]

 Crushed natural stone is alsoused similarly without a binder for riprap, railroad track ballast, and filter stone. It may also beused with a binder in a composite material such as concrete, tarmac, or asphalt concrete.

According to the United States Geological Survey, 1.72 billion tonnes of crushed stone worth$13.8 billion was sold or used in 2006, of which 1.44 billion tonnes was used as constructionaggregate, 74.9 million tonnes used for cement manufacture, and 18.1 million tonnes used tomake lime. Crushed marble sold or used totaled 11.8 million tonnes, the majority of which wasground very fine and used as calcium carbonate.

In 2006, 9.40 million tonnes of crushed stone (almost all limestone or dolomite) was used for  soil 

treatment, primarily to reduce soil acidity. Soils tend to become acidic from heavy use of nitrogen-containing fertilizers, unless a soil conditioner is used. Using aglime or agriculturallime, a finely-ground limestone or dolomite, to change the soil from acidic to nearly neutral particularly benefits crops by maximizing availability of plant nutrients, and also by reducingaluminum or manganese toxicity, promoting soil microbe activity, and improving the soilstructure.

In 2006, 5.29 million tonnes of crushed stone (mostly limestone or dolomite) was used as a fluxin blast furnaces and in certain steel furnaces to react with gangue minerals (i.e. silica and silicateimpurities) to produce liquid slag that floats and can be poured off from the much denser moltenmetal (i.e., iron). The slag cools to become a stone-like material that is commonly crushed andrecycled as construction aggregate.

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In addition, 4.53 million tonnes of crushed stone was used for fillers and extenders (includingasphalt fillers or extenders), 2.71 million tonnes for sulfur oxide removal-mine dusting-acidwater treatment, and 1.45 million tonnes sold or used for poultry grit or mineral food.

Crushed stone is recycled primarily as construction aggregate or  concrete.

Landscape use

Crushed stone or 'road metal' is used in landscape design and gardening for gardens, parks, andmunicipal and private projects as a mulch, walkway, path, and driveway pavement, and cell infillfor modular  permeable paving units. As a mineral mulch its benefits include erosion control,water conservation, weed suppression, and aesthetic qualities. It is often seen used in rock gardens and cactus gardens.

3. Explain the types of Building tiles and their uses?

Ans3

A tile is a manufactured piece of hard-wearing material such as ceramic, stone, metal, or 

even glass. Tiles are generally used for covering roofs, floors, walls, showers, or other 

objects such as tabletops. Alternatively, tile can sometimes refer to similar units made from

lightweight materials such as  perlite, wood, and mineral wool, typically used for wall and

ceiling applications. In another sense, a tile is a construction tile or similar object, such as

rectangular counters used in playing games (see tile-based game). The word is derived from

the French word tuile, which is, in turn, from the Latin word tegula, meaning a roof tile

composed of fired clay. Tiles are often used to form wall and floor coverings, and can range

from simple square tiles to complex mosaics. Tiles are most often made from porcelain, fired

clay or ceramic with a hard glaze, but other materials are also commonly used, such as glass,

metal, cork, and stone. Tiling stone is typically marble, onyx, granite or slate. Thinner tiles

can be used on walls than on floors, which require thicker, more durable surfaces.

Earthenware

Ceramic with a water absorption rate of more than 10% after firing it at temperatures between950 - 1150°C is known as earthenware. Earthenware is easy to work and easy to decorate.Because it is so porous though, it should only be used indoors to prevent weathering caused byfrost. Earthenware is mainly used as glazed wall tiles.

Two different procedures for manufacturing earthenware can be distinguished: In themonoporasa technology, i.e. single firing technology, the liquid glaze is applied onto the tileimmediately after shaping. Then the desired decoration can be applied onto the tile. In the doublefiring technology (biporosa) the body is fired first. Afterwards it is glazed, decorated and then

fired again.

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Stoneware

Stoneware has a water absorption rate of less than 3% percent. Stoneware is frost proof due to itslow porosity. Compared to earthenware, stoneware has a higher density and a better mechanicalstrength. Almost all tiles for floor coverings exposed to high traffic such as for industry,commerce or public areas are made of unglazed stoneware that can be seen, for instance, at

 Nuremberg Central Station. Stoneware tiles with glaze are classical ceramics for floors. Abrasionand slip resistance are determined by the technical properties of the glaze.

Unlike earthenware, stoneware is fired at temperatures between 1150 - 1300°C. Porosity can bereduced by adding fluorite and other fluxes.

Porcelain stoneware

Porcelain stoneware is characterised by its very low water absorption rate of less than 0.5%.Thus porcelain stoneware is a further development of stoneware tiles, whose water absorptionrate lies under 3%. Porcelain stoneware is manufactured under high pressure by dry-pressing fine

 processed ceramic raw materials with large proportions of quartz, feldspar and other fluxes.Afterwards, the body is baked at high temperatures (1200 - 1300°C) in a roller passage kiln.

Due to its high breaking and wear resistance properties porcelain stoneware is often used in public areas and areas where wear conditions are particularly extreme.

At the beginning of the development, porcelain stoneware was manufactured but unglazed.

The low porosity permits polishing a tile and thus creating an extraordinary beautiful and brilliant surface.

By applying ceramic powders of different colours or using soluble salts, unglazed porcelainstoneware can be decorated in different ways. However, the variety of possible visual effects islimited. Therefore it becomes more and more usual to manufacture glazed and imprinted porcelain stoneware. A huge variety of decors can be created due to the properties provided bythis material. For instance, the most different types of stones, woods, fabrics, cork, leather etc.can be imitated.

Glazed porcelain stoneware differs from glazed stoneware by a slightly higher breakingresistance and a complete frost resistance. Other properties, such as, for instance, chemicalresistance, slip resistance and scratch hardness may vary significantly depending on the type of surface.

Cleaning, protection,care

Porcelain stoneware polished and matt

•  Newly laid areas

Adherence of dirt on hardly visible remains of joint material or adhesives makes later maintenance cleaning difficult.Thus all floor coverings should be cleaned with a standard cementresidue remover. Residues of joints containing plastic can be removed with an intensive cleaner.

• Preliminary cleaning in case of protective treatment of used and soiled tiles

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Treatment of a used floor covering requires a thorough preliminary cleaning. All impurities andmaintenance agents have to be removed from the surface and the pores. For this purpose, acommercially available intensive cleaner should be used under observance of the instructions for use.

• Protective treatment against stains

Depending on the type of use of the floor covering, stains may appear despite the exceptional properties of porcelain stoneware tiles. A single treatment with a standard protectiveimpregnation reduces delicateness and increases ease of care. Ingress of dirt, oil, grease, wax, paint etc. can be significantly reduced, so that hardly any stains appear or stains can be easilyremoved. This treatment is recommended for newly laid floor coverings with a polished surface.Whether or not this treatment is suitable for structured or matt surfaces has to be checked. Inmost cases an impregnation of very light or dark coloured floor coverings is effective.

Some manufactureres offer factory-sealed matt ( currently even polished ) porcelain stonewaretiles.

• Regular maintenance care

4. Write short notes on partition and cavity wall?

Ans4

The principle of the cavity wall is quite simple. The cavity prevents moisture passing through the wall. As long as the cavity is kept clean and the wall ties arecorrectly positioned the house should remain dry even if the external leaf 

 becomes saturated. Water is free to run down the inner face of the external leaf (and this is quite likely in severe exposures) and is either ejected via weep-holesor drips safely below the DPC.

Early wallswere usually brick in bothleaves.During the1930s blockwork 

 became more popular for the internalleaf. Blockscontained allmanner of aggregatesdepending onwhat wasavailablelocally. Earlycavity wallsare usually

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250mm thick ( 10 inches)with thecavity 50 mm(2 inches). Inmodernconstructioncavities areoften 75mmor more widetoaccommodateinsulationand allow aclear space betweeninsulationand outer leaf.

Of course, if cavities are bridged damp penetrationcan occur.The mostcommoncause of 

 bridging isdebris in thecavity but itcan also becaused byties whichslope towardsthe inner leaf or ties (somedesigns only) being laid

upside down.Thisendoscope pictureclearly showsmortar on thetie. The purpose of the ties is to bind the twohalves of the

wall together.Many early

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ties havefailed prematurely.This isusually because theyhadinsufficient protection(usually inthe form of galvanising).

Sometimes,where wallswererendered the

wall could be built from 2 block leavesor 2 leaves of common bricks.Spottingwhether earlywalls arecavity or solid can be

quite difficultif propertiesare rendered.The depth of the reveals isone clue;another can be found inthe roof space ateaves level.

2 Early Cavity Walls

By the end of the Victorian period cavitywalls were not uncommon although mostexternal walls were still built as solid walls.London Building Regulations (and manylocal by-laws) insisted that either the inner or outer leaf of a cavity wall should be 1 brick thick. The two leaves were held together bycast iron or wrought iron ties (left), or, insome cases, special cavity bricks (right).

Click  here for a drawing showing a Victoriancavity wall (taken from an 1898 textbook).

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To see a shortvideoclipexplaining the

problems anddemiseof thesolidwall,and theintroduction of thecavitywall

click here

By the 1920s the Regulations had been

relaxed and most new houses were built withcavity walls, but with both leaves half-brick thick. The wall was typically 250mm thick (10inches). However, solid walls continuedin some parts of the country for many years.Many Victorian houses, for example, thosere-built after the Second World War (following bomb damage) were built withsolid walls.

The most common form of an early cavitywall is shown on the left. An outer leaf of  brickwork would be built in facing bricksand usually in stretcher bond (sometimesFlemish bond was used with 'snapped'headers, ie, headers broken in two). Theinner leaf was usually formed in common bricks, ie, bricks intended to be plastered or 

kept out of sight. As with solid walls theinternal plaster was usually lime based andapplied in two or, preferably, three coats. Inthe 1930s and 40s this slowly gave way togypsum plaster.

early cavity walls

In a solid wall headers bind the walltogether. In a cavity wall this is not possibleand the two leaves are tied together by wallties. Early ties were sometimes formed inwrought iron or mild steel. They were

sometimes unprotected or possibly coated in bitumen or zinc (galvanising). The ties weretypically positioned every sixth coursevertically and about 900mm aparthorizontally. In practice these centres wereoften 'stretched' to save money. The tie onthe right is from a 1920s house. You can seesome deterioration at the bottom of the tie.The galvanised protection has disappearedleaving the steel free to rust. The rusty partwas in the external leaf.

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Click here to seeanexampleof modern

bricklayers inaction.Thebasictechnique is thesamenowadays as itwas ahundred

yearsago.

By the 1930s some developers were usingconcrete blocks for the inner leaf. Thesewere often made from locally availableaggregates, often industrial wastes. However,the use of blockwork was slow to catch onand even as late as the 1950s bricks were stillused for internal leaves of cavity walls andinternal partitions.

By the 1920s most walls included DPCs. Nowadays two separate DPCs are used (seeleft), one for each leaf. In some early cavitywalls large pieces of slate were used whichactually bridged the cavity. Other materialsincluded lead, copper, asphalt and lead cored bitumen felt. Today, most DPCs are madefrom polythene.

The inner andouter

leaf of acavitywall

shouldnever

touch -

theyshouldalways

beseparate

d by aDPC.

3 Early Cavity Walls - Head, Sill and Jamb

Openings in early cavity walls could takemany forms. This page shows one or two of 

them for cavity walls built in the first half of the 20th century. Many aspects of good practice were ignored and the consequencesof this sometimes manifested themselves in problems of damp penetration. However,many of these walls are still functioningquite adequately.

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As shown in the top right photo the lintel was often formed in precastor insitu concrete. It could be in two halves, one for each leaf, or as asingle deep lintel as shown in the left-hand examples. It should be clear that with a solid lintel damp penetration is a possibility due to mortar droppings bridging the cavity, or to water running across the top of thelintel. The example on the right of the graphic includes a cavity tray -designed to prevent the above problems. However, condensation is stilla risk and is easily confused with damp penetration. This is explainedin more detail below.

Cavity trays were not always used at the heads of openings. On manyolder houses they have been added subsequently. Look for tell talesigns, usually a few new courses of brickwork over the lintel. In this photo the cavity tray appears to be made from copper - you can just seethe front 'strip' of the tray projecting from the wall.

The construction on the left, known as a boot lintel, alleviated the problems shown above. The top of the lintel was usually coated in tar (from coal) or bitumen (from oil) to prevent water soaking into thelintel itself. However, even where these exist there is still another  potential problem; condensation. This can occur on the inside face of the lintel because it is cold. The phenomenon is sometimes referred toas cold bridging. Moist air in a room comes into contact with the coldinner face of the lintel and condenses. The problem is often confusedwith damp penetration and, as a result, the diagnosis is often wrong.This can lead to expensive repairs which do nothing to alleviate theunderlying problem.

Some windows have soldier arches abovethem. This is a row of bricks on end, usuallyonly in the outer leaf. The inner leaf oftencomprises a concrete lintel. In narrowopenings the soldier arch stays in place dueto the adhesive affects of the mortar. Inwider openings you can sometimes find asteel or wrought iron bar as shown on theleft. In a few cases the bricks may have steelreinforcing rods running through the holes inthe bricks.

At the jambs, ie, the sides of the opening,cavities were often closed to provide a goodfixing for the frame and a good base for theinternal plaster. The example on the leftshows a cavity wall with the inner leaf returned to the outer leaf. This creates a pathfor damp penetration but there are still lots of examples of this construction, some of themdamp free. Sometimes the cavity was left

open as shown on the right. This does not

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 provide a very good fixing for the window.

These examples both show a cavity closed but with the addition of a DPC. In the lefthand example the DPC is a sheet material, possibly bitumen felt or even lead. The right

hand example shows a cavity closed with plain tiles bedded in mortar. This principle,ie of providing a DPC, remains today.

There were a variety of sill details. Twoexamples are shown here. In the left handexample the timber sill is bedded in mortar on the external leaf. A drip at the end of thesill prevents water from running back under the sill. In the right hand example a smaller sill section sits deeper in the jamb. A sub sill

formed from plain tiles is bedded in mortar on a DPC. In this example the cavity isclosed with a three quarter brick.

4 Modern Cavity Walls - Generally

Below ground level it is common to find blockwork. Dense blocks and most aerated blocks are suitable for use below the ground.Holes in the blockwork, with lintels over for top for support, can be left for buildingservices (water will be lower).

Modern brick/block cavity walls vary inthickness depending on the nature of thecavity and the nature of the inner leaf. Thecavity will normally be 50mm, 75mm or even 100mm wide. The thickness of the inner leaf depends on the type of blocks; 125mmaerated blocks are quite common. The use of thicker lightweight internal leaves or specialaerated blocks can preclude the need for 

additional insulation. See the section onBuilding Regulations or Insulation for currentrequirements. Click here for another exampleof a modern cavity wall.

If bricks are usedin theouterleaf itsthickness isnormally102.5mm; often

referredto as100mmor half-brick.

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Where insulationisrequiredit caneither

be inthecavityor in theform of drylining.Externalinsulation israre innew

cavitywalls.

 

Where cavitiesarefilled orpartially

filledgoodworkmanship isvital topreventrainpenetration.Followthe tipsin the

bulletpointsbelow.

• Ensure the cavity is kept clean

• Make sure all joints are well filled

with mortar • Use a tooled joint which compresses

mortar and forms a good seal with the brick 

•

Ensure wall ties are level (or slopeoutwards) and keep ties clean

• Provide cavity trays (with stop ends if 

necessary) over lintels etc. which bridge the cavity

• Make sure DPC details are correct

• Make sure trapped water can escape

through weep-holes

• Ensure cavity insulation is fitted in

accordance with manufacturer's

recommendations.

Although cavity walls are formed in twoleaves they should be regarded as a singlestructural unit. Neither leaf should normally be built over 1.35metres high (about 6courses of blockwork) on its own; singleleaves are more likely to suffer wind damage.Where rigid ties are used this differenceshould not exceed 2 blocks (rigid ties are lesstolerant of difference in bed joint thickness

and trying to bend them will dislodgemasonry.) Details on the spacing of ties can

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 be found elsewhere on this site. The pictureon the right shows an internal leaf which has been 'lifted' a bit high.

5. What are the advantages of partition wall?

Ans5

A partition wall is a non-load bearing wall, positioned either part or all the way across a room.They allow better use of the space in your home, for instance, if you find a room too large for your needs, you can use a partition wall to split the space. Partition walls are also great for creating or increasing privacy in homes or offices.

Types of partition walls

Partition walls can be used to organise large

Spaces

Partition walls can be made of any one of a variety of materials and can contribute to your homesdesign - glass partition walls, for instance will suit a modern or minimalistic property. The actual“wall” is made of glass that slides along a ceiling track and the glass is substantially reinforced to prevent accidental breakages.

Other materials used to create partition walls include normal bricks, concrete or fibre cementsheet partitions. Bricks and concrete are understandably tougher than fibre cement sheets but allwill withstand a fair bit of damage. An alternative is a partition made of metal sheets which tendsto be good value for money as well as fire resistant, thin and durable.

Wooden partition walls are considerably more expensive than the other materials available toyou, but for good reason. Wooden partition walls can really give a homely, vintage feel to your house and bring warmth to any room. Or you could go completely in the opposite direction andopt for an art-deco style of wooden partition walls that provide a fresh modern look.

It is also possible to have a moving partition installed so that you can open up or shrink the roomwhenever you like. Some partition walls slide along rails but usually won’t fully move out theway unless you have them retract into the wall. If you want your partition out of the way as muchas possible, an alternative option is a partition wall which folds back on itself when not in use.

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Benefits of partition walls

The benefits of installing a partition wall are easy to see. They allow you to turn an overly largeor mostly unused room into a useful space and can also provide privacy. If you need a newworking space or a playroom for your children, a partition wall is a fairly cheap and quick option.

Partition walls will naturally increase the value of your home, although not necessarily enough to pay for themselves. If designed and installed cleverly though, they could add real value to your home.

Installing partition walls

Unless you have building experience you will want to hire a professional to install your partitionwalls. Sliding partition walls may require fixing to the walls or ceiling and without the relevantexperience you could put your home as well as yourself in danger. By hiring a building professional you cut the risk of causing problems to your home, as well as ensuring the work isdone quickly and efficiently.

6. Give difference between arch and Lintel?

Ans6

 Arches and lintels are found wherever it is necessary to support a wall etc. over an openingwhich is usually not more than about two metres wide. They provide support in completelydifferent ways and an understanding of this is fundamental to selecting, specifying andassessing them.

Both arches and lintels occur naturally to some extent. The natural arch at Durdle Dor in Dorsetis famous. It was many centuries before mankind understood the mechanics of the arch anddevised the means to successfully construct them. However, the lintel was in a sense easier touse, if not understand. There are now so many different types of arches and lintels that acomplete listing would be outside the scope of this Paper.

Lintels are much simpler than arches, and the forces involved are completely within the lintel.They provide support by resisting the bending moments and shear forces resulting from theloads that are applied to them. The first examples were probably trees falling across a stream,and mankind quickly learnt how to make use of lintels. There are examples of stone being usedas lintels as far back as prehistoric times. The earliest lintels were probably of stone, as used inThe Great Pyramid of Giza, built about 2560 BC, and Stonehenge, built about 2300BC. The

use of timber for lintels probably developed in parallel with stone and was greatly assisted bythe development of Bronze Age tools in the Middle East before 3000BC. Much later, theintroduction of iron tools in the Iron Age after 1200BC greatly increased the ability to work bothstone and timber.

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Diagram showing the main forces associated with a lintel.

General.

There are many different shapes of lintels, determined by the properties of the material and thepurpose for which the lintel is required. Stone and timber lintels are generally rectangular incross section. Concrete lintels are usually either rectangular, ‘L’ shaped (known as ‘boot’lintels), or rectangular but with one vertical face sloping (used in cavity walls).

The development of concrete and steel lintels, together with the fashion for larger windowsintroduced in the 1950’s and extended further in the1960’s, required the use of stronger lintelsto carry the increased loads. Windows up to 2.4m wide were not uncommon in the 1960’s.These larger spans in turn required more attention to be paid to the bearings at the ends of these lintels due to the greater loads from them onto the masonry below.

Further developments in building introduced corner lintels, which act as cantilevers, box lintels,and eaves lintels. As steel lintels were developed designs for solid walls, and internal wallsbecame available. To improve the thermal insulation properties and provide easier fixings for items such as curtain rails open back lintels were introduced.

 As timber frame houses grew in popularity with developers timber frame lintels made of steel

appeared. In recent years the increased thermal insulation requirements have precluded thecontinued use of some types of lintels for the external walls of buildings e.g. concrete ‘boot’lintels. Others, such as steel lintels, have had their designs revised by the inclusion of insulationwithin the cavity space of the lintel.

British Standards. 

The design and manufacture of lintels are covered by various British Standards. BS 5977covers the Specification for Prefabricated Lintels, and BS 7543 The Durability of Buildings,Building Elements, Products and Components their design life.

There are also material specific Standards for the main materials used for lintels. BS EN ISO1461 covers the Hot Dipped Galvanising of steel lintels. BS 7973 covers the requirements for spacers that can be used in reinforced concrete lintels.

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Materials.

Stone.

Stone lintels can be found made from a variety of, usually local, stone. Hard durable stone,such as granite, resists natural deteoriation well, but softer stone, such as limestone, can besignificantly weathered away over time. In theory the stone has no tensile strength and thuscannot be proven by calculation to be adequate to support the load. Stone is also vulnerable todefects within it, and to fractures occurring either naturally, or as a result of the quarrying,transporting and placing of the stone, or as a result of loading or thermal movement. For layered stone, such as some limestones, the direction of the layering in the lintel cansignificantly affect its weathering and strength.

Once the stone has fractured its actual strength can fall to zero. It would then require carefulremoval and replacement, with adequate temporary support for the masonry above, in order torestore the structural strength and support to the wall.

Lintels can also be made from reconstructed stone, sometimes called cast stone. These arecommon in areas where the external face of the wall is built of a local stone e.g. the Purbeckarea. Reconstructed stone lintels are usually reinforced with steel bar reinforcement of the typeused for reinforced concrete lintels. However, the stone and the manufacturing process bycasting can result in a porous texture in the lintel and this can allow moisture to reach and thencorrode the steel reinforcement. The lintels then require replacement which can be anexpensive process as they need to be specially manufactured to the same size and with thesame or matching stone as the original ones. The use of stainless steel reinforcement in theselintels is very cost effective and preferred to plain steel reinforcement. The reinforcementshould always be positioned using spacers complying with BS 7973.

7. What are the properties and uses of special cement? Write their advantages?

8. What are vertical and horizontal DPC?

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