Rudiments of the Art of Buildin - Dobson, Edward, 1816-1908

8/10/2019 Rudiments of the Art of Buildin - Dobson, Edward, 1816-1908

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PEEFACE.

In offering this little volume to the

public, it may be desirable to say afew words, by way of preface, as tothe object and character of the

work. It has been written at thesuggestion of the publisher, toaccompany the KudimentarySeries^ and aa a first book on the

.rt of Building, intended for theuse of young persons who arealK>ut to commence their

professional training for anypursuit connected with the erectionof buildings ; and, also, for the useof amateurs who wish to obtain a

general knowledge of the subject


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without devoting to it the timerequisite for the study of the largerworks that have been written on the

different branches of construction.

To avoid imnecessarily extending

the limits of the work, thosesubjects are omitted which aretreated of in other volumes of thisseries, as Building Stone, Brick-

making, and the Composition ofColours and Varnishes. For thesame reason little has been said of

the manufacture of glass and thesmelting of metallic ores, becausethey have been repeatedly treated on various elementary works, whilst

a considerable space has been


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devoted to the consideration of thedifferences between hot and coldblast irons, and to the description o

the operations of the iron-founder,subjects which are not generally tobe met with but in expensive works

The equilibrium of retaining wallss a subject which has long engaged

the attention of mathematicians

with little practical success, theresults arrived at by differenteminent writers being quite at

ariance with each other. For thechapter on this subject a few simpleformulas are given, which embraceaJl the conditions of the thnist of

the earth and of the resistance of


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the

wall, the friction of the earth

against the back of the wall beingalso taken into account *,

In the article on the strength ofoast-iron flanged beams a simplerule is given for calculation,foimded on the assumption that the

position of the neutral axis in acast-iron rectangular beam, at thetime of fracture, is at about fth ofts whole depth below its top

surface, which is now prettygenerally admitted to be the case.

mongst various works, the

following have been carefully


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consulted during the compositionof this little work The publicationsof the Institution of Civil Engineers

and of the Royal Institute of Britishrchitects, Professional Papers of

the Royal Engineers, Weale's

Quarterly Papers on Engineeringand Architecture, Weale's Bridges,the Works of Peter Nicholson,Gwilt's EncyclopaBdia of

rchitecture, Dr. Ure's Dictionary orts and Manufactures, Tredgold's

Carpentry, the works of Pasley and

icat on Limes and Cements,ikin*s Papers on Arts and

Manufactures, Barlow on theStrength of Materials, Tredgold and


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Hodgkinson on Cast Iron, andBartholomew on PracticalSpecifications ; all these works will

be found extremely valuable to thestudent

I have great pleasure inacknowledging the kind assistanceof my friend Mr. H. W. Eibby, C.E.,n the articles on the equilibrium of

retaining walls, and on the strengthof cast-iron beams; to whom I amalso indebted for the valuable notes

appended to the article on retainingwalls.

The articles on Iron-Founding,

Carpenter and Joiner's Work, and


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House-Painting, have been carefullyrevised by friends practicallyencased in those pursuits.

K DOBSON.

CONTENT&

SBGTION L

OENEBAL PBINOIPLES OFCOMSTBUCTION.

FoosDAnoHBTwo principal canse

of fiulure, 1. NainunUFcwndatumM^ 2; lome loilg onlyrequire to be protected from theaction of the atmoaphere, 8.


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rmiciaL Found tionspartly natural and partly artificial,6; piles used as props from a hard

nnder-stiatum, 7; piles used toconsolidate soft ground where theres no hard bottom, 8.

Fowiida;tioni in Water, 9;

Foundations formed wholly of piles10; iron piles, 11; screw piles, 12;cast-iron piling at Qravesend Pier,

13; foundations formed with cast-ron cylinders, 14; Indian

foundations, 15; solid foundations,where there is no danger from the


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scour of the water, 16; foundationsof pierre perdue, 17; foundations ofcoursed masonry, 18; hHan, 19;

caissons, their use, 20; caissons onfoundations of hiUm, 21; caissonson pile foundations, 22; solid

foundations laid in cofferdams, 28;cofferdams on a foundation ofhiton, 24; reference to Tolume on *Foundations and Concrete Works,*

25.

RATAnmra Walls Difference

between retaining walls and breastwalls, 20; theoretical rules for thestrength of retaining walls of littlepractical use, 27; calcuhition of

stability divided under two heads,


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is., pressure of earth andresistance of wall, 28; definitions,29; Pressure of Earth On what it

depends, 80; calculation ofminimum thrust, 81; calculation ofmaximum thrust, 82; action of a

wedge without friction, similar tothat of a fluid, 88. Resistance qfWall Calculation of^ 84 ; bestform, idem; adrantages of

triangular form, 85; modification ofthe triangular form commonlymade use of, 86; illustrations of the

comparative strength of differently-shaped walls, 87; protecting the toof a retaining wall, 88; counterforts89.


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Bebast Walls Principalprecautions to be taken in building40; to indined strata, 41; drainage

essential, 42.

iumnArcb defined, 48; fiiils by

taming on the edges of theousaoira^ 44; curre ofequilibrium, 45; experimental archwith cunred Tonseoin, 46;

coincidence of the catenarian curveand cuTTe of equilibrium, 47; twomethods of equilibrating arches,

ii., by suiting the curre to theweight, or the weight to the curre,48; illustration of the mode ofcalculating the required load on the

haunches, 49; minimum thickness


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required to contain the curre ofequilibrium, 50; in semicirculararoLea the springing forms part of

the abutment, 51; depth of theoussoirs must be calculated for the

maximum load, 52. Brkh Arehu

Common mode of buildingdefectire, 58; best method, 54.

rchet qflron and Timber, 55;aminated arched beams, 56. Siew

rche$ Causes which led to theirconstruction, 57; peculiarity of theskew arch, 58. Centering defined

59; points to be attended to inconstruction of, 60; centering forGloucester Over Bridge, 61;centering to QrosYenor Bridge, 62;


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defects of ordinary centering; 68. hubMnU, three modes of

preventing fiiilure in, 64; wing wall

of bridges, 65. Faulting Definitions, 66; oman vaulting, 67Gothic vaulting, peculiarity of, 68;

domes, 69.

Ma&onrt Bbiokwobe Bond Term masonry sometimes includes

brickwork, 70; three'classes ofmasonry, 71; diferent kinds ofmasonry used in connection with

each other, 72; mortar essential tostrength of mbble work, 78; defectsn ashlar work, 74; bed-doweloggles, 75, stone filings to

brickwork should be backed up in


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cement, 76; ashlar must bond withbrickwork, 77; bond, in whatconsisting, 78; brick bond, 79; three

points to be attended to in buildingwalls, 80; n-famity qfconstruction, 81; bond fir bond,

82; hoop-iron bond, 83; dittribuUonqf tke load, 84; inverted arches, 85;intels, 86; bret* summers of cast-ron not fireproof, 87.

PABTinoirsPrinciples of firaming88.

Ploobs Naked flooring, 89;objections to inserting timbers inwalls, 90; fireproof floors, 91; tile

floors, 92.


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RoomrQTimbering of a roofsimilar to a double-framed floor,98. Trusted Roqft Collar truss,

94; king truss, 95; queen truss, 96;ron roofr, 97; roo& of Houses of

Parliament, idenif these roo6

covered with galyaniied sheets ofcast iron, 98; roof of Biding Houseat Moscow, 99; bow suspensiontruss, 100. Roqf* on the principle

qf the ^reAPhilebert de Lorme'ssystem, 101; disadvantages of, 102;Colonel Bmy's employment of the

aminated arch rib in 1825, 108;aminated rib used in England by

Messrs. Green, in 1837. OoihieRo


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ess thrust on the walls, 104; roof cfClialdon Church, Surrey, 105;alteration of many high-pitched

roofs to

CONTENTS tt

abtain a clerestory, 106; flat roof,with tie beams and principals, 107;king-post roof, with struts under tie

beam, 108 ; these roo& not soundexamples of construction, 109;general principles of large opentimber roofs of fifteenth andsixteenth centuries, idem; roof ofGreat Hall, Hampton Court, 110;roof of hall at Eltham, 111; roof of

Westminster Hall, 112; roofs of this


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kind not to be executed in firwithout using iron straps or bolts,113. Roof Covering* Slate and

stone, 114; tiles, 115; shingles, 116;metallic coverings, 117; lead, 118;copper, 119; sine, 120: cast-iron,

121; contraction and expansion ofmetallic coTei ings, 122; weights ofdifierent coverings, idem,

SvppLT OF Water Influooce ofthe two modes of supply, vis.,constant and intermittent, on the

arrangements of a building^manner of fitting up privatecisterns, 128.

Warmino ahd Ybntilation


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Warming by fire-places and byheated aii, 124; two systems of

entilationventilation by

exhaustion, 125; ventilation byforcing, 126.

SECTION II.

MATERIALS USED IN BUILDING.

of bnildmg materials, 128. TimberStructure' of a tree, 129; points tobe attended to in preparing timberfor the use of the builder, 180; age

of timber, 131; time of felling, 132;seasoning, 138; decay, causes of,184; prevention of, 135; timber

chiefly used by the builder, 136; fir,


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187; oak, 138; fiancy woods, 189.Limes and Cements, Mortar,Concrete, B^tonProperty of

mortar depends on the chemicalcomposition of the limestones used140; three classes of limestones,

141; process of making mortar, 142;pure limesch&lk, 148; gypsum,144; water cements, 145; Dorkingime, 146; lias limes, 147;

composition of vmter limes, 148;puzzolana always used for hydrauliworks previous to the discovery of

natural cements, 149; artificial puz-Bolana, 150; artificial cements, 151;quality of sand fit for mixing withdifferent limes, 152; concrete and


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beton^rubble masonry of smallstones bedded in mortar used at a

ery early period, 153; differences

between concrete and b^ton, 154;composition of concrete, 155.

sphalts its composition, 156.

Metals list of metals used asbuilding materials, 157. Iron difference between cast andwrought iron, 158; the weald of

Kent and Sussex the principal seatof the iron manufacture, previousto the introduction of smelting with

pit-coal, 159; pit-coal now used asfuel, and steam power employed toproduce the bias* 63

OONTENTB.


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IS the smelting fnniace, 160; twosets of proceMt required for thproduction of wrought iron, 161;

mode of imelting, 162 ; introductionof the hot blast, 168; east irondirided into three qualities, 164;

casting, 165; couTersion of forge pignto bar-iron, 166; lead, 167; copper

168; sine, 169; brass, 170; bronie,difficulty in casting, 171; boll metal,

172.

SECTION IIL

8TBENGTH OF MATERIALS

Materials of a building exposed to

compression, tension, and cross-


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stiain, 178; resistance tocompression, 174; resistance totenuon, 176; cros*-ttrain.

Strength of Beams twoconsiderations, yiz., the mechanicalefiect of the load and the resistance

of the beam, 176; mechanical effectof a given load under varyingcircumstances, 177; resistance ofthe beam, 178; consideration of the

best form for cast-iron beams, 179;calculation of the strength offlanged beams, 180; use of a strong

top flange, 181; proving, 182;trussed timber beams, 188;ttrenffth qf nory posu cmd Cut-4ron pillars; wooden story posts,


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184; strength of cast-iron pillars,185; cases of transverse strainarising from settlements, 186.

SECTION IV. USB OF MATEBIAI&EZOATATOB, 187.

Brioklateb Nature of the business188; tools, 189; bricklayer'sabourer, 190; bricklayer's scaffold,

191; amount of day's work, 192;tools for tiling, 198; measurementof brickwork, 194; of paving, 195; oftiling, 196.

Mason Business of the mason,stone-cutter, and carver, 197;

preparation of stone for the use of


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planei, 214; diiteli, 215; Ixniiig tools216; other implement!, 217;dovetailing and mortiiing, 218;

oints, 219; scribing, 220; circularwork, 221; lodged, framed, andclamped work, 222; stnight joint

and folding floors, 228; glue, 224 ;meamrement of joiner's work, 225;ronmongery^principal

descriptions o^ 226; hinges, 227;

ocks, 228; latches, 229.

Bawtbk, 230.

Blatbb Nature of the business,281; tools, 282; mode of layingsktet, 233; measurement of slater's

work, 284.


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Plastxbbb Nature of plasterer^swork, 235; tools, 286; materials,237; operations of plastering, 238;

summary of above, 289;measuremept of plasterer's work,240.

Pmith akd Iroh-foxthder, 241.

Cor?BBSMITH, 242.

WABMnra Appabatus, &c., suppliedby the mechanical engineer, 248.

BELirHAHGBBModo of hangingbells, 244; how paid for, 245.

pLnxBESNature of plumber's


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259; materials, 260; tools, 261;operation of painting, 262; paintingon stucco, 263; graining, 264;

clearcoling, 265; distempering, 266 measurement of painter's work,267; scagliola, 268; gilding, 269;

paper-hanging, 270.

SECTION V.

WOBKINO DRAWINGS,SPECIFICATIONS, B8TIMATER,

ND CONTRACTS

Design and superintendence ofarge works the business of the

architect, 271; profession of the

architect and trade of the builder


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sometimes united, this notdesiimble, 272; business of asurveyor, 278; mode of conducting

arge wcrks, 274. Plan u/ Site, 275 Levels, the import

ance of correct levels, 276; mason'sevel, 277; spirit lerel, 278, levellingstaff, 279; mode of enteringobservations in level book, 280;

Bench marks, 281; making up levelbook, 282; checking thecomputations, 283; Datum line,

284; the water level, 285.

Working Drawinos Qualificationsof a draughtsman, 286; three

classes of working drawings, viz.,


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block plans, general drawings, anddetailed drawings, 287.

Spboifioations Nature of 288 ;conditions of cantract, 289;description of the works, 290; meri

of a specification consists inexplicitnessi 291.

Bills of Quantities, prepai^sd by the

surveyor, 292; three distinctoperations in taking out quantities,293; taking dimensions, 294 ;abstracting, 295; bringing quantitiento bill, 296; skeleton estimate,

297; quantities furnished tobuilders, 298; extra works, 299;

surveyors, how paid, 800;


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architect's charges, SOI.

Motes and Illustrations.

Retaining walls (p. 13), A; easingdown centering (p. 30), B; fire-proofloors (p. 42), C; roofs of large span

(p, 47),D; zinc coating (p. 59), E;heating and ventilation (p. 62), F;preservation of timber (p. 68), G;steel manufacture (p. 75), H; cast

ron, &c., (p. 77), I; tensileresistance (p. SO), K; strain ougirders (p. 88), L.

SECTION L

Fio.


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1

5;

8 9

n 11

12}

\v

U\

16

17 .

18


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19 J

20

21

22

28

24

25

2d)

27

10


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Single dam. Cofferdam with puddlewall Cofferdams on a b^tonfoundation. Retaining and breast

wall.

Diagrams illustrating the mode of

calculating tne strength of retainingwalls.

41 Breast walls to support inclined

strata.

"I

50 > DiagTsmi illaatiating theiritim at sichea.

58 Skew arch built in spiral courses


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61 Centering of the Gloucester OverBridge.

^A Abutment built as acontinuation of the arch.

butment built in an arched formto throw the thrust of the arch onthe wing walls.

IV LIST OP ILLU8TRATI0N&

DsioRiPTioir. Diflgram showing themanner in which wing walli of

bridges

often ul from the pressure of theearth at the back li the


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abutment Best form for anabutment to resist the piassare of ahmry hsak:^ Cylindrical vault

GoTed vault Groined Tault Qothicaulting. Rubble masonry. Gonraed

masonry. Ashlar masonry. Brick

wall with ashlar fiacing. Englishbond. Flemish bond.

Girderl..into.re. j|^.7J^,^^

Section of a dwelling houses^iowing the framing oi the timber

partition dividing the back and fronrooDis. Single flooring. Doubleflooring. Double framed flooring.


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Different methods of fixing ceilingJoists.

Fire-proof floor formed with brickarches resting on iron girdoiK

Flat roof fonned of plain tiles laidon light cast-iron girders.

Gollar truss.

King truss.

King truss with queen posts.

Queen truss with straining piece.

Diagram of the construction of the

trusses of the iron roof over


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the New House of Lords,Westminster. gQ B.oof of thecelebrated Riding House at

Moscow.

Details of arched beam in the roof

of the Riding House ut

Moscow.

59 101 Philibert de Lorme's systemof arched ribs.

60 103 Sketch of a roof at Marac,

near Bayonne, by Colonel Bmy.

61 ) Section of Chaldon Church,Surrey, showing the form of the |>


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105 original rool

62 I Details of roof, Chaldon

Church, Surrey.

68 *] Diagram showing the mannern which the high pitched roofs of

^QQ many country churches havebeen altered in order to introdonc

clerestory windows above the roofsof the aisles.

64 ' Flat Gothic roof without

principal rafters.

65 Mode of securing spandril strutswithout the use of iron Bimy^


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66 I Roof of nave West BridgefordChurch, Notts.

67 107 Plat Gothic roof withprincipal rafters.

68 108 Gothic kingpost roofs.

60)

Q I 109 Diagrams illostiating theprinciples of Gothic roofing.

XV

Fis. Art. Dbsoription.

71 110 Hampton Court Palace,

Middlesex, sketch of the {raming of


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the

roof of the Great Hall, omittiDg the

decoratiTe details.

72 111 Bltham Palace, Kent, sketchof the constmctlon of the roof of

the Great Hall.

78 112 Westminster Hall, London,sketch of one-half of a tmsi,showing the principal timbers only.

74 123 CKstem.

SBOTION II.-No iLLVBiRiLnoNB

SECTION IIL


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Beam fixed at one end and loaded athe other.

Beam loosely supported at the endsand loaded in the middle.

Beam supported in the middle andoaded at the ends.

Beam fixed at both ends and loaded

n the middle.

Diagram illustrating the pdiition ofthe neutral axis in beams.

Diagram illustrating the mode ofcalculating the strength of cast


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ron beams. Wooden beam trussedby increasing the resistance tocompreit sion.

Wooden beam trussed by increasinthe resistance to tension. Diagram

llustrating the mode of increasbgthe strength of cast iron pillars.

84 202

whs

87 205

88^

89


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? Uo9

92

98 j

94 214

97 219 98)

99 ( 221 100'

101 I

102 V 222 108 I

SECTION IV.

Mason's lewis for hoisting stone.


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Mode of working plane sur&ces.

Mode of working moolded surfaces

Joggle joint.

Mode of scarfing timbers.

Mode of securing the foot of aprincipal rafter to a tie beam.

Mode of suspending a tie beamfrom a king post.

Purlin framed into a principalrafter.

Purlin notched on to the principal

rafter.


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Slate boarding laid on purlin rafters

Rebate.

Dovetail.

Mortise and tenon.

Joints in woodwork.

Circular work glued up inthicknesses and Teneered.

Circular work bent round in

thicknesses.

Circular work bent the wholethickness of the stuff.


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Lodged door.

Framed door.

damped work.

Fi. Art. DsfCRimoir.

\lt\ 283|^li 8UUg. -^

106 nia Lead roll. > . . .

107 I ^^ Drip and flariiing. '

SBOTION V.

108 274 Mode of setting outfonndadozis.


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F0Uin>ATI0K8.

1 Ik preparing the foundation for

any building, there are two sourcesof failure which must be carefullyguarded against: viz., inequality of

settlement, and lateral escape of thesupporting material; and, if theseradical defects can be guardedagainst, there is scarcely any

situation in which a goodfoundation may not be obtained.

2. Natural Foundations, The bestfoundation is Sinatural one, such asa stratmn of rock, or compactgravel. If cir-cmnstances prevent

the work being commenced from


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the same level throughout theground must be carefully benchedout, i.e. cut into horizontal steps, so

that the courses may all be perfectlyeveL It must also be borne in mind

that all work will settle, more or

ess, according to the perfection ofthe joints, and therefore in thesecases it is best to bring up thefoundations to a uniform level, with

arge blocks of stone, or withconcrete, before commencing thesaperstructure, which would

otherwise settle most over thedeepest parts, on account of thegreater number of mortar

B


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oints, and thus cause unsightlyfractures, as shown m Hg. 1.

L

X

3. Many soils form excellentfoundations when kept from the

weather, which are worthless whenthis cannot be effected. Thus blueshale, which is often so hard whenthe ground is first opened as to


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require blasting with gun powder,will, after a few days* exposure,slake and run into sludge. In

dealing with soils of this kindnothing is required but to keepthem from the action of the

atmosphere. This is best done bycovering them with a layer ofconcrete, which is an artificial rock,made of sand and gravel, cemented

with a small quantity of Ume. Forwant of this precaution manybuildings have been fractured from

top to bottom by the expansion andcontraction of their clayfoundations during the alternationsof drought and moisture, to which


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they have been exposed insuccessive seasons.

4. Artificial Foundations Wherethe ground in its natural state is toosoft to bear the weight of the

proposed structure, recourse mustbe had to artificial means ofsupport, and, in doing this,whatever mode of construction be

adopted, the principle must alwaysbe that of extending the bearingsurface as much as possible; just in

the same way, that, by placing aplank over a dangerous piece of ice,a couple of men can pass over aspot which would not bear the

weight of a child. There are many


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ways of doing this as by a thickayer of concrete, or by layers of

planking, or by a network of timber

or these different methods may

be combined. The weight may also

be distr bated over tLe entire area othe fomidation by inverted arckes.

6. The use of timber is

objectionable where it cannot bekept constantly wet, as alternationsof dryness and moisture soon causet to rot, and for this reason

concrete is very extensively used insituations where timber would beiable to decay.


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6. In the case of a foundation partlynatural and partly artificial, theutmost care and circumspection are

required to avoid unsightlyfractures in the superstructure; andt cannot be too strongly impressed

on the mind of the reader, that it isnot an unyielding, but a uniformly

ielding foimdation that is requiredand that it is not the amount, so

much as the inequality, ofsettlement that does the mischief

The second great principle whichwe laid down at the commencemenof this section wasTo prevent theateral escape of the supporting

material. This is especially


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necessary when building in runningsand, or soft buttery clay, whichwould ooze out from below the

work, and allow the superstructureto sink. In soils of this kind, inaddition to protecting the smface

with planking, concrete, or timber,the whole area of the foundationmust be inclosed with piles drivenclose together;this is called sheet

piling.

n example of a wide-spread

foimdation in soft ground is shownn fig. 2 (p. 4), which is a section ofthe foundation for the walls of theLeyden station of the Amsterdam

and Kotterdam Eailway, built a.d.


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1843.* The station stands uponsuch bad ground, that it wasnecessary to support the walls upon

a kind of raft resting on oak piles.

7. Where there is a hard stratum

below the soft groimd, but at toogreat a depth to allow of the solidwork being brought up from itwithout greater expense than the

circumstances of the case willallow, it is usual to drive down

* From the " Minutes ofProceedings of the Institution ofCivil 1^ gmeem," 1844.

B 2


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8. Where a firm foimdation isrequired to be formed in a situationwhere no firm bottom can be found

within an available depth, piles aredriven, to consolidate the mass, afew feet apart over the whole area

of the foundation, which issurroimded by a row of sheet-pilingto prevent the escape of the soil; thspace between the pile heads is

then filled to the depth of severalfeet with stones or concrete, andthe whole is covered with a timber

platform, on which to commencethe solid work.

9. Foundations in Water, Hitherto

we have been describing ordinary


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foundations; we now come to thosecases in which water interferes withthe operations of the builder,

oftentimes causing no little troubleanxiety, and expense.

Foundations in water may bedivided under three heads: 1st,Foundations formed wholly withpiles. 2nd, Solid foundations laid on

the surface of the ground, either ints natural state, or roughly levelled

by dredging. Srdly, Solid

foimdations laid below the surface,the ground being laid dr} bycofferdams.

BT OF BUILDING. D


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T i n if mi!

Hf

In deep water the bracing of thepiles becomes a difficult matter,

and an ingenious expedient for


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effecting this was made use of byMr. Walker, in the erection of theOtiso Bridge, on the Leeds and

Selby Railway, a.d. 1840. Thisconsisted in roimding the piles towhich the braces are at* tached for

a portion of their length, to allowthe cast-iron

b BCTDIMXrS OF TUB

sockets in which they rest todescend and take a solid bear< ingupon the square shoulders of thebrace-piles. After the brace pileswere driven, the braces were boltednto their sockets and dropped

down to their required position, and


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their upper ends were then broughtto their places and bolted to thesuperstructure

11. There is always, however, a greaobjection to the use of piles partly

above and partly under water,namely, that, from the alternationsof dryness and moisture, they soondecay at the water-line, and

erections of timber requireextensive repairs from this cause.In tidal waters, too, they are often

rapidly destroyed by the worm,unless great expense is undergonen sheathing them with copper.

To obviate the inconveniences


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attending the use oi timber, castron is sometimes used as a

material for piles: but this again is

objectionable in salt water, as theaction of the sea-water upon theron converts it into a soft

substance which can be cut with aknife, resembling the Cumberlandead used for pencils.

12. In situations where a firm holdcannot be obtained for a pile of theordinary shape, such as shifting

sand, Mitchell's patent screw-pilesmay be used with great advantage.These piles terminate at the bottomn a large iron screw 4 ft in

diameter, which, being screwed into


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the ground, gives a firm foot-hold tothe pile. This is a very simple tndefficient mode of obtaining a

foimdation where all other meanswould fail, and has been used inerecting light-houses on sand-bank

with great success. The Maplin sandight-house at the mouth of the

Thames, and the FleetwoodLighthouse, at Fleetwood, in

Lancashire, both erected a.d. 1840,may be instanced.

13. An ingenious system of cast-ironpiling was adopted by Mr. TiemeyClark, in the erection of the TownPier at Gravesend, Kent, a.d. 1834,

n forming a foundation for the


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cast-iron columns supporting thesuperstructure of the T head of thepier. Under tJie site of each column

wen driven three cast-iron piles, onwhich an adjusting plate vvas

firmly keyed, forming a broad basefor the support of the column,which was adjusted to its correctposition, and bolted down to the

adjusting plate

14. A kind of foundation on thesame principle as piling has beenately much used in situations

where ordinary piling cannot beresorted to with advantage. The

method referred to consists in


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sinking hollow cast-iron cylindersuntil a hard bottom is reached. Thenterior of the cyUnder is then

pumped dry, and filled up withconcrete or some equally solidmaterial, thus making it a soUd pie

on which to erect thesuperstructure. The cylinders aremade in lengths, which aresuccessively bolted together as each

previous length is lowered, theexcavation going on at the bottom,which is kept dry by pumping. It

often happens, however, in sinkingthrough sand, that the pressiu-e ofthe water is so great as to blow upthe sand at the bottom of the


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cylinder; and, when this is the case,the operation is carried on bymeans of a large auger, called a

miser, which excavates and bringsup the materials without thenecessity of pumping out the water

The lower edge of the bottomength of each cylinder is made with

a sharp edge, to enable it topenetrate the soil with greater ease

and to enter the hard bottomstratum on which the work is torest. This method was adopted by

Mr. Kedman in the erection of theTerrace Pier at Gravesend, Kent,finished a.d. 184S.

15. Before closing our remarks on


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pile foundations, we must mentiona very curious system of carrying upt foundation through loose wet

sand, which is practised i Indiaand China, and is strictly analogousto the sinking of cast-iron cylinders

ust described.

It consists in sinking a series ofwells close together, vhich are

afterwards arched over separately,and covered \rith a system of

aulting on which the

superstructure is aised. The methodof sinking these wells is to digdown, as far as practicable, withouta Uning of masonry, or until water

s reached; a wooden curb is then


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placed at the bottom of theexcavation, and a bhck cylinderraised upon it

to the height of 8 or 4 ft above theground. As soon m the work is

sufficiently set, the curb and thesuperin> cumbent brick-work areowered by excavating the ground

under the sides of the curb, the

peculiarity of the process being thatthe well-sinker works under water,frequently remaining submerged

more than a minute at a time.These cylinders have beenoccasionally sunk to a depth of 40 f

16. Solid Foundations simply laid


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on the Surface of the Ground. Where the site of the intendedstructure is perfectly firm, and

there is no danger of the work beingundermined by any scoiur, it will besufficient to place the materials on


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**pierre perdue^** or random workand is used for breakwaters,foundations of sea-walls, and

similar works. Plymouthbreakwater is an example on a largescale.

18. Coursed Masonry, Anotherway, much used in harbour work, isto build up the work from the

bottom (which must be firstroughly levelled) with large stones,carefully lowered into their places;

and this is a very successful methodwhere the stones are of sufficientsize and weight to enable the workto withstand the run of the sea. The

diving-bell affords a ready means of


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erifying the position of each stoneas it is lowered.

19. Beton.On the Continentfoimdations underwater arefirequently executed with blocks of

beton or hydraulic concrete, whichhas the property of setting underwater. The site of the work is firstnclosed with a row of sheet piling,

which protects the beton firomdisturbance, until it has set Thissystem is of very ancient date, being

described by Vitruvius, and waspractised by the Romans, who

have left us many examples of it on

the coast of Italy. The French


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engineers have used heton in theworks at Algiers, in large blocks of324 cubic feet, which were floated

out and allowed to drop into theirplaces from slings. This method,whicn proved perfectly successful,

was adopted in consequence of thesmaller blocks first used beingdisplaced and destroyed by the forcof the sea

20. Caissons. A caisson is a chestof timber, which is floated over the

site of the work, and, being kept ints place by guide pUes, is loadedwith stone until it rests firmly onthe giound. The masonry is then

built on the bottom of the caisson,


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and when the work reaches theevel of the water the sides of the

caisson are removed.

This method of building has beenmuch used on the Continent, but is

not much practised in this coimtry.Westminster Bridge, London, is anoted instance of its failure. Thebottom of the river has been

scotu'ed out to a depth oi severalfeet since the erection of the bridgeand the foundations of the piers

remained in a dangerous state untilthey were secured in the recentrepairs by driving sheet-piling allround them, and underpinning the

portions which had been


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undermined.

21. An improvement on the above

method consists in dredging out theground to a considerable depth, andputting hi a thick layer of beton on

which to rest the bottom of thecaisson.

22. There is a third method of

applying caissons which is practisedby our continental neighboinrs, andwhich is firee fi'om the objectionswhich commonly attend the use ofcaissons. A firm foundation is firstformed by driving piles a few feetapart over the whole site of the

foundation. The tops of the piles ar


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building in caissons on pilefoundations is shown in figs. 4 and6. The

Fig, A.

^2

.'T^i I

piers of the Pont du Val Benolt at

Liege, built a.d. 1842 which carriesthe railway across the Meuse, havebeen built on pile foundations inthe manner here described.


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Fig. 6.

Q3. Solid Foundations laid in

Cofferdams. There are manycircumstances under which itbecomes necessary to lay Ihebottom dry before commencingoperations. This is done bynclosing the site of the foundation

with a watertight wall of timber,

from within which the water can bepmnped out by steam power orotherwise. Sometimes, in shallowwater, it is sufficient to drive a


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single row of piles only, the outsidebeing protected with clay, as shownn fig. 6; but in deep water two or

even foiu* rows of piles will berequired, the space between thembeing filled in with well-rammed

puddle, so as to form a solid water-tight masa

BT OF BUILDlNa.

U

J%.0


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See fig. 7 ) The great diflficulties inthe construction of a cofferdam areIst, to keep it water-tight; and,2nd, to support the sides against thpressure of the water outside,

which in tidal waters is sometimesso great as to render it necessary toallow a dam to fill to prevent itsbeing crushed


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auasTAATUM or tnaunATto MnitLfl 1 I l|l 1 I I I ^FP

24. In order to save timber, and toavoid the difficult) of keeping outthe bottom springs, it has been

proposed by a French engineer,after driving the outer row, todredge out the area thus inclosed,

and fill it up to a certain height with


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beton. The cofferdam is then to becompleted by driving an inner rowof piles resting on the beton, and

puddling; between the two rows inthe usual manner; and the

BUDIMENTS OF THB

masoniy is earned up on the b^tonfoundation thus pre pared. This

construction is shown in fig. 8.


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26. The limits of the presentolume prevent our enter-mg into

any detail as to the preparation ofconcrete and beton, the methods inuse for driving piles, and the

construction of cofferdams: thereader who wishes to piu*sue thesubject further is referred to the

olume of this series on "


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Foundations and Concrete Works,"where he will find a detaileddescription of these operations.

RETAINING WALLS.

26. The name of retaining wall isapplied generally to aU walls builtto support a mass of earth in anupright or nearly upright position;

but the term is, strictly speaking,restricted to walls built to retain anartificial bank, those erected tosustain the face of the sohd groundbeing called breast walls, (See fig.9.)

27. Retaining Walls. Many rules


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have been given by different writersfor calculating the thrust which abank of earth exerts against a

retaining wall, and for determiningthe form of wall which affords thegreatest resistance with the least

amount of material. The applicationof these rules to practice is,however, extremely difficult,because we have no means of

ascertaining the exact manner inwhich earth acts against a wall; andthey are, therefore, of littio

BT OF BUILDING.

T3


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alue except in determining thegeneral principles on which thestability of these constructions

depends. (See Note A, p. 165.) ^ ^^

as. The calculation of the stability oa retainiDg wail divides itself intotwo parts.

1st The thrust of the earth to be

supported.


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2nd. The resistance of the wall.

29. Definitions (see fig. 10). The

ine of rupture is that along whichseparation takes place in case of aslip of earth.

-F^. 10.

The slope which the earth wouldassume, if left totally un^tt3(^ \^um rj!?u

slide over each other, may becounteracted in three ways 1st, thearch may be continued through the

abutment until it rests on a solidfoundation, as in fig. 26 2nd, bybuild-

Fig. 27.


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ng the abutments so as to form ahorizontal arch, the thrust beingthrown on the wing walls, which ac

as buttresses (fig. 27). 3rd, whereneither of these expedients ispracticable, by joggUng the coursestogether with bed-dowel joggles, soas to render the whole abutmentone soUd mass (fig. 86).

66 Wing Wails. ^Where the wing


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fisdlure of this kind.

66. VatdHng. The ordinary forms

of vaults may be classed underthree heads, viz. cylindrical, coved,and groined.

cylindrical vault is simply asemicircular arch, the ends of whichare closed by upright walls, as

shown in fig. 30. When a vaultsprings from all the sides of itsplan, as in fig. 31, it is said to becoved. When two cylindrical vaultsntersect each other, as in fig. 82,

the mtersecUons of the

Fiff. 80. Fig. 81.


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aulting surfaces are called groins,and the vault is siud to be groined.

67. In the Eoman style ofarchitecture, and in all commonaulting, the vaulting surfaces of

the several compartments are

portions of a continuous cylindricalsurface, and the profile of a groin issimply an oblique section of a semi

cylinder.

68. Gothic ribbed vaulting is,however, constructed on a totally

different principle. It consists of a


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fi^mework of light stone ribssupporting thin pannels, whencethis mode of construction has

obtained the name of rib andpannel vaulting. The curvature ofthe diagonal ribs or cross springers

and of the intermediate ribs, is notgoverned in any way by the form ofthe transverse section of the vault,and in this consists the peculiarity

of ribbed vaulting. Thit will beunderstood by a comparison of figs32 and 33. For a description of the

several varieties of Gothic vaults,and the modes of tracing the curvesof the ribs, the reader is referred tothe volume of this series on **


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Masoniy and Stone-cutting."

a 8

RUDIMENTS OF THE

Fig. S2. J^. j$a

Roman Taiiltmg. Gothic raulting.

69. Domes are vaults on a circularplan. The equili brium of a domedepends on the same conditions asthat of a common arch, but with

this diflference, that, although a


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dome may give way by the weight othe crown forcing out the haunchesfailure by the weight of the

haunches squeezing up the crown impossible, on account of the

support the voussoirs of each

course receive from each other.

MASONRYBRICKWORKBOND

70. The term masonry is sometimesapplied generally to all cementedconstructions^ whether built ofbrick or stone ; but in England theuse of the term is confinedexclusively to stone-work.

71. There are many kinds of


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masonry, each of which is known bysome technical term expressive ofthe manner in which the stone is

worked; but they may all be dividedunder three heads.

1st Eubble work (fig. 34), in whichthe stones are used without beingsquared

2nd. Coursed work (fig. 86), inwhich the stones are squared, moreor less, sorted into sizes, and rangedi; courses.


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^.85.

^. 86.

-0i-tJ-

BT OF BUILDIMa.

H5

3rd. Ashlar work* (fig. 36), in which

each stone is squared and dressed


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to given dimensions.

72. Different kinds of masonry are

often united. Thus a wall may hehuilt with ashlar facing and ruhhlehacking; and there are many

gradations from one class ofmasonry to another, as coursedrubble^ which is an intermediatestep between ruhhle work and

coursed work.

73. In ashlar masonry, tho stabilityof the work is independent, inordinary cases, of the adhesion ofthe mortar. Rubble work, on thecontrary, depends for support in a

great measure upon it


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74. In dressing the beds of ashlarwork, care must be taken not towork them hollow, so as to throw

the pressure upon the edges of thestones, as this leads to unsightlyfractures, as 6 6, fig. 36.

76. Where there is a tendency of thecourses to slide on each other fromany lateral pressure, it may be

prevented by bed-dowel joggles, asshown at a a, fig. 36

76 Where the facing and thebacking of a wall do not contain thesame number of coinrses, as in thecase of a brick wall with stone

facings (fig. 37), the work will be


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iable to settle on the inside, asshown by the dotted lines, from thegreater number of mortar joints.

The only way of Fig, 87. preventingthis is to set the backing in cement,or some hard and quick-setting

mortar

77. In facing brickwork with stoneashlar, the stones should be all

truly squared, and worked to sizesthat will bond with the brickwork. Ithis be neglected, there will be

numerous vacuities in the thicknesof the wall (see fig. 37) and thefacing and backing will have atendency to separate


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78. Bond, in masonry, consists inthe placing of the stones in suchrelative positions that no

oint in any course shall be in thesame plane with any

In London the term " ashlar" iscommonly applied to a thin fiicingol ftODc placed in front of

brickwork.


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96 BUDDCENTS OF THl?

other joint in the course

mmediately above or below it Thiss called breaking joint

79. Stones placed lengthwise in anywork are called iCretcliers, andthose placed in a contrary directionare called -^ gg headers. When a

header extends through-

out the whole thickness of a wall, its called a thnmgh.

79. There are two kinds of bondmade use of by bricklayers, called

respectively English bond and


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Flemish bond. In the Fig. 80. fij.g|;t}jQ courses are laid alternatelywith

headers and stretchers (fig. 38); inthe second, the headers and

stretchers alternate in the samecourse (fig. 39). This is consideredto have the neatest appear-

-i I II I I 1 I I

I II II II I

L^'-''

^c


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5

II I I I -Tt

TTT

'l i i!!iil!ii

|" l l"M"il

ance: but, as the number of headersrequired is fewer than in Englishbond, there is not so much lateraltie, and on this accoimt it is

considered to be much inferior to itn strength. A common practice,

which cannot be too muchreprobated, is that of building brick


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walls with two qualities of bricks,without any bond between them,the headers of the facing bricks

being cut in two to save the bettermaterial, thus leaving an uprightoint between the facing and

backing.

80. In building upright walls whichhave to sustain a vertical pressinre,

three leading principles must bekept in view.

1. Uniformity of constructionthroughout the whole thickness.

2. The bonding of the work together

8. The proper distribution of the


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oad.

81 Uniformity of Construction.

^We have already spoken of thedanger arising firom the backing ofa wall containing more

compressible material than thefacmg; but it cannot be too oftenrepeated, that in all buildingoperations it is not the amount^

but the irregularity of settlementwhich is 80 dangerous. Thus arubble wall, with proper care, may

be carried up to a great height, andbear safely the weight of the floorsand roof of a large building, whilst a

wall built of bricks and mortar, and


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faced with dressed ashlar, will,under similar circumstances, befractured from top to bottom, from

the difference in settlement of thefacing and backing

It is a common but vicious practiceto build the ends of joists and othertimbers into the walls, and to restthe superincumbent work upon

them. This is liable to lead tosettlements from the shrinking ofthe timber, and should always be

guarded against by leaving properrecesses for the ends of the timbersso that the strength of the masonryor brickwork shall be quite

ndependent of any support from


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them.

82. Bond. ^In addition to the

bonding together of the materialsabove described, a further securityagainst irregular settlement is

usually provided for brick walls, inthe shape of ties ot timber, calledbond, which are cut of the depthand thickness of a brick, and built

nto the work. There is, however, agreat objection to the use of timbern the construction of a wall, as it

shrinks away from the rest of thework, and often endangers itsstability by rotting.

83. Instead of bond timbers, hoop-


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u'on bond is now very generallyused. This is formed of ironhooping, tarred, to protect the iron

from contact with the moilar, andaid in the thickness of the mortaroints. This forms a very perfect

ongitudinal tie, and has all theadvantages, with none of thedisadvantages, of bond timbers.

84. DistribtUion of the Load, It isalways advisable, when a heavy loadhas to be supported on a few points

as in the case of a large floor restingon girders, to bring the weight asnearly as possible on the centre ofthe wall, and to distribute it over a

arge bearing surface, by stone


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bonding through its wholethickness; this arrangement isshown in figures 40 and 41.

85. It is of importance in designingbuildings to arrange the apertures

for doors, windows, &c., in thedifferent floors.

BUDIMENTB OF THB

BO that openings shall be overopenings, and piers oveT piers; ifthis be not attended to, it is scarcely

possible to

Fig. 40.


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prevent settlements In addition tothis, as the pressure on thefoundations will be greatest underthe piers, it is desirable to connect

these with inverted arches, bywhich means the weight isdistributed equally over the whole

surface of the foundations.


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86. All openings in walls for doors,windows, gateways, &c., should bearched over throughout the whole

thickness of the walls in which theyoccur; and wooden lintels andbressummers should only be

ntroduced as ties to counteract thethrust of the arches, and asattachments for the internalfinishings.

87. Bressummers of cast iron areoften used for supporting the walls

of houses over large openings, as inthe case of shop fronts; but theyhave the disadvantage of beingiable to be cracked, in case of fire,

f water is thrown on them whilst in


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a heated state, which renders theiruse very objectionable, as nodependence can be placed upon

them after having been suddenlycooled in this manner, even if theydo not actually break at the time.

PABTinONS.

88. The partitions forming the

nterior divisions of a building maybe either solid walling of brick orstone, or they may be constructedentirely of timber, or they may boframes of timber filled in withmasonry or brickwork.

It will always be best, both for


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durability and security against lire,to make the partitions of solidwalling; bul this is not always

practicable, and, in the erection ofdwelling houses, they are for themost part made of timber.

The principles to be kept in view inthe construction of framed timberpartitions are veiy simple. Care

must be taken to avoid anysettlement from cross strain, andthey should not in any way depend

for support upon subordinate partsof the constniction, but should forma portion of the

F%g, 42.


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main carcase of the building, and be

quite independent of the floors,


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wnich should not support, butshould be supported by them.

BUDIMENTS OF THE

WTiere a pai*tition extends throughtwo cr more storiei of a buildmg, itshould be as much as possible acontinuous piece of framing, withstrong sills at proper heights to

support the floor joists.

Where openings occur, as forfolding doors, or where a partition

rests on the ends of the sill only, itshould be strongly trussed, so thatt is as incapable of settlement as

the walls themselves. From want of


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attention to these points, wefrequently see in dwelling-housesfloors which have sunk into curved

ines, doors out of square, crackedceilings and broken cornices, andgutters that only serve to conduct

the roof water to the interior of thebuilding, to the injury of ceilingsand walls, and the great discomfortof its inmates. The above remarks

will be better understood by a studyof flg. 42, which is an example of aframed partition extending through

three stories of a dwelling house.

FLOORS.

89. The assemblage of timbers


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forming any naked flooring may beeither single or double. Singleflooring is formed with joists

reaching from wall to wall, wherethey rest on plates of timber builtnto the brickwork, as in fig. 43. The

floor boards are nailed over theupper edges of the joists.

Single flooring, whose lower edgesreceive the lathing and plastering othe eilings. Double floors are

constructed with stout binding


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oists, a few feet apart, reachingfrom wall to wall, and sup portingceiling joists which carry the

ceiling; and bridging iaists, onwhich are nailed the floor boards(fig. 44).

BT OF BUILDIKO

41

In double-framed flooring, thebinders, instead of resting in thewails, are supported on girders, as

shown in fig. 45

Fig 44.


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Double flooring. Single flooring is,n many respects, inferior to double

flooiing, being liable to sag, or

deflect, so as to make tho

Fig. 46.


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Double-framed flooring.

floor concave, and the vibration ofthe joists occasions injury to theceilings, and also shakes the walls.

In double flooring the stifl&iess ofthe binders and girders preventsboth deflection and vibration, andthe floors and ceilings hold their


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ines, that is, retain their intendedform much better than in singleflooring.

90 The joists in a single floor areusually laid on a plate

BUDDCENTB OF THB

built into the wall, as shown in fig.

43; it is, however, preferable to restthe plate on projecting corbels,which prevents the wall beingcrippled in any way, by the insertion

of the joists. The plates of basemenfloors are best supported on smallpiers carried up from the footings.

This is an important point to be


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attended to, as the introduction oftimber into a wall is nowhere likelyto be productive of such injurious

effects as at the foundations, wherefrom damp and imperfect

entilation, all wood-work is liable

to speedy decay.

The ends of all girders should restn recesses, formed as shown in

figs. 40 and 41, and with a space forthe free circulation of air round thetimber, which is one of the best

preventives of decay.

The manner in which ceiling joistsand bridging joists are framed to

the binders, and these latter


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tenoned into the girders, is shownn figs. 46, 47, 48, and 49.

Fig. 46.

Fig.i1.

Fig.iS.

BMDGINC MIST

BRIDCIMO JOItT


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Fig.i9.

fLeow BOAWOt

fkiiWfiWimu

a a, bridging joists; h h, exiling

oists; e, girder. 91. Fire-proof floorsare usually constructed with irongirders a short distance apart, whichserve as abutments for a series of

brick arches, on which either awooden or plaster floor may be laid(see fig. 60V (See Note 0, p. 156.)


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ST OF BUILDING Fig, 60.

43

92. Of late years many terraces andflat roofs have been constructedwith two or more courses of plain

tiles, set in cement, and breakingoint with each other, supported at

short intervals by cast-iron bearers,as shown in fig. 61. This mode ofconstruction, although appearing

ery slight,

Fig, 61.


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possesses great strength, and is noweiy much used in and about

London

BOOFING.

98. In roofs of the ordinaryconstruction, the roof covering isaid upon rafters supported by

horizontal purlinsj which rest on

upright trusses or frames of timberplaced on the walls at regulardistances from each other. Uponthe framing of the trusses dependsthe stability of the roof, thearrangement of the rafters andpurlins being subordinate matters

of detail. The timbering of a roof


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may be compared to that of adouble-fr'amed floor, the trusses ofthe former corresponding to the

girders of the latter, the purlins tothe binders, and the rafters to theoists.

Timber roofs may be divided undertwo heads

1st Those which exert merely aertical pressure on the walls on

which they rest.

2nd. Those in which advantage istaken of the strength of the walls toresist a side thrust, as in many of

the Gothic open timbered roofs.


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94. Trussed Boofs, exerting no SideThrust on the Walls. tn roofs ofthis kind each truss consists

essentially of a pair of principalrafters or principals, and ahorizontal tie

BUDIMENTS OF THE

beam and in large roofs these are

connected and strength ened byking and queen posts and struts(see figs. 53 and 64).

Fig. 52 shows a very simple truss inwhich the tie is above the bottom othe feet of the principals, which is


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often done in small roofs for the

sake of obtaining height The tie inthis case is called a collar. The feetof both common and principal

rafters rest on a waU plate. Thepurlins rest on the collar, and theconmion rafters but against a ridgerunning along the top of the roof.

This kind of truss is only suited toery small spans, as there is a cross

strain on that part of the principals

below the collar which is rendered


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harmless in a small span by theextra strength of the principals, butwhich in a large one would be very

ikely to thrust out the walls.

95 In roofs of larger span the tie

beam is placed below the feet of theprincipals, which are tenoned into,and bolted to it. To keep the beamfrom sagging^ or bending by its

own weight, it is suspended fromthe head of the

Fig, 68.


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BT OF Bl7ILDl

45

principals by a king post of wood orron. The lower part of the king pos

affords abTitments for struts

supporting the principalsmmediately under the purlins, sothat no cross stndn is exerted onany of the timbers in the truss, but

they all act in the direction of their


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ength, the principals and strutsbeing subjected to compression,and the king post and tie beam to

tension. Fig. 53 shows a sketch of aking truss. The common rafters buton a pole plate, the tie beams

resting either on a continuous plateor on short templates of wood orstone.

96. Where the span is considerable,the tie beam is supported atadditional points by suspension

pieces called queen posts (fig. 64),from the bottom of which spring

Fig.H.


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additional struts ; and, by extendingthis principle ad infinitum, we

might construct a roof of any span,were it not that a practical limit ismposed by the nature of the

materials. Sometimes roofs areconstructed without king posts, thequeen posts being kept apart by astraining piece. This construction is

shown in fig. 66, which shows the


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design of the old roof (nowdestroyed) of the chm'ch of St. Pauloutside the walls, at Kome. This

truss is interesting from its earlydate, having been erected "about400 years ago; the trusses are in

pairSjj. king post being keyed

UNIVERSITY )

BODIMRKTS OF TH Fig, 65.


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wf^^CirAK SPAM.

....y...T y

n between each pair to support thetie beams in the centime.

97. Of late years iron has beenmuch used as a material for the

trusses of roofs, the tie beams and


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suspension rods are of flat bar ironthe principal and eommon raftersare of rolled T iron, the struts and

purlins

BT OF BUILDIHG

47

are of cast iron, and the whole isfitted together with cast-iron shoes


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98. The great novelty in theconstruction of the roofs justmentioned consists in their

covering, which is formed ofgalvanized sheets of cast iron,apping over each other at the

oints, and forming a very perfectand water-tight covering, which isat the same time perfectly fire-proof,


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timber, notched out to prevent theisliding on each other, a methodwhich is objectionable on accountof the danger of the splitting of tiie

timber under a considerable strain.(See Note D, p. 156.)

100. The principle of the bowsuspension truss, as this system oftrussing is called, has been muchused within the last ten years for

railway bridges and similar works.One of the best executed works ofthis kind is a bridge over the Kiver

Ouse, near Downham Market, in


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Norfolk, on the line of the Lynn andEly Eailway, the trusses of whichare 120 ft. span.

101. Roofs on the principle of therch, In the 16th century,

Philibert de Lorme, a celebratedFrench architect, published a workn which he proposed to construct

roofs and domes with a series of

arched timber ribs in place oftrusses, these ribs being formed ofplanks in short lengths, placed

edgewise, and bolted together inthicknesses, breaking joint (fig. 59)This mode of construction has beenmore or less used ever since the

time of its author. An instance of its


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successful application on a largescale was the original dome of theHalle au Ble, at Paris, 120 ft. in

diameter, built by Messrs. Legrandand Molino. This roof

Fiff.69.

has since been replaced by an ironone, the original domo having beendestroyed by fire.

The roof of the central


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compartment of tne PantheonBazaar in Oxford Street, London, 38ft. span, is another very elegant

example.

102. There are, however, some grea

disadvantages connected with thissystem. There is considerable wasteof material; the labour is great ascompared with roofs of similar span

of the ordinary construction; and,as the chief strength of the ribdepends upon the lateral cohesion

of the fibres of the wood, it isnecessary to provide such anamount of surplus strength as shallnsure it against the greatest cross

strain to which it can be exposed


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from violent winds or otherwise

RT OF BUILDINO.

49

108. Struck by these disadvantages,

Colonel Emy, a French militaryengineer, proposed, in 1817, anmprovement on the system of

Philibert de Lorme, which wasprecisely the laminated arched ribso much in use at the present day.It was not until 1825 that he

obtained permission to put hisdesign into execution in theerection of a large roof 65 fk. span

at Marac, near Bayonne (fig. 00).


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Fiq. 60.

The ribs in this roof are formed of


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planks bent round on templets tothe proper curve, and kept fromseparating by iron straps, and also

by the radiating struts which are inpairs, notched out so as to clip therib between them.

The principle of the roof isexceedingly good. The principals,wall-posts, and arched rib, form two

triangles, firmly braced togetlier,and exerting no thrust on the wallsand the weight of the whole roof

being thrown on the wails at thefeet of the ribs, ajid not at the poleplate, the

D


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BUDIMENTS OF TfiS

^alls are not tried by the action of a

heavy roof, and the consequentsaving m masonry is very great*

The great difference in principlebetween the arched rib of Philibertde Lorme, and the laminated rib ofColonel Emy, is, that in the latter

the direction of the fibre of thewood coincides with the curvatm-eof the rib; and, as a consequence ofthis, the joints are much fewer; therib possesses considerableelasticity, so as slightly to yieldrather than break under any violent

strain; and, from the manner in


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Fig. 61.

See Tredgold's Carpentrj, new and

much improved edition^ iu 4to.1858.

RT OF BUILDIKO.


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Bl

though there are many fine

examples in which this is not thecase.

We propose to describe theprincipal varieties of these roofs,without reference either to theirdecorative details, or to their

chronological arrangement, ourobject here being simply to explainthe principles on which they wereconstructed.

105. Fig. 61, which is a section ofthe parish church of Chaldon, near

Merstham in Surrey, shows a


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system of roofing formerly verycommon. This may be compared tosingle flooring, as there are no

principals, purlins, or even ridge. Its a defective form of roof, as the

rafters have a tendency to spread

and thrust out the walls. In theexample before us, this effect hasbeen prevented by the insertion oftie beams, from which the collars

have been propped up (fig. 62),thus, in fact, balancing the roof onthe centres of the collars, which are

n consequence violently strained.

106. After the introduction of the 4-centred arch, a great many church

roofs of the construction just


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described were altered, as shown bythe dotted lines in fig. 63, in orderto obtam more light by the

ntroduction of clerestory windowsover the nave arches. The flat roofswhich superseded the former ones

were often formed without anytruss whatever, being simply anarrangement of main beams,purlins, and rafters, precisely

similar to a double-framed floor,with the difference only that themain beams, instead of being

perfectly straight, were usually cutout of crooked timber so as todivide the roof into two inclinedplanes.


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RUDIMBNTB OF TRB

the ends of the mam beams are

often supported on upright Fig, 64.posts placed agamst the walls andrest-

ng on projecting corbels, the wallposts and beams being connectedby struts in such a waj that

deflection in the centre of the beamcannot take place, unless the loadbe sufficient to force out the walls,as shown by the dotted lines in fig.64. The struts are often cut out ofstout plank, forming solid spandrilsthe edges of which are moulded to

suit the profile of the main beam


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(see fig. 65), which also

Fi0.tt,


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shows the manner of securing thestruts to the wall posts and to thebeam with tongues and wooden

pins. A very good example of thisconstruction is shown in fig. 66,which is from West Bridgeford

Church, Nottinghamshire. Thereare many very beautiful examplesremaining in different parts of thecoimtry.

107. A somewhat similarconstruction to that last described

s shown in fig. 67, in whichprincipals are introduced, struttedup from the main beam, so as togive a greater slope to the roof than

could well be obtained with a single


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beam.

RT OF BUIUilNd. Fig. 66.

w


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^.68.

Fig, 67. 108- Fig. 68 exhibits aconstruction

often to be met with, which, in

general appearance, resembles atrussed king post roof, but which isn reality very different, the tie

beam being a strong girder

supporting the king post, which,nstead of serving to suspend the tie

beam from the principals, is a prop

to the latter. In this and the


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previous example, any tending todeflection of the tie beam isprevented by struts: the weight of

the roof is thrown by means of wallposts considerably below the feet ofthe rafters, so that the weight of the

upper pai't of the wall is madeavailable to resist the thrust of thestruts.

109 The roofs we have beendescribing are not to berecommended as displaying any

great amount of constructive skill.Indeed, although they answer verywell for small spans with timbers oarge scantling and side walls of

sufficient thickness to resist a


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considerable thrust, they ai-e totallymsuited to large spans, and are in

every way inferior to trussed roofs.

The above remarks do not apply tothe high pitched

H

BUDIMENTS OF THK

roofs of the large halls of thefifteenth and sixteenth centuries,which, for the most part, are

trussed in a very perfect manner, so


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as to exert no thrust upon the wallsalthough, in some instances, as atWestminster Hall, they depend

upon the latter for support.

The general design of these roofs is

shown in figs. 69 and 70. Theessential parts of each truss are, apair of


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principals connected by a collar ortuind bearriy and two hammerbeams, with queen posts over them

the whole forming three triangles,which, if not secured in theirrelative positions, otherwise than

by the mere transverse strength ofthe principals, would turn on thepoints c c (fig. 70), the weight of theroof thrusting out the walls in the

mariner shown in the figure. Thereare two ways in which

-%. 70.


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RT OF BUILDING.

6^

a tmfls of this kind may beprevented from spreading. Ist. Theends of the hammer beams may beconnected with tlie collar by tensionpieces, a a (fig. 69), by which tliethrust on the walls will be

converted into a vertical pressure.


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2nd. The hammer beams may bekept in their places by stmts, b b,the walls being made sufficiently

sti'ong by buttresses, or otherwise,to resist the thrust.

In existing examples, we findsometimes one and sometimes theother of these plans followed; andoccasionally both methods are

combined in such a manner that its often difficult to say what parts

are in a state of compression, and

what are in a state of tension.

110. The roof of the great hall atHampton Court (fig. 71) is very

strong, and so securely tied, that


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were the bottom

Fiff. 71.

WTuts, 6 5, removed, there would


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be little danger of tlie principalsthrusting out the walls; and, on theother hand, from the weight of the

roof being carried down to aconsiderable distance below tliehammer beams by tlie wall

UDIMENTS OF THE

posts, the walls themselves offer so

much resistance to skie thrust, thatthere would be no injurious sti'ainon them wore the tension pieces, aa, removed.

Ill, The constraction of the roof ofthe hall at Eltbam Palace, Kent (fig.

72), differs very considerably from


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that of

the Hampton Court roof. The wholeweight is thrown on the top of thewall, and the bottom pieces, b 6, aremerely ornamental, the tension

pieces, a a, formmg a complete tie.


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This has been shown by a partialfailure which has taken place. Thewall plates having become rotten in

consequence of the gutters beingstripped of their lead, the weighthas been thrown on the pseudo

struts, which have bent under thepressiu*e, and forced out the upperportion of the walls.

112. The roof of Westminster Hall(fig. 73) is one of the finestexamples now existing of open

timbered roofs. The peculiar featureof this roof is an arched rib m threethicknesses, something on theprinciple of Philibert de Lorme; but

t is so slight, compared with the


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great span, that it is probable indesigning the roof, the architecttook

RT 0? Run^uia.

57


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full advantage of the supportafforded by the thickness of thewalls and the buttresses ; if, indeed

the latter were not added at thetime the present roof was erected,n 1396. It has been ascertained tha

the weight of the roof rests on thetop of the walls, the lower part oftlie arched rib only serving todistribute the thrust, and to assist

n preventing the hammer beamsfrom sliding on die walls.

D S

113. The mediseval architectsgenerally employed oak in the

construction of their large roofs, th


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timbers being morticed and pinnedtogetiier, as shown in fig. 65. Thissystem of construction is

mpossible in fir and other softwoods, in which the fibres haveittle lateral cohesion, as the timber

would spUt witii the strain; andtherefore, in modem practice, it isusual to secure the connectionswith iron straps or bolts passing

roimd or through the wholethickness of the timbers.

BOOF GOVEBINGB.

114. The dififerent vaiieties of roofcovermgs principally used may be

classed under three heads: stone,


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wood, and metsl.

Of the first class, the best kind is

slate, which is used either sawn intoslabs or split into thin laminae. Thedifferent sizes of roofing slate in

common use are given in thedescription of Slaters' Work, article234.

In many parts of the coimtry thinslabs of stone are used in the sameway as roofing slate. In the Wealdof Sussex the stone found in theocality is much used for this

purpose, but it makes a heavycovering, and requires strong

timbers to

Rudiments of the Art of Buildin - Dobson, Edward, 1816-1908

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Transcript of Rudiments of the Art of Buildin - Dobson, Edward, 1816-1908