Architectural Engineering 1000063563

7/27/2019 Architectural Engineering 1000063563

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- ARCHITECTURAL ENGINEERING;

WITH SPECIAL REFERENCE TO

HIGH BUILDING CONSTRUCTION,

INCLUDING MANY EXAMPLES OF

CHICAGO OFFICE BUILDINGS.

BY

JOSEPH KENDALL FREITAG, B.S., C.E.n

FIRST EDITION.FIRST THOUSAND.

OF THE"

NEW YORK:JOHN WILEY " SONS.

LONDON: CHAPMAN " HALL, LIMITED.1895.


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T HI toll

COPYRIGHT, 1895,Bi

JOSEPH K. FREITAG.

ROBERT DRUMMOND, ELECTROTVPER AND PRINTER, NEW YORK.


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^"XTT)JL-" -^

PREFACE.

THE author has attempted, in the following-pages, todefine and illustrate,in a manner as practicable as possible,such of the fundamental principlesin the design of themodern high building as may prove useful to architectsand engineers alike.vWhile the technical press of the country has devoted

considerable attention to many of the individual subjectshere considered, yet the realisation of a want of collectivedata on the subject of Architectural Engineering hasinduced the writer to present this volume.

As more and more of the principlesof construction arebeing added to the curricula of our architectural schools,and as many of our engineering students are adoptingbuilding construction as a specialty,t is hoped that thiseffort will serve to unite still more closelythe work of theone with that of the other.

The author would mention the efforts of one highlyesteemed and dearly beloved in the engineering profession,Mr. E. L. Corthell, who has been strivingfor several yearsto see the two professionsunited by establishingan Inter-ational

Institute of Engineers and Architects, as well as atechnical School of Architecture and Engineering at thenew University of Chicago. The writer would alsoacknowledge the warm interest displayed in this work byhis former professor of engineering,Prof. C. E. Greene, ofthe University of Michigan.

iii


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IV PREFA CE.

The following chapters are arranged in the order inwhich the calculations for such structural work must pro-eed,

starting with the load-bearing floor system, thencethrough the successive stages to the foundations. Thelatter would seem to require the first attention ; but as theyare the last to be calculated, being dependent on all otherconsiderations, they have here been placed last. The illus-rations

and examples given have been largely obtainedthrough the courtesy of the architects of the respectivebuildings. An endeavor has been made to present only themost practical methods.

JOSEPH KENDALL FREITAG.CHICAGO, MAY, 1895.


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CONTENTS.

CHAPTER I.PAGE

INTRODUCTORY i

CHAPTER II.

FIRE PROTECTION 9

CHAPTER III.

SKELETON CONSTRUCTION" EXAMPLES" ERECTION, ETC 24

CHAPTER IV.

FLOORS AND FLOOR FRAMING 54

CHAPTER V.

EXTERIOR WALLS" PIERS 88

CHAPTER VI.

SPANDRELS AND SPANDREL SECTIONS" BAY WINDOWS 100

CHAPTER VII.

COLUMNS 113

CHAPTER VIII.

WIND BRACING 136V


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VI CONTENTS.

CHAPTER IX.

PARIITIONS" ROOFS" MISCELLANEOUS 163

CHAPTER X.

FOUNDATIONS ". 171

CHAPTER XL

UNIT-STRAINS"SPECIFICATIONS 201

CHAPTER XII.

BUILDING LAWS.. 216


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LIST OF ILLUSTRATIONS.

FIG. PAGE

1. Reliance Building, Chicago - 172. Arrangement for Pipe-space in Halls 223. Chicago Stock Exchange Building. Perspective 254. Chicago Stock Exchange Building. Basement Plan 275. Chicago Stock Exchange Building. Ground Floor Plan 286. Chicago Stock Exchange Building. Typical Office Floor Plan. 297. Marquette Building, Chicago. Perspective 308. Marquette Building, Chicago. Typical Office Floor Plan 319. Reliance Building. Typical Office Floor Plan " . 32

10. Masonic Temple, Chicago 341 1

.New York Life Insurance Building. Perspective 35

12. New York Life Insurance Building. Plan of Banking Floor...

3613. New York Life Insurance Building. Typical Office Floor

Plan 3714. Fort Dearborn Building. Perspective 3815. Fort Dearborn Building. Typical Office Floor Plan 4016. Champlain Building. Typical Office Floor Plan 4117. Old Colony Building. Perspective 4218. Typical Framing Plan of Fort Dearborn Building 4319. Typical Framing Plan of Reliance Building 4420. Reliance Building during Construction 4821. Reliance Building during Construction 4922. Brick Arch Construction 5523. Corrugated Iron Arch , 5524. Tile Arch used in Equitable Building, Chicago (1872) 5525. Tile Arch used in Montauk Building, Chicago (1881) 5626. Tile Arch used in Home Insurance Building, Chicago (1884)

. .56

27. Arch showing Tile Filling Blocks used in Woman's Temple,Chicago 57


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VI 1 1 LIST OF ILL US TRA TIONS.

FIG. PAGE28. Panelled Beam, Fire-proofed 5829. Fire-proofedGirder 5830. The Lee Flat Arch 5931. The Johnson Type of Flat Arch . 6132. The Austria Tile Arch 6533. The Melan Arch, Short Span .. : 6734. The Melan Arch, Long Span 6735. Arch of Metal Straps and Concrete 6936. Arch of Wire and Concrete, Panelled Soffit 6937. Arch of Wire and Concrete, Flush Soffit 7038. EllipticalConcrete Arch 7139. Segmental Tile Arch 7240. Segmental Tile Arch used in SibleyWarehouse, Chicago 7241 . Standard Connection-angles 8542. Standard Connection-angles 8643. Isometrical View of Connection of Floor-beam to Girder 8744. Detail of Terra-cotta Front. Reliance Building 9345. Section through Wall at Main Entrance to Masonic Temple. . . 9446. Detail of Corner Pier for Reliance Building 9747. Detail of Wall Girders in Reliance Building 9848. Diagram of Thickness of Walls for BuildingsDevoted to Sale

and Storage of Merchandise 9949. Diagram of Thickness of Walls for Hotels and Office Buildings

other than Skeleton Construction 9950. Diagram of Thickness of Walls for Office Buildings carrying

Wall Weight only 9951. Spandrel Section. Ashland Block 10152. Spandrel Section. Reliance Building 10153. Connection

of Cast Mullions. Reliance Building 10154. Spandrel Section, nth floor. Fort Dearborn Building 10255. Spandrel Section, I2th floor. Fort Dearborn Building 10356. Spandrel Section, ist floor. Fort Dearborn Building 10357. Spandrel Section, Roof and Cornice. Fort Dearborn Building. 10458. Spandrel Section. Marquette Building 10559. Spandrel Section. Marshall Field Building 10660. Spandrel Section. Marshall Field Building 10661. Spandrel Section through Court Wall of Marshall Field Building 10762. Spandrel Section through Typical Court Wall 108


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"LIS T OF IL L US TRA T1ONS. 1X

FIG. PAGE

63. Spandrel Section through Bay Window. Masonic Temple .... 10964. Spandrel Section at Bottom of Bay Window. Masonic Temple. 10965. Half Plan of Metal-work in Bay Window. Reliance Building. . no66. Half Plan through Bay-window Walls. Reliance Building.... no67. Spandrel Section through Centre of Bay. Reliance Building. in68. Spandrel Section at Side of Bay. Reliance Building 1 1 169. F'loor and Ceiling Supports in Bay Window. Reliance Building 11270. Details of Joints for Cast Columns 11471. Detail of Larimer Column 12272. Detail of Larimer Column 12273. DetalTof Gray Column and Connecting Girders 12574. Detail of Phcenix Column 12575. Detail of Z-bar Column. Monadnock Building 12776. Detail of Phcenix Column 12877. Detail of Phcenix Column used in Old Colony Building 12978. Detail of Box Column 12979. Section of Z-bar Column used in " The Fair " Building 13080. Method of Fire-proofingPhcenix Column 13481. Method of Fire-proofing Box Column 13482. Method of Fire-proofingZ-bar Column 13483. Method of Fire-proofingColumns in Monadnock Building. . . 13484. Diagram of Wind Bracing by means of Sway-rods 13985. Diagram of Wind Bracing by means of Sway-rods 13986. Diagram of Wind Bracing by means of Portals 13987. Diagram of Wind Bracing by means of Knee-braces 13988. Figure showing Analysis of Sway-rod Bracing 14189. Figure showing Typical Sway-rod Bracing 14390. Wind Bracing used in Masonic Temple 14491. Floor Plan of Venetian Building 14492. Wind Bracing in Venetian Building 14593. Detail of Channel-struts. Venetian Building 14694. Detail of Cast Blocks. Venetian Building 14695. Partial Cross-section of Venetian Building 14796. Figure showing Analysis of Portal Bracing 14997. Portal-strut used in Monadnock Building 15198. Cross-section showing Portals in Old Colony Building 15199. Detail of Portal in Old Colony Building 152100. Figure showing Analysis of Knee-bracing 153


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X LIST OF ILLUSTRATIONS.

FIG. PAGE

101. Detail of Knee-bracing used in Isabella Building 154102. Channel-struts and Gussets used in Exterior Walls of Fort

Dearborn Building 155

103. Detail of Column Joint in Pabst Building, Milwaukee 158

104. Detail of Column Splice in Reliance Building 159

105. Detail of Book Tile 164

106. Hall and Main Entrance to Marquette Building 166

107. Hall and Main Entrance to New York Life Insurance

Building 167108. Hall and Main. Entrance to Fort Dearborn Building 168

109. Rail Footing 1741 10. Masonry Footing 174in. Beam and Rail Footing 181

112. Beam Footing used in Marquette Building,

184

113. Double Footing used in Marquette Building 1841 14. Plan of Cantilever Footing 1 86

115. Elevation of Cantilever Footing 186116. Line of Flexure for Continuous Girder 187

117. Figure showing Analysis of Cantilever Footing,

187118. Figure showing Analysis of Continuous Girder 189

119. Plan of Foundations. Manhattan Life Insurance Building,New York 199

120. Cross-section showing Foundations of Manhattan Life Insur-nce

Building, New York 200


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ARCHITECTURAL ENGINEERING.

CHAPTER I.INTRODUCTORY.

AMONG the most noteworthy examples of ArchitecturalEngineering in recent years, " Le Tour Eifel " stands unique

" a most perfect expression of this recently coined term,signifying a complete union of the great art of architectureand the science of engineering. While universallyacceptedas distinctlyn engineering feat,this tower possesses suchperfectstructural beauty that it may well lay claim to theeulogies of architectural critics " eulogies that should be allthe more emphatic when we stop to consider how few andfar between, in modern times, are the creations of the engi-eer

that can, at the same time, appeal to the architecturalartist or designer, as embodying the beauty of form withthe excellence of construction ; while the reverse may trulybe said of modern architecture. For who may claim justlythat our present architectural efforts are true, characteristicexpressions of modern life,or reflections of the progressthat has characterized our age " as classical architectureembodied classical life and mediaeval architecture expressedmediaevalism ?

The science of engineering has, at least,been progress-ve,keeping pace with modern developments, while archi-ecture,

for the most part, has been stationary,content to


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2 ARCHITECTURAL ENGINEERING.

copy the original form of a civilization whose substancehas undergone ages of evolution. Hence arise the causesfor the present antagonism in these two closelyrelated pro-essions.

There should be none, but that there is,no onewill deny. One of the most prominent engineers of theUnited States has been heard to characterize architects as" milliners/'and their work as " millinery or " gingerbreaddecoration "; while the architect,on his own little pedestalofpure art, scorns the engineer as incapable of producing thebeautiful. There is, doubtless, partialjustice in each ofthese criticisms; the architect's blind devotion to classicforms becoming as much of a hindrance to the practicalaims of the engineer, as the barren stamp of utility,laringfrom a purely engineering work, is an offence to the eye ofthe artistic designer. But the keynote has already beensounded for a more perfectunion between these two pro-essions,

each of which is the necessary complement of theother.

Although the term architectural engineering has butrecentlysprung into use, the perfect union of the two artsis as old as the arts themselves. Pyramids, obelisks,temples, palaces,nd sepulchres,all show that the architectsof earlydays were the engineers as well. Vitruvius, theonly ancient whose ideas on architecture have' been pre-erved

for us, established three qualitiesas indispensablein a perfectbuilding : stability,tility,nd beauty," the firsttwo of which certainlylie within the range of the scienceof engineering. As a proof that those early architectswere governed by the laws of Vitruvius, we have but tolook upon the pyramids of Egypt, the vast monoliths ofRome, the temples of Sicily,r the massive Parthenon.Their graceful proportions and harmony of design havefor centuries made of the architect an admiring copyist,while their massiveness and stabilitysuggest to the en-


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IN TR OD UCTOR Y. 3

gineer the possibilitiesf human power. Take lor exampleone of the largest pyramids not far from the cityof Cairo.This rough, awe-inspiring mass of masonry covers 11 acresof the sands of the Nile, while its height is but little lessthan our Washington Monument, or nearly 500 feet.Again, consider the temple of Babylon, 660 feet in height,built of blocks of stone 20 feet long,used in a brick-likefashion, some of them being 15 feet broad and 7 feet thick ;or the massive remains of an Egyptian temple, the wallsof which were found to be 24 feet thick; while at the gatesof Thebes the foundation walls were 50 feet thick and per-ectly

solid.The ethnologist tells of an age of clay,then stone in

the rough and, later,polished; an age of bronze, then iron ;and now we add steel and the newer materials. Architec-ure,

as represented in the temples, tombs, palaces, andhabitations of man, has always been, like literature,thesurest indication of the customs, arts, and needs of thepeople who produced it in fact,a perfectreflection of thecivilization in which it is found. " Cain, the son of Adam,builded a city," the rude mud hut or the flimsystructureof reeds serving as man's habitation in primitive times, imi-ating

the nests of birds, of which modifications still existin China and other Eastern countries, as well as in manyparts of dark Africa. The later days of clayand straw andthen burned brick were succeeded by the age of stone,reaching such a height of excellence in the works of theGreeks and Romans, and the castles and cathedrals of themiddle ages. The temple of Solomon, rebuilt by Herodat Jerusalem, was, so the Bible states, 46 years in erection,with stones 46 feet long, 21 feet high, and 14 feet thick,while some were of the great length of 82 feet. Would itnot tax the ingenuityof an engineer in our own advancedage to handle such masses of stone ? Architecture and en-


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gineering certainlyworked in harmony in these examples,which must ever rank with the greatest creations of man.

Now, with the hurrying strides of civilization,comes ademand for a cheaper and quicker construction, a mediumcapable of being more easilyhandled than the huge blocksof stone of earlyages; while the principles of statics andthe economics of construction present themselves withever increasing clamor for solution and application,untilwe boast that our age is one of specialties,involvinganexactness hitherto unknown in the observance of all thelaws of nature formulated, as they are, into exact sciences.

It was but natural, in the examples we have considered,,that architecture should go hand in hand with engineering,for the architect was the engineer,employing rule of thumbmethods, to be sure, and knowing little of the laws ofstatics or dynamics. Indeed it was not till the thirteenthcentury that the solution of the theory of arches and vaultswas attempted. Old, old indeed, is the relation of friend-hip

that has existed between the naturallyallied arts ofarchitecture and engineering a mutual bond, which will,we believe, give us still more perfect examples of thestrength and beauty that architectural engineering makespossible: architectural,in reference to the expression andbeauty of the edifice " engineering(perhaps partially,if notwholly, hidden from the eye),in construction, durability,ndmagnitude that result from the possibilitieshich open upbefore the mind accustomed to dealing with the matterand forces of nature, and adapting them to the ever-increas-ng

wants of an exacting public. The materials of natureassume higher and higher planes in the fulfilment of man'sneeds, as he constantly overcomes more of the natural de-tructiv

elements and agencies by applying himself withscrupulous exactness to every detail of work. Consideringthe present tendency to specialization,t seems absurd to


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IN TROD UCTOR Y. 5

suppose that the architect may eventually be employedsimply as an ornamental draughtsman by the engineer, orthat the engineer may become subservient to the architect.Either professionis too noble and comprehensive in itselfto permit of such absorption. It is but a natural prejudiceto give first importance to one's own branch of work ; and,indeed, the engineer quite justlyclaims a prerogative,sinceupon the accuracy of his calculations depend the stabilityof the structure and the safetyof the tenants. But, on theother hand, one cannot severely censure the architect forridiculingsuch work as many of our best engineers sendforth, as devoid of beauty or even harmony of line. It isapparent, therefore, that the truest expression of our lifeand civilization must be found in a more perfectharmonyof these two professions.The architect of earlydays wasenabled by rule of thumb methods, good judgment, and aknowledge of past examples to produce the structures hebuilt; but with the exactness of our professionalork atthe present time, and the multifold necessities of our com-rehensive

civilization,the architect who endeavors tocompass the sphere of the trained engineer will find thelongevityof Methuselah desirable for his education. Letthe engineerknow more of art and appreciate its value, andlet the architect know as much as possible of constructionand the laws of the forces of nature. But that either mayfullygrasp the details of both professionsseems well-nighimpossible.

The architect has been accustomed to say that such aperfectunion is impracticable,ut the architectural critics ofto-day are demanding it,as is shown by the following: " Inart, as in nature, an organism is an assemblage of interde-endent

parts, of which the structure is determined by thefunction, and of which the form is an expression of thestructure." Again : " That form is pleasing to good taste


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which shows and reveals its use. That form reveals theuse most successfullyhose surface and outlines and whoseskeleton or frame speak for themselves, and are not ob-cured

by misplaced ornament."If these quotations from purely architectural critics,

without reference to engineering, are to be given value,then surely a more rational union of excellent structuraldesign on economic principles,ith perfect architecturalexpressionof the underlying organism, is not only possiblebut necessary for a proper reflection of our civilization.The people of our country have demanded " sky-scrapers,"in accordance with the strong tendency to centralization.Newr problems have been created and new necessities im-osed,

and the engineer has come to the front with thesteel and terra-cotta of the "Chicago construction," as themeans of solution on his part ; but it remains for the archi-ect

to give true expression and permanent form to whatthe engineer has evolved. It is from the union of theresults obtained by a rational division of labor in the art ofbuilding that we hope for the perfect architecture of thepresent age.

It has been said that our civilization has demanded amedium of construction more in accord with the push andhurry and economy of our day than is found in the mas-ive

masonry construction ; a substance combining thestrength, durability,and adaptabilityrequired by the de-ands

of commerce and rapid progress. In the architec-uralhistory of our own country we have not confined

ourselves to any one material long enough to develop forit a unique, characteristic style of representation. Ourarchitectural form has, rather, been a series of rapidchanges. The refined and sober examples of our colonialforefathers rapidly gave way to the more ostentatiousefforts of the jig-saw in our frame construction, and this


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zation of business operations is attended by many vexing-difficulties,he attempted solution of which has caused anumber of clauses of restriction to appear in the municipalbuilding laws. Considerable discussion has been going onabout the sanitary aspect of this question ; the damp, un-holesome,

and microbe-laden air which must lurk in thedeep valleysor streets between mountainous structures oneach side ; the dark and uninviting offices of the lowerstories,which would soon become vacant ; and the con-ested

condition of our sidewalks when our vertical carry-ngcapacity is greater than our horizontal or street

capacity ail are considerations of grave importance.But that the proper regulationof building operations,

with their attendant difficulties and future possibilitiesfdevelopment and style,ay be successfullyaccomplishedby general municipal ordinances is very doubtful. Thebuilding laws of many of the larger cities alreadyprescribea maximum heightfor all structures; but consideringhighbuildings,/^se, it is evident that it is not so much legisla-ion

limitingthe possibilitiesf design that is needed, as itis laws compelling the appointment of competent engineersto supervise the designs,specifications,nd execution oflarge buildings,and possiblya competent board of archi-ects

to pass on the proposed location of an extraordinarilyhigh structure. It would be well if we adopted more ofthe European practice,giving harmonious appearance toour thoroughfaresand considering the specificconditionsof each new structure of monumental pretensions,nsteadof binding all through an inflexible law. Edifices frontingon parks or open spaces might then be treated in moreheroic proportionsthan those of narrow by-ways, and theincongruous mixture of ups and downs, side by side,mightgive place to some semblance of harmony betweenneighbor and neighbor.


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CHAPTER II.

FIRE PROTECTION.

BEFORE considering the details of skeleton constructionit will be well to consider the general subject of fire-proof-ng,

with its effectiveness and its limitation.The total fire loss in the United States during the year

1894 was about $128,000,000, of which the insurance com-aniespaid, as their share, some $81,000,000. This stupen-ous

drain on the resources of the nation may be betterappreciated if we consider that the full value of the pigiron production for the same year was about $75,000,000.

When to this fire loss we add the estimated amountnecessary to maintain the fire departments, and to sustainthe fire insurance companies, the grand total will exceed$175,000,000 annually.

If,then, it is true, as stated by underwriters that fortyper cent of all fires are attributable to causes easily pre-ented,

a proper treatment of the fire problem certainly be-omesa very practical and economic inquiry.

The subject of proper fire protection is now recognizedas a legitimate and important branch of engineering. It isno longer confined exclusively to endeavors to protecthuman life, but is greatly increasing in scope, demandingvery careful thought from its economic standpoint as well.The old adage of an ounce of prevention being better thana pound of cure is slowly but surely demonstrating itstruth as applied to the ravages of fire,as well as of disease,and the specialist who enters this broad field of researchand improvement must meet causes and effects with a pre-

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cision not less exact than does his medical brother. Con-lagrationhas formerly been looked upon as an inevitable

calamity,inflicted by a supernatural agency ; and property-owners have been content, year after year, to pay enormousinsurance rates, suffering with resignation the destructionof their property and the annihilation of their business.Add to these the loss of articles of peculiar associations,heirlooms and treasures of art and science," and the possi-ility

of relief from this Damoclean sword of conflagrationis a liberation indeed. And that this question of fire wasteis being seriously considered in all its aspects and by allclasses of society is shown by the widening facilities forthe use of fire-proofonstruction. The realization of lowprices in the building market has served to overthrowmany of the hitherto unquestioned prejudices in regard tofire-proofonstruction, and the economy of such design asopposed to the fire-trapmethods so long in vogue is nowbeing daily emphasized by architects, engineers, and thetechnical press. And what is most gratifyingis the factthat this economy is beginning to be appreciated not onlyby the owners of palatialoffice buildings,tores, and mag-ificent

residences, but also by people of limited means, asis evidenced by the start already made in fire-proofingheordinary cityhouse, at a figurenot exceeding the cost ofpresent methods. It was found recently,n taking figuresfor a building in Philadelphia to cost $125,000,that a thor-ughly

fire-proofedconstruction would cost only 3.6 percent more than the ordinary method of building. This in-rease

would be compensated for in a very short time bythe decreased insurance.

The tide has turned, and nothing can stay the flood ofprogress in this direction. The dawn of the twentieth cen-ury

will undoubtedly see nearly all of our mercantile,manufacturing, and even dwelling houses, except those of


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FIRE PROTECTION. II

the very cheapest description,built according to fire-resist-ngprinciples.Steel, the clay products, and cement or

concrete are the" materials of the future, permanent, fire-resisting,f ready adaptability,nd of remarkably low cost.The fire-traptimber construction, threateningthe exhaus-ion

of our vast forestry resources, accompanied by itssusceptibilityo dampness, drought,heat, and cold, involv-ng

dry-rot,s shown by the collapse some years ago of aprominent hotel in Washington, must give way to new con-itions,

and further improvement in a field of such promise.The insurance burden will be gradually lightened, andhuman life be better protected.

While buildings could be erected with absolutely noinflammable material in their construction, there wouldstill remain the furniture and property of the tenants tofeed possiblefire. This element of danger cannot be elimi-ated

; and added to this are the dangers that come fromwithout as well as from within. For as long as highly in-lammab

buildingssurround even the most excellent ofmodern fire-proofstructures the term is but mockery.Fire-proofstructures must stand in fire-proofities. Hencethe word " fire-proof,"s applied to modern structures, doesnot mean one that claims immunity from all danger of fire,for considerable woodwork must still be used in interiors,and the average contents are dangerous in the extreme ;but it does claim to embody principleswhich have reducedthe fire hazard, both interior and exterior, to a minimum,according to the best skill and judgment of the day. Theterm implies that all structural parts of the edifice must beformed entirelyof non-combustible material, or materialwhich will successfullyithstand the injurious action ofextreme heat. Following is the definition given in thenew building ordinance of Chicago: " The term 'fire-proofconstruction ' shall apply to all buildingsin which all parts


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that carry weights or resist strains,and also all stairs andall elevator enclosures and their contents, are made entirelyof incombustible material, and in which all metallic struc-ural

members are protected against the effects of fire bycoverings of a material which must be entirelyincom-ustible

and a slow heat-conductor. The materials whichshall be considered as fulfillinghe conditions of fire-proofcoverings are: First,brick; second, hollow tiles of burntclay applied to the metal in a bed of mortar, and con-tructed

in such manner that there shall be two air-spacesof at least three-fourths of an inch each by the width of themetal surface to be covered, within the said claycovering ;third, porous terra-cotta, which shall be at least two inchesthick,and shall also be applied direct to the metal in a bedof mortar; fourth, three layersof plastering on metal lath,so applied upon metal furring that there shall be a solidlayer of mortar at least one-half inch thick between themetal to be covered and the metallic lath,and then two air-spaces of at least three-fourths of an inch in the clear be-ween

the first-mentioned layerof plasteringand the outersurface of the finished covering."

There are many materials quite satisfactory as fire-proofing mediums for the constructional parts of a building,but the inventor has yet to supply an acceptable incom-ustible

material for the interior finish. The best that canbe done, at present, is to reduce the inflammable elementsto a minimum, and endeavor to confine the fire by means offire-proofloors and partitions,o that it may do no injurybeyond the consumption of local woodwork and furnish-ngs.

This may be accomplished largely by means offloors of concrete or terra-cotta with I-beams, using mosaicor marble tile instead of wood flooring, partitions ofplasterboard, cement or metallic lath, or terra-cotta blocks,and bases and wainscoting of marble. The possibilityf


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FIRE PROTECTION. 1 3

using frames and casings for doors and windows madeeither of metat^o^ sheet metal over wood, and doorscovered with sheet metal, seems but a question of shorttime in adding further efficiencyo high-class fire-proofstructures. A metal-covered door has lately been intro-uced

in this country, giving a well-appearing,light,andincombustible contrivance, and serving as an effectualbarrier against the spread of flames. The success that hasattended the use of wire glass in skylights has alsoprompted the suggestion to reduce the exterior hazard byprotecting all windows, which offer the most vulnerablepoints of attack, by using a plate glass with silvered orgilded wires imbedded therein,in gracefulpatterns or net-ork,

serving the purpose of additional fire protection, aswell as architectural effect. The planningof the building,and the proper location and installation of the variouspower plants and mechanical features, also become vitalproblems in fire-proofing.

The success that has attended past efforts in this direc-ionmay be judged by such examples of fire as have been

afforded in protected structures. The largest and mostinterestingof such tests of the new methods was the burn-ng

of the Chicago Athletic Club building while underconstruction. Though not entirelysatisfactorys a test ofpresent building methods, u this building furnishes an assur-nce

that was lacking before " that the metal parts of abuilding if thoroughly protected by fire-proofing,roperlyput on, will safelywithstand any ordinary conflagration,fthe quantity of combustible materials the building containsis not greatly in excess of that which enters into the con-truction

of the building itself."This extract from 'the report of experts employed toinvestigatethis fire and its effects,emphasizes two very

important facts,namely, the danger of the indiscriminate


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use of combustible material not absolutelynecessary in theconstruction, and second, the evident superiorityf terra-otta

as a fire-proofingubstance.The above fire,which occurred on November i, 1892,

was the first case on record of a fire in a building intendedtc be fullyfire-proofhere the loss to the insurance com-anies

was more than thirtyper cent of its value. It isfurther stated in the report that " if the building had beencompleted, it would never have contained combustiblematerial enough (or so distributed)to have produced suffi-ient

heat to have done any considerable damage to thebuilding by burning."

The fire in question was of very intense heat, inasmuchas a vast quantity of scaffolding,looring,trim, etc., wascollected in mass, preparatory to use ; but, in spite of this,there seemed no reason for questioning the integrityandstrength of the building,as a whole, after the fire,and nodoubt existed that the fire-proofinground the columnssaved them from utter collapse,because it remained inplace until the fuel that had fed the flames was well-nighexhausted. The result to the building included the entiredestruction of all the interior finish,plastering,iping,andwiring, as well as parts of the elaborate front of Bedfordstone and pressed brick. But the steel columns and beamswere uninjured, except a few of the latter where unpro-ected

; and the tile arches, built after the end constructionmethod, were almost uninjured, in spite of the combinedaction of great heat and frequent applications of coldwater.

It is not advocated that fire-proofings efficient (or in-fficientwhen the preservation of human life is considered)

as the foregoing example is sufficient for present needs-it certainlyis not. But certain underlying facts have beenclearlyproved by this test, and taking these essential points


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l6 ARCHITECTURAL ENGINEERING.

First used in interior work only, it soon appeared in beltcourses, sills,caps, ornamental panels and modelled workin the hard-finished terra-cotta, until to-dayits use is almostmore general than stone, appearing in entire fronts, as abold-faced impersonationof soliditytself.

The field of architectural expression in terra-cotta hasrecently been widened to a still more remarkable degreeby the successful completion in enamelled terra-cotta ofthe fa"adesof the Reliance Building, Chicago,supplied bythe Northwestern Terra-Cotta Co. (see Fig. i). Shouldthis material successfullywithstand our severe climaticchanges, and undergo the same course of rapid improve-ent

as did the ordinary terra-cotta used in exteriors, avast field for more extensive coloring effects would then beopened up to the architect who strives to create " a thingof beauty forever" in the smoke and soot-laden air of ourAmerican cities. The underlying idea of enamelled ex-eriors

is,of course, that they may be readilywashed downand cleansed of the soot which so soon destroys any at-tempts at lightcoloring.

With this general review of the fire problem, and terra-ottaas a weapon of defence, it becomes evident that a fire-roofstructure must possess :

1. General excellence of design.2. All floors of fire-proofonstruction.3. All columns of masonry or steel,protected from fire.4. All outside piers and walls of masonry or steel,pro-ected

from fire.5. All partitionsand furring of fire-proofonstruction.There are three methods of general design advocated

at the present time as means of reducing the fire risk " the" slow burning construction," the so-called " mill construc-ion,"

and the still more effectual "fire-proofonstruction."The term " slow burning construction " is applied to build-


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FIRE PROTECTION.

FIG. i. " The Reliance Building. D. H. Burnham " Co., architects.


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1 8 ARCHITECTURAL ENGINEERING.

ings in which the structural members, carrying the floorand roof loads, are made of combustible material, butprotected throughout from injury by fire,by means olcoverings of incombustible, non-heat-conducting materials.Thus the wooden floor joistsre protected on the underside by a singlecovering of plaster on metal lath,while athickness of Ij-inches of mortar or incombustible deaden-ng

is required above the joists. Columns, if of oak, witha sectional area of 100 square inches or over, need not havespecialfire-proofcoverings. Partitions and elevator en-losures

must be wholly of incombustible material, and nowood furring is allowed.

Buildings of " mill construction " are those in which allfloor and roof joistsand girders have a sectional area of atleast 72 square inches, with a solid timber flooringnot lessthan 3f inches in thickness. Columns of wood need not beprotected,but they should have a sectional area of at least100 square inches. Partitions and elevator enclosures areof incombustible material, and no wooden furring or lath-ng

is used." Fire-proofonstruction" has alreadybeen defined. The

two types first mentioned do not, then, depend on the use ofmaterials wholly incombustible, but rather on the judiciousdesign and careful use of ordinary buildingmaterials, theaim being to provide structures so open and free fromfire-lurkingcorners that they may offer no obstacles to aspeedy suppression of the conflagration.These types arepeculiarlyadapted to large mills,warehouses, and the like.

The scientific fire-proofingof a building does not con-istin a proper selection of materials alone, for a structure

may be reasonably secure against accidental fire,or theextension of fire,even when built of combustible materials ;nor does it lie merely in guarding against the causes offire. It can be secured only by a thorough acquaintance


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FIRE PROTECTION. 19

with all the general features and minutest details of allkinds of structures, and by a quick perception " for thenumerous elements of danger that are constantlycreepinginto modern systems of buildings." The plan must becarefullystudied to secure means of cutting off communi-ation

between floor and floor,and between and arounddangerous sources, isolating,f possible,all stairways andelevator-shafts by means of fire-resistingalls, and con-ining

all power and mechanical plantsin such a way thatthere can be no possibleeans of fire extension. It is truethat most high office buildings do not possess the isolatedstair- well or elevator-shaft,but if they do not, great caremust be taken in making the halls and corridors of morethan ordinarysecurity. They will still be the means for arapid distribution of smoke from floor to floor,and thusmake the danger from suffocation assume an importanceequal to that of fire. This threatening possibilityas notyet verified itself,and it is to be hoped that it will bedenied the opportunity.

No less important is the cuttingoft of all communica-ionbetween pipe- and air-passages.Piping and passages

of all kinds should be carefullyconsidered as a part of thefundamental design, for they not only become great eye-ores

from their exposed positionsin offices,but they alsoserve to make many of our fire-proofingndeavors quiteuseless.

The architect or engineer must finallye well informedin regard to the details and varied uses of approved fire-proofing materials. These must include terra-cotta in allthe different shapes made by the terra-cotta companies,cement, concrete, fire-brick, asbestos, mackolite, etc. Ajudiciousand economic use of all these materials is neces-ary,

so that the most practicableform may be chosen tosecure the desired end.


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Some of these important minutiae may properly receivedetailed attention, when we remember that the strength ofa structure is gauged by its weakest point.

The metal columns, for example, are properly figuredfor their safe dimensions, but from this step on they areapt to become a bug-bear to both architect and owner, theformer desiring to reduce their size to a minimum onaccount of appearance, while the latter considers that theydeprive him of the revenue of just so much floor-space.Any measures are therefore adopted to reduce their size.First,the various waste-, heat-,and supply-pipesare run upalongsidethe columns from floor to floor. For the passageof these pipes openings must be made in the tile floorarches, which, in the rush of buildingoperations,may neverbe properly filled up again. These openings come insidethe line of the fire-prooflabs of the column, thus formingone long continuous flue from basement to roof. Thefinished line of the fire-proofedand plastered column isoften not more than 2 in. from the extreme points of themetal-work, and then, deducting " in. or " in. for plaster,little enough is left for the fire-proofingroper. Thevarious pipes before mentioned will very often projecteven farther than the column itself,thereby tempting thefire-proofero trim and shave till the originallittlehas be-ome

still less.In the Athletic Club Building fire some of these points

were illustrated with glaring prominence. A steel frame-orkand fire-proofcovering having been used as the

main elements of construction, further consideration of firehazards were apparentlyslighted. In no case did the fire-proofing extend more than 2 in. from the outermost edgeof the ironwork, while wooden nailing-stripswere em-edded

in the tile at intervals of about 3 ft.starting fromthe floor (a4-in.face exposed),making successively ft. of.


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FIRE PROTECTION. 21

tile and 4 in. of wood. These nailing-stripsere employedas grounds for the panelledoak wainscoting,and a furthererror was made in leaving an air-space behind this panel-ing,

with no " back " plastering.The ceilingalso left anair-space,ue to i-in. raised nailing-strips.

As a matter of course the wooden grounds around thecolumn burned out, letting the fire-proofingall in 3-footsections. It so happened that but two columns werebadly bent by the intense heat, but who can say what thestabilityf those re-used unbent columns reallyis ? Werethey cooled slowly, or suddenly by the application ofstreams of water, and thus rendered brittle,and were theyheated unevenly,thus causing great strain in the materialon but one side of the column? What was the amount of

expansion and contraction ? No experiments could bemade with reasonable economy and safetyto satisfyhesequeries, leaving the present state of the buildingan un-ertain

conjecture.The proper installation and distribution of the mechani-alfeatures in a modern office building have been given

considerable attention by John M. Carrere (seeEng. Mag.,October, 1892),and the system proposed by him will un-oubtedly

add greatlyto the efficiencyf fire-proofing,ndremedy many of the weak details just considered. Inorder to avoid chases, or continuous flues,the lowering ofthe hall ceilingss suggested, " thereby obtaining a hori-ontal

space under the floors of the halls at each story,lined and fire-proofed,here all the mechanical featuresexcept steam heat can be placed " (see Fig. 2). An arrange-ent

of this character would certainlypossess many greatadvantages " it would always be accessible for repairs, easyof connection with all offices,and would serve as a safeand at the same time hidden conduit for all wiring, pip-ng,

and ventilatingair-ducts,either exhaust or indriven.


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The additional expense would not be great either, andwhen its permanency is considered, never being affectedby the moving of partitions,tc., as is now the case, it issurprising that such a system has not attained moregeneraluse.

At the ends of these horizontal ducts are vertical chasesor ducts built solidlyof fire-proofblocks or brick fromcellar to roof, and connected at each floor with the hori-

OFFICE OFFICE

OFFICE

FIG. 2.

zontal leads,but stillpartitionedff at each floor with wireand plaster partitions,o prevent the spread of possiblefire. All of the vertical risers could be placed in thesechases, thus avoiding the unsightlinessof pipes in the officespace, or the necessity of placing such piping within thecolumn space.

The growing importance of adequate fire protectionmay be judged from the care displayed in the encasing ofthe large girders at the new Tremont Temple in Boston.These girders carry columns of great load, and any warp-ng

tendency from great heat would be attended by mostserious results. The steel girders were first surroundedby blocks of terra-cotta on all sides, and these blockswere then bound by iron bands. Over these blocks wasstretched expanded metal lathing with a heavy coat of


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CHAPTER III.

SKELETON CONSTRUCTION" EXAMPLES, ERECTION, ETC.

MANY of the details which will be discussed in the fol-owing

pages may be better appreciated in their relationto the whole subject if a few typical skeleton structuresare examined. The scope of this outline will not permit ofa discussion of the architectural problems involved in thedesign of a modern office building, hotel, or any of thestructures which are now built according to skeletonmethods. The points here considered are, rather, those ofconstruction pure and simple. But the comprehensiveview of the subject necessary to the architect or architec-ural

engineer may only be obtained through an accurateknowledge of the manifold items which become a part of asuccessful plan. These accessories to the mere frame-worklie within the province of the engineer as well as of thearchitect, and here, as in the execution of the external ex-ression

of architectural engineering, a perfect harmonymust exist between the two branches in the perfection ofall mechanical details, if results are to be secured whichmay be looked upon as creditable to both professions.

The value of such accessories may be more fully real-zedwhen the self-sufficiencyof a modern office building,

containing all modern improvements, is considered. Elec-riclight, the telephone, mail-chutes, and well-appointed

toilet-rooms are already demanded as absolute necessities,while late examples provide telegraph and messenger ser-ice,

cigar- and news-stands and barber-shops, besides24


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SKELETON CONSTRUCTION. 2$

restaurants and cafes in the basements. It is true thatmany of these factors would seem to. have little bearing onthe duties of the engineer,and yet it was justsuch condi-ions,

imposed on the designer of the foundations of officebuildings,that produced the successful development of theso-called raft or floatingfoundations, in order that the base-ents

might be unencumbered by the large pyramidal

FIG. 3." Chicago Stock Exchange. Adler " Sullivan,architects.

masses -of stone previouslyused as footings,nd the base-entspace might be added to the available rentingarea, or

be used for the mechanical plants. The rigid economy offloor space which is demanded may only be obtained bycareful attention to the most advantageous uses to whichthe different floors and rooms in the structure may be put.

Some examples of office buildingsrecentlyconstructedin Chicago will here be given.


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THE CHICAGO STOCK EXCHANGE.A perspective of this building by Adler " Sullivan,

architects, is shown in Fig.3. The facades are constructedof a yellow-drabterra-cotta, with white enamelled brick inthe interior court.

Fig. 4 shows the basement plan,containingthe boiler-and engine-rooms,restaurants, etc.

Fig. 5 is a plan of the ground floor,showing the en-rancevestibules,elevators,store areas, etc.

Fig. 6 gives a plan of the arrangement of the offices,etc., on the sixth floor. The toilet-rooms,barber-shop,ventspaces, and the arrangement of the lightingcourts are plainlyshown.

THE MARQUETTE BUILDING.This office building(see Fig. 7),designed by Messrs.Holabird " Roche, architects,has but justbeen completed.

The exterior walls are built mainly of a dark red brick,withterra-cotta base, cornice, and trimmings.

A typicalfloorplan,howing possible sub-divisions, isgiven in Fig. 8. Many of the floors in the larger officebuildingsare never subdivided until rented, in order thatthe arrangement of offices may be made to suit the tenant.

RELIANCE BUILDING.

Fig. 9 gives a typical floor plan of this building byD. H. Burnham " Co., architects. This arrangement ofoffices is intended for rooms to be used in suites. Thepipe space at the side of the elevators,and the space forcounterweights behind the elevators, are plainlyshown, asis the circular smoke flue.

The elevator accommodations in these various buildingsmay be seen on the plans. Rapid passenger and freightservice must both be provided for,and the necessary spaceallowed for the hydraulic cylindersin the basement, aswell as for the vertical counterweights. Beams must be


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SKELE TON CONS TR UCTION.

Dd


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SKELETON CONSTRUCTION. 29

f ---"--.


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3O ARCHITECTURAL ENGINEERING.

FIG. 7. " The Marquette Building. Holabird " Roche, architects.


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FIG. 9. " Typical Office Floor Plan of theReliance Building.


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supplied to support the elevator sheaves, and water-tankslocated to supply the hydrauliccylinders.

If the basement, as in Fig.4, lies below the sewer level,and it is to be occupied by stores, cafes,or by the boiler-and engine-rooms, an ejector pit will be necessary to raisethe sewage to the proper level. Pumps for water-supply,dynamos for electric light,boilers and steam plant forpower and heating all must be definitelydeterminedand carefullyweighed in their relation to the character ofthe building,and as affectinghe design of foundations andall structural details.

The followingdata may be of interest as descriptiveofsome of the mechanical furnishingsof one of Chicago'smost celebrated office buildings, the Masonic Temple,shown in Fig. 10.The entire drainage is carried through the buildingbymeans of a system of vertical risers,about one half of whichconnect directlywith the street mains, through pipingsuspended from the basement ceiling.-he remainder ofthe risers,and all drainage from the boiler-room and base-ent

space, are connected by a system of undergroundpiping,with two 5o-gallonShone ejectors,placed in a pitin the basement, from which the sewage is forced to thestreet sewer. This was necessary in order to keep thebasement stores, cafes,etc., free from exposed pipes. Allvertical pipes in the building,both for water-supply anddrainage, were carried in fire-proofipe-spacesespeciallyprovided. The water-supply is pumped from the citymains, by pumps located in the basement, to storage tankson the twentieth floor,with a combined capacity of 7000gallons. On the twentieth floor also are four compressionelevator tanks of 18,500gallonscapacitytotal. For elevatorand water-supplyservice seven pumps are required,havinga total capacity of from 2000 to 3800 gallons per minute.


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FIG. io." The Masonic Temple. Burnham " Root, architects.


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SKELE TON CONS TR UCTION. 35

Each office and store has a privatewash-basin, with gen-raltoilet-rooms and barber-shop on the nineteenth floor.

The main toilet-room contains 64 closets, besides addi-ionalrooms on the third and twelfth floors and in the base-ent,with from 8 to 18 closets each.

FIG. ii." The New York Life Insurance Building. Jenney " Mundie, architects.

Forty thousand square feet of radiation surface are re-uired,all in direct radiation. The steam is supplied on the

" overhead " system through i6-in. mains running directly


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to the attic,thence around the exterior walls and down.Six dynamos supply 7000 i6-candle-powerlamps. For thepower and steam planteight horizontal tubular boilers areused, with a total of 1000 horse-power.

There are several features in the Masonic Temple de-ignworthy of especialnote. Several of the upper floors

FIG. 12. " Banking Floor, New York Life Insurance Building.are devoted to Masonic purposes, and the largeassembly-,drill- and banquet-rooms were kept free from columns byspanning the areas with lattice girders,on which rest thearched ceiling and roof trusses. The interior court alsopossesses specialfeatures in the galleriesprovided at each


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SKELE TON CONS TR UCTION. 37

story for the lower ten floors. This plan was intended toattract small storekeepers and the like as occupants of theadjoiningstores or offices,thus concentrating many trades-

o "5 /" reefFlG. 13." Typical Office Floor Plan, New York Lhe insurance Building.

men under one roof. The scheme has not proved a success.The roof of the Masonic Temple is covered by an en-losure

of glass,serving as a summer-garden and place ofobservation.

NEW YORK LIFE INSURANCE BUILDING.A perspectiveof this building,designed by Jenney "

Mundie, architects,is shown in Fig. n. The lower three


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38 ARCHITECTURAL ENGINEERING.floors are built of granite,with brick and terra-cotta above.The plan of the first floor,devoted to banking purposes, isshown in Fig. 12, while the typicaloffice plan is shown inFig. 13.

FIG. 14. " The Fort Dearborn Building. Jenney " Mundie, architects.FORT DEARBORN BUILDING.

This building,shown in Fig. 14, is but just completed.It was designed by Jenney " Mundie, architects, and anumber of the details used in its construction will be


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ARCHITECTURA L ENGINEERING.

FIG. 15." Typical Office Floor Plan, Fort Dearborn Building.


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SKELE TON CONS TR UCTION.


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FlG. 17. " The Old Colony Building. Holabird " Roche, architects.


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It is comparatively seldom that complete detail plansfor the steelwork of a buildingare made by the architect.Still less frequent are the cases where such detail planscould be used as actual shop drawings by the contractor,

L/N"

FIG. 18. " Typical Framing Plan of the Fort Dearborn Building.

as in nearly every case the manufacturer much prefers tomake his own shop drawings,to conform to the usage ofhis own plant. The architect has generallybeen contentto specifythe sizes and weights of the material to be used"


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leaving the details to be worked out by the contractor withthe approval of the architect.

The trained engineer,however, is not usually satisfiedi --[

FIG. 19. " Typical Framing Plan of the Reliance Building.

with such license on the part of the contractor, and thebest classes of work are made in accordance with definitedetails furnished by the engineer,after a careful considera-


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tion of the conditions to- be fulfilled. This does not meanthat complete shop drawings are made, but rather suchconnections and specialpoints in the design as need par-icular

attention. The balance of the detailingmay bemade to suit the contractor, with the approval of the en-ineer,

in conformity with the sizes of material marked onthe plan,and the carefullydrawn specifications.

The idea of allowing the manufacturer to prepare com-letedetails after his own general scheme, and following

specificationsnly, is not consistent with best results, inthe judgment of the writer, though such an arrangementhas often been advocated. It is true that it has been avery common practicewith bridge engineers to furnish themoving-load diagram, and allow the bidders to design thestructure as they saw fit,o long as it fulfilled all require-ents

of the specifications.his has probably been onereason for the high degree of excellence shown in the workof the better bridge companies, as each bidder endeavorsto use his material to the best possible advantage. Sucha practice,however, in building work will require a verycareful supervisionof the work by the engineer,and as thevarious contractors will use those shapes most in favor, orof least cost, at their particularworks, the calculations,con-ections,

details,etc., must all be gone over and thoroughlychecked, that all conditions may be satisfactory.A carefulchecking is necessary in any case, but where such completefreedom is accorded the bidder, it will rarely be that heis able to grasp the general ensemble in such a manner asto make satisfactoryetails in the required time. Again,only the most responsibleand experienced firms could beintrusted with such a task.

Carefullydrawn specifications,omplete and accurateframing plans,sufficient spandrel sections and any specialdetails,with all sizes and dimensions of material, will insure


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46 ARCHITECTURAL ENGINEERING.rapid and satisfactoryork on the part of the iron con-ractor.

The shop drawings may then be examined, andstamped with the approval of the engineeras received.

ERECTION.

In skeleton construction, the erection of the frameworkprogresses very rapidlyafter the material is once deliveredon the ground. All punching and rivetingof the membersis done at the shop, leaving only the assembling and field-riveting to be done on the ground, besides the adjustmentof the laterals. Field-rivetingas entirelysuperseded theuse of bolts in the best class of work. Bolt connectionswere tried, but were soon discarded on account of thecracks which developed in the plasteredceilings,adiatingfrom the column connections with the floor system. Thiswas due to the play of the bolts in the holes.

Steam cranes built expresslyfor the purpose have beenused in some cases in Chicago. They were operated ontracks which were quicklylaid over the floor system, andthese cranes would pull themselves up an incline, fromstory to story, as fast as erected. The crane boom and en-ine

platform revolved on a pivot, so that the membersrequired very little handling. The old-fashioned derricksor gin-polesare, however, generally used, some contractorspreferringthe short gin-pole,erecting one story at a time,while others use a large boom derrick, setting severalstones in place before shiftingthe derrick. The erectionof ironwork costs from $6 to $8 per ton.

Two stories can generallybe erected in six days of tenhours each. In the Unity Building of seventeen stories themetal-work, from the basement columns to the finishedroof, was accomplished in nine weeks.

The following data Avill give a better idea of the ra-idityof building operations in Chicago as shown in the

erection of the New York Life Building :


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FIG. 21. " The Reliance Building during Construction, August I, 1894.


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Figs. 20 and 21 show the Reliance Building during con-truction.

PERMANENCY OF SKELETON CONSTRUCTION.Aside from the question of fire resistance,considerable

discussion has arisen of late concerning the permanency ofskeleton construction. This controversy between friendsand indifferent observers of skeleton methods has beenaggravated by the reluctance of the supervisingarchitectof the Treasury seriouslyo consider such construction asworthy the dignityand solidityof government edifices"notably in the proposed new Post-Office building forChicago. While the architectural pros and cons of terra-otta

and steel,or concrete and steel,versus solid masonryconstruction may not here be gone into,the engineeringside of this matter beer nes one of great importance.Serious as it is,it must still be admitted as dependinglargelyon personal views, for the want of reliable dataunder present conditions. Many architects are not slowto pronounce judgment against such practice,hile otherswarmly champion the cause of steel in combination withtile,concrete, or cement. The divergence of presentopinion was well shown in a recent discussion before theAmerican Institute of Architects on this very subject,where examples of the deterioration of iron or steel underpeculiarconditions were emphatically offset by instancesof remarkable preservation under other peculiar condi-ions.

The point would then seem to be to definetheseconditions. Prominent Chicago architects and engineershave said that experience seems to show that if no limemortar is used the corrosion of the metal will not amountto enough to be of any danger, while others point to thewell-known preservativequalities of lime, and urge itsexclusive use in connection with iron or steel. Our knowl-dge

of wrought iron or steel,therefore, under definite


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SKELETON CONSTRUCTION. 5 I

variations of heat and moisture, and in association withlimes, cements, and concrete, as found in present practice,must continue to be unsatisfactoryuntil defined by moreaccurate data. Chicago engineersand builders show theirdailyfaith in such comDinations of material, and this typeof construction is rapidlybecoming more and more generalin the United States.

The effects of lime, whether as one of the ingredientsofmortar or limestone, as a corrosive factor in connectionwith ironwork seem to depend very largely upon thepeculiarconditions of each particularcase. Examples arerecorded of anchorage cables in American suspensionbridges which were found, on disclosure after some years,to be partlyeaten away where the strands had come intopermanent contact with the limestone masonry. The pres-nce

of water was possiblyaccountable for this corrosiveaction ; but it becomes a very difficult matter to constructmasonry which will allow of no permeation of moisture,especiallyn walls,piers,or foundations, as found in build-ng

practice. Dry air and pure water produce but slightoxidizingeffects on iron or steel ; " but when the formerbecomes moist, and the latter impure or acidulated, oxida-ion

of the material is speedilyset up, and when once com-enced,unless the process is arrested, its ultimate destruc-ion

becomes a simple question of time." The use of limemortar would, therefore,seem limited to localities where nofear of moisture may be anticipated for any dampness incombination with the lime, must soon show its effects onthe metal-work.

Considering the parts of a skeleton structure which areexposed to the weather, or liable to the presence of mois-ure,

we have : all exterior walls, piers,etc., and the basement members, includingfoundations. From the foregoingit would seem that lime mortar should not be used in any


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of these positions. The foundations and basement walls,columns, etc., are either surrounded by constant moisture,or by wet clay or earth itself,while the exterior wallsand supporting steelwork are subjected to the climaticchanges, frost,rain, and penetrating dampness, which mustsooner or later pierce the terra-cotta and brick envelope,and so reach the metal-work. For such positions cementmortar should undoubtedly be used ; it seems a most per-ect

conservator of metal-work, and instances are recordedof iron found in perfectcondition after a 4OO-years'entomb-ent

in cement concrete below water. Links of anchoragesin American suspensionbridges have been taken up aftermany years in a perfect state of preservation where em-edded

in cement. A further recommendation of the useof cement lies in the fact that the thermic expansion ofPortland cement is practicallyhe same as that of iron " afact which insures perfectcohesion under any changes oftemperature.

The interior members of the framework do not need ascareful consideration, being maintained at a more uniformtemperature, aad protected from the exterior dampness.Interior columns, the floor system, and wind bracingwould, therefore^ seem safe in connection with lime mortar,but it is questionablewhether the best work should notcall for cement mortar and even cement plaster through-ut.

Cement has rapidly cheapened of late years, andcement plastersare largelybeing used on account of theirbetter fire-resistingualities.

It has been suggested to relyentirelyn the preservingqualitiesof cement rather than on a proper paintingof themetal-work. Prof. Bauschinger states that his experimentsshow a cohesion between iron and concrete after hardeningof from 570 to 640 Ibs. per square inch. This is even morethan the tensile strength of the best concrete, but in build-


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ing work a perfectunion between the cement mortar andmetal-work can never be attained at all points, and athorough coating of paintmust largelybe relied upon.

All constructive ironwork should, therefore, be wellcoated with either lampblack mixed with oil,or red leadand linseed-oil. The very best of materials should be em-loyed.

The oxide of iron or mineral paint which hasgenerallybeen specifiedfor all paintingof the metal-workhas been found to separate from the steel,and form anoxidation of the metal behind the paint. A mixture of redlead and linseed-oil is now considered as the best protec-ive

coating for iron or steel. A careful inspectionof allpainting,oth at the shop and in the field,should be rigidlyenforced.

The followingare the requirements of the New' Yorkbuilding law in regard to the protectionof iron or steelwork against rust, etc :

" All ironwork and steelwork used in any buildingshall be of the best material and made in the best manner,and properly painted with oxide of iron and linseed-oilpaintbefore being placed in position,r coated with someother equally good preparation or suitablytreated forpreservationagainst rust."

The Chicago ordinance makes no mention of paint orcoatings to prevent rust in the metal framework except asspecifiedfor fire-proofingurposes as follows ; " In allcases the brick or hollow tile shall be bedded in mortarclose up to tne iron or steel members, and all jointsshallbe made full and solid."

The Boston law requires a protection from heat only,by means of brick, terra-cotta, or by three fourths of aninch of plastering.

The requirements for metal-work in foundations aregiven in Chapter XII.


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CHAPTER IV.

FLOORS AND FLOOR FRAMING.

THERE is scarce a subjector detail in the present fieldof architectural engineeringthat has provoked such wide-pread

attempts at improvement and perfectionas thequestion of fire-proofloor systems. The present day isespeciallyprolificn new patents and systems, all claiminga complete revolution in existing methods, until botharchitect and engineer alike are well-nighbewildered intheir endeavors to keep track of the novelties that are con-inually

being presented as the " cheapest and best " solu-ionof a much-discussed problem.

A proper solution cannot be realized by either architector engineerworking independentlyof each other, and per-ection

in present attempts must result from legitimatecriticism on the part of the architect as to the adaptabilityof the material to exterior form, as well as from the appli-ation

of the laws of statics as demanded by the engineer.Before investigatingresent methods and future prob-bilitie

it will be profitableo examine earlier systems,with their weak pointsand causes of failure.

The oldest so-called fire-proofrches consisted of Ibeams, placed about 5 feet centres, with 4-inch brick archesturned between, then levelled up with concrete containingthe nailing-stripsor the wooden flooring. Corrugatediron,sprung from flange to flange,as also used in placeof the brickwork, and this latter type may still be seen insome of the more substantial buildingsot that epoch, which

54


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56 ARCHITECTURAL ENGINEERING.manufacture into a floor of the required strength,and relia-ility

against fire.TILE ARCHES.

The earlier forms of tile arches were made as in Fig. 24,which shows the arch used in the Equitable Building inChicago (1872),and Fig. 25, which shows tile arch in the

FIG. 25.

Montauk Building, Chicago (1881). The latter may be saidto have been the first buildingof modern designin Chicago.The arches were 6 inches deep, with a span of 3 to 4 feet.But as these forms still left the lower flangesof the I beamsunprotected,they were soon superseded by the type shown

". $0*-.

FIG. 26.

in Fig. 26. This arch was used in the Home' InsuranceBuilding, Chicago (1884),the tile being 9 inches deep and6 foot span. This was the first instance in which the beamsoffits were protected against fire by anything more thanplaster; and as many of the features in this arch are essen-ially

the same as in the types of tile arches as found inpresent practice,a brief descriptionwill here be in place.

The pieces form radial joints,s in any segmental arch,or are key-shaped with a centre " key." The arches are seton " centres " of plank, hung from the beams by hook-bolts,and these centres should remain in place at least twenty-


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FLOORS AND FLOOR FRAMING. 57

four hours after the arches are set. The " skew-backs,"or butment piecesof the arch, take the shape of the I beamagainst which they bear, settingfirmlyand squarelyon thebeam flanges. Different sized skew-backs are at hand foruse with different sized beams, as arches are often sprungbetween beams of different depths. The soffit of the tilearch extends about one inch below the bottoms of the beams,and the skew-back pieces are made in such a manner thata piece of fire-proofingile may be slipped in and sup-orted

directlyunderneath the beam flange,to completethe fire-proofing,s shown in Fig. 26. A coat of plasteror cement is then given the whole surface, after which itis read}7for such decorative treatment as may be desired.

A concrete fillings placed over the arch, to distributethe load from block to block, and to receive and embedthe wooden nailing-stripshich take the finished flooring.The metal beams are thus entirelysurrounded by fire-clay,concrete, and cement.

The depth of the tile arch depends upon the span, andthe load to be carried. The maximum spans of the various

2 CONCRETE-TILLING

FIG. 27.

depths are generallyfurnished by the manufacturer of thetype in question,but such data should be fullyestablishedby adequate tests, as will be pointed out later. Slightvariations in the span from centre to centre of beams aremade by using " half intermediate " tile,and different-sizedkeys. The tile blocks are laid with lime mortar or cement


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58 ARCHITECTURAL ENGINEERING.joints,nd in no case should the jointexceed \ inch inthickness.

In many cases, where the panel length required beamsof a considerablygreater depth than the tile arch itself,tile filling-blocksere used, as being lighter than theordinary concrete fillingas shown in Fig. 27, taken fromthe Woman's Temple, Chicago. Special shapes for skew-backs, panelled beams, etc., made in this character of tile,are shown in Figs.28 and 29.

FIG. 28. FIG. 29.The best semi-porous tile used in these types was made

from clay found at Chaska, Minn., at Brazil, Ind.,and inparts of eastern New Jersey.

In the foregoing examples of arches, known generallyas the " Pioneer " arches (because made by the PioneerFire-proofingCompany of Chicago), the voids in the tileblocks ran parallelto the supportingbeams, and hence theprincipalor side webs of the individual tile blocks alsoran parallelo the beams, or at right angles to the line ofthrust in the arch. This limited the effective arch area tothe top and bottom flanges,involving a serious waste ofmaterial.

To remedy this defect a new arch was patenteda few years ago, known as the " Lee " arch, in whichthe voids ran parallelto the line of thrust, or at rightangles to the supporting beams. One of these arches isshown in Fig. 30, and it will be seen that the effectivearea now comprises the vertical webs, as well as the hori-ontal

ribs; in other words, all of the material performsuseful work as an arch. A further improvement wasattempted by the use of a porous terra-cotta, made from


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FLOORS AND FLOOR FRAMING. 59

a fire-clayhich, before it is burned, is mixed with saw-ustand finelycut straw. These ingredientsare con-umedduring the firing,leaving the material in a very

porous condition, and thus greatly reducing the dead

i "^i A.... I. ""

/ rFIG. 30.

weight of the arch itself. A comparison of the weights ofthe old Pioneer and the newer Lee arch may be made asfollows (weightgiven is per square foot)

Pioneer. Lee.9" arch 33 Ibs. 25 Ibs.10" " 37 " 30 "12" " 40 " 35 "15" " 40 "

Another step of progress lay in the skew-back or but-ment pieces,which gave a better bearing against the beamwebs by means of intermediate cross-ribs,s well as by thetop and bottom flanges.

Some very interestingand valuable tests of fire-prooffloor arches built after the Pioneer and Lee methods werepublished in No. 796 of the American Architect and Build-ng

News " undoubtedly forming one of the most satisfac-oryand extensive series of public tests yet attempted on

such construction. The trials were made in Denver, Col.,1892, for the Denver Equitable Building Company, underthe supervisionof a board of architects. The arches weresprung from beams placed 5 ft. centres, as shown in Fig.30,and the conditions included static loading, drop test, afire and water test, and a continuous fire test.

In the test for static loads the Lee arch deflected grad-


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uallyunder the increased weights to .065 of a foot,sustain-nga final load of 15,145 Ibs. for two hours. The Pioneer

arch gave way suddenly at the haunches under a load of5,429 Ibs.

In the drop test a piece of wood 12" X 12" X 4' waslet fall from a height of 6' o". The Pioneer arch was shat-ered

at the first blow, while the Lee arch, under the sametest, stood up to the eleventh drop, the former blows shat-ering

but parts of the arch.In the fire and water tests, three applicationsof water

combined with fire destroyed the Pioneer arch, while theLee arch received eleven applicationsf water, and at theend of twenty-threehours remained practicallyninjured,requiring eleven blows from the ram to break it.

In the continuous fire test the fire was maintained con-inuouslybeneath a Lee arch for twenty-four hours, and

the arch then supported a load of bricks of 12,500 Ibs. ona space 3'o" wide in the central portion of the arch.

Considering the static loads, the results may be betterjudged as follows :

This certainlyhows a great step of advancement forthe Lee arch, but, assuming a factor of safety of 8, asrecommended by Rankme, and a total load of 165 Ibs. persquare foot (85 Ibs. dead + 80 Ibs. live), uniform break-ng-load

of 1320 Ibs. per square foot is needed before thetile arch can be considered fullyacceptable.

Tests of the 12" blocks of the Empire Fire-proofingCompany might also be mentioned, made in 1891 by thecityengineer of Richmond, Va. A variation in the break-


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FLOORS AND FLOOR FRAMING. 6l

ing-loadwas recorded of from 554 to 1057 H"s. Per squarefoot. But it must be remembered that too much impor-ance

must not be placed on these maximum figures. Theaverage breaking-loads of such tests must be considered afair figureat which to judge the general run of arches asplaced in actual use by these companies; and in this lightthe room and actual necessityfor still further improve-ent

becomes self-evident.A still later patent known as " Johnson's patent flat

arch," (seeFig.31),is the one used most extensivelyin the

FIG. 31.

buildingsof late erection. It is made of hard terra-cottawith thinner webs than were formerly employed, and is ofthe " end construction," thus utilizingll of the material asin the Lee arch. This type seemed to meet with muchfavor at first,and it was used in quite a number ofChicago's best buildings,but experience would seem topoint to the porous tile as being far more satisfactorynits fire-resistingualitiesthan the hard tile. A test byfire and water of a wall of hard tile blocks occurred sometime ago in the rear of the Schiller Theatre Building,Chicago. The combined action of heat and cold watercaused the blocks to crack to such an extent that they soonfell from the metal uprights in considerable areas.

Soft tile or porous terra-cotta has been specifiedor allfire-proofingork in the latest buildingsdesigned by Mr.W. L. B. Jenney, notably the New York Life Insuranceand the Fort Dearborn buildings.


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Tie-rods are necessary in all these forms of arches, totake up the horizontal thrusts without dependence on theadjoining-rches. Such rods are generallyf inch diameter,and spaced from 5 to 7 feet apart. All tests of tile archesshould require the tie-rods to be without initial strain ; forif the rods be screwed up sufficientlyo give an initialstrain equal to the tensile strength of the tile or cement-ng

material between the blocks, then is the tensilestrength of the arch for the breaking-loadreduced to o,and the beam may be reloaded to the same amount.

Reference to the Appendix table giving the principalpoints of construction in the notable office buildings inChicago will show that either the " Pioneer," " Lee," or" Johnson's " type of floor arch is used in nearly everycase, although it must be admitted that such a general useof tile construction is far from being a guarantee of its per-ection.

Indeed, it is no exaggeration to say that there isscarcelya singlematerial used in constructional work inregard to which we have as limited a knowledge of itsgeneral or specificpropertiesof resistance as is found interra-cotta or tilework ; and yet, in the modern buildingthe use of this style of floor has become so widely ex-ended

that terra-cotta or hollow tile has become one of themost ordinary materials of construction. Its functions areno less positive than those of the structural steelwork ormasonry-work, forming, as it does, the supporting area forall dead and live loads coming on the floor system " crowdsin halls,theatres, and other places of public gathering, aswell as small safes,desks, and the many articles formingconcentrated loads.

Any failure in the hollow tile would be apt to resultin quite as great disaster or loss of life and limb as wouldproceed from any failure in the iron or steel skeleton. Itis apparent, therefore, that the sustaining power of hoi-


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64 ARCHITECTURAL ENGINEERING.figuresinto deceiving records of tests, as is often done, orto furnish poorer and poorer material as competition in-reases

and searching inquirydecreases.Rankine advises the use of % to \ the ultimate strength

in metals, \ to -^ in wood, and \ to \ in masonry. Consider-nghollow tile as coming under the head of the poorest

class of masonry, an ultimate strength should therefore berequired of eight times the allowable stress, if it is wishedto procure uniform safetyin a floor of steel beams and tilearches. Assuming an arch carrying a live load of 80 Ibs.per square foot,a dead load of 85 Ibs. per square foot (or 165Ibs. total),he manufacturer should be required to show bytests on the site that the type submitted is able safelytostand a load of 1320 Ibs. per square foot,and this beforebeing allowed to compete in the question of cost. Thewriter is aware of the objectionsof time and cost to suchmethods, but in this way only can the excellence be main-ained,

and assurance be provided that the floor arch iswhat it should be.

The unusual interest which is being displayed in thesubject of fire-proofloors,of tile and other materials,isevidenced by the series of articles but latelybegun in aperiodicaldevoted to the interests of the clay products.This series of articles contemplates a complete record, asfar as possible,of all tests on fire-proofarches of ordinarypatterns, up to present date, with comments on the causesof failure and possibilitiesf improvement. Such workcannot fail to be productive of the most beneficial results.

The writer believes that the section devoted to the arch-like action in present tile floors is still too small. This isindicated by the sudden collapse of many arches at thehaunches while under test. It would also seem, throughpast tests, that too much reliance has been placed in theuse of strong cementing materials between the blocks, thus


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FLOORS AND FLOOR FRAMING. 65,making the arch act as a monolithic piece. Hollow tileblocks, as

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