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By JOSEPH WHITE Engineer, Department of Public Works Allegheny County, Pe"nnsylvania and M. W. VON BERNEWITZ Mining and Metallurgical Engineer United States Bureau of Mines

First Edition

PUBLISHED BY

CRAMER PRINTING ~ PUBLISHING COMPANY CRAFTON STATION, PITTSBURGH, PENNSYLVANIA 1928 Copyright, 1928. by the CRAMER PRINTING 8 PUBLISHING COMPANY

Printed by the Cramer Printing 8 Publishing Company Engraved by the Liberty Engraving Company Bound by Tarner Bros. Pittsburgh. Pennsylvani;i -:-!'.:.....•, . . . .' .-.~ .. : __ :-~: ~ ··-\}t~·; ... .· ...

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(1.:.cproduccd by permission of tbe Pittsburgb Pboto-Engrm;mg Company.) THE BEGINNINGS OF PITTSBURGH-IN 1758.

(l.:.cpr.oduad by permission of Trinity Court Studios.) AIR VIEW OF PITTSBURGH IN 1928.

CONTENTS

Page Pittsburgh before the era of bridges and now ______Frontispiece Fore\vord ------VI How one may recognize various types of briqges ______1 The bridge as an architectural structure ______10 Influence of automobiles on modern bridge construction ______16 Negotiations necessary in building a bridge over a· navigable stream------20 Absence of toll bridges in the Pittsburgh District______2 3 Disastrous bridge fires a danger of the past______26 Vibrations in bridges______29 Photographic review: Our bridges as seen from a river steamer_ 3 1 Map showing position of bridges and when erected ______Facing 32 Monongahela River bridges ______.. 3 3 Youghiogheny River Bridges______45 Allegheny River bridges______4 7 Ohio River bridges------62 Beaver River Bridges______66 Bridges over ravines and minor streams______67 Railroad bridges ------7 4 Map ------Facing 7 4 Baltimore and Ohio Railroad Bridges______7 5 Bessemer and Lake Erie Railroad Bridges______75 Union Railroad Bridges ______. 7 6 Pennsylvania Railroad Bridges______76 Pittsburgh and Lake Erie Railroad Bridges______7 8 Pittsburgh and West Virginia Railway Bridges______78 Street railways and bridges______79 Map ------Facing 78 Hot-metal bridges ------80 Weight and cost of bridges------83 Technical description of the four bridges at Sixth Street, Alle- gheny River ------­ 84 First bridge ------­ 84 Second bridge ------84 Third bridge ______85 Fourth bridge ------86 Floating the Sixth Street bridge to Coraopolis ______91 Description of the suspension bridge formerly at Smithfield Street, across the Monongahela River ______95 Description of the suspension aqueduct formerly across the Alle­ gheny River at Eleventh Street ------97 Description of an old-type railroad bridge which formerly spanned the Monongahela River ______99 Corrosion of steel bridges ------101 Pittsburgh, a self-contained bridge-building community ______104 Acknowledgmen~ ------109 Index ------. __ _ 1 1 1

V FOREWORD.

EARS ago, three wide rivers-the Allegheny, Monongahela, and Ohio - divided the territory now defined as Allegheny YCounty into three separate areas. In 1818 the first river bridge was built; it spanned the Monongahela River at Smithfield Street. Since then our steadily growing community has been energetically knitting together its three-pieced fabric so that today 4 3 large river bridges unify the interests of this district. Over these structures every year pass many millions of people and more than 15 0 million tons of freight in trains, and under them pass more than 3 0 million tons of raw materials and manufactured products in vessels built in the district. Massive river structures, however, do not embrace the complete bridge system of our district. The Y oughiogheny River entering the Monongahela River at McKeesport; Turtle Creek flowing into the same river east of Braddock; Chartiers Creek emptying into the Ohio River at McKees Rocks; and the Beaver River flo\ving into the Ohio River at Rochester are large streams requiring bridges of fair size. The deep ravines of the district also require for traffic conven­ ience imposing structures such as the Panther Hollow Bridge in Schen­ ley Park; the John P. Moore Memorial Bridge at Knoxville; the Lincoln Avenue, Larimer Avenue, and Bloomfield Bridges in the eastern section of Pittsburgh; and the Jack's Run and California Avenue Bridges in the north borough areas. Including the 4 3 river bridges there are more than 500 bridges throughout the district, about one-quarter owned by the City and the remainder by the County. Truly we may be desigp.ated as The Region of Bridges. If nature divided our territory by wide waterways, compensat­ ingly she conveniently provided materials whereby these streams could be bridged. Growing on the hillsides were giant oaks from which our first bridges were fashioned. Protruding from these hills were quarries of durable stone for the early masonry bridges. In the

VI FOREWORD.

Allegheny Mountains were iron ores and near Pittsburgh was an abundance of good coal for making-coke for smelting these ores. Rock deposits with cement-making qualities were next found, and the river beds yielded clean sand and gravel. All of these materials are essential for the construction of durable steel and concrete structures. At an early date local bridge-building companies ,vere organized and pioneer bridge engineers came to the front, who not only bridged our own rivers but faraway rivers of the nation and distant nations. Not only may we be designated as The Region of Bridges, but also a self-contained bridge-building community. Undoubtedly many of us move about our daily tasks paying little heed to the bridges which enable us to cross rivers and ravines with convenience and safety. If these bridges were swept out of exist­ ence overnight, their almost incalculable importance to the commu­ nity would be forcibly impressed upon all. This book presents for the first time a compact and simple record of our bridges. It may help to stimulate wider local knowledge and greater national recognition of these structures, conceived by farseeing citizens; promoted by pro­ gressive public, railroad, and industrial officials; designed by skilled engineers and architects; constructed by enterprising steel-making and bridge-building companies, and erected by fearless workmen.

JOSEPH WHITE l\1. W. VON BERNEWITZ Pittsburgh, Pennsylvania, November, 1928.

VII

THE BRIDGES OF PITTSBURGH

HOW ONE MAY RECOGNIZE VARIOUS TYPES OF BRIDGES.

ROM its general appearance, a bridge may be readily recognized as a "deck bridge" or a ''through bridge.'' In the former, the roadway is open to the sky as the deck of ]f a ship; its supporting steel work is below the roadway, as in the Liberty Bridge. In through bridges much of the supporting steel is above the roadway, as in the Smithfield Street Bridge. As one crosses a through bridge on either side are great steel frames; over­ head are cross bracings of steel. From this aspect of passing through a lattice of steel is derived the term through bridge. Deck bridges, generally speaking, are more popular than through bridges because of the feeling of openness and the less obstructed view. Another reason volunteered by a friend of the authors has a distinctively feminine touch. This lady, proficient at bridge, declares that she does not understand how steelwork extending up into the air keeps a bridge roadway from falling down into the river; as she feels safer when the steel mass is underneath, between her footsteps and the water, she prefers deck bridges. In justice to popular sentiment, it can be appreciated that when the clearance space between the river and bridge is restricted because of the demands of river navigation, deck bridges cannot always be erected. On navigable streams the Federal Government requires a certain unobstructed space between the river at "pooi-full" and the under part of the bridge. Pool-full is the water level of a river poor established by the crest of the nearest dam below any bridge. Another classification of bridge types, less simple than the former, is based upon· structural design. There are five such types - arch, cantilever, suspension, truss, and plate girder. These types often vary ,videly in form; frequently more than one type is in­ cluded in a single bridge. Arch bridges of stone or masonry, old as antiquity, are readily recognized. By means of an arch, space can be spanned by unsupported stone blocks cut in such a way as to form a curve, which becomes self-supporting when locked together by a central key­ stone. There are several beautiful examples of stone arch bridges, large and small, in this district. Outstanding among the imposing large ones is the Pennsylvania Railroad Bridge over Silver Lake near Highland Park. THE BRIDGES OF PITTSBURGH

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STONE-ARCH BRIDGE OF PENNSYLVANIA RAILROAD CROSSING LINCOLN AVENUE STONE-ARCH, HIGHWAY AND STREET-CAR BRIDGE.

Steel-arch and reinforced-concrete arch·bridges are numerous here. The Robert McAfee Bridge over Woods Run is an example of the former type. The bridge leading to Schenley Park from Bigelow Boulevard is an example of a reinforced concrete arch. The steel-arch bridge is to be recognized not by the curve alone but also by the manner in which the arch conveys to solid earth the load which it supports. If this latter characteristic is understood, a steel arch will not be confused with other steel bridges which may happen to have an arched or curved member. If the reader will compare the picture of the steel-arch bridge over Panther Hollow ·with that of the proposed bridge over East Street, "\\7 hich is a cantilever bridge with curved bottom chord. it will be noted how the thrust of the arch is provided for in the Panther Hollo~r Bridge, ·whereas no provision is made for such a thrust in the East Street Bridge.

, i STEEL-ARCH HIGHWAY BRIDGE. CALIFORNIA AVENUE. NORTH SIDE, KNOWN AS THE ROBERT McAFEE BRIDGE. THE BRIDGES OF PITTSBURGH

REINFORCED-CONCRETE ARCH HIGHWAY BRIDGE LEADING TO SCHENLEY PARK FROM BIGELOW BOULEVARD

STEEL-ARCH HIGHWAY BRJDGE OVER PANTHER HOLLOW, SCHENLEY PARK. The lake below is used for boating in summer and skating in winter.

CANTILEVER HIGHWAY BRIDGE WITH CURVED BOTTOM CHORD OVER EAST STREET, NORTH SIDE. THE BRIDGES OF PITTSBURGH

A cantilever bridge projects over midstream and is so balanced that the projected_ part or bracket is counter-weighted and anchored down by the shore ends of the struc­ ture. I:ri a cantilever the stability of the structure depends upon shore anchorage, whereas the stability of the arch depends upon the locking member over midstream. Consequent­ ly, in a cantilever bridge, construction proceeds from the shore with no temporary sup­ ports over the river channel, whereas an arch during construction is usually supported

METHOD OF CONSTRUCTING A C.l\.NTILEVER BRIDGE WITHOUT OBSTRUCTING THE RIVER CHANNEL BY TEMPORARY SUPPORTS-THE LIBERTY BRIDGE OVER THE MONONGAHELA RIVER.

METHOD OF CONSTRUCTING A REINFORCED-CONCRETE ARCH BRIDGE USING TE.\IPORARY SUPPORTS-THE JOHN P. MOORE MEMORIAL BRIDGE, KNOXVILLE. See picture of the finished structure on page 72. . ' THE BRIDGES OF PITTSBURGH

until the arch is "sprung"-that is, until the locking member at the center is placed. Be­ cause it is not necessary to block a river channel during construction and to encounter the hazards of river floods, cantilever bridges are extensively used. Compare the photograph showing the Liberty cantilever bridge under construction with that showing the John P. Moore Memorial Bridge - an arch structure-under construction. Cantilever bridges differ widely in appearance. The Glassport-Clairton Bridge is a cantilever with bottom chord curved do,vnward. 'The Sewickley Bridge is a cantilever with top chord curved upward. The Point Bridge is a cantilever with both top and bot­ tom chords curved downward. The Highland Park Bridge over the Allegheny River is a cantilever with bottom chord curved down ward and top chord curved upward. · A simple way to recognize a cantilever bridge is to stand at a point where the entire structure can be viewed; if the general proportions of the bridge conveys the impression that the structure would remain standing if a section in the center were removed, it is probably a cantilever bridge. On the other hand, if it is apparent that the entire span would collapse if cut at center, it is not a cantilever.

• CANTILEVER BRIDGE WITH BOTTOM CHORD CURVED DOWNWARD -THE GLASSPORT-CLAIRTON HIGH- WAY BRIDGE OVER THE MONONGAHELA RIVER.

CANTILEVER BRIDGE WITH TOP CHORD CURVED UPWARD--THE SEWICKLEY HIGHWAY BRIDGE OVER THE OHIO RIVER. THE BRIDGES OF PITTSBURGH

CANTILEVER BRIDGE WITH BOTH TOP AND BOTTOM CHORDS CURVED DOWNWARD--THE POINT HIGHWAY BRIDGE OVER THE MONONGAHELA RIVER.

CANTILE\'ER BRIDGE WITH BOTTOM CHORD CURVED DOWNWARD AND TOP CHORD CURVED UPWARD--THE HIGHLAND PARK HIGHWAY BRIDGE OVER THE ALLEGHENY RIVER Any bridge whose roadway is hung to freely suspended cables, which pass over towers and are anchored to the shore at each end, is termed a suspension bridge. The suspension member may be either a wire cable or eye-bars linked together in chain-like form. The bridge over the Ohio River between Rochester and Monaca is of the cable type; the Sixth, Seventh, and Ninth Street bridges are of the eye-bar type. In a suspen­ sion bridge, once the cable has been extended across stream, construction can proceed without blocking the river channel, as the bridge is built from the cable down. Con­ versely, when a suspension bridge is being demolished, the cable is the last member to be removed. An extremely interesting statement regarding cable suspension bridges ap­ peared in The New York Times for November 4, 1928. 0. H. Ammann, chief engineer of bridges for The Port of New York Authority, in an interview by C. G. Poore, said that the suspension bridge is the type capable of the longest span. Cables are made by running single strands of wire back and forth ("spinning") across a river, squeezing them to the desired diameter, binding them, and then covering them. In the Rochester-Monaca Bridge there are 7 strands of 214 vvires in each cable, which has a diameter of 7 ¾ inches. Eye-bars are made of steel bars forged at the ends to disc-like heads through which holes are punched or drilled to receive the joint pins. In the alternate links of the Sixth Street Bridge there are 8 and 9 eye-bars, 14 inches in width and varying in thickness up to 2 inches. THE BRIDGES OF PITTSBURGH

CABLE SUSPENSION BRIDGE ACROSS THE OHIO RIVER BETWEEN ROCHESTER AND MONACA.

DISMANTLING THE OLD SEVENTH STREET BRIDGE OVER THE ALLEGHENY RIVER.

DISMANTLING TI IE OLD POINT BRIDGE OVER THE MONONGAHELA RIVER. Suspension member being cut by oxy-acetylene flame operated by The cut suspension member at the moment of falling bridge-worker suspended by derrick. into the river. THE BRIDGES OF PITTSBURGH

The Sixth, Seventh, and Ninth Street Bridges are a special suspension type known as self-anchored suspension bridges. 'The huge mass of shore masonry into which cables are an~hored in true suspension bridges is absent in these structures. In these bridges the eye-bar cables are anchored to the body of the bridge itself, most of the strain being taken up in the main girders of the bridge. This design requires that these girders be unusually heavy and deep. Part of these girders can be seen extending above the road­ '\\ray, separating the side,valk from the roadway. These were the first bridges of this type built in the United States. A truss bridge consists of framework of triangles whose ends are pin-connected or riveted to continuous top and bottom chords. The chords may be horizontal, inclined, or curved. Many of our bridges are built on this principle and are of widely different ap­ pearance. l~he Manchester Bridge is an example of a truss known as the "camel-back" type, as is the Pennsylvania Railroad Bridge at Eleventh Street. The Smithfield Street Bridge is a truss known from its appearance as the "fish-belly" type. It also resembles a flattened figure 8 lying on its side. The old Sixth Street Bridge ·which was moved to Co­ raopolis, is a truss knovvn as the · 'bO'w-string'' type.Truss bridges, if assembled in place, require temporary supports in the ri·ver chan!1e! during the course of construction.

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A BOW-STRING TRUSS BRIDGE. FOR~!ERLY AT S!XTH STREET. NOW CCNi':ECT!NG CORAOPOLIS 1'.ND NEViLLE'ISLAND. THE OLD BRIDGE IN THE BACKGROUND HAS BEEN DISMANTLED. A plate-girder bridge consists of a solid steel plate strengthened along the top and bottom edges ·with steel angles riveted or ,velded on. The main plate is aiso strength­ ened at certain panel lengths vvith steel angles placed vertically. The main plate is known as the web; the reinforced edges are called the flanges. Plate girders vary from 3 feet to 10 feet in depth and from 25 feet to 125 feet in length. A large plate girder can be seen ,vhere the Boulevard of the Allies crosses Forbes.Street. It is 9 ;,'i feet in depth and 125 _,..{;.( 8 l~~."- -·L Ji. THE BRIDGES OF PITTSBURGH feet in length. Plate girders are used on both short and long railroad bridges and high­ way bridges. They also frequently form a part of large river bridges - generally at the approach. Plate girders may be of the deck type, in vvhich the floor rests on the top flange, or of the through type, in which the floor is carried by the bottom flange.

PLATE-GIRDER BRIDGE CARRYING THE BOULEVARD OF THE ALLIES OVER FORBES STREET. The steel \Vork that comprises the bridge proper. is termed the "superstructure": the piers upon which this rests and the abutments that support the approach spans are knovvn as the ''substructure." Before piers can be built. borings have to be made to de­ termine the depth at which rock lies. In the Pittsburgh District, rock occurs beneath sand and gravel at a depth of 40 to 53 feet in the Allegheny River, 40 to 45 feet in the Monongahela River, and 34 to 40 feet in the Ohio River. Ordinarily a coffer-dam is next constructed around the site of the proposed pier. It consists of rows of piles or­ planks or interlocking sheet piles driven into the bottom of a river. The water that leaks in is pumped out by centrifugal pumps \Vorking on a barge. The bottom is next cleaned out to rock, the masonry is started and the concrete is poured; this is continued to the required height above pool-level. Piers are sometimes constructed by means of caissons, in which work is done under air pressure. The pictures on this page show a coffer-dam around a shore pier, also a completed pier.

CONSTRUCTION OF PIER FOR A RIVER BRIDGE, SHOWING A COFFER-DA1l AND J\ COMPLETED PIER.

-· .;':! '0l 9 i:,~···-r· A BEAUTIFUL BRIDGE, ARTISTICALLY ADAPTED TO ITS ENVIRONMENT, ALONG THE MOUNT WASHINGTON ROADWAY.

THE BRIDGE AS AN ARCHITECTURAL STRUCTURE

A discussion of the influence of art in the everyday affairs of life all too fre­ quently baffles the husy workaday world. Art coupled with the mechanics of a bridge structure might be made doubly baffling. The authors- are indebted to Stanley L. Roush, Pittsburgh architect who. through his connection with the Department of Public Works of Allegheny County and the City of Pittsburgh. has had much to do with the construction of our bridges. for this practical state­ ment on the bridge as an architectural structure. HE bridge, as an accomplishment of man's handiwork and one of the most dra­ matic things of life, has stirred man's imagination and constructive ability from 1L earliest times. When we see the highway leave its natural bed and soar through air on thin steel construction or on sturdy, massive stone arches, and when from this road­ way \Ve look into the dark flowing water beneath there is a deep-seated emotional reac­ tion to this human accomplishment. Artists and writers for centuries have appreciated this attraction and expressed its qualities in picture and in verse. It is the reaction of man to something vastly beyond him in size which has been brought about by his knowledge and constructive ability. On this psychological fact we have a firm founda­ tion for what should be, wherever possible, a work of art. During the last twenty years there has been an endeavor on the part of engineers, architects, and governmental authorities to improve the artistic design of bridges in the Pittsburgh district. This movement started with the formation of governmental art commissions-state and municipal-whose duty is to pass on the artistic merit of pub­ lic structures. In 1911 the Art Commission of the City of Pittsburgh was created by Act of Pennsylvania State Legislature; the Art Commission of the Commonwealth of Pennsylvania was created in 1919. As bridges especially influence the landscape, the local Art Commissions immediately determined that they be made more beautiful. To­ day \Ve see the results of this collaboration of architects and engineers in such structures as those at Sixth, Seventh, Ninth, and Sixteenth Streets, Washington Crossing, Mount Washington Roadway Bridge, and others. It is, however, not always possible to achieve an artistic bridge, though everyone connected with its erection desires it and though ample funds are available· for its con- THE BRIDGES OF PITTSBURGH

struction. Owing to mountainous topography there are more than 500 bridges in the Pittsburgh district, more perhaps than in any other comparable district in the world. On account of varied conditions of site, restrictions imposed by state and municipal governmental commissions, corporate interest affected, and funds available or reason­ ably advisable for certain positions, it is impossible to achieve an artistic result for the majority of these structures. We have bridges where the natural conditions alone have developed an artistic structure, and others where only through earnest cooperation be~ tween architects and engineers can reasonable success be attained. Important influences in the success or failure of bridge design arises in the first inception of the project; the architect should be consulted at the very beginning before such factors as position, grades, piers, clearances, and cost are determined. The appeal to the laymen and the thrill to the artist in the successful bridge design is largely psychic, and consists of a peculiar mental reaction to the mechanics of the problem, as balanced by the esthetic rule of human scale. Of what appeal is there in the typical cantilever or simple span railroad bridge on the thinnest of piers which will carry the load? The only appeal is to the engineer who knows the stresses of its mem­ bers, the economy of its construction, length of spans, and weight of loads carried. We all have passed over hundreds of such bridges without giving them a second thought. These bridges are not to be condemned; they may be doing the ,vork of the world eco­ nomically in a section or particular industrial district where more expensive types would be inappropriate. Such bridges, however, should not be built in populous cities or where the natural scenery is of impressive beauty. Beauty of a bridge generally ,vill be noted when the soaring roadway is supported underneath by \Vell-proportioned masonry or steel arches \Vhose thrust is received in adequate piers. Beauty will also be noted when the roadway is supported with spider­ like suspenders hung from cables gracefully draped over masonry or steel towers. In one bridge it is the power and strength of the arch that impresses; in the other it is the grace of the cables creating the wonder that such slight material can carry so great a load.

A SOARING ROADWAY CARRIED OVER ONE OF OUR DEEPEST RAVINES-THE JACK'S RUN BRIDGE. NORTH SIDE. The span is 3 2 0 feet; the roadway is 3 8 feet in width, with two 10-foot sidewalks. THE BRIDGES OF PITTSBURGH

Bridges are built with the supporting structure above the roadway for one of two reasons; first, some factor under the road\vay of the bridge is considered to be of more importance than its artistic appearance: or, satisfactory foundations for spans of rea­ sonable length are impossible; therefore we must have the structure above the roadway as the condition does not permit a single arch of long span below it. In my opinion, it is impossible to construct a bridge with the structure above the rca~hvay in a city of any size ·without destroying appearances to some extent. The structure itself may be beau­ tiful. but in relation to the city a pleasing effect is not created. Large bridges of the suspension type, if ·well designed may excite interest and admiration and under some conditions from certain points of view will make beautiful pictures, but like the sky..: scraper, they are destructive to civic art generally by reason of the approach. Where the length of span and height of crossing is of great magnitude or the relation of nat­ ural or artificial contrasts do not compete, the most economical engineering structure will sometimes be impressive, such as the Quebec Bridge over the St. La,vrer.ce River and the Firth of Forth Bridge in Scotland. It is a current erroneous opinion that a bridge to be beautiful must be elaborately embellished vvith ornamental features. This is not necessarily true; a bridge may be made beautiful without embellishment of any kind. However, if the general lines of the bridge are good and the environment of the structure justifies the expense, addi­ tional ornamental features properly placed and designed ,vill add to its appearance.

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THE ORNAMENTAL PORTAL OF THE MANCHESTER A PYLCN USED AS AN ORNAMENTAL FEATURE AT THE BRIDGE. APPROACH OF A BRIDGE. We can and should be proud of our bridges: but it is still possible to improve them in many v..rays, particularly in respect to the tern1.ination of the bridge with adjacent streets. In many instances \Ve are forced, by restrictive legislation, to stop the bridge structure at some definite line ,:vithout regard for its proper ending and its connection to the streets at either end. Ivlore property should be bought at bridge approaches so that unsightly buildings ,:vould not encroach on and spoil the appearance of the bridge. also so that the roadvi::ay\>f the bridge may be joined to the streets easily and gracefully with plenty of vision~· ·o·~ bridges at important points, ample funds should be allo\\red for architectural design, terminals, and approaches. THE BRIDGES OF PITTSBURGH

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THE SPACIOUS APPROACH TO THE NEW KENSINGTCN BR!DGE. Bridge road,vays and sidewalks should be ·wider ·wherever possible. This of course increases the cost and should be more carefully considered in preliminary estimates. Handrailings should be given more careful consideration. The appearance of the bridge from the roadway can be greatly improved at little additional expense if railings and lighting fixtures are properly designed. This effect may be observed in the railings of the Liberty Bridge and Mount Washington Roadway Bridge.

A PLEASING EFfECT OF A GRACEFUL BRID0E. THE BRIDGES OF PITTSBURGH

APPEARANCE OF A BRIDGE ENHANCED BY ARTISTIC HANDRAILS AND LIGHTING FIXTURES. This handrail is malleable iron and is said to be the first used anywhere. In the event of a collision, this iron will not break like cast iron, and is therefore much safer.

Beauty of the bridges may be helped by greater attention to-the colors used in paint­ ing the steel work and the care with which it is applied. There are endless combinations of colors which could be used to break the monotonous similarity we now have. To me personally. steel bridges are attractive in their first coat of vermillion paint. but un­ fortunately this color does not stand up under our weather conditions and has to be protected by other more permanent colors. The aluminum paint used extensively in the last few years has improved the appearance of many of our bridges.

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DETAIL OF A POST OF THE HANDRAIL SHOWN ABOVE. THE BRIDGES OF PITTSBURGH

AN ATTRACTIVE ORNAMENTAL LIGHTING FIXTURE ON ONE OF OUR BRIDGES. Pittsburgh has offered to the bridge designers and builders many opportunities and will continue to do so. Those who have a vision of a great and beautiful city should insist that legislators, engineers, and architects should build b!·idges that are increas- ingly suitable, substantial, and beautiful. ·· These opinions are shared by many others, and it is in order to add what trans­ pired at the sixth annual convention of the American Institute of Steel Construction, held at Biloxi. Mississippi in November, 1928. J. H. !vlcFarland, chairman of the Art Commission of Pennsylvania, said this: The delightful flexibility of the material you use will suggest to you and to those with whom you will associate yourselves, forms not always on the same old pattern, but running into new lines of beauty, no less efficient, no more expensive, but infinitely more sightly and therefore more satisfactory. 1\.. committee on the esthetic design of steel bridges recommended that an annual award be made to the bridge which would be chosen by a jury as the most artistic built during the year. The committee, among other things, recommended that an illustrated report on bridge design and esthetics be com piled. INFLUENCE OF AUTOMOBILES IN MODERN BRIDGE CONSTRUCTION

RIDGES, as many other elements of modern life, have been affected in several ways by the extensive introduction of automobiles. Unfortunately, in general. auto­ ]B mobiles have increased the costs of bridge structures. Bridges cross streams; railroads follo\v streams; inevitably the twain do meet. The crossing of railroad tracks at grade was never a safe experience, but with the extensive introduction of automobiles this practice has become so unduly hazardous that railroad grade cross­ ings at bridge approaches .in this district are being abolished. This necessitates longer and more expensive bridge structures. l\1any of the new bridges recently constructed in Allegheny County illustrate this fact, and a few examples are given. The new bridge near Crafton and Thornburg, crossing Chartiers Creek along the Steubenville Pike, abolished a dangerous railroad grade crossing and also corrected un­ favorable conditions at the bridge approaches. The length of the new structure is 718 feet and its cost $338,000. The bridge \vhichitreplaced, built in 1875, was 130 feet in length and cost approximately $6,500. The Nevv Kensington bridge over the Allegheny River abolished a railroad grade crossing at the New Kensington end. The length of the ne ..vV structure is 1,508 feet; its cost approximately $825,000. The structure which it replaced, built in 1900, vvas I, I 69 feet in length and was freed of tolls at a cost of approximately $ I 12,.140. The new bridge over the Monongahela River connecting the cities of McKees­ port and Duquesne abolished dangerous grade crossings over the tracks of the Penn­ sylvania, Pittsburgh f6 Lake Erie, and Baltimore 8 Ohio railroads. The new struc­ ture, not including the McKeesport approach is 2,251 feet in length; its cost was ap­ proximately $2,000,000. 1'he structure which it replaced, built in 1891 and freed of tolls at a cost of approximately $275,000, was 1,650 feet in length. In general, more liberal widths must be allowed on bridge roadways, due both to the increased width of automobiles and trucks, also because of the speed at which automobiles, trucks, and street-cars pass one another. The space allowed for clearance in passing must be greater than allo\ved for the slower moving vehicles of years ago. The large· river bridges have a roadway of 3 8 feet. THE BRIDGES OF PITTSBURGH

INSUFFICIENT CLEARANCE WHICH HAS DEVELOPED ON OLDER BRIDGES-THE BOSTON BRIDGE OVER THE YOUGH­ IOGHENY RIVER WHICH IS TO REPLACED. NOTE CAUTION SIGN AGAINST SKIDDING. The bridge roadway, unlike the normal roadway, is exposed to the weather un­ derneath as well .as above, so that a sudden drop in temperature may cause the forma­ tion of a treacherous film of ice not existing on the roadway approaches to the bridge. The unexpectancy to the casual driver of this condition often results in skidding. Tests are being made of new types of non-skidding bridge floors. One of 'the difficul­ ties is to effect non-skidding qualities without unduly increasing the roughness, as too rough a floor will cause excessive pounding by heavy trucks with solid ties. A smooth non-skidding surface is required. The placing of ashes on bridge floors during winter increases the maintenance cost; iikewise ashes and rain may form an acid which has a destructive effect on steel of the bridge. Caution signs on part of officials and careful driving on the part of automobilists must be the rule for the present. If it be assumed that skidding ,vill occur, the curbs along the bridge roadways must be higher than formerly to prevent the automobile from swerving across the side­ walk, thus endangering pedestrians or resulting in a possible fatal accident by crashing through the bridge rail. This is particularly true on deck-type bridges with their open-type roadway. The recent raising of the curbs on the Schenley Park Bridge along Wilmot Street is a noteworthy safety measure. Wooden floors, particularly wood plank floors, are expensive to maintain due to excessive automobile traffic, and heavy trucks with solid tires. Many of the present bridges are not strong enough to carry a modern concrete. asphalt, or brick road sur­ face. Steel traffic strips have been placed on many local bridges to avoid the constant repairing of wood floors. Such strips may be seen on the Smithfield Street Bridge. Drivers of automobi1es may have observed the defl~ction in County roads which occurs when old-time bridges are crossed. The explanation is that the shortest bridge possible is one at right angles to the creek. Formerly, regardless of the trend of the THE BRIDGES OF PITTSBURGH road, for economy, the shortest bridge possible was built. This quirk in the road direc­ tion, unimportant in the days of horse-drawn traffic, is retardant and hazardous to swift-moving automobiles. Many of these old bridges throughout the County are be­ ing reconstructed to suit the direction of the road rather than of the stream. This will necessarily increase the number of skew bridges-that is, bridges which cross streams obliquely.

AUTOMOBILES NECESSITATE REPLACEMENT OF NUMEROUS BRIDGES WHICH WERE SUITABLE FOR HORSE-DRAWN TRAFFIC .

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A SKEW-TYPE BRIDGE WHICH CORRECTS UNSUITABLE ROAD ALINEMENT. THIS BRIDGE, HOWEVER. CROSSES A RAIL­ ROAD WHICH RUNS OBLIQUELY TO THE STREET. THE BRIDGES OF PITTSBURGH

A notable example of this type of correction can be observed in the reconstructed Shades Run bridge on the Lincoln road in Penn Township, about one mile east from Pittsburgh's eastern boundary line. Formerly, the roadway approaches to this bridge zigzagged down a decline at each end of the bridge. In order to eliminate these danger­ ous bends and to form a straight-way approach to the bridge, the road,vay of the bridge was elevated 3 5 feet above its former level, the steel bents for carrying the new floor rest­ ing on the arches of the original bridge. In raising the floor, the length of the bridge structure was increased from 221 feet to 411 feet.

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AN EXAMPLE OF CORRECTING AN UNSUITABLE ROADWAY APPROACH WHICH INVOLVED NOTABLE LENGTHEN­ ING OF THE BRIDGE-THE SHADES RUN BRIDGE. ¼:~· ~.-· ~-.

NEGOTIATIONS NECESSARY IN BUILDING A BRIDGE OVER A NAVIGABLE STREAM.

The complexity of modern times is pointedly illustrated by the negotia­ tions necessary in the building of a bridge across a navigable stream. Likewise the legal, civic and industrial negotiations that must transpire before plans for a new bridge over such a stream can be advertised for construction constitute an element of engineering endeavor not fully appreciated by the people at large. Norma:n F. Brown. director of the Department of Public Works of Allegheny County. has furnished the following instructive statement on the detailed pro­ cedure required.

N order to build a bridge over a navigable stream, °: charter must first be obtained from the United States Congress. This charter must be passed upon by both the ] [ United States Senate and the House of Representatives, and signed by the Presi­ dent. This charter, however, is only provisional and requires that the plans of the bridge be approYed by engineers of the War Department. This is done only after the Chief of Engineers, through his local representative, holds a public hearing which is properly advertised for three ·weeks in the local newspapers. To this hearing all in­ terested parties are invited vvho may be in favor of the plan or opposed to it. If the plans do not have to be changed they are then sent for approval to v._r ashington with the recommendation of the United States District Engineer, and are then passed upon by the Chief of Engineers and forwarded to the Secretary of War for his final approval. An example of such a hearing is that held at McKees Rocks on October 24, 1928, when plans for a new County bridge over the Ohio River were discussed. The War Department. ho,vever, will not issue this permit for a bridge in Penn­ sylvania until the structure is first approved by the Pennsylvania State \\later and Power Resources Board, arid this body will not approve the bridge until the same is satisfactory to the Flood Commission of Pittsburgh. The War Department is interested in the navigability of the stream for com­ mercial development and national defense; the Flood Commission and the State Water and Power Resources Board are interested in preventing damage which might be caused by obstr·ucting the stream flow or altering the water levels on adjoining lands. These approvals take into consideration the effect of the bridge upon the river. Distances be­ tween piers, size, shape, position and number of piers, and clearances under the bridges are the factors which are given consideration in connection with these investigations. THE BRIDGES OF PITTSBURGH

As the bridge carries a public highway which must be properly inter-related with existing City streets and County highways, the plan of the bridge is submitted to the County Planning Commission, City Planning Commission, and Citizens Commit­ tee on City Plan for the consideration of its effect upon traffic conditions. The Plan­ ning Commissions take under consideration the position, width, grade, and approaches as well as the paved roadway of the bridge. To expedite their considerations, the three Planning Commissions appoint a committee with representatives from each, known as a Joint Planning Conference, and it is before this Conference that the plans of the bridge are presented and discussed. After these deliberations take place, the plans are considered by each of the constituent bodies of the three major Planning Commissions. After the Planning Commissions have approved the bridge as to its roadway, ap­ proaches, and grades, ordinances must be passed by the Council of the City of Pitts­ burgh and approved by the Mayor so that the grades and lines of the streets affected by the bridge can be established. The plans of a bridge at Pittsburgh after reaching this stage are ready to be ap­ proved by the Art Commission of Pittsburgh, which deals with the structure solely as to its form and esthetic appearance. This Commission is composed of seven men, among whom are representative architects, artists, sculptors, and business men. As a rule, several different studies of a bridge are submitted to the Commission for consid­ eration before its final approval on a type of bridge is obtained. If public utilities cross under or over the bridge it is necessary for the proposed bridge to be submitted to the Public Service Commission for approval. Numerous conferences are necessary with railroad officials and other utility companies interested before the plans are submitted to this Commission. The Public Service Commission sets a date and holds a hearing in Pittsburgh for the consideration of plans. Two or three railroad companies are nearly always inter­ ested in the proposed structure, inasmuch as it may cross their main tracks and require certain changes in their yard tracks to accommodate the new piers and any other mat­ ters of vital importance. Adjudication of costs must be determined by the Public Ser­ vice Commission where a liability rests upon the railroad corporation. The approval of bridge plans both as to design and construction details must then be obtained from the Grand Jury and Court of Quarter Sessions of Allegheny County before the County Commissioners are allowed either to advertise a contract or award same. Prior to a hearing before the Grand Jury for consideration of plans, the hearing must be advertised once a week for three consecutive weeks, in advance of the hearing, so that all interested citizens whose property might be appropriated or dam­ ag•ed in connection with the bridge construction may have an opportunity to present th1~ir views. After the Grand Jury gives approval, the Court of Quarter Sessions gives final authority to the County Commissioners to proceed with the letting of a construc­ tion contract. At the time the bridge is approved by the Grand Jury, individual dam­ age claims are not settled. These claims are settled later before a Board of Viewers, \vhose awards, if not satisfactory to either party, may be appealed to the Courts. THE BRIDGES OF PITTSBURGH

Briefly summarizing, after the approval of the United States Congress, the War Department, State Water and Power Resources Board, the Pittsburgh Flood Com­ mission, the County Planning Commission, the City Planning Commission of Pitts­ burgh, the Citizens Committee on City Plan, the Pittsburgh City Council, the Art Commission of Pittsburgh, the Public Service Commission of Pennsylvania, and the Grand Jury and Court of Quarter Sessions, the plans are submitted to the County Commissioners for approval. They then refer the plans and specifications to the County Controller, whose engineer reviews the plans before the contract is finally advertised. Before the contract is awarded, the proposed v.rork must be advertised once a week for three consecutive weeks. After the bids have been opened in public a tabu­ lation of the unit prices is compiled by the Engineering Department in conjunction with the Controller, and submitted to the County Commissioners who award the contract to the lowest responsible bidder. After the contractor has furnished the proper bond, actual work on the bridge may then be started. ABSENCE OF TOLL BRIDGES IN THE PITTSBURGH DISTRICT

~~~PREVAILING condition of the giant bridge system of the Pittsburgh District, of noteworthy consequence to citizens and taxpayers, is the fact that all of our high·way bridges are free to the public. There are no toll bridges among the .500 crossings throughout Allegheny County; nor in adjoining counties. During the past eight years there has been an extensive bridge building program in this district, and is to continue for some time to come as $14,000,000 has been voted for new structures. Throughout the United States there have been similar activities due to the demands for more and better high·ways and bridges for the use of automobiles. This sudden and extensive demand for expensive bridges has in many places revived the practice of the private :financing of such structures and recouping this by means of tolls. Alle­ gheny County is fortunate that its :financial condition is so healthy that all of its bridges may be :financed through public taxes: this is better than travelers buying in­ dividual tolls each time our rivers are crossed. Thirty-two years ago all of our large river crossings were toll bridges. The pres­ ent bridge across the Monongahela River, between Brady Street and South Twenty­ second Street, built by the City of Pittsburgh in 1896, was the first free river bridge in the district. · In 1897, the Point, Smithfield, and South Tenth Street Bridges over the Monon­ gahela River were purchased by the City of Pittsburgh and made free to the public. In 1904, through the joint effort of ·Washington County and Allegheny County, the inter-county bridge over the Monongahela River at Monongahela was made free. During December 19 I 0, the inter-County bridge over the )'.,.. oughiogheny River near Suterville was declared free by the joint action of the Commissioners of West­ moreland County and Allegheny County. On March I 6, 19 I 1, the following nine bridges were declared free by the Com­ missioners of Allegheny County: Sixth Street, Seventh Street, Ninth Street, Six­ teenth Street, and Thirtieth Street bridges over the Allegheny River; Third Avenue, Fifth Avenue, Thirteenth Street, and Fifteenth Street bridges over the Youghiogheny River. THE BRIDGES OF PITTSBURGH

On June 8, 1912, the Forty-third Street and Sharpsburg Bridges over the Alle­ gheny River and the bridge at Boston over the Youghiogheny River were made free. On December 6, 1913, the bridge over the Monongahela River between Eliza­ beth and \Vest Elizabeth was made free. In 1914, the present Manchester bridge over the Allegheny River at the Point was built by the City of Pittsburgh. It replaced the old Union Bridge, a private wooden structure on which tolls were charged. On June 16, 1915, the bridge over the Monongahela between Dravosburg and McKeesport was declared free; on June 1 7, 19 15, the bridge over the Monongahela River at Homestead kno"¼rn as Brown's Bridge; on June 18, 1915, the Highland Park Bridge over the Allegheny River; and on December 16 of the same y~ar the bridge over the Monongahela River bet\veen McKeesport and Duquesne. This makes a total of four large river bridges freed of tolls during the year 1915. On May l, 1916, the inter-county bridge over the Allegheny River at New Kensington was set free by the joint action of the Commissioners of Allegheny County and Westmoreland County. On June 2, 1917, Jack's Run Bridge, connecting the City of Pittsburgh and Bellevue Borough, was declared free to the public by the County Commissioners. The present structure was completed during 1925. On August 22, 1923, the bridge over the back channel of the Ohio River, con­ necting Neville Island and Coraopolis was made free. This left only two toll bridges. both over the Monongahela River, one at Rankin and one connecting Hays Boro and Glenwood. In the People's bond issue, approved April 22, 1924, was included an amount for the freeing of these t·wo bridges. The Rankin Bridge was declared free September 6, 1924; and the Hays-Glen"¼rood Bridge April 5, 1926. The significance of our free bridge system may be more intelligently appreciated if a more national viewpoint is taken on this very live subject of toll bridges. A year ago, according to a survey undertaken by the Bureau of Public Roads and submitted to the Committee on Roads, House of Representatives, 70th Congress, there were 4 2 4 toll bridges in operation, under construction, or proposed for which information was available. Of these at that date there "¼rere 233 toll bridges in operation on the highways of the United States-42 o·wned by the public and 191 owned by private in­ terests. The latter (and of course the former) are dependent for their income upon traffic flowing to them over highways built from public funds. In 13 States there are no toll bridges. In Pennsylvania there are 19 toll bridges in operation and five pro­ posed, but there are none in Allegheny, Beaver, and Westmoreland counties which are included in this brochure on our bridges. All of the old toll crossings have been bought by these Counties and made free to the public, many new structures free to all travel have been built, others are to be erected, and arrangements have been made for the re­ tirement of bonds issued to pay for these bridges. THE BRIDGES OF PITTSBURGH

The Federal report cited is a good analysis of the toll-bridge problem. It lists all of the structures; discusses their types, construction rating, capital outlay and earn­ ings; shows that the average yearly cost of service to the public of a toll bridge (not including taxes) is much higher than a free bridge (including sinking fund and in­ terest); tells how the Federal High-way Act can now grant financial aid in the con­ struction of publicly-operated toll bridges; and suggests that the rates of toll should be subject to regulation by suitable public agencies which also should have power to enforce necessary requirements as to methods of operation, the maintenance of the structure, and other matters in order to promote the public convenience and protect life and property. In its issue for July 19, 1928, the Engineering-News Record (New York) re­ views the problem throughout the country and argues that the new activity in the construction of large highway bridges is the outgrowth of the rapid development of high\vay use by motor vehicles, \vhich early revealed the inadequacy of existing facil­ ities for crossing the large rivers of the country. With this new growth of bridge construction has come the problem of private toll bridges. This development is due t9 the limited liability or willingness of public bodies to provide tax or bond money for costly bridges, and the readiness of private interests to finance such work on a toll basis. Ample proof has been shown of the service that private capital can render in this respect, but strong opposition has sprung up to the permanent laying of toll barriers across our road system. Publicly-built toll bridges, such as those at Phila­ delphia and Buffalo, have developed one answer to the conflict of conditions, and eventually public initiation and prosecution of such enterprises can be improved nearly to the point of equaling private enterprise. Progress toward a solution is slow. The final result, though it can not yet be foreseen definitdy, is unlikely to be such as to maintain perpetual tolls, but will in due time make the entire highway transport system a network free to travel. Mean-\vhile much remains to be done before the country's road system will have adequate connection at major streams. Great activity in the building of highway bridges will undoubtedly continue for at "least a number of years to come. In its issue for July 28, 1928, The Saturday Evening Post takes the stand that the automobilist demands the shortest and most convenient route, and prefers to have toll bridges erected at once by private capital rather than await their slow completion out of necessarily limited public funds. The public is protected from excessive charges by the fact that net earnings tend to increase through a reduction of rates, and the principle of recapture by the public at the end of a stated period is well recognized by private capital. Another way out lies in the construction, ownership, and opera­ tion of toll bridges by the State itself. Exclusive reliance upon private enterprise hardly seems wise; sole dependence upon public action will fail to provide adequate facilities. The journal cited feels certain that neither highways nor bridges are going to be free; they must be paid for, and it only clouds the work to call them free. . - .. --_, __ ,,., - -... -; - . ' ·" -- ·:::..~:~~~~~--~J'r>'-

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DISASTROUS BRIDGE FIRES A DANGER OF THE PAST

ODERN bridges of steel and concrete are not subject to the danger of fire as in ~ [ the days ·when bridges ,vere built of timber. Insurance against fire, once cur- ~ rent practice, is no longer carried on modern bridges. Several disastrous bridge fires have occurred in this district in the past; recaliing them ,vill serve to em­ phasize the advance made in modern bridge cons~ruction methods. The covered wooden bridge over the Monongahela River, at Smithfield Street, our first river bridge, built in 1818, was destroyed in the famous fire of 1845. It ,vas immedi­ ately replaced by a suspension bridge designed by Roehling; this bridge in turn ,vas replaced in 1883 by the present structure. The covered wooden bridge across the Allegheny River at Sixteenth Street. built originally in 183 7 had an unusually checkered career. It was completely de­ stroyed by fire January 26, 1851. It was immediately rebuilt only to have two of its spans ,vashed away in the flood of June, 1865. Rebuilt again, its wooden super­ structure was completely destroyed by fire April 23, 1918. The present modern structure was completed in 1923. THE BRIDGES OF PITTSBURGH

The bridge at Thirtieth Street, across the main channel of the Allegheny at Herr's Island, built in 1887, was burned on July 8, 1921. Free ferry service was established until the present suspension foot bridge was erected by the County. A modern steel and concrete bridge is now under construction at this point. The floor system of the Roehling suspension bridge over the Allegheny River at Sixth Street, built in 1860, was seriously damaged by a mysterious fire on June 19th, 1881. Most of the superstructure of this bridge was iron: the floor joists how­ ever were of 4 by 18-inch white pine on top of ,vhich was a course of 2 ½-inch white pine plank laid transversely; on this was a course of 3-inch v{hite oak laid horizontally. ·------■

DESTRUCTION BY FIRE OF THE THIRTIETH STREET BRIDGE, ALLEGHENY RIVER ON JULY 8, 1921. At the time of this fire there vvas great local consternation due to the import­ ance of the bridge and because it was considered to be non-flammable. Various theories of ho\\r the fire started were rife-a burst gas pipe; spontaneous combustion; incendiarism, and others. The bridge was set afire by some evil designed person, and 'Old Peter,' the night man at the Allegheny Toll House, said last night there was no doubt in his mind but that it was set on :fire.-Pittsburgh Dispatch, June 20, 1881. THE BRIDGES OF PITTSBURGH

The culprits were finally tracked to their lair by none other than John Harper, president of the bridge company. His expose', given in the Pittsburgh Dispatch for June 20, 188 L is interesting: Another theory of the manner in which the fire caught was given by Mr. Harper. He says 'those feathered English pests. the sparrows, had built a good many nests on the under part of the bridge, and in the fabrication of these. the birds used great quantities of hay, straw, and other combustible material. Several steam boats passed under the bridge yesterday and their smoke stacks came near the bridge at the present stage of water." He rejects the burst gas pipe theory, spon­ taneous combustion theory and all others, and considers that the sparks and perhaps flame from the stacks set fire to the nests and from thence the bridge caught. The term ":fireproof' is commonly used erroneously, but a glance at a modern bridge shows that there is not any flammable material in its construction, hence it is :fireproof. VIBRATIONS IN BRIDGES

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A second story found its way into the Proceedings of this same Engineer's ~ociety. During one of the meetings held in the year 18 91, devoted to the discussion of the strains set up in bridges, it was asked by 0. P. Scaife if any of the engineers had ever determined by actual measurement the strains set up in the various bridge members. Max J. Becker made this reply: The only thing I know of was the attempt of a learned professor in a techni­ cal school. He calculated that if a fiddle string sustaining a certain amount of tension would give so many vibrations per second producing low G or high Fas the case might be. then the members of a bridge might be tuned up the same way. If loaded to a certain strain they would sing one song: if improperly loaded they would sing another: so that he ( the professor) might go on a bridge and play some tune like Yankee Doodle and if there were no false notes the structure would be all right. A waik across any of our new bridges, and halting at say one-third across, at the center, and at two-thirds across will reveal that beyond the rumble of street­ cars there is virtually no vibration. PHOTOGRAPHIC REVIEW: OUR BRIDGES }\.S SEEN FROM A RIVER STEAMER

~~:SiLL OF our river bridges can be seen from the city streets and from the highways which parallel the three rivers; but the best way to study the structures is from the deck of a river boat. This the authors have done several times, and the vievvs on the following pages show what may be seen, together with pictures of some of the bridges that preceded the present structures. The map and table show their position, when erected, and for what purpose. The boat trip starts at the Point, proceeds up the Monongahela River to Elizabeth and returns to Pittsburgh; up the Allegheny River to Free­ port and returns to Pittsburgh; and then down to Beaver on the Ohio River. THE BRIDGES OF PITTSBURGH

List of river bridges in Allegheny County and some in adjoining counties. as shown on the map facing this page. Monongahela River: Year erected 1. Point Highway Bridge ______l 876 2. Wabash Railroad Bridge near Ferry Street______1904 3. Smithfield Street Highway Bridge (first highway bridge) ______l 818 4. Pennsylvania Railroad Bridge to Fourth Avenue Station ______l863 5. Liberty Highway Bridge to Liberty Tunnel______1927 6. South Tenth Street Highway Bridge ______I 8 61 7. South Twenty-Second Street Highway Bridge ______189 6 8. Monongahela Connecting Railroad Bridge (hot metal) ______I 887 9. Highway Bridge at Hays Borough ______l895 10. Baltimore ~ Ohio Railroad Bridge at Glenwood ______1882 11. Highway Bridge at Homestead Borough ______J 8 94 12. Pittsburgh ~ Lake Erie Railroad Bridge at MunhalL ______l 883 13. Union Railroad Bridge at Rankin (hot metal) ______190 I 14. Highway Bridge at Rankin Borough ______1897 15. Union Railroad Bridge at Port Perry (hot metal) ______J 898 16. Pennsylvania Railroad Bridge at Port Perry ______l 874 l 7. McKeesport-Duquesne Highway Bridge ______I 891 18. McKeesport Connecting Railroad Bridge ______1890 19. Highway Bridge at Dravosburg Borough ______l889 20. Glassport-Clairton Highway Bridge ______} 928 21. Union Railroad Bridge at Clairton ______1903 22. Highway Bridge at Elizabeth Borough ______l893 23. Inter-County Highway Bridge at Monongahela ______-:,. ______1838 Allegheny River: 24. Manchester Highway Bridge at the Point______1874 2 5. Sixth Street High way Bridge ______l 81 9 26. Seventh Street Highway Bridge ______1885 2 7. Ninth Street Highway Bridge ______J 840 28. Pennsylvania Railroad Bridge (first railroad bridge) ______185 7 2 9. Sixteenth Street Highway Bridge __ ------183 7 30. Highway Bridge at Thirty-first Street over Herrs Island ______l 887 31. Baltimore ~ Ohio Railroad Bridge at Herrs Island ______1884 3 2, Washington Crossing Memorial Bridge at Fortieth Street______I 870 3 '3. Highway Bridge at Sharpsburg Borough ______1856 34. Highway Bridge, Highland Park to Aspinwall Borough ______1902 3 5. Pennsylvania Railroad Bridge (Brilliant cut-off) ______190, 36. Highway Bridge at Oakmont Borough ______1909 3 7. Bessemer ~ Lake Erie Railroad Bridge------1897 3 8. Inter-County Highway Bridge at New Kensington ______1900 3 9. Inter-County Bridge. Natrona to Braeburn (not completed) ______1929 Highway Bridge at Freeport to Garvcr·s Ferry------Pennsylvania Railroad Bridge at Freeport------___ J 914 Ohio River: 40. West End-North Side Highway Bridge ( not completed) ______1930 41. Ohio Connecting Railroad Bridge at Brunot Island ______l 888 42. Highway Bridge at McKees Rocks Borough (not completed) ______J 931 4 3. Highway Bridge at Sewickley Borough ______J 91 I Highway Bridge between Ambridge and Aliquippa______I 927 Highway Bridge between Rochester and Monaca ______I 896 Pittsburgh ~ Lake Erie Railroad Bridge between Beaver and Monaca______191 0 Beaver River: Pennsylvania Railroad Bridge at Rochester______19 I 8 Pennsylvania Railroad Bridge between Beaver Falls and New Brighton, and ad- jacent bridges ______l 926

In the above table. the year given does not indicate when the present structure was completed. but the year the river was spanned for first time at a given point. In some cases. in rebuilding a bridge, the site of the new structure was moved up or down stream from the original site, but the later structure fulfilled the purpose of its predecessor. The present Sixth Street Bridge is the fourth structure at that site. WOODLAWN•

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ABETH j3RIDGE MAP OF .ATJEGBENY COUNTY LEGEND HIGHWAY BRIDGE--­ NQY-1928 RAIL ROAD BRIDGE_ )OOiiiiflifl( Sc.t.1.E .1 lH. -.SOOO FT. PROPOSED 8RIDGE~ ) ■ •I ( 0 ,S. IO • JI) - RAVINES & MINOR SrREAMS- -

THE BRIDGES OF PITTSBURGH

MONONGAHELA RIVER BRIDGES

THE OLD AND NEW POINT BRIDGES AT THE CONFLUENCE OF THE MONONGAHELA AND ALLEGHENY RIVERS. The former was an eye-bar suspension: the new structure is a through cantilever highway and street-car bridge. Note the congestion on the old bridge a few days before the new one was opened to traffic. THE BRIDGES OF PITTSBURGH

THROUGH CANTILEVER BRIDGE. PITTSBURGH AND WEST VIRGINIA RAILWAY, KNOWN AS THE WABASH BRIDGE. THE BRIDGES OF PITTSBURGH

PITTSBURGH END OF THE FIRST SMITHFIELD STREET BRIDGE. BUILT IN l 818. From a painting by Leander McCandless. Esquire. given by Colonel Edward Jay Allen to the Historic.:il Socic~y of Western Pennsylvania. This picture is of the year 1825. The first house on the left is that of General William Wil­ kins, where many notables were entertained. The next building is a woolen mill and the site of the first free school in Pittsburgh and the site of the present Monongahela House. The buildings beyond are Irwin's Tavern. a famous old hostel; Anderson· s mansion: and Bakewell' s glass works. On the river are two "pi rogues." a craft poled by hand. Near the bridge a high sand bar had a crop of rye raised on it in 18 2 5. ( See Frontispiece.)

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THE SECOND BRIDGE AT SMITHFIELD STREET, BUILT IN 1846 BY JOHN A. ROEBLING. AS DESCRIBED ON PAGE 95. (From a print in the Historical Society of \Vestern Pennsylvania. Lithographed by Tappen and Bradford, Boston; published by G. W. Smith. New York.) THE BRIDGES OF PITTSBURGH

FORMER AND PRESENT PORTALS OF THE SMITHFIELD STREET BRIDGE

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PRESENT THROUGH-TRUSS HIGHWAY AND STREET-CAR BRIDGE AT SMITHFIELD STREET. THE BRIDGES OF PITTSBURGH

THROUGH-TRUSS BRIDGE OF PENNSYLVANIA RAILROAD FROM FOURTH AVENUE STATION TO THE SOUTH SIDE.

THE LIBERTY BRIDGE, A DECK CANTILEVER HIGHWAY BRIDGE. Beyond are the Pennsylvania Railroad, Smithfield Street and Mount Washington roadway bridges, also one of the seven inclines in the district. THE BRIDGES OF PITTSBURGH

THROUGH-TRUSS HIGHWAY AND STREET-CAR BRIDGE AT TENTH STREET. This is soon to be replaced.

THROUGH CANTILEVER HIGHW:\ Y AND STREET-CAR BRIDGE AT TWENTY-SECOND STREET.

THROUGH-TRUSS PLATE-FLOOR AND OPEN-TIE. HOT-METAL BRIDGE OF MONONGAHELA CONNECTING RAILROAD, ABOVE THE TWENTY-SECOND STREET BRIDGE. THE BRIDGES OF PITTSBURGH

THROUGH-TRUSS HIGHWAY AND STREET-CAR BRIDGE AT GLENWOOD.

THROUGH-TRUSS BRiDGE OF BALTIMORE AND OHIO RAILROAD AT GLENWOOD.

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THROUGH-TRUSS HIGHWAY AND STREET-CAR BRIDGE AT HOMESTEAD. THE BRIDGES OF PITTSBURGH

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DECK-TRUSS AND THROUGH-TRUSS BRIDGE OF THE PITTSBURGH AND LAKE ERIE RAILROAD AT MUNHALL. The far end of this structure runs into the Ho::nestead Works of the Carnegie Steel Company.

THROUGH-TRUSS HOT-METAL BRIDGE OF THE UNION RAILROAD AT RANKIN. THE BRIDGES OF PITTSBURGH

THROUGH-TRUSS HIGHWAY AND STREET-CAR BRIDGE BETWEEN RANKIN AND MUNHALL. •. ,: -t;~il~l4t1 . ,' .~· ~ ... . •... .. :.··- ~;... .

TWO BRIDGES AT PORT PERRY. Beyond 1s the through-tru.:s hot-metal bridge of the Union Railroad: in the foreground is the deck-truss and through-truss bridge of the Pennsylvania Railroad. THE BRIDGES OF PITTSBURGH

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THROUGH-TRUSS COUNTY HIGHWAY BRIDGE BETWEEN DUQUESNE AND McKEESPORT

THROUGH-TRUSS AND DECK-TRUSS BRIDGE OF McKEESPORT CONNECTING RAILROAD AT McKEESPORT. THE BRIDGES OF PITTSBURGH

THROUGH-TRUSS HIGHWAY AND STREET-CAR BRIDGE BETWEEN DRAVOSBURG AND McKEESPORT.

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GLASSPORT-CLAIRTON DECK-CANTILEVER HIGHWAY BRIIXiE. THE BRIDGES OF PITTSBURGH

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THROUGH-TRUSS BRIDGE OF THE UNION RAILROAD ACROSS THE MONONGAHELA RIVER AT CLAIRTON. This bridge is for general traffic. It has space for two tracks, but only one is used. There is provision. as can be seen. for an upper deck for vehicular traffic, but it is doubtful whether this will ever be used. The bridge is 113 9 feet in length and weighs 3 5 9 8 tons. It was erected in I 9 0 3.

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THROUGH-TRUSS HIGHWAY BRIDGE AT ELIZABETH. THE BRIDGES OF PITTSBURGH

THROUGH-TRUSS HIGHWAY BRIDGE AT MONONGAHELA.

YOUGHIOGHENY RIVER BRIDGES

NEST OF BRIDGES AT CONFLUENCE OF THE YOUGHIOGHENY AND MONONGAHELA RIVERS AT McKEESPORT. THE BRIDGES OF PITTSBURGH

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THROUGH-TRUSS AND DECK HIGHWAY AND STREET-CAR BRIDGE AT McKEESPORT.

THROUGH-CANTILEVER BRIDGE FARTHER UP THE YOUGHIOGHENY RIVER-THE BOSTON BRIDGE. THE BRIDGES OF PITTSBURGH

ALLEGHENY RIVER BRIDGES

THE UNION BRIDGE, A WOOD-FRAME STRUCTURE, THE PREDECESSOR OF THE PRESENT MANCHESTER BRIDGE.

THE MANCHESTER BRIDGE, A THROUGH TRUSS, AT THE CONFLUENCE OF THE ALLEGHENY AND MONONG.A.HELA RIVERS. Beyond is the Point Bridge. THE BRIDGES OF PITTSBURGH

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FIRST BRIDGE (IN FOREGROUND) AS IN 1849. (From a print in the Historical Society of Western Pennsylvania. Lithographed by Tappen and Bradford, Boston: published by G. \V. Smith. New York.)

SECOND BRIDGE. THE BRIDGES OF PITTSBURGH

THIRD BRIDGE.

FOURTH AND PRESENT BRIDGE.

FOUR GENERATIONS OF BRIDGES OVER THE ALLEGHENY RIVER AT SIXTH STREET. First bridge (page 48)-Wood-frame structure built in 1819. Second bridge (page 48)-Cable-suspension type built in 1859. Third bridge-Through-trus:. bow-string type built in 1892. Fourth bridge-Self-anchored eye-bar su'."pension type built in 1928. THE BRIDGES OF PITTSBURGH

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THE OLD SEVENTH STREET BRIDGE.

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BRIDGING THE ALLEGHENY RIVER-THE NEW SEVENTH STREET BRIDGE UNDER CONSTRUCTION. THE BRIDGES OF PITTSBURGH

THE OLD NINTH STREET BRIDGE.

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OLD PIER OF NINTH STREET BRIDGE IN STATE OF DISINTEGRATION WHEN DEMOLISHED. THE BRIDGES OF PITTSBURGH

THE NEW NINTH STREET BRIDGE UNDER CONSTRUCTION.

THE TRINITY OF BRIDGES-AT SIXTH, SEVENTH. AND NINTH STREETS-OF HEAVY CONSTRUCTION, YET GRACEFUL IN SIMPLE LINES. THE BRIDGES OF PITTSBURGH

THROUGH-TRUSS AND CAMEL-BACK TRUSS BRIDGE OF THE PENNSYLVANIA RAILROAD AT ELEVENTH SRTEET. Upper picture-the bridge in 1911. before raising. Lower pi.:turc-the bridge in 1 918. during raising operations. THE BRIDGES OF PITTSBURGH

THROUGH-TRUSS HIGHWAY AND STREET-CAR BRIDGE AT SIXTEENTH STREET.

CONSTRUCTING THE DECK-ARCH BRIDGE AT THIRTY-FIRST STREET. Beyond is a temporary cable suspension bridge to Herr's Island. THE BRIDGES OF PITTSBURGH

THROUGH-TRUSS BRIDGE OF BALTIMORE AND OHIO RAILROAD AT THIRTY-THIRD STREET. THE BRIDGES OF PITTSBURGH

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THE OLD WOOD-FRAME BRIDGE AT FORTY-THIRD STREET, REMOVED IN l 924 WHEN THE BRIDGE SHOWN BELOW WAS OPEN FOR TRAFFIC.

THE WASHINGTON CROSSING MEMORIAL DECK-ARCH HIGHWAY BRIDGE AT FORTIETH STREET- A HANDSOME STRUCTURE. THE BRIDGES OF PITTSBURGH

THROUGH-TRUSS HIGHWAY AND STREET-CAR BRIDGE BETWEEN MORNINGSIDE AND ETNA.

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DOUBLE-CANTILEVER HIGHWAY AND STREET-CAR BRIDGE FROM HIGHLAND PARK TO ASPINWALL. THE BRIDGES OF PITTSBURGH

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THROUGH-TRUSS BRIDGE (THE BRILLIANT CUT-OFF) OF THE PENNSYLVANIA RAILROAD TO ASPINWALL.

THROUGH-TRUSS HIGHWAY BRIDGE AT OAKMONT. THE BRIDGES OF PITTSBURGH

TWO VIEWS OF THE DECK-TRUSS BRIDGE OF THE BESSEMER AND LAKE ERIE RAILROAD NEAR CHESWICK. THE BRIDGES OF PITTSBURGH

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THROUGH-TRUSS INTER-COUNTY (ALLEGHENY AND WESTMORELAND) HIGHWAY AND ST~EET-CAR BRIDGE AT NEW KENSINGTON. THE BRIDGES OF PITTSBURGH

THROUGH-TRUSS HIGHWAY BRIDGE AT FREEPORT.

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THROUGH-TRUSS BRIDGE OF THE PENNSYLVANIA RAILROAD AT FREEPORT. THE BRIDGES OF PITTSBURGH

OHIO RIVER BRIDGES

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DECK-TRUSS AND THROUGH-TRUSS BRIDGE OF THE PENNSYLVANIA RAILROAD ACROSS THE BACK CHANNEL (IN FOREGROUND), BRUNOT ISLAND, AND THE MAIN CHANNEL OF THE OHIO RIVER. This is the Ohio Connecting Bridge. THE BRIDGES OF PITTSBURGH

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THE FLOOR SYSTEM OF THE TRUSS OF THE BRIDGE SHOWN ON THE OPPOSITE PAGE, ACROSS THE MAIN CHANNEL OF THE RIVER. THE BRIDGES OF PITTSBURGH

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Tl;!ROUGH-CANTILEVER HIGHWAY AND STREET-CAR BRIDGE AT SEWICKLEY.

THROUGH-CANTILEVER BRIDGE BETWEEN AMBRIDGE AND ALIQUIPPA. The total length is 1907 feet, with a 27-foot roadway and 9-foot walk. The height above pool-level is 76 feet. THE BRIDGES OF PITTSBURGH

CABLE-SUSPENSION HIGHWAY AND STREET-CAR COUNTY BRIDGE BETWEEN ROCHESTER AND MONACA. It was built in 1896 and is now being superseded by a bridge somewhat similar to that between Ambridge and Aliquippa. The channel span is 800 feet in length.

THROUGH-CANTILEVER AND THROUGH-TRUSS BRIDGE OF THE PITTSBURGH AND LAKE ERIE RAILROAD BETWEEN BEAVER AND MONACA-AN IMPRESSIVE STRUCTURE. THE BRIDGES OF PITTSBURGH

BEAVER RIVER BRIDGES.

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THROUGH-TRUSS BRIDGE OF THE PENNSYLVANIA RAILROAD AT THE MOUTH OF THE BEAVER RIVER.

(Original panorama by P. L. .A.!abaffey of tbe Pennsylvania News.) DECK-TRUSS BRIDGE (THE DIAGONAL ONE) OF THE PENNSYLVANIA RAILROAD BETWEEN BEAVER FALLS AND NEW BRIGHTON. The Railroad Company and Beaver County exchanged bridge sites: that in the foreground was a highway bridge: the company gave the third bridge shown to the County for its old highway bridge so that the new railroad bridge could be built as shown. The former highway bridge h~s been dismantled. BRIDGES OVER RA VINES AND MINOR STREAMS

~ T ITHIN the City of Pittsburgh are many important and ~~ handsome bridges crossing ravines and creeks. U nfortu­ r ' nately, the beauty of many of these steel or concrete struc­ tures cannot be seen unless from a distant point; in fact, save for the 'high parapet or railing on each side. the roadway appears almost to be an ordinary highway. Within the County of Allegheny are also many important bridges crossing ravines and minor streams. Of course, these structures are not, nor-should they be, of such design as are found in the city; nevertheless, they are worthy and practical bridges. A selection of views of City and County bridges will now be given: THE BRIDGES OF PITTSBURGH

SPANDREL-ARCH ( 180 FEET) BRIDGE ON BAUM BOULEVARD ABOVE THE BALTIMORE AND OHIO RAILROAD.

SPANDREL-ARCH BRIDGE ON MURRAY AVENUE.

REINFORCED-CONCRETE BRIDGE AT HOVELER STREET. Color was used in the concrete for this bridge and with satisfactory results. THE BRIDGES OF PITTSBURGH

SPANDREL-ARCH (312 FEET) BRIDGE ON LARIMER AVENUE OVER THE WASHINGTON BOULEVARD.

HAIGHT'S RUN BRIDGE. THE BRIDGES OF PITTSBURGH -

STEEL-ARCH BRIDGE OVER FERN HOLLOW, FRICK WOODS.

THE BLOOMFIELD BRIDGE, A DECK CANTILEVER ABOVE THE PENNSYLVANIA RAILROAD. Upper picture--extending the brackets. Lower picture-the cantilever finished. THE BRIDGES OF PITTSBURGH

STONE-ARCH BRIDGE OVER-SEWICKLEY CREEK.

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A STONE BRIDGE OVER ROBINSON RUN IN OAKDALE BOROUGH. THE BRIDGES OF PITTSBURGH

TWO TYPES OF ORDINARY SHORT HIGHWAY BRIDGES.

THE SAME BRIDGE AS SHOWN UNDER CONSTRUCTION ON PAGE 4. The main span is 210 feet in length; the roadway is 27 feet wide, with two 6-foot sidewalks. THE BRIDGES OF PITTSBURGH

THROUGH-TRUSS HIGHWAY AND STREET-CAR BRIDGE CONNECTING NEVILLE ISLAND WITH THE LEFT BANK or- THE O:--1.IO.

DECK-TRUSS HIGH\VAY BRIDGE OVER CHARTIERS CREEK BETWEEN CRAFTON AND THORNBURG. This bridge eleminated a dangerous railroad crossing and corrected an unsatisfactory road alinement. :~~~~(.:'::-- _:;_ ~1,;g;-1,,°',_,_£,7_. -·

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VIADUCT UNDER CONSTRUCTION BY ALLEGHENY COUNTY. Compare this steel and concrete construction with the wooden trestle ( on the righi:) it is to replace. It will carry the Duquesne boule­ vard and street-cars over many railroad tracks in Duquesne. -◄ 73 ►·- RAILROAD BRIDGES

ITTSBURGH is a major railroad center and is served by 22 steam railroads. Six of these are trunk lines, and over their own rails thes~ roads reach almost three­ ]P quarters of the cities and towns of this country with populations exceeding 50,000. The other 16 lines are industrial and terminal-switching railroads. The prin­ cipal lines are the Baltimore 8 Ohio; Bessemer 8 Lake Erie, including the Union Rail­ road; Buffalo, Rochester 8 Pittsburgh; Pennsylvania; Pittsburgh 8 Lake Erie (New York Central); and Pittsburgh 8 West Virginia, including the West Side Railroad. They enter and leave the Pittsburgh district, which means crossing the rivers, over a dozen main bridges of varied design and length. This is within the limits of Freeport on the Allegheny River, McKeesport on the Monongahela River, and Beaver on the Ohio River. The accompanying map shows the several routes. The total movement of freight by the railroads exceeds 150,000,000 tons a year. The most concentrated traffic of the Pennsylvania System is within the Pittsburgh district, and as through traffic predominates, the district is really a gateway for this rail­ road. Although only part of the through business of the Baltimore 8 Ohio System passes through Pittsburgh, its total business here assumes large proportions. The Pitts­ burgh 8 Lake Erie System is an important artery to Pittsburgh, and although the greater part of the traffic originates within the district, all of it may be said to pass through Pitts­ burgh as a gateway. The many connections with trunk lines make for an exceptionally good service by the Pittsburgh~ West Virginia and West Side Belt lines. The Buffalo, Rochester 8 Pittsburgh line enters Pittsburgh by trackage right over the Baltimore ~ Ohio system. The Bessemer 8 Lake Erie line, with the Union Railroad, serves a most important part of Pittsburgh's industrial area, and makes connections with all other roads. Its heaviest traffic consists of ore from the Great Lakes, and other raw materials, inbound; and :finished products and coal outbound. ·Passenger traffic in and out of Pittsburgh is unusually dense for a city of its size. The number of trains varies with industrial activity and the season. As many as 5 93 trains have entered and left the City during each day of a month. Of these, 3 2 7 were MAP OF PITl'SBURGH . SHOWING RAILROADS AND THEIR BRIDGES

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THE BRIDGES OF PITTSBURGH suburban and had their origin or destination at from 16 to 45 miles from Pittsburgh. The remainder of 266 were either through trains or trains operating bet,veen Pitts­ burgh and distant points, according to information collected by the Citizens' Commit­ tee on City Plan of Pittsburgh. With these railroad systems in mind, with their heavy freight and passenger traf­ fic, and that Pittsburgh is largely a gateway for some of the lines and the principal source of their traffic, we pass on to qescriptions of the bridges over which this move­ ment is 1nade. Viev.rs of them are shown in the preceding section. BALTIMORE AND OHIO RAILROAD BRIDGES In addition to its main line along the Youghiogheny River to McKeesport and thence on to Pittsburgh along the Monongahela River, the Baltimore~ Ohio Railroad enters and leaves the district by bridge No. 74, Pittsburgh Division, across the Monon­ gahela River at Glenwood; and by bridge No. 203, Pittsburgh Division, across the Al­ legheny River at Thirty-Third Street, Pittsburgh. Both structures have through riveted-truss ·spans over the main channels, with plate-girder approaches. They ,vere built in 1914 and 1920, respectively, by the American Bridge Company, in 22 and 21 months. Bridge No. 74 has one track and a continuous footwalk on one side; ·whereas bridge No. 203 has two tracks and a continuous footwalk between them. The respec­ tive lengths are 2397 feet and 4270 feet, v.rith channel spans of 465 feet and 434 feet. These bridges are 14 feet and 22 feet in width, and the rails are 5 9 feet and 62 feet above pool-level. The traffic is as follows: Bridge No. 74-19 freight trains and 12 passenger trains per day, carrying 7,333,580 tons and 219,000 persons per year; bridge No. 203 -29 freight trains and 34 passenger trains per day, carrying 27,469,990 tons and 620,500 persons per year. 1~he setting of these bridges, at points where there is considerable industrial activ­ ity, particularly No. 203, more or less obscures their features and few residents are able to tell what they are. Nevertheless, nearly 3 5 million tons of freight and more than three-quarters of a million passengers a year indicates heavy traffic. BESSEMER AND LAKE ERIE RAILROAD BRIDGES Near Cheswick, the Bessemer~ Lake Erie Railroad crosses the Allegheny River by a great deck-truss type bridge 2327 feet in length, with the rails 165 feet above pool­ level. It was erected in 1918 by the American Bridge Company to replace one built in 1896. The work occupied 29 months. The setting of this structure is rather pleasing. On looking upstream one sees this massive bridge towe~ing high above the river ( the lowest member is 8 7 feet above the water) . One end ( the north) , runs on to a high bank; the other end ( the sou th) , dis­ appears in a cut. Between are eight spans from 60 to 520 feet in length resting on stone piers. The Allegheny River here is divided into two parts by an island, so that the bridge crosses this island. As the bridge is so long and the immediate country so flat, a good picture is difficult to obtain. The luxuriant growth of shrubs and trees nearby adds considerably to the scene. On each side of the river the bridge crosses two tracks of the Pennsylvania System. The Allegheny River Bridge, the name applied to this structure, is 32 .½ feet in width between railings. It has two tracks and two sidewalks. There is somewhat more THE BRIDGES OF PITTSBURGH than I 0,000 tons of steel in the bridge. It is essentially a freight bridge and the daily crossings are 3 7 freight trains and 6 passenger trains. These average about 11,000,000 tons of freight and 28,000 passengers per year. Of the freight, 9,500,000 tons are iron ore inward bound from the Great Lakes to blast furnaces, and 1,500,000 tons are coal outward bound from mines to the Lakes. The record tonnage was 18,000,000 in l 923~ UNION RAILROAD BRIDGES North Bessemer is the terminus of the Bessemer ~ Lake Erie Railroad. Thence, the inward bound freight. and the outward freight for this system, is hauled by the Union Railroad Company. Both lines are subsidiaries of the United States Steel Cor­ poration. The Union System is of great importance to the district, particularly in delivering iron ore to blast-furnace plants and in assembling and hauling out coal and finished mill products. It connects with all of the other railroads. From the Allegheny River to the Monongahela River, by way of the Bessemer 8 Lake Erie and Union Sys­ tems the distance is approximately 10 miles. At Port Perry, a mile above Braddock, the Union line crosses Monongahela River by a double-track, open-tie and plate-floor bridge; the latter design is for hot metal and hot cinder trains described later. The spans are as follows: One pin-connected Petit type through-truss span, 397 feet center to center of end piers; one pin-connected Baltimore type through-truss span, 245 feet center to center of end piers; three pin-connected Pratt type deck-truss spans, 176 feet center to center of end piers; and one pin-connected Pratt type of deck-truss span, 146 feet center to center of end piers. On the north side the single open-tie track crosses the Baltimore 8 Ohio and Pittsburgh 8 Lake Erie lines. This bridge is for general traffic, including much iron ore, and for hot metal and slag. At Rankin, about I ¼ miles below Braddock, the Union System again crosses the Monongahela River to Munhall and Homestead. The bridge is also of the open-tie and plate-floor design. It is made up of one pin-connected Petit type through-truss span, 496 feet center to center of end piers; and one pin-connected Baltimore type through­ truss span, 248 feet center to center of end piers. This bridge is for general traffic and for hot metal and slag. Further description of these two bridges is given under Hot-Metal Bridges. Be­ cause of their position in the midst of furnaces and mills, also as they are paralleled by the bridges of railroad companies. these spans are not easily seen nor are they known by the general public. Yet they are being crossed frequently by heavy trains; in fact, the authors do not know of any more concentrated traffic in the Pittsburgh District than that between Homestead and Duquesne on the left bank and between Rankin and Braddock on the right bank, and on the four railroad bridges in this area. From the heights near Kennywood Park the scene is almost an endless movement of trains. At Clairton the Union Railroad has another bridge, for general traffic only. It is pictured and described in the photographic review. PENNSYLVANIA RAILROAD BRIDGES Pittsburgh is the headquarters of the Central Region of the Pennsylvania Rail­ road. 'The lines entering Pittsburgh form four main divisions, and cross the rivers as follows: Allegheny River-by a through-truss and deck bridge near Freeport, by a THE BRIDGES OF PITTSBURGH

through-truss (three) bridge with girder approaches ( the Brilliant cut-off) at Aspin­ wall and by a double-deck through-truss camel-back bridge with girder approaches at Eleventh Street, Pittsburgh. Monongahela River - by a through-truss bridge from Port Perry to near Duquesne, and by a deck and through-truss bridge with girder ap­ proaches from Try Street, Pittsburgh, to the South Side. Ohio River-by a deck truss and two through trusses with girder approaches ( the Ohio Connecting Bridge), which crosses the back channel of the Ohio River, Brunot Island, and the main channel. An­ other large bridge of this System spans the Beaver River at its confluence with the Ohio River. This consists of two through trusses. Farther up this river, at Beaver Falls, is a large deck-truss bridge which carries considerable traffic. These bridges are large and important structures, all in busy districts. The best way to describe them is to tabulate the detaiis. It will be noted that the traffic on these bridges is heavy, amounting for the four bridges for which traffic :figures are available, to 132 freight trains a day carrying more than 48 million tons a year and 264 passenger trains carrying more than 12 ¼ million persons a year.

Tabulated description of the Pennsylvania Railroad bridges ------Oh:o River Beaver River Allegheny River Monongahela River Ohio Mouth of Freeport Aspinwall 11th Street Port Perry Try Street Connectin~ nver ------Name applied to bridge ______No. 47.83. No. 0.68. No. 0.33 No. 10.19, No. 0.95. No. 1.90. No. 0.07. Conemaugh Conemaugh Eastern Port Perry Panhandle Ohio Con­ Cleveland Division Division Division Branch. Division necting Division Pittsburgh R.R., Division Panhandle Division Year bridge was built______1914 1903 1901-1904 1903 1903 1914-'15 1918 How long in building. years______2 3 2 2 2 Name of bridge company______McClintic- American American American Keystone American American Marshall Bridge Bridge Bridge Bridge Bridge Bridge Approximate cost ______$585.000 $2,000,000 $565,000 $2.300,000 $354,oooa How many tracks______2 2 4 on 2 levels 2 2 2 2 Length, feet ______I 067 1050 965 1179 1172 2822 655 Length of main channel span ( clear span). feet ------·---- 4 i 9 396 327 393 351 406 and 525 320 Width, feet ------·---- 3 2 30.6 5 L3 30 31 33.25 32 Height of rails above pool-level. feet_ 45 53½ 55 80 Height of lowest member of truss above pool-level. feet ______50 56.5 · 47.75 46.1 50.9 74.9 42.8 Number of freight trains a day ____ _ 56 14 8 54 Annual tonnage of freight (ap- proximate) ______13,000.000 2. I 10,000 113,400 32,822.295 Number of passenger trains a day __ _ 25 Ill 128 (Freight Number of passengers a year (ap- only) proximate) ______1,529,600 3,830,000 6.996.000 n Exclusive of masonry.

A note regarding the danger to trespassers on railroad bridges may be added here: According to T. H. Carrow, superintendent of safety for the Pennsylvania Railroad, in the lvational Safety News for November, I 928, a large number of persons, includ- THE BRIDGES.OF PITTSBURGH ing many children and youths, are killed and injured every year while trespassing on bridges. These may be a short cut but the hazard of being run over is ever present and sometimes inescapable.

PITTSBURGH~ LAKE FRIE RAILROAD BRIDGES The Pittsburgh 8 Lake Erie Railroad enters the Pittsburgh district from the northwest by a cantilever bridge ,vith one through approach truss across the Ohio River between Beaver and Monaca, and enters from the southeast by a three-truss, double­ track bridge, with deck-girder approaches over the Youghiogheny River at McKeesport and by a three-truss, double-track bridge with three deck trusses over the Monongahela River at Rankin. At McKees Rocks the line crosses Chartiers Creek by a double, single­ span, through-truss bridge. The Ohio River bridge is a magnificent structure, particularly as seen from a hill near the mouth of the Beaver River, with the Pennsylvania through-truss and Rochester suspension bridges nearby. The two other bridges of the Pittsburgh 8 Lake Erie Rail­ road are so hemmed in by parallel bridges and works that they are seldom seen unless a person is very observant. Yet they are of considerable size, as the respective river spans exceed 500 feet and 630 feet in length, and the approach spaI!S add several hundred feet. The Ohio River bridge was built by the McClintic-Marshall Construction Com­ pany during a period of 23 months in 1908 to 1910. The cost, including substructure, was $1,550,000. It carries two tracks and is 1800 feet in length and 34 ¼ feet-in width center to center of trusses. The main span is 7 69 feet in length and the rails are 89 feet above pool-level. The traffic across this bridge is heavy: freight-.-38 trains a day and 47,649,655 tons a year; passengers-SO trains a day and 1,774,948 persons a year.

PITTSBURGH~ WEST VIRGINIA RAILWAY BRIDGE The Pittsburgh~ West Virginia Railway Company, the successor of the Wabash Pittsburgh Terminal Raihvay Company. itself a consolidation of three other lines, has a terminal in downtown Pittsburgh. The road then crosses the Monongahela River near the Point by a cantilever bridge known as the Monongahela River Bridge No. 0-A. and passes through the South Hills by a tunnel. This is a handsome structure and its design may be studied from the river banks and from the Smithfield Street and Point bridges. The main span is 8 12 feet in length; the two anchor spans total 6 9 2 feet, a deck plate-girder viaduct 262 feet, and a through truss over the Pennsylvania line 13 9 feet, making a total length of 190 5 feet. The bridge is 3 2 feet in width, center to center of trusses. The height of the two tracks above pool-level is 80 ¼ feet. The American Bridge Company erected the superstructure at a price of $917,000 during 30 months of 1902-'04. The piers cost $230,000. Four freight trains and six passenger trains pass over this bridge every day. , ,, I ,I , , ' ,, I I• I l I I ' ~

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CAR ROUTE SYSTEM OF PrrrSBURGH ~WAYS COMPANY SHOWING BRIDGES CROSSED

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STREET RAILWAYS AND BRIDGES

HE Pittsburgh Railways Company serves 89 municipalities of suburban districts in addition to the City of Pittsburgh. It has 1,419 passenger cars which are oper­ 1L ated over 107 routes on 586 miles of track. During the year 1927 these cars car­ ried 389,615,236 passengers. Many of the routes include the crossing of bridges over the Allegheny, Monongahela, Youghiogheny, and Ohio Rivers, as shown in the map prepared by J. L. Lewis. The approximate number of cars crossing the bridges and the passengers carried per day for the years 19 2 4 and 19 2 7 are as follows: Street Cars and Passengers Crossing River Bridges Year 1924 Year 1927

Street-cars Passengers Street-cars Passengers Bridge per day per day per day per day

Allegheny River. Manchester ______(No street-car tracks until 1926) 260 5.931 Sixth Street (old)______2,872 63,106 (New bridge under construction) Seventh Street ______(New bridge under construction) 2,962 85,645 Ninth Street ______1.994 27.883 1.354 19,693 Sixteenth Street ______(No street-car tracks until 1926) 486 8,450 Morningside to Etna______3 5 2 ____ _ 320 6,726 Monongahela River. Point ______1.404 34,771 1.556 43,741 Smithfield Street______2.7 62 71. 3 62 3,398 98.757 Tenth Street' ______424 488 16,853 • Twenty-second Street ______346 568 29,360 Homestead ______302 372 7,504 McKeesport ______276 216 1. 91 1

Passenger counts for some of the bridges are not known for the year 1924. The latest passenger counts available were made on April 14, 1927 and are considered to be a typical illustration of the traffic over the bridges for any week-day except Saturday or Sunday. It is believed that a more re.cent check would indicate no appreciable change in these figures. In any event, the opening of the Sixth Street Bridge will undoubtedly alter the figures for all of the Allegheny River bridges except the one from Morningside to Etna. A traffic survey of the business area of Pittsburgh taken between 8 a. m. and 6 p. m. showed that 594,000 persons entered and departed as follows-52 per cent by street-car, 20 per cent by passenger automobile, 15 per cent on foot, 11 per cent on trains, 1.6 per cent by taxi, and 0.83 per cent by motor-bus. Automobiles consti­ tuted 90 per cent and street-cars 8 per cent of the vehicles. HOT-METAL BRIDGES.

ITTSBURGH has three unique bridges-that is, their purpose is unique-span­ ning the Monongahela River; these are the three so-called and rightly so, ,.hot­ ]P metal bridges," of the Jones f1 Laughlin Steel Corporation ( one) and of the Union Railroad Company (United States Steel Corporation) (two). The latter are partly described under Union Railroad Bridges. One of the many plants of the Jones f1 Laughlin Steel Corporation on the north side of the river are the six Eliza blast furnaces. They produce molten iron for the open­ hearth furnaces and converters at the South Side Works, and this is hauled across the river over a through-truss, open-tie and plate-floor type of bridge. This was built in 1900 by the Edgemore Boiler Works and is 1161 feet in length. Of the five river spans the main span is 321 feet in length. \Vhen five blast furnaces are in operation, 24 trains a day cross the bridge. Each train is made up of a steam locomotive and two ladles each weighing 8 7 tons and carrying 9 0 tons of metal. and a caboose. In effect, every hour of the day about 180 tons of molten iron, or say 4300 tons a day, is hauled across the river for converting into steel. As already stated, the two bridges of the Union Railroad Company are of the open-tie and plate-floor type. The latter construction is for protection of traffic on the river against spillage of hot metal and hot cinder from trains crossing from the north side to the south side. 'The plate-floor section of the bridges is on the down river side. The Port Perry bridge has side-plate protection on each side of the track against spill­ age, except where the Homestead branch connects with the bridge. At this point the plate floor is extended under the open-tie side with sufficient side protection on the down~river side. The bridge at Rankin is approached from the Carrie furnaces of the Carnegie Steel Company by an open-tie and plate-floor viaduct. From the l\1unhall end the bridge is THE BRIDGES OF PITTSBURGH

VIEW SHOWING CONSTRUCTION OF A HOT-METAL BRIDGE. At the right is the plate-floor section protecting against spillage of hot metal or slag; at the left is the open-tie section for ordinary traffic. approached by a single track Y. The Homestead or down-riv~r leg of the Y is a com­ bination of deck and through plate-girder spans with plate floor. The up-river leg is a combination of deck and through plate-girder span with open-tie floor. The hot­ metal track throughout has side-plate protection on each side, excepting at the junc­ tion of the legs of the Yon the harbor line pier, where the protection is on the outside of each track and extends to the main truss spans. The procedure at the blast-furnace plants at Braddock and Rankin, particularly the latter, is to send molten iron to the open-hearth furnaces at Homestead, also slag to the dumps. There are no regular runs of metal across the Port Perry bridge, but oc­ casional trains consist of three or four 3 5-ton ladles. Thirty trains a day, each made up of four 35-ton ladles, or ~ay 4200 tons in all, are moved across the bridge at Rankin from the 7 Carrie blast furnaces. As to molten slag, 12 trains of eleven 17-ton ladles and 8 trains of twelve 17-ton ladles, or a total of 3 800 tons are moved across the re­ spective bridges and onto the dumps ,vhere it is poured. Some granulated slag is made and hauled across the bridges in cars of 50- to 70-ton capacity. THE BRIDGES OF PITTSBURGH

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A TRAIN OF 12 LADLES OF MOL TEN SLAG ( 200 TONS), FROM THE EDGAR THOMSON FURNACES OF THE CARNEGIE STEEL COMPANY.

A TRAIN OF TWO LADLES OF MOLTEN IRON (180 TONS), FROM THE ELIZA FURNACES OF THE JONES 8 LAUGHLIN STEEL CORPORATION. WEIGHT AND COST OF BRIDGES

HE Sixth Street Bridge, recently opened to traffic, is approximately 1000 feet in length, weighs 6000 tons (steel only), and cost $1,440,000. Stated in another 1L way, each foot of the structure contains 6 tons of steel and cost $1440 completed. The roadway, rails for street-cars, and sidewalks add several hundred tons to the total. The length, weight, and cost of the Seventh Street and Ninth Street Bridges are almost similar to that of the Sixth Street Bridge. As doubtless many persons in crossing a bridge or in viewing one from a distance think in terms of weight and money spent thereon, the length, weight of steel, type, and cost of certain bridges will now be given: Length, Weight, and Cost of Certain Bridges

Length, Weight of Cost of fin- Bridge River Type feet steel, tons ished bridge

Liberty ______Monongahela Deck cantilever 2775 12,000 $3,77 i,000 Point______Monongahela Through cantilever 1120 7.200 2,000,000 V.Tabash ______Monongahela Through cantilever 1905 7,500 1,147.000 Sewickley ______Ohio Through cantilever 1856 ----- 537,000 Ambridge-Aliquippa ______Ohio Through cantilever 1820 2,450 571.000 Pittsburgh 8 Lake Erie ______Ohio Through cantilever 1800 16,000" 1.550,000 Washington Crossing ______Allegheny Deck arch 2365 7,000 2,870.000 Bessemer 8 Lake Erie ______Allegheny Deck truss 2327 10.140 ------Baltimore 8 Ohio ______Monongahela Through truss 2088 3,238 ------McKeesport-Duquesne ______Monongahela Through truss 2250 7,400 2,000,000 Baltimore 8 Ohio ______Allegheny Through truss 2600 6.674 ------Sixteenth Street______Allegheny Through truss 1900 5,200 1,682,000 Pennsylvania ______Ohio Through truss and 2822 }5,068b 2,300,000 deck truss Pennsylvania ______Beaver Through truss 655 3,430 354.000" n Cantilever span alone. 13,600 tons . ., Two through trusses of 940 feet, total 8,346 tons. " Exclusive of masonry. A \Vord regarding the cost of bridges prior to the year 1915 and at present is in order: As an example, the steel for the Pittsburgh ~ Lake Erie Railroad Bridge at Beaver cost 4 cents a pound in 1915; for a structure of similar size in 1928 the cost would be slightly more than 7 cents a pound. Compare the cost of the new bridges in the foregoing table with $400,000 and $310,000 for the 2234-foot and 1417-foot bridges at Twenty-Second Street and Tenth Street, Monongahela River, built in 1896 and 1903; and $890,000 for the 3258-foot Manchester Bridge at the Point, Alle­ gheny River, built in 1914. If this great increase in the price of steel, like\vise that of other materials used. is realized, the people will better understand why so much money is required for our new bridges. TECHNICAL DESCRIPTION OF THE FOUR BRIDGES ERECTED AT SIXTH STREET, ALLEGHENY RIVER

NORDER to give some idea of the technicalities involved in erecting bridges, a short description is now given of the four bridges that were built across the Allegheny ] [ River at Sixth Street in 1819, 1859. 1892, and 1928. The following notes re­ garding the first bridge is from a paper of W. G. Wilkins in the Proceedings of the Engineers' Society of Wes tern PennsyI van ia for 18 9 5: FIRST BRIDGE The first bridge was built in 1819 by Mr. Lothrop, a prominent contractor of that time. who also built the Ninth, or Hand Street Bridge, as it was formerly called. This latter was torn down about four years ago [ 18 9 0] and replaced by a steel bridge suitable for rapid transit, the work being done under the direction of Messrs. Ferris and Kaufman, members of this society [the Engineers' Society] The first bridge consisted of four spans of 185 feet each, one 170 feet, and one 137 feet; total, 1,037 feet. The superstructure was of wood, and the trusses were probably of the Burr type, as in the Hand Street Bridge, reinforced with wooden arches, as the skew backs can still be seen in the Allegheny abutment. The roof was fl.at, and had a railing at the sides and steps at each end. It was used as a promenade by the belles and beaux of days gone by. The old wooden structure stood forty years, when it was torn down to be replaced by the wire suspension bridge. While the latter was being built there was no attempt made to take care of the traffic, and the old bridge was entirely removed before the work was begun on the new one. SECOND BRIDGE The description foilowing of the second bridge is also quoted from the paper of W. G. Wilkins: The Allegheny Suspension Bridge was long noted as the most beautiful and graceful in its lines of the earlier bridges built by the late John A. Roehling. and a brief description may not prove uninteresting before passing to the subject proper of this paper. There were two main spans of 3 44 feet each. and two shore or half spans of I 77 feet and 171 feet. The main cables at each side of the roadway were 22 feet apart center to center, at the center of the spans. and 27 feet at the towers. The smaller cables at the outside of the sidewalks were 4 2 feet apart at center of spans and 3 5 feet at the towers. THE BRIDGES OF PITTSBURGH

The main cables were 7 3-~ inches in diameter and composed of seven strands of 700 wires each, and weighed 115 pounds per foot. The smaller cables were 4 ;/2 inches in diameter with 300 wires, and weighed 38 pounds per foot. These weights include the wrapping wire, and are actual weights obtained by weighing sections of the cables after they were taken down. The cables passed over saddles supported by towers. each formed of four cast:.iron columns of 22 inches in diameter and about 27 feet high. The floor beams were 7-inch I-beams 4 3 feet 1 inch long, and were spaced 5 feet center to center. They were suspended f.rom the cables by wire ropes 1 inch in diameter, which were attached to the cables by wrought iron collars. The lower ends of these wire ropes were attached to the stirrup which supported the floor beams. Near the centers of the spans, where the suspenders were short, they were of 1 ¾ -inch rods instead of wire rope. These floor beams were curved to give the proper crown to the roadway. On top of these floor beams, at the center and 10 feet each side were lines of 9-inch I-beams running the entire length of the bridge, which were riveted to the floor beams. On the center line, and under the floor beams and riveted to them was an­ other line of 8-inch I-beams. Between the upper and lower I-beams there were fillers of cast-iron, I-beam shape extending from floor beam to floor beam. The two I-beams and the filler were riveted together. The lower beams acted as a strut for the truss rods which trussed the floor beams the width of the roadway. On the under side of the floor beams, at IO feet and 19 feet 6 inches each side of the center line, there were 10 by I 0-inch timbers running the full length of each span: These timbers were replaced by box girders, when the repairs were made after the fire in 1881. The floor joists were 4 by 18-inch white pine. The joints of the joists were halved for three feet and bolted together, making the joists practically continuous. The joists were fastened to the floor beams by U-bolts. The floor consisted of a course of 2 ,½-inch white pine plank laid transverse­ ly, and on this a 3-inch course of white oak laid longitudinally. Beginning at the second floor beam from the piers, and then at every second beam to the twenty-first, there were, in addition to the vertical suspenders. wire rope stays, which ran from the longitudinal I-beams up over the saddles and down to the corresponding beam on the other side of the pier. \}/here these stays crossed the suspenders they were lashed together with small wire. THIRD BRIDGE In 1891, according to W. G. Wilkins, Theodore Cooper prepared plans for the third bridge. It was to be capable of taking care of the rapidly increasing travel and allow electric cars to cross without reducing their speed. The proposal and design sub­ mitted by the Union Bridge Company was accepted as the best and it was awarded the contract. As the bridge stood at Sixth Street from 1892 until 1927, all Pittsburghers are familiar with its design. The principal parts were two spans of the bow-string or camel-back type, 440 feet in length, 44 feet in width, and 80 feet in height, ,veighing 1600 tons each. A description of the building of this bridge, of supporting the old bri4ge and allowing traffic to continue, of dismantling the old bridge, and of completing the new bridge is of considerable interest, but is too difficult to understand without sketches of the operations, which are unavailable. Briefly, it may be said that No. 2 pier, ·which was in the middle of the channel. was the only part of the masonry that was of especial interest. It was within 10 ¼ feet of the old bridge pier and the bottom of the founda­ tion was 7 3~ feet lower than that of the old pier. Great care had to be taken to pro­ tect the old pier, as it had to support the old bridge until the falsework could support -,~ 85 ~-- THE BRIDGES OF PITTSBURGH the old floor. In order to protect both the old and new piers during construction of the latter, a breakwater of piles was built 80 feet upstream from the new pier. This pier was built by dredging to hard bottom, then sinking a coffer-:dam, and building up the masonry. The whole job occupied 95 days. In the erection of the superstr"ucture the falsework consisted of pile and timber bents and 8 by 16-inch stringers. Eight hundred piles and 500,000 feet, board meas­ ure, of pine timber were used. The piles were driven so that their tops were about 10 feet above pool-level and were capped with 12 by 12-inch timber. On top of these caps was a second-story framed bent of 12 by 12 inches. These bents were of such height that the floor of the old bridge could be blocked up and temporarily supported on these stringers. J..3t third-story bent was then put up on each side of the old bridge to support the traveler (hoist and derrick) tracks. In this job the floor of the old bridge had to be elevated enough to permit the erec­ tion of the new bridge floor underneath it. The car tracks had to be shifted from one side of the bridge to the other three times to allow stringers and buckle plates to be put in place. This was safely accomplished virtually without interruption of street­ car and foot traffic. Then the trusses were erected for each span; the old floor was lowered onto the ne\V floor and then torn out. Many accidents happened during the erection of this third bridge. Thirteen men fell from the false work or traveler:but none of them were seriously injured.

FOURTH BRIDGE On September 14, 1928, the fourth bridge at Sixth Street was opened to pedes­ trians and on October 19 to all forms of vehicular traffic. From any fairly high point of vantage along the Allegheny River the Sixth, Seventh, and Ninth Street Bridges may be seen. As they are all practically similar in design, size, and cost, it is now pro­ posed to give a technical description of the Seventh Street Bridge, abstracted from Engineering News-Record (New York) for December 18, 1924, and September 23, I 926. This was mainly written by V. R. Covell, chief engineer of bridges, Depart­ ment of Public Works, Allegheny County. TYPE AND DESIGN OF SEVENTH STREET BRIDGE The superstructure plans show a remarkable type of bridge, namely, a chain suspension bridge without anchorage, the chain pull being resisted by compression in the stiffening girder. A bridge of this type built across. the Rhine River at Cologne, Germany, about ten years ago, is probably the only other example in existence. The Allegheny River project is unique also in that three bridges of like de­ sign are being erected f now complete] as a group, effecting, among other things. economy in design, fabrication, and construction work. The designs were worked out by the engineering division of the Depart­ ment of Public Works. Allegheny County, under the general direction of Norman F. Brown, director, and C. M. Reppert, assistant director. They were prepared by V. R. Covell. county engineer, and T. J. Wilkerson, consulting engineer, and A. D. Nutter, engineer of bridge design, and H. K. Dodge, designer, of the Bu­ reau of Bridges. ·However, the City Art Commission played a part in determining the type of structure. It reported that it preferred a structure of suspension type for all three sites. Thereupon the Engineering Division restudied the bridge sites with a view to adapting the suspension type. As a ·result, it selected the self­ anchoring type of suspension bridge. THE BRIDGES OF PITTSBURGH

Past experience has indicated that suspension bridges in Pittsburgh are sub­ ject to slip of the anchorages. Rock is about 50 or 60 feet below water. Space is not available for anchorages of the ordinary type of suspension bridge, as at both ends of the crossing in each of the three cases there are obstructions to carrying the cables to a satisfactory land anchorage. On the north side of the river a railroad track passes between abutment and shore pier, which would make it necessary to carry the cables over the track, and at the south end, proposed wharf improve­ ments interfere. It was therefore highly desirable to use a type of structure which would not require any portion of the main bridge to pass over the railroad track on the south side. In the adopted type, anchorages are eliminated by utilizing the stiffening girder of the structure as a compression member to resist the horizontal pull of the suspension chain. The end supports thus are subjected to vertical forces only. In working out the self-anchored suspension bridge design, it was early de­ cided that eyebar chains would be superior to wire cables, because of permitting easier connection to the stiffening member at the ends. In order to have as little as possible of the structural steelwork above the roadway, it was decided to use a plate girder for the stiffening member. This girder as designed extends above the roadway surface about 3 feet, sufficient to give a· separation between roadway and sidewalk. The chains are of heat-treated eyebars, of minimum yield-point of 50,000 pounds per square inch and minimum ultimate strength of 80,000 pounds per square inch. Each chain is made up of 8 and 9 bars alternating, the bars being 14 inches wide and of varying thickness up to 2 iIJ.ches. The maximum section, at the tower top, comprises 7 bars 14 by I .¼ inches and 2 bars 14 by I.¾ inches, a total section of 229.25 square inches. The suspenders are attached to stirrups riveted to the vertical stiffeners of the stiffening girders. The floor construction comprises a simple floor beam and stringer system carrying a concrete slab. Floor beams and sidewalk brackets are riveted direct to the sides of the stiffening girders. The bridges were proportioned for live-load equivalent to two 18-tori trucks and two 60-ton cars, together with a sidewalk live-load of 66 pounds per square foot. The total live-load is equivalent to 6,590 pounds per lineal foot of span. In proportioning the stiffening girders and cables, an impact factor of 16.9 per cent was applied to the live-load. The eyebars were proportioned for a unit stress of 27,000 pounds per square inch. GENERAL DESCRIPTION OF BRIDGE The Seventh Street bridge is a highway structure carrying four lines of traffic (two lanes for vehicles and two street-car tracks) on the roadway, and a cantilevered footwalk on each side. The roadway pavement consists of a 2 ¼­ inch layer of asphaltic concrete laid on a concrete base averaging 5 inches in thick­ ness on ¾ -inch buckle-plates, and the sidewalk pavement consists of a I-inch surface of rock asphalt laid on a 5-inch reinforced-concrete slab: The dimensions of the main or suspended portion of the structure are: Width of roadway, 3 7 feet 6 inches between curbs. Width of sidewalk, 12 feet I¼ inches center of girders to center of railing. Width center to center of girders and suspension system, 42 feet 6 inches. Length of each side span, 10 panels of 22 feet 1 ¼ inches; 221 feet ¼ inch. Length of center span, 20 panels of 22 feet 1 ¼ inches, or 442 feet I inch. Height of towers, 77 feet 11 ¼ inches. Sag of suspension chain, 5 5 feet 5 .¼ inches. Grade, 4.175 per cent, with a vertical curve for 8 panels at the center. The structure may be briefly described as a self-anchored suspension bridge. The suspension system consists of 14-inch eyebars extending from anchorage to anchorage, having two pins on the top of each tower, and carrying the roadway by 4-inch eyebar suspenders at the panel points. The stiffening system consists of triple-web plate girders placed parallel to the grade. The horizontal component of the stress in the eye bar chain is taken by the stiffening girders; the reactions at THE BRIDGES OF PITTSBURGH

the ends are vertical. The girders are thus subjected to stresses due to bending combined with direct compression. ERECTION OF THE STRUCTURE Three principal methods were considered: I. To provide a temporary anchorage to support the suspension chain until the stiffening girders were connected up. This was discarded on account of lack of room for anchorage and unfavorable soil conditions combined with the time element, which was an important factor. 2. To erect the entire structure on falsework. This was not practicable be­ cause of navigation requirements; it would also have delayed erection about six months. 3. To erect as a cantilever. This method was independent of temporary anchorages and practically independent of navigation and flood conditions. The choice of method was left to the bidders, the only restrictions being those required for navigation and the time of completion. The American Bridge Co. was the successful bidder, and its engineers developed the third method, one never before used on this type of structure. For convenience the sketch may be referred to. In the following descrip­ tio~, panel-points Uo to U20 denote the south or Pittsburgh half. Erection was carried on simultaneously from the north and south to the center of the bridge at U:!O. UIO

Temporary ] . Teiescoping strvl, trvss mgmt,vs . C.L I- SOO·ton jack _... I SOUTH ANCHORAGE

DIAGRAM EXPLAINING THE ERECTION METHODS USED FOR THE EYE-BAR SUSPENSION BRIDGE

Wood piles carrying steel bents were driven at panel points 1 to 9, inclusive, those at panel points 4 and 7 being extra strong to provide for protection against floods in case the remainder of the falsework w~s carried out. All material except that for the girder approach spans was delivered at the bridge site in steel barges and picked up directly from them as needed for erection. The floor system was first erected from Uo to Urn by locomotive crane weighing I 00 tons, running on tracks on the erected floor, after which the stiffen­ ing girders and the eyebar chains were set. The girders were then jacked to their cambered position and the splices fully bolted up, the tower bases having been previously set. The towers were erected and held in position by adjustable struts joined at the bottom to the stiffening girders. The eyebars and hangers were erected in their final position from panel points Oto 3. From panel points U:1 to U:; and u~. to U. the eyebars were cradled and had their intermediate pins at U, and Uu supported by the I-beam cradles. Points U" and U. were carried on special struts. Eyebars U. to Urn were similarly carried on I-beams supported at U. and the top of the tower, U10; the intermedi­ ate points Us and Ut, were carried by the I-beam cradles by means of plates with slotted holes engaging the pins. THE BRIDGES OF PITTSBURGH

To permit the eyebar chains to be connected at U!!O, the distance between the towers was decreased one foot and the bottom hanger pins were not connected at U, to Uo inclusive and at U1 •. The decreasing of the distance between the towers one foot was accomplished by starting the erection of Uo one foot toward the cen­ ter of the span from its final position and setting the segmental rollers at U10 in an inclined position corresponding to this movement. The segmental rollers were then locked by temporary plates to prevent any further movement. The corresponding north part of the structure was erected in its final position. The difficulty in connecting pins at U:?O was due to the deflection of the can­ tilever, which was on a 4.175 per cent grade, and the cambered length of the members. A telescopic strut, containing one 5 00-ton jack, so constructed that it could act either in tension or compression, supported the eyebar chain at U:;, normal to the tangent of the curve of the chain. The function of this strut was to control the secondary stresses in the can­ tilever by pulling the tower back as deflections increased, to control the elevation of Uw to assist in the final closure, and to permit connecting the bottom pins at panel points U~ and Ua inclusive.

THE COMPLETED BRIDGE.

CANTILEVER ERECTION The remaining portion of the structure was erected as an ordinary cantilever arm, temporary diagonal erection struts being placed in panels 10 to 11 to 15 to 16, inclusive. The struts had pin plates at their upper ends, engaging the pins out­ side the bars, and temporary bolted connections to the girders at the lower ends. The erection stresses were of the same kind as the permanent stresses, but it was necessary to increase the section of the hangers Un. Beyond point U1. the inclination of the erection diagonals would have been too flat, so that it was necessary to construct a truss having its top chord and web THE BRIDGES OF PITTSBURGH system entirely independent of any permanent material, the stiffening girders still acting as the lower chord. This truss was a second cantilevered arm attached to the first by means of a tie from U17 to the pin at U10, having an effective depth of 16 !/2 feet, with the verticals placed ahead of the permanent panel points. This allowed the completion of the erection up to the splices 3 feet 8 inches beyond panel points Urn and U'w. The nominal distance between these splices is 44 feet 2 ;/2 inches less 7 feet 4 inches, or 3 6 feet 10 ;/2 inches: and as panel-point 19 was one foot north of its final position the opening would be approximately 3 5 feet 10 :/2 in length. The girder section Uw U'w was fabricated 3 5 feet 8 ¼ inches in length, or 14 inches short, thus leaving 2 inches for clearance. This section was supported from the cantilever truss while the eyebar chains were connected. Four 500-ton jacks were placed in each chord in such a manner that their combined force would pass through the center or gravity of the cross-section of the stiffening girders. These jacks acted on suitable diaphragms, built into the chords near U1 ... With the center heavy girder section in place, together with the jacks, the locking plates on the roller shoes at Urn were taken off. The pins at U::o were then driven, completing the eyebar chain with practically no stress. The hanger pins from U17 to U'17 were the-n driven and, immediately following, the pins at U,, u~, and u .. and the corresponding pins on the opposite half were driven. Connect­ ing these pins placed some stress on the bottom-chord jacks. Jacking was then started, converting the spans from cantilever to suspension type. The cantilever spans had the regular cantilever droop, so that, as jacking pr.9ceeded, the center of the channel span rose vertically and at the same time the south half of the struc­ ture was moved to its final position. As the jacking stress approached the compression stress in the heavy chords ( dead weight of steel plus erection equipment), the diagonals of the cantilever truss freed themselves, leaving the bridge a suspension span. At this point the clos­ ing 14-inch section of the girder was entered, thus completing the stiffening gird­ ers. This 14-inch section was then restrained by adequate cover splices, all points riveted up and the jacks remo"ved. · It was observed that when the span had reached its final position the stress as indicated by pressure gages on the jacks agreed very closely with the computed stress in the girders for the load then on the structure.·; The erection of the steelwork of this bridge was commenced July 7, 1925: closure of the stiffening girders was made February 9, 1926: and the bridge was thrown open to traffic June 1 7, 1 9 2 6. FLOATING THE SIXTH STREET BRIDGE TO CORAOPOLIS

ECULIAR interest attended the removal of the old Sixth Street Bridge, because in two sections it was floated dovvn the Ohio River 12 miles and re-erected over ]P the back channel of that river at Coraopolis. The County engineers estimated that the removal of the bridge saved $300,000 over what it would cost to build a new similar one at Coraopolis. The job vvas done by The Foundation Company of New York at a price of $316,000. The bridge was of the through-truss bow-string type, pin-connected, with one end on i;ollers for expansion. Each truss was 440 feet in length, 44 feet in width, and 80 feet in height, and weighed, as prepared for removal, 1600 tons. The bridge was closed to street-car and vehicular traffic on January l, 1927. The two sidewalks \Vere cut off; the concrete pavement was stripped off the deck and shore connections were cut. Before each span could be lowered vertically the masonry on which it rested had to be removed; but before this could be done, substitute sup­ ports for the bridge had to be provided and so arranged as not to interfere with the lowering of the bridge. To provide these, steel frames were fitted in the center pier and the two shore abutments. This procedure is opposite··to what is currently seen in modern building construction. We see steel frames rising later to be filled in with masonry; in this instance, the steel frame vvas inserted into masonry already existing. Although complicated in detail, the method used in lowering the bridge \Vas sim­ ple in principle. It consisted in riveting to a lowering platform within the steel frame mentioned, 8 pairs of vertical steel straps, whose upper ends were arranged in such a way as to be slipped down·ward slowly. The straps were 4 7 feet long, 18 inches wide, and 1 inch thick. Each strap was punched with 26 holes, 7 inches in diameter and 15 inches center to center. They did not work singly but were paired so as to function like a sling or a loop. At the upper end of each loop was inserted a steel forged mov­ able pin 3 8 inches long. By transferring this pin from one set of holes to the set above, the length of the loop could be lengthened 15 inches. The steel pin rested upon the THE BRIDGES OF PITTSBURGH plunger of a jack, which in turn rested on the steel tower. Eight 500-ton jacks, one for each loop, were used. 'I'hroughout the operation the jacks remained at the same elevation; as the bridge was lowered the length of the loop was lengthened 15 inches by shifting the movable pin to the set of holes above, and so on until lowered the full distance. The jacks used in lo\vering the bridge consisted of a steel cylinder 12 ¼ inches in diameter and 15 inches in height into which fitted a tight plunger. A bleeder pipe led off from the bottom of the cylinder. The cylinder was filled with water and pumped to a pressure of 3,200 pounds per square inch. The lower end of the plunger rested against this water; and the bridge rested on the top end of the plunger. At a given signal, water was permitted to bleed away from the four jacks at one time; the four plungers gradually lowered and vvhen they had moved downward their full

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THE SIXTH STREET SPAN SAFELY PLACED ON THE PONTOONS AND BEING NOSED DOWNSTREAM.

distance, one end of the bridge had been lowered 15 inches. At another signal, the four jacks at the other end of the bridge were bled, then that end of the bridge was lowered 15 inches; th us the bridge was tilted dovvn end by end in steps of 15 inches for the complete distance of 18 feet. The total actual lowering period was 14 hours. Each span was lowered on four steel coal barges each of 1000-ton capacity, two fastened side by side in front and two side by side in back. Special preparation was made on the barge float so that it would accommodate its unusual cargo. Steel string­ ers ,vere placed cross-wise the float the same distance apart as the floor beams of the bridge. On each of these stringers ( 14 of them) three pyramids of wooden blocks ·were built up, making in all 42 points of support for the bridge. But the bridge did not rest directly on block pyramids. At each point of support was an ordinary 40- ton screw-jack which permitted the raising and lovvering of the bridge at will, mak­ ing it easier to load and unload. THE BRIDGES OF PITTSBURGH

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AFTER THE UPPER SEGMENT HAD BEEN REMOVED. THE SPAN WAS TOWED UNDER BRIDGES AND THROUGH A LOCK TO CORAOPOLIS. When the bridge had been lowered onto the pontoon, it was gradually swung around and nosed down stream. Before it was started on its journey, it was anchored along the north shore, just east of the Manchester Bridge. There, workers dismantled about 27 feet from the top of the arch in order that the truss might clear the l\1anchester Bridge at the Point and the Ohio Connecting Bridge at Brunot Island. This disconnecting of part of the top chord is another reason why it was necessary to support the bridge under each floor beam. The Sixth Street Bridge is a bow - type truss; the string of the bow is made up of I 6 eye-bar panels pinned together. As long as the bow is kept intact the structure is rigid, and could be moved by sup­ porting it at its two ends, if necessary. But if the bow or the arch were cut the en­ tire structure becomes unstabilized and requires support at every panel point through- out its length. ·

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THE SIXTH STREET BRIDGE IMMEDIATELY AFTER RE-ERECTION AT CORAOPOLIS. THE BRIDGES OF PITTSBURGH

Two tug-boats were used to convey the bridge-laden pontoon to its destination. After passing under the· t\\7 0 bridges mentioned, the structure arrived at the Govern­ m·ent dam and locks at Emsworth, through which it passed easily. At the lower end of Neville Island the dismantled top chords were re-assembled and the barges were towed some distance below the end of the Island to prevent possible grounding; then they were backed up the channel to the site of the present bridge. The operation at Coraopolis was just the reverse from that at Pittsburgh, but instead of lowering the bridge 18 feet it was necessary to raise it 32 feet. The same steel towers that were used at Pittsburgh were used at Coraopolis; and the bridge was elevated to its final position by the same straps and by the same jacks. A log of the operation ( during 192 7) reads like this: Work started dismantling bridge ______January I South Span: Lowered onto barges ______May 4 Dismantled to go under Manchester Bridge ______June 22 Towed down Ohio River ______June 22 Re-built at Neville Island ______July 26 Re-erected at Coraopolis ------·-· ------=---·------September 3 North Span: Lowered onto barges------·· _____ July 29 Dismantled to go under Manchester Bridge ______August 22 Towed down Ohio River ------______August 22 Re-built at Neville Island ______September 14 Re-erected at Coraopolis (first lift) ______September 21 Total actual period of dismantling, removal, and re-erection ______I 40 days The "new" bridge is now in use. DESCRIPTION OF THE SUSPENSION BRIDGE FORMERLY AT SMITHFIELD STREET, ACROSS THE MONONGAHELA RIVER

N VOLUME 1 (1846, reprinted 1876) of The Olden Time (Pittsburgh), a monthly publication devoted to the preservation of documents, edited by Neville ][B. Craig, the following is given regarding the wire suspension bridge formerly at Smithfield Street over the Monongahela River. It is abstracted from the American Railroad Journal (New York) and written by John A. Roehling who constructed the bridge: The new suspension bridge over the Monongahela River, at Pittsburgh. was commenced in June, 1845, and opened for travel in February, 1846. The piers and abutments of the old wooden structure, which was destroyed by the great fire, required extensive repairs to be fitted for the reception of the new superstructure. The whole length of the work between the abutments, is exactly 1500 feet, and is divided into eight spans of 188 feet, average distance from center to center. The piers are 5 0 feet long at bottom, 3 6 feet high, and 11 feet wide on top, battering 1 inch to the foot. Two bodies of substantial cut stone masonry, measuring 9 feet square and 3 feet high, are erected on each pier, at a distance of 18 feet apart. On these the bed plates are laid down for the support of the cast iron towers, to which the wire cables are suspended by means of pendulums. Each span being supported by two separate cables, there are therefore, 18 cables suspended _to 18 towers. The towers are composed of four columns moulded in the form of a two­ sided or cornered pilaster; they are connected by four panels, secured by screw bolts. The panels up and down stream close the whole side of a tower, but those in the direction of the bridge form an open doorway, which serves for the con­ tinuation of sidewalks from one span to the other. On top of the pilasters or columns, a massive casting rests, which supports the pendulum to which the cables are attached. The upper pin of the pendulum lies in a seat which is formed by the sides and ribs of a square box occupying the center of the casting. For the purpose of throwing the whole pressure upon the four columns underneath, 12 segments of arches butt against the center box, and rest with the other end upon the four corners. The pendulums are composed of four solid bars of 2 feet 6 inches long, from centre to centre of pin, 4 inches by one inch-the pins are three inches in diameter. To the lower pin, the cable of one span is attached directly and the connection formed with the next cable by means of four links of 3 feet 6 inches long and 4 inches by 1 ¼ inch. The opposite cables, as well as the pendulums, are inclined towards each other-the distance between being 27 feet at the top of the towers, and 22 feet at the center of a span. The pendulums on the abutments, however, occupy a verti­ cal position. THE BRIDGES OF PITTSBURGH

The two sidewalks are outside of the cables. and 5 feet wide. The roadway is contracted to 20 feet, and separated from the sidewalks by fender rails. which are raised from the floor by means of b!ocks 6 inches high. 8 feet apart. The total width of the bridge between the railings is 3 2 feet. The anchor chains which hold the cables of the first and last span. are secured below the ground in the same method which was applied to the aqueduct-their oxidation is guarded against in the same manner. The cables are 4 ½ inches in diameter, and protected by a solid wrapper: they are assisted by stays. made of I ¼ inch round charcoal iron: the suspenders are of the same material. I½ inch diameter. and placed 4 feet apart. The peculiar construction of the Monongahela bridge was planned with the view of obtaining a high degree of stiffness. which is a great desideratum in all suspension bridges: this object has been fully attained. The wind has no effect on this structure, and the vibrations produced by two heavy coal teams, weighing seven tons each, and closely following each other, are no greater than is generally observed on wooden arch and truss bridges of the same span. The bridge is principally used for heavy hauling: a large portion of the coal consumed in the City of Pittsburgh passes over it in four and six horse teams. As a heavy load passes over a span, the adjoining pendulum, when closely observed, can be noticed to move correspondingly-the extent of this motion not exceeding one-half inch. By this accommodation of the pendulums, all jarring of the cast iron towers is effectually avoided. Another object of the pendulums is to direct the resultant of any forces to which the work may be subjected, through the centre of the towers, as well as of the masonry below. Two of the piers of the old structure had once given way in consequence of the shaking and pressure of the arch timbers, when subjected to heavy loads. Such an accident can never take place on the new structure, as the piers are only subjected to the quiet and vertical pressure of the towers. I do not recommend the application of pendulums in all cases: but in this, it appeared to me the best plan which could be adopted. The two towers on each pier are connected by a wooden beam, properly encased and lined by the same mouldings which ornament the top of the castings. The lightness and graceful appearance of this structure is somewhat im­ paired by the heavy proportions of these connections, but I had to resort to it for motives of economy. The whole expense of this structure does not exceed $55,000-a very small sum indeed for such an extensive work. A great portion of this work had to be done during the winter, and in cold weather; it was accomplished without any accident, with the exception of one of the workmen who was seized with :fits and killed by falling off a pier. Table of Quantities of Monongahela Bridge Length of bridge between abutments, feet______1.500 Number of spans ______8 Average width of spans from centre to centre. feet ______188 Diameter of cables, inches______4½ Number of wires in each ______750 Weights and tension, tons: Weight of superstructure of one span. as far as supported by the cables______70 Tension of cables resulting from it______122 Weight of four six horse teams. loaded with 104 bushels of coal each ------28 Tension resulting from it when at rest ______------49 Weight of 100 head of cattle at 800 pounds ______40 Tension resulting from it when at rest------­ 70 Aggregate weight of one span as far as supported by the cables. plus 100 cattle at rest ------110 Tension resulting from it______------192 Ultimate strength of two cables______860 Section of anchor chains. inches______26 Section of pendulums, inches ______63 (Reproduced from Palmer's Pittsburgh, 190;.) THE PENNSYLVANIA CANAL IN 1850 AT THE SiTE OF THE PRESENT ~NION STATION. This canal crossed the Allegheny River as described.

DESCRIPTION OF THE SUSPENSION AQUEDUCT FORMERLY ACROSS THE ALLEGHENY RIVER AT ELEVENTH STREET

N 1836, the State of Pennsylvania built a wooden aqueduct at the western termi­ nus of the Pennsylvania canal ayer the Allegheny River a short distance below ] [ the point where Washington and Gist crossed the river on a raft. In 1845 this structure was replaced by a wire suspension aqueduct designed and built by John A. Roehling at a total cost of only $62,000. This included re_moval of the old structure. Work was commenced in September, I 844, and the boats were passed through the new aqueduct in May, 1845, according to an article in the American Railroad Journal (New York), and reprinted in volume I ( 1846, reprinted 1876) of The Olden Time (Pittsburgh) edited by Neville B. Craig. A few excerpts of interest follow: The 'trunk' consisted of 7 spans each 160 feet long. It was of wood l, 140 feet long, 14 feet at the bottom, 16 ¼ feet at the top, and 8 ¼ feet deep. The depth of the water was 4 feet. Two 7-inch cables each consisting of I 900 wires .½ inch thick, were suspended next to the trunk, one on each side. THE BRIDGES OF PITTSBURGH

The extremities of the cables did not extend below ground, but connected with anchor chains which, in a curved line, passed through large masses of ma­ sonry. The last links occupied a vertical position. The extreme links were anchored to heavy cast-iron plates 6 feet square, held down by the foundations, upon which the weight of 700 'perches' of masonry rested. The resistance of the anchorage was twice as great as the greatest strain to which the chain could ever be subjected. A table of quantities follows: Dimensions and Weights of Aqueduct Length of aqueduct without extensions, feet______1.140 Length of cables, feet______1.175 Length of cables, and chains, feet ______1,283 Diameter of cables, inches ______7 Total weight of both cables, tons______110 Section of 4 feet of water in trunk, square feet ______: ______59 Weight of water in aqueduct, tons______2.100 Weight of water in one span, tons______295 Weight of water in one span between piers, tons ______275 Total weight of a loaded span, tons______420 Deflection of cables, feet______14½ Tension of cables resulting from this weight, tons ______392 Tension of a single wire, tons------:------­ 206 Average ultimate strength of one wire, pounds_ __ ------,------1.100 Ultimate strength of cables, tons______2,090 Tension resulting from weight of water upon one solid square inch of wire cable. pounds------14,800 Tension resulting from weight of water upon one square inch of anchor chains, . pounds------11.000 THE CAST- AND WROUGHT-IRON RAILROAD BRIDGE OVER THE MONONGAHELA RIVER IN. 1863.

DESCRIPTION OF AN OLD-TYPE RAILROAD BRIDGE WHICH FORMERLY SPANNED THE MONONGAHELA RIVER

N The Engineering Record for December 19, I 903, is t:he following account of an unusual type of bridge which formed y spanned the Monongahela River at Try ] [ Street, Pittsburgh: · The old bridge consisted of one 260-foot double-track through span about 40 feet deep and four 186-foot deck spans. The trusses were of Linville type with very short panels and double-intersection diagonals. All compression mem­ bers were made of cast iron, and the details throughout were of the earliest types of long-span iron railroad bridges in the United States. The top chords and end posts were made with double tubular cross sections and the end posts were trussed, as shown in the accompanying photograph, with pairs of screw-ended rods which had center bearings on saddle castings and virtually hog-chained the members. The top lateral and sway-brace struts were double :flanged castings with open panels. The portal girders resembled modern portals, but were made with girders, brackets, and web trussing of cast iron. The vertical posts were made with twin uprights connected by webs having large open panels. THE BRIDGES OF PITTSBURGH

The lower chords were made with eye-bars of a maximum width of 6 inches having welded heads. They were connected by pins with a maximum diameter of 4 inches which carried on their inner ends wrought-iron double­ wing plates to which were attached the clevis heads of bottom lateral diagonals. The other ends of the diagonal rods had nuts bearing on the inner surfaces of heavy welded octagonal rings in the centers of the floor-beam panels, which were used instead of sleeve-nut connections. The floor-beams were made with pairs of channels king-post-trussed with pin-connected rods and seated in chairs resting on the bottom chords. The track was carried on wooden stringers. The main diagonal rods were square bars with screw ends and nuts bearing on beveJled seats cast on the top chords and on_ the feet of the vertical posts. The old bridge was built by the Keystone Bridge Company nearly forty years ago, had sustained constant and increasing service ever since, and was found in a remarkably good condition when taken down. Pile falsework piers were built to support it and the traveler and the new bridge during the erection of the latter. The new bridge has an ordinary Pratt-truss superstructure supported on some of the old piers, and two new ones, and is being built by the American Bridge Company, S. P. Mitchell, engineer of erection; H. A. Greene, manager of western division, and James Sheedy, superintendent of erection. CORROSION OF STEEL BRIDGES jj\:~NUMBER of bridges in the Pittsburgh district have been badly corroded by an atmosphere containing more or less sulphurous fumes liberated by works and locomotives. Several small and large bridges have either been repaired or re­ placed when their strength became endangered, and maintenance amounts to a large sum. Doubtless many Pittsburghers have noted the repair work to corroded bridge members, some of which are shown here. As early as 1845, although there were few or no fumes here then, John A. Roehling, who designed and built the wire suspen­ sion aqueduct over the Allegheny River and the suspension bridge over the Mononga­ hela River, realized the importance of protection against corrosion or "oxidation" as he termed it. The anchor chains of the Monongahela Bridge were treated in the same manner as the wire cables and anchor bars for the aqueduct, \\.,.hich was as follows, according to volume I ( 1846, reprinted in 1876) of The Olden Time (Pittsburgh), a monthly publication devoted to the preservation of documents and edited by Neville B. Craig:

Oxidation [ of the wires] is guarded against by a varnish applied to each wire separately; their preservation, however, is insured by a close, compact, and continuous wrapping, made of annealed wire, and laid on by machinery in the most perfect manner. A continuous wrapping is an imp_ortant improvement, which in this case has for the first time [ 1845] been successfully applied. The bars [ anchor chains] ~re painted with red lead; their preservation is rendered certain by the known quality of calcareous cements [ in which were the chains] to prevent oxidation. If moisture could find its way to the chains, it will be saturated with lime, and add another calcareous coating to the iron. This por­ tion of the work has been executed with scrupulous care, so as to render it un­ necessary on the part of those who exercise a surveillance over the structure, to examine it. The repainting of the cables every two or three years will insure their duration for a long period.

Apparently, great care was also taken of the suspension bridge erected in 1859 across the Allegheny River at Sixth Street. In 1883, according to W. G. Wilkins in the Proceedings of the Engineers' Society of Western Pennsylvania for 1895, Francis Collingwood had all of the old paint scraped off the cables and repainted. In 1888, THE BRIDGES OF PITTSBURGH

A CORRODED HANDRAIL.

W. Hildenbrand was employed to examine the cables and anchorages. He cleaned the anchor bars from tar and rust, and coated them (two) with linseed oil and red lead, and imbedded them in paraffin mixed with beeswax and rpsin. He treated the vvires where they joined the links in the same manner. He also saturated the cables with oil, 4 ¼ barrels of which \Vas poured in at many places along the cables. When the cables were taken down in 1890 this oil was found to be ''moist'!-that is, the wires vvere still oily. Although the parts of a steel bridge receive a 'good coat of paint after they have been fabricated at the shop and another coat when they are in place,· also at more· or less irregular intervals thereafter, corrosion continues its destructive action, especially where a bridge crosses a railroad. In simple language, the coal burned by locomotives contains sulphur; the blast from the stack carries some of this sulphur in another form, resulting from burning and contact with the exhaust steam. This is impinged against the under side of a bridge floor; the paint is gradually worn off the steel and the sul­ phurous acid starts to attack the n1etal. Rain and fog also aid the action of the acid.

CORROSION OF A BRIDGE FLOOR. Top side, under roadway. Bottom side of floor beam. THE BRIDGES OF PITTSBURGH

The coating of the under side of a bridge by a method long used in lining tun­ nels and mine shafts, and for many other purposes including fireproofing, is now done in the Pittsburgh district. A mixture of I part of portland cement to 3 ¼ parts of good sharp river sand is applied under air pressure to surfaces with a mechanical de­ vice called a cement gun. Technically, this mixture is a cement plaster applied pneu­ matically. It differs from regular cement plaster in that water is added to the cement and sand during application; combined with the tamping action of the sand and gravel, this method gives the resultant mixture a greater density, and it is more impervious and stronger than ordinary cement plaster. Another desirable quality is that it makes excellent adhesion to rock, brick, tile, concrete, and other surfaces used in construc­ tion. In coating a bridge, the metal should be free of paint; wire netting is fastened to the steel work, and then the mixture is applied in layers to a thickness of I ;/2 to 2 inches. The finish is smooth and of good appearance, and the steel is fully protected. It is most effective if the finish is left in its natural state, not troweled in any manner. Many new and old bridges are now coated ,vith aluminum paint. Actually. this is a coat of flaked or leafed metal, waterproof and resistant to fumes, reflects instead of absorbs the heat of the sun, and is attractive in appearance. PITTSBURGH: A SELF-CONTAINED BRIDGE-BUILDING DISTRICT

ITTSBURGH is virtually a'self-contained bridge-building district. Many materials ] contribute to the construction of a bridge and many contracts are let before the PL structure is complete. The only material that we lack to be fully self-con­ tained is iron ore; this is imported from Minnesota, but in the western Allegheny Mountains is ore remaining from that which supplied Pittsburgh furnaces· during the period 1780-1830. The pictures following are represenfative of the industries that produce materials which contribute to the complete construction of a bridge. Refrac­ tory clays and silica which are made into bricks and various shapes for the many types of furnaces are mined and fabricated in the district.

A TRIP OF CARS IN A LARGE, MODERN COAL MINE. THE BRIDGES OF PITTSBURGH

WHERE 30,000 TONS OF COAL ARE DAiLY CONVERTED INTO COKE. GAS, TAR. AMMONIA .. AND BENZOL. The coke is used in blast furnaces. and the gas and tar in open-hearth furnaces.

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DRIFT MOUTH AND TIPPLE OF A LIMESTONE MINE AT KAYLOR. NEAR EAST BRADY, ARMSTRONG COUNTY. PENNSYLVANIA. This mine produces 4,000 tons a day. Limestone is used for the following purposes in connection with bridge construction: Fine dust for applying to coal dust in mines to render it non-explosive; lump as a flux in blast furnaces and open-hearth furnaces; finely ground for making cement; calcined for making mortar; lump for use in concrete; and blocks for masonry. THE BRIDGES OF PITTSBURGH

A TRAIN OF lRON ORE r-ROM l\IINNESOTA FOR PITTSBURGH BLAST FURNACES.

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ONE or- A GROLiP OF SiX ;'\lCD[Ri'\ BLAST l~URNACES l\.IAKiNG IRON.

106 THE BRIDGES OF PITTSBURGH

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TAPPING STEEL FROM A LARGE OPEN-HEARTH FURNACE.

ROLLING STEEL PLATE. THE BRIDGES OF PITTSBURGH

A PLANT USING LIMESTONE AND BLAST-FURNACE SLAG AND .MAKING 50,000 BAGS OF CEMENT A DAY.

A MODERN DREDGE DIGGING AND PRODUCING FROM THE OHIO RIVER SEVERAL THOUSAND TONS OF CLEAN SAND AND GRAVEL A DAY, USED FOR MAKING CONCRETE. ACKNOWLEDGMENTS

N THE preparation of these records on the bridges of Pittsburgh the authors nat­ ] [ urally became imbued with a profound respect for the men who were responsible in various ways for the existence of these- great engineering structures. Unfortu­ nately, it is not feasible to record their names nor to evaluate the work they did be­ cause of a large number of bridges involved and because this review covers a period of more than a century. It so happens, however, that during the past four years the most concentrated bridge-building program of our history was consummated, and it is eminently fitting to pay respect to the public officials who guided this work. Joseph G. Armstrong, a former mayor of the City of Pittsburgh, acted as chairman of the Board of County Commissioners which formulated and directed the program. His associates were E. V. Babcock, also a former mayor of Pittsburgh, James Houlahen, and Addison C. Gumbert who died in 1925 in the midst of these activities. · The County Department of Public Works carried out the engineering and construction work under the direction of the Board of County Commissioners. Nor­ man F. Brown, the director of this Department, has exerted over a period of years a marked influence on the bridges of this district. He vvas formerly the director of the Department of Public Works of the City of Pittsburgh, and before this, as engineer with the Pennsylvania Railroad he participated in the construction of the· great rail­ road bridges here. Charles M. Reppert was the assistant director of the County De­ partment of Public Works and later became chief engineer of the City of Pittsburgh. Vernon R. Covell, chief engineer of the County Bureau of Bridges has rendered thirty years of expert service on the bridges throughout the County. John D. Stevenson, chief engineer of the Bureau of Bridges and Structures of the City of Pittsburgh, has been responsibly engaged on the bridges of the City for a long period of years. Other engineers who courteously supplied information and illustrations are: Beaver County-through T. J. Wilkerson, engineer of bridges. Westmoreland County-through W. A. Wynn, engineer, Department of Roads and Bridges.

Railroads-Baltimore ~ Ohio, through P. G. Lang, Jr., engineer of bridges; Bessemer ~ Lake Erie, through F. I. Snyder, vice-president and general manager; Pittsburgh~ Lake Erie, through A. R. Raymer, assistant vice-president and chief en­ gineer; Pennsylvania Railroad, through J. T. Leonard, chief engineer, Division of Bridges and Structures; Pittsburgh ~ West Virginia, through H. H. Temple, chief engineer; Pittsburgh Railways Company, through M. W. Cooke, superintendent of traffic, and C. W. Wilson, research manager; and Union Railroad, through W. S. McAbee, general superintendent. Bridge-builders - American Bridge Company, Contract Division; McClintic­ Marshall Company, Independent Bridge Company and Fort Pitt Bridge Works. THE BRIDGES OF PITTSBURGH

Substructures-Dravo Contracting Company, through J. S. Miller, vice-presi­ dent, and W. H. Fowler, secretary. - Steel companies-Carnegie Steel Company, through A. N. Diehl, vice-president; and Jones~ Laughlin Steel Corporation through T. M. Girdler, president, and W. T. Mossman, advertising manager. The authors are also indebted to Stanley L. Roush, consulting architect to the City and County, for his essay on the architectural features of bridges; to E. K. Morse, consulting engineer for information regarding the suspension bridge in Beaver County: to the Historical Society of Western Pennsylvania, through \Villiam H. Stevenson, president, for information and the right to reproduce certain old pictures; and to the following for various pictures used: Universal Portland Cement Company; Pitts­ burgh Limestone Company; Portland Cement Association; Pittsburgh Photo-En­ graving Company; Trinity Court Studios: United States Bureau of Mines and United States Engineer Office. INDEX.

Page Page Acid. effect of on bridge metal______I 7, IO 2 Bridges. beauty in ______1 1 formation of ------I 02 Beaver River ------· 66 Alinement of highways and bridges ______l6. 18. 19. 73 cable is first part made and last part dis- Allegheny County bridges freed of tolls______23-24 mantled ______6- 7 formerly split by rivers______VI cable suspension ______7. 35. 45. 48. 65. 97 Allegheny River as in 17 5 8 ______Frontispiece cantilever ______3, 4. 5. 6. 33. 34. 37. 38. 41. as in 1849 ______35.48 46. 57. 64, 65. 70 as in l 928 ______frontispiece cantilever types explained______2-6 bridges ------32. 47-61 comparison of types------2-9 depth of rock in ______9 construction of various__l-9. 19. 50. 52. 54. 63. 70, Aluminum paint. use of on bridge::; ______14, I 03 73. 88. 93 American Bridge Company. acknowledgment to . IO 9 corrosion of steel ______101-103 Ammann, 0. H., cited for cable suspension crossed by street railways ______79 bridges ------­ 6 curve of various types of______2-6 Aqueduct across the Allegheny River. descrip- deck-cantilever ______3, 4. 5. 43. 70 tion of ------9 7 -9 8 deck-truss ______38. 40. 41. 42. 46. 59. 62. 66. 73 Arch, locking an------I derricks for erecting __ 4, 7. 9, 19. 50. 52. 54. 63. 70. bridges. types of______1-5 73. 93 of reinforced concrete ______3, 4, 10. 11. 68. 69, 72 differenc~ between cable and eye-bar sus- of steel ______2, 3, 54. 56 penEon ______6 of stone ------2, 71 embellishment of ______12 Architects and engineers. collaboration of______I 0 enhanced safety of malleable-iron handrails . 14 Architectural structure. the bridge as an ______10-15 erection of self-anchored suspension ___ 50. 52. 86-90 Armstrong, Joseph A., cited for bridge-building examples of reconstruction due to automo- program ______109 . biles and railroads ______16 Art Commission of Pennsylvania ______10 eye-bar suspension ____ 7, 13. 33, 49. 50. 52. 88. 89 Art Commission of Pittsburgh ______IO falsework for ______4. 5 O. 5 2. 54 Art Commissions, function of ______10 freed of tolls in Allegheny county. record of 23-24 Art in bridges ------­ I 0, 11 (highway) over railroads__8, 18. 33. 36, 37, 38. 39, Automobiles. influence of on bridge construction 16- I 9 41.42.43.44.45.46.47.49, 52. 54. 56, 57. 58. 60, 64. 65. 68. 70. 73 Babcock. E. V., cited for bridge-building pro- over rivers __ 33. 36. 37. 38. 39. 41. 42. 43. 44, gram------109 45. 46. 47, 49. 52. 54. 56. 57, 58. 60. 61. Baltimore and Ohio Railroad bridges______3 9. 5 5. 7 5 64. 65. 66 Baltimore and Ohio Railroad Company. acknowl- hot-metal ______38. 40. 41 edgment to ------·------109 how to recognize types of ______1-9 Beaver River bridges ______32. 66 lengthened by correcting road alinement ____ 1 9 Bessemer and Lake Erie Railroad bridges ______59. 75 Monongahela River ______3 3-45 Bessemer and Lake Erie Railroad Company ack- of Pittsburgh district photographic review__ 3 1-6 6 nowledgment to ------109 Ohio River ------62-65 Blast furnace, view of a ______10'5 over navigable streams. requirements of Fed- Boring for rock in rivers------­ 9 eral Government ______l, 11. 20-22 Bridge as an architectural structure----·------l 0- 1 5 over ravines and minor streams ______l 0. 11. 6 7 -7 3 building community. Pittsburgh a self- plate-floor type ______80 contained ______.VII. I 04-108 plate-girder ______9. 18. I 9. 7 3 construction. influence of automobiles on ___ I 6-1 9 Point ______Frontispiece. 3 3 description of suspension at Smithfield Street 9 5- 9 6 (railroad) description of______7 4-7 8 design. art in ______11 over higT1way ______2 designers and builders. opportunities for at over rivers_ __ 34, 37. 38. 39. 40. 41. 42. 44. 45. Pittsburgh ______1 5 53, 55. 58. 59. 61. 62. 65. 66 fires a danger of the past ------­ 26-28 over railroads ___ 34, 37. 38. 39. 40. 41. 42. 44. fish-belly type ------­ 8. 36 53. 55. 58. 59. 62. 65 floating Sixth Street to Coraopolis------­ 91-94 reinforced-concrete ______3, 4. 10. 11. 68, 69. 7 2 floor. corroded ------· ------102 safety in aliriement of highways and bridges 18 handrails and lighting fixtures ______14-1 5 in not walking across railroad______7 7 over navigable stream. negotiations before precautions against skidding______I 7 building ______------20-22 shortest are at right angles to streams______I 7 portals ______I 2. I 3. 33. 36. 40, 47. 60. 81. 99 skew------18 (railroad) cast- and wrought-iron ______99-100 spandrel-arch ------68-69 roadways and sidewalks______l 3 steel-arch ______2, 3. 54. 56 width of river______16 The Region of______VI types. classification of______I through cantilever __ 5, 6. 33. 34. 38. 46. 57. 64. 65 Bridges. absence of toll in Pittsburgh district___ 2 3-2 5 through-truss ____ 8, 13. 17. 18. 36. 37. 38. 39, 40. Allegheny River ______4 7 -61 41. 42. 43. 44. 45, 46. 47. 49. 51. 53. 54, and environment ______10-13 55. 57. 58. 60. 61. 62. 66, 73. 81. 99 art in------IO truss with curved chord ___ 8, 13, 36, 37, 38. 39, 40. artistic ------10 41.42,43.44,45,47,49, 53. 54. 55. 57, • at Sixth Street, description of the four_____ 84-90 58, 60, 61, 62, 66 INDEX

Page Page Bridges, truss with horizontal chord ____ ! 7. 38. 40. 41. Gunite, use of______I 03 42.45.46. 51. 73. 99 Handrail. a corroded______102 type§ of arch ___ l, 2. 3, 4, 5. 10. 11. 54, 56. 68. 69. Handrails and lighting fixtures______14-15 71. 72 Highway bridges over railroads_ __ 8. 18. 33. 36. 37. 38, vibrations in ------29-30 what are self-anchored suspension ______8 39.41. 42.43. 44.45. 46.47,49. 52. 54. wooden ______26. 35.47,48. 56 56. 57, 58. 60. 64. 65. 68. 70. 73 , Youghiogheny River ______45-46 over rivers __ 33. 36, 37, 38. 39. 41. 42. 43. 44, 45. Brown. Norman F., cited for essay on bridge 46.47.49, 52. 54. 56. 57. 58. 60, 61. 64. negotiotions ______20 65. 66 Historical Society of Western Pennsylvania. cited for work in bridge-building______109 acknowledgment to ______11 O Hot-metal bridges______3 8. 40. 41. 80-81 Cable and eye- bar suspension bridges. difference what are ______80-82 between ------6 suspension bridges______?, 35. 45. 48. 65. 97 Houlahen. James, cited for bridge-building pro- Cables. how made______6 gram------109 Caisson. what is a______9 Independent Bridge Company. acknowledgment Cantilever bridges ____ 3, 4. 5. 6. 33. 34. 37. 38. 43. 46, to------109 57. 64. 65. 70 Iron. hauling molten over bridges______80. 82 types of explained______2-6 Iron ore from Minnesota for Pittsburgh______106 changed to suspension______90 supply ______VII. I 06 Carnegie Steel Company. acknowledgment to __ 110 hot-metal bridges ______80. 81 Jones t!S Laughlin Steel Corporation. acknowl- Cast- and wrought-iron railroad bridge ______99-100 edgment to______110 hot-metal bridge ______80 Cement gun. use of------103 plant, view of a______108 Coal for coking ______VII. 104 Ladles, types of for molten iron and slag ______. 82 Lang. P. J .. acknowledgment to ______109 mine. scene in a------104 Legal procedure required before building bridge Coffer-dam. what is a ------9 over a navigable -stream ______Coking plant by-products of a______I 05 20-22 view of a______I 05 Leonard. J. T .. acknowledgment to ______109 Lewis. J. L.. acknowledgment for map ______79 Construction of various bridges __ l-9, 19, 50. 52. 54. 63. Lighting fixtures and handrails______70. 73. 88. 93 14-15 Limestone mine, view of a ______105 Cooke. M. W .. acknowledgment to______109 ures of ______Coraopolis, moving Sixth Street bridge to_____ 91-94 105 Corrosion, early protection against______101 Map of Allegheny County bridges ______of bridge steel ______102 32 of railroads and bridges______74 Cost and weight of certain bridges______83 of street-railways and bridges______78 of bridges increased by abolishing railroad crossings ______1 6 McAbee. W. S .. acknowledgment to ______109 McClintic-Marshall Company, acknowledgment Covell. V. R .. cited for work in bridge-building 109 to------109 quoted description of Seventh Street bridge__ 86-90 .McKeesport, bridges at or near______42, 43, 45, 46 Curve of various types of bridges______2-6 Miller. J. S., acknowledgment to______110 Deck bridge. what is a______1 Monongahela River. as in 175 8 ______Frontispiece -cantilever bridges ______3, 4. 5, 37, 43. 70 u in 1849 ______35, 48 Definitions of types of bridges______1-9 as in 1928 ______Frontispiece Derricks. ere~tion _ 4. 7. 9. 19. 50. 52. 54, 63. 70, 73. 93 bridges ------______3 2. 3 3-4 5 Diehl. A. N .. acknowledgment to ______.:_____ 110 depth of rock in------9 Dravo Contracting Company acknowledgment to 110 Morse. E. K .. acknowledgment to ______1 1 0 Dredge. view of a______10 8 Mossman. W. T .. acknowledgment to______110 Embellishment of bridges______12 Navigable stream. negotiations required before Engineers and architects. collaboration of______10 building bridge over a______20-22 and bridges ------VII. 11 streams, bridge requirements of Federal Gov- Environment of bridges ______10-13 ernment ______1. 11. 20-2 2 Eye-bar and cable suspension bridges. difference Ohio River bridges ______32, 62-65 between ------6 depth of rock in______9 suspension bridges ____ 7, 13, 33. 49. 50. 52. 88. 89 Eye-bars. cutting ______7 Open-hearth furnace, scene at a______107 Ornamental features of bridges______1 2 Falsework. use of______4, 50. 52. 54 Paint (aluminum) on bridges ______14. 103 Fires. attributed cause of certain bridge______27-28 Painting bridges ______------101. 102. 103 on bridges a danger of the past______26-28 Pennsylvania Railroad bridges__ 3 7. 41. 5 3, 5 8. 61. 6 2. Fish-belly type bridge______8. 3 6 66. 76. 77 Fort Pitt Bridge Works. acknowledgment to ___ 109 Pennsylvania Railroad Company. acknowledg- Foundation Company. cited for moving bridge_ 91 Fowler. W. H .. acknowledgment to______110 ment to------109 Furnace, blast ______106 Piers. construction of______9 open-hearth ______107 disintegration of______51 Pittsburgh and Lake Erie Railroad bridges-40, 45, 65, 78 Girder, construction of plate______8 Pittsburgh and Lake Erie Railroad Company, ranges in sizes ------9 acknowledgment to______109 Girdler, T. M .. acknowledgment to______110 Pittsburgh and West Virginia Railway bridges__ 34, 78 Gumbert, A. C., cited for bridge-building pro- Pittsburgh and West Virginia Railway Company, gram------109 acknowledgment to______I 09 INDEX

Page Page Pittsburgh as a railroad center______74 Skew bridges ------I 8 a self-contained bridge-building commun- Skidding on bridges______17 ity ______VII. 104-108 Slag. hauling molten across bridges______82 Art Commission of______10 Snyder. F. I.. acknowledgment to______109 certain bridge fires of______26-28 Spandrel-arch bridges ______68-6 9 district. absence of toll bridges in______23-25 Steel-arch bridges ------2, 3. 54. 56 in 1758 ______Frontispiece bridges. corrosion of ______l O1-10 3 in 1845 ------26 cost of in 1914 and 1928 ______.:..____ 83 in 1849 ------35. 48 plate, rolling ______107 in 19 28 ______Frontispiece traffic strips. use of ______:______I 7 opportunities for bridge designers and builders 1 5 Stevenson. J. D .. cited for work in bridge- traffic inflow and outflow------79 build:ng ______------109 Pittsburgh Photo-Engraving Company. ack- Stevenson. W. H., acknowledgment to ______110 nowledgment to ______110 Stone-arch bridges ______2. 71 Pittsburgh Limestone Company. acknowledg- Street railways and bridges ______ment to ______79 110 Substructure. what is the ______:.... ______9 Pittsburgh Railways Company. acknowledg- Superstructure. what is ______9 ment to------109 Suspension aqueduct across the Allegheny River. Plate-girder bridges______9, 18. 19. 73 description of------97-9 8 Point bridges ______Frontispie.:e. 3 3 bridge . (~oebling) at Smithfield Street. de- Pool-full or pool-level. what is______1 scription of .. ______95-96 Portals of bridges_ ___ l2. 13. 33. 36. 40. 47. 60. 81. 99 bridges. cable is first part made and last part Portland Cement Association. acknowledgment dismantled ______6-7 to------110 definition of self-anchored ______8 Pylons, a feature of bridges______1 2. 3 7. 4 9. 5 2. 8 9 Temple. H. H .. acknowledgment to______109 Raiiroad bridge cast- and wrought-iron______9 9-100 Through bridge. what is a______1 bridges. description of______7 4-7 8 cantilever bridges ___ 5, 6. 33. 34. 38. 46. 57. 64. 65 over highway bridges ______2 Toll bridges in Pittsburgh district. absence of___ 23-25 over railroads ___ 34. 37, 38. 39. 40. 41. 42. 44. views of Federal Government and certain 53. 55. 58. 59. 62. 65 journab ------24-25 over rivers_ __ 34. 37. 38. 39. 40. 41. 42. 44. 45. Trinity Court Studios, acknowledgment to____ 110 53. 55. 58. 59. 61. 62. 65. 66 Truss bridges, deck-type ____ 38. 40. 41. 42. 46. 59. 62. grade crossings. danger of______1 6 66. 73 traffic in Pittsburgh district______VI. 7 4 with curved chord ____ 8, 13. 36, 37. 38. 39, 40. 41. Raymer, A. R .. acknowledgment to______109 "42.43.44.45. 47.49. 53. 54. 55. 57. 58. Reinforced-concrete arch bridges_3, 4. 1 O. 11. 68. 69. 72 60. 61. 62. 66. 73 Reppert, C. M .. cited for work in bridge-build- with horizontal chord ___ l7, 38, 40. 41. 42. 45. 46. 109 51. 73. 99 River bridgesing ------of district______31-66 Union Railroad bridges ______44. 76. 80 steamer, bridges as seen from a ______31-66 Rivers, clearance space between pool-level and Union Railroad Company. acknowledgment to__ 109 United States Bureau of Mines, acknowledgment bridg~ ------1. 20 Roadways and sidewalks. wider ______13 to------110 Rock. depth of in rivers______9 United States Engineer Office. acknowledgment Roehling. John A .. quoted for pioneer bridge- to------110 building and corrosion ______95-98. 101 Universal Portland Cement Company. acknowl- Roush. Stanley L.. acknowledgment to ______110 edgment to______110 essay on architecture by ______10-15 Viaduct. Duquesnl? ______73 Vibrations in bridges______Safety enhanced by malleable iron handrails____ 14 29-30 in alinement of highways and bridges_____ 18 Weather. effect of on bridge roadways______17 in higher curbs______17 Weight and cost of certain bridges______8 3 in not walking across railroad bridges_____ 77 Wilkerson. T. J .. ·acknowledgment to______109 precautions against skidding______I 7 Wilkins. W. G .. quoted description of bridges__ 84-85 Sand and gravel dredge______108 Wilson. C. W .. acknowledgment to ______.:____ 109 Self-anchored suspension bridges. erection of___ · Wooden bridges------···--- 26. 35. 47. 48. 56 50. 52. 86-90 Workmen. fearless ______VII wh~ are______8 Wynn, W. A .. acknowledgment to______109 Sixth Street bridge. floating to Coraopolis ----- 91-94 bridges. technical description of the four---- 84-90 Youghiogheny River bridges______45-46