Table Of ContentThe Colossus of 1812:
An American Engineering Superlative
by Lee H. Nelson
Published by the
American Society of Civil Engineers
345 East 47th Street
New York, New York 10017-2398
ABSTRACT
This book presents the developments in bridge building that
occurred in the United States toward the end of the eighteenth
century and in the beginning of the nineteenth century. With the
growing need for bridges and the willingness to invest in such
enterprises, American bridge builders were encouraged to be
daring and inventive in their design. Their inventiveness led to
the development of long-span wooden bridges with laminated
members where the laminated members were used not only for
major chords but for arched ribs in compression as well. This
structural evolution in bridge design culminated with the build-
ing of the "Colossus" of Philadelphia, a 340 ft clear span wooden
bridge designed and built by Lewis Wernwag in 1812. After
explaining the historical context of this superstructure, the book
then discusses "Colossus" in relationship to its wind bracing,
abutments, and structural defects. In addition, a summary of a
computer analysis of the bridge is presented. Due to Wern-
wag's innovated and superlative design, "Colossus" captured
the imagination of both the romantic and technological minds
of the day and influenced American bridge building for some time
to come.
Library of Congress Cataloging-in-Publication Data
Nelson, Lee H.
The colossus of 1812: an American engineering superla-
tive/by Lee H. Nelson.
p. cm.
ISBN 0-87262-737-9
1. Lancaster-Schuylkill Bridge (Philadelphia, Pa.) 2. Bridges,
Wooden—Pennsylvania—Philadelphia—Design and con-
struction—History. 3. Philadelphia (Pa.)—Buildings, struc-
tures, etc.
I. Title.
TG25.P52N45 1990
624'.6'0974811—dc20 89-18612
CIP
The Society is not responsible for any statements made or
opinions expressed in its publications.
Authorization to photocopy material for internal or personal use
under circumstances not falling within the fair use provisions of
the Copyright Act is granted by ASCE to libraries and other users
registered with the Copyright Clearance Center (CCC) Trans-
actional Reporting Service, provided that the base fee of $1.00
per article plus $.15 per page is paid directly to CCC, 27 Con-
gress Street, Salem, MA 01970. The identification for ASCE
Books is 0-87262/88. $1 + .15. Requests for special permis-
sion or bulk copying should be addressed to Reprints/Permis-
sions Department.
Copyright © 1990 by the American Society of Civil Engineers,
All Rights Reserved.
Library of Congress Catalog Card No: 89-18612
ISBN 0-87262-737-3
Manufactured in the United States of America.
Preface
Mr. Nelson deserves the thanks of all civil al career in the rewarding field of historic preservation
engineers for his scholarship and dedication in pro- and so has an intimate knowledge of structures. He
ducing this oustanding book. It concerns one of the couples this knowledge with his sense of history to
greatest structures ever produced by an American civil produce a book that gives the reader both technical
engineer, but one that has received very little attention and historical insights which give it a double appeal to
by historians. To put this in perspective, "The Colos- both civil engineers and historians.
sus" had the greatest span [340 ft] of any wooden Although it has been the long-term policy of the
bridge ever built. [N.B. Burr's McCall's Ferry Bridge, American Society of Civil Engineers to publish out-
which lasted only a very short time, may have had a standing scholarly works on civil engineering history,
slightly greater span, but this has never been verified.] there have been far too few to have even been
In any case, with the publication of this book a long- considered. When this book was received by the
term historical oversight will have been rectified. Committee on the History and Heritage of American
The writing of this book is a story in itself. Mr. Civil Engineering, it was unanimously approved for
Nelson's interest in bridges stems from his boyhood in publication.
Portland Oregon, which is famous for its many
It is hoped that the publication of this book will
crossings of the Willmette River. It was largely due to
encourage architects, civil engineers, and historians to
his publication of 'Oregon Covered Bridges,' in about
undertake the necessary research and writing to
1960, that a citizen's effort to save the state's remain-
produce other works of this nature and caliber.
ing structures was inaugurated. Later, Mr. Nelson
Manuscripts or even ideas would be welcomed by the
went to Philadelphia to work on the preservation of
Committee.
Independence Hall and other historic structures. In the
library of the Historical Society of Pennsylvania he
came across the papers of the Colossus Bridge. Then, Neal FitzSimons, Fellow ASCE
for over 15 years he pursued the task of writing this Chairman, Committee on
book. History and Heritage of
Mr. Nelson, an architect, has spent his profession- American Civil Engineering
iii
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CONTENTS
Introduction 1
American Experiments with "Laminated" and Multiple-Membered Arches 5
The "Colossus": An Historical Outline 19
The "Colossus" Superstructure 27
Superstructure: Statics Discussion 36
Summary Report on the Computer Analysis of the "Colossus,"
by Jon E. Morrison, P.E 38
Wernwag's Design in Historical Perspective 39
Wind Bracing 42
The Abutments and the Structural "Defect" 43
Conclusion 47
Footnotes 53
A Brief Chronology of Lewis Wernwag 59
Index 61
V
ILLUSTRATIONS
FIG. 1. Engraving of "The Wooden Bridge at Schaffhau- FIG. 16. Engraving of "Wernwag's Bridges," Published
sen in Switzerland/' Built 1756-1758 ca.1815
FIG. 2. Engraving of "Geometrical Elevation of the Tim- FIG. 17. Engraving of Thomas Pope's "Flying Pendent
ber Bridge at Wettingen [Switzerland]/' Built in Lever Bridge," Published in His Treatise on Bridge
mid-1760s Architecture, 1811
FIG. 3. Engraving of Anonymous American Bridge De- FIG. 18. Scale Elevation Drawing Showing Four Bays of
sign, Published in Columbian Magazine, Philadel- "Colossus" Superstructure, by Lee H. Nelson
phia, Jan., 1787 FIG. 19. Isometric Drawing Showing Details of Six Wood-
FIG. 4. Title Page from Charles Willson Peale, An Essay on en Members which Comprised Arch of "Colos-
Building Wooden Bridges, Philadelphia, 1797 sus," by Lee H. Nelson
FIG. 5. Plan and Elevation, from Peale's 1797 Pamphlet
FIG. 20. Isometric Drawing Showing Arched Rib, Trussing,
FIG. 6. Lamination Details, from Peale's 1797 Pamphlet
and Supplementary Ironwork, at Mid-Span, by
FIG. 7. Typical Trussed "Railing/' from Peale's 1797
Lee H. Nelson
Pamphlet.
FIG. 21. Enlarged Details from ca. 1815 Engraving of
FIG. 8. "Official" View of Schuylkill Permanent Bridge,
"Wernwag's Bridges"
Philadelphia, Built 1801-1804, by Timothy Palm-
FIG. 22. Framing Diagram and Force Diagram Showing
er
Arrangement of Wooden and Iron Structural
FIG. 9. C.A. Busby Drawing of "Permanent" Bridge,
Members and Relative Tension and Compression
Published in London in 1823
Forces in Various Members, Based upon Computer
FIG. 10. E.H. Gill Drawing of "Permanent" Bridge, Pub-
Analysis, by Lee H. Nelson
lished by Weale, London, 1839-1847
FIG. 23. Diagrammatic Plan and Cross Section of "Colos-
FIG. 11. Details of "Permanent" Bridge, by Gill, Published
sus" Showing Three Ribs Bearing against Abut-
by Weale
ments of Stone and Piling, by Lee H. Nelson
FIG. 12. C.A. Busby Drawing of "Celebrated" Bridge
FIG. 24. Incorrect Delineation of "Upper Schuylkill
Across Delaware, built at Trenton, N.J., by Theo-
dore Burr, 1804-1806, from Measurements Taken Bridge," by C.A. Busby, Published in London,
"on the Spot," 1819 1823
FIG. 13. Partial Plan and Elevation of Delaware River FIG. 25. Jacob Plocher Engraving of "Upper Ferry Bridge,"
Bridge, at Trenton, 1804-1806, from ASCE Trans- from Painting by Thomas Birch
actions article by Theodore Cooper, 1889 FIG. 26. Birch View of "Upper Ferry Bridge" as Represent-
FIG. 14. Drawing Showing Comparative Aspects of Four ed on English Staffordshire Plate
Early American "Laminated" Arch Bridges, by FIG. 27. Watercolor of "Upper Ferry Bridge," by David J.
Allan Lee Nelson Kennedy, 1836
FIG. 15. "Official" Plan and Elevation of "Colossus" (i.e., FIG. 28. Painting of Fairmount Water Works and the
Lancaster-Schuylkill Bridge), Published 1814 "Colossus"
vi
Introduction
The last decade of the eighteenth century and the 1-3).
first decade of the nineteenth century was one of those Starting in the last decade of the eighteenth
incredibly innovative periods in the history of Ameri- century, American bridge builders began to demon-
can bridging—a period that encompassed the building strate their own daring and inventiveness in the
of mighty wooden bridges in America—bridges that development of long-span wooden bridges with lami-
were daring (or reckless) by modern standards—with nated members; and, shortly after the turn of the
builders that were inventive in their efforts to elimi- nineteenth century, some American bridges utilized
nate the traditional (and inefficient) mortise and tenon laminated members not only for major chords, but for
joints—structures that pushed American wooden arched ribs in compression as well. Perhaps the use of
bridge technology a bit beyond the state of the art as it such arched ribs is the most interesting aspect of this
then existed in Europe—and, bridges that met the early American "track" of laminated bridge construc-
almost unrealistic expectations of local governments tion.
and speculators for the economic expansion of Ameri- Today, of course, there are more modern defini-
ca in the early days of the Republic. tions for the term laminated wood, but, with our
When you look at the European bridge construc- historic focus on laminated arch construction, we are
tion context (primarily German and Swiss) for the defining it as meaning wooden arches consisting of
latter part of the eighteenth century as it might have multiple members of wood, bound together with bolts
influenced American bridge builders, you are left with or pins or iron bands so as to intentionally act as one
the impression that American builders did surprisingly larger composite arched structural member, bearing
little borrowing from the Old World for their structural against the faces of the abutments rather than resting
ideas, despite the fact that some European wooden on top of the abutments.
bridges were well known in America through builder's The leading American theoreticians and experi-
treatises, traveler's accounts, and published engrav- menters in this new phase of laminated construction
ings of the bridges. From these early views and from were Charles Willson Peale (1741-1827), whose con-
the rare surviving wooden bridges in Switzerland, we tributions to the subject have (unfortunately) been
can draw some tentative conclusions about American largely discounted; Timothy Palmer (1751-1821), a
bridges at the end of the eighteenth century. First, they productive and innovative Yankee bridge builder
had a structural design clarity that was lacking in most whose long-lived constructions began to "bridge" the
European wooden bridges, which were then burdened gap between conventional carpentry and more effi-
with very complicated, wood-wasteful carpentry, in- cient ways of spanning American waterways; and
volving multiple Queen-post trusses within a given Theodore Burr (1771-1822), an ingenious and daring
bridge, resulting in many diagonal members between (and perhaps overly ambitious) builder whose designs
the vertical posts, and with the most dazzling, labor- attracted European interest and had a long-lasting
intensive use of continuous zig-zag joints, secured impact on American bridge building.
with wedges, to laminate several timbers into a larger The remarkable structural evolution that marked
chord member. American bridges tended to have the latter stages of American engineering empiricism
structural bays that, by present standards, were more in the early nineteenth century was culminated in a
rational, that is, consisting of simple triangles rather dramatic way with the "Colossus" of Philadelphia, a
than structural bays with polygonal shapes. 340-ft clear span wooden bridge designed and built
There had been a long tradition of wooden truss (and named) by Lewis Wernwag in 1812. It was world
bridges in Germany and Switzerland, where (like famous in its own time, and for good reason. By
America) there was a plentiful supply of strong, Victorian standards, it was a romantically handsome
straight timbers, and some of their eighteenth century structure in a picturesque setting adjacent to the
bridges were well known to Americans. The bridge at Philadelphia Waterworks. It was the longest clear span
Schaffhausen, in Switzerland, for example, was fa- wooden bridge in the world when it was built. For that
mous in its own time (from engravings and published reason, as well as for its setting, it was admired by
descriptions); but neither the Schaffhausen bridge nor engineers and artists from the United States and
its contemporaries seem to have had much structural abroad. In short, it was America's premier engineering
influence in America, though they did demonstrate superlative of the early nineteenth century. In histori-
that long-span bridges could be built of timber (Figs. cal perspective, it was a world-class structure.
1
FIG. 1. complicated roof framing, are what typifies many of the
'The Wooden Bridge at Schaffhausen in Switzerland." Swiss bridges from the last half of the eighteenth
This bridge was internationally famous in its own time, century. They were made even more complex with
having been built 1756-1758 by Hans Ulrich Gruben- their auxilary struts and longitudinal zig-zag scarf
mann of the then-celebrated Grubenmann family of joints, which laminated several timbers into one larger
carpenters. He first proposed a single-span bridge, but chord. Fig. 5, along the bottom of this plate, shows the
this was too daring for the authorities, who required zig-zag joint with its wedges that interlocked the
that the center pier from a previous multispan bridge multiple members into one larger composite member.
be reutilized. The story goes that Grubenmann cleverly Figure 6 (just above) shows a somewhat more conven-
redesigned his single-span bridge into what only tional scarfed joint that spliced the ends of individual
appeared to be a two-span bridge (to satisfy the timbers into longer continuous members. These as-
authorities), but that it did not rest on the center pier pects were typical of many less ambitious spans in
(to prove that he could do what he had proposed). Germany and Switzerland.
Despite this story, the consensus of opinion of those Although it must be admitted that structural
who inspected the bridge was that it was a true two- details are not available on American bridges until the
span bridge, and that it did rest on the center pier. latter 1790s, there is no evidence that American
There are a number of discrepancies about its length bridges utilized such multiple queen-post trusses, nor
and its details, but the two unequal spans were do they seem to have used other aspects of those
approximately 193 and 171 ft. It was a daring and complicated carpentry systems, such as the zig-zag
large-scale project, consuming 400 large fir trees. It continuous scarfing for laminating timbers.
was visited and admired and depicted by many. Plate LXXXIX, entitled "BRIDGE," engraved by
Although this bridge was atypical in terms of its [William] Kneass, a Philadelphia engraver, is probably
length and scale, it was similar to many other bridges from one of the numerous encyclopedia published in
of the day in that structurally it was a multiple queen- Philadelphia in the early nineteenth century. Courtesy
post system. The many resulting diagonals, with very of Nicolas F. Veloz, Jr.
2
FIG. 2.
"Geometrical Elevation of the Timber Bridge at Wettin- of about seven feet.
gen." This remarkable structure, over the Limmat (near If any European bridge can be said to have
Baden in northeast Switzerland), was built in the mid- influenced an American bridge, it was probably the
1760s by members of the Grubenmann family. Like the Wettingen Bridge. To the extent that it utilized laminat-
Schaffhausen bridge, the Wettingen bridge was well
ed arched ribs that supported a level roadway, it was
known and was visited by a number of engineers,
similar to, and may have influenced Theodore Burr in
architects, and interested travelers, resulting in a
his construction of, the multispan bridge over the
variety of written descriptions, dimensions, and details,
Delaware at Trenton in 1804-1806 (see Figs. 12-13).
none of which seem to have agreed except as to its
This American view of the Wettingen Bridge is
general configuration. Its span was approximately 200
ft, with wooden frames supported by laminated arched from the book by Thomas Pope ("Architect and
ribs that were comprised of approximately seven Landscape Gardener"), A Treatise on Bridge Architec-
courses of wood that were notched and banded ture. . . (New York, 1811), Plate 7. Courtesy of Eric
together with iron hoops and keys, for a total rib depth DeLony.
3
