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Transcriber's Notes:

This is Paper 36 from the Smithsonian Institution United States National
Museum Bulletin 240, comprising Papers 34-44, which will also be
available as a complete e-book.

The front material, introduction and relevant index entries from the
Bulletin are included in each single-paper e-book.

Inconsistencies in punctuation have been corrected without note.
Inconsistent hyphenation is as per the original.




    SMITHSONIAN INSTITUTION

    UNITED STATES NATIONAL MUSEUM

    BULLETIN 240

    [Illustration]

    SMITHSONIAN PRESS




    MUSEUM OF HISTORY AND TECHNOLOGY

      CONTRIBUTIONS
      FROM THE
      MUSEUM
      OF HISTORY AND
      TECHNOLOGY

      _Papers 34-44_
      _On Science and Technology_

    SMITHSONIAN INSTITUTION . WASHINGTON, D.C. 1966




_Publications of the United States National Museum_


The scholarly and scientific publications of the United States National
Museum include two series, _Proceedings of the United States National
Museum_ and _United States National Museum Bulletin_.

In these series, the Museum publishes original articles and monographs
dealing with the collections and work of its constituent museums--The
Museum of Natural History and the Museum of History and
Technology--setting forth newly acquired facts in the fields of
anthropology, biology, history, geology, and technology. Copies of each
publication are distributed to libraries, to cultural and scientific
organizations, and to specialists and others interested in the different
subjects.

The _Proceedings_, begun in 1878, are intended for the publication, in
separate form, of shorter papers from the Museum of Natural History.
These are gathered in volumes, octavo in size, with the publication date
of each paper recorded in the table of contents of the volume.

In the _Bulletin_ series, the first of which was issued in 1875, appear
longer, separate publications consisting of monographs (occasionally in
several parts) and volumes in which are collected works on related
subjects. _Bulletins_ are either octavo or quarto in size, depending on
the needs of the presentation. Since 1902 papers relating to the
botanical collections of the Museum of Natural History have been
published in the _Bulletin_ series under the heading _Contributions from
the United States National Herbarium_, and since 1959, in _Bulletins_
titled "Contributions from the Museum of History and Technology," have
been gathered shorter papers relating to the collections and research of
that Museum.

The present collection of Contributions, Papers 34-44, comprises
Bulletin 240. Each of these papers has been previously published in
separate form. The year of publication is shown on the last page of each
paper.

    FRANK A. TAYLOR
    _Director, United States National Museum_




    CONTRIBUTIONS FROM
    THE MUSEUM OF HISTORY AND TECHNOLOGY:
    PAPER 36

    THE ENGINEERING CONTRIBUTIONS
    OF WENDEL BOLLMAN

    _Robert M. Vogel_




    EARLY CAREER                          80

    THE BOLLMAN TRUSS                     85

    W. BOLLMAN AND COMPANY                91

    FINAL USE OF THE BOLLMAN TRUSS        95

    KNOWN BOLLMAN WORKS                   99

    BIBLIOGRAPHY                         104




[Illustration: Figure 1.--WENDEL BOLLMAN, C.E. (1814-1884). (_Photo
courtesy of Dr. Stuart Christhilf._)]


_Robert M. Vogel_


THE ENGINEERING CONTRIBUTIONS OF WENDEL BOLLMAN


     _The development of structural engineering has always been as
     dependent upon the availability of materials as upon the
     expansion of theoretical concepts. Perhaps the greatest single
     step in the history of civil engineering was the introduction
     of iron as a primary structural material in the 19th century;
     it quickly released the bridge and the building from the
     confines of a technology based upon the limited strength of
     masonry and wood._

     _Wendel Bollman, self-taught Baltimore civil engineer, was the
     first to evolve a system of bridging in iron to be consistently
     used on an American railroad, becoming one of the pioneers who
     ushered in the modern period of structural engineering._

     THE AUTHOR: _Robert M. Vogel is curator of civil engineering in
     the Smithsonian Institution's Museum of History and
     Technology._


Wendel Bollman's name survives today solely in association with the
Bollman truss, and even in this respect is known only to a few older
civil and railroad engineers. The Bollman system of trussing, along with
those of Whipple and Fink, may be said to have introduced the great age
of the metal bridge, and thus, directly, the modern period of civil
engineering.

Bollman's bridge truss, of which the first example was built in 1850,
has the very significant distinction of being the first bridging system
in the world employing iron in all of its principal structural members
that was used consistently on a railroad.

The importance of the transition from wood to iron as a structural and
bridge building material is generally recognized, but it may be well to
mention certain aspects of this change.

The tradition of masonry bridge construction never attained the great
strength in this country which it held in Europe, despite a number of
notable exceptions. There were several reasons for this. From the very
beginning of colonization, capital was scarce, a condition that
prevailed until well into the 19th century and which prohibited the use
of masonry because of the extremely high costs of labor and transport.
An even more important economic consideration was the rapidity with
which it was necessary to extend the construction of railways during
their pioneer years. Unlike the early English and European railways,
which invariably traversed areas of dense population and industrial
activity, and were thus assured of a significant financial return almost
from the moment that the first rail was down, the Baltimore and Ohio
and its contemporaries were launched upon an entirely different
commercial prospect. Their principal business consisted not so much in
along-the-line transactions as in haulage between principal terminals
separated by great and largely desolate expanses. This meant that income
was severely limited until the line was virtually complete from end to
end, and it meant that commencement of return upon the initial
investment was entirely dependent upon the speed of survey, graduation,
tunneling, and bridging.

[Illustration: Figure 2.--MODEL OF B. H. LATROBE'S TRUSS, built in 1838,
over the Patapsco River at Elysville (now Daniels), Maryland. (_Photo
courtesy of Baltimore and Ohio Railroad._)]

The need for speed, the general attenuation of capital, and the simple
fact that all the early railroads traversed thickly forested areas
rendered wood the most logical material for bridge and other
construction, both temporary and permanent.

The use of wood as a bridge material did not, of course, originate with
the railroads, or, for that matter, in this country. The heavily wooded
European countries--Switzerland in particular--had a strong tradition of
bridge construction in timber from the Renaissance on, and naturally a
certain amount of this technique found its way to the New World with the
colonials and immigrants.

America's highway system was meager until about the time the railroad
age itself was beginning. However, by 1812 there were, along the eastern
seaboard, a number of fine timber bridges of truly remarkable structural
sophistication and workmanship.

It was just previous to the advent of the railroads that the erection of
highway bridges in this country began to pass from an art to a science.
And an art it had been in the hands of the group of skilled but
unschooled master carpenters and masons who built largely from an
intuitive sense of proportion, stress, and the general "fitness of
things." It passed into an exact science under the guidance of a small
number of men trained at first in the scientific and technical schools
of Europe, and, after about 1820, in the few institutions then
established in America that offered technical instruction.

The increasing number of trained engineers at first affected highway
bridge construction not so much in the materials used but in the way
they were assembled. In a bridge designed by a self-taught constructor,
the cheapness of wood made it entirely feasible to proportion the
members by enlarging them to the point where there could be no question
as to their structural adequacy. The trained engineer, on the other
hand, could design from the standpoint of determining the entire load
and then proportioning each element according to the increment of stress
upon it and to the unit capacity of the material.

By the time railroads had started expanding to the West there had been
sufficient experience with the half dozen practical timber truss systems
by then evolved, that there was little difficulty in translating them
into bridges capable of supporting the initial light rail traffic.

In spite of its inherent shortcomings, wood was so adaptable that it met
almost perfectly the needs of the railroads during the early decades of
their intense expansion, and, in fact, still finds limited use in the
Northwest.




Early Career


Wendel Bollman was born in Baltimore of German parents in 1814. His
father was a baker, who in the same year had aided in the city's defense
against the British. Wendel's education, until about the age of 11, was
more or less conventionally gained in public and private schools in
Baltimore. He then entered into informal apprenticeship, first to an
apothecary in Sheperdstown, Virginia (now West Virginia), and then to
one in Harpers Ferry. In 1826 or 1827 he became ill and returned to
Baltimore for cure. From that time on his education was entirely
self-acquired.

[Illustration: Figure 3.--TRUSSED BEAM.]

It is of interest, in light of his later career, to note that on the
Fourth of July 1828, he marched with other boys in a procession that was
part of the Baltimore and Ohio Railroad's cornerstone-laying ceremony.
Shortly afterward, he apprenticed himself to a carpenter for a brief
time, but when the work slacked off he obtained work with the B. & O.
The right-of-way had been graded for about five miles by that time, but
no rail was down. The boy was at first given manual work, but soon
advanced to rodman and rapidly rose as he gained facility with the
surveying apparatus. In the fall of 1829 he participated in laying the
first track. As his mother was anxious that he continue his education in
carpentry, he left the railroad in the spring of 1830 to again enter
apprenticeship. He finished, became a journeyman, helped build a
planter's mansion in Natchez, and returned to Baltimore in 1837 to
commence his own carpentry business. The next year, while building a
house in Harpers Ferry, he was asked to rejoin the B. & O. to rebuild
parts of its large timber bridge over the Potomac there, which had
fallen victim to various defects after about a year's use.

[Illustration: Figure 4.--SIMPLE BEAM of 50-foot span with three
independent trussing systems. Bollman's use of this method of support
led to the development of his bridge truss. This drawing is of a
temporary span used after the timber bridge at Harpers Ferry was
destroyed during the Civil War. (In Baltimore and Ohio Collection,
Museum of History and Technology.)]

Shortly after the Harpers Ferry bridge reconstruction, Bollman was made
foreman of bridges. It is apparent that, on the basis of his practical
ability, enhanced by the theoretical knowledge gained by intense
self-study, he eventually came to assist Chief Engineer Benjamin H.
Latrobe in bridge design. He later took this work over entirely as
Latrobe's attentions and talents were demanded in the location and
extension of the line between Cumberland and Wheeling.

[Illustration: Figure 5.--BOLLMAN'S ORIGINAL PATENT DRAWING, 1851. (In
National Archives, Washington, D.C.)]

The B. & O. did not reach its logical destination, Ohio (actually
Wheeling, West Virginia, on the east bank of the Ohio River) until 1853.
In the years following Bollman's return to the railroad, the design of
bridges was an occupation of the engineering staff second in importance
only to the location of the line itself. During this time Bollman
continued to rise and assume greater responsibilities, being appointed
master of road by Latrobe in 1848. In this position he was responsible
for all railroad property that did not move, principally the
right-of-way and its structures, including, of course, bridges.

The recognition of Bollman's abilities was in the well-established
tradition of the B. & O., long known as America's first "school of
engineering," having sponsored many early experiments in motive power,
trackwork, and other fundamental elements of railroad engineering. It
furnished the means of expression for such men as Knight, Wright,
Whistler, Latrobe, and Winans.

[Illustration: Figure 6.--PLAN OF HARPERS FERRY BRIDGE as built by
Latrobe. The second Winchester track was later removed.]

Of these pioneer civil and mechanical engineers, some were formally
trained but most were self-taught. Bollman's career on the B. & O. is of
particular interest not only because he was perhaps the most successful
of the latter class but because he was probably also the last. He may be
said to be a true representative of the transitional period between
intuitive and exact engineering. Actually, his designing was a composite
of the two methods. While making consistent use of mathematical
analysis, he was at the same time more or less dependent upon empirical
methods. For years, B. & O. employees told stories of his sessions in
the tin shop of the railroad's main repair facility at Mount Clair in
Baltimore, where he built models of bridges from scraps of metal and
then tested them to destruction to locate weaknesses. It seems most
likely, however, that the empirical studies were used solely as checks
against the mathematical.

[Illustration: Figure 7.--RECENT MODEL of Bollman's Winchester span.
Only two of the three lines of trussing are shown. The model is based on
Bollman's published description and drawings of the structure. (USNM
318171; Smithsonian photo 46941.)]

In the period when Bollman began designing--about 1840--there were fewer
than ten men in the country designing bridges by scientifically correct
analytical methods, Whipple and Roebling the most notable of this group.
By 1884, the year of Bollman's death, the age of intuitive design had
been dead for a decade or longer.

[Illustration: Figure 8.--THE BALTIMORE AND OHIO RAILROAD'S Potomac
River crossing at Harpers Ferry, about 1860. Bollman's iron "Winchester
span" of 1851 is seen at the right end of Latrobe's timber structure of
1836, which forms the body of the bridge. (_Photo courtesy of Harpers
Ferry National Historical Park._)]

The B. & O. was in every way a truly pioneer enterprise. It was the
first practical railroad in America; the first to use an American
locomotive; the first to cross the Alleghenies. The spirit of innovation
had been encouraged by the railroad's directors from the outset. It
could hardly have been otherwise in light of the project's elemental
daring.

The first few major bridges beyond the line's starting point on Pratt
Street, in Baltimore, were of rather elaborate masonry, but this may be
explained by the projectors' consciousness of the railroad's
significance and their desire for permanence. However, the
aforementioned economic factors shortly made obvious the necessity of
departure from this system, and wood was thereafter employed for most
long spans on the line as far as Harpers Ferry and beyond. Only the most
minor culverts and short spans, and those only in locations near
suitable quarries, were built of stone.

In addition to the economic considerations which prompted the company to
revert to timber for the major bridges, there were several situations in
which masonry construction was unsuitable for practical reasons. If
stone arches were used in locations where the grade of the line was a
relatively short distance above the surface of the stream to be crossed,
a number of short arches would have been necessary to avoid a very flat
single arch. In arch construction, the smaller the segment of a circle
represented by the arch (that is, the flatter the arch), the greater the
stress in the arch ring and the resulting horizontal thrust on the
abutments.

[Illustration: Figure 9.--BOLLMAN SKEW BRIDGE at Elysville (now
Daniels), Maryland, built in 1853-1854. (_Photo courtesy of Maryland
Historical Society._)]

The piers for the numerous arches necessary to permit an optimum amount
of rise relative to the span would have presented a dangerous
restriction to stream flow in time of flood. By the use of timber
trusses such crossings could be made in one or two spans with, at the
most, one pier in the stream, thus avoiding the problem.

The principal timber bridges as far west as Cumberland were of Latrobe's
design. These were good, solid structures of composite construction, in
which a certain amount of cast iron was used in joints and wrought iron
for certain tension members. They were, however, more empirical than
efficient and, for the most part, not only grossly overdesigned but of
decidedly difficult fabrication and construction.

What is interesting about the Latrobian timber trusses, however, is the
effect they appear to have had upon Bollman's subsequent work in the
design of his own truss. This effect is evidenced by the marked analogy
between the primary structural elements of the two types. The Latrobe
truss at Elysville (fig. 2) was only partially a truss, inasmuch as the
greater part of the load was not carried from panel to panel, finally to
appear at the abutments as a pure vertical reaction, but was carried
from each panel (except the four at the center) directly to the bearing
points at the piers by heavy diagonal struts, after the fashion of the
famous 18th-century Swiss trusses of the Grubenmanns. It was a
legitimate structural device, and the simplest means of extending the
capacity of a spanning system. However, it was defective in that the
struts applied considerable horizontal thrust to the abutments,
requiring heavier masonry than would otherwise have been necessary.

It is quite likely that Latrobe did not have absolute confidence in the
various pure truss systems already patented by Town, Long, and others,
and preferred for such strategic service a structure in which the panel
members acted more or less independently of one another. It will be seen
that, similarly, the individual panel loads in Bollman's truss were
carried to the ends of the frame by members acting independently of one
another.




The Bollman Truss


There had never been any question about the many serious inadequacies of
wood as a bridge material. Decay and fire risk, always present, were the
principal ones, involving continuous expenditure for replacement of
defective members and for fire watches. It was, in fact, understood by
the management and engineering staff of the B. & O. that their timber
bridge superstructures, though considered the finest in the country,
were more or less expedient and were eventually to be replaced. In this
regard it is not surprising that Latrobe, a man of considerable
foresight, had, at an early date, given serious thought to the possible
application of iron here.

[Illustration: Figure 10.--POTOMAC RIVER CROSSING of the Baltimore and
Ohio at North Branch, Maryland, built in 1856. There are three Bollman
deck trusses. (_Photo courtesy of Baltimore and Ohio Railroad._)]

[Illustration: Figure 11.--THE FINK TRUSS. (_Smithsonian photo
41436._)]

[Illustration: WENDEL BOLLMAN'S

Patent Iron Suspension Railroad Bridge.

The undersigned would inform the officers of Railroads and others, that
he is prepared to furnish Drawings and Estimates for Bridges, Roofs,
etc., on the plan of Bollman's Patent.

The performance of these bridges, some of which have been in use for six
years, has given entire satisfaction. Their simplicity of construction
renders repairs easy and cheap, and by a peculiar connection of the Main
and Panel Rods at the bottom of the Posts, all danger from the effects
of expansion, which has heretofore been the chief objection to Iron
Bridges, is entirely removed.

    J. H. TEGMEYER,
    Baltimore, Md.

Figure 12.--ADVERTISEMENT in the _Railroad Advocate_, August 1855.]

The world's first major iron bridge, the famed cast-iron arch at
Coalbrookdale, England, had been constructed in 1779. Its erection was
followed by rather sporadic interest in this use of the material. The
first significant use of iron in this country was in a series of small
trussed highway arches erected by Squire Whipple over the Erie Canal in
the early 1840's, over 60 years later. In these, as in most of the
earlier iron structures, an arch of cast iron was the primary support.
The thrust of the arches was counteracted by open wrought-iron links
with other wrought- and cast-iron members contributing to the truss
action.

The Whipple bridges promoted a certain amount of interest in the
material. In the B. & O.'s annual report for the fiscal year 1849
appears the first record of Latrobe's interest in this important matter.
In the president's message is found the following, rather offhand,
statement:

     $6,183.19 have been expended toward the renewal of the Stone
     Bridges on the Washington Branch, carried off by the flood of
     Oct. 7th, 1847. Preparations are made and contracts entered
     into, for the reconstruction of the large Bridges at Little
     Patuxent and at Bladensburg which will be executed in a few
     months.... It is proposed to erect a superstructure of Iron
     upon stone abutments, at each place--with increased span, for
     greater security against future floods.

It is interesting to note that it was indeed Bollman trusses to which
the president of the railroad had referred. How much earlier than this
date Bollman had evolved his peculiar trussing system is not clear. The
certain influence of Latrobe's radiating strut system of trussing has
been mentioned. As likely an influence was another basic technique
commonly used to increase the capacity of a simple timber beam--that of
trussing--i.e., placing beneath the beam a rod of iron that was anchored
at the ends of the beam and held a certain distance below it at the
center by a vertical strut or post. This combination thus became a truss
in that the timber portion was no longer subject to a bending stress but
to a simple one of compression, the rod absorbing the tensile stress of
the combination. The effect was to deepen the beam, increasing the
distance between its extreme fibers and--by thus reducing the bending
moment--reducing the stress in them (see fig. 3).

[Illustration: Figure 13.--THE FOUR BOLLMAN SPANS at Harpers Ferry that
survived the Civil War. The spans were completed in 1862-1863. (_Photo
courtesy of Baltimore and Ohio Railroad._)]

It apparently occurred to Bollman that by extending the number of rods
in a longitudinal direction, this effect could be practically amplified
to such an extent as to be capable of spanning considerable distances.
He almost certainly did not at first contemplate an all-iron system, but
rather a composite one such as described. It is entirely likely that
such trussed beams, with multiple systems of tension rods, were used by
Bollman as bridging in temporary trestlework along the line as early as
1845 (see fig. 4).

It is impossible to say whether Bollman himself, or Latrobe, was struck
with the logic of further elaborating upon the system and,
simultaneously, translating the timber compression member into one of
cast iron. Cast iron would naturally have been selected for a member
that resisted a compressive stress, as it was considerably cheaper than
wrought iron. But more important, at that time wrought iron was not
available in shapes of sufficient sectional area to resist the
appreciable buckling stresses induced in long compression members. The
cost of building up members to sufficient size from the very limited
selection of small shapes then rolled would have been prohibitive.

The trussing rods, subjected to tension, were of wrought iron inasmuch
as the sectional area had only to be sufficient to resist the primary
axial stress.

The first all-iron Bollman truss was constructed over the Little
Patuxent River at Savage Factory, near Laurel, Maryland, in 1850. In the
chief engineer's report for the year 1850, Latrobe was able to state
that the truss had been completed and was giving "much satisfaction."
He went on at some length to praise the "valuable mechanical features"
embodied therein, and expressed great confidence that iron would become
as important a material in the field of civil engineering as it was in
mechanical engineering.

[Illustration: Figure 14.--THE HARPERS FERRY BRIDGE as completed after
the Civil War. It was used by the Baltimore and Ohio until 1894, and as
a highway bridge until 1936. (Photo 690, Baltimore and Ohio Collection,
Museum of History and Technology.)]

The cost of this first major Bollman bridge was $23,825.00. Its span was
76 feet. Latrobe's confidence was well placed. The Savage span and
another at Bladensburg may be considered successful pilot models, for,
in spite of a certain undercurrent of mistrust of iron bridges within
the engineering profession--due mainly to a number of failures of
improperly designed spans--Latrobe felt there was sufficient
justification for the unqualified adoption of iron in all subsequent
major bridge structures on the B. & O.

Almost immediately following completion of the Savage Bridge, Bollman
undertook the design of replacements for the large Patapsco River span
at Elysville (now Daniels), Maryland, and the so-called Winchester span
of the B. & O.'s largest and most important bridge, that over the
Potomac at Harpers Ferry. Harpers Ferry bridge, a timber structure, had
been designed by Latrobe and built in 1836-1837 by the noted bridge
constructor Lewis Wernwag. It was peculiar in having a turnout, near the
Virginia shore, whereby a subsidiary road branched off to Winchester
(see fig. 6). Only the single span on this line, situated between the
midriver switch and the shore, was slated for replacement, as the other
seven spans of the bridge had been virtually reconstructed in the decade
or so of their history and were in sound condition at the time.

The Winchester span (fig. 8), which was the first Bollman truss to
embody sufficient refinement of detail to be considered a prototype, was
completed in 1851. Bollman was extremely proud of the work, with perfect
justification it may be said. The 124-foot span was fabricated in the
railroad's extensive Mount Clair shops. It was subdivided into eight
panels by seven struts and seven pairs of truss rods. An interesting
difference between this span and Bollman's succeeding bridges was his
use of granite rather than cast iron for the towers. The span consisted
of three parallel lines of trussing to accommodate a common road in
addition to the single-track Winchester line.

The distinctive feature of the Bollman system was the previously
mentioned series of diagonal truss links in combination with a cast-iron
compression chord, which Bollman called the "stretcher." The spacing
between the chord and the junction of each pair of links was maintained
by a vertical post or strut, also cast.

[Illustration: Figure 15.--NORTH STREET (now Guilford Avenue) bridge,
Baltimore. In this transitional composite structure cast iron was used
only in the relatively short sections of the upper chord. For the long
unsupported compression members of the web system, standard wrought-iron
angles and channels were built up into a large section. The decorative
cast-iron end posts were non-structural. (Photo in the L. N. Edwards
Collection, Museum of History and Technology.)]

Much of the appeal of this design lay unquestionably in the sense of
security derived from the fact that each of the systems acted
independently to carry its load to the abutments. The lower chords,
actually nonfunctional in the primary structure, were included merely to
preserve the proper longitudinal spacing between the lower ends of the
struts. A certain lack of rigidity was inherent in the system due to
that very discontinuity which characterized its action; however, this
was compensated for by a pair of light diagonal stay rods crossing each
panel. These rods served the additional function of distributing
concentrated loads to adjacent struts much in the manner of the bridging
between floor joists in a building.

In the Winchester span the floor system was of timber for reasons of
economy. This was a very minor weakness inasmuch as any stick could be
quickly replaced, and without disturbing the function of the structure.
Bollman received a patent for his truss in January 1852, and in the same
year published a booklet describing his system in general and the
Harpers Ferry span in particular. Here, he first calls it a "suspension
and trussed bridge," which is indeed an accurate designation for a
system which is not strictly a truss because it has no active lower
chord. (The analogy to a suspension bridge is quite clear, each pair of
primary rods being comparable to a suspension cable.) Thereafter,
Bollman's invention was generally termed a suspension truss.


INFLUENCE OF THE TRUSS

Bollman's 1852 publication was widely disseminated here and abroad and
studied with respectful interest by the engineering profession. Its
drawings of the structure were copied in a number of leading technical
journals in England and Germany. Although there is no record that the
type was ever reproduced in Europe, there can be little doubt that this
successful structural use of iron by the most eminent railroad in the
United States and its endorsement by an engineer of Latrobe's status
gave great impetus to the general adoption of the material. This
influence was certainly equal to that of Stephenson's tubular iron
bridge of 1850 over the Menai Strait, or Roebling's iron-wire suspension
bridge of 1855 over Niagara gorge. The Bollman design had perhaps even
greater influence, as the B. & O. immediately launched the system with
great energy and in great numbers to replace its timber spans; on the
other hand, Roebling's structure was never duplicated in railroad
service, and Stephenson's only once.

[Illustration: Figure 16.--_Left:_ CONJECTURAL SECTION of Bollman's
segmental wrought-iron column, about 1860, and section of the standard
Phoenix column; _right:_ Phoenix column as used in truss-bridge
compression members.]


EVALUATION OF THE TRUSS

By the late 1850's iron was well established as a bridge material
throughout the world. Once the previous fears of iron had been stilled
and the attention of engineers was directed to the interpretation of
existing and new spanning methods into metal, the Bollman truss began to
suffer somewhat from the comparison. Although its components were simple
to fabricate and its analysis and design were straightforward, it was
less economical of material than the more conventional panel trusses
such as the Pratt and Whipple types. Additionally, there was the
requisite amount of secondary metal in lower chords and braces necessary
for stability and rigidity.

A factor difficult to assess is Bollman's handling of his patent, which
was renewed in 1866. There is sufficient evidence to conclude that he
considered the patent valuable because it was based upon a sound design.
Therefore, he probably established a high license fee which, with the
truss's other shortcomings, was sufficient to discourage its use by
other railroads. As patron, the B. & O. had naturally had full rights to
its use.

An additional defect, acknowledged even by Bollman, arose because of the
unequal length of the links in each group except the center one. This
caused an unevenness in the thermal expansion and contraction of the
framework, with the result that the bridges were difficult to keep in
adjustment. This had the practical effect of virtually limiting the
system to intermediate span lengths, up to about 150 feet. For longer
spans the B. & O. employed the truss of another of Latrobe's assistants,
German-born and technically trained Albert Fink.

The Fink truss was evolved contemporaneously with Bollman's and was
structurally quite similar, being a suspension truss with no lower
chord. The principal difference was the symmetry of Fink's plan, which
was achieved by carrying the individual panel loads from the panel
points to increasingly longer panel units before having them appear at
the end bearings. This eliminated the weakness of unequal strains. The
design was basically a more rational one, and it came to be widely used
in spans of up to 250 feet, generally as a deck-type truss (see fig.
11).




W. Bollman and Company


Bollman resigned from the Baltimore and Ohio in 1858 to form, with John
H. Tegmeyer and John Clark, two of his former B. & O. assistants, a
bridge-building firm in Baltimore known as W. Bollman and Company. This
was apparently the first organization in the United States to design,
fabricate, and erect iron bridges and structures, pioneering in what 25
years later had become an immense industry. The firm had its foundation
at least as early as 1855 when advertisements to supply designs and
estimates for Bollman bridges appeared over Tegmeyer's name in several
railroad journals (see fig. 12).

Bollman's separation from the B. & O. was not a complete one. The
railroad continued its program of replacing timber bridges with Bollman
trusses, and contracted with W. Bollman and Company for design and a
certain amount of fabrication. There is some likelihood that eventually
fabrication was entirely discontinued at Mount Clair, and all parts
subsequently purchased from Bollman.

The firm prospered, erecting a number of major railroad bridges in
Mexico, Cuba, and Chile. Operations ceased from 1861 to 1863 because of
difficult wartime conditions in the border city of Baltimore. Following
this, Bollman reentered business as sole proprietor of the Patapsco
Bridge and Iron Works.

[Illustration: QUINCY BAY BRIDGE

Figure 17.--CHICAGO, BURLINGTON AND QUINCY RAILROAD BRIDGE over Quincy
Bay (branch of the Mississippi River) at Quincy, Illinois. The pivot
draw-span was formed of two Bollman deck trusses supported at their
outer ends by hog chains. The bridge was built in 1867-1868 by the
Detroit Bridge and Iron Co., Bollman licensee. (Clarke, _Account of the
Iron Railway Bridge ... at Quincy, Illinois_.)]

The most noteworthy of Bollman's works in this period was a series of
spans at Harpers Ferry. The B. & O.'s timber bridge had been destroyed
by Confederate forces in June 1861, and the crossing was thereafter made
upon temporary trestlework. This was a constant source of trouble, with
continuing interruptions of the connection from high water, washouts,
and military actions. The annoyance and expense of this became so great
that the company decided to risk an iron bridge at the crossing. In July
and August 1862, two sections of Bollman truss, spans no. 4 and no. 5
were completed. As this occurred during the time when W. Bollman and
Company was inoperative, the work was produced at Mount Clair to
Bollman's design and, undoubtedly, erected under his supervision. Five
weeks later, on September 24, these and Bollman's famous Winchester span
of 1851 were blown up by the Confederates, and the line's business was
again placed at the mercy of trestling.

The spirit of the B. & O. administration indeed seems to have been
unshakable when, in the face of such heartbreaking setbacks, it
determined to again bridge the river with iron, even at the height of
the hostilities. In November, span no. 5 was erected, and by April 1863
nos. 3, 4, and 6 also. These were the four straight spans in midriver
between the "wide" (or "branch," or "wye") span and the span on the
Maryland shore over the Chesapeake and Ohio Canal (see fig. 13).
Although the wood floor system of these spans was burned for strategic
reasons by U.S. troops later in 1863, they survived the war.

In 1868 the remaining trestlework was replaced with Bollman trusses.
This magnificent structure served the railroad until 1894 when the
right-of-way was realigned at Harpers Ferry. However, the half used by
the common road remained in use until carried away by the disastrous
flood in 1936. The piers may still be seen.

During the prewar years, Bollman evolved a structural development of
most profound importance, which is usually associated with the Phoenix
Iron Works and its founder, Samuel J. Reeves. In the erection of a high
trestlework viaduct for the Havana Railroad, Bollman apparently became
concerned with the tensile weakness of cast iron when applied in long,
unsupported columns. Although a column is normally subjected to
compressive stresses, when the slenderness ratio--that is, the length
divided by the radius of gyration of the cross section--becomes great, a
secondary bending stress may be produced. If this stress becomes great
enough, the value of the tensile stress in one side of the column may
actually exceed the principal compressive stress, and a net effect of
tension result.

[Illustration: Figure 18.--OHIO RIVER CROSSING of the Baltimore and Ohio
at Benwood, West Virginia, completed in 1870. Bollman deck trusses were
used in the approaches on both sides. (Photo 693, Baltimore and Ohio
Collection, Museum of History and Technology.)]

[Illustration: Figure 19.--PATAPSCO RIVER crossing of the Baltimore and
Ohio between Thistle and Ilchester, Maryland. (Photo 695, Baltimore and
Ohio Collection, Museum of History and Technology.)]

As already mentioned, the few available rolled-iron shapes were of
relatively small area and quite unsuitable for use as columns unless
combined and built up in complex fabrications. The normal practice at
the time was to use cast compression members in iron bridges and
structures, with their sectional area so proportioned to the length that
a state of tension could not exist. In the case of long members, this
naturally meant that an excessive amount of material was used.

[Illustration: Figure 20.--TWO VIEWS OF BOLLMAN-BUILT "water-pipe truss"
that carries Lombard Street over Jones Falls in Baltimore. Built in
1877.]

Bollman was conscious of the problem from his experience with the
stretchers and struts of his truss, and he must have been aware of the
great advantage which would be obtained by a practical method of forming
such members in wrought iron, the tensile resistance of which is
equivalent to the compressive. He eventually developed the forerunner of
what came to be known as the Phoenix form by having special segmental
wrought-iron shapes rolled by Morris, Tasker and Company of
Philadelphia, these shapes being combined into a circular section with
outstanding flanges for riveting together. The circular section is
theoretically the most efficient to bear compressive loading. A column
of any required diameter could be produced by simply increasing the
number of segments, the individual size of which never exceeded
contemporary rolling mill capacity (see fig. 16).

The design exhibits the inspired combination of functional perfection
and simplicity that seems to characterize most great inventions.

[Illustration: Figure 21.--THE HARPERS FERRY BRIDGE toward the end of
its career, carrying a common road over the Potomac. The westernmost
line of trussing and span no. 1 had been removed long before. View
through the Winchester span looking toward Maryland in 1933. (_Photo
courtesy of Harpers Ferry National Historical Park._)]

It may have been because he had no facilities for rolling that Bollman
communicated his idea to Reeves, although this seems illogical. At any
rate, Reeves and his associates patented the system extensively, and the
Phoenix column was eventually employed to the virtual exclusion of
cast-iron and other types of wrought-iron columns. By the end of the
19th century it began to pass from use, as mills became capable of
producing larger sections with properties relatively favorable to column
use and more adaptable to connection with other members.




Final Use of the Bollman Truss


The Bollman truss found occasional use elsewhere than on the B. & O.
lines, but generally only when erected on contract by Patapsco Bridge
and Iron Works. However, the fact that Bollman could profitably erect
this bridge in the severely competitive 1870's indicates that the harsh
criticism of the system by authorities of such stature as Whipple was
not necessarily justified. Bollman's advertisements, in fact, refer to
the favorable recommendations of other such renowned engineers as
Herman Haupt and M. C. Meigs.

[Illustration: Figure 22.--BOLLMAN DECK TRUSSES in the North River
Bridge built in 1873 at Mount Crawford, Virginia, on the Valley Railroad
of Virginia (B. & O.). Each end span is 98 ft. 6 in.; the river span is
148 ft. 9 in. (Photo 756, Baltimore and Ohio Collection, Museum of
History and Technology.)]

An interesting application of the system was in a drawbridge, formed of
two Bollman deck spans, over an arm of the Mississippi at Quincy,
Illinois (see fig. 17). The first iron bridge in Mexico was erected by
Bollman over the Medellín River about 1864. Another work of this period,
which attracted considerable attention, was a pair of bridges that
Bollman erected over North Carolina's Cape Fear River in 1867-1868.
These bridges were notable for their foundation on cast-iron cylinders,
sunk pneumatically. This was one of the first instances of the use of
the process in America, and the depth of 80 feet below the water surface
reached by one cylinder was considered remarkable for years afterward.

In the last active decade or so of his career, Bollman produced hundreds
of minor bridges and other structures. In 1873 he supplied the castings
for the splendid iron dome of Baltimore's City Hall and erected the
ingenious water-main truss which carries Lombard Street over Jones Falls
in that city. In this structure the top and bottom chords of the central
line of trussing are cast-iron water mains, bifurcated at the abutments,
and joined by cast- and wrought-iron web members (see fig. 20).

In the mid 1870's Bollman saw his truss pass into obsolescence. This was
due primarily to the generally increasing distrust of cast iron for
major structural members due to its brittleness, but advances in
structural theory, availability of a greater variety of rolled
structural shapes, and the increasing loading patterns of the period all
contributed.

[Illustration: Figure 23.--THE ONLY SURVIVING BOLLMAN TRUSS BRIDGE, at
Savage, Maryland. The bridge was built elsewhere in 1852 and was moved
to this now-abandoned Baltimore and Ohio industrial siding in about
1888.]

Although no Bollman trusses were built by Bollman or the B. & O. after
1875, those in use were only removed as required by heavier motive
power. The Harpers Ferry span, as noted, remained in full main-line
service until 1894. Bollman trusses on feeder lines were continued in
use until much later; a number of them on the Valley Railroad of
Virginia (see fig. 22) were not removed until 1923. However, only on the
most isolated spurs was the Bollman truss permitted to reach really ripe
age. The sole known remaining example (fig. 23) stands on such a
branch--ironically, at Savage, over the Little Patuxent, the site of the
first Bollman span. This is not the 1850 bridge, but one built in 1852
and moved to the present site 30 years later. The fate of the first span
is not known.

[Illustration: Figure 24.--HOT-WATER AND CHOCOLATE PITCHERS of the
10-piece, silver tea service presented to Bollman by his fellow
employees when he resigned from the Baltimore and Ohio in 1858. A
railroad motif was used throughout, each piece being circled at top and
bottom by a track, complete with rail of accurate section and ties.
Spouts are in simulation of hexagonal sheet-iron chimneys, with seams
riveted, and the handles are in the form of a surveyor's telescope. On
the various pieces are engraved the designs of the more important B. &
O. bridges. Throughout is a wonderful profusion of bits and objects of
railroadiana in low relief, high relief, and fully modeled. In Board of
Directors Room, Baltimore and Ohio Railroad Company, Baltimore, Md.
(_Photo courtesy of Baltimore and Ohio Railroad._)]




Known Bollman Works


(All B. & O. works listed were designed by Bollman and built by the
railroad, unless otherwise indicated.)

  Dates of   Location             Type     No. spans  Remarks
  service                                  / length
                                           of each

  1850-?     Savage, Md., Little  Bollman    1/76'    First Bollman truss
             Patuxent River       through             erected; granite towers;
                                  truss               cost, $23,825. B. & O. RR.

  1851-?     Bladensburg, Md.,    Bollman    1/?      Second Bollman truss
             Anacostia River      through             erected; granite towers;
                                  truss               cost, $19,430. B. & O. RR.

  1851-1862  Harpers Ferry, Va.,  Bollman    1/124'   Winchester span; first
             Potomac River        through             major Bollman truss; three
                                  truss               lines of truss; granite
                                                      towers; blown up by
                                                      Confederate Army on
                                                      September 24, 1862.
                                                      B. & O. RR.

  1851-?     Baltimore, Md.,      Trestle    --       Wood trestle bents with
             Carey Street                             wrought-iron diagonals.
                                                      First use of iron
                                                      structural members in
                                                      trestlework. Total length
                                                      76 feet. B. & O. RR.

  1852-      Savage, Md., Little  Bollman    2/±80'   Still standing. Moved to
             Patuxent River       through             Savage in 1888; original
                                  truss               location unknown. This and
                                                      succeeding Bollman trusses
                                                      use iron towers. B. & O.
                                                      RR.

  1852 (or   Marriottsville,      Bollman    1/50'    One of first Bollman
  1853)-?    Md., Patapsco River  truss               trusses with iron towers.
                                                      B. & O. RR.

  1853-?     Zanesville, Ohio,    Bollman    4/124'   Double track, Central Ohio
             Muskingum River      truss      (or      RR. Designed by Bollman;
                                             5/160')  built by Douglas, Smith &
                                                      Co., Zanesville.

  1854-      Elysville (now       Bollman    3/97'9"  Upper bridge, skew. Cost,
  1870(?)    Daniels),  Md.,      through             $24,477.59. B. & O. RR.
             Patapsco River       truss

  1854-1862  Monocacy, Md.,       Bollman    3/119'   Blown up September 8,
             Monocacy River       truss               1862; rebuilt in 1864.
                                                      Cost, $22,722.59.
                                                      B. & O. RR.

  1854-?     Eastern Ohio         Bollman    1/40'    C. O. RR. Section 76
                                  truss(?)            adjacent to 300-ft.
                                                      tunnel.

  1855-?     Bridgeville, Ohio,   Bollman    1/71'    C. O. RR.
             Salt Creek           deck truss

  Pre-1855-? Buffalo, N.Y.        --         --       Unidentified. Mentioned by
                                                      George Vose in Railroad
                                                      Advocate (June 9, 1855).

  1856-?     Elysville, Md.,      Bollman   3/111'    Lower Bridge. B. & O. RR.
             about 1-1/4 miles    through
             east of 1854         truss
             bridge, Patapsco
             River

  Pre-1856-? Marriottsville,      Bollman   1/48'9"   Referred to as "Tunnel
             Md.                  truss(?)            Bridge" in B. & O. RR.
                                                      annual report, 1856.

  1856-?     Near Ijamsville,     "Iron     3/23'9"   Possibly trussed beams;
             Md., Bush Creek      girders"            mentioned in B. & O. RR.
                                                      annual report, 1856.

  1856-?     Near Ijamsville,     "Iron     2/23'9"   As above.
             Md., Bush Creek      girders"

  1856-      North Branch, Md.,   Bollman   3/142'    Partially destroyed in
  c.1862     Potomac River        deck truss          Civil War. B. & O. RR.

  1860-1906  Chile, Angostura     Bollman   4/115'    Chilean Railways.
             River                truss(?)            Designed and built by
                                                      Bollman. Replaced by
                                                      bridge built by French
                                                      firm of Schneider,
                                                      Cruesot & Co.

  1860-1910  Chile, Paine River   Bollman   1/?       As above.
                                  truss(?)

  Post-      Ilchester, Md.,      Bollman   1/?       B. & O. RR.
  1860-?     Patapsco River       through
                                  truss

  Pre-1861-? Cuba                 Bridges   --        All bridges on Havana
                                  and                 RR., including iron
                                  station             station house and bridge
                                  house               at Guines. Designed and
                                                      built by Bollman.

  Pre-1861-? Cuba                 Bridges   --        All bridges on Cienfuegos
                                                      RR., Cárdenas RR., and
                                                      Havana & Matanzas RR.
                                                      Designed and built by
                                                      Bollman.

  Pre-1861-? Cuba                 Trestle   --        Trestle with wrought-iron
                                                      columns (the first such
                                                      ever constructed). Havana
                                                      RR. Designed and built by
                                                      Bollman.

  1862-1862  Harpers Ferry, Va.,  Bollman   2/160'    Span no. 3 (July 24) and
             Potomac River        through             span no. 4 (August 21).
                                  truss               Blown up September 24,
                                                      1862. B. & O. RR.

  1862-1936  Harpers Ferry, Va.,  Bollman   1/160'    Span no. 5 (November).
             Potomac River        through             B. & O. RR.
                                  truss

  1863-1936  Harpers Ferry, Va.,  Bollman   3/160'    Spans nos. 3, 4, and 5.
             Potomac River        through             Constructed previous to
                                  truss               April 1863. B. & O. RR.

  1863-?     Berwyn, Md., Paint   Bollman   ?         Iron bridge mentioned in
             Branch               truss(?)            B. & O. RR. annual report,
                                                      1863.

  1863(4?)-? Clinton, Iowa,       Pivot     1/360'    Built by Detroit Bridge
             Mississippi River    draw                & Iron Works. It was the
                                                      longest in the world at
                                                      time of completion.
                                                      Designed by Bollman.

  1864-?     Laurel, Md.,         Bollman   ?         Replaced stone arch that
             Patuxent River       truss               had been washed out. B. &
                                                      O. RR.

  c. 1864-?  Near Veracruz,       Bollman   1/115'    Veracruz & Jucaro RR.
             Mexico, Medellín     through             First iron bridge in
             River                truss               Mexico. Designed and
                                                      built by Bollman.

  1864-?     Near Point of        Bollman   1/80'(?)  Iron bridge mentioned in
             Rocks, Md., Back     truss(?)            B. & O. RR. annual
             Creek                                    report, 1864. The span
                                                      length given is that of
                                                      previous stone arch.

  1864-?     Bladensburg, Md.,    Bollman   1/?       Span for second track, to
             Anacostia River      truss               match 1851 span. B. & O.
                                                      RR.

  1868-?     Cape Fear, N.C.,     Bollman   2/146'6"  Wilmington Railway Bridge
             Northeast Branch,    truss(?)  1/164'    Co. This bridge was
             Cape Fear River                pivot     connected to that over
                                            draw/150' the Northwest Branch by
                                                      2-1/2 miles of timber
                                                      trestling. Designed and
                                                      built by Bollman.

  1868-?     Cape Fear, N.C.,     Bollman   1/217'(?) See above.
             Northwest Branch,    truss(?)  pivot
             Cape Fear River                draw/150'

  1868-?     Quincy, Ill.,        Bollman   4/85'     Chicago, Burlington &
             Quincy  Bay (in      deck      pivot     Quincy RR. The pivot draw
             Mississippi River)   truss     draw/190' was formed of two 85-ft.
                                                      simple Bollman deck spans
                                                      whose outer ends hung from
                                                      hog chains. Designed by
                                                      Bollman; built by Detroit
                                                      Bridge & Iron Works.

  1869-      Baltimore, Md.,      Warren     2/100'   North Avenue Bridge.
  c.1892     over Jones Falls,    truss      2/55'6"  Composite double
             B. & O. RR., and                         intersection truss;
             Northern Central                         timber top chord and
             RR.                                      posts, wrought-iron lower
                                                      chord and ties. In 55-ft.
                                                      spans, both chords
                                                      timber. Cost, $73,588.
                                                      Built by Bollman.

  c.1869-    Harpers Ferry, Va.,  Bollman    4/?      Canal span (no. 8), Wide
  1936       Potomac River        through             span  (no. 2), Winchester
                                  truss               span, and West End span.
                                                      Destroyed by flood in
                                                      1936. B. & O. RR.

  1870-      Baltimore, Md.,    Iron         1/108'   Charles Street Bridge.
  c.1895     Jones Falls        "Isometrical          Three lines of trussing.
                                truss"                Cost, $20,297. Built by
                                (probably             Bollman.
                                Pratt type)

  1870-      Bellaire, Ohio-      Bollman    9/107'-  In approaches; 2 spans on
  1893 &     Benwood W. Va.,      deck       125'     Ohio side; 7 on West
  1900       Ohio River           truss               Virginia side. B. & O. RR.

  1870-      Belpre, Ohio-        Bollman    16/?     In approaches; 7 spans on
  c.1895     Parkersburg, W.      deck                Ohio side; 9 on West
             Va., Ohio River      truss               Virginia side. B. & O. RR.

  1870-?     Elysville, Md.,      Bollman    4/?      Skew; replacement of
             Patapsco River       through             Upper Bridge(?). B. & O.
                                  truss               RR.

  1871-      Baltimore, Md.,      Timber     ?        Decker Street (now
  c.1895     Jones Falls          and iron            Maryland Avenue) Bridge.
                                  truss               Cost, $24,975. Built by
                                                      Bollman.

  1871-      Baltimore, Md.,      Warren     1/100'   North Avenue Bridge.
  c.1892     over Northern        truss               Composite double
             Central RR. at                           intersection truss;
             Jones Falls                              cast-iron top chord and
                                                      posts; wrought-iron
                                                      bottom chord and ties.
                                                      West span. Built by
                                                      Bollman.

  1873-1923  Cave Station, Va.,   Bollman    1/98'7"  Valley Railroad of
             Middle River         deck       1/63'5"  Virginia (B. & O.) Bridge
                                  truss               no. 120. The main span
                                                      was a Whipple deck truss.
                                                      Replaced with plate
                                                      girders. Designed by
                                                      Bollman.

  1873-1923  Mount Crawford,      Bollman    2/98'6"  Valley Railroad of
             Va., North River     deck       1/148'9" Virginia (B. & O.) Bridge
                                  truss               no. 117. Designed by
                                                      Bollman.

  1873-1923  Verona, Va., North   Bollman    3/98'7"  Valley Railroad of
             River                deck                Virginia (B. & O.) Bridge
                                  truss               no. 129. The main span
                                                      was a 147-ft. Whipple
                                                      deck truss. Designed by
                                                      Bollman.

  1873-?     Wadesville, Va.,     Bollman    1/147'8" Span length given is that
             Opequon Creek        through             of previous wood span
                                  truss               that burned in 1862. B.
                                                      & O. RR.

  c. 1873-   Baltimore, Md.       Iron roof  ?        First Presbyterian
                                  trusses             Church. Built by Bollman;
                                                      possibly designed by him.

  1873-      Baltimore, Md.       Cast-iron           City Hall. Cost, $12,840.
                                  stairs              Designed by George A.
                                                      Frederick, architect;
                                                      built by Bollman.

  1873-      Baltimore, Md.       Cast-iron           Dome of the City Hall.
                                  framework           Cost, $70,525. Designed
                                                      by George A. Frederick;
                                                      built by Bollman.

  1875-      Baltimore, Md.,      Iron truss 1/?      Fayette Street Bridge.
  c.1913     Jones Falls                              Cost, $9,396. Built by
                                                      Bollman.

  1876-      Baltimore, Md.,      "Single-   1/?      Canton Avenue (now Fleet
  c.1913     Jones Falls          beam iron           Street) Bridge. Cost,
                                  bridge"             $8,904. Built by Bollman.
                                  (truss?)

  1876-      Baltimore, Md.,      "Single-   1/?      Eastern Avenue Bridge.
  c.1913     Jones Falls          beam iron           Cost, $12,382. Built by
                                  bridge"             Bollman.
                                  (truss?)

  1877-      Baltimore, Md.,      Pratt and  1/88'6"  Lombard Street Bridge.
             Jones Falls          bowstring           Three lines of truss;
                                  truss               two outer trusses,
                                                      composite cast- and
                                                      wrought-iron polygonal
                                                      Pratt type; center
                                                      composite bowstring with
                                                      Pratt-system web. Both
                                                      chords are cast-iron
                                                      water mains, bifurcated
                                                      at the end bearings;
                                                      cast-iron posts and
                                                      wrought-iron ties. In
                                                      service. Cost, $7,632.
                                                      Designed by Jas. Curran,
                                                      Baltimore water
                                                      department; built by
                                                      Bollman.

  1877-      Baltimore, Md.,      Iron truss  1/?     Bath Street Bridge. Cost,
  c.1913     Jones Falls                              $4,172. Built by Bollman.

  1879-?     Baltimore, Md.       Drawbridge  1/?     Over entrance to City
                                                      Dock. Cost, $13,182.
                                                      Built by Bollman.

  1879-      Baltimore, Md.,      Warren     2/173'9" North Street (now
  c.1930     over Jones Falls     truss               Guilford Avenue) Bridge.
             and railroad                             Composite trusses;
             tracks                                   cast-iron top chord and
                                                      end posts; wrought-iron
                                                      bottom chord and web
                                                      members. Cost, $38,772.45.
                                                      Built by Bollman;
                                                      designed by Latrobe.

  1881-1960  Baltimore, Md.,      Wrought-   1/?      Union Avenue Bridge.
             (Woodberry),         iron Pratt          Built by Bollman;
             Jones Falls          truss               possibly designed by him.

  ?-?        Harpers Ferry, Va.,  Bollman    1/148'   Arsenal Branch, B. & O.
             Arsenal Canal        through             RR. Skew type. Span
                                  truss               length is that of
                                                      previous timber span.

  ?-?        Baltimore, Md.,      Bollman    2/?      B. & O. RR.
             Gwynns Falls         through
                                  truss




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INDEX


Bollman, W., and Company, 91, 92

Bollman, Wendel, 79, 80, 85, 88, 94


Clark, John, 91


Fink, Albert, 79, 91


Grubenmann, Hans, 85

Grubenmann, Johann Ulrich, 85


Haupt, Herman, 96


Knight, ----, 83


Latrobe, Benjamin H., 82, 83, 85, 87

Long, Stephen H., 85


Meigs, M. C., 96

Morris, Tasker and Company, 94

Mount Clair shops, 83, 89, 92


Patapsco Bridge and Iron Works, 92, 95

Phoenix Iron Works, 92

Pratt, Thomas W., 91


Reeves, Samuel J., 92, 95

Roebling, John A., 83, 90


Savage Factory, 88

Stephenson, Robert, 90


Tegmeyer, John H., 91

Town, Ithiel, 85


Wernwag, Lewis, 89

Whipple, Squire, 79, 83, 87, 91, 95

Whistler, George W., 83

Winans, Ross, 83

Wright, Benjamin, 83