The Bollman Truss of Harper's Ferry / M.F. Brothers

The Bollman Truss

OF

Ha & pers Fehh y

Mf. Brothers.

THE BOLLMAH . . KPER'S FERRY.

a Bollman truss bridge of ^r f s Ferry, W
Virginia .. xa ouilt in 1S52 and was designed and con-
structed by ..ell Bollman - a prominent bridge en-
it that time. This bridge was built for the
Baltimore and Ohio Rail Road and was known as the

Lnohester Span of the Baltimore and Ohio R. R. Via-
duct at Harper's Ferry.

The bridgi vs used by the Rail Road until about
7, when another bridge was ouilt for railroad traf-
fic. However, the Bollman Bridge is yet In use for
vehicular traffic.

Tho span of this bridge is one hundred and twenty-
four feet ments and the length of cast iron
in the stretcher is one hundred and twenty-eight feet.

In designing this orid^e Bollman used a combii
tion of cast and wrought iron; the former being used
for members which were to oe subjected to compression
and tne latter in those which would be subjected to
t jnsion, thus utilizing the special qualities of the
two metals. tit of cast iron used in the

truss is sixty-five thousand, one hundred and thirty-
sevBn pounds and of wrought iron is thirty- three thou-
sand five hundred and twenty-seven i ounds , making a
total wei at of ninety-eight thousand, six hundred and
sixty-four pounds.

This type of bridge unites the principles of the suspen-
sion ana the truss oridges. Each bar performs its own
part m supporting the lo^d in proiortion to its distance
from the abutment, so that the entire series of i id-
ing rods , transmits the some tension to the point of sup-
port, as would be equally transmitted from thence to the
center of the bridge. Eaoh bar or rod is straight and
of uniform size and therefore the principle of calcula-
tions is that of a lever.

The stretcher or straining beam, the vertical posts
and. suspension bars compose the ^s^ential features of the
bridge. -eh post is hung oy ti><j bars from both ends of
the stretcher independently of all the others and each
post and pair of tension bars , with the stretcher form a
I arate truss. Seven independent js are used and
these transfer the weight concentrated on each floor beam,
directly to the abutments without aid. from any other con-
nections; and not from panel to panel ^s in general use.

Since the weight of the bridge has only a vertical
pressure at the i-iertj., the necessary dimensions of masonry
may be very moderate; and <a.re four feet square at the base,
twelve feet high and two feet nin3 inches at the top*

v

Tills syst

am,

althou

rfe

et

in its

elf,

•udition-

illy

connected

oy

diagonal

rOv

in

each p

j,lso by

Ii

, hollow

oas

tinge acting as

S'

truts .

The

di *.ocnal

side rods might safely be dispensed with, for the pecu-
liar merit of the truss is its perfect independence of
such provision. -hey a.rc therefore used as a u^rd
only, m c^se of ta^ fracture of any of the principal sus-
pension rods.

Bollrrun states that the advantage of this type of
bridgeis ,that it carries out fully the permanent prin-
ciple of bridge; building, which is;- the direct transfer
of force to abutments, simple caleulatio ns a,nd certainty
of expense items , all of which tend to facilitate the er-
ection of secure, economical and durable structures.

It is interesting to note, however, that this type
of bridge has become ob^oluta in modern bridj 3 construct-
ion.

prove the rigidity of construction of the
"Bollman Truss'' a test is made. Three locomotives "vith
tenders^ were weighed and then run upon the brii it tire
same time, nearly covering its whole length and weighing
in aggregate one hundred and thirty-six tone, or about
one ton per foot.

This burden was tried it about di^ht miles per hour,
and the deflection at the oentei post was one and three
fhth inches and at the first post was nine sixteenth
of an inch.

References : -

Transactions of American Society of Ciyil

Engineers Vol. 21, July, 1689.

Technology.... Vol. 1, number 9.
THE BALTIMORE AMD OHIO RAILROAD BRIDGE aT
HARPER'S FERRY? WEST VIRGINIA.
. ...• Wendell Bollman.

THE BOLL MAN TRU55

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