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Full text of "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* 




















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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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