Ottumwa weekly courier. (Ottumwa, Wapello County, Iowa) 1872-1899, 1878-12-18
the BRIDGE BUSINESS.
n~rv-NS.V. vx~~x,. IAo~ ~ 1910


OrTUMwA, Iowa, Dec. IL, 1873.
Committee of Citizens-- Gentlemen:
In compliance with your request
that should make . careful and |
thorough examination of the wagon |
bridge across the Des Moines river |
which was erected In 1870 and has |
been operated ~ . toll bridge, per.
init me to submit the following:
The records show that the Board of |
Supervisors employed Mr.. L. NJ.
johnson, an engineer, to examine this |
bridge and report % to its character,
safety and the advisability of the |
county purchasing 1t to be used as q
free bridge. I have not the honor Of
an acquaintance with Mr.. johnson,
nor kno wledge of HE qualifications
as an engineer competent to examine |
and pass upon the safety and durabil-
ity of structure Of this kind, but
judging from his report, which Ihave |
carefully examined, I should say that |
he was competent, but has fallen into
some errors for the want of Q suffi-
GENTLY thorough investigation.
The strongest Recommendation that
he makes 10 that the county, if 1t
concludes to build . new bridge,
should locate 1t on Jefferson street |
and build an iron bridge of the Pratt
type. Now, do not for . moment
wish to be understood a. intimating
that Mr.. johnson had any interest, di- |
rect or indirect, in having the county
adopta particular kind Of bridge, but !
what surprises me 10 that being q |
| h r;xS NJ. IN oop hn mt hIo
willing to recommend some other
kind as well, so as to give the county
. choice, especially as there are so
many good bridges In use, and few,
at least, net of the pratt type" I re-
fer here generally to the report and
shall do 90 more particularly here
after, 80 the impression has gotten
out that MIR. johnson utterly con-
demned the bridge in nis report and
therefore the purchase and use
of it as q free bridge by the coun-
ty 10 altogether out of the question,
and hence they must of necessity
build q new bridge.
The part of the bridge to which I
first directed my attention wae the
piers. These piers are built Of .
framework of oak timbers, the sills
Of which are laid on solid and even
bed of solid rock and to which they
are firmly bolted. They are covered
the interior LIED with spAwls or
email stones. The oak timbers !
found to be almost as sound as when
first erected, as tested by boring into
them with an anger. The planking
on the piers is decsyed In places,
though generally sound, but whenev-
er the pIanks decay they can easily be
replaced by sound ones. I should
say that the timber portion of the
piers will last for from eight to ten
years longer. Mr.. johnson says in
regard to these piers, "The piers and
ice breakers will be worth nothing
after period which may vary from
less than one to about three years"
In view Of the fact that this report
|, was made one year ago last Septem-
Der and that the piers are practical
ly sound to-day, it Is conclusive evil
dence to my mind that Mr.. J. made
no examination Of them whatever.
He says further on that Experience
shows that implanted oak, alternately
: i
carefully If 1t be trusted after eight
years and it cannot be trusted 1T oil
after ten or eleven years." Every
where in the domain Of science, theo-
ry and the experience of others are
recognized as having a greater or
less value corresponding to the proofs
adduced to sustain the theory on the
one hand and the similarity of the
circumstances, &C., under which the
observations are made on the other
hand, but when q case like the pres
! ent one occurs where simple exam
! ination only is necessary to find out
! the actual condition Of things and q
theory 10 cited it shows either of two
, things. gross carelessness or inten-
tional neglect. The piliug between
+ the bridge proper and tho roadway
thrown up by the county is some
what decsyed and probably will have
, to be replaced in from three to five
years. The iron work Of the bridge
is sound and uniDjured 90 far as
can observe, either from strains re-
: sulting from heavy loads, from rust.
4 or from any other causes. What Mr..
y j. says as regards the lightness Of the
bridge and the vibrations resulting
from the transit of heavy loads Is true
. Of all bridges Of the kind, to-wit
J, wrought iron bridges Mr.. J.says that
many Improvements have been made
in bridge designs and manufacture
: since this bridge was erected. This
!, is also ndoubtedly true, but the
only question that the people Of the
city and county are interested in is
the bridge safe and will 1t be good
i investment to purchase it2 Mr.. j
3 Gays the bridge weighs about 2S5 D.
a per lineal foot. / have not made q
! calculation on that point, but presume
!. it is practically correct. One span
will therefore weigh 28,5OO lbs. He
Q says: ut 10 proper 10 assume that the
r bridge may be loaded with 80 lbs pei
q square foot for "a # clear width
, Now the above load per square &
would give for one span Of 100 fl
I 192, 900 lbs, which added to the weight
r Of one span of the bridge gives us the
total weight of one span with it,
load 220. 500 lbs, and would produce
tensile strain on the lower
q chords Of about Is 600 lbs per square
inch, a. he says. Wrought iron will
bear without breaking Q tensile strain
offrom $4,000 to 10000 lbs per square
Q inch, but for safety not more than
9 from j to u Of that amount 10 al
, lowed. Now am willing to admi;
that If Mr.. Us premises are correct,
then the bridge Is too weak. But IL
Q 1t correct TO assume that the bridge
3 may be loaded with 30 lbs per square
y foot? AS we have seen this gives VI
1920 lbs, which would be equal ia
1880 men weighing $50 lbs each, or
: or 192 head Of cattle weighing LOCO
lbs each, neither Of which number
r could be placed on one span. There il
: not room Tor more than 1876 head OF
t cattle of the above weight, even II
a they were crowded together % close
0 as possible, and while we are assum-
:, ing will venture the assertion and
Q will be endorsed by every ono who Il
: not anxious to commit suicide in that
9 particular manner that after GOO men
Q have gone on one span the other CSC
! will, instead of searching for room
0 for themselves, wait anxiously for
: their safe return. ] do not believe
1 that there 10 any danger of the bridge
ever giving way from the results OF
8 any load that will ever be brought
upon it. Many bridges Of the same
! pattern have been erected In various
Q parts Of the state and used - free
bridges and do not know Of any one
of them having failed.
understand that the Bridge Co.
makes the following propositions:
lat. To sell the bridge Sept. !, 1879,
for $l2, 600, one year before the 'exclu-
sive license which they have, ex.
y pires, and one year before a free
bridge can be operated except by a
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