The San Angelo press. (San Angelo, Tex.) 1897-1907, 1905-05-25

STEEL CONCRETE BRIDGE, PLA1SwELL,
MICH.
when beautiful bridge is suggested
we take alarm at the cost and are apt
to decide offhand that the older type
without its good appearance is we'll
enough.
This is a phase of the subject that is
very pertinent, whether 1t should be de-
plored or not. 1t Is only by reason of
this careful consideration OF cost that
our country is able to compete with
European countries in the construction
of bridges in foreign dependencies. 1t
has been said that any fool could build
II bridge II he had money enough, but
1t takes az engineer to do 1t cconom-
lcally.
This matter of cost has compelled us
to limit the construction of stone arch
bridges to Il very small number and to
put in their place metal truss of
straight lines and sharp angles. 1t is
not that we have failed to appreciate
the beauty of the curved arches, but
rather that we could not afford the lux
ury when we needed so many Of them.
Thirty years ago our bridge builders
were crying the need of reform as to
aesthetic design, but had to offer us in
place of sham decorations only the
simplicity and harmonious construction
Of well built truss suitably painted,
and there can be no doubt that great
improvement has been made. The
l,I, 81
up the outlines Of the truss and which
were what Ruskin would have called
constructed decorations" have been
abandoned, and the bridge is left to
depend for its beauty on the noble lines
Of strength and the general symmetry
Of its construction.
AS progress has been made in the
building Of our roads so have we moved
forward In the design of our bridges.
For many centuries cement and broken
stone have been used to replace the eX-
pensive cut stone In arch construction,
but only recently have we succeeded IN
surmounting n difficulty long recogniz-
ed. Concrete Is a building material
generally accepted when 1t Is to be sub
jected only to q compressive force. 1t
lacks sufficient strength II any pull or
tension is applied. This fact has so
limited us In the use Of concrete that
only in rare instances has It been eco
nomical to use It in bridge construc-
ton.
A feature that requires careful con-
sideration In the design Of any engl-
neering structure Is the effect of the
changes In temperature upon the ma
terial used. The fact that steel and
concrete are affected In the same way
and to the same extent by heat first
suggested their use in combination.
This idea has been developed now to
such an extent that we are able to use
the steel to resist the tension In our
structure and the concrete to take care
of the compression and to so design the
whole that there will be a sufficient
amount of each material and yet no
expensive waste. We have found the
stone arch too expensive and the steel
truss lacking in beauty. Combine the
two, and the result is the steel-concrete
arch having the requisites as to beauty
and comparing very favorably as to
cost.
When one Is considering the construc
ton of Il bridge several points should
be considered:
First-That 1t shall answer the util
itarian purpose for which 1t Is wanted
Second.-It should be n monument tc
the progressive ideas Of the community
and serve us an education and an In
spiration to others.
Third.-It should be built for the fu
ture as well as the present, ana It's per
manence should be assured.
These can all be met by the use o.
steel concrete.
One of the difficulties in the desigl
of steel truss is so to arrange the de
tail as to afford ready access to al
the parts for painting. And with TN
best this is impossible where tw
pieces come into contact. This trouble
does not exist with the steel-concret
bridge The steel is not painted AM
hence can be readily inspected. II !
entirely lmbedded in concrete, whicl
has been proved to be perfect Pre-
lection to the steel. Implanted stee
has been found imbedded in concret
after many years as bright and clea
as ever.