The Montgomery advertiser. [volume] (Montgomery, Ala.) 1885-1982, 1904-07-03
PREPARING FOR THE ERA
OF PORTLAND CEMENT
INxE A
DONE
THE APPLICATION CEMENT


Boston, July Am elaborate series
of investigations into the tensile
strength OF concrete, or Portland &C.
m4nt: studies that can best be carried
on in the summer time when there are
hardly any students about TO tread
even lightly upon the hoors Oh the
building in which the work is conduct
ed; observations that for the most part
have to be recorded around the hours
of midnight so that the jar from pass
ing trains, trolley cars and other We
hicles may be reduced to minimum
this is a vacation undertaking which
an instructor and ii few advanced stu
dents have lust started in the engineer
ing department of the Massachusetts
Institute of Technology.
This work of testing the elasticity or
huge beams of concrete will be the
first that has as yet been projected on
any large scale anywhere although
some Investigations have already been
made on little blocks of cement by an
English Investigator. Whether what
is true of small masses of the mate
rial is also true of the great sticks
and bars of 1t used in commerce re-
mains to be discovered.
At any rate anybody who knows
anything at all about modern building
usages is aware that beams and girders
of concrete are being employed more
and more each year. 1t has become a
great commercial desideratum 10 I'M
derstand the laws governing the be
havior of the material when subject to
stress and strain. All sorts of devices
have in fact been adopted by the man
ufacturers to strengthen concrete for
constructive purposes Most of the
beams now in commercial use contain
bars of iron or steel of various shapes
sometimes straight. sometimes bent
into spirals. most often "splaVed" at
the end. The reason for this splaying.
or division. of the reinforcing rod into
a number of outgoing filaments is that
when a beam breaks it usually cracks
near one end or the other. The spe-
ciaI object of reinforcement is to
strengthen it about the points where
fracture is likely to occur.
This use of iron rods imbedded in the
concrete has been very largely mat
ter of rough -and-ready calculation and
even of guesswork rather than of sci
eutific determination of all the ele-
ments contributing to make up the
strength of a bar of the material. A
good many of these factors have al
ready been investigated in the engi-
neering department of the Institute and
eIsewher6 One of the most vital in
calculation. however that of the tensile
modulus of elasticity, is still to be ac-
,uratelv determined. To use the sci
Antif1c term. the modulus OF elasticity
Ia the load per square inch divided by
the COMMISSION or the tension per
inch of length, or the stress over the
strain.
The actual process of testing Is APP
nIied TO a section just 100 inches long
in the centre of somewhat longer bar
~ concrete Through the beam at
aither end of the indicated section run
steel rods which give an opportunity
for graphing to the big machine by
means of two wire ropes. Once the
bar of concrete is in position II Is sun
iected to such a racking as lXlon, in
the Greek myth, never eXpeVlehctu On
his wheel. If under the most intense
compression or stretching the hlg
beam gives as much rs on" ten-thouS-
andth of an inch this difference Will ne
measured in a greatly magnined way
on an Indicator which has been lngeni-
ously devised. over one Of the pro-
jecting ends of each of the rods set INTO
the beam is a ball and socket arrange
ment, from which bag runs out par
allei to the beam. These rods overlap
each other at the centre Of the loo-lnch
section with a fine needle-like roller
between them. 80 that one can slide
over the other when any changes take
place in the concrete beam. Attached
at this point is a mirror which re-
ceives a ray of light from an adjacent
lamp and throws it upon an indicator
close by. So delicate is the apparatus