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We
shall assume that the lines by which we have represented forces F, 0, H, and K
represent struts which are hinged at their intersections with the forces A, B,
and C, which represent loads; and that the two end struts F and K are hinged at
two concrete abutments located at y and z. Then all of the struts will be in
compression, and the rays of the force diagram will represent, at the same
scale as that employed to represent forces or loads A, B, and C, the
compression in each of the struts. In the force diagram, draw a line from o,
parallel with the line. It intersects the load line in the point shown. Considering
the triangle as a force diagram, the side represents the force provided, while
the point and on may represent the direction and amount of two forces which
will hold F in equilibrium. Therefore pit would represent the amount and
direction of the vertical component of the concrete abutment reaction at y, and
on would represent the component in the outward direction. Similarly we may
consider the triangle as a force diagram; that represents the vertical
component shown and that on represents the component in the direction. There is an old saying, "There is nothing
new under the sun." This holds true regarding the history of cement. To
many the use of cement is of recent origin, the result of modern methods of
con3truction.
Nothing is further from the truth. With the dawn of civilization
came the use of cement. Ancient Egypt and Assyria contributed wonderful
examples of its use, one notable instance being the Queen's Chamber in the
Great Pyramid. The Appian Way and the Pantheon at Rome, together with her
aqueducts, are other examples of concrete art, some of which are in actual use
at the present day. From the time of the Romans until about 1756, little was
done in the manufacture of cement. In 1824, Joseph Aspdin,
of Leeds, England, discovered the method of making cement and named it
"Portland Cement" from the fancied, though really slight, resemblance
to the noted limestone, which by the way is used in the London Westminster
Cathedral, found on the Isle of Portland, on the south coast of England. Although
European countries began manufacturing cement at once it was not until about
1850 that its commercial success was assured. In 1818 natural cement was
discovered in New York State by a man named White, an engineer on the Erie
Canal. The first American mill was built at Rosendale, N. Y., and from this
fact obtained the name of "Rosendale Cement." The first artificial or
true cement was not manufactured until 1875, and it was not until 1896 that the
annual production reached the million barrel mark.
Previous to this time the
English and German cements were regarded as having the greatest strength. The
growth of this important industry has increased wonderfully and today
individual firms are turning out over 9,000,000 barrels yearly and preliminary
figures for 1919 show that the annual production for the United States will be
in excess of 80,000,000 barrels. Pennsylvania is the banner state in production
of cement, producing over 28,000,000 barrels yearly, or nearly three times as
much as her nearest competitor, Indiana. Cement is substantially an artificial
stone made by uniting in very exact proportions, two materials, one of them a
rock-like limestone, or a softer material like chalk, which is nearly pure
lime, with a material like shale, which is hardened clay. Since on is common to
both of these force concrete triangles, they neutralize each other, and the net
resultant of the two forces F and K is the two vertical forces R and R";
but since the resultant II is the resultant of F and K, we may say that R' and
B" are two vertical forces whose combined effect is the equal and opposite
of the force R. Although an indefinite number of combinations of forces could
begin and end at the points y and z, and could produce equilibrium with the
forces A, B, and C, the forces R' and R" are independent of that particular
combination of struts, F, 0, H, and K. The method of manufacture determines the
three classes into which cement is generally, divided.
Are You in Biddeford Maine? Do You Need Concrete Cutting?
We Are Your Local
Concrete Cutter
Call 207-284-0788
We Service Biddeford,
ME and all surrounding Cities & Towns
