oops do not effect this. Thin joints of lime mortar are known to
be many times stronger than the same mortar in cubes. Why, in the many
books on the subject of reinforced concrete, is there no mention of this
simple principle? Why do writers on this subject practically ignore the
importance of toughness or tensile strength in columns? The trouble
seems to be in the tendency to interpret concrete in terms of steel.
Steel at failure in short blocks will begin to spread and flow, and a
short column has nearly the same unit strength as a short block. The
action of concrete under compression is quite different, because of the
weakness of concrete in tension. The concrete spalls off or cracks apart
and does not flow under compression, and the unit strength of a shaft of
concrete under compression has little relation to that of a flat block.
Some years ago the writer pointed out that the weakness of cast-iron
columns in compression is due to the lack of tensile strength or
toughness in cast iron. Compare 7,600 lb. per sq. in. as the base of a
column formula for cast iron with 100,000 lb. per sq. in. as the
compressive strength of short blocks of cast iron. Then compare 750 lb.
per sq. in., sometimes used in concrete columns, with 2,000 lb. per sq.
in., the ultimate strength in blocks. A material one-fiftieth as strong
in compression and one-hundredth as strong in tension with a "safe" unit
one-tenth as great! The greater tensile strength of rich mixtures of
concrete accounts fully for the greater showing in compression in tests
of columns of such mixtures. A few weeks ago, an investigator in this
line remarked, in a discussion at a meeting of engineers, that "the
failure of concrete in compression may in cases be due to lack of
tensile strength." This remark was considered of sufficient novelty and
importance by an engineering periodical to make a special news item of
it. This is a good illustration of the state of knowledge of the
elementary principles in this branch of engineering.

Mr. Turner states, "Again, concrete is a material which shows to the
best advantage as a monolith, and, as such, the simple beam seems to be
decidedly out of date to the experienced constructor." Similar things
could be said of steelwork, and with more force. Riveted trusses are
preferable to articulated ones for rigidity. The stringers of a bridge
could readily be made continuous; in fact, the very riveting of the ends
to a floor-beam gives them