ands, but
they evidently did not do so until their elastic limit was passed,
at which time of course they would be expected to fail.

"4. With reference to columns, _A_, _B_, _C_ and _L_, which were
essentially hooped columns, the failure appears to have been caused
by the greater deformation which is always found in hooped columns,
and which in the earlier stages of the loading is apparently due to
lack of homogeneity caused by the difficulty in placing the
concrete around the hooping, and in the later stage of the loading
to the excessive expansion of the concrete. This greater
deformation in a hooped column causes any vertical steel to pass
its elastic limit at an earlier stage than in a column where the
deformation is less, and therefore produces the buckling between
the bands which is noted in these two sets of columns. This
excessive deformation is a strong argument against the use of high
working stresses in hooped columns.

"In conclusion, then, it may be said that the columns reinforced
with vertical round rods showed all the strength that would be
expected of them by theoretical computation. The hooped columns, on
the other hand, that is, the columns reinforced with circular bands
and hoops, gave in all cases comparatively low results, but no
conclusions can be drawn from them because the unit-strength would
have been greatly increased if the columns had been larger so that
the relative area of the internal core to the total area of the
column had been greater."

From this letter, it will be seen that every one of Mr. Godfrey's
comparisons of plain _versus_ reinforced columns requires explanations
which decidedly reduce, if they do not entirely destroy, the force of
his criticism.

This discussion can scarcely be considered complete without brief
reference to the theory of longitudinal steel reinforcement for columns.
The principle[R] is comparatively simple. When a load is placed on a
column of any material it is shortened in proportion, within working
limits, to the load placed upon it; that is, with a column of
homogeneous material, if the load is doubled, the amount of shortening
or deformation is also doubled. If vertical steel bars are embedded in
concrete, they must shorten when the load is applied, and consequently
relieve the concrete of a portion of its load. It is therefore
ph