ard
is furnished by making the diagonals of flat straps. The stress in the
rods at this point, moreover, is not generally the maximum allowable
stress, for considerable is taken out of the rod by adhesion between the
point of maximum stress and that of juncture.

Mr. Godfrey wishes to remedy this by replacing the diagonals by rods
curved to a radius of from twenty to thirty times their diameter. In
common cases this radius will be about equal to the depth of the beam.
Let this be assumed to be true. It cannot be assumed that these rods
take any appreciable vertical shear until their slope is 30 deg. from the
horizontal, for before this the tension in the rod would be more than
twice the shear which causes it. Therefore, these curved rods, assuming
them to be of sufficient size to take, as a vertical component, the
shear on any vertical plane between the point where it slopes 30 deg. and
its point of maximum slope, would need to be spaced at, approximately,
one-half the depth of the beam. Straight rods of equivalent strength, at
45 deg. with the axis of the beam, at this same spacing (which would be
ample), would be 10% less in length.

Mr. Godfrey states:

"Of course a reinforcing rod in a concrete beam receives its stress
by increments imparted by the grip of the concrete; but these
increments can only be imparted where the tendency of the concrete
is to stretch."

He then overlooks the fact that at the end of a beam, such as he has
shown, the maximum tension is diagonal, and at the neutral axis, not at
the bottom; and the rod is in the best position to resist failure on the
plane, _AB_, if its end is sufficiently well anchored. That this rod
should be anchored is, as he states, undoubtedly so, but his implied
objection to a bent end, as opposed to a nut, seems to the writer to be
unfounded. In some recent tests, on rods bent at right angles, at a
point 5 diameters distant from the end, and with a concrete backing,
stress was developed equal to the bond stress on a straight rod embedded
for a length of about 30 diameters, and approximately equal to the
elastic limit of the rod, which, for reinforcing purposes, is its
ultimate stress.

Concerning the vertical stirrups to which Mr. Godfrey refers, there is
no doubt that they strengthen beams against failure by diagonal tension
or, as more commonly known, shear failures. That they are not effective
in the beam as built is plain, for, if one consi