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 considers a vertical plane
between the stirrups, the concrete must resist the shear on this plane,
unless dependence is placed on that in the longitudinal reinforcement.
This, the author states, is often done, but the practice is unknown to
the writer, who does not consider it of any value; certainly the
stirrups cannot aid.

Suppose, however, that the diagonal tension is above the ultimate stress
for the concrete, failure of the concrete will then occur on planes
perpendicular to the line of maximum tension, approximately 45° at the
end of the beam. If the stirrups are spaced close enough, however, and
are of sufficient strength so that these planes of failure all cut
enough steel to take as tension the vertical shear on the plane, then
these cracks will be very minute and will be distributed, as is the case
in the center of the lower part of the beam. These stirrups will then
take as tension the vertical shear on any plane, and hold the beam
together, so that the friction on these planes will keep up the strength
of the concrete in horizontal shear. The concrete at the end of a simple
beam is better able to take horizontal shear than vertical, because the
compression on a horizontal plane is greater than that on a vertical
plane. This idea concerning the action of stirrups falls under the ban
of Mr. Godfrey's statement, that any member which "cannot act until
failure has started, is not a proper element of design," but this is not
necessarily true. For example, Mr. Godfrey says "the steel in the
tension side of the beam should be considered as taking all the
tension." This is undoubtedly true, but it cannot take place until the