Some Mooted Questions in Reinforced Concrete Design | Page 5

of all shearing stress, for the stress in the rod will have a
vertical component equal to the shear. The concrete will rest in the rod
as a saddle, and the rod will be like the cable of a suspension span. The
concrete could be in separate blocks with vertical joints, and still the
load would be carried safely.
By end anchorage is not meant an inch or two of embedment in
concrete, for an iron vise would not hold a rod for its full value by such
means. Neither does it mean a hook on the end of the rod. A threaded
end with a bearing washer, and a nut and a lock-nut to hold the washer
in place, is about the only effective means, and it is simple and cheap.
Nothing is as good for this purpose as plain round rods, for no other
shape affords the same simple and effective means of end connection.
In a line of beams, end to end, the rods may be extended into the next
beam, and there act to take the top-flange tension, while at the same
time finding anchorage for the principal beam stress.
The simplicity of this design is shown still further by the absence of a
large number of little pieces in a beam box, as these must be held in
their proper places, and as they interfere with the pouring of the
concrete.
It is surprising that this simple and unpatented method of design has not
met with more favor and has scarcely been used, even in tests. Some
time ago the writer was asked, by the head of an engineering
department of a college, for some ideas for the students to work up for
theses, and suggested that they test beams of this sort. He was met by
the astounding and fatuous reply that such would not be reinforced
concrete beams. They would certainly be concrete beams, and just as
certainly be reinforced.
Bulletin 29 of the University of Illinois Experiment Station contains a
record of tests of reinforced concrete beams of this sort. They failed by
the crushing of the concrete or by failure in the steel rods, and nearly all
the cracks were in the middle third of the beams, whereas beams rich in
shear rods cracked principally in the end thirds, that is, in the
neighborhood of the shear rods. The former failures are ideal, and are

easier to provide against. A crack in a beam near the middle of the span
is of little consequence, whereas one near the support is a menace to
safety.
The seventh point of common practice to which attention is called, is
the manner in which bending moments in so-called continuous beams
are juggled to reduce them to what the designer would like to have
them. This has come to be almost a matter of taste, and is done with as
much precision or reason as geologists guess at the age of a fossil in
millions of years.
If a line of continuous beams be loaded uniformly, the maximum
moments are negative and are over the supports. Who ever heard of a
line of beams in which the reinforcement over the supports was double
that at mid-spans? The end support of such a line of beams cannot be
said to be fixed, but is simply supported, hence the end beam would
have a negative bending moment over next to the last support equal to
that of a simple span. Who ever heard of a beam being reinforced for
this? The common practice is to make a reduction in the bending
moment, at the middle of the span, to about that of a line of continuous
beams, regardless of the fact that they may not be continuous or even
contiguous, and in spite of the fact that the loading of only one gives
quite different results, and may give results approaching those of a
simple beam.
If the beams be designed as simple beams--taking the clear distance
between supports as the span and not the centers of bearings or the
centers of supports--and if a reasonable top reinforcement be used over
these supports to prevent cracks, every requirement of good
engineering is met. Under extreme conditions such construction might
be heavily stressed in the steel over the supports. It might even be
overstressed in this steel, but what could happen? Not failure, for the
beams are capable of carrying their load individually, and even if the
rods over the supports were severed--a thing impossible because they
cannot stretch out sufficiently--the beams would stand.
Continuous beam calculations have no place whatever in designing
stringers of a steel bridge, though the end connections will often take a

very large moment, and, if calculated as continuous, will be found to be
strained to