osition, of stresses takes place.
The portion which is laid off below the bottom rods will probably not
act unless there is sufficient concrete below the reinforcing bars and
on the sides, and, as that is not the case in ordinary construction, it
is very probable, as Mr. Goodrich has pointed out, that the concrete
below the rods plays an unimportant part, and that the triangle which is
now shown below the rod should be partially omitted.
The triangles in Fig. 13 show the intensity of stress in the concrete at
any point, or at any section where it is wanted. They show conclusively
where the components are located in the concrete, their relation to the
tensile stresses in the rods, and, furthermore, that they act only in a
general way at right angles to one another. This is in accordance with
the theory of beams, that at any point in the web there are tensile and
compressive stresses of equal intensity, and at right angles to one
another, although in a non-homogeneous web the distribution is somewhat
different.
After having found at the point of junction the intensity of stress, it
is possible to tell whether or not a bond between the stirrups and the
bottom rods is necessary, and it would not seem to be where the stirrups
are vertical.
It would also seem possible to tell in what direction, if any, the bend
in the inclined stirrups should be made. It is to be assumed, although
not expressly stated, that the bends should curve from the center up
toward the end of the beam, but an inspection of the stress triangles,
Fig. 13, will show that the intensity of stress is just as great on the
opposite side, and it is probable that, if any bends were required to
reduce the maximum stress in the concrete, they should as likely be made
on the side nearest the abutment.
From the stress triangles it may also be shown that, if the stirrups
were vertical instead of inclined, the stress in the concrete on both
sides would be practically equal, and that, in consequence, vertical
stirrups are preferable.
The next issue raised by the author is covered in his seventh point, and
relates to bending moments. He states: "* * * 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, * * *."
The author seems to imply that such juggling is wrong. As a matter of
fact, it is perfectly allowable and legitimate in every instance o
|