necessary to state that one weak detail will limit the strength of the
truss.

The author has only condemnation for the use of longitudinal rods in
concrete columns (Point 15). It would seem that if the longitudinal bars
are to carry a part of the load they must be supported laterally by the
concrete, and, as before, in the beam, it may be likened to a framed
structure in which the web system is formed of concrete alone, or of a
framework of poorly connected members, and the concrete and steel must
give mutual support in a way not easy to analyze. It is scarcely
surprising that the strength of such a structure is sometimes less than
that shown by concrete alone.

In the Minneapolis tests, quoted by the author, there are certain points
which should be noted, in fairness to columns reinforced longitudinally.
Only four columns thus reinforced failed below the strength shown by
concrete alone, and these were from 52 to 63 days old only, while the
plain concrete was 98 days old. There was nothing to hold the rods in
place in these four columns except the concrete and the circular hoops
surrounding them. On the other hand, all the columns in which the
hooping was hooked around the individual rods showed materially greater
strength than the plain concrete, although perhaps one should be
excepted, as it was 158 days old and showed a strength of only 2,250 lb.
per sq. in., or 12% more than the plain concrete.[G]

In considering a column reinforced with longitudinal rods and hoops, it
is proper to remark that the concrete not confined by the steel ought
not to be counted as aiding the latter in any way, and that,
consequently, the bond of the outside bars is greatly weakened.