concrete. No more variable property of concrete is known than its
coefficient of elasticity, which may vary from 1,000,000 to 5,000,000
or 6,000,000; it varies with the intensity of stress, with the kind of
aggregate used, with the amount of water used in mixing, and with the
atmospheric condition during setting. The unknown coefficient of
elasticity of concrete and the non-existent condition of no initial
stress, vitiate entirely formulas supported by these two props.

Here again destructive criticism would be vicious if these mathematical
gymnasts were giving the best or only solution which present knowledge
could produce, or if the critic did not point out a substitute. The
substitute is so simple of application, in such agreement with
experiments, and so logical in its derivation, that it is surprising
that it has not been generally adopted. The neutral axis of reinforced
concrete beams under safe loads is near the middle of the depth of the
beams. If, in all cases, it be taken at the middle of the depth of the
concrete beam, and if variation of intensity of stress in the concrete
be taken as uniform from this neutral axis up, the formula for the
resisting moment of a reinforced concrete beam becomes extremely simple
and no more complex than that for a rectangular wooden beam.

The eleventh point concerns complex formulas for chimneys. It is a
simple matter to find the tensile stress in that part of a plain
concrete chimney between two radii on the windward side. If in this
space there is inserted a rod which is capable of taking that tension at
a proper unit, the safety of the chimney is assured, as far as that
tensile stress is concerned. Why should frightfully complex formulas be
proposed, which bring in the unknowable modulus of elasticity of
concrete and can only be solved by stages or dependence on the
calculations of some one else?