While Mr. Meem’s formula for a reinforced concrete beam is simple and much like that which the writer would use, he errs in making the moment of the stress in the steel about the neutral axis equal to the moment of that in the concrete about the same axis.  The actual amount of the tension in the steel should equal the compression in the concrete, but there is no principle of mechanics that requires equality of the moments about the neutral axis.  The moment in the beam is, therefore, the product of the stress in steel or concrete and the effective depth of the beam, the latter being the depth from the steel up to a point one-sixth of the depth of the concrete beam from the top.  This is the method given by the writer.  It would standardize design as methods using the coefficient of elasticity cannot do.

Professor Clifford, in commenting on the first point, says, “The concrete at the point of juncture must give, to some extent, and this would distribute the bearing over a considerable length of rod.”  It is just this local “giving” in reinforced concrete which results in cracks that endanger its safety and spoil its appearance; they also discredit it as a permanent form of construction.

Professor Clifford has informed the writer that the tests on bent rods to which he refers were made on 3/4-in. rounds, embedded for 12 in. in concrete and bent sharply, the bent portion being 4 in. long.  The 12-in. portion was greased.  The average maximum load necessary to pull the rods out was 16,000 lb.  It seems quite probable that there would be some slipping or crushing of the concrete before a very large part of this load was applied.  The load at slipping would be a more useful determination than the ultimate, for the reason that repeated application of such loads will wear out a structure.  In this connection three sets of tests described in Bulletin No. 29 of the University of Illinois, are instructive.  They were made on beams of the same size, and reinforced with the same percentage of steel.  The results were as follows: 

Beams 511.1, 511.2, 512.1, 512.2:  The bars were bent up at third points.  Average breaking load, 18,600 lb.  All failed by slipping of the bars.

Beams 513.1, 513.2:  The bars were bent up at third points and given a sharp right-angle turn over the supports.  Average breaking load, 16,500 lb.  The beams failed by cracking alongside the bar toward the end.

Beams 514.2, 514.3:  The bars were bent up at third points and had anchoring nuts and washers at the ends over the supports.  Average breaking load, 22,800 lb.  These failed by tension in the steel.