The proper design of concrete slabs supported on four sides is a complex and interesting study.  The writer has recently designed a floor construction, slabs, and beams, supported on four corners, which is simple and economical.  In Fig. 7 is shown a portion of a proposed twelve-story building, 90 by 100 ft., having floors with a live-load capacity of 250 lb. per sq. ft.  For the maximum positive bending in any panel the full load on that panel was considered, there being no live load on adjoining panels.  For the maximum negative bending moment all panels were considered as loaded, and in a single line.  “Checker-board” loading was considered too improbable for consideration.  The flexure curves for beams at right angles to each other were similar (except in length), the tension rods in the longer beams being placed underneath those in the shorter beams.  Under full load, therefore, approximately one-half of the load went to the long-span girder and the other half to the short-span girder.  The girders were the same depth as the beams.  For its depth the writer found this system to be the strongest and most economical of those investigated.

E.P.  GOODRICH, M. AM.  SOC.  C. E.—­The speaker heartily concurs with the author as to the large number of makeshifts constantly used by a majority of engineers and other practitioners who design and construct work in reinforced concrete.  It is exceedingly difficult for the human mind to grasp new ideas without associating them with others in past experience, but this association is apt to clothe the new idea (as the author suggests) in garments which are often worse than “swaddling-bands,” and often go far toward strangling proper growth.

While the speaker cannot concur with equal ardor with regard to all the author’s points, still in many, he is believed to be well grounded in his criticism.  Such is the case with regard to the first point mentioned—­that of the use of bends of large radius where the main tension rods are bent so as to assist in the resistance of diagonal tensile stresses.

As to the second point, provided proper anchorage is secured in the top concrete for the rod marked 3 in Fig. 1, the speaker cannot see why the concrete beneath such anchorage over the support does not act exactly like the end post of a queen-post truss.  Nor can he understand the author’s statement that: 

“A reinforcing rod in a concrete beam receives its stress by increments imparted by the grip of the concrete; but these increments can only be imparted where the tendency of the concrete is to stretch.”

The latter part of this quotation has reference to the point questioned by the speaker.  In fact, the remainder of the paragraph from which this quotation is taken seems to be open to grave question, no reason being evident for not carrying out the analogy of the queen-post truss to the extreme.  Along this line, it is a well-known fact that the bottom chords in queen-post trusses are useless, as far as resistance to tension is concerned.  The speaker concurs, however, in the author’s criticism as to the lack of anchorage usually found in most reinforcing rods, particularly those of the type mentioned in the author’s second point.