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The many failures which have recently occurred in concrete constructions emphasize the necessity for a revision of some of the current methods of design and erection, and the formulation and strict .enforcement of -building laws of a thoroughly searching character. As we have frequently pointed out in these columns, there is no material of construction that offers such inducements to cheap and fraudulent work on the part of the unscrupulous contractor as armored concrete. As throwing a great deal of much-needed light on this subject, we direct attention to a voluminous paper read before the Western Society of Engineers by Dr. W. Michaelis, Jr., and published in the current issue of the SUPPLEMENT. The author of the paper deals at great length with the merits and limitations of cement and concrete and the causes of failure in concrete construction, and suggests means for the prevention of such failure. While, on the one hand, manufacturers exaggerate the advantages of cement, on the other hand the engineer and architect make unreasonable demands, and misinterpret the failures in concrete construction that so often occur. The best way to establish confidence in this modern building material would be to minimize the danger of failure by establishing proper building ordinances, which would compel the contractor to handle the material in the prescribed way, and to make proper tests of it while the building is in course of construction. The principles governing modern concrete construction are thoroughly understood, according to the author of the paper, by comparatively few; and this explains the divergence of opinion on many points pertaining to this branch of the building industry. While some engineers are careful to specify concrete of ample strength, others blame such over-cautious builders for making use of an excessive factor of safety. In reply to the statement frequently made by engineers that cement is not sufficiently uniform at present, and that if it could be so manufactured as to give as uniform results as steel, it would be possible for the engineer to reduce the larger factor of safety now demanded for concrete over that required for steel, the author of the paper answers that such a statement is entirely without foundation. Steel is a well-defined chemical compound rolled into the desired shape, while concrete is the sum of a number of factors. The calculation of a steel girder and that of a reinforced concrete girder can never be based on equal safety factors, no matter how much the properties of cement may be improved in the future; and it will not be improved in the future for the reason that we have arrived at the limits of its good qualities. In the opinion of Dr. Michaelis, the author of the paper, failures of concrete steel can be materially lessened, if not entirely prevented, by making it compulsory to use concrete of specified proportion of crushed stone, sand, and cement, and to use the proper kind of reinforcement in each case, and the necessary amount of it. Certain standard rules should be laid down by a Board of Building Examiners, and certain types of reinforcing material should be excluded where they are not in their proper place. Moreover, the erection of the building should be accompanied by continuous tests of the concrete that goes into the construction, and the builder should be compelled to inform himself of the strength of each column, girder, beam . and fioor slab before striking the forms and placing the load upon them.
