Compilation of “Instructions for designing concrete and reinforced-concrete features of hydraulic structures”

Abstract

The new standards specification has been compiled to replace the construction norms 55-59 and to supplement the construction norms and specification in special sections. In connection with the fact that each of these documents has remained in force, unmodified, for at lest 10 years and their contents are to some extent traditional, a critical revision is essential, obsoletestatements being replaced and brought up to date.In the present article we consider certain sections of the projected ~Instructions" and suggest improvements in these important standards. Individual problems have akeady been discussed [1-3].1. Point 1.3 of the projected "Instructions ~ is intended only for structures of class IV strength: for structures of classes I and II strength, however, and, in certain cases class-III structures also, individual technical restrictions must be compiled. We think it expedient to extend the applicability of the ~Instructions" so that they contain only a compilation of the individual technical restrictions for class-I structures; for structures of class-II, and in special eases for class-ilI structures also, asupplement must be provided.2. In point 2.3 the concrete strength for axialtension mustbe given in round figures, at intervals of 5 kg/cm z, i.e., 10,15,20, 25, 30, 35, and 40, The strength of prestressed concrete represents an independent characteristic, and in parts of structures designed on the basis of tensile strength of the concrete, it must be chosen independently of the type of compression concrete.3. The coefficients of the working conditions, which are connected with the level of the production process (Point 3.3b), rcu~t be subdivided according to the conl~olled values of the strength variation coefficients.A great many laboratory data and industrial parameters prove that in an operative accelerated quality control, the modern mean level of concrete-work industrialization enables us to achieve values of the variation coefficient of cv = 0.15. In this case we must take mb= 1 and the coefficient of homogeneity equal to 0.55. When the level of the production process is higher and Cv= 0.10-0.12, which corresponds to a homogeneity coefficient of 0.6-0.65, we can take mb=l.2. Finally, when the production is not well organized and cv=0.18-0.25, which corresponds to a homogeneity coefficient of 0.45-0.50, the coefficient mb of the working conditions must be taken at 0.8.Here it is opportune to repeat the suggestions [1 and 2] on the differentiation of the homogeneity coefficients according to the significance of the complex and class of structures by altering the number of deviation standards.