Strength Requirements for Round Conduit

For many years, vitrified day has been the principal material for underground conduit used as cable duct by the Bell System. Vitrified clay conduit has, in general, given excellent service. It has more than adequate strength and durability for the wide variety of conditions under which it must be used and for the long service life expected of it. For this reason, relatively little attention has been given to the formulation of special strength requirements for this type of conduit during the period in which it has been standard for Bell System use. For some time other types of conduit, mainly in the form of single duct, have appeared on the market. Many of their properties make them attractive enough to be considered for Bell System use. However, to prevent possible failure or excessive deformation of the conduit under field conditions each type of conduit should meet minimum strength requirements, in order to provide the same reliable service that clay conduit has given. The main purpose of this investigation was to determine the minimum strength requirement for round conduit under various field conditions. An extensive investigation of the effects of external loads 011 closed conduits has been conducted at the Iowa Engineering Experiment Sta737