Bending of composite cylinders

Abstract

A study is made with the purpose of investigating the behavior of composite cylinders under the action of bending loads. A theoretical approach is proposed in which several simplifying assumptions are made, and an experimental analysis is carried out with the view of establishing the degree of validity of these assumptions as well as for purposes of investigating the general behavior of the composite cylinders. The principal assumptions made in the theoretical treatment of the problem are: (1) Plane transverse sections remain plane both within the elastic limit of the materials and in the post-yield stages. (2) The steel behaves in accordance with Hooke's Law up to a strain of 2000 microinches per inch (0.2%). For higher values of strain, the steel stress has a constant value determined by the "0.2% offset" standard as shown in the figure below. (3) The stress-strain relationship for concrete is as established in "A Study of Combined Bending and Axial Load in Reinforced Concrete Members", University of Illinois Engineering Experiment Station, Bulletin Series No. 399, 1951, by Eivind Hognestad. (4) Concrete has negligible tensile strength. (5) Somastic and wrap coat, component materials in the composite cylinders, have negligible capacity to withstand tension or compression. (6) The test specimens used in the experimental analysis are composite cylinders made up of an inner steel cylinder, an intermediate somastic cylinder or wrap coat cylinder, and an outer, wire reinforced concrete cylinder. In practice these composite cylinders are used in the construction of under-water pipelines (the concrete cylinder serves the primary purpose of providing negative buoyancy, while the somastic and the wrap coat are asphaltic substances for protection of the steel cylinder against corrosion).