Experimental and numerical databases are presented for thick pipes (10<DoIt<40) under pure bending and combined tension and bending loads. Equations to predict collapse moment, critical curvature, moment-tension and curvature-tension interactions are proposed based on the databases.
The paper presents numerical and experimental databases and ultimate limit states of thick pipes (10<DoIt<40) subjected to pure bending and combined tension and bending loads. The study is motivated primarily by the development of design codes for pipelines, risers and TLP (tension leg platform) tendons, but is also relevant for thick-walled tubulars used in buildings, offshore platforms, piping systems and other engineering structures. The collapse behaviour of thick pipes is strongly influenced by mean diameter to thickness ratio Dolt, material properties (yield stress and strain-hardening parameters), and initial imperfections. The bifurcation type of failure with ripples and a subsequent kink on the compression side of the pipe looks very similar to the plastic buckling of an axially compressed pipe (Timoshenko and Gere, 1961). The limit load type of failure is caused by increased ovalization of the pipe. Brazier (1927) solved a limit load type of instability of long elastic pipes in pure bending due to ovalization of the cross-section. The solution was extended by Ades (1957) for long elastic-plastic pipes in pure bending by assuming that the cross-section always ovalizes into an elliptical form. The Dolt value which separates limit load instability and bifurcation buckling is dependent on the material properties of the pipes. Experiments conducted by Corona and Kyriakides (1988) and Kyriakides and Ju (1992) show that this Dolt value is around 35 for typical pipeline material. The present study, therefore, only deals with the limit load type of instability, and the ultimate capacity is defined as the point at which the limit load type of instability occurs.