by Charis Eleftheriadis
Diploma Thesis, July 2002
The work examines the collapse of tubular members subjected to lateral (transverse) quasi-static loading in the presence of uniform pressure. In particular, it investigates pressure effects on the ultimate lateral load of tubes and on their energy absorption capacity. External pressure is mainly considered, whereas internal pressure effects are also discussed. Tubes are modelled with shell finite elements, accounting for geometric and material nonlinearities. Relatively thick steel and aluminum tubes (D/t£50), which exhibit significant inelastic deformations, are considered. Two-dimensional cases are examined first, where lateral loading is imposed by either two rigid plates or by two opposite radial loads. Three-dimensional cases are also analyzed, where the load is applied either through a pair of opposite wedge-shaped indenters or a single spherical indenter. The results are presented in terms of load-deflection curves for different levels of pressure, and indicate that the presence of pressure has significant effects on tube response. Deformed shapes of tubes are depicted and discussed, and comparison with test data from non-pressurized pipes is conducted. Finally, simplified analytical models are presented for two-dimensional and three-dimensional load configurations, which yield closed-form expressions, compare fairly well with the finite element results and illustrate some important features of tube response in an elegant manner.
Figure: Deformed shapes and distribution of plastic deformation of short-length Steel tube 1 (L/D=5) for zero and non-zero external pressure; load deflection is x=δ/R=δT/D=0.976.