A Full 3D Finite Element Model for Buckling Analysis of Stiffened Steel Liners in Hydroelectric Pressure Tunnels

The availability of tools for safety evaluation of a pressure liner is a relevant issue in both structural and hydraulic engineering. A numerical procedure for assessing the stability of a stiffened steel liner in a hydroelectric pressure tunnel is presented in this paper. First, a review of some analysis methods for steel liners is outlined. Relevant aspects for the critical buckling pressure assessment are considered, specifically boundary conditions and geometric imperfections. General 2D and 3D nonlinear finite element modeling procedures, including large displacements formulation are presented. Some relevant factors in the liner response, such as the annular gap, the stiffeners, and the interaction with the elastic medium surrounding the steel liner are taken into account. As a result, some simple modeling guidelines for thin-walled steel pressure liners are depicted. Also, some conclusions regarding the influence of stiffeners as well as of the surrounding medium are drawn. The procedure is applied to an actual steel tunnel liner which failed by global instability in 2010 in Spain. The aim is to simulate the causes of collapse as well as to draw some design criteria.