Design and analysis of structural steel tower assembly subject to high axial and transverse stresses using BS EN1993-1-1 and BS EN1993-1-5

Abstract eng:
This paper describes the process developed to analyze and design a plated structural steel tower used to support the stay cables on a curved cable stayed rail bridge. The tower’s internal steel assembly was relatively complex because of the varying vertical and transverse geometry of each cable anchorage. These anchorages subject the plated steel sections to both high axial and transverse stresses. The accurate modelling of the ultimate and serviceability limit state behaviour was therefore critical. For this reason a detailed three dimensional Finite Element Model (FEM) was used to verify the design. This paper describes the practical implementation of the methodology provided by BS EN1993-1-1:2005 and BS EN1993-1-5:2006 for the design of a steel plated section using hand calculations and using a FEM. When checking a design using a FEM, the loss in stiffness due to a deformed and deflected shape can be modelled in a non-linear analysis. The deformed shape of the structure (obtained from a previous analysis) can be used as the initial imperfect shape to give a reduced section resistance (Cl. 5.3.5 of Hendy & Murphy, 2007). The paper describes how imperfections applied to the model were therefore used to account for both geometric imperfections and residual stresses. The paper also describes how the critical buckling analysis was performed on the tower anchorage using the same three dimensional, finite element shell model used for the ultimate limit state design check. This buckling analysis was performed in two parts: firstly as a linear eigenvalue buckling analysis; and then secondly a geometrically nonlinear analysis. The aim of the paper is to document benefits and challenges of the chosen methodology for the design of irregular steel plated section subject to both axial and transverse stresses. It hopes to provide some practical insight into the use of BS EN1993-1-1:2005 and BS EN1993-1-5:2006 for this purpose.

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