Behaviour and design of prestressed columns

Abstract

The load-carrying capacity of slender columns is limited by global instability. However, through the addition of strategically placed cross-arms and external prestressed cables, buckling displacements can be inhibited and the load-carrying capacity considerably enhanced. Such systems, known as prestressed stayed columns offer efficient and lightweight structural solutions. Previous research on prestressed stayed columns has been largely analytical and numerical studies. To the knowledge of the author, experimental investigations into the antisymmetric and interactive modes of buckling in stayed columns have not been attempted hitherto. In addition, although some previous studies have attempted to investigate the optimum prestressing configuration of stayed columns for design purposes, generic design guidance for this type of structural component has been lacking. Therefore, the primary aim of the current study is to conduct experimental and numerical investigations into the possible buckling and post-buckling behaviour and to develop an efficient design method for these structural components. A full scale experimental investigation has been conducted with a total of 18 test specimens to demonstrate the critical modes of buckling (symmetric and antisymmetric) with interactive post-buckling. This has also investigated the imperfection sensitivity of the stayed columns. Nonlinear finite element (FE) modelling was conducted in parallel with the experiments. These models were utilized, after successful validation against the experimental results, to investigate the sensitivity of the stayed system to the variation of key parameters. Subsequently, an efficient design method for prestressed stayed columns has been developed, including design charts and equations relating the resistance of the stayed column system to the level of the initial prestress in the cables for varying cross-arm lengths and global imperfection levels. Structural reliability analysis, using the procedures in Annex D of EN 1990, was conducted to evaluate the design safety factor. Worked examples of the proposed design method are also presented to demonstrate the developed procedure for diiferent key cases. It is shown that a straightforward yet rational design method has been formulated.