Behaviour and design of prestressed columns
Author(s)
Osofero, Adelaja Israel
Type
Thesis
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.
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.
Date Issued
2012-03
Date Awarded
2012-04
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Wadee, Ahmer
Gardner, Leroy
Sponsor
Engineering and Physical Sciences Research Council
Publisher Department
Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)