The effects of cold forming on material properties and post-yield behaviour of structural sections.
This thesis examines the effects of cold forming on the material properties of steel and
stainless steel structural members. Extensive research has been carried out over many
years on both of these materials as they are used to manufacture structural sections to
various design specifications which exist in many different countries. However, to date,
no design code exists in the UK for cold formed stainless steel structural members.
A significant amount of research has focused on the localised effect of cold forming on
material properties such as the yield and ultimate tensile strengths, particularly of steel,
and this is discussed at length in Chapter 1- Literature Review.
Less attention has been placed on stainless steel, but over the last 20 years with the advent
of design specifications particularly in the USA, stainless steel has gained popularity for
cold forming. Chapter 1 describes the research that has been carried out on stainless steel,
with particular emphasis on localised forming effects.
Chapter 2 gives a general introduction to Thin-Walled Structures since cold-formed
structural sections are commonly used as thin-walled members. The deformation and
properties of metallic materials are described in Chapter 3 showing the particular
relevance to the cold forming process. This chapter is extended into Chapter 4 where the
strengthening, forming and properties of metallic materials are discussed in detail, with
particular attention given to the cold forming processes.
Chapter 5 describes existing analytical and design code approaches to determine the
increase in strength of cold formed steel structural sections, along with an empirically
derived relationship to calculate the increased yield strength of stainless steel sections.
Chapter 6 describes the recommendations provided by various design specifications on
evaluation of the axial compression capacity of short struts subject to varying degrees of
cold forming. This chapter also describes the recommendations provided by various
design specifications on evaluation of both the axial compression and the combined bending and axial compression load capacities of cold formed lipped channel section
stainless steel columns of short-to-medium length. The results obtained from Chapters 5
and 6 are compared to the results obtained from an extensive experimental approach as
described in Chapter 7.
A finite element non-linear analysis using the ANSYS finite element software package is
presented in Chapter 8 which models the behaviour of cold formed stainless steel lipped
channel section columns of short-to-medium length subject to pure axial compression
loading and also combined bending and axial compression loading.
Chapter 9 presents the experimental findings showing the relationship between material
hardness and material yield strength for cold-formed areas. The results are then compared
to the theoretical results from Chapter 6 to determine their accuracy in prediction of the
structural behaviour of full cold formed structural member cross-sections. The load
capacity obtained for axially compressed steel and stainless steel struts from experiments
are compared to those obtained from the various design code predictions described in
Chapter 6. Also presented are the experimental findings, design code recommendations
and finite element predictions for the load capacity of stainless steel columns.
Chapter 10 concludes on the work by discussing the various issues arising from the
experiments, from the design code recommendations and from finite element analysis