In this thesis, some nonlinear effects associated
with the buckling behaviour of plated steel structures
are examined using a modified finite strip method. To
include the effects of plasticity over parts of the
cross-section, a more general stress-strain relationship
than previously included has been used. The method is
also extended to account for the large deflection
behaviour of perfect and imperfect plates in the elastic
range. The only restriction on the method presented
here is that the buckling mode varies sinusoidally in the .;,
longitudinal direction, which implies either that the ends
of the structure are simply supported or that the wavelength
of the buckled mode is small in comparison with the
overall length of the structure.
The present study may be divided into three parts.
In the first part the small deflection theory is used to
determine the stiffness and stability matrices of ~
individual strip and these are assembled to form an overall
stiffness matrix, representing a structure which may be
under concentric load, eccentric load or pure bending. In
some cases a structure with an overall initial imperfection
is considered. The Wittrick-Williams Algorithm is used to
obtain the smallest critical buckling load. The method is
applicable to the analysis of various structures such as
isolated plates, stiffened panels, rolled sections and
stiffened box-girder bridges. To check the accuracy of the
method a comparison with some published theoretical and
experimental results is undertaken.
Secondly, a parametric study for stiffened panels,
columns, and beams is presented. For the stiffened
panels, the effect of seven parameters (slenderness ratio,
residual stress, dimensions and shape of the stiffener,
mode of buckling, the longitudinal boundary conditions,
and the yield stress) has been investigated. Approximate
design curves for the optimum dimensions of panels
stiffened by flat stiffeners are given. The capability
of the method for the analysis of a stiffened box-girder
in bending is also shown. The effect of seven parameters
(dimensions and shape of the cross-section, the slenderness
ratio, the material yield stress, the residual stress,
the initial overall imperfection and the eccentricity of
the applied load) on the inelastic buckling of columns and
beams has been studied. All the results are given in nondimensional
graphs or tables.
Finally large deflection plate theory is applied to
study the post-buckling behaviour of both perfect plates
and those with initial imperfections. The work in this
section is restricted to the elastic state. The longitudinal
axial compression is assumed to act on the plate through
two rigid bars at the ends, and various in-plane boundary
conditions for the longitudinal unloaded edges have been
considered. The Newton-Raphson method is used for the
solution of the non-linear equations.