Abstract: Due to the numerous advantages of steel corrugated
web girders, its application field is growing for bridges as well as for
buildings. The global stability behavior of such girders is
significantly larger than those of conventional I-girders with flat web,
thus the application of the structural steel material can be
significantly reduced. Design codes and specifications do not provide
clear and complete rules or recommendations for the determination of
the lateral torsional buckling (LTB) resistance of corrugated web
girders. Therefore, the authors made a thorough investigation
regarding the LTB resistance of the corrugated web girders. Finite
element (FE) simulations have been performed to develop new
design formulas for the determination of the LTB resistance of
trapezoidally corrugated web girders. FE model is developed
considering geometrical and material nonlinear analysis using
equivalent geometric imperfections (GMNI analysis). The equivalent
geometric imperfections involve the initial geometric imperfections
and residual stresses coming from rolling, welding and flame cutting.
Imperfection sensitivity analysis was performed to determine the
necessary magnitudes regarding only the first eigenmodes shape
imperfections. By the help of the validated FE model, an extended
parametric study is carried out to investigate the LTB resistance for
different trapezoidal corrugation profiles. First, the critical moment of
a specific girder was calculated by FE model. The critical moments
from the FE calculations are compared to the previous analytical
calculation proposals. Then, nonlinear analysis was carried out to
determine the ultimate resistance. Due to the numerical
investigations, new proposals are developed for the determination of
the LTB resistance of trapezoidally corrugated web girders through a
modification factor on the design method related to the conventional
flat web girders.
Abstract: Lateral torsional buckling is a global buckling mode
which should be considered in design of slender structural members
under flexure about their strong axis. It is possible to compute the
load which causes lateral torsional buckling of a beam by finite
element analysis, however, closed form equations are needed in
engineering practice for calculation ease which can be obtained by
using energy method. In lateral torsional buckling applications of
energy method, a proper function for the critical lateral torsional
buckling mode should be chosen which can be thought as the
variation of twisting angle along the buckled beam. Accuracy of the
results depends on how close is the chosen function to the exact
mode. Since critical lateral torsional buckling mode of the cantilever
I-beams varies due to material properties, section properties and
loading case, the hardest step is to determine a proper mode function
in application of energy method. This paper presents an approximate function for critical lateral
torsional buckling mode of doubly symmetric cantilever I-beams.
Coefficient matrices are calculated for concentrated load at free end,
uniformly distributed load and constant moment along the beam
cases. Critical lateral torsional buckling modes obtained by presented
function and exact solutions are compared. It is found that the modes
obtained by presented function coincide with differential equation
solutions for considered loading cases.
Abstract: Metal thin-walled members have been widely used in
building industry. Usually they are utilized as purlins, girts or ceiling
beams. Due to slenderness of thin-walled cross-sections these
structural members are prone to stability problems (e.g. flexural
buckling, lateral torsional buckling). If buckling is not
constructionally prevented their resistance is limited by buckling
strength. In practice planar members of roof or wall cladding can be
attached to thin-walled members. These elements reduce
displacement of thin-walled members and therefore increase their
buckling strength. If this effect is taken into static assessment more
economical sections of thin-walled members might be utilized and
certain savings of material might be achieved. This paper focuses on
problem of determination of critical load of steel thin-walled beams
with lateral continuous restraint which is crucial for lateral torsional
buckling assessment.