Nonlinear analysis of steel frames considering lateral Torsional buckling effect

The use of nonlinear analysis methods is widely preferred to determine the realistic
behavior of the structures through the computer technologies developed in recent
years. However, the stability problems that significantly affect the structure behavior
are often neglected in nonlinear analysis and in computer programs that are frequently
used to the realization of these analyses. Lateral torsional buckling behavior, which is
one of the stability problems, is considered to be neglected in many studies using
nonlinear analysis methods in the literature. As a result, the realistic behavior of the
structures cannot be achieved, the designs are carried out that the structures can carry
much more load than the foreseen load carrying capacities.
Due to the necessity of achieving realistic behavior of the structures in this study, the
steel frames are selected which are previously neglected in the literature for the
calculation of lateral torsional buckling behavior and analyzed by nonlinear analysis
methods. The steel frames are analyzed with and without considering lateral torsional
buckling effect and their effect on the structure behavior are shown. Approaches
presented in the regulations have been used in the analyses.
The analysis taking into account the lateral torsional buckling effect is first carried out
on a single element and followed by the nonlinear analysis steps of the steel frames.
The results of the analysis are given comparatively and significant effects of lateral
torsional buckling on the load carrying capacity of the structure have been
demonstrated. Besides, out-of-plane motions are prevented by lateral supports, the
frames with different frame span lengths and floor heights are also examined. Also,
TSDC and TS 4561 regulations are compared in the results of this study.
It has been observed that lateral torsional buckling reduces the load carrying capacity
of the structures significantly in all the frames examined by the nonlinear analysis
methods. Moreover, order of plastic hinge formations occurred in steel frames has
changed and displacement capacities of frames have decreased because of the lateral
torsional buckling effect. Horizontal displacements can be avoided with sufficient
lateral support. Thus, the lateral torsional buckling effect can be eliminated. According
to the obtained analysis results, it is concluded that lateral torsional buckling is very
important in determining the actual behavior of the structures and that it should be
taken into account in the analyses.