Lateral‐torsional buckling of a stiffened beam with semi‐rigid joints

Abstract The paper presents an experiment and a numerical analysis of a steel beam subjected to three‐point bending. The beam was connected to short column stubs by bolted end plates. The joints were designed as semi‐rigid and their influence on the lateral‐torsional buckling resistance of the beam was evaluated. The cross‐sections of the beams and the columns were IPE 180 and HEB 140, respectively. The columns were 1 m long and were rigidly connected to the loading frame at their ends. The beams were 3.3 m long and were loaded at midspan. 9 beams were tested in total, from which 3 beams were without any stiffeners, 3 beams had two inclined stiffeners welded prior to the test, and 3 beams upon which the stiffeners of the same geometry were welded under load equal to 50 % of the bending resistance of the unstiffened beam. The stiffeners were at one third and two thirds of the beam span. The experiment was modelled in software using Component‐based Finite Element Method. Shell elements were used for plates and special nonlinear springs and interpolation links for simulation of bolts and welds. Geometrically and materially nonlinear analysis with imperfections was used. The experimental results were compared to the model. A sensitivity study with various levels and kinds of initial imperfections was performed.