In situ investigation of the evolution of the deformed state of the surface of a bending steel beam

The paper presents the results of experimental studies on the determination of the deformed state of an I-beam. A step-like character is established on the “load–deflection” diagram at bending deformation of an I-beam. It is shown that stages I and II are conditioned upon the deformation behavior of a steel vertical wall of the beam. Stages III and IV are determined by the geometry of the sample and the type of the deformation effect. The presence of stage III is conditioned upon slow buckling of an I-beam shelf under the place of the applied load. A correlation between the distribution of local plastic deformation foci on the lateral surface of the steel I-beam and stages I and II on the deformation curve in the “load–bending” coordinates is established. It has been revealed that the transition from the elastic stage I and the parabolic stage II is accompanied with a change from the chaotic distribution of local plastic deformation foci to the laminated one with a well-defined stratification of compressive and tensile plastic deformations in the upper and lower sides of the I-beam at the macro-scale level.