Web-tapered tapered H-shaped beams, which have a continuous reduction in section, have been utilized in steel-frame structures for more efficient utilization of structural materials. On the other hand, section stiffness decreases along a beam's axis, and the member stress increases. For this reason, it is more important to investigate the buckling behavior and the progress of the plasticity of a tapered H-shaped beam than that of a uniform H-shaped beam.
In the past, the authors investigated elastic plate buckling strength and lateral torsional buckling strength using an energy method and numerical analysis. An estimation method and formula were proposed in those research studies.
This study examines the inelastic buckling strength and plastic deformation capacity of Web-tapered H-shaped beams with depth tapered through by a cyclic loading test and numerical analysis. Twelve tapered beams and five normal straight beams were tested. The cyclic behavior and collapse mode of these specimens were investigated. In addition, multiple simulations using numerical analyses were carried out. Then, the collapse mode and plastic deformation capacity of the tapered beam were evaluated by using indexes that were determined on the basis of the elastic buckling strength.
First, it is clear that the behavior and collapse mode of tapered beams are changed by the following characteristics: taper gradient, flange plate slenderness, web plate slenderness, and lateral bracing length. The skeleton curves of each specimen are taken from the load-displacement relationships obtained by a cyclic loading test. Using these skeleton curves, the effects of a tapered gradient on the performance of an H-section beam are examined. The value of the plastic deformation capacities of beams collapsed by web plate buckling or lateral torsional buckling are estimated from the eigenvalue of each tapered beam. This means that the plastic deformation capacity increases when the eigenvalue is higher. On the other hand, the values of the plastic deformation capacity of a beam collapsed by flange plate buckling are almost the same without regard to its own eigenvalue. Because the flange plate buckling strength decreases when the tapered gradient is steep, and plastic reason in flange is longer.
Second, the effect of a cyclic load on tapered beams is considered. It is evident that beams with low plate slenderness and large plastic deformation capacity are affected by cyclic loads. That value The plastic deformation capacity of these beams decreases by cyclic loading.
Third, the authors propose a new plate buckling slenderness index (WFγ) and lateral buckling slenderness index (γb). These slenderness indexes are obtained from the elastic buckling strength. It is clear that the collapse mode of a tapered beam can be classified using these indexes. In the range of WFγ / γb > 2.4, the collapse mode is plate local buckling, and in the range of WFγ / γb < 2.4, the collapse mode is lateral torsional buckling.
Finally, the maximum strengths and plastic deformation capacities of tapered beams are estimated by using the plate buckling slenderness index and lateral buckling slenderness index when the collapse mode of tapered beams is classified by these indexes. The elastic buckling strength of the tapered beams do not decrease as a result of the coupled instability effect between the plate local buckling and lateral torsional buckling. However, the maximum strength and the plastic deformation capacity decrease as a result of these effects.
