Experimental investigation of a substructure in a frame with castellated steel beams in case of a column loss

Abstract

In addition to strengthening or weakening the connections, castellated steel beams can realize plastic hinge rotation, which is a common strategy for improving the resistance of steel structures against progressive collapse. This paper presents experimental and numerical investigations of a substructure with castellated steel beams under a column removal scenario considering the diameter D of the openings, first opening position A, and spacing B between openings. The deformation capacity, vertical force–deformation response, failure mode, and contributions of the flexural and catenary action were studied as having different parameters for the openings. The test results demonstrate that the first web opening underwent the greatest deformation, changing from a circular to shuttle shape at the cracking moment, whereas the second and subsequent openings exhibited only small deformations in all specimens. The vertical force vs. deformation response can be divided into four states: elastic, plastic, catenary transition, and catenary states. The final resistance against progressive collapse was dependent on the catenary action caused by excessive axial tension. Moreover, the bearing capacity and deformations in the specimens having a small diameter of openings, D < 0.6 h, decreased with an increase in the opening diameter, whereas the respective properties in the specimens having a large diameter of openings, D > 0.6 h, increased with an increase in D. The recommended distance from the edge of the first opening to the surface of the column is equal to the depth h of the beam section. A large value of spacing B between the openings has a minor influence on the bearing resistance in the collapse analysis.