No abstract

In recent decades, interest in the resistance of buildings and structures to progressive collapse has been increasingly sparked in research communities. Although several experimental, numerical, and analytical research projects on the robustness of building frames under a column removal scenario have been implemented, some aspects of this problem remain understudied. These aspects encompass failure mechanisms of reinforced concrete frames with slender columns, as well as criteria used to evaluate such failures. This paper focuses on experimental and numerical investigations of the structural behavior and failure of a scale reinforced concrete frame with slender columns under a sudden corner column removal scenario. In addition, we analyze the stability failure mechanism of a reinforced concrete frame with slender columns and the tangent stiffness criterion, which allow for evaluation of the ultimate state of a structure subjected to an accidental impact. A scale physical model of a reinforced concrete frame of a multistory building was designed and tested using the theory of functional similarity. For numerical study purposes, a finite element model was made that exactly the same as the test frame. We validated the findings by comparing simulation results and experimental data. The studies on the behavior of a reinforced concrete frame subjected to quasistatic loading with unequal concentrated loads identified the load transfer between columns through beams. Although these effects were minor in the frame under consideration, they can become more significant in cases of long-term loading. Numerical simulation and physical modeling of an accidental impact allowed for identification of the mechanism of load capacity exhaustion triggered by stability failure. Such failure was fragile. The moment of stability failure of the column of the experimental frame corresponded to the extremum on the force–displacement curve, indicating that zero tangent stiffness was reached. Hence, a criterion of tangent stiffness can be proposed for evaluation of the ultimate state of a structure subjected to an accidental impact.

The results of experimental and theoretical studies of crack formation, deformation and failure of monolithic reinforced concrete frames under accidental action caused by the sudden removal of one of columns of the first floor. Experimental studies were carried out on the model of structural fragment of a three-story two-span reinforced concrete frame, designed from fine-grained concrete class B40 with reinforcement A500. The test of experimental structures is executed by the gravitational load, with use of specially designed lever loading device. Special effect in the form of sudden removal of central columns of the frame was modelled using a specially designed mechanism in the form of sudden switching-off device. The obtained experimental values of widths of cracks, deflections, pictures of cracking and failure of experimental structures of the frames before and after beyond-design action. The experimental values of these parameters are compared with the results of calculation by the method taking into account the specifics of static-dynamic loading of physically and constructively nonlinear structures under the considered special actions.

A calculated model of a building frame fragment is presented for calculating the dynamic additional loading of structural elements in the zone of possible local destruction after the failure of one of the structures. To model such a fragment, a substructure isolated from a structural system of the building frame was used in the form of a two-span statically indeterminate continuous beam under various boundary conditions on the extreme supports, loaded with a specified design load. The sudden removal of the middle supporting column of the substructure is modelled by reducing to zero for some short-time the internal force in this column, obtained when calculating the entire frame of the building. The use of level calculated schemes and analytical description of the movement of reinforced concrete substructure with variable stiffness due to cracking for determining the dynamic additional loading of frame elements of a multi-story building after the failure of one of the structures allows to define the parameters of the dynamic response of the substructure and simulate in more detail the zones of possible local destruction of the building under the considered special action. The developed algorithm for calculating physically and structurally nonlinear reinforced concrete systems can be used for the calculated analysis of the frame of multi-story buildings when designing their protection against progressive collapse.