Dynamic response of the building construction system with a finite degree of freedom under a special action

Introduction. In the normative documents of a number of countries on the standardization of the protection of buildings and structures from progressive collapse, for the calculation analysis under special impact, such a concept as a “zone of possible local destruction” of a structural system is used, outlined by a fragment of the building frame in places of hypothetically removed structural elements. The purpose of identifying such most stressed zones in the form of substructures is engineering visibility of the consequences of an emergency impact with an assessment of the stress-strain state of elements falling into such a zone. In this regard, in the work under consideration, a variant of modeling the dynamic additional loading of the reinforced concrete frame of a multi-storey building caused by its structural restructuring is proposed, which makes it possible to determine the parameters of the dynamic response of the substructure in the form of a two-span continuous beam with a finite number of degrees of freedom and to model in more detail the zone of possible local destruction of the elements of the building frame at the sudden removal of one of the structural structures in this area. Materials and methods. The zone of possible local destruction of the building frame is modeled by a fragment of the structural system adjacent to this zone. The process of removing a column was simulated by applying a load P(t) in the opposite direction, equal to the force in the removed column, calculated when calculating the entire frame of the building. To solve the system of equations of motion of the substructure, we use the method of expansion in terms of natural vibration modes, which is well known in the dynamics of structures. Results. The results of theoretical studies of the dynamic effect of a reinforced concrete structural system of a building with a finite number of degrees of freedom during its sudden restructuring caused by a special emergency impact in the form of a hypothetical removal of one of the load-bearing structures are presented. Conclusions. The equations of motion of a substructure in the form of a two-span continuous beam with a finite number of degrees of freedom constructed on the basis of the theory of the dynamics of structures can be used to analyze the special limiting state of reinforced concrete elements of structural systems of frames of buildings and structures.