A computational model is presented for determining deformations in complexly stressed beams of a structurally non-linear reinforced concrete frame in a transcendental state caused by a special emergency action in the form of a sudden removal of one of the structural elements. The determination of the stress-strain state after the formation of spatial cracks in the reinforced concrete elements of the frame was carried out using the calculated spatial section. At the same time, dynamic additional loads in the design section of the reinforced concrete frame element from a special impact are determined on an energy basis using the “bending moment-curvature” and “torque-angle of rotation” diagrams. The considered calculation algorithm includes the determination of forces in compressed concrete, longitudinal and transverse reinforcement for primary and secondary design schemes and verification of special limit state criteria. The results of a numerical analysis of the effect of cracking, the ratio of torque and bending moment on the stress state in transverse and longitudinal reinforcement and on the dissipative properties of a frame structural system are presented

The results of studies of monolithic reinforced concrete frames of multi-storey buildings and reinforced concrete frames simulating fragments of such frames in over-extreme limit states caused by special actions are presented. Two options for reinforcing the beams of the frames are considered: with double reinforcement, which ensures the operation of the beam when the force flows in the frame and, accordingly, the sign of the moment change; option with double reinforcement and installation of additional indirect reinforcement in the support zones of the beams for the entire height of the section. Primary and secondary design models were built using volumetric finite elements for concrete and reinforcement rods. The obtained design parameters of deformations, crack patterns and frame failure patterns for all options are compared with each other and with the results of testing physical models of these structures. To assess the effect of mixed reinforcement on the limiting deformations of compressed concrete in over-extreme limit states, based on the theory of plasticity of concrete and reinforced concrete G.A. Geniyeva, deformation dependencies are constructed for a typical reinforced concrete element reinforced with rods in one direction and meshes in the other two under uniaxial compression and volumetric deformation. It has been established that the use of indirect reinforcement in combination with double longitudinal reinforcement in bending elements under static-dynamic loading conditions significantly increases the ultimate deformation of the compressed zone. This reinforcement option can working way to protect monolithic reinforced concrete frames of multi-storey buildings from progressive collapse under special actions.

On an energy basis, without involving the apparatus of dynamics of structures, an analytical solution of the problem was obtained to determine the dynamic additional loads in complexly stressed reinforced concrete elements of multi-storey frames in a transcendental state caused by special emergency effects. The stress state, crack patterns and fracture patterns in the crossbars of the considered frame structures are determined by the complex stress state of the frame elements caused by the combined action of torsional and bending moments. The assessment of the bearing capacity of such structures was carried out by the diagram method based on the use of energy ratios in the structural elements before and after a special impact, which makes it possible to determine the maximum dynamic deformations, curvatures and forces in the first half-wave of vibrations using the results of nonlinear static calculations according to the primary and secondary design schemes.

The paper presents a new structural solution of the precast-monolithic frame for prefabricated residential and civil buildings of various storeys manufactured from prefabricated industrial reinforced concrete elements. The precast frame structures include L-shaped and inverted U-shaped precast elements, installed in the longitudinal and transverse directions and forming a frame, hollow-core slabs and bracing perforated beams of the outer contour, on which fencing non-bearing wall structures are supported within each storey. The computational model of the precast-monolithic building frame was developed using different degrees of discretization at different stages of the analysis. This allowed to obtain both a general picture of structural system deformation in the limiting and over limit states caused by special and emergency actions, and a detailed picture of the stressed state in concrete and reinforcement of structural elements before and after cracking. The paper provides the results of the comparative analysis of the effectiveness of application of the proposed structural system in the mass construction as compared with the applied constructions of large-panel buildings. It has been shown that the application of the proposed structures of panel-frame elements allows considerably reduce the material capacity, cost and transportation expenses of the reinforced concrete frame by up to 30 %, ensuring the mechanical safety of the building.