Structural transformation of reinforced concrete structural system at sudden loss of stability of one of its elements

Abstract

Reconstruction or changing of the functional purpose of operated buildings and structures buildings are requires an assessment of its residual life, which should be made on the basis of the modern standards and building codes, the requirements of which were greatly expanded by the range of possible loads and impacts, including especial emergency impacts. Analysis of collapses and accidents of buildings and structures, that occurred in Russia and abroad in recent years, shows that the progressing in time accumulation of damage in structural elements (for example, in columns, in compressed belts of trusses, etc.) may lead to sudden loss of stability of one of the bearing structural elements of the system. The instant structural transformation of the system, which occurs at this moment, may produce total loss of stability of the whole structural system. At the same time this process in each element may be determined by the different physical phenomena: internal force acting or kinematic impacts from nearby elements. Academicians of RAACS A.V. Alexandrov and V.I. Travush proposed to use the work A (M, Q) of nodal bending moments and shear forces as an energy criterion to assess the kind of the buckling of each element of the structural system. In this case bifurcation, which is determined by the internal force acting, should be considered as the active loss of stability, the work of which is negative (i.e. A < 0), buckling caused by the kinematic impacts from nearby elements is called passive loss of stability and has the positive work A > 0. Following these studies, in this paper the analytical relationships to assess the kind of buckling of individual nonlinear deformable concrete elements of the frame structural system with different variants of boundary conditions are obtained. The solution of these equations is given and it can be used to assess stability of reinforced concrete (RC) columns of the frame, damaged by corrosion. Herewith the constructive elements are considered as part of the whole structural system. Structural transformation of RC frame at sudden buckling of one of the bearing structural element subjected corrosion is analysed. The results of this study can be used to calculate frames of the reconstructed buildings and structures (in particular at the emergency impacts) for assessment of their sustainability, protection against the progressive collapse, as well as evaluation of their residual life of operated structures.