Justification of the special limit state characteristics for monolithic reinforced concrete bearing systems in the progressive collapse mode

The paper studies the problem of criteria selection for limit states of monolithic reinforced concrete bearing systems in the progressive collapse mode. Based on the design assumptions and theoretical studies outcome, structural elements and structural units of the monolithic reinforced concrete buildings are defined; the destruction of them occurs primarily in the event of failure of the vertical supporting structure and leads to the evolution of progressive collapse. A computational and theoretical analysis has been performed to determine the ultimate deformation effects or load values according to those criteria that determine the bearing capacity of the core units of monolithic reinforced concrete systems of different spans. It is proved that as a basic criterion to estimate the stress-strain state of the monolithic reinforced concrete structures in view of the failure of a vertical bearing system there can be adopted relative deformation value corresponding to the formation of a 'fracture' zone of the near-support slab section under the action of transverse forces. (paper)