Robustness and technical condition of reinforced concrete frame structures as a result of accidental action

Risks associated with accidental actions on buildings and structures lead to the demand for design measures aimed at protection against progressive collapse. In this case, the actual task is to assess the sufficiency and effectiveness of structural measures to protect both newly designed and reconstructed buildings and structures to prevent their collapse in an accidental situation. The solution of this problem is possible with the usage of criteria and measures of robustness. A variant of the relative robustness index, which takes into account the degree of damage to the elements of the structural system of the building during long-term operation and the level of the current load, has been proposed. The relation between the relative measure of robustness and technical condition of structures is examined. The results of robustness check of reinforced concrete multistorey building frame with plane beamless floor slabs, in which perimetric, longitudinal and transverse internal ties, selected by the method of tie forces, are provided as a structural measure to protect against progressive collapse. The effectiveness of using a system of additional ties to provide protection against progressive collapse has been demonstrated. It is shown that at the design load level the lowest relative robustness index corresponds to the accidental situation caused by the loss of bearing capacity of the corner column of the building, and the highest - to the middle column. As a result of concrete and reinforcement strength reduction by 30% (or equivalent reduction of effective cross-sectional dimensions as a result of aggressive medium action), the relative robustness index decreased to RRI = 0.65 under the action of constant and long-term characteristic loads and accepted characteristic properties of construction materials.