Forecasting the life cycle of reinforced concrete structures in severe climatic conditions

Abstract

The article considers the problem of design forecasting of the life cycle of reinforced concrete structures operated in severe climatic conditions using the methodology of limit states. The authors propose to use the reliability index β, conditionally regulated by the norms for design limit states, as a criterion index of the functional suitability of structures. The kinetics of the reliability index β during cyclic freezing and thawing is evaluated by means of multifactor periodic experimental control of strength and deformability indices in frozen and thawed states. Testing was conducted using prismatic (100×100×400 mm) and cubic (100 mm) specimens of the B25 mature concrete (180 days), F270 frost resistance grade. In this case, the parametric failure of an element was identified by the moment when the criterion parameter reached the threshold value. The threshold is extablished (with the required level of reliability) by normative functional models of the limit state, transformed to a form describing the dependence of the concrete resistance parameter on the value of the estimated force and section parameters. Test intervals were determined considering the specificity of concrete frost degradation as a multistage process of structural adaptability, as well as microcrack formation and accumulation. Statistical aspects of resistance parameters were identified from experimental data using the maximum likelihood method and Pearson’s criterion (χ2) in assessing their consistency with the theoretical distribution. Additional transient design situations that consider the thermal-moisture state of the structures are considered. The presented experimental data confirmed the feasibility of the proposed approach.