ESTIMATES OF PRESTRESS LOSSES AND FORCES SCATTER IN REINFORCEMENT OF SPAN REINFORCED CONCRETE STRUCTURES

Subject: the article is devoted to investigation of prestress losses and force distribution in the reinforcement of span reinforced concrete structures. As the long-term studies have shown, these quantities are very unstable, which should be taken into account in structures design. However, the existing normative documents take into account the possible deviations of losses and forces in prestressed reinforcement from their design values in a fairly general form. Since each of the types of losses, according to the formulas, depends on one or several random factors, they should be considered from a probabilistic point of view. Research objectives: determine the scattering of different losses and acting forces in the prestressed reinforcement to identify the factors affecting its value. Materials and methods: in this work, we used the normative technique of prestress losses calculation and characteristics of the variability of physical and mechanical properties of concrete and reinforcement, obtained from the previous studies. The distribution laws of investigated parameters were assumed to be normal (the Gaussian law). To calculate the coefficients of variation, the method of statistical testing (the Monte-Carlo method) and the linearization method (the Taylor series expansion) implemented in MATLAB software package were applied. Results: in the process of numerical experiment, the values of prestress losses and forces scatter in the reinforcement were obtained for all prestressing methods stipulated by the current design codes. It was established that both values depend significantly on the method of reinforcement tensioning, its type and class, and also on the diameter of wire. Moreover, many concomitant factors affect the variability of the above-mentioned characteristics such as the plant-manufacturer, stability of technological process, qualification of the service staff, etc. Conclusions: the obtained data is recommended to be used to determine the accurate values of strength, deformability and crack resistance of span reinforced concrete structures as well as in probabilistic calculations related to the assessment of their reliability by various limit states. In particular, the described technique was applied in calculating the reliability of bent prestressed elements from the viewpoint of strength of oblique sections.