Iš anksto įtemptais bazalto pluošto strypais armuotų lenkiamųjų betoninių elementų įlinkių analizė veikiant ciklinei apkrovai

The behaviour of prestressed concrete beams reinforced with non-metallic reinforcement under cyclic loading is analysed in this doctoral thesis. Review on the advantages and disadvantages of non-metallic reinforcement is provided, strength properties and the most crucial parameter values, necessary for the development of the topic of this thesis, are investigated and determined. Arguments on why and at which certain situations the use of this reinforcement can be superior compared to steel are provided. A separate experimental program is developed to determine the behaviour of non-metallic reinforcement undergoing repetitive or cyclic loading. The effect of initial prestressing level and stress range caused by the cyclic load to the final number of load cycles endured is also analysed. Moreover, the influence of cyclic loading on the mechanical properties of concrete is being investigated in this study. The dissertation consists of introduction, three main chapters, general conclusions, the lists of references and author’s publications on the topic of the dissertation. The introductory chapter presents the problem formulation, the relevance of the thesis and research object, formulates the aim of the study, describes research methodology, scientific novelty and practical significance of the obtained results. Chapter 1 describes the fatigue phenomena and the main reasons causing fatigue to concrete and composite reinforcement. Besides, attention to static, cyclic creep of concrete and recommendations of the evaluation of these effects in design codes are reviewed. Chapter 2 is dedicated generally for the description of the proposed deflection calculation method based on the principles of structural dynamics concerning cyclic creep of concrete and a possible decrease in mechanical properties of composite reinforcement due to cyclic loading. A detailed calculation algorithm of the proposed method and general assumptions are provided. The 3rd and final Chapter describes in detail the experimental study performed investigating basalt fibre reinforced polymer bars and tests of BFRP prestressed concrete beam deflection estimation results which are compared to the proposed and other authors methods. The adequacy of proposed method is evaluated thru statistical analysis. The topic of the thesis has been published in 7 articles: 5 – in the jour-nals with an Impact Factor, 1 – in scientific journals of other international databases and 1 in the conference proceedings referred by the Clarivate Analytics Web of Science.Dissertatio