Iš anksto įtemptais bazalto pluošto strypais armuotų lenkiamųjų betoninių elementų elgsenos analizė

In general, prestressed concrete (PC) is by far one of the most economical concrete construction techniques, but at the same time, it requires specific knowledge of the properties and behavior of this material. Precompression of the concrete by transferred prestressed force flexural stiffness can be increased and the main issue – cracking might be eliminated, correspondingly. Based on the development progress PC is widely being utilized in the construction of the structures for transport and energy sectors (bridges, viaducts, gasholders, reactors, oil&gas tanks, etc.). It has been used in order to store potentially dangerous materials during operation and to resist dynamic effects. However, even in PC case cracking appears, and it is common that it causes corrosion of conventional reinforcement. Finally, it influences the maintenance of existing infrastructure. Within this research, the author develops the particular subject of concrete – application of new composite material – basalt fiber reinforced polymer (BFRP) to be used for prestressed concrete structures considering subsequent loading stages (stretching at the bulkheads, prestress transfer to concrete, application of service load, etc.). In order to design PC structures, it is significant to estimate effective prestress force with respect to the time-dependent process of concrete and reinforcement. In accordance with design codes requirements, typical formulas from regular concrete structures (RC) are to be used for the estimate of serviceability conditions of flexural PC members. However, a complete review of prestress losses and serviceability shall be employed in order to avoid errors in the structural prognosis of the PC structures with non-conventional composite reinforcement. Unlike other composites, experimental test work and calculation methods have yet to be developed for BFRP reinforcement in order to determine stress relaxation behavior. Currently, this phenomena is not fully documented in the literature. Based on this, the author approached an innovative stress relaxation test method to describe the effect of stress relaxation and its impact on the final value of the effective prestress force. Full-scale testing beams were tested in order to evaluate the impact of prestress level (degree) to the flexural stiffness of concrete beams internally prestressed with BFRP bars. The dissertation is structured within the introduction, three main chapters, verification of the results, the lists of references and author’s publications on the subject of the dissertation. The topic of the thesis has been discussed in 9 articles: 3 – in the journals with an Impact Factor, 5 – in scientific journals of other international databases and 1 in the conference proceedings referred by the Clarivate Analytics Web of Science