Tytarenko R. Reliability of reinforced concrete beams, strengthened under load

The thesis is devoted to developing of the principle methods for reliability assessment of intact rectangular reinforced concrete beams, strengthened by adding of stretched reinforcing bars and composite tape, as well as of reinforced concrete jacket under the action of load, the principal feature of which is the proposal to consider as a stochastic parameter of the level of loading of beams at the moment of strengthening. The calculation of the bearing capacity of the normal sections of reinforced beams was performed on the basis of experimental and theoretical studies, that performed at the laboratory of the Department of Building Structures and Bridges at the Lviv Polytechnic National University. On the basis of power and deformation calculation models of the normal section, the developed methods have been tested on real reinforced concrete beams, strengthened under the action of load. The recommended values of the reliability indicators of the investigated constructions are obtained – reliability indexes and probabilities of failure-free operation, respectively. Thus, for reliability indexes, the range of values was from 3.06 to 5.86, and for the probability of failure-free operation from 0.998893 to 0.999999998 (towards increasing the reliability level at the larger percent of reinforcement and decreasing at the increment of load level at the moment of strengthening). The discrepancy between identical values of indexes found in accordance with engineering and deformation models of calculation was about 8 %. The values of partial reliability coefficients – from 1,16 to 1,28 for all methods of strengthening – for the engineering calculation of the considered types of reinforced beams is proposed, in terms of providing their guaranteed service life in accordance with national norms governing the principles of ensuring the reliability of new design constructions. In addition, the obtained results of reliability study make it possible to operate with those variable parameters that have the maximum influence on variance of the limiting bending moment of beams studied with sufficient accuracy of calculation. The developed principal methods for assessing reliability make it possible to design strengthened reinforced concrete bending elements with the assigned level of reliability (efficiency of solutions) - probability of failure-free operation. Finally, the obtained results allow to choice the most effective strengthening method.