Ющук, О. В. та Yushchuk, O. V. (2021) НЕСУЧА ЗДАТНІСТЬ, ТРІЩИНОСТІЙКІСТЬ І ДЕФОРМАТИВНІСТЬ НЕРОЗРІЗНИХ ЗАЛІЗОБЕТОННИХ БАЛОК ЗА ДІЇ МАЛОЦИКЛОВИХ ПОВТОРНИХ І ЗНАКОЗМІННИХ НАВАНТАЖЕНЬ. [Автореферати, дисертації] (Неопублікований)

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Анотація

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.23.01 – будівельні конструкції, будівлі та споруди. – Національний університет водного господарства та природокористування, Рівне, 2021. Дисертація присвячена вивченню впливу малоциклових знакозмінних навантажень на напружено-деформований стан двохпролітних нерозрізних залізобетонних балок. Отримано нові експериментальні дані про характер руйнування, напружено-деформований стан нерозрізних залізобетонних балок та перерозподіл зусиль в них за дії малоциклових знакозмінних навантажень. Підтверджено різницю між розрахунковими і експериментальними даними по несучій здатності, тріщиностійкості і деформативності. Для задовільної збіжності розрахунків з реальною роботою, нерозрізних залізобетонних балок за дії малоциклових знакозмінних навантажень, необхідно вводити коефіцієнти умов роботи.

Title in English

Load-bearing capacity, crack resistance and deformability of reinforced concrete continuous beams under the action of low-cycle repeated and alternating loads - Qualified scientific work on the rights of the manuscript

English abstract

Thesis for a Candidate of Technical Science Degree in Specialty 05.23.01 «Construction structures, buildings and structures» (192 – Construction and civil engineering). - National university of water and environmental engineering, Rivne, 2021. The introduction outlines the relevance of the topic, the purpose and objectives of research, the scientific novelty, the practical value of the work, the personal contribution of the degree seeker. Section 1 analyzes the studies on this topic, carried out both in our country and abroad. It describes the conditions under which reinforced concrete continuous beams are exposed to alternating loads. Section 2 presents the program and methods of experimental research. Three batches of monolithic reinforced concrete continuous beams were made for the experiments. Each batch included three beams. Beams in each batch differed in loading modes during testing. The length of each beam was 300 cm, with cross-section 100×160 mm. The beams were symmetrically reinforced, so that they could redistribute forces during loading and supporting loads when changing of sign. Working reinforcement А400С class 2Ø12 mm was used for the beams. For transverse reinforcement, B500 class reinforcement wire Ø6 mm was used with 20 cm pitch in the span sections of the beam. In the supporting sections, the pitch of the transverse reinforcement was reduced to 10 cm by inserting additional rods. Longitudinal and transverse rods were combined into a spatial frame. First, the flat frames were welded using 2 longitudinal rods of working reinforcement A400C Ø 12 and transverse rods B500 Ø6 mm. Further, 2 flat frames were welded together into a spatial frame using rods B500 Ø6 mm. The beams were tested as those with central prop, under load of four concentrated forces, applied at a distance of 60 and 100 cm from the center of the fixed support. Beams BDS-1, BDS-2 and BDS-3 were loaded one time for a short term up to fracture. The concentrated forces were applied in equal steps (0.08 ... 0.10) Fu, where Fu – is estimated breaking load, determined by calculation. Beams BLCR-1, BLCR-2 and BLCR-3 were subjected to repeated short-term loads, 60% of the destructive level ( сyc cyc u η = F / F , where cyc η – is the relative level of re-load; cyc F – load in cycles; u F – breaking load, determined by testing the beams BDS-1, BDS-2, BDS-3). Beams BLCAL-1, BLCAL-2 and BLCAL-3 were exposed to alternating repeated short-term loads, 60% of the destructive level ( сyc cyc k η = F / F , where cyc η – is the relative level of repeated load; cyc F – load in cycles; k F – breaking load, determined by testing beams BDS-1, BDS-2, BDS-3). The relative load level was chosen to simulate the loading action as closely as possible during the actual operation of the beams (operational load). Loading and unloading in cycles was carried out by steps, the value of which was assumed to be the same as for a one time loading. Beams BLCR-1, BLCR-2, BLCR-3, BLCAL -1, BLCAL -2, BLCAL -3 were loaded repeatedly for ten cycles, and they were brought to fracture at the eleventh half-cycle. Section 3 presents the results of strength, deformability and cracking resistance of reinforced concrete beams. The analysis of the obtained results of experimental tests showed decreasing of the load-bearing capacity of reinforced concrete beams affected by low-cycle repeated and alternating loading in comparison with beams loaded with a static load until fracture. However, the following feature of the beams operation was noticed: under the action of repeated loads according to the loads level, the processes of cracking and deflections are stabilized, while under the action of alternating loads, there is a constant increase of deformation, up to fracture. This occurs due to the formation of main cracks, cutting the entire cross-section and changing the bending stiffness properties of the normal cross-section. The model of cracking under the action of a low-cycle alternating load differs significantly from the model of crack opening under an non-alternating static load. Section 4 presents a comparison of the calculation (according to the current regulatory documents) of reinforced concrete beams under the action of low-cycle repeated and alternating loads with experimentally obtained data. The indicated changes in the stress-strain state must be taken into account when calculating statically undefined bending elements under the action of the above mentioned loads by introducing the corresponding coefficients of operating conditions.

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