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Prestress and bearing capacity loss of pre-tensioned concrete beams due to corrosion cracks

Abstract : Bridges, as the structures built to cross obstacles and generally has a relative larger span, play a key role in the road traffic. Pre-tensioned concrete structure is widely used in the bridge construction due to its superiority and advantages. However, with the mass exchange of its environment (water, CO2 and other chemical agents), the prestressing strand would be easy to corrode. Strand corrosion can cause concrete cracking, degrade the bond performance at the strand-concrete interface, lead to prestress loss, and deteriorate the capacity of beams. The present study mainly focuses on the concrete cracking, prestress loss and flexural capacity of pre-tensioned concrete beams after strand corrosion. The main research works are as follows: (1) The relationship between corrosion-induced crack widths and filling proportion of corrosion products has been established. The effect of stirrups on corrosion-induced cracking has also been investigated. An empirical model for crack width, considering the filling proportion of corrosion products and twisting shape of strand, is developed. The proposed model is validated by experimental data. Results show that the filling of corrosion products extends with crack propagation until a critical width. Beyond the critical width, the rust filling extent keeps stable. When the stirrups are used, the critical crack width decreases by 20%, comparing to that without stirrups. (2) The influence of prestress on the strand corrosion-induced concrete cracking is investigated by both experimental and analytical approaches. Experimental data on the critical time of cover cracking, crack width and corrosion loss obtained from the accelerated corrosion test are presented. An analytical model, incorporating the coupled effects of prestress and strand corrosion, is proposed to predict the global process of concrete cracking from initiation to propagation. Results show that prestress can accelerate the corrosion-induced cracking process. By varying prestress from 0 to 75% of strand tensile strength, the critical time of cover cracking decreases by 22% and the crack propagation rate increases by 9%. It is found that the proposed model is accurate in predicting corrosion-induced crack width in prestressed concrete beams. (3) A novel model is proposed to predict the corrosion-induced prestress loss in pre-tensioned concrete beams. The coupling effects of concrete cracking and bond degradation are included into the model. The effective prestress in eight corroded pre-tensioned concrete beams under various stress levels is conducted by the four-point flexural test. Experimental results are employed to verify the proposed model. Prestress loss in corroded pre-tensioned concrete beams depends on corrosion level. Corrosion-induced concrete cracking may not degrade bond strength and effective prestress unless the corrosion level exceeds 6.6%. As corrosion further progresses, bond strength and effective prestress reduce monotonically, and then decrease to zero when the corrosion level reaches 34.0%. (4) An analytical model, incorporating the effects of strand cross-section reduction, material deterioration, concrete cracking and bond degradation, is developed to predict the flexural capacity of corroded prestressed concrete beams. Additionally, the effects of flexural cracks are also included in the model. An equivalent bond stress concept is introduced to consider the effect of flexural cracks, which is further implemented into the flexural capacity prediction of corroded PC beams. The proposed model is validated by the experimental results collected from the previous studies. The flexural capacity deterioration of prestressed concrete beams depends on corrosion degree. Strand corrosion less than 5.5% leads to a slight decrement of flexural capacity. As corrosion progresses, the flexural capacity will exhibit a significant deterioration.
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https://hal.univ-lorraine.fr/tel-02558359
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Submitted on : Tuesday, November 24, 2020 - 9:03:42 AM
Last modification on : Friday, February 26, 2021 - 2:48:03 PM
Long-term archiving on: : Thursday, February 25, 2021 - 6:22:05 PM

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  • HAL Id : tel-02558359, version 1

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Lizhao Dai. Prestress and bearing capacity loss of pre-tensioned concrete beams due to corrosion cracks. Materials. Université de Lorraine; Changsha University of Science and Technology (Chine), 2019. English. ⟨NNT : 2019LORR0266⟩. ⟨tel-02558359⟩

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