In order to study the durability behavior of marine reinforced concrete structure suffering from chloride attack, the structural service life is assumed to be divided into three critical stages, which can be character...In order to study the durability behavior of marine reinforced concrete structure suffering from chloride attack, the structural service life is assumed to be divided into three critical stages, which can be characterized by steel corrosion and cover cracking. For each stage, a calculated model used to predict the lifetime is developed. Based on the definition of durability limit state, a probabilistic lifetime model and its time-dependent reliability analytical method are proposed considering the random natures of influencing factors. Then, the probabilistic lifetime prediction models are applied to a bridge pier located in the Hangzhou Bay with Monte Carlo simulation. It is found that the time to corrosion initiation to follows a lognormal distribution, while that the time from corrosion initiation to cover cracking t~ and the time for crack to develop from hairline crack to a limit crack width t2 can be described by Weibull distributions. With the permitted failure probability of 5.0%, it is also observed that the structural durability lifetime mainly depends on the durability life to and that the percentage of participation of the life to to the total service life grows from 61.5% to 83.6% when the cover thickness increases from 40 mm to 80 mm. Therefore, for any part of the marine RC bridge, the lifetime predictions and maintenance efforts should also be directed toward controlling the stage of corrosion initiation induced by chloride ion.展开更多
Due to the low water-cement ratio of ultra-high-performance concrete(UHPC),fluidity and shrinkage cracking are key aspects determining the performance and durability of this type of concrete.In this study,the effects ...Due to the low water-cement ratio of ultra-high-performance concrete(UHPC),fluidity and shrinkage cracking are key aspects determining the performance and durability of this type of concrete.In this study,the effects of different types of cementitious materials,chemical shrinkage-reducing agents(SRA)and steel fiber(SF)were assessed.Compared with M2-UHPC and M3-UHPC,M1-UHPC was found to have better fluidity and shrinkage cracking performance.Moreover,different SRA incorporation methods,dosage and different SF types and aspect ratios were implemented.The incorporation of SRA and SF led to a decrease in the fluidity of UHPC.SRA internal content of 1%(NSRA-1%),SRA external content of 1%(WSRA-1%),STS-0.22 and STE-0.7 decreased the fluidity of UHPC by 3.3%,8.3%,9.2%and 25%,respectively.However,SRA and SF improved the UHPC shrinkage cracking performance.NSRA-1%and STE-0.7 reduced the shrinkage value of UHPC by 40%and 60%,respectively,and increased the crack resistance by 338%and 175%,respectively.In addition,the addition of SF was observed to make the microstructure of UHPC more compact,and the compressive strength and flexural strength of 28 d were increased by 26.9%and 19.9%,respectively.展开更多
Bridges, especially highway bridges, are a key factor in nations’ development and flourish. Thus, great care should be taken to maintain and inspect their safety and serviceability. An immediate repair will prevent t...Bridges, especially highway bridges, are a key factor in nations’ development and flourish. Thus, great care should be taken to maintain and inspect their safety and serviceability. An immediate repair will prevent the loss of life and vehicles damage while crossing underpass and overpassing the heavy deteriorated bridges. Reinforced or pre-stressed concrete bridge girders become structurally deficient because of severed reasons including, increasing in the load requirements, corrosion of pre-stressing strands or reinforcement bars and collision of over-height trucks with the bulb of the concrete girders. The purpose of this case study is to evaluate and assess the damages of the highway bridges in Jordan. Since there is no mandatory program in Jordan for inspection of bridges and evaluating their conditions, this paper presents an inspection and assessment of two highway bridges along the desert highway which is the essential nerve connecting Jordan cities, and it also serves as an international road between many middle east countries. These two Bridges have never been investigated or checked since their construction in the late 1980s. The study results showed that the main factor causing the deterioration of these bridges is the collision of the over-height trucks with their elements. Relying on the collected data, solutions and repair methods were introduced to rehabilitate these bridges and assure their structural safety.展开更多
To improve the quality of the steel-concrete composite segment of the box girder,to ensure the compactness of concrete to avoid debonding and to enhance the fatigue strength of concrete are critical to the concrete pr...To improve the quality of the steel-concrete composite segment of the box girder,to ensure the compactness of concrete to avoid debonding and to enhance the fatigue strength of concrete are critical to the concrete preparation for such site. Furthermore,the coordination ability to deformation between steel and concrete is also important because of great difference of the elastic modulus between them. Concrete for the steel-concrete composite segment with high fluidity,excellent crack resistance and low shrinkage was prepared by adding efficient poly-carboxylic water-reducing agent,high quality fly ash and expansion agent to it. The quality of the concrete of the half partial testing block showed that the optimal mix proportion of polypropylene fiber reinforced concrete had achieved expected effect,ensured high quality,thus meeting the requirements of construction.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 50538087, 50908103 and 50878098)
文摘In order to study the durability behavior of marine reinforced concrete structure suffering from chloride attack, the structural service life is assumed to be divided into three critical stages, which can be characterized by steel corrosion and cover cracking. For each stage, a calculated model used to predict the lifetime is developed. Based on the definition of durability limit state, a probabilistic lifetime model and its time-dependent reliability analytical method are proposed considering the random natures of influencing factors. Then, the probabilistic lifetime prediction models are applied to a bridge pier located in the Hangzhou Bay with Monte Carlo simulation. It is found that the time to corrosion initiation to follows a lognormal distribution, while that the time from corrosion initiation to cover cracking t~ and the time for crack to develop from hairline crack to a limit crack width t2 can be described by Weibull distributions. With the permitted failure probability of 5.0%, it is also observed that the structural durability lifetime mainly depends on the durability life to and that the percentage of participation of the life to to the total service life grows from 61.5% to 83.6% when the cover thickness increases from 40 mm to 80 mm. Therefore, for any part of the marine RC bridge, the lifetime predictions and maintenance efforts should also be directed toward controlling the stage of corrosion initiation induced by chloride ion.
基金the Key Research and Development Program of Hubei Province(2022BCA082 and 2022BCA077).
文摘Due to the low water-cement ratio of ultra-high-performance concrete(UHPC),fluidity and shrinkage cracking are key aspects determining the performance and durability of this type of concrete.In this study,the effects of different types of cementitious materials,chemical shrinkage-reducing agents(SRA)and steel fiber(SF)were assessed.Compared with M2-UHPC and M3-UHPC,M1-UHPC was found to have better fluidity and shrinkage cracking performance.Moreover,different SRA incorporation methods,dosage and different SF types and aspect ratios were implemented.The incorporation of SRA and SF led to a decrease in the fluidity of UHPC.SRA internal content of 1%(NSRA-1%),SRA external content of 1%(WSRA-1%),STS-0.22 and STE-0.7 decreased the fluidity of UHPC by 3.3%,8.3%,9.2%and 25%,respectively.However,SRA and SF improved the UHPC shrinkage cracking performance.NSRA-1%and STE-0.7 reduced the shrinkage value of UHPC by 40%and 60%,respectively,and increased the crack resistance by 338%and 175%,respectively.In addition,the addition of SF was observed to make the microstructure of UHPC more compact,and the compressive strength and flexural strength of 28 d were increased by 26.9%and 19.9%,respectively.
文摘Bridges, especially highway bridges, are a key factor in nations’ development and flourish. Thus, great care should be taken to maintain and inspect their safety and serviceability. An immediate repair will prevent the loss of life and vehicles damage while crossing underpass and overpassing the heavy deteriorated bridges. Reinforced or pre-stressed concrete bridge girders become structurally deficient because of severed reasons including, increasing in the load requirements, corrosion of pre-stressing strands or reinforcement bars and collision of over-height trucks with the bulb of the concrete girders. The purpose of this case study is to evaluate and assess the damages of the highway bridges in Jordan. Since there is no mandatory program in Jordan for inspection of bridges and evaluating their conditions, this paper presents an inspection and assessment of two highway bridges along the desert highway which is the essential nerve connecting Jordan cities, and it also serves as an international road between many middle east countries. These two Bridges have never been investigated or checked since their construction in the late 1980s. The study results showed that the main factor causing the deterioration of these bridges is the collision of the over-height trucks with their elements. Relying on the collected data, solutions and repair methods were introduced to rehabilitate these bridges and assure their structural safety.
文摘To improve the quality of the steel-concrete composite segment of the box girder,to ensure the compactness of concrete to avoid debonding and to enhance the fatigue strength of concrete are critical to the concrete preparation for such site. Furthermore,the coordination ability to deformation between steel and concrete is also important because of great difference of the elastic modulus between them. Concrete for the steel-concrete composite segment with high fluidity,excellent crack resistance and low shrinkage was prepared by adding efficient poly-carboxylic water-reducing agent,high quality fly ash and expansion agent to it. The quality of the concrete of the half partial testing block showed that the optimal mix proportion of polypropylene fiber reinforced concrete had achieved expected effect,ensured high quality,thus meeting the requirements of construction.
