Research On Durability Of Retard-bonded Prestressed Reinforced Concrete Beams Under Combined Action Of Load And Chloride Drying And Wetting Cycles

By the national guidance of strategic goal of development to the sea and underground space and the output of a large number of construction engineering technology due to "The Belt and Road" policy,the projects of coastal construction,marine construction,port engineering and underground space engineering are increasing,in which large span members and prestressed technology are needed.The retard-bonded prestressed technique is a major reform of the traditional prestressed technique which has great market potential because of its simple construction process and good mechanical properties.The problem of durability of retard-bonded prestressed members under coupling effect of long-term load and corrosion as well as the flexural capacity of corrosive members must first be studied in order to promote the application of retard-bonded prestressed technique in a large number of offshore and large span structures such as roofs of urban underground space which are attacked by salt water.At present,there are very little research results in this field.Based on the above background,in this paper,the durability of retard-bonded prestressed reinforced concrete beams under combined action of load and chloride drying and wetting cycles are studied and the following works are submitted.(1)22 retard-bonded prestressed and ordinary reinforced concrete beams under combined action of load and chloride drying and wetting cycles were carried out to research chloride penetration law from four perspectives of the influence of different parameters on the distribution of chloride concentration,the effect of flexural load on chloride diffusion velocity,the influence of transverse crack on chloride transportation and steel bar corrosion and its suggested index as well as the convection effect in surface and to research steel bar corrosion law from three perspectives of the characteristics,corrosion rate and weightlessness rate of corroded steel bar and nondestructive testing for it.(2)Multi-physics combined analysis of chloride diffusion due to flexural load on RC member were carried out with ABAQUS subroutine by considering the function Fd of influence on concrete mechanical damage under loads.Based on the experimental results,the model of chloride diffusion coefficient under the influence of multiple factors was summarized and modified which was used to analyze the experiment in this paper in COMSOL and compare the experiment results with the finite element analysis one.Furthermore,different parameters on chloride diffusion were studied.Finite element calculation of chloride convection-diffusion in unsaturated concrete were carried out to analyze the mechanism of drying and wetting cycles and research the influence of the ratio of dry and wet time and initial pore water saturation on chloride penetration.(3)Static loading test of 10 corroded retard-bonded prestressed and ordinary reinforced concrete beams were carried out to study their bending behavior.The change characteristics of the bending behavior of corroded beams are studied from five perspectives including cracking development,flexural capacity & deflection,stiffness & ductility ratio,strain of steel bar and failure mode and the effect of load ratio and retard-bonded prestressed technology on the bending behavior of corroded beams were further refined.A typical theoretical model was used to calculate the flexural capacity of the test members and the results were compared with the experimental values.By using the experimental results,formulas for calculating the flexural capacity of corroded RC beams under nondestructive testing condition were established.