| Prestressed concrete structures are generally used for structures requiring high levels of fracture control;Large span or a large forced component;the structures requiring high levels of stiffness and deformation control.Such as wharves and the large-span beam components in bridges.Some large prestressed concrete bridges located in the cold area of northern China should not only bear the fatigue load of the vehicle but also bear the influence of freezing and thawing of the environment during the design reference period.Due to Freeze-thaw cycles(FTCs)and fatigue loading,the reliability of prestressed concrete members is reduced continuously.Therefore,the life prediction and reliability evaluation index of prestressed concrete structure in freeze-thaw environment is an urgent problem to be solved in engineering field.Based on “Research on durability test and life prediction of prestressed structure under double index erosion environment” which is sponsored by National Natural Science Foundation of China(item approved number:50878098)and “Research on durability fatigue of prestressed concrete flexural members under freeze-thawing environment” which is sponsored by Ministry of Housing and Urban-Rural Construction of the People's Republic of China(item approved number: 2013-k4-26),the main research contents are as follows:1.Based on the ANSYS Workbench software platform,according to the rules of coagulation strength degradation,elastic modulus degradation rule,stress-strain curve and S-N equation in freezing and thawing environment,the parameters of the model were modified according to the ANSYS Workbench software platform to simulate different freezing and thawing and fatigue Concrete Damage,Safety Factor,Fatigue Life under Loading.The fatigue life of rebar is simulated and theoretically combined.Finally,the simulation results are compared with the experimental results.The comparison results show that the simulation results are in good agreement with the experimental results.2.The fatigue behavior of prestressed concrete under freeze-thaw environment was analyzed by ANSYS Workbench software.Based on the experimental derivation,the elastic modulus decay model of concrete under the action of freeze-thaw and fatigue is obtained.The fatigue constitutive model of concrete is obtained based on the fatigue envelope after freeze-thaw,and the strength attenuation law of reinforced concrete and concrete is takeninto account.Constitutive equation,modify the Workbench model material parameters.The stress-strain behavior of prestressed concrete flexural members subjected to freeze-thaw and fatigue alternation was studied.The effects of the freezing-thawing and fatigue on the mid-span deflection,the change of the equivalent stress of the concrete,the axial force of the reinforcement and the ultimate bearing.The results are compared with the experimental results,which proves that the simulation method is feasible.3.Based on the experiment of freeze-thaw and fatigue alternation of prestressed concrete beams,the probability density model of fatigue residual strength of concrete considering the effect of freezing and thawing is established.It is proved that the fatigue residual strength of the concrete after FTCs still obeys the three-parameter Weibull distribution through the parameter estimation and hypothesis test of the test data.The effect of FTCs on the fatigue residual strength distribution parameters of concrete was introduced.The model can provide a reliable method for fatigue reliability analysis of prestressed concrete structures under freezing and thawing conditions.4.Based on the reliability principle of structural system,the fatigue failure of the prestressed concrete beams under freezing and thawing environment is equivalent to the failure of the structural system of reinforced concrete and concrete.And a stress-strength interference model was introduced to study the fatigue reliability of the concrete under freezing and thawing environment,and a set of calculation method for fatigue reliability calculation of prestressed concrete beams under freeze-thaw environment was established.And MATLAB-based numerical calculation will be compiled into MATLAB code,to facilitate the reader to verify and use.This paper will study the fatigue numerical simulation and reliability of prestressed concrete beams under freeze-thaw environment.The results will provide theoretical and technical support for the reliability evaluation,structural design and maintenance of prestressed concrete structures in cold regions of China. |
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