Research On Reliability Evaluation Model Of Existing Concrete Building Structure In Seasonally Frozen Regions

With the increase of service life and the number of loads.various types of damages such as cracks and deformations will appear in the existing building structure,resulting in the decrease of reliability level.However,the damage of in-service building structures in the extreme climate environment such as low temperature and snow has its particularity.Therefore,it is not reasonable to evaluate the reliability level of in-service building structures in the normal climate environment by the reliability evaluation method.In order to reflect the extreme climate characteristics of the seasonally frozen regions,improve the evaluation index system of the reliability of the in-service building structure in the seasonally frozen regions,establish the reliability evaluation model applicable to the in-service building structure in the seasonally frozen regions,draw the reliability theory of the in-service building structure according to the reliability theory comparison of the proposed building structure,and take it as the theoretical basis of the reliability evaluation of the in-service building structure.The damage of the climate in the seasonally frozen regions to the building structure is caused by the freeze-thaw action.The typical projects in the seasonally frozen regions are selected to analyze the change trend of the structural performance indexes affected by the freeze-thaw action.Two freeze-thaw damage models of the concrete structure are established,and two typical indexes suitable for the reliability evaluation of the building structure in the seasonally frozen regions are proposed,which are the dynamic elastic modulus Loss value and flexural strength loss value.According to the national standard and the characteristics of building structure,the evaluation index system of the reliability of the existing building structure in the seasonally frozen regions is constructed by taking the life cycle,the foundation,the enclosure system,the concrete structure components and the integrity of the structure as the index of the building structure,and the loss value of the dynamic elastic modulus and the loss value of the bending tensile strength as the use environment index.The BP neural network is established with MATLAB.The reliability evaluation index value of typical projects in the seasonally frozen regions is taken as the training sample.The network structure is set up and the network parameters are adjusted.After the BP neural network training,the reliability evaluation model of the existing building structure in the seasonally frozen regions is established and verified.The research results show that the theoretical basis of reliability evaluation of in-service building structure is scientific and reasonable.The two models of freeze-thaw damage of concrete structures are in line with the actual situation.The damage values of dynamic elastic modulus and flexural tensile strength of two structural performance parameters quantified by the freeze-thaw damage model can be used as an important reference to measure the reliability level of the structures in service in the seasonally frozen regions,and a reliability evaluation index system with the characteristics of the seasonally frozen regions is established.BP neural network achieves the best training effect after 556 steps of training,and the decisive coefficient of the model is close to 1.It is proved that the fitting degree is high and the model has statistical applicability.The reliability grade of the model evaluation is compared with the actual grade,and the grade is basically consistent.At the same time,the countermeasures corresponding to the evaluation grade are compared with the AHP.The countermeasures of the model are more consistent with the actual results,and the model has practical significance.The research results can provide an effective evaluation method for the reliability level of buildings in service in the seasonally frozen regions,which is of great significance to reduce the hidden danger of building safety and extend the service life of buildings.