| Most of the prestressing concrete bridges are gradually entering "middle age" or "old age".During its service period,due to the influence of adverse conditions such as load,corrosion,fatigue,aging and environmental factors,the pre-stressed bridge structure will produce damage accumulation,resistance attenuation and even lead to sudden accidents.Damage detection and health assessment of pre-stressed structures have become an important research topic in civil engineering.the prestressed concrete bridge structure is used as the engineering object to carry out the permanentstress detection and health assessment of prestressed concrete,mainly from the following aspects:Through the indoor model test,the permanent stress release law of the prestressed concrete structure is established,and the related tests on the physical and mechanical aspects of concrete materials are carried out.The numerical simulation experiments of ordinary concrete and reinforced concrete models are carried out by using the finite element analysis software ANSYS,and the variation law of strain(stress)with the depth of borehole under elastic and elastic-plastic conditions is discussed.The theoretical research and numerical model analysis results are used to carry out the bridge research,and the permanent stress of the real bridge is measured.The main research results are as follows: The strain release law is obtained: the borehole release method is an effective non-destructive test method for measuring the existing stress in the prestressed concrete beam.The complete release curve of the existing stress is obtained by this method.The results show that the diameter of the borehole,the depth of the borehole and the initial value of the surface stress are important factors affecting the stress release process curve.The larger the bore diameter,the slower the stress release rate.However,the full release depth will increase as the diameter of the borehole increases.The actual stress value during release is proportional to the initial stress value,but the full release depth and release rate are not affected by the initial value.The concept of “stress(strain)release rate”was successfully introduced,and the general law of existing stress release was obtained:The stress release rate at the measuring point is related to the ratio of the drilling depth and the aperture,and is independent of the cross-sectional shape,size,stress state,load and other factors of the member.A simple and effective production process has been formed: the selection of the diameter of the borehole and the strain gauge,and the determination of the optimum drilling depth during the stress releaseThe research results used borehole release method to study the persistent stress level in prestressed concrete beams.The process of borehole release was studied by means of model test and numerical simulation.The concept of stress release rate was introduced.The law of stress release was obtained.A set of convenient and feasible experiment and production technology was explored.A complete set of equipment for borehole release was developed.The results of real bridge test show that the research methods and conclusions are correct. |
