| With China's economic development and people's living standard improving day by day,people's traffic demand is constantly improving,and the number of bridges built near the coast and the estuary of the river is increasing all over the country.As an important part of China's infrastructure system,the durability of bridges has a significant impact on maintenance costs and structural safety.Most of the concrete structures in northern China suffer from freeze-thaw damage to varying degrees.Freeze-thaw cycle is one of the important factors affecting the durability of concrete structures.In order to study the influence of freeze-thaw cycle on the seismic performance of concrete piers in offshore environment,and to simulate the influence of concrete mechanical properties attenuation on the piers through numerical methods,the research in this thesis is as follows:1.Fast freeze-thaw test was used to perform the seawater freeze-thaw cycles for C40 concrete prismatic specimens 0 times,25 times,50 times,75 times,100 times and 125 times,and the mass loss and relative dynamic elastic modulus loss of specimens with different freezethaw times were measured.The stress-strain curves and repeated loading and unloading curves of C40 concrete specimens with different seawater freeze-thaw times were obtained by cyclic compression test.The relationship between the mechanical parameters of C40 concrete and the number of freeze-thaw cycles in seawater was established.2.In order to simulate the freeze-thaw phenomena of plastic hinge zone at the bottom of pier in winter sea area,the precast concrete pier bottom segments and foundations were respectively precast by precast assembling construction method,and the seawater freeze-thaw cycle of precast bottom segments were carried out.The changes of pier segments after freezethaw cycle in different times were described.Ultrasonic testing equipment was used to scan the cross-section of pier sections after seawater freezing and thawing,and CT imaging of pier section was used to analyze the change of freeze-thawing depth of pier section,and the relationship formula between average freeze-thawing depth of pier section and the number of freeze-thawing cycles of sea water was established.The pseudo-static test was carried out on the assembled piers,and the horizontal force-displacement hysteretic curves of the piers were obtained after seawater freezing and thawing.The results of the pseudo-static test show that with the increase of the number of seawater freeze-thaw cycles,the bearing capacity of the pier gradually decreases,the horizontal lateral stiffness of the pier specimens continuously decreases,and the cumulative energy dissipation of the specimens gradually decreases.3.ABAQUS software was used to establish the finite element model of the pier specimens after freezing and thawing of seawater,and to simulate the pseudo-static test of the pier specimens after freezing and thawing of seawater.In the model,the delamination between freeze-thaw concrete and unfreeze-thaw concrete and the attenuation of material properties of bridge piers subjected to freezing and thawing of seawater were calculated by using the relationship formulas fitted before.The numerical simulation results show that the finite element model of reinforced concrete piers after freezing and thawing by seawater can reflect the hysteretic behavior of piers after freezing and thawing by seawater under repeated horizontal loads.The skeleton curves obtained by numerical calculation are in good agreement with the skeleton curves obtained by test,and the difference of their horizontal bearing capacity is not big,the slope of the curve descending section is close.The delamination model can be used to analyze the reinforced concrete bridge piers after the freezing and thawing of seawater. |
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