| China is located at the junction of plates,with very active seismic belt movements.Earthquakes occur with high frequency and large magnitude,covering almost the entire land area.Over one-third of the land earthquakes have occurred in China that accounts for only 7% of the global land area.The severe situation of earthquake disasters is the long-term development trend of China.Bridges are important hubs of transportation lines,and their seismic performance has an important impact on the safety of road traffic,and they are also extremely vulnerable to earthquake damage.As load-carrying components,bridge piers are highly vulnerable,and their seismic performance to a certain extent determines the overall seismic capacity of the bridge.They play a crucial role in evacuation during earthquakes and rescue after earthquakes.In China,a large number of old bridges adopt the concept of strength seismic design,and the construction standards are generally low during construction.During long-term use,with the superposition of environment and load,its durability and seismic performance have decreased,making it difficult to meet current seismic design standards.Considering many factors such as economic and social development,it is not possible to demolish and rebuild all old bridges that do not meet the current seismic design standards,resulting in an increased demand for maintenance and reinforcement of old bridges.Performance based seismic design is the most advanced design concept in the field of civil engineering seismic design.It not only requires the structure to meet seismic requirements,but also needs to adapt to social and economic development.How to make bridge piers meet the seismic performance requirements after reinforcement and choose appropriate reinforcement methods from numerous seismic reinforcement methods has become a research hotspot.Based on the above analysis,the main research works of this thesis are as follows:(1)Three scaled models of reinforced concrete bridge piers were designed and fabricated.The MTS electro-hydraulic servo actuation system was used to simulate the seismic damage state of the bridge piers.Low cycle cyclic loading pseudo static tests were conducted on ordinary RC(Reinforced Concrete,abbreviated RC)columns strengthened with CFRP(Carbon Fiber Reinforced Polymer,abbreviated CFRP)wrapped considering seismic damage.The test shows that CFRP reinforcement can effectively improve the seismic performance of damaged bridge piers.The ultimate displacement of the repaired pier after earthquake reaches 87.8 mm,which is 18.2% higher than the original column without reinforcement,and the cumulative energy consumption is 35.3%higher than the original one.The structural ductility and energy dissipation capacity have enhanced,and the reinforcement effect is good(Chapters 2 and 3).(2)The Open Sees platform is used to establish a numerical model of the bridge pier.The bridge pier adopts a displacement based nonlinear beam column element,and the section adopts a fiber model method.The zero-length section element is used at the bottom of the pier.The constitutive relationship of the reinforcement in the zero-length section element is replaced by the constitutive relationship of the bond slip material,The elastic modulus of steel and concrete in the material constitutive equation is multiplied by the corresponding reduction coefficient,and the bond slip value between steel and concrete is multiplied by the amplification coefficient to simulate the seismic damage state of bridge piers.A numerical model of reinforced concrete bridge piers considering seismic damage and bond slip of longitudinal reinforcement at the pier bottom is established(Chapter 4).(3)Comparing the numerical simulation results with the experimental data,the hysteretic curves of the numerical simulation agree well with the hysteretic curves of experimental data,and the peak bearing capacity error is between 0.4% and 6.7%.Among the four simulated reinforcement schemes,the outsourced CFRP method and the outsourced ECC(Engineering Cement Composite,abbreviated ECC)method improved the seismic performance of seismic damaged bridge piers in terms of yield displacement and ultimate displacement,and the horizontal bearing capacity regained to the pre-earthquake level.The outsourced CFRP method can enhance the energy consumption capacity and exceed the pre-earthquake level by 25.3% to 30.8%,while the energy consumption capacity of the outsourced ECC method after reinforcement can only recover to about 92% of the pre-earthquake level.The horizontal peak load after reinforcement by increasing the section method increases with the increasing of reinforcement height.When the reinforcement height is 50% of the calculated height of the column,there is a significant improvement in seismic performance.The horizontal peak load increased by 117.8%,and when the height continues to increase to the full height,the increase is 119.7%.Within the range of 50% to the full height of the column,the increase in reinforcement height does not bring a significant increasing in peak load.When using outsourcing steel pipe reinforcement,the horizontal peak load after reinforcement increases with the increase of reinforcement height.Within the range of equivalent plastic hinge height to 50% of the calculated height,the ultimate displacement shows a downward trend,and the deformation capacity of the pier column decreases with the increase of steel pipe height.When using outsourcing steel pipe full height reinforcement,the overall stiffness of the bridge pier is strengthened,the tensile performance of the steel is fully utilized,and the seismic performance of the bridge pier is "qualitatively" improved,the ultimate displacement increased by 21.1%,the peak load is 3.2 times of the original,and the cumulative energy consumption is 5.1 times of the original.(4)Comparing the advantages and disadvantages of various reinforcement methods.It is recommended that the height of the reinforced bridge pier should reach half or more of the original calculated height in order to achieve good reinforcement effects when using the increased section method.When using wrapped steel pipes for reinforcement,full height reinforcement is required to fully utilize the mechanical properties of the steel and achieve good reinforcement effects.The peak load and ultimate displacement after reinforcement with the outsourcing ECC method basically regained to the pre-earthquake level,and the energy consumption capacity is about 92% of the pre-earthquake level.In practical engineering,it is not recommended to replace the concrete protective layer with ECC material to repair the earthquake damaged bridge piers.The peak load of the CFRP method after reinforcement has basically returned to the level before the earthquake,with the ultimate displacement increased by 10.8% and the energy consumption capacity increased by 25.3% compared to those before the earthquake(taking the simulated reinforcement height as half of the column length as an example).Moreover,the construction of CFRP method is simple and the construction period is short,making it an ideal reinforcement method(Chapter 5). |
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