Life-cycle Seismic Performance Analysis Of Offshore Reinforced Concrete Bridges

The life safety of lifeline engineering is the top priority in earthquake engineering, especially for the bridge structures which have a vital bearing on social economy play an important role in seismic design of engineering structures. After years of rapid development, there are huge numbers of existing bridges China. However, the seismic performance of newly-built bridges is always addressed according to the conventional design approach, and the seismic performance variation of the existing bridges in their life-cycle periods is considered insufficiently which may results in losing capacities. Therefore, the seismic capacities of existing bridges serving in severe environmental should be addressed sufficiently in their life-cycle periods, especially for the offshore reinforced concrete (RC) bridges of which the reinforcement are easly corroded according to chloride ions corrosion effect. Based on theoretical analyses and numerical simulations, the researches on seismic performance analysis of offshore RC bridges in life-cycle periods are carried out through static and dynamic nonlinear analysis. The primary contents are listed as follows:(1) The research on seismic performance of existing RC bridges considering reinforcement corrosion and damage effects is carried out. The deterioration and nonlinear response of existing RC bridges are simulated by the proposed damaged-member plastic hinge model. The seismic levels of existing bridges are also proposed. The seismic performance of existing RC bridges is evaluated using nonlinear static analysis method.(2) The research on nonlinear dynamic analysis of RC bridges under bidirectional excitations is carried out based on the fundamental concept of the Force Analogy Method (FAM). The flexural-shear interaction of RC piers is studied, and the biaxial flexural and shear local plastic mechanisms are established based on the concept of strengths interaction curves and hysteretic models. The strength deterioration, stiffness degradation and pinching effect of RC members can be well simulated by aforementioned local plastic mechanisms. Besides, the dynamic analysis model of RC bridges is proposed, of which the mass are concentrated to the joints and the piers are modeled with the proposed biaxial local plastic mechanisms. Due to unchanging stiffness matrices, the equations of motion can be solved by the state space method, which makes the analysis process efficient and stable.(3) The research on seismic damage analysis of RC bridges is carried out based on the fundamental concept of the FAM. The evolution of damage due to concrete cracking of RC members is studied based on the concept of continuum damage mechanics and fracture mechanics, and the local damage mechanism is proposed to simulate the stiffness degradation behavior due to concrete cracking. By introducing damage index to the local damage mechanism, the real-time damage level of RC bridges can be obtained and the seismic responses considering damage effect can be evaluated.(4) The research on seismic performance analysis of offshore RC bridges under chlorine ions corrosion effect is carried out based on the fundamental concept of the FAM. Through the chlorine ions corrosion model, the corrosion mechanism and procedure of reinforcement are studied, and the biaxial local plastic mechanisms considering chlorine ions corrosion effect are proposed. The seismic damage effect can also be considered in aforementioned biaxial local plastic mechanisms when the bridge had already undergone earthquakes. Coupling the proposed biaxial local plastic mechanisms with the basic theory of the FAM, the life-cycle period structural nonlinearity can be reasonably simulated.