Research On Seismic Performance And Optimization Design Method Of Multi-age Frame Structure Under Acidic Atmospheric Environment

In the recent years, Earthquakes occur frequently, the steel structure has been widely used in civilian residential on account of its excellent seismic performance.Under the background of steel structure widely used, Durability problem which is caused by corrosion has become more and more serious, the corrosion weakened steel member’s cross section and reduces steel mechanical property, and then affects the seismic performance of steel structure. In view of the above problems, this paper studied respectively the influence of corrosion on steel mechanical properties, seismic performance of steel frame column, seismic performance of steel frame structure, the seismic damage model, restoring force model and probabilistic seismic vulnerability model of the corrosion steel frame structure are established which is based on the test results. Considering the steel frame structure will suffer the effects of corrosion and the earthquake in the whole length of life, the whole life optimization design of steel frame structure was carried out which is based on damage reliability, the optimization design of steel frame structure is realized. The main research work and achievements of this paper include:(1)Using outdoor accelerated natural exposure test method to simulate the urban atmospheric environment, the acidic atmospheric corrosion of 63 standard steel material specimens and space steel frames was carried out, the steel material specimens and the space steel frame structures with different corrosion degrees were obtained. The tensile tests of the steel material specimens with different degrees were carried out, the test data are fitted and the mathematical relationship between the mechanical properties of steel(including yield strength, ultimate strength, elastic modulus and elongation) and weightloss rate are established. Based on the material test results and the theory of structural mechanics, the steel structure seismic damage model proposed by Ou Jinping et al is modified, the time-varying seismic damage model of existing steel frame is established.The time-varying damage model is applied to the example; the results show that the time-varying damage model can reflect the influence of corrosion damage on seismic performance of steel frame.(2)The urban acidic atmospheric environment was simulated by means of the aerosol corrosion box, 6 specimens of steel frame columns were subjected to acidic atmospheric corrosion. By changing degree of corrosion, axial compression ratio, 6specimens of steel frame columns were tested under cyclic loads. The failure process and characteristics of the corroded steel frame columns are obtained, the influence of degree of corrosion, axial compression ratio on load-displacement relationship, skeleton curve, strength and stiffness degradation, deformability and energy dissipating capacity are studied. Based on above experimental results, the restoring force model of the corrosion steel frame column is established on account of damage.(3) Based on the shaking table tests of 2 specimens of space steel frame structures with different corrosion degrees, the dynamic characteristics and seismic response of 2specimens of space steel frame structures under different earthquake intensity were measured, the impact of corrosion damage on natural vibration frequency, vibration mode shape, displacement response, acceleration response, strain response and damage condition of the structure is compared and analyzed. According to the similarity relationship to calculate the natural vibration frequency, vibration shape, acceleration response, displacement response and shear stress distribution of prototype structures under different level of earthquake.(4)Based on the time-varying seismic damage model, the analysis method and steps of probabilistic seismic vulnerability of multi-age steel frame structure under the action of acidic atmospheric environment are proposed; considering the influence of service age on seismic performance of steel frame structure, the time-varying probabilistic seismic demand model, time-varying probabilistic seismic capacity model and time-varying vulnerability model are established respectively. Based on the analysis of probabilistic seismic demand and probabilistic seismic capacity, the vulnerability modeland the vulnerability curve of multi-age(20 years, 30 years, 40 years, 50 years) steel frame structure are obtained.Based on “investment – benefit” rule, seismic optimum design mathematical model of steel frame structure in the whole life is established. The weighted coefficient is introduced into the optimal design model; it is used to adjust the relative importance of the initial structural cost and the expected loss in the objective function. The reliability analysis theory of damage is applied to seismic optimization design of steel frame structure in the whole life, the whole structure damage is calculated by use of the time-varying seismic damage model, it is used for the reliability evaluation of structures and the calculation of failure probability of structures in every performance condition.The software platform of MATLAB is used to program, the seismic optimization design of steel frame structure in the whole life is realized.