Research On Seismic Behavior And Seismic Fragility Of Multi-aged Masonry Structure Under Offshore Atmospheric Environment

With respect to traditional architectures in the world,masonry structure is one of the main structure type and widely applied to office building,residential building,teaching building,hospital building and other construction projects.A large number of building structures affected by salt erosion,leading to the reduction of their safety,applicability,durability.At present,there are a large number of masonry buildings with different ages as well as ancient architectures,which are suffering from environmental erosion for a long term,resulting in the degradation of mechanical properties and seismic performance.Therefore,the seismic performance and fragility of the multi-aged masonry structures in offshore environment are studied,which is of great significance for the prediction of earthquake damage and damage assessment.In view of the above problems,the main contents and achivements are listed as follows:(1)21 groups of mortar blocks,4 groups of brick masonry shear specimens,4 groups of brick masonry compressive specimens were tested in simulated offshore atmosphere environment by applying the artificial climate simulation technology.Then the compression tests were conducted on mortar blocks,from which the compressive performance indices of mortar blocks with different corrosion degrees were obtained;the changing law of compressive strength of mortar blocks suffered from different corrosion cycles were revealed,and the decay model of compressive strength were established.Then the shear tests were performed,the shear performance indices of specimens with different corrosion degrees were obtained,the deteriorating law of shear behavior of masonry were revealed.Then the axial compression tests were conducted.The failure process and characteristics were investigated and the effect of corrosion degree on mechanical properties(axial compression strength,elastic modulus,and stress-strain relation)were revealed.In addition,considering the effect of chloride corrosion on the degradation of mechanical properties of brick masonry,the damage constitutive models were established based on the damage mechanics theory and the strain equivalence principle.(2)8 groups of wall specimens were tested in simulated offshore atmosphere environment,then the pseudo-static tests were conducted on the wall specimens with different corrosion degrees.The apparent morphological,cracking and failure patterns of masonry walls were observed,the effect of salt corrosion on hysteresis loops,characteristic value of lateral load and displacement,skeleton curves,stiffness degradation and energy dissipation capacity were analyzed.Combined with the existing experimental data and based on statistical regression method,the calculation model of the load and stiffness of the characteristic points of the brick wall skeleton curve was obtained,then the skeleton curve of the intact brick wall was obtained.The seismic performance test data of the corroded brick wall was fitted,and the degradation model of the load and displacement was given,then skeleton curve of the corrosion brick wall was established.Based on the I-K model,the resilience model of brick masonry wall with the deterioration of mechanical properties in the offshore atmosphere was determined.A good agreement was observed on comparing the calculated results of the model with experimental results.(3)Considering the bending and shearing effects of masonry structures,numerical analysis of brick wall components and structures were carried out.Based on the actual measurement,experimental research and existing research results,the quantitative relationship between the durability damage degree of multi-age masonry structure and the service age in the offshore environment were established.Based on the material degradation and corrosion hysteretic model,numerical model of the overall structure considering the service age were established.The applicability of the model was verified by comparison with the experimental results.(4)Combining Chinese seismic codes,seismic information and relevant research results,the maximum interlayer displacement angle was taken as the structural performance parameter.Considering the multi-age characteristics of masonry structures,probabilistic seismic capacity models of multi-age masonry structures were established.Finally,the thresholds for mild,moderate,severe damage and collapse limit state were determined.(5)The typical structure of brick masonry with seismic construction measures and masonry buildings with bottom frames were selected,and the numerical model of the typical structure were established based on the material degradation and hysteretic model.The probabilistic seismic demand models of typical masonry structures were established.By employing theoretical frame of seismic fragility based on displacement,seismic fragility analysis of typical masonry structures were performed.Finally,the fragility curves of typical masonry structures corresponding to different layers,service ages,fortification intensity were obtained.