Analysis On Seismic Collapse Resistant Behavior Of The Large-bay Multistory Brick Masonry Structures

The poor seismic behavior of large-bay multistory brick masonry structures is determined by architectural function, which causes mass collapse in earthquakes, leading to terrible death and negative effects on society. In order to investigate the seismic collapse resisitant capacity of such kind of structures, numerical simulation is used to study the collapse modes and collapse analysis method. Besides, the performance index of collapse resisitant capacity is obtained. The main contents and achivements of this thesis are summarized as follow.First of all, through a large amount of earthquake disaster data, the failure modes and degrees of both masonry walls and structures are summed up. According to comparing with story yield collapse mechanism of frame structures, the vertical collapse mechanism of multistory masonry structures is expounded. On this basis, a standard large-bay multistory brick masonry structure model is analyzed by means of alternate path method, and the typical collapse modes are proposed to set the stage for collapse analysis method.Then, the available numerical models for brick masonry are sorted out and commented. For reconstructing the entire collapse process of both the model with precast slabs and the model with cast-in-place slabs in earthquakes effectively, Holmquist-Johnson-Cook damage constitutive model is introducted in explicit dynamic calculation based on3D finite solid elements model. According to the simulation results, the vertical collapse mechanism is tested and verified. On this basis, a collapse analysis method called two-phases method is proposed for multistory masonry structures.Moreover, the numerical models used for two-phases method are researched, while the three spring elements model which can supply complete restoring force model of masonry walls is proposed for nonlinear dynamic time history calculation. The masonry walls are classified into4types depending on tie columns and openings, of which the key parameters formatting restoring force model are obtained by means of statistical analysis on nearly a hundred of experimental results. Besides, the modified Drucker-Prager failure criterion is used for vertial collapse analysis, which is proved to be more applicable than smeared crack model by comparing the calculation results. In addition,10masonry wall specimens and1sub-structure model are tested under pseudo-static load, which are used to verify the accuracy and effectiveness of the numerical models mentioned above.Furthermore. a two-parameter seismic damage model of brick masonry is improved by making a distinction between different types of masonry wall and redefining the damage index. On this basis, the seismic response of a large-bay multistory brick masonry structure under different intensity is calculated for researching the distribution of seismic damage. Then the nonlinear static alternate path method is used to analyze the variation of collapse resistant capacity affected by cast-in-place slabs, tie columns and ring beams, meanwhile, the limit values of depth, breadth and height are obtained.Lastly, based on the collapse analysis method and related judgement criterion proposed above, the collapse margin ratios of4types of structure model are obtained by means of incremental dynamic analysis, which can be used as the quantitative description method for seismic collapse resistant capacity of large-bay multistory brick masonry structures.