Damage Mechanism And Retrofitting Method Of Multi-story Masonry Structure With First Story Used As Shops Against Earthquake

Weak earthquake vs severe disaster is a predominant characteristic in China. Oneimportant reason of casualty and loss is the severe damages and collapse ofbuildings. The bottom-business multi-story masonry structure is the mostseverely damaged building form. In Wenchuan earthquake,80%of this kind ofbuildings were ruined, while bottom-business multi-story masonry structure isvery popular in the small and middle towns in the south of China. According toinadequate statistics, there are about two million such buildings existing in China,and120million residents are involved. As a result, it is urgent to study theearthquake resistant mechanism of this building form and the methods toreinforce the existing buildings in order to reduce the damages caused byearthquakes.The main content of this paper can be concluded as follows:1. After investigating the post-earthquake sites, we found that different from theoverall collapse of ordinary concrete structure and the cracking of the bearingparts, the most vulnerable parts of the bottom-business multi-story masonrystructure distribute among the weak layers of the bottom story. As a result, thebottom story usually collapses along the longitudinal direction, while the secondstory suffers slight damages. The reasons lie in the inconsequence of frame nodesteel anchorage, the misusing of coarse aggregate materials, the unreasonableplane layout and so on. In addition, it is also found that in the same meizoseismalarea, individual bottom-business multi-story masonry structure has shown verygood seismic performance. The difference between these buildings and otherbottom-business multi-story masonry buildings lies in the fact that winged wallsand winged columns were added to the side of columns in the longitudinal wall ofthe bottom floor. This structural measure raises the earthquake resistant capacityof the building, and reduces the rigidity difference between the front and backvertical walls in the bottom floor, namely reduces the earthquake load differencebetween the longitudinal walls, so as to remain the damage rate of this building aslow as middle in zone.2. Through a comparative experiment between the earthquake simulation shakingtable test of two single-deck models, the influence of the steel anchorage shape ofthe front frame node on earthquake resistant performance is analyzed. Theexperiment proves that the length of steel anchorage and the set of hook may putoff the invalidation of the node and the collapse of the whole structure. Themodels with poor steel anchorage reach "collapse" state after0.34g, while themodels with good steel anchorage just reach the "moderate damage" level.3. Through a comparative experiment between the earthquake simulation shakingtable test of two single-deck models, the influence of adding winged wall andwinged column on the earthquake resistant capacity of the whole structure isstudied. The experiment shows that after adding winged wall and winged column,the structures "crack but not collapse", while the structures without them collapse suddenly; the self-quake frequency of the winged structure decreases little after0.31g, while the self-quake frequency of the contrast structure decreases60%;and the acceleration amplification is lower as well.4. Through a comparative experiment between the earthquake simulation shakingtable test of three double-deck models, the differences in the aspects of structurefrequency, acceleration, displacement and strain state between the commonbottom-business multi-story masonry structure, bottom-business multi-storymasonry structure with adding winged wall and winged column, and thebottom-business multi-story masonry structure reinforced through rectangle steelpipe and profiled bar are analyzed. Based on the test results, the destroy mode ofeach longitudinal wall and the invalidate order are obtained; the key function ofwinged wall and winged column in earthquake resistance is validated; thefeasibility and practicality of the reinforcement method through rectangle steelpipe is proved. Finally, the reinforcement method of balancing stiffness andincreasing ductility is put forward.