Study On Aseismic Behavior Of Frame Structure With Weakness Floor At Bottom

Many building structures with lower weak story damaged severely in the Chi-Chi earthquake in Taiwan in 1999. The building styles are similar in Xiamen and Taiwan, which are in the same seismic zone. Therefore, in order to learn some lessons from the Chi-Chi earthquake, it is necessary to evaluate the seismic performance of the building structures with lower weak story in Xiamen, establish the rational analysis model, find the weak parts that are negative to earthquake resistance and take some effective measures.Xiamen Bureau of Construction and Management supported the project "Collapse-Resistant Design Methodology of the Buildings Structures with Lower Weak Story under Severe Earthquakes", and the State Key Laboratory of Structural Analysis of Industrial Equipment in Dalian University of Technology was responsible for the relevant research task. Since masonry wall have both negative effect (decrease of the structural period and increase the earthquake action) and positive effect (attribution to the story stiffness) on the frame structures filled with masonry walls, the method of equivalent lateral story stiffness is employed to transform the original frame with masonry walls to the equivalent frame, and the elastic analysis under the minor earthquake and nonlinear static pushover analysis under the severe earthquake of a practical 7-story building structure with the lower weak story in Xiamen (assume there is no masonry wall in the first story, and several cases are treated with the first story height from 3.6m to 7m) are performed, and based on the previous results the optimum design of this building structure is executed.To the frame structures filled with masonry walls in the upper stories except the first one, the following solutions can be obtained from the research:(1) The masonry walls may reduce the structural period due to the stiffness contribution to the structure. Because the discount factor of the stiffness of the masonry walls under the minor earthquake is smaller than that under severe earthquake, the masonry walls reduce the structural period much more under the minor earthquake than under the severe earthquake.(2) The masonry walls may reduce the story drift ratio of the middle and upper stories to some degree due to their contribution of stiffness, however they made the weak lower story much weaker relatively and cause the drift ratio of the weak storybecame larger, which is the major index to evaluate the damage state. Thus, the effect of masonry walls is negative to the structural seismic performance.(3) The optimization design can reduce the structural cost by 10%, in which the sizes of the columns are optimized with the constraints of column strength and story drift.Finally, the modification factors of the effect of masonry walls on the structural fundamental period, earthquake action and story drift ratio of the first story are suggested.