Study On Seismic Weakness Of RC Frame With L-shaped Plane Arrangement

Reinforced concrete frame is widely used in China as teaching buildings,residential buildings and marketplaces for its characteristics of flexible arrangement of columns,easy construction and good seismic performance.As the places for education,teaching buildings are highly populated,and the people in the building are young students who are lacking in the ability of self-help and self-rescue.Moreover,teaching places are often used as emergency shelter for earthquake relief.It will cause more serious losses if they are damaged.However,in the previous earthquakes,reinforced concrete frame is one of the building types which is severely damaged due to easily stress concentration,lateral rigidity shortage and low bearing capacity.Due to the need for art and beauty for the buildings as well as the conditions of the construction site and the function of the buildings,buildings with irregular plane arrangement are built,which have large deviation of stiffness center and quality center,and their force situation is more complicated,they can result in the whole or local collapse and other serious damage.This paper presents a method to analyze the seismic performance and torsion effect for buildings with irregular plane arrangement,and to find the seismic weakness of these buildings by nonlinear time-history analysis with finite element model.This paper set up 6 different teaching buildings with L-type plane arrangement based on teaching building in Lushan middle school.Combined with the research of the severest design ground motions and calculation,the ground motion record which has largest effect on the torsion effect of the structure was selected,it's the Western Washington ground motion which was recorded by the Olympia Hwy Test Lab observation site in 1949.The amplitude of the ground motion would be adjusted according to PGA of Frequent earthquake,Design earthquake,Rare earthquake,Super-rare earthquake,then the ground motion would be input in the models with its 356 component along X axis and its 86 component along Z axis.The storey torsional angle will be used to measure the torsion effect of the structure,the storey drift angle will be used to measure the integral deformation of the structure,and the compression damage of the concrete will be used to measure the damage of the column.Calculated and analyzed by using the research methods in this paper,we can come to the following conclusions:1.In the process of selecting the ground motion,the storey torsional angle of the structure is different if changing the inputting directions of the two components along defferent sides,which proves that for the same ground motion record,once the input method of the horizontal component is different,the torsional effect of structure is also different.So the influence that the input direction of the ground motion would have on the structure should be considered.2.It is proved that the torsional effect and the integral deformation of the RC frame structure with L-shaped plane arrangement would increase with the eccentricity of the structure.Moreover,the relationship between the integral deformation and the torsional effect for the L-shaped structure follows the cubic polynomial function.3.The weak parts of RC frame with L-shaped plane arrangement are distributed in the direction of the long side and outer corner of the frame.Through the comparative analysis,the method of adjusting the distribution of weak parts and reducing the torsional effect of the RC frame structure with L-shaped plane arrangement is obtained.The distribution of the damaged columns can be adjusted by changing the sectional dimension of some columns.If the sectional dimension of the column in the short side of the structure is increased,the torsional effect of the structure will increase by more than 30% and the damage of the most dangerous column will increase by about 10% in the super-rare earthquake.If the sectional dimension of columns in the long side of the structure is increased,the torsional effect of the structure can be reduced by about 18% and the damage of the most dangerous column will decrease about 20% in the superrare earthquake.Besides it can make the distribution of the column damage more uniform,it can avoid the occurrence of seismic weakness and reduce the risk of local collapse.