Study On Strengthened Concrete Column's Bearing Performance By The Method Of Enlarging Section

The old building's reinforcement is one of emerging professions in the present construction industry, and the reinforcement of concrete structure approximately composes above 50%. At present, the researches of bearing performance of strengthened concrete members by enlarging section are less, even most of which are on the primary loading. So it is necessary to strengthen the study of the secondary loading members. So the paper mainly studies on bearing performance of strengthened concrete members under cyclic load and putting forward specifications for strengthening of building, which are significant for theory and practice.Using the finite element programming package of ANSYS, the paper studies on the bearing performance of strengthened concrete members and systematically analyzes the effect of major parameters to behavior of the strengthened concrete members under cyclic load. The major parameters include initial stress level index, strength grade of enclosed concrete, ratio of added longitudinal bar and axial compression ratio and so on. Through the study of finite element, it obtains some chief conclusions as follows: After enlarging section, the bearing and energy dissipation capacity of concrete column are enhanced greatly, and the ductility is improved, which could meet the requirements of current design code for structures. The whole seismic behavior of column strengthened, the method is effective for seismic strengthening of concrete column. When the initial stress level index is small, the effect of seismic strengthening of concrete column is better, and the paper argues that the upper load should be removed as far as possible before strengthening. When designing for strengthening structures, the great difference between the old and new concrete strength grades should be avoided. When the strength grade of enclosed concrete is higher one level than the core concrete which accords with a good agreement with the specification, the effect of seismic strengthening of concrete column is best. When the ratio of added longitudinal bar increases, the bearing capacity and seismic behavior are enhanced, but there is upper limit value rather than the better. The axial compression ratio has a great effect on the seismic behavior of the column. When the axial compression ratio is more, the seismic behavior of column could not meet the requirement of seismic strengthening. In the case of large eccentric compression column, because of the role of the initial stress, the stress excess of core concrete is obvious but steel not, which is the difference to axial compression and small eccentricity. The bearing capacity, distortion and ductility of strengthened concrete members, secondary loading members, under secondary loading is worse than under primary loading, which indicates that it trends towards to unsafe on the basis of primary loading when carrying out seismic strengthening.The analysis of the strengthened concrete members'response under monotonous load and hysteretic behavior under cyclical load in a rather comprehensive and systematic way is very useful for revising design specifications and guiding design of engineering, which will play a basic role in the further study on bearing performance of strengthened concrete members.