Research On Seismic Damage For Steel Reinforced Concrete Irregular Section Column And Frame With Irregular Section Columns

As a new type of composite structure,steel reinforced concrete(SRC)irregular section column not only has the advantages of high bearing capacity and good ductility,but also has the advantages that the column limb is equal to the width of infilled wall.The characteristics of the structure make it widely used in the construction of high-rise building structure in the high seismic fortification intensity zone.However,in recent years,earthquake disasters have occurred frequently,and lots of buildings are suffered various degrees of damage under earthquake.How to evaluate the structural damage degree reasonably and effectively becomes an important basis for post-earthquake repair and reinforcement.At present,there are many researches on SRC irregular section columns in China,but mainly focus on the seismic performance(bearing capacity,hysteretic behavior,stiffness,strength)of components or structures under earthquake.There are less of researches on the damage performance of this kind of structure under different horizontal loadings.Therefore,this paper aims to study the damage behavior of SRC irregular section columns by mean of experiments and numerical simulation.The research contents and results are as follows:(1)16 specimens are designed and manufactured,which contains 10 T section columns,3 cross section columns,3 L section columns.The experiment research is carried out for these specimens.During the test,the loading systems,axial compression ratio and steel ration are taken as the various parameters to research the effect on seismic performance of specimens,and furthermore the damage law is revealed.The test results show that for the specimen with large shear span,bending failure is mainly showed and the obvious shearing bond failure is also accompanied during the late loading.The hysteresis curves of the specimens are plump.Compared with other specimens,the hysteresis curves of L section columns are slightly thinner and its ductility is relatively poor.The damage history of specimens can be divided five phases: no damage phase,minor damage phase,moderate damage phase,less serious damage phase and severe damage phase.Compared with the specimens under the variable-amplitude cyclic loading,the specimens have a slow development step of damage degree under monotonous loading,mixed loading and constant amplitude loading.With the increase of steel ratio,the damage degree of the specimen is relatively slight.The larger the axial compression ratio is,the faster the damage degree increase.What's more,the bearing capacity decreases rapidly after the maximum bearing capacity for specimen with larger axial compression ratio.(2)The numerical simulation analysis is carried out by OpenSees software.Compared with the test results,the method of numerical simulation has a high accuracy.At the same time,considering the influence of local steel ratio and loading direction on the mechanical properties of the specimens,16 SRC irregular section columns are designed and reciprocally loaded along their limbs.The results show that for the T section column and cross section column,when the local steel ratio at the limb perpendicular to the loading direction is changed,the seismic properties of specimens have no significant change.On the contrary,when the local steel ratio at the limb along the loading direction is changed,the seismic properties of specimens will be improved as the steel ratio increases.For the L section column,when the local steel ratio of any one limb is changed,the seismic performance of specimen is significantly changed.(3)Based on the experimental study of SRC irregular section columns,the damage law of seismic behavior is studied.Considering the effects of concrete cracking,effective hysteretic energy consumption and loading path,the improved Park-Ang damage model is proposed.According to the data obtained in the experiment,the damage degree of sepcimen under different loading stages is evaluated.Compared with the test results,the accuracy of damage model is validated.It is proved that the damage model proposed in this paper can reasonably describe the macroscopic failure phenomenon at different stages.At the same time,the seismic behavior levels are divided into five phases and the damage thresholds corresponding to the different levels are given.(4)Considering the influence of damage on the degradation of strength and unloading stiffness,a resilience model is proposed.The calculated hysteresis curve is obtained according to the proposed resilience model and compared with the experimental hysteresis curve.The results show that the proposed resilience model can reasonably describe the hysteretic behavior of the specimens under low cyclic reversed load.(5)The relationship between member(beam and column)damage,story damage and overall structure damage is revealed.The weighted coefficient method is used to establish a seismic damage model that can reflect the relationship between members and overall structure damage.Based on the previous test results of SRC frame with irregular section columns,the damage evaluation is made for two SRC frames with irregular section columns.According to the experimental test and damage evaluation results,the damage thresholds corresponding to different seismic behavior levels are given.(6)By referring to the structural seismic design method and existing research on SRC frame with irregular section columns,the seismic design method based on damage performance is proposed and the detailed design steps are given.Finally,the 12-story SRC frame with irregular section columns is taken as an example to illustrate the design method based on damage performance.