Research On The Seismic Behavior Of Strengthened R. C. Frame Structure

Seismic appraisal and strengthening of buildings and its analysis of seismic behavior after strengthening are important approaches to decreasing seismic damage. They are also the major research topics of earthquake resistant engineering and retrofitting. Since 5.12 Wenchuan earthquake in China, the project of ensuring the safety of primary and middle school buildings has been proposed by State Department. In order to carry out the project, we have completed the seismic appraisal and strengthening the R.C. frame structure of school buildings, and analyzed the seismic behavior of the strengthened buildings. The main work and conclusions are as the following:(1) The present state and development tendency of seismic appraisal and strengthening of buildings are introduced. The analysis methods of seismic behavior are also summarized.(2) The structure inspection items, methods and estimate system are presented in detail. Meanwhile, we have measured and detected the structure of school building with drilled core method, and calculated the intensity of members. Then the inspection estimate has been given according to the inspection data.(3) The seismic appraisal of R.C. frame structure is studied. The standard for seismic appraisal of buildings (GB50023-2009) is introduced. Based on the inspection data, we have carried out the two-level seismic appraisal. The first level, i.e., the seismic resistant construction measure, shows that some of the buildings can not meet the requirement of China’s seismic code. The second level, i.e., the bare capacity of members calculated by PKPM software, shows that some of members can not meet the code. So it’s necessary to strengthen these buildings.(4) A seismic reinforcement design of these buildings is carried out. Principle and method of seismic reinforcement are summarized. Based on the results of seismic appraisal, we have strengthened the school buildings. The structure members which can not meet the code are strengthened with reinforced concrete method, CFRP method, externally bonded steel frame method, strand steel polymer mortar method or bonded rebars method, etc. Using the modal response spectrum analysis method, we have calculated and checked the capacity, displacement and deformation of the strengthened structure members. The results can meet the code requirement.(5) The seismic behavior of the strengthened building is discussed. The analysis methods of seismic behavior are summarized. We have analyzed the elasticity capacity of strengthened building with elastic time-history analysis method and analyzed the elasto-plastic character with Push-over analysis method. Then we have analyzed and checked the results with that of modal response spectrum analysis method contrastively. The analysis results are given as follows: (1) the seismic fortification category of the strengthened school buildings increases from the third level to the second and the seismic fortification class of the structure members improves from the third level to the second;(2) the strengthened building can meet the seismic code.