Experimental Research On Seismic Appraisal Method Of Existing Reinforced Concrete Frame Structures

Seismic appraisal and strengthening existing structures is an important way to reduce seismic damage. This paper reviews the development of seismic appraisal in China and analyzes the problem existing in seismic appraisal, with emphasis on the RC (reinforcement concrete) frames. Integrating earthquake testing and analyzing, this paper improves the seismic appraisal method for RC frame structures. The main aspects of research are as follows:1. According to the equal probability of exceedance, this paper indicates that there is an accordant seismic precautionary target for existing buildings and new construction, i.e."three seismic precautionary criterions", and presents the respective return periods of different continuous seismic working life and seismic precautionary criterion (frequent earthquake, fortification earthquake and rare earthquake). The values of and simplified way to calculate the parameters of the ground motion are presented, which is necessary for the seismic appraisal based on different continuous working life.2. According to standard for seismic appraisal of buildings (GB50023-2009), this paper attaches much importance to three types of RC frame columns, type AO (designed without taking seismic load into consideration), type A (meeting standard for seismic appraisal buildings requirements for RC frames of type A) and type B (meeting standard for seismic appraisal of buildings requirements for RC frames of type B). This paper describes the low cycle cyclic loading tests of fifteen column specimens, on the scale of1:1.5, aiming at the RC columns seismic performance with different details of seismic design. Test results indicate the columns ductility has pertinence with stirrup spacing, arrangement of longitudinal bars and axial-force-ratio, which is necessary to identify the structural system factor in seismic assessing. This paper promotes that the RC columns with stirrup space great than or equal to200mm and axial-force-ratio great than0.6, should be strengthened.3. A nonlinear program concerning the shear deformation of the RC frame columns is written in Matlab. The influence of different factors on ductility is analyzed on the base of the test results and calculation. The analysis result indicates that axial-force-ratio and spacing of stirrup are the key factors affecting ductility. With the axial-force-ratio increasing, the influence of the stirrup ratio on columns ductility has weakened. The denser the stirrup space is the more influence the stirrup ratio has on the columns ductility. Only if the spacing of stirrup is dense, the great stirrup ratio can increases the ductility obviously.4. Besides the low cycle cyclic test of columns, low cycle cyclic tests of two frames (type A meeting standard for seismic appraisal buildings requirements for RC frames of type A and type B meeting requirements for type B),aiming at studying the different seismic performance with different details of seismic design, are finished. The results indicate that although type A is more vulnerable than type B, the deform ability of type A can meet the requirement not to collapse in the rare earthquake. Different from other frame models, the beams in the6times plate thickness is taken into consideration in the test, which is closer to the reality. The frame joints have slight damage, which reflects the reality more exactly.5. This paper introduces a fiber-beam plus layer-shell finite element analysis model to the pushover of type A and type B. The calculating results are consistent with the test results to a large extent. The case that both type A and type B can meet the requirement not to collapse in the rare earthquake illustrates that the requirements to different continuous seismic working life of standard for seismic appraisal buildings are appropriate.6. Summarize the research result. Present the method to calculate the compound seismic capability of the existing buildings. Promote the values of structural system factor with different axial-force-ratio, stirrup spacing and volume stirrup ratio. And give some engineering projects.The above research indicates the following innovative achievements:1. According to equal exceedance probability, make the three levels seismic fortification target clear. Determine the return period of seismic fortification criterion with different continuous seismic working life respectively. The values of and simplified way to calculate the parameters of the ground motion are presented.2. Present that in order to avoid shear damage, the axial-force-ratio of RC columns with stirrup space great than or equal to200mm should be less than0.6.3. The results of tests and pushover analysis indicate that type A frame and type B frame of standard for seismic appraisal buildings can meet the requirement not to collapse in the rare earthquake.4. Present the method to calculate the compound seismic capability of the existing RC frames, promote the values of structural system factor with different axial-force-ratio, stirrup spacing and volume stirrup ratio, which can make sure that the seismic precaution target of existing buildings with different seismic continuous working life have the same probability.