Research On Seismic Evaluation Method Of Existing Reinforced Concrete Frame Structures

The continuous seismic service life should be determine by the era of the design and construction that can be found in the Standard for seismic evaluation of buildings(GB50023-2009).Different evaluation methods are adopted for buildings with different continuous seismic service life.It lays a foundation for the performance-based seismic evaluation methods.Although the existing buildings are divided into three types: A,B and C,which is the minimum requirement for seismic evaluation.The owners can raise the requirements according to the economic conditions and technical capability.However,the division is too clear,the increase evaluation requirement may lead to significant increase in economic,but the improvement of seismic performance can't be quantitative.The basic principle of seismic evaluation of existing buildings is that the seismic precautionary criterion is not lower than original design.All existing buildings should meet the collapse prevention performance objectives,but the acceptable level of damage was not given.In this dissertation,the theoretical analysis,numerical simulation and experimental research methods are used to study performance-based seismic evaluation methods of existing frame structures.The main contents and achievements as follows:(1)The earthquake generation model was established based on the Homogeneous Poisson Process,and the probability distribution of ground motion parameters was analyzed incorporating the influence of all potential earthquakes sources.Then seismic hazard curve formulas of ground motion parameters were obtained.Different methods were employed to estimate the extreme distribution parameters of ground motion parameters based on the seismic record in recent years.Based on the equal exceeding probability principle,an available approach according to current code was proposed to modify corresponding ground motion parameters for different continuous seismic service life.The results have shown that: the probability distribution of ground motion parameters was embodied by Extreme Value Type ?.When the continuous seismic service life and seismic precautionary intensity were same,the reduction factor of ground motion parameters is the same for different seismic fortification levels.The reduction factor of ground motion parameters with continuous seismic service life of 30,40 and 50 years are 0.8,0.9 and 1.0,respectively.(2)According to the statistics analysis of the frame structures damage and the case studies,several conclusive observations are made that the seismic performanceof reinforced concrete frames is deficient when subjected to earthquakes.A prototype reinforced concrete moment frame representative of existing frame buildings was selected and designed for evaluation under seismic loads.A large-scale specimen from the prototype was incorporated into the design of shaking table test.The response of the specimen to a series load histories was marked by gradual structural softening and yielding of the steel reinforcing throughout the structure.The design of shaking table test,response of the structure to seismic loads,qualitative evaluation of the test method is discussed.The experimental results were used to define in terms of performance levels associated with reference ultimate damage states,a method of solving the limited values and the performance levels is put forward.Furthermore,the performance leveling system and description method of the existing frame structure are proposed.(3)Based on actual mechanical properties,the components model was developed to address the deficiencies of existing frame structure and was incorporated in the finite element structural models.Its applicability and accuracy are checked by comparing with existing tests.Based on the model of typical existing frame structures,five existing frame structures were designed according to seismic design code of different ages.The seismic records incorporating the influence of source mechanism,magnitude were used in the finite element-based simulations for determining the seismic demand on the frames structure by nonlinear time history analysis.(4)A fragility analysis method of performance-based is given which incorporate the influence of collapse.For developing fragility curves,the mean values of interstory drift were evaluated for each seismic precautionary intensity.A suitable regression function is used for developing fragility curves of performance levels are proposed.Furthermore,seismic fragility analysis is carried out for typical pre-seismic code reinforced concrete structure of different ages to assess the seismic fragility.The influence of seismic demand variation is discussed.The results show that the existing frame structures designed by old seismic design code do not meet the life safety and collapse prevention performance objectives.The seismic measures that are found in recent seismic design code significantly improve the seismic performances of reinforced concrete frame structures.(5)The seismic performance of a key seismic fortification building before and after reinforcement were compared by using performance-based seismic assessment methods for existing frame structures,and the effect of seismic reinforcement wasanalyzed.