| RC frame is widely used for its advantages like spacing flexibility,concise structural analysis,material saving and so on.In nature,the building is damaged mostly by frequent earthquake,the biggest part of economic lose and casualties was shown in near-fault zones.Therefore,it is necessary to study RC frame's responses under near-fault seismic action,so as to lay the foundation for the seismic design and reduction measures of the structures built around near-fault.The main works are summarized as following:1.First,the characteristics of near-fault ground motions are summarized.Three are two significant characteristics of near-fault ground motions,one is the unneglectable vertical ground motions which is that the PGA of vertical ground motions may reach,sometimes even exceed the PGA of horizontal ground motions;the other one is large velocity pulse of near-fault ground motions.Near-fault pulse-like ground motions can be divided into near-fault pulse-like ground motions with forward directivity effect and near-fault pulse-like ground motions with fling step effect according to the mechanism of the near-fault pulse.In order to study the responses of RC frame under pulse-like ground motions and none-pulse ground motions,response spectrums and energy flux of those two kinds of ground motions are compared,the response spectrums of near-fault pulse-like ground motions with forward directivity effect and near-fault pulse-like ground motions with fling step effect are also compared.2.One four-floor RC frame and another eight-floor RC frame are designed according to the national codes.RC frame under unneglectable vertical ground motions and pulse-like ground motions are analyzed by using calculation software ABAQUS.Unneglectable vertical ground motions:Three ground motions are selected from Wenchuan earthquake,Imperial valley earthquake and Chi-chi earthquake,then adjust the ratio of PGA of vertical ground motion and PGA of horizontal motion to 1,0.5 and 0.The influences on horizontal displacement of RC frame,axial force,shear force and moment of columns from vertical ground motions are studied.It is shown that vertical ground motions have little influence on displacement and story drift of each floor;Vertical ground motions have bigger than that on side columns,tensile force may appears in columns due to vertical ground motions;There is little influence on moment capacity of columns while much influence on shear capacity of columns from vertical ground motions,especially the columns in middle positions.Pule-like ground motions:9 ground motions are selected based on classification of near-fault pulse-like ground motions with forward directivity effect,near-fault pulse-like ground motions with fling step effect and none-pulse ground motions,each kind with 3 ground motions.The influences on horizontal displacement of RC frame.axial force,shear force and moment of columns from pulse-like ground motions are studied.The story displacement and story drift of each floor are amplified by pulse-like ground motions.The biggest story drift shows at 1st floor due to pulse-like ground motions in case of four-floor RC frame,forward directivity pulse-like ground motions only amplify the story displacement and drift of each floor without moving biggest story drift from 4th floor to 2nd floor like fling step pulse-like ground motions do in case of eight-floor RC frame;Pulse-like ground motion have bigger effects on shear and moment of columns than axial force of columns,the influences of pulse-like ground motions on axial force,moment and shear of columns,in case of four-floor RC frame,drop dramatically with the increasing number of floor,pulse-like ground motions show the same pattern about axial force and shear of columns in case of eight-floor RC frame,while the moment of column increased at the beginning and then decreased with the increasing number of floor.Pulse-like ground motions weaken the moment capacity of columns of RC frame,but nearly change nothing about the shear capacity of columns. |
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