Energy-based Seismic Design And Damage Performance Control Of Precast Concrete Frames With Semi-rigid Connections

The application of precast concrete structures indicates that good seismic performance can be achieved.However,unreasonable design on connections and structures also caused serious earthquake-induced damage.Design of precast concrete(PC)structures in current codes are limited to the capacity design in the elastic stage and appropriate performance-based seismic design in plastic stage is still a lack.Moreover,structures with semi-rigid connections are not considered properly.As a consequence,the application and development of PC structures are limited to a certain extent,especially in high-rise buildings and high seismic intensity area.The concept of energy-based seismic design can reflect the cumulative actions of ground motions on structures and has obvious advantages in the plastic design and damage control.However,the relation between the energy-based seismic design and current seismic codes is not clear,and the energy demand and capacity of a structure are closely related to its structural characteristics.As a result,general design approach has not been established.For PC structures with semi-rigid connections,the energy-based seismic design has better applicability because of the concentrated energy dissipation in connections.Study on the key issues in the energybased seismic design with the consideration of characteristics of PC structures,multi-level seismic performance design can be realized,and the effect of semi-rigid connections on the controlment of damage performance can be exploited.The energy-based seismic design and damage performance control of PC frame structures with semi-rigid connections are studied as the research object in this thesis.To estimate the hysteretic energy demand of the structure within the current seismic design framework,codecomplaint input and hysteretic energy design spectra are proposed,together with the derivation of the hysteretic energy distribution among stories.Estimation of the multi-level energy dissipation capacity of the structure is determined based on the low-cycle fatigue model of connections and the energy dissipation mechanism control of the structure.On the basis of the above research,the damage-oriented seismic design procedure is proposed.Furthermore,the controlment of multi-level seismic damage performance of the structure by the hybrid arrangement of connections is studied.The achievements of this thesis are as follows:(1)Input and hysteretic energy design spectra consistent with the background of seismic code is established,through the combination of the theoretical derivation and time history analysis of the response of the single degree-of-freedom(SDOF)system.The relation model between the earthquake input energy and pseudo acceleration of a ground motion is derived based on the frequency domain response of the SDOF system,and then the design input energy spectrum can be obtained in accordance with the code-specified design response spectrum.The spectral model of the input-to-hysteretic energy ratio is established through the time-history analyses with the combination of theoretical discussions.The ground motion selection principle based on the fitting of the input energy spectrum is proposed as the supplement of the code-specified principle.The study indicates that the design energy spectra combined with the theoretical model fit well with the results of time history analyses.The proposed energy spectra have good applicability in the estimate of input energy and hysteretic energy demand of PC frame structures.The ground motion selection principle based on the input energy spectrum can limit the input energy and hysteretic energy demand of the structures within a range close to the design spectra.(2)The bending-shear story model of PC frame structures with semi-rigid connections is established and the distribution of hysteretic demand within stories is derived.The bending-shear story model is established based on the derivation of the stiffness matrix of the precast beam element considering the location and stiffness of the semi-rigid connections,which provides a simplified method to calculate modal parameters.Based on the bending-shear story model and the assumption of modal decomposition,an equation for the estimate on the hysteretic energy demand distribution within stories is derived and expressed in a form related to modal parameters.The accuracy of the estimate equation is verified through time history analyses of the structures.The parameter influence study of the connections on the hysteretic energy distribution is also provided.The study demonstrates that the bending-shear story model can reasonably reflect the vibration characteristics of PC frame structures and the accuracy of the predicted hysteretic energy demand distribution is significantly improved compared with the shear story model.(3)The energy dissipation capacity of the semi-rigid connection is derived based on the low-cycle fatigue model,and the energy dissipation capacity of the story and the structure is further determined combined with the controlment of structural energy dissipation mechanisms.The Coffin-Manson low-cycle fatigue model is calibrated by the experiment of PC beam-column specimens with welded connections and the energy dissipation capacity of the connection is then derived.For the case of energy dissipation concentrated on connections,the realization of corresponding energy dissipation mechanisms is proposed through the parameter influence analysis of connection parameters on the location of plastic hinges.On this basis,the energy dissipation capacity of the story is derived and approximately expressed as a function of the inter-story drift ratio.The study indicates that the low-cycle fatigue model is applicable to characterize the connection behavior of semi-rigid PC connections,and its energy dissipation capacity decreases with the increase of the plastic rotation amplitude.The structural energy dissipation mechanisms can be controlled by the design of performance parameters of the connections.(4)The hysteretic energy-displacement formatted capacity and demand spectra are established,and the damage-oriented energy-based design method is proposed with the determination of performance point.The energy dissipation capacity of the equivalent SDOF system of the structure is derived based on the low-cycle fatigue model of connections and expressed as a function of the modal displacement to form the capacity spectrum.The demand spectrum is generated by expressing the demand under a ground motion in the form consistent with the coordinates of the energy dissipation capacity spectrum.The damage-oriented capacity spectrum is obtained according to the relation between the connection damage and structural damage.The performance point is determined by the intersection of the capacity and demand spectrum,and an energy-based seismic design method is proposed.The reasonability of the derived energy dissipation capacity spectrum and the applicability of the design method is verified by the numerical analysis of a PC frame structure.The results illustrate that the derived capacity spectrum fit well with the numerical results.Moreover,the seismic performance of the structure can be satisfied through the design of the yielding moment of the semi-rigid connections.(5)Considering the hybrid arrangement of the semi-rigid connections,the design and adjustment of connection performance parameters based on multi-level seismic damage performance of the structure is established.The relation between the connection location and stiffness and the inter-story drift ratios of the structure is studied based on the simplified shear-bending story model,and the design of connections based on the control of inter-story drift ratios under the frequent-level earthquake is proposed.For the damage control of the structure under the rare-level earthquake,the design method of the connection performance parameters in plastic stage based on objective global damage and damage distribution is established.The failure modes and collapse margin ratios of the structures with different types of hybrid connections are analyzed,and the applicability are discussed.The research indicates that the control of inter-story drift ratios and damage under frequent-level and rare-level earthquakes,respectively,can be achieved through the adjustment of stiffness and yield moment of the connections.The hybrid type of connections all located on the beams is suitable to achieve uniform damage distribution,while the type with connections on both beams and columns is more suitable for concentrated damage.