Theory And Method Of Performance-Based Seismic Design Of Structures With Passive Energy Dissipation Systems

Passive energy dissipation is an emerging new technology that may be used to improve the seismic performance of buildings by providing extra damping.Structural passive control systems have been developed with a design philosophy different from that of the traditional seismic design. A structural installed with energy dissipation devices dose not rely on the plastic hinges to consume the input seismic energy.On the contrary,the dissipation of energy is concentrated on the some added dampers so that the damage to the main structure is reduced and the main functions of the structure can then be possibly preserved.The philosophy of performance-based earthquake engineering,which is to design a structural system to sustain a pre-defined level of damage under a specified level of earthquake intensity,has been widely accepted by the community of earthquake engineering and would be incorporated into the seismic codes of next generation. Although much research on performance-based design of conventional structures has been carried out worldwide,investigation focused on performance-based design and analysis of structures with energy dissipation devices has been lacking.The principal objective of this dissertation is to develop simplified approaches of design and analysis of structures incorporating passive energy dissipation systems.The work presented in this dissertation includes:1.Development of simplified methods of analysis for elastic and inelastic SDOF structures with energy dissipation devices.The base shear for a highly damped structure is equal to the mass times the actual spectral acceleration,rather than the pseudo-acceleration,due to damping effect.The design formulation of actual spectral acceleration is derived in this paper for exact estimate of base shear for a damped structure.A structure added with the damper can be modeled as a linearly elastic one with the long period and high damping ratio when estimating its seismic response by response spectrum method.So evaluation of the effective period and effective damping ratio are key points in the simplified analysis of a damped structure.Formulas of these two quantities are provided in this paper for elastic and inelastic SDOF structures with various energy dissipation devices and employed for assessment of their seismic performance under a major earthquake based on the capacity spectrum method.In addition,the effect of the brace stiffness on the damper efficiency and equivalent transformation between Maxwell and Kelvin model for damper-brace assembly are also investigated.2.Development of performance-based seismic design and analysis approach for structures with nonlinear fluid viscous dampers.Mechanical properties of nonlinear FVD(Fluid Viscous Dampers)are analytically investigated.Equivalent linear viscous damping ratio provided by nonlinear FVD installed in buildings is introduced.Load combination factors used for evaluation the response of the structure with supplemental damping systems at the stage of maximum acceleration are given.A simple design and analysis procedure for the building incorporating nonlinear FVD is proposed based on Chinese design response spectrum,in which the damping coefficient of damper is determined such that the horizontal component of the damper force is proportional to the corresponding story shear force,demand.Application of the simple procedure is illustrated using an example.Comparing the earthquake-induced demands for the structure with nonlinear FVD determined by the simple method of analysis and the rigorous time history analysis, it is demonstrated that the presented method is effective and straightforward for design of buildings with nonlinear FVD,particularly at the stage of preliminary design.3.Analytical study and simplified design of toggle-brace-damper systems.Various damper installation configurations,particularly Constantinou toggle-brace-damper systems,are detailed and compared each other in this paper.Followed by is the introduction of improved installation configuration of the toggle-brace-damper,in which the damper and brace elements are connected directly to the beam-column joints.Damper displacement and force magnification factors are derived and geometry constraint conditions for obtaining desired damping ratio are established for practical applications.A simplified approach for design and analysis of a structure with the improved toggIe-brace-damper systems are proposed based on the Chinese design response spectrum.The accuracy of this method is verified by nonlinear dynamic analysis.It is found that this improved damper installation configuration not only decreases significantly floor displacement response but reduces story shear demands when compared with the conventional installation configuration of diagonal brace-damper.4.Approximate establishment of pushover curves for frame with supplemental dampers based on plastic analysis.Nonlinear static procedure is used to evaluate the seismic performance of a newly designed or existing structure with passive energy dissipation systems.The pushover curve of a structure needs.to be established before seismic performance evaluation.This paper introduces a simplified method based on plastic analysis theory to rapidly and effectively construct the idealized bilinear pushover curve for the moment resisting frame added with viscoelastic dampers and metallic yielding dampers,without,the aid of the structural analysis program. Application of the presented method is illustrated with an example.Comparing the results determined by the proposed method using three force distribution patterns with those obtained by computer analysis,it is demonstrated that the presented simple method produces the exact estimate of the pushover curve provided the beam sideway mechanism develops in the primary structure.5.Seismic design of structures with viscous dampers based on improved capacity spectrum method.The common practice for design of supplemental dampers in existing buildings requires performing the iterative computation to achieve a given performance objective. In the context of performance-based seismic design,a simplified yet effective design procedure for viscous dampers is presented based on the improved capacity spectrum method,in which the target displacement of a structural to be retrofitted is determined as the intersection of the locus of performance points and its capacity curve.The amount of added viscous damping required to meet a given performance objective is evaluated,from the difference between the total demand for effective damping and inherent damping plus equivalent damping resulting from hysteretic deformation of system.Application of the method to inelastic SDOF is illustrated with two examples,using Chinese design response spectrum and mean response spectrum generated by an ensemble of earthquake ground motions recorded on the firm sites.Nonlinear dynamic analysis results indicate that the maximum displacements of structures installed with supplemental dampers designed in accordance with the proposed method match well with the given target displacements. Subsequently this method is extended to performance-based seismic retrofit of a 10-story building. In order to take into account higher modes effect three lateral load patterns are used to obtain the capacity curves.The required amount of supplemental damping to meet a given performance objective is distributed throughout the stories of the original structure using three proposed distribution patterns of dampers.The final design is verified by time history analyses using a artificial earthquake record compatible with the design spectrum.According to the analysis results, the roof displacements of the structure retrofitted by viscous dampers match well with the given target value and the interstory drift ratios of the designed structure essentially meet the given performance objective.6.Development and validation of seismic performance assessment methods for structures with energy dissipation systems based on Chinese design response spectrum.Four seismic performance evaluation procedures,i.e.,Linear Static Procedure,Linear Dynamic Procedure, Nonlinear Static Procedure and Nonlinear Dynamic Procedure,for conventional structures are introduced.Subsequently these four procedures are applied to seismic performance assessment of structures with energy dissipation systems.The step-by-step methods for Linear Static Procedure, Linear Dynamic Procedure and Nonlinear Static Procedure are proposed based on Chinese design response spectrum.Application of these three simplified methods of analysis is illustrated with an example.Comparing the earthquake-induced demands for the 3-story building obtained by simplified methods of analysis and nonlinear dynamic analyses,the accuracy of various methods in estimating seismic demands on the damped structures is evaluated.