A Study On Estimating Target Displacement In Capacity-Demand-Diagram Methods For Seismic Design

With the concept of performance based seismic design (PBSD) proposed and itsapplication in Civil engineering community, people began to pay attention to NonlinearStatic Method. It is a research hotspot to assess the seismic performance relying onNonlinear Static Method in Civil engineering community. Estimating the targetdisplacement is an important part of PBSD in both pushover method and MPA method.Nonlinear Static Method will be actually applied to PBSD when finding a simple andeffective approach to estimate target displacement.This paper relies on capacity-demand-diagram methods, establishes inelasticdemand spectra based on standard design response spectrum and so that can find asimple and effective approach to estimate target displacement. To achieve these goals,the author considers two issues. On one hand, how to establish inelastic demand spectrabased on standard design response spectrum. On the other hand, how to find thedifferences between some methods that are to estimate target displacement by someexample models.To solve these problems, this paper firstly summarizes the research of PBSD andNonlinear Static Method, focuses on the basic principle of capacity-demand-diagrammethods. Then, there is a research on the basic ideas and operating points of FEMAdisplacement coefficient method, ATC-40inelastic demand spectrum method andR_y-μ-Tinelastic demand spectrum method. Also, by PK program in PKPM, theauthor designs11RC plane frame structures whose floors is respectively3,7,12,15and which is respectively located in zone where fortification intensity is6,7(0.1g),8(0.2g). The11RC plane frame structures are selected as the inelastic analysis objectsby OpenSees software. At last, based on time history analysis results, this paper findsthe differences between the above methods that are to estimate target displacement.After above works, the main conclusions of this article are:①The ATC-40inelastic demand spectrum method is based on theories ofequivalent damping and secant stiffness. The theory has some defects, so that it usuallyunderestimates displacement response of structures. There are some differences betweenR_y-μ-Tmodels. Usually, the target displacement is maximal in Newmark-Hall modeland is minimal by Zhai Changhai model. FEMA displacement coefficient method isbased on empirical formula that parameters are uncertain. The error of estimating target displacement by FEMA displacement coefficient method is much larger.②Based on our standard design response spectrum, the capacity-demand-diagrammethods is different from foreign. In ATC-40inelastic demand spectrum method, theerror is much discrete. The error byR_y-μ-Tinelastic demand spectrum method isminimal. Comprehensively considering the factors of site classification and design ofseismic grouping, the author suggests Lu Xilin model which is little discrete asR_y-μ-Trelation. Otherwise, the principle of equal displacement can be as a simpleand effective method to estimate target displacement which is simple operation, lesstime-consuming and the error could be accepted in Civil engineering community.③Inelastic demand spectrum is high because the descent stage of standard designresponse spectrum is a little high. Thorefore, the target displacement would be larger.The factor gives a greater impact on structure with long-period.