Report - PEER - University of California, Berkeley

4.1.2 Elastic vs. Inelastic ModelsFigure 7 (right) also shows the difference between linear and nonlinear responses ofthe multiple frame model. In some cases, particularly for the 2%/50 year records, thevariation is significant. However, for practical purposes, the differences are smallenough to be ignored. The elastic model is based on effective stiffness properties(40% of initial stiffness for columns and 60% of initial stiffness for beams). TheEDP-IM relationship and P(DV) distribution for the two cases are displayed in Figure8. The results suggest that a simplified elastic model with effective stiffnessproperties is a reasonable approach to modeling such systems that are flexurallydominant and flexible (initial period greater than 0.5 seconds). When the hazardcurve is integrated, the closure probability in 50 years for the nonlinear model is0.95% and 0.85% for the linear model.Simulation #35with P-Delta30no P-Delta25201510500 2 4 6Peak Drift (%)Simulation #109876Nonlinear Model (2%/50)5Linear Model (2%/50)4Nonlinear Model (10%/50)3Linear Model (10%/50)2Nonlinear Model (50%/50)1Linear Model (50%/50)00 5 10EDP, Drift (%)Figure 7. Effect of modeling details on peak system response.EDP, Drift (%)4321Nonlinear ModelElastic ModelP(Closure|IM)0.50.40.30.20.1Nonlinear ModelElastic Model00 1 2 3 4IM, Sa (T), g00 1 2 3 4IM, S a (T), gFigure 8. EDP-IM relationship and P(DV) for different member models.73