PEER GMSM Program Recommendations for Selection and Scaling

PEER GMSM Program: Recommendations for Selection and Scaling of Ground Motions and Evaluation of the ATC-58 Procedures Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 1

Collaboration Among Many Researchers • • Program Members: Norm Abrahamson Jack Baker Yousef Bozorgnia Allin Cornell Christine Goulet Curt Haselton • • • Erol Kalkan Nico Luco Tom Shantz Jonathan Stewart Polsak Tothong Jennie Watson. Lamprey • Farzin Zareian Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 2

Collaboration Among Many Researchers • • • Program Collaborators: Arzhang Alimoradi Paolo Bazzurro Greg Deierlein Jamshid Ghaboussi Mahmoud Hachem Charlie Kircher Praveen Malhotra Frank Mc. Kenna Coleen Mc. Quoid • • • Jack Moehle Farzad Naeim Maury Powers Ellen Rathje Nilesh Shome Brian Skyers Gang Wang Andrew Whittaker Bob Youngs Tony Yang Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 3

GMSM Mission • To provide guidance and tools to the engineering community on appropriate GMSM methods for nonlinear dynamic analyses. Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 4

Ground Motion Selection and Modification • Selection based only on seismological principles leads to large variability of results. Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 5

Large Variability in Results • Building Code Mini-Study led by Jack Baker • ASCE 7 -05 • 6. 5 < M < 7. 6 • 0 < R < 30 km • Strike slip events only • Target spectrum exceeded as per code requirements Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 6

Building Code Method Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 7

Building Code Method Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 8

Building Code Method • Median estimates are approximately one sigma above the expected median response. – Bias in results – Implied increase in return period of ground motion • From this small sample there is a factor of 1. 5 difference in median estimates. – Large variability of results Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 9

Ground Motion Selection and Modification • Selection based only on seismological principles leads to large variability of results. • There are two solutions to this problem: – Perform a high end analysis that uses more records – Be smarter about picking records Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 10

Solution 1. High End Analysis • Large number of ground motions • Regression on the results of the nonlinear dynamic analysis • Coupling the regression with ground motion prediction equations gives a best estimate of structural response Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 11

Example building results from over 300 ground motions Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 12

Example building regression • Identify key record properties that are important to building response - this will be building specific. • Perform a regression to determine distribution of EDP as a function of the key properties. • For example: Use spectral values at different periods to model the EDP. Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 13

Example building best estimate of response • Scenario Event - magnitude & distance • Design Event - magnitude, distance & ground motion • Risk Based - full hazard curve for an engineering demand parameter Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 14

Example - Scenario Event Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 15

Example - Design Event Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 16

Example - Risk Based Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 17

Example - Risk Based Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 18

High End Analysis • More time consuming • Highly accurate estimate of both median and variability of structural response Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 19

Solution 2. Smarter Selection • A large number (100 s) of records is impractical in many cases • We want a method of ground motion selection and modification that has a higher degree of accuracy using only a small number of records – Median – Variability - not discussed today • In order to do this we have to know something about the building so we know what’s important for response 20 Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007

Solution 2. Smarter Selection • Objection: The ground doesn’t know the building is there. The motions should be the same no matter what the building is. Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 21

Solution 2. Smarter Selection • There is a distribution of record properties (Dur, PGV, RMS) for a given design event. • These record properties affect the nonlinear response of structures. Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 22

Solution 2. Smarter Selection • IF we could sample the entire distribution of all record properties with the ground motions then the set wouldn’t need to depend on the building. • BUT when using a small number of ground motions it is impossible to capture so many record properties at once. • THEREFORE we have to know which ones are important and select based on those important properties. • In order to do this we have to know something about the structure. Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 23

COSMOS 2006 Results • There are many simplified methods for selecting a small set of records. • Depending on the method used there can be a factor of 3 difference in your results. Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 24

GMSM Mission • To provide guidance and tools to the engineering community on appropriate GMSM methods for nonlinear dynamic analyses. • To do this we need to evaluate the simplified methods and determine which ones produce the desired response. Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 25

GMSM Evaluation Procedure • Identify an application for which the ground motions will be employed. – 4 structural models, 4 - 20 stories – Curt Haselton will discuss • Identify the candidate GMSM methods. – 46 methods are now being looked at – Draft summaries of the methods are available on the GMSM website Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 26

GMSM Evaluation Procedure • Identify the goal of the application. – The building code made me do it – Learn something about the building – PBEE - defined distribution of EDP • We start with median EDP | M, R, Sa this is the building block for other more complicated analyses Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 27

GMSM Evaluation Procedure • Calculate a best estimate of response using a high end analysis to serve as the point of comparison (POC) • Compare the results from each GMSM method with the POC Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 28

GMSM Results 2007 • Overview of Results - Curt Haselton – Bias in results can be reduced by taking into account spectral shape. – In order to reduce the variability between suites of motions the selection must be optimized based on record properties that are important for nonlinear response. – This means we have to know something about the structure. Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 29

GMSM Results 2007 • Evaluation of ATC-58 35% - Farzin Zareian – Time-based selection method overestimates median response for above average ground motion because it ignores spectral shape. – Time-based selection has variability in median estimates of response because the motions are selected from an M, R bin. Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 30

GMSM Results 2007 • Evaluation of ATC-58 35% - Farzin Zareian – Scenario-based selection method overestimates the variability of response because it double counts the ground motion variability at periods other than T 1. Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 31

GMSM Results 2007 • Wrap up - Nico Luco Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 32

Thank You Jennie Watson-Lamprey COSMOS Annual Meeting Technical Session November 9, 2007 33