Meeting Overview

1. Benchmarking of Nonlinear Geotechnical Ground Response Analysis ProceduresPEER Lifelines Project 2G02http://cee.ea.ucla.edu/faculty/jstewart/groundmotions/PEER2G02/

2. Meeting Overview • Review results of code usage exercise • Discuss verification plan • Other business

3. Other Business • Subcontracts • Request for contract revision: Dec. 3 2004 • Current status: Davinder Gabhi (2-11-05): The contract between PEER and PEA has been sent to our Sponsored Projects Office for formal paperwork and final signatures.  This has been approved by the Lifelines Program Manager.

4. Other Business • Turkey Flat project • PI is Charles Real of CGS • Workshop Fall 2005 • http://www.quake.ca.gov/turkeyflat.htm • Web posting of code reports • Reimbursements

5. Project Overview Two-year project July 2004 – June 2006 Three general tasks: Develop parameter selection protocols Verification studies Parametric studies Effects of parametric variability Benefits of NL relative to EL and application in PSHA

6. Schedule

7. Today’s Agenda • Review of code usage exercise (Stewart) • Objective and plan for work • Reporting/response protocols • Common issues for all codes • Code specific issues • Developer presentations • 10-15 min each • Selection of model parameters and input motions • Analysis results and comparison to UCLA results • Reasons for differences • Verification plan (Stewart)

8. Objective of Code Usage Exercise From September meeting minutes: “One of the urgent needs is to establish protocols for evaluating input parameters and checking that the results provided are “reasonable.” This gets to the issue of how usable the codes are to users other than the code developers. The establishment of those protocols, and demonstrating that they can be used by novice users, is a key first objective of the project.”

9. Plan for Code Usage Exercise • Described in “white paper” dated 9/29/04 • Developers provide parameter selection and code use protocols • Information for all codes forwarded to UCLA team by mid-October, although some codes unusable in initial form • Parameter values in sand given Vs, r, N, s’ • Parameter values in clay given Vs, r, PI, Su, s’ • Parameter uncertainty • List of common errors and unreasonable results associated with those errors Difficult for fitting parameters

10. Plan for Code Usage Exercise • Novice user (AK, JS) runs codes for example sites • Developers run codes in parallel • Based on outcome of above: Refine parameter selection and use protocols, as needed

11. Code Usage Exercise Reporting and response protocols: • UCLA team completes initial report, sends to developer • Developer provides feedback, factual errors in initial reports are corrected • Final report prepared and returned to developers with comments for code and/or user manual improvement • Developer response: • Agree with comment and will make change • Agree with comment but insufficient time and resources to make change • Disagree with comment and change will not be made Would like to post (3) and (4) to project web page – agree?

12. Code Usage Exercise

13. Code Usage Exercise Common issues for all codes: • Use of reference strain (gr) in lieu of shear strength (tmo) to describe G/Gmax and b curves • Input motion specification (outcropping versus within) • Layer thickness criteria

14. Code Usage Exercise – Common Issues Reference strain issue • Typical existing parameters to describe backbone curve: • Gmax • tmo • Various fitting parameters • Ref. strain definition gr=tmo/Gmax • Problem: • Parameter tmo is unknown, especially at depth, for most sites • No guidelines in users manuals

15. Code Usage Exercise – Common Issues Reference strain issue • Possible solution when data on tmo unavailable: • Estimate gr using guidelines from Darendeli and Stokoe or from material specific G/Gmax curve (gr where G/Gmax = 0.5) • Calculate tmo as gr Gmax • Then use fitting parameters • Provides excellent fit (in all codes) to G/Gmax curve • How does gr Gmax compare to tmo (when known) gr = f(PI, OCR, s’), defined uncertainty a = 0.92

16. Code Usage Exercise – Common Issues Input motion issue • Two general formulations • Lumped mass (DMOD, DEEPSOIL) • Continuum (OpenSees, SUMDES, TESS) • Extensive email discussion on correct form of input motion when recording is from outcropping site: • Modify recorded outcropping motion to within (using SHAKE) • Original outcropping motion

17. Code Usage Exercise – Common Issues Input motion issue Walt Silva’s thoughts (2-7-05): “I still feel an essential issue is outcrop verses total (in layer) motions. It is simply not acceptable to have a nonlinear code that does not treat control motions as outcrop, there is no good reason for this restriction. To treat control motion as total motion, a nonlinear code can treat the control point as a rigid half space. This is exact for this case. To treat the control motion as outcrop, the control point can be taken as a flexible half-space. I hope this gets clarified at the meeting.”

18. Code Usage Exercise – Common Issues Input motion issue (lumped mass) • Similar to dynamic response of structure • Requires total motion at base as input • From Oct. 2004 correspondence, recommendation was to use SHAKE within motion • Use of outcropping motion may be preferred (following slides…) Graphic: Y. Hashash

19. Test I • Treasure Island soil profile • Linear soil properties • Input motion: outcrop motion • Frequency domain analysis • Input at bedrock+ elastic base • Input at bedrock+ rigid base • Input at outcrop+ elastic base • Input at outcrop+ rigid base Y. Hashash

20. Result of Test I 1 2 3 4 Y. Hashash • Case 2 is correct case • In SHAKE, there are two options to input motion. If inputting at outcrop, • then rock base is treated as elastic. If inputting at bedrock, then rock base • is treated as rigid. Therefore, if choosing bedrock as input, no matter using • rigid base or elastic base, the result is the same

21. Test II • Treasure Island profile • Linear soil properties • Input at bedrock • Time domain analysis • Input motion: outcrop motion • Input at bedrock+ rigid base • Input at bedrock+ elastic base • Input motion: within motion (I convert it from outcrop motion) • Input at bedrock+ rigid base • Input at bedrock+ elastic base • Two red case should have identical result Y. Hashash

22. Result of Test II (outcrop motion + elastic base) is equal to (within motion + rigid base) Y. Hashash

23. Compare time domain and frequency domain analysis 1 2 3 4 Y. Hashash 1. Case 2 is correct one 2. If we follow rules of “outcrop motion + elastic base” and “within motion + rigid base” doing time domain analysis, we can get almost identical result as frequency domain analysis

24. Code Usage Exercise – Common Issues Input motion issue (continuum) • Motion transformed to shear stress time history applied to base of soil column • Wave equation solution implies: • Input could be specified as incident (1/2 of outcropping) • Reflected calculated as part of solution • Total motion taken as incident + reflected • Recommendations from Oct. 2004 correspondence • OpenSees: input is ½ of outcrop (??) • SUMDES: input is full outcrop motion • TESS: user specifies full outcrop, code has ½ modifier built in (??)

25. Code Usage Exercise – Common Issues Layer thickness issue • Soil layers cannot propagate waves with f > fmax = Vs/4H. • Results sensitive to layer thickness, especially at high frequencies • User’s manuals need to make note of this issue

26. Code Usage Exercise – Code Specific Issues • DMOD_2 • DEEPSOIL, v2.5 • SUMDES • TESS • OPENSEES

27. Code Usage Exercise – Code Specific Issues Treasure Island Site Source: Darragh and Idriss, 1997

28. Code Usage Exercise – Code Specific Issues Treasure Island Site: SHAKE results

29. Code Usage Exercise – Code Specific Issues Gilroy II Site Source: Darragh and Idriss, 1997

30. Code Usage Exercise – Code Specific Issues Gilroy II Site: SHAKE results

31. Code Usage Exercise – Code Specific Issues DMOD_2 • MKZ model overestimates the damping at large strain • How to trade off between fitting MR vs. damping curves? • Clearer guidelines for more advanced parameters (gray literature references)

32. Code Usage Exercise – Code Specific Issues DMOD_2: Results Treasure Island Gilroy II Underprediction at high frequency: Possibly due to simplified Raleigh damping?

33. Code Usage Exercise – Code Specific Issues DEEPSOIL • Utilizes modified MKZ model – so similar issues with fit of MR and damping curves as with DMOD: • Damping at large strain is overestimated • How to trade off between good fits of MR and damping curves? • Modified MKZ model includes pressure-dependent coefficients • When use coefficients vs. specifying depth-dependent curves? • Need recommendations for selecting coefficients

34. Code Usage Exercise – Code Specific Issues DEEPSOIL • Viscous damping formulation: • 3 possible formulations • Select matching frequencies that provide good match of the linear time domain and frequency domain solutions • Examples of good and poor matches needed to assist users • Issues with equivalent linear model Figure from Hashash

35. Code Usage Exercise – Code Specific Issues DEEPSOIL: results Treasure Island Gilroy II

36. Code Usage Exercise – Code Specific Issues SUMDES • Used Model 6 for simplified total stress analysis • Problems matching large strain damping • Hr fixed at 0.7726 due to gr definition • Viscous damping contribution not included in code-generated damping plot

37. Code Usage Exercise – Code Specific Issues SUMDES: results Treasure Island Gilroy II Same viscous damping formulation as DMOD (except match frequency specified as 1 Hz): why results so different?

38. Code Usage Exercise – Code Specific Issues TESS • Need to synthesize and update code documentation • Five possible levels of analysis: we use Level 1 • Guidelines needed for selection of higher-level parameters (which are also required for Level 1 analysis) • Good match of MR and damping curves

39. Code Usage Exercise – Code Specific Issues TESS: results Treasure Island Gilroy II

40. Code Usage Exercise – Code Specific Issues OpenSees • Nonlinear soil curves: • Can specify MR, damping calculated automatically per Masing • Can adjust MRiteratively to reduce damping error • Issues of trade off between fitting MR vs. damping curves • Pressure-dependent coefficients option – see DEEPSOIL comments • Viscous damping contribution not included in code-generated damping plot

41. Code Usage Exercise – Code Specific Issues OpenSees • Viscous damping formulations: • 2 options for Raleigh damping • Simplified + Full • Guidelines needed regarding frequencies where damping specified • Clearer guidelines for parameters of more advanced models • Documentation needed for new GUI version of code Figure from Hashash

42. Code Usage Exercise – Code Specific Issues OpenSees: results Treasure Island Gilroy II

43. Code Usage Exercise Synthesis of results • Consistently lower PGA • Amplification at site period relative to SHAKE: • Less for TI • Similar for Gilroy 2 • Mixed results at mid-periods (between site period and PGA) Tdegraded = 1.04s Tdegraded = 1.40s

45. Verification Plan • Verification of element behavior • Verification at different strain conditions • Very small strain (visco-elastic) • Small to medium strain • Large strain • Goodness of fit

46. Verification of Element Behavior • Suggested by Kramer • Apply cyclic load to single element at various rates • Plot g vs. t • Look for spurious features at zero crossing, upon unloading, etc. • Is this possible with the codes? Graphic: Hashash

47. Verification at Very Small Strain • Why? • Verify wave propagation part of the codes • Check effects of viscous damping formulations • Check input specification procedure • Take linear frequency domain elastic solution as exact • Compare to time domain elastic solution • Specified: Vs, Dmin, layer thicknesses • Vary: • Profile depth • Layering of Vs • Depth variation of Dmin • Pulse and broadband inputs

48. Vs Verification at Small to Medium Strains • Site selection criteria: • Should be vertical arrays or nearby rock/soil pairs • Deep characterization • Range of input motions • Soft and stiff sites • Reasonably well known dynamic properties • Silva recommended sites: • Lotung • Port Island (liq.) • Gilroy I, II • Kik Net (inquery made regarding data resolution) • Others: • Frasier River, BC • Garner Valley • La Cienega • Turkey Flat

49. Verification at Large Strain • Vertical array data - ? • Centrifuge data • UC Davis (http://cgm.engineering.ucdavis.edu) • RPI ?

50. Verification at Large Strain Available data • UCD Experiment series DKS02, DKS03 • dense unsaturated sand • Input motions: sine sweeps and scaled Santa Cruz LP eqk. • UCD clay experiments • Performed in early 1990s • Refs: Idriss et al. (1994); Fiegel et al. (1998) • Data available? Ref: Stevens et al. 1999