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Published on January 22, 2008

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Benchmarking of Nonlinear Geotechnical Ground Response Analysis Procedures PEER Lifelines Project 2G02 http://cee.ea.ucla.edu/faculty/jstewart/groundmotions/PEER2G02/ :  Benchmarking of Nonlinear Geotechnical Ground Response Analysis Procedures PEER Lifelines Project 2G02 http://cee.ea.ucla.edu/faculty/jstewart/groundmotions/PEER2G02/ Meeting Overview:  Meeting Overview Review results of code usage exercise Discuss verification plan Other business Other Business:  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. Other Business:  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 Project Overview:  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 Schedule:  Schedule Today’s Agenda:  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) Objective of Code Usage Exercise:  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.” Plan for Code Usage Exercise:  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 Plan for Code Usage Exercise:  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 Code Usage Exercise:  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? Code Usage Exercise:  Code Usage Exercise Code Usage Exercise:  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 Code Usage Exercise – Common Issues:  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 Code Usage Exercise – Common Issues:  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 Code Usage Exercise – Common Issues:  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 Code Usage Exercise – Common Issues:  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.” Code Usage Exercise – Common Issues:  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 Test I:  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 Result of Test I:  Result of Test I 1 2 3 4 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 Y. Hashash Test II:  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 Result of Test II:  Result of Test II (outcrop motion + elastic base) is equal to (within motion + rigid base) Y. Hashash Compare time domain and frequency domain analysis:  Compare time domain and frequency domain analysis 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 1 2 3 4 Y. Hashash Code Usage Exercise – Common Issues:  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 (??) Code Usage Exercise – Common Issues:  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 Code Usage Exercise – Code Specific Issues:  Code Usage Exercise – Code Specific Issues DMOD_2 DEEPSOIL, v2.5 SUMDES TESS OPENSEES Code Usage Exercise – Code Specific Issues:  Code Usage Exercise – Code Specific Issues Treasure Island Site Source: Darragh and Idriss, 1997 Code Usage Exercise – Code Specific Issues:  Code Usage Exercise – Code Specific Issues Treasure Island Site: SHAKE results Code Usage Exercise – Code Specific Issues:  Code Usage Exercise – Code Specific Issues Gilroy II Site Source: Darragh and Idriss, 1997 Code Usage Exercise – Code Specific Issues:  Code Usage Exercise – Code Specific Issues Gilroy II Site: SHAKE results Code Usage Exercise – Code Specific Issues:  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) Code Usage Exercise – Code Specific Issues:  Code Usage Exercise – Code Specific Issues DMOD_2: Results Underprediction at high frequency: Possibly due to simplified Raleigh damping? Treasure Island Gilroy II Code Usage Exercise – Code Specific Issues:  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 Code Usage Exercise – Code Specific Issues:  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 Code Usage Exercise – Code Specific Issues:  Code Usage Exercise – Code Specific Issues DEEPSOIL: results Treasure Island Gilroy II Code Usage Exercise – Code Specific Issues:  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 Code Usage Exercise – Code Specific Issues:  Code Usage Exercise – Code Specific Issues SUMDES: results Same viscous damping formulation as DMOD (except match frequency specified as 1 Hz): why results so different? Treasure Island Gilroy II Code Usage Exercise – Code Specific Issues:  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 Code Usage Exercise – Code Specific Issues:  Code Usage Exercise – Code Specific Issues TESS: results Treasure Island Gilroy II Code Usage Exercise – Code Specific Issues:  Code Usage Exercise – Code Specific Issues OpenSees Nonlinear soil curves: Can specify MR, damping calculated automatically per Masing Can adjust MR iteratively 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 Code Usage Exercise – Code Specific Issues:  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 Code Usage Exercise – Code Specific Issues:  Code Usage Exercise – Code Specific Issues OpenSees: results Treasure Island Gilroy II Code Usage Exercise:  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 Verification Plan:  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 Verification of Element Behavior:  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 Verification at Very Small Strain:  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 Verification at Small to Medium Strains:  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 Verification at Large Strain:  Verification at Large Strain Vertical array data - ? Centrifuge data UC Davis (http://cgm.engineering.ucdavis.edu) RPI ? Verification at Large Strain:  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 Goodness of Fit:  Goodness of Fit Anderson (2004) criterion Based on quality of fit for 10 ground motion parameters Scores range from 0 to 10 (perfect agreement) for each parameter Overall score = average of 10 scores from each parameter

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