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67 Table continued from p.66 Other--please describe: Haven't used it yet Nonlinear analyses were used by some of our consultants Deep basins typically not performed When we believe that it will reduce the design spectra NA up to the design consultant Rarely NA when large strains occur not typically used None Never is nonlinear analysis required, and rarely is it used. Only for very critical projects have I ever been able to justify its use. Sometimes the motivation is to reduce the seismic demand Do not use non-linear analysis. Not used. 24.) What soil models do you usually use for nonlinear total stress site response analyses (mark all that applies)? [ ] Hyperbolic with Masing criteria [ ] Modified Hyperbolic with Masing criteria (e.g., M-K-Z) [ ]Modified Hyperbolic with non Masing criteria (e.g., MRDF to match both modulus reduction and damping curves) [ ] Cundall-Pyke model [ ] Mohr-Coulomb [ ] Other--whatever model is included in my software--please specify [ ] It is important for the model to match both modulus reduction and damping curves [ ] It is only important that the model matches modulus reduction regardless of the damping curve. TABLE B30 SOIL MODELS FOR NONLINEAR TOTAL STRESS SITE RESPONSE ANALYSES Count Hyperbolic with Masing criteria 4 Modified Hyperbolic with Masing criteria (e.g., M-K-Z) 12 Modified Hyperbolic with non Masing criteria (e.g., 4 MRDF to match both modulus reduction and damping curves) Cundall-Pyke model 2 Mohr-Coulomb 2 Other--whatever model is included in my software-- 9 please specify It is important for the model to match both modulus reduc- 13 tion and damping curves It is only important that the model matches modulus 0 reduction regardless of the damping curve. Table continued on p.68
68 Table continued from p.67 Other-- Don't know We work with the models in DMOD, FLAC, and PLAXIS--trying out different options to see the effects of these changes. up to the design consultant insufficient experience None Strongly prefer to match both modulus and damping curves, but not all software/mod- els do this currently. multiyield plasticity pressure independent We usually use UBCHYST a nonliner total stress model developed at the U of British Columbia- it is important to consider shear failure. Not used. 25.) When is a nonlinear effective-stress (with pore water pressure generation) analysis used or required? [ ] Site class dependent--please list site class [ ] Seismic hazard level--please specify [ ] Structure type--please specify [ ] When porewater pressure ratio exceeds a given value--please specify [ ] Other, please describe: TABLE B31 CONDITIONS FOR NONLINEAT EFFECTIVE-STRESS (WITH POREWATER PRESSURE GENERATION) ANALYSIS SEE NEXT PAGES FOR DETAILS Count Site class 12 Seismic hazard level 6 Structure type 10 When porewater pressure ratio exceeds a given value-- 10 please specify Other 16 Site class dependent--please list site class: Site Class F, or sometimes even for E to lower the seismic design category F Sf F Site Class F for IBC projects and when liquefaction is predicted for DOT projects F, T > 0.5 sec F E,F F F, Liquefiable Table continued on p.69
69 Table continued from p.68 Seismic hazard level--please specify: Other--please describe: high Haven't used it yet Whenever porewater pressure buildup is expect--might be as low as 0.15 Nonlinear analyses were used by some of our to 0.2 g consultants PGA > 0.3 g When liquefaction is an issue or very soft depos- its, or deep basins >0.4 g Used when soil strain levels of equivalent--lin- ear methods exceed limits, for pore pressure Structure type--please specify: generation and liquefaction analysis, to develop response spectra considering liquefied Critical facilities soil effects critical, essential when interested in pore pressure generation Near-shore structures for liquefiable site essential bridges in liquefiable soils up to the design consultant Critical and essential bridges and where lateral spreading is expected. rarely High importance, sensitive NA important insufficient experience to say none When porewater pressure ratio exceeds a given value--please specify: Typically only when potentially liquefiable soils close to 90 eff. overburden are present. 0.8 Never. I have encountered few professionals that 0.5 would dare use such analysis on a design project. around 0.9 or so For larger project we do FLAC analysis with coupled effective-stress analysis and may use the 0.2 results for near surface response spectrum. (limited experience on this) Do not use nonlinear analysis. Ru > 0.3 Not required. 26.) What soil models and porewater pressure generation models do you use in nonlinear effective-stress site response analyses (mark all that applies)? [ ] Dobry [ ] Elgamal [ ] GMP (Green) [ ] Martin-Finn-Seed [ ] Matasovic (Modified Dobry et al. porewater pressure model) [ ] UBC Sand [ ] Other TABLE B32 SOIL MODELS AND POREWATER PRESSURE GENERATION MODELS IN NONLINEAR EFFECTIVE-STRESS SITE RESPONSE ANALYSES Value Count Dobry 3 Elgamal 3 Martin-Finn-Seed 5 Matasovic (modified Dobry et al. porewater pressure 16 model) UBC Sand 8 Other 7 Table continued on p.70
70 Table continued from p.69 Other: Haven't done it yet up to the design consultant insufficient experience to say None Locally developed Multi-yield plasticity pressure dependent, Dafalias-Manzari Not required. Page Six--Evaluation and use of results 27.) What do you consider to be the top three uncertainties in the input to a typical seismic site response analysis? [ ] Low-strain stiffness (represented by Gmax or Vs) [ ] Higher strain stiffness (represented by modulus reduction or backbone curve) [ ] Small strain damping behavior represented by viscous damping [ ] Large strain damping behavior (represented by damping curve or unloadingreloading model) [ ] Soil layer thickness [ ] Depth to bedrock [ ] Character of bedrock (Vs, modulus reduction and damping behavior) [ ] Input motions [ ] Other TABLE B33 THE TOP THREE UNCERTAINTIES IN THE INPUT TO A TYPICAL SEISMIC SITE RESPONSE ANALYSIS Value Count Low-strain stiffness (represented by Gmax or Vs) 11 Higher strain stiffness (represented by modulus reduction 15 or backbone curve) Small strain damping behavior represented by viscous 5 damping Large strain damping behavior (represented by damping 17 curve or unloading-reloading model) Soil layer thickness 1 Depth to bedrock 13 Character of bedrock (Vs, modulus reduction and damping 6 behavior) Input motions 19 Other 7 Other: uncertainty in pore pressure models This assumes that Vs profiles are either available or can be estimated with confidence. If the Vs Information is not available, then Vs would move to the top of the list. All liquefaction resistance properties, permeability all of them depth to B-C boundary
