Practices and Procedures for Site-Specific Evaluations of Earthquake Ground Motions (2012) / Chapter Skim
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From page 47... ...
Bray, "Simplified tion Against Vertical Array Data," Geotechnical Earth Frequency Content Estimates of Earthquake Ground quake Engineering and Soil Dynamics IV Congress Motions," Journal of Geotechnical & Geoenvironmental 2008 -- Geotechnical Earthquake Engineering and Soil Engineering, Vol.
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From page 48... ...
Chin, "Hysteretic Damp- Youd, T.L., "Compaction of Sands by Repeated Shear Strain ing Correction and Its Effect on Non-Linear Site Response ing," Journal of Soil Mechanics and Foundation Divi Analyses," Geotechnical Special Publication, Sacra- sion, Vol.
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From page 49... ...
shear wave velocity of the top 30 meters NL: Nonlinear R : Rayleigh damping coefficient PEER: Pacific Earthquake Engineering Research Center : damping or coefficient in Newmark-type numerical inte gration of equation of motion PI: Principal Investigator R : Rayleigh damping coefficient PSHA: Probabilistic Seismic Hazard Analysis : shear strain pwp: pore water pressure c: cyclic shear strain ReMI: Refraction Microtremor c: cyclic shear stress RVT: Random Vibration Theory tar: Target damping ratio SASW: Spectral Analysis of Surface Waves : Wilson time stepping coefficient sCPT: seismic Cone Penetration Test : mass density of soil SFSI: Soil-Foundation-Structure Interaction (the same as SSI: Soil-Structure-Interaction) 1-D: One dimensional SPT: Standard Penetration Test 2-D: Two dimensional SSI: Soil-Structure Interaction 3-D: Three dimensional UHRS: Uniform Hazard Response Spectrum CMS: Conditional Mean Spectrum USAEC: United States Corps of Engineers COSMOS: The Consortium of Organizations for Strong Motion Observation Systems USGS: United States Geologic Survey
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From page 50... ...
This study will help establish and improve the state of practice, providing a summary of best design practices, as well as identifying research and development needs on this important topic. This questionnaire will help us understand the current practice in site specific analysis of ground motions at selected state departments of transportation and will help us identify some of the challenges encountered when conducting the analyses.
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From page 51... ...
Other -- please describe 7.) Of the total number of site response analyses you perform, indicate the approximate percentages that fall within each of the following categories: One-dimensional equivalent-linear: _________________________________ One-dimensional nonlinear total stress (no pore water pressure)
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From page 52... ...
Please describe validation/verification requirements you have for computer code usage. Page Three -- Seismic hazard motion input required for site response analysis Note for the following questions: Input ground motions are required for performing site response analysis based on specific hazard levels.
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Page Four -- Soil profile input information required for site response analysis 16.) What special geotechnical field and laboratory investigations do you require/perform to obtain information suitable for site response analysis?
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From page 54... ...
What soil models and porewater pressure generation models do you use in nonlinear effective-stress site response analyses (mark all that applies)
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From page 55... ...
What output do you use from site response analysis?
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From page 56... ...
for liquefaction analyses, how often do you do so by means of site response analyses (as opposed to using the simplified method)
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From page 57... ...
Your manual has provisions for site response analysis/provide title and web link TABLE B3 RESPONDENTS WHO USE GUIDELINES AND MANUALS FOR SEISMIC SITE RESPONSE Count Your agency has a manual for seismic design 12 Your manual has provisions for seismic site 10 response analysis
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From page 58... ...
Army Corps of Engineers EM110-2-6050 8 AASHTO LRFD Specifications 9 http://www.dot.ca.gov/hq/esc/earthquake_engineering/SDC_site/ 10 Geomotions 11 ODOT Geotechnical Design Manual ftp://ftp.odot.state.or.us/techserv/Geo-Environmental/Geotech/ GeoManual/FinalGDM12-10-09/Volume1GeotechDesignManualFinal_Dec2009.pdf 12 http://www.wsdot.wa.gov/Publications/Manuals/M46-03.htm 13 http://www.scdot.org/doing/bridge/bridgeseismic.shtml, http://www.scdot.org/doing/bridge/ geodesignmanual.shtml 14 GA DOT website 15 http://www.dot.ri.gov/documents/engineering/br/RILRFDBridgeManual.pdf Page Two -- Criteria and programs used 5.) When is the use of code-based site factors acceptable for characterizing site effects?
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From page 59... ...
Other, please describe: TABLE B7 CIRCUMSTANCES WHEN SITE RESPONSE ANALYSIS IS REQUIRED Count Site class dependent 27 Seismic hazard 14 Ground conditions (e.g., liquefiable soils, or organic 28 soils, or very soft soils subjected to strong shaking) Structure Type 19 Always 12
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From page 60... ...
2 hazard level not covered by codes 3 PBA > 0.2 g 4 PGA > 0.6 g and the site is near major fault(s) capable of generating large earthquakes 5 PGA values that could result in soil nonlinearity or liquefaction 6 High 7 high ground motions 8 PGA > 0.15g 9 For certain conditions specified by CBC 2010 10 When the design is required for higher hazard level than the 2500 year return earthquake 11 high hazard TABLE B10 GROUND CONDITIONS WHEN SITE RESPONSE ANALYSIS IS REQUIRED 1 Liquefaction 2 Liquefiable soils, or organic soils 3 Site class F sites 4 F sites, deep E sites 5 Liquefiable site 6 Section 6.5.1.4 in ODOT GDM 7 Sites with soft soils that display significant degradation of strength and stiffness under strong ground shaking.
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From page 61... ...
7 Essential Bridges 8 Critical or essential bridges -- or where there is a significant cost associated with use of simplified site factors 9 high risk 10 Critical structures 11 Critical structure or base-isolated structure 12 high importance 13 Nuclear Structure in Safety Category I and II 14 critical structures 15 irregular, special structures 16 For larger projects; e.g., bridges and dams will be required regardless of site class 17 Significant or complicated structure requiring more in-depth analysis for economical design TABLE B12 OTHER CONDITIONS WHERE SITE RESPONSE ANALYSIS IS REQUIRED 1 offshore structures 2 For projects where earthquake time histories at depths are needed for design analysis of the structures. 3 performance-based structural analysis 4 http://www.dot.il.gov/bridges/AGMU%20091.pdf 5 We rely on site class definition based on Method B (N values)
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From page 62... ...
: ____________________ One-dimensional nonlinear -- Effective-stress (with pore water pressure) : ______________ Two- or three-dimensional equivalent-linear: _____________________________________ Two- or three-dimensional nonlinear: ___________________________________________ TABLE B14 SOFTWARE PROGRAMS USED FOR SITE RESPONSE ANALYSIS, NUMBER IN PARENTHESES IS NUMBER OF RESPONDENTS One-dimensional equivalent-linear SHAKE2000 (12)
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From page 63... ...
Prior to completing a 1-D nonlinear effective-stress analysis, the soil liquefaction analysis using the simplified method and the 1-D nonlinear total stress analysis must be completed. Prior to completing a 2-D analysis, a compatible 1-D analysis must be completed along with simplified analysis that will help calibrate the soil models used.
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From page 64... ...
Site specific probabilistic -- describe program [ ] Other, please specify: TABLE B16 METHODS TO DEFINE THE SEISMIC HAZARD AND THE TARGET ROCK RESPONSE SPECTRA- SEE DETAILED RESPONSES UNDER EACH ITEM ON THE NEXT TWO PAGES Value Count USGS Maps 22 Code Provision -- List code 19 Site specific deterministic -- describe program 13 Site specific probabilistic -- describe program 21 Other, please specify: 9 Code Provision Site specific deterministic AASHTO LRFD (USGS 1000 year hazard maps)
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From page 65... ...
Other, please specify: TABLE B17 METHODS TO DEVELOP HAZARD COMPATIBLE GROUND MOTION TIME HISTORIES AT ROCK (FIRST ONE IS SIMPLE SCALING) -- SEE DETAILED COMMENTS ON THE NEXT PAGE Value Count Simple scaling of motions from widely available libraries 18 Rigorous spectral matching (specify method if known)
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From page 66... ...
Other, please specify: TABLE B18 NUMBER OF MOTIONS TIME HISTORIES GENERATED OR REQUIRED FOR A GIVEN HAZARD LEVEL Value Count 3 motions 4 7 motions 10 Other, please specify 20 Other, please specify: 3 real + 1 synthetic This is so seldom done, that we have no standard or requirements. We generally look at perhaps 3.
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From page 67... ...
Other, please specify: TABLE B19 SPECIAL REQUIREMENTS IMPOSED ON THE SUITE OF INPUT GROUND MOTIONS FOR SITES WHERE NEAR FAULTS EFFECTS ARE SIGNIFICANT Value Count None 7 Incorporate directivity 15 Include velocity pulse 14 Use two component motions (e.g., Fault normal/parallel) 16 Check cross-correlation of the input ground motion time 6 histories?
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From page 68... ...
If the objective of the site response analysis is to develop a mean response spectrum for design, then I will use 7 pairs of time histories that are scaled within ±50% of the target spectrum and computed site specific soil amplification factors. If the objective is to evaluate the site response for a given force level specified by the target spectrum, then a suite of 7 spectrally matched time histories that has the seismic characteristics (e.g., near-fault, duration)
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From page 69... ...
Cyclic triaxial, direct simple shear or resonant column tests [ ] Other, please specify: TABLE B22 SPECIAL GEOTECHNICAL FIELD AND LABORATORY INVESTIGATIONS DO YOU REQUIRE/PERFORM TO OBTAIN INFORMATION SUITABLE FOR SITE RESPONSE ANALYSIS Value Count None 4 Direct measurement of shear wave velocity 30 Cyclic triaxial, direct simple shear or resonant column 12 tests Other, please specify: 6 Table continued on p.60
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From page 70... ...
However, we do use in-house RCTS testing when needed. Cyclic hollow-cylinder tests Usually shear wave velocity along with G/Gmax and damping curves out of literature.
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FOR SITE RESPONSE ANALYSIS Count Laboratory testing 11 Darendeli 15 Vucetic-Dobry 20 Seed-Idriss 18 Other, please specify 20 Other, please specify: Honestly not sure EPRI For Peat we may use no G-gamma reduction or Rollins et al. In-house for east coast soils EPRI (1993)
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From page 72... ...
20.) Please include other comments you may have related to the topic of soil profile input TABLE B26 OTHER COMMENTS RELATED TO THE TOPIC OF SOIL PROFILE INPUT Response 1 Georgia is a low risk seismic state and most of this is not required.
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From page 73... ...
Other, please describe: TABLE B27 CONDITIONS WHERE EQUIVALENT-LINEAR ANALYSIS (E.G., SHAKE OR SIMILAR PROGRAM) IS USED OR REQUIRED -- DETAILED DESCRIPTION IS PROVIDED NEXT Count Site class 22 Seismic Hazard 13 Structure Type 19 Other 16 Site class dependent -- please list site class: Site F Site Class F, or sometimes even for E to lower the seismic design category deep E, F, shallow sites Sd or Se or Sf Site Class F C, D, E, & F
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From page 74... ...
non-essential bridges Critical or essential bridges or when the cost of mitigation is high Major tall structures over soft soils Critical structures-hospitals, lifeline highway bridges, power plants, waste containment facilities Often used when structural analysis requires time histories Critical or base-isolated structures medium to high importance important structures important structures important structures Other -- please describe: That is all we have used so far. We rarely use SHAKE, but if the soils are very susceptible to liquefaction, we have been known to do the analysis, but this is not always the case.
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From page 75... ...
Darendeli [ ] Other: TABLE B28 DISTRIBUTION OF EQUIVALENT-LINEAR DYNAMIC SOIL MODEL PROPERTIES USED IN PRACTICE Value Count EPRI 17 Ishibashi-Zhang 6 Iwasaki 3 Seed-Idriss Sand 18 Seed-Idriss Clay 9 Vucetic-Dobry 21 Darendeli 15 Other 10 Other soil models Not sure Others may be considered depending on soil types, or based on lab testing up to the design consultant NA Menq Hardin and Drnevich Table continued on p.
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From page 76... ...
ANALYSIS IS USED OR REQUIRED SEE NEXT PAGES FOR DETAILS Count Site Class 15 Seismic Hazard 11 Structure type 10 Strain amplitude -- please specify 14 Other 18 Site class dependent -- please list site class: Structure type -- please specify: Site Class F, or sometimes even for E to lower the seismic design category critical facilities Sd or Se Very tall structure w period > 5 s (> 4050 story) E&F Essential bridges in liquefiable soils Site Class E deep clay sites or when unusual soil profiles occur -- maybe Essential or critical bridges -- or where lateral spreading could when shallow rock occurs.
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