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47 APPENDIX B Compiled Survey Responses 2.) Do your following responses apply to (check all that applies)? [ ] Your own individual practice [ ] The practice of your office/number of engineers [ ] The practice of your agency/number of engineers TABLE B1 APPLICABILITY OF RESPONSE TO ENGINEERING PRACTICE Respondents Count # of Engineers Range of # of Engineers Ave/Total Your own individual practice 10 The practice of your office 17 93/1298 3500 The practice of your agency 14 49/246 1100 3.) Approximately how many of your projects involve site response analyses in a given year? ( ) 12 ( ) 36 ( ) 712 ( ) 1325 ( ) 2650 ( ) >50 TABLE B2 NUMBER OF PROJECTS INVOLVING SITE RESPONSE ANALYSES IN A GIVEN YEAR No. of Projects Count 12 12 36 3 712 8 1325 3 2650 1 4.) Guidelines and manuals for seismic site response [ ] Your agency has a manual for seismic design; please provide title and web link [ ] 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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48 TABLE B4 GUIDELINES AND MANUALS FOR SEISMIC SITE RESPONSE 1 Caltrans Seismic Design Criteria http://www.dot.ca.gov/hq/esc/earthquake_engineering/SDC_site/ 2 http://www.wsdot.wa.gov/Publications/Manuals/M46-03.htm 3 Internal draft guidelines that are not for public release. 4 http://www.dot.il.gov/bridges/brmanuals.html 5 2009 LRFD Seismic Design Provisions; NCHRP Report 611 6 2009 LRFD Seismic Design Provisions; NCHRP Report 611 7 ASCE 7, ASCE 4, ASCE43-05, NRC RG 1.208; U.S. 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? [ ] Preliminary design [ ] Small structures [ ] Seismic hazard is low [ ] Always [ ] Never [ ] Other, please provide a brief narrative: TABLE B5 CIRCUMSTANCES WHEN THE USE OF CODE-BASED SITE FACTORS IS ACCEPTABLE FOR CHARACTERIZING SITE EFFECTS Count Preliminary design 16 Small structures 12 Seismic hazard is low 14 Always 11 Never 0 Other See next table 17
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49 TABLE B6 ADDITIONAL CIRCUMSTANCE WHEN THE USE OF CODE-BASED SITE FACTORS IS ACCEPTABLE FOR CHARACTERIZING SITE EFFECTS 1 Site Classes A through E 2 All cases except for Site Class "F" locations, which are typically susceptible to liquefaction. 3 Exceptions: Non-ordinary structures as defined in SDC, Soil type F 4 For buildings it is acceptable for sites other than Site Class F, for bridges it is acceptable for site class other than F and when the bridge is not critical, for other structures it depends on the code standards and the criti- cality of the project. 5 More conservative site is assumed. 6 As per AASHTO recommendations, site class F and also as per ODOT GDM Section 18.104.22.168 7 Most structures except when the conditions stated in Q6 below apply. 8 We will generally use the code-based site factors either at the start of a project or to compare/check results from site response analyses 9 Although it is important to understand the general site response behavior in your environment (i.e., if you work in Boston--you should have done at least one site response computation with a typical profile--to understand the local issues. 10 Always, except very large expensive/critical structures 11 For soils other than soft/liquefiable soils 12 We only use for small to mid-size CBC projects. Almost everything else uses some form of NGA. 13 structures of low importance 14 For most of the bridges in New York State being in low seismic zone. 15 When the site is not site class F 16 Code-based site factors are used where seismic hazard is simple (no long duration, directivity, basis) and site conditions are not anticipated to result in a code exceedance, and where the cost impact of conservative design is not significant 17 A. Typically SCDOT uses the site factors for the vast majority of our bridges; however, depending on the bridge a Site-Specific Response Analysis may be required. The SCDOT 2008 Seismic Design Specifica- tions for Highway Bridges and the 2010 Geotechnical Design Manual delineate when a Site-Specific Response Analysis is required. In addition, SCDOT may require a Site-Specific Response Analysis for bridges that are considered major. Currently SCDOT has a research project reviewing and developing new site factors for South Carolina. 6.) When is the use of computer analysis required for site response analysis? [ ] Site class dependent--please list site class [ ] Seismic hazard level--please specify [ ]Ground conditions (e.g., liquefiable soils, or organic soils, or very soft soils subjected to strong shaking, please specify) [ ] Structure type--please specify [ ] 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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50 TABLE B8 SITE CLASS REQUIRED FOR SITE RESPONSE ANALYSIS (NUMBER IN PARENTHESIS IS RESPONDENTS COUNT) F(20), F (for all bridges, T > 0.5 sec), E(10) E (deep sites, high motion, critical bridges), D(3), C(2). When required by code, when unique soil conditions exist, when there appears to be advantage to the client, or when the client requires. Often we will look to the site analysis for higher PGA values and for deeper soil profiles. B. A Site-Specific Response Analysis is required for Site Class F as defined in the 2010 Geotechnical Design Manual. Certain bridge types (i.e., spans greater than 300 feet, etc.) or as determined by SCDOT personnel. See p. 12-22, GDM (2010) TABLE B9 SEISMIC HAZARD LEVEL REQUIRED FOR SITE RESPONSE ANALYSIS 1 We do site specific analysis to determine input parameters for simplified liquefaction analysis. 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 22.214.171.124 in ODOT GDM 7 Sites with soft soils that display significant degradation of strength and stiffness under strong ground shaking. Sites with surficial soil lay- ers that have drastically different strength and stiffness (e.g., soft clay over rock). 8 Deep soils, liquefiable soils, very soft soils 9 Liquefiable soils, deep soft clay profiles, or when the soil profile makes the simplified site factors suspect 10 Any unusual soil conditions--very deep, liquefiable, organic soils--or other soils with unusual behavior, sharp impedance contrasts... 11 liquefiable soils 12 liquefiable soils 13 soft soils such as Bay Mud and liquefiable soils in strong shaking areas 14 large impedance contrast 14 brittle quarry slopes subject to strong shaking 16 Most codes require site response for liquefiable sites 17 liquefiable soils or significant amounts of soft soils 18 liquefiable soils, expected significant site effect, soft soils 19 all conditions that will classify the site as site class F 20 Liquefiable soils 21 liquefiable soils, soft soils 22 same as site class F 23 liquefiable or soft soils, high impedance contrasts
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51 TABLE B11 STRUCTURE TYPE WHERE SITE RESPONSE ANALYSIS IS REQUIRED 1 lifeline, "mega-bridge" structures such as the Knik Arm Crossing 2 Non-ordinary structures as defined in SDC (life line bridges, large toll bridges, etc.) 3 Occ IV, critical facilities 4 high-rise tower >>50 story 5 Base isolation 6 High rises/highly irregular structures that requires dynamic time history analysis to be completed for design, and essential buildings/ structures/bridges. 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) and use USGS maps to calculate the 5% damped design response spectrum 6 client request 7 To be considered in the future 8 Liquefiable Soils 9 Sometimes done when SE is doing sophisticated time history analyses, so more sophisticated ground motion development is warranted. 10 Research 11 We do a computer analysis for bridges in Seismic Performance Category B zones. Georgia does not have and SPC C or D bridges 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): ____________________ One-dimensional nonlinear--Effective-stress (with pore water pressure): ______________ Two- or three-dimensional equivalent-linear: _____________________________________ Two- or three-dimensional non-linear--Total Stress Analysis: ________________________ Two- or three-dimensional non-linear--Effective-Stress Analysis: ____________________
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52 TABLE B13 APPROXIMATE PERCENTAGES OF SITE RESPONSE ANALYSES THAT FALL WITHIN EACH OF THE FOLLOWING CATEGORIES, NUMBER IN PARENTHESES IS NUMBER OF RESPONDENTS One-dimensional equivalent-linear 0% (2), 30% (2), 35% (1) 40% (1), 50% (2), 60% (1), 65% (1), 70% (2), 75% (2), 80% [28, respondents] (2), 90% (1), 100% (13) One-dimensional nonlinear--Total stress (no pore 0% (3), 3% (1), 5% (1), 10% (3), 100% (1), 15% (1), 20% (3), 25% (1), 30% (1), 50% water pressure)  (2), 70% (1), 85% (1) One-dimensional nonlinear--Effective-stress (with 0% (2), 3% (1) 10% (3), 15% (2), 20% (2), 25% (2), 30% (2), 40% (2), 100% (1), always pore water pressure)  in parallel with equivalent linear Two- or three-dimensional equivalent-linear  0% (4), 10% (1), 15% (2) Two- or three-dimensional non-linear--Total Stress 0% (4), 5% (1), 10% (1), 15% (1), 100% (1). usually we run FLAC analysis and use one Analysis  dimensional analysis to get the input motion at the base of the model Two- or three-dimensional non-linear--Effective- 0% (1), 5% (4), 15% (1), 20% (1), 25% (1), 40% (1) Stress Analysis  8.) What computer program(s) do you use for each of the following types of analyses (list more than one if appropriate; leave blank if you do not perform one of these types of analyses)? One-dimensional equivalent-linear: _____________________________________________ One-dimensional nonlinear--Total stress (no pore water pressure): ____________________ 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), SHAKE (10), DEEPSOIL (4), SHAKE 91 (4), PROSHAKE (3), Shake-Edit (1), SCDOT SHAKE, in-house, No limits in the past - any program, Assi- maki and Kausel. One-dimensional nonlinear--Total stress (no pore D-MOD2000 (12), DEEPSOIL (7), FLAC (3), OpenSees (1), SIREN (1), Finite differ- water pressure) ence code developed @ GATech (1) One-dimensional nonlinear--Effective-stress (with D-MOD2000 (13), DEEPSOIL (3), FLAC (4), OpenSees (1), DYNAFLOW (1), various pore water pressure) Two- or three-dimensional equivalent-linear QUAD4M (6), FLAC (3), SIGMA/W (1), Quake/W (2), SUMDES (1), SASSI (1), ABAQUS (1), Seisab (1) Two- or three-dimensional non-linear FLAC (8), ABAQUS (2), PLAXIS (2), Dynaflow (1),
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53 9.) Please describe validation/verification requirements you have for computer code usage. TABLE B15 VALIDATION/VERIFICATION REQUIREMENTS FOR COMPUTER CODE USAGE Count Response 1 Compare with code spectra 1 Comparison between different codes; comparison to known solutions 1 Comparison between different computer codes. 1 Downhole array data, centrifuge experimental studies 1 None used 1 Peer review 1 SHAKE--verified according to nuclear standards Deepsoil--used verification from literature 1 Site Response Analysis has been done by the Consultants. 1 We have been using FLAC and SHAKE for a long time and have developed a feel for it. 1 Described in Kwok et al. paper in JGGE 1 in-house procedure 1 None 1 Verify total stress between DMOD and SHAKE under small PBA where nonlinearity is minimal. 1 Peer review of non-linear Comparison of equivalent-linear, non-linear, and predicted ground motions of code and attenuation models. 1 Compare with previous studies--Check strain levels to see if 1-D equiv. lin. is applicable--Check stress levels to see if 1-D equiv. lin. is applicable--Check 2-D equiv. lin. results with 1-D equiv. lin.--Check 1-D total stress and effective-stress results with 1-D equiv. lin.--Do parametric runs to check model sensitivity (input motions, G-gamma curves, depth to bedrock, Vs). 1 All of the site response work I do is for research purposes. We use vertical array data to validate the code and make recommendations on site response methodology. 1 Typically, validation requirements involve an alternate calculation showing similar/identical results. However, critical and nuclear projects have required NQA-1 software V&V standards, which are much more stringent. 1 Prior to completing a 1-D nonlinear total stress analysis, a equivalent-linear must be completed. 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. I would not consider a 3-D analysis for design unless the earthquake loading can be modeled in 3-D and that research has shown the soil models available are adequate for 3-D analysis. 3-D modeling may be used to augment the 2-D modeling for design. 1 Varies highly by project. Some projects have no requirements. Some DOTs require only software from "pre-approved lists" be used. NRC and DOE require highest levels of V&V. 1 We are now using CSI Bridge (SAP) and we are in the process of working out our differences with our geotechnical engineers regard- ing liquefaction. 1 Check output (shear stress, strain levels, etc.) to see how they compare with reasonable ranges for the modeled soils, compare spectra to results from other previous analysis of sites with similar conditions. 1 Compare several programs of similar capabilities and against case studies with documented field data of performance. Some centri- fuge tests as well. 1 During our extensive seismic retrofit program (1990 to 2000) we validated SHAKE with recordings from downhole arrays. 1 First let me explain that if we are using an effective-stress analyses, we are always conducting total stress analyses with the same pro- gram. So I made the numbers for these methods the same. We rarely would conduct a nonlinear total stress analysis by itself, because we don't find many sites that would warrant only this type of analysis. This is a little different for PLAXIS and FLAC where we have conducted seismic slope stability analyses for clay slopes. Now regarding calibration, we try to validate use of the code when we receive it by comparing to problems in the user's manual. If a person is running the code for the first time, we make sure he/she can validate the code against the user's manual. For equivalent-linear SHAKE analyses, we validate by checking input/output during our QA/QC process. We will also run suites of EQ records to define a range of motions, and we will vary the soil model to evaluate typical response. We will also compare against code-based site class factors (though usually these differ). We follow much the same process for the nonlinear codes. We will also compare total stress from SHAKE versus DMOD. We will also calibrate the soil model against lab and field data. For FLAC and PLAXIS we would calibrate a column versus SHAKE for the free field. 1 Validation checked by running results in Bridge Pier Program and looking at changes in footings and column sizes. 1 C. According to Chapter 26 of the GDM (2010) commercially available software packages are typically produced by either a univer- sity or software development firm and sold for profit. Software developed in this manner normally goes through extensive QA/QC prior to being sold. Therefore, the only documentation SCDOT requires for these software packages is the contact information for the developer. Software obtained from the FHWA website requires no additional information. 1 For NQA1 projects, we do have a V&V process. For all other projects, we rely on the V&V done by the vendor of the commercial software.
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54 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. The questions below will help us understand how you develop these ground motions. 10.) How do you define the seismic hazard at your site and the target rock response spectra? [ ] USGS maps [ ] Code Provision--List code [ ] Site specific deterministic--describe program [ ] 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) New Generation Attenuation Equations (NGA) AASHTO LRFD Bridge Design EZ-FRISK Ibc gis-hazard ASCE 7 SISMIC, Open SHA ASCE 7-05 and AASHTO GMPE available in SHAKE-2000 for Subduction Zone Earthquake and the NGA GMPE spreadsheets AASHTO available from PEER web site AASHTO CD for DOT projects MathCAD with NGA models for crustal motions. IBC Our California offices use Tom Blake's programs AASHTO LRFD EZ-FRISK/PEER NGA spreadsheet International/California Building Code Spreadsheets (NGA-based) AASHTO, USEPA guidance NGA CBC, IBC EZ-FRISK or deterministic attenuation model spreadsheet NEHRP EZ-Frisk, Spreadsheet Template NYCDOT Seismic Guidelines in-house IBC, NEHRP, AASHTO NBCC (national building code of Canada) USGS deagg AASHTO 17th Edition AASHTO Site specific probabilistic Other, please specify: PSHA Deaggregate PSHA maps for fault data to use with liquefaction analysis Deaggregated data from USGS website Most of the time we are using the USGS Maps An internal tool (ARS online) based on USGS 1,000 yr RP Seismologist Table continued on p.55
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55 Table continued from p.54 Site specific probabilistic Other, please specify: EZ-FRISK USGS deaggregation gis-hazard, EZ-FRISK USGS Interactive Deaggregation website HAZ38 & USGS software USGS NSHMP Java program SISMIC, Open SHA Source-specific attentuation for predominant sources, CMS utilized for target Site specific PSHA completed by others that uses the computer program HAZ-38 or later D. SCDOT uses software exclusively developed for SCDOT called SCENARIO_PC to determine We subcontract this to a specialist ground motions for both geologically realistic and Rarely do these analyses, but we have our own hard rock. The software was developed by a part- PSHA model and we have leased the PSHA code nership of USC (University of South Carolina) and from Risk Engineering. We have also used Tom Virginia Tech. The program accounts for the Blakes program in the past for locations in extremely thick (in excess of 2,900 feet) soil thick- California. ness adjacent to Coastal South Carolina. EZ-FRISK openSHA EZ-FRISK EZ-FRISK EZ-FRISK or HAZ42 compared with USGS maps Developed by Geophysical Institute of Israel EZ-Frisk in-house in house 11.) How do you develop hazard compatible ground motion time histories at rock? [ ] Simple scaling of motions from widely available libraries [ ] rigorous spectral matching (specify method if known) [ ] Synthetic ground motions [ ] 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) 19 Synthetic ground motions 12 Other, please specify 8 Rigorous spectral matching methods Other, please specify: RASCAL Synthetic and Scaled Real RSPMATCH we don't do this Inhouse No RspMatch (rarely used) Risk Engineering Time Histories for NYCDOT RSPMatch 2005 It usually comes from owner's engineers--the majority are based on spectral matching--some agencies prefer RSPMatch linear scaling for a specific period of interest We typically subcontract this SigmaSpec used for predominant periods of interest We use RSMatch in SHAKE2000. We also have a version Don't use. of the Abrahamson code that we have used on projects. Table continued on p.56
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56 Table continued from p.55 Rigorous spectral matching methods RSPMatch Rspmatch done by others Typically we use RSPMatch. Have also used Tinker. RSPMatch software RspMatch Jack Baker Abrahamson RSPMATCH Shahbazian, A. and S. Pezeshk. (2010). "Improved Velocity and Displacement Time Histories in Fre- quency-Domain Spectral-Matching Procedures." Bulletin of the Seismological Society of America, 100(6), pp. 32133223, Dec. 2010, doi: 10.1785/0120090163 RSPmatch 12.) How many motion time histories do you generate or require for a given hazard level ( ) 1 motion ( ) 3 motions ( ) 7 motions ( ) 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. 1 for Resp. Spect. Analyses and 3 for Time Histories Use 3 if matched to design bedrock spectra, use 7 if simple scaling is used 7 pairs or 14 time histories We will use 3 to 7, depending on the project. Most of the time we would like to have at least 3 motions represent- ing the 3 seismic sources in the PNW (crustal, subduction interface and subduction intraface). For geotechnical modeling, we will usually use a minimum of 7. We will use three if we are doing spectra matching for structural purposes. we don't use 0 NA 5 or 7 varies by project, usually selected by SE multimodal not considered Table continued on p.57
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57 Table continued from p.56 Other, please specify: 3 to 7. But we typically try to use at least 7. If using spectral matching, typically only 3 motions. If using scaling, 7 or more. Monte Carlo convergence Nuclear 1, hydro facility 3, other facility 7 We generate thousands to develop a probabilistic approach For the recent large projects the trend has been 6 motions per level of earthquake (say 6 for 475 yr EQ)- some agen- cies (for school retrofit) require 10 motions Typically 3 if matched, 7 or more if not, depending on the problem Not used. 13.) For sites where near faults effects are significant, what special requirements do you impose on the suite of input ground motions? [ ] None [ ] incorporate directivity [ ] include velocity pulse [ ] use two component motions (e.g., Fault normal/parallel) [ ] check cross-correlation of the input ground motion time histories [ ] 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? Other, please specify: 10 Other, please specify: never encountered Work in progress; near faults reviewed for significance, depending on importance of bridge detailed analysis may be performed considering directivity and pulse effects. We use the Caltrans approach for adjusting the spectra. not applicable Presently considering different approaches Select the existing motions near the faults that have velocity pulse No experience or any structures near faults This is beyond my expertise. No faults are visible in South Carolina due to the thickness of the Coastal Plain deposits.
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66 Table continued from p. 65 Other soil models measured, usually with RCTS locally developed correlated from SPT information 23.) When is a nonlinear total stress (no pore water pressure generation) analysis used or required? [ ] Site class dependent--please list site class [ ] Seismic hazard level--please specify [ ] Structure type--please specify [ ] Strain amplitude--please specify [ ] Other, please describe: TABLE B29 CRITERIA WHERE NONLINEAR TOTAL STRESS (NO PORE WATER PRESSURE GENERATION) 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. be an issue F often used when structural analysis requires time histories E, F important structures F important D, E >D Strain amplitude--please specify: E or liquefiable greater than 1 percent Strain > 1% and used for design of the deep foundation or Seismic hazard level--please specify: below grade structures PGA > 0.6 g at soft sites, PGA > 1 g for stiff sites >1 to 2% PGA > 0.5 to 0.7 strain >1% See CBC 2010 Preferred where shear strain is greater than about 1% > 0.5 g >1 percent high hazard High > 1% > 0.4g large anticipated strain >0.5g >1% Table continued on p.67
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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
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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
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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
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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
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71 28.) How do you typically account for such uncertainties in design? [ ] Select reasonably conservative values of input parameters [ ] Use "best estimate" input parameters, then apply conservatism to results [ ] Perform sensitivity analyses [ ] Perform probabilistic analyses (e.g., FOSM, Monte Carlo) [ ] We don't address uncertainties explicitly [ ] Other, please specify: TABLE B34 ACCOUNTING FOR UNCERTAINTIES IN DESIGN Value Count Select reasonably conservative values of input parameters 5 Use "best estimate" input parameters, then apply conservatism to results 11 Perform sensitivity analyses 19 Perform probabilistic analyses (e.g., FOSM, Monte Carlo) 6 We don't address uncertainties explicitly 6 Other--please specify 6 Other--please specify: How do you typically account for such uncertainties in design? See answers to 14 and 19 We subcontract this to specialists NA Follow ASSHTO and avoid site class f classification We usually come up with a range for results (a practical upper and lower range and a best estimate) 29.) How do you evaluate the validity of the overall site response model at your site? [ ] Compare with empirical correlations [ ] Perform sanity checks [ ] Other, please specify: TABLE B35 EVALUATION OF THE VALIDITY OF THE OVERALL SITE RESPONSE MODEL AT A SITE Count Compare with empirical correlations 21 Perform sanity checks 18 Other--please specify 13 Other--please specify: Not sure. Comparison with recorded motions at similar sites compare with IBC spectra check soil response output to lab test results We will compare to site class factors, published data, or alternate methods. For example, we check DMOD total stress versus SHAKE analyses. with vertical arrays Compare with code-based spectra and nearby recorded motions Table B35 continued on p. 72
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72 Table B35 continued from p. 71 TABLE B35 EVALUATION OF THE VALIDITY OF THE OVERALL SITE RESPONSE MODEL AT A SITE Count We do not Use judgment informed by previous analyses and recorded ground motions for similar sites. field recordings at similar sites Compare with response spectra from building codes Compare results of two programs if applicable Compare the results of the Site-Specific Response Analysis to the results of the 3-point method. 30.) What output do you use from site response analysis? [ ] Surface response spectra [ ] Surface velocities [ ] Surface Displacements [ ] Surface time histories [ ] Profiles of PGA [ ] Profiles of strains [ ] Profiles of displacements [ ] Profiles of shear stress [ ] Other, please specify: TABLE B36 OUTPUT USED FROM SITE RESPONSE ANALYSIS Count Surface response spectra 29 Surface velocities 7 Surface Displacements 8 Surface time histories 21 Profiles of PGA 17 Profiles of strains 17 Profiles of displacements 10 Profiles of shear stress 14 Other--please specify 6 Other--please specify: What output do you use from site response analysis? amplification factor at surface The output that will be used really depends upon the purpose of the analysis; i.e., ground motions for building response analysis versus CSR for a liquefaction triggering analysis. profiles of PPR, peak acceleration pore pressures Deeper response spectra are also used (Depth-to-Motion concept). seismic reactions
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73 31.) Do you use output of profiles of strains and lateral deformations in a structural analysis? (e.g., pile lateral loading...), please explain, do you perform any baseline correction of the output motions? TABLE B37 USE OF OUTPUT OF PROFILES OF STRAINS AND LATERAL DEFORMATIONS IN A STRUCTURAL ANALYSIS (E.G., PILE LATERAL LOADING, AND BASEELINE CORRECTION OF THE OUTPUT MOTIONS) Count Response 1 No 5 No 1 No 1 No. No. 1 No. Yes. 1 No. 1 Rarely 1 Yes, sometimes we can use this as input to the response of the structural elements. 1 Yes, we use soil profile curvature to estimate kinematic bending moments 1 Yes. Yes. 1 No 1 no and no 1 None 1 not explicitly 1 Pile lateral loading, base line correction if necessary usually using long period filter 1 Yes, in some cases 1 We perform baseline corrections of displacement time histories at different soil layers to drive p-y soil springs attached to piles (soil- structure interaction). 1 I haven't personally, but my colleagues have to estimate kinematic loading on piles. Baseline correction is typically performed prior to using any of the ground motions. 1 The relative strain within the structure (e.g., piles or tunnel) is provided for use in the structural analysis. The force based method will also be used to check if the strain method is reasonable. I typically do not use the output ground motions for the design analysis. 1 Yes, we have used peak displacement profiles from site response analysis to as input to Winkler beam on nonlinear foundation analysis of kinematic pile bending. 1 Bridge Designer Response: typically AKDOT does not use the lateral deformation profile from the Site-Specific analysis. 1 We usually use baseline corrected input motions. But anyways what is important for us are the relative movements (movement at each point minus movement of the excited base). 1 A sub-consultant is currently running DESRA for us and using the displacements in a lateral pile response program to estimate con- densed stiffness matrix for the pile group and kinematic motions. This is a fairly specialized area, and so we prefer to have a specialist do this type of analysis. 1 Sometimes the output strains are used in the structural analysis of piles and also of racking of underground structures. Input motions are baseline corrected and then output motions are checked for baseline corrections 32.) Do you use profile of peak ground acceleration for liquefaction analysis? Please explain. When you evaluate cyclic stress ratio (CSR) for liquefaction analyses, how often do you do so by means of site response analyses (as opposed to using the simplified method)? What criteria do you use for deciding when to do so? TABLE B38 USE OF PROFILE OF PEAK GROUND ACCELERATION FOR LIQUEFACTION ANALYSIS Count Response 1 No 1 No, we don't have liquefaction. We don't evaluate CSR. 1 Not typical 1 Not very often unless the simplified method gives marginal safety factors for liquefaction. Table B38 continued on p. 74
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74 Table B38 continued from p. 73 TABLE B38 USE OF PROFILE OF PEAK GROUND ACCELERATION FOR LIQUEFACTION ANALYSIS Count Response 1 We always use the simplified method. 1 When the project and importance of the structure demands the site response, both are performed. 1 Yes, use the PGA for the site. Rarely done. 1 Yes, importance of structure. 1 http://www.dot.il.gov/bridges/AGMU%20101.pdf 1 No 1 No, perform effective-stress analyses when liquefaction is to be predicted. 1 Yes, when a site response analysis is performed. They are compared. No criteria are used. 1 We don't do this very often. Perhaps only for critical projects where 2-D effects are important. 1 Two approaches used in parallel: 1. PGA from SHAKE used as input for simplified analysis 2. Effective-stress analysis using D-MOD. 1 Almost never. For liquefaction analysis of level grounds, we almost always use the simplified method and don't rely on CSR from the site response. For cases with static shear stresses, we need to get CSR from numerical modeling such as QUAD4M-U. 1 I have not used the profile of PGA for a liquefaction analysis. I have used CSR computed from site response in a liquefaction evalua- tion before, but only when strain levels were reasonable (i.e., less than 1%) and when I was performing the site response analysis for another reason. I have never performed site response solely for obtaining estimates of the CSR. 1 No. Rarely. I typically use the simplified liquefaction method based on PGA from site response or code-based procedure at ground surface. 1 We sometimes use site-specific CSR, but we first check it with the Cetin et al. (2004) CSR to see if it makes sense to use it with the simplified method. 1 I prefer to use CSR from site response for liquefaction analysis, as long at the triggering method isn't based on biased CSR estimates. 1 Yes. For most projects, use a simplified method. For critical structures, use the site response output directly. 1 Use CSR from analysis for determining liquefaction potential when FOS (liquefaction) is close to 1.0 by using the simplified methods (and expensive mitigation may be required). Also to evaluate liquefaction effects below depths for about 50 feet. 1 We will use the CSR from the site response analyses for liquefaction analyses. This probably represents less than 10% of our liquefac- tion analyses. Most of the time, we use the simplified liquefaction method. 1 Yes, PGA is used for liquefaction analysis. I don't understand the second part of this question. By simplified method you mean the code procedure. If I perform site specific analysis, I use site response analysis results for liquefaction analysis. 1 In some cases CSR from site response is chosen on the basis of reflecting better the "rd" reduction. 1 Yes, use peak ground acceleration for liquefaction analysis. Usually do not use site response analysis in CSR evaluation. If an active fault is within 10 km of the bridge site, then we use site response analysis. 1 Yes, to check the induced stress using simplified method; then compare to direct CSR from site response analyses. 1 The liquefaction will be completed using the simplified method with the PGA computed from equivalent-linear or total stress site response analysis. The PGA profile calculated by the site response analysis will also be compared to the simplified method. The site response analysis method is used for sites with soil deeper than 70 feet that are suspected to be liquefiable. 1 For screening purpose of for very small projects we may use simplified method. For final design and for larger projects, we may use CSR directly out of site response analysis. I know Idriss does not like this and recommends using PGA from site response analysis in conjunction with rd from simplified method which in way does not make a lot of sense. Needs to be clarified. For larger projects dis- placements are important and not liquefaction assessment. We generally calibrate UBCSAND to liquefaction charts and lab test results and then estimate the displacements. There is a great need for lab test results with shear stress bias. 1 Whenever we run SHAKE for ground motions we use shear stress profiles to estimate CSR for liquefaction analyses. 33.) Do you use profile of peak ground acceleration for slope stability analysis? Please explain. TABLE B39 USE OF PROFILE OF PEAK GROUND ACCELERATION FOR SLOPE STABILITY ANALYSIS Count Response 1 Hardly working on this subject. 1 No 1 No, but I could see doing that sometime. 1 No. Table B39 continued on p. 75
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75 Table B39 continued from p. 74 TABLE B39 USE OF PROFILE OF PEAK GROUND ACCELERATION FOR SLOPE STABILITY ANALYSIS Count Response 1 No. 1 No. Sometimes PGA at slope base obtained from 1-D analysis for rock input at depth. 1 Not sure. 1 Not very often, only on dams and embankment slope stability. 1 We use half of the PGA by seismic coefficient. 1 Will use percentage of PGA for pseudostatic slope stability analysis. 1 Yes--as input for Newmark analyses. 1 Yes, to evaluate horizontal equivalent accelerations within slide mass. 1 Yes. 1 I have not been using it. 1 No 1 No, developing new method based on shear stress distribution. 1 We use 500 yr. PGA for most slopes. 1 Yes; peak at ground surface and distribution with depth to evaluate effective value for design. 1 The PGA at various depths are used to compute the equivalent maximum horizontal acceleration for the critical failure surface identi- fied, which will then be used in the Newmark analysis to estimate deformation. 1 We have, but not very often. If you are going to all the trouble of developing time histories and dynamic properties for response analy- sis of a slope, you might as well go ahead and do a 2-D analysis instead of 1-D plus Newmark. 1 Typically no... In a limit equilibrium method, we will consider the most critical failure surface and use the shear stress profile from site response analyses to calculate the acceleration for the mass above the critical surface. 1 SCDOT slope stability begins at PGA to determine if the slope is stable. If a slope instability is encountered then a displacement analy- sis (Newmark) is performed after determining the yield acceleration. 1 Use 50% of PGA for slope stability analysis. For determination of permanent displacement we use yield acceleration/peak acceleration. 34.) For analyses where pore water pressure generation is evaluated, how do you use the analysis output? TABLE B40 USE OF COMPUTED PORE WATER PRESSURE 1 Check ru vs. time for the various layers. 1 Consider effect of decreased effective-stress on soil/foundation behavior. 1 Develop a profile where ru generated is > 0.7 1 Don't use. 1 Evaluate surface spectrum and displacement profile. 1 Examine ru vs. time 1 I compare it to the equivalent-linear output and nonlinear output. 1 I have never performed such an analysis in engineering practice. 1 Just to verify if liquefaction does occur due to increase in pore pressure. 1 Not sure 1 Not used 1 Considered for total stress only. 1 Do not consider 1 Examine level of pore pressures 1 input for effective-stress SSI problems 1 insufficient experience with this 1 To check whether liquefaction expected. Don't trust results post-liquefaction Table B40 continued on p. 76
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76 Table B40 continued from p. 75 TABLE B40 USE OF COMPUTED PORE WATER PRESSURE 1 To evaluate potential for liquefaction 1 To understand soil behavior 1 For important project we usually use effective-stress FLAC analysis in which the above is automatically considered. 1 For layers which have high excess pore water pressure, we reduce the strength of that layer for stability analysis. 1 We used the porewater pressure to determine whether liquefaction is occurring. We will use the porewater pressure information to decide whether to modify P-y curves and to select residual strength values. 1 To determine liquefaction potential in soil column, however, these programs may mask the actual pore pressure generation and lique- faction potential in the upper layers in some conditions due to soil softening in lower layers. FE analysis methods may be required. 1 Evaluate liquefaction potential using the excess pore pressure ratio, checked with the results of simplified methods for the top 40 to 70 feet and cyclic lab test results if available. 35.) Please include other comments you may have related to the topic on evaluation and use. TABLE B41 OTHER COMMENTS RELATED TO THE TOPIC ON EVALUATION AND USE Count Response 1 Georgia is a low risk seismic state and most of this doesn't apply. 1 We rarely perform these analyses internally as they are needed infrequently. 1 None 1 Based on CPT or SPT, the site will liquefy. But site response indicated the pore pressure did not increase to induce liquefaction. Pore pressure parameter in effective-stress site response is difficult to determine, such the computed pore pressure is less reliable. 1 I have lots of not sure answers, I know. Perhaps this is a reflection on the need to involve Geotechnical and Structural simultaneously when this type of work is done. 1 I have learned that the interpretation of results from effective-stress analyses is very complex. Issues such as shielding of upper layers, dilation, model calibration become critical. Further guidance is needed in these areas. 37.) Please feel free to include any thoughts or comments you would like to share with us. TABLE B42 GENERAL COMMENTS ON THE OVERALL SURVEY Count Response 1 Not using site specific analysis in the state of Indiana. 1 Thanks for including me on this. Please send me the results when they are available. 1 Use Japan 2011 data for validation exercises of existing site response methodologies. 1 I think you have the names for others in Kleinfelder already. Thanks for doing this study. I look forward to seeing the results. 1 My responses come from the perspective of a researcher who is interested in site response--and does research in the evaluation and validation of different methods. I primarily use vertical array data where both the down hole and surface ground motions are known. We use this to investigate the effect of soil variability on site response--and are currently doing a project that tries to identify sites where 3-D nonlinear (effective-stress) is required versus 1-D equivalent-linear. 1 This survey is overly addressed for a state that has low seismic risk. Our peak accelerations in Georgia are around 0.1 g. Most of the state is even less. 1 In real world, we must correct the 1-D site response with various correction factors i.e. basin, basin edge effect, directivity, sloping bedrock. I hope few empirical factors can be developed to include to account for those factors. Software and study on SSI must be enhanced, to allow complete modeling of structure. Need to research on combined kinematic and inertial lateral load acting on pile. 1 This is a good survey. I am looking forward to the report. Current practice for the site response analyses mainly focus on the horizontal motions, and seldom on the vertical motions. More and more important facilities need the time history analysis for either design or safety evaluation. It would be greatly helpful if some guideline can be provided for generating the site specific vertical motion. 1 I wish I could have been more help. But the fact is, we rarely do site specific analysis, other than USGS Deaggregation then attenuation relationships plus site factors to get motions for the simplified liquefaction analysis. 1 I suggest contacting Wall Silva and Bob Youngs to get their perspective. Their applications have been mainly for nuclear projects. Though they are using equivalent-linear analyses, they are also conventionally looking at the sensitivity to material property variations and they use pretty deep soil columns. Their experience might prove to be interesting. Carl Costantino is another person working in the same area, who is very knowledgeable in site response analyses using equivalent-linear and nonlinear methods. I suggest Ernie Naes- gaard because of his work with Peter Byrne at UBC and his use of the program FLAC and the UBC sand model. If you do not have or cannot find contact information for these people, let me know. I can provide e-mails and telephone numbers.