Comparison of nonlinear and equivalent-linear site response analysis for soft-soil sites along the Wasatch Front and site-specific response predictions for the Legacy Parkway

The resultant spectra from equivalent-linear and nonlinear methods of site response analysis on three soft and deep soil sites were compared for high levels of ground shaking in the urbanized area of the Wasatch Front near Salt Lake City, Utah. Site response methods were performed in accordance with a guidance document prepared for UDOT (Bartlett 2004) and a research document in preparation for publication in Earthquake Spectra (Bartlett et al., 2008). Findings indicate that nonlinear site response analysis more appropriately models the behavior of soft soils subject to high levels of ground shaking. Formal ground shaking predictions are provided for the North Interchange of Legacy Parkway for rupture scenarios including rupture of the Weber, Brigham, and Salt Lake City segments of the Wasatch Fault, and an additional scenario to model a 475-year event. Guidance and recommendations for accelerometer instrumentation of subsurface soil profiles are provided for the North Interchange of Legacy Parkway.

COMPARISON OF NONLINEAR AND EQUIVALENT-LINEAR SITE RESPONSE ANALYSIS FOR SOFT-SOIL SITES ALONG THE WASATCH FRONT AND SITE-SPECIFIC RESPONSE PREDICTIONS FOR THE LEGACY PARKWAY by Robert Wayne Snow II A thesis submitted to the faculty of The University of Utah in partial fulfillment of the requirements for the degree of Master of Science Department of Civil and Environmental Engineering The University of Utah August 2008 Copyright © Robert Wayne Snow II All Rights Reserved 2008 T H E U N I V E R S I T Y OF U T A H G R A D U A T E S C H O OL SUPERVISORY COMMITTEE APPROVAL of a thesis submitted by Robert Wayne Snow II This thesis has been read by each member of the following supervisory committee and by majority vote has been found to be satisfactory. Chairy Steven F. Bartlett "7/ f i Id 0 0 S James C. Pechmann Chris Pantelides THE UNIVERSITY UTAH GRADUATE SCHOOL APPROVAL ~if~ Chair· Steven F. Bartlett dill:, 9~-k~ r ~F T H E U N I V E R S I T Y OF U T A H G R A D U A T E S C H O OL APPROVAL To the Graduate Council of the University of Utah: I have read the thesis of Robert Wayne Snow II in i t s f m a i form and have found that (1) its format, citations, and bibliographic style are consistent and acceptable; (2) its illustrative materials including figures, tables, and charts are in place; and (3) the final manuscript is satisfactory to the supervisory committee and is ready for submission to The Graduate School. 7/t/z** f cY-D a t e / SfevenT. Bartlett / Approved for the Major Department UL Paul J. Tikalsky Chair/Dean Approved for the Graduate Council David S. Chapmam Dean of The Graduate School THE UNIVERSITY UTAH GRADUATE SCHOOL FINAL READING APPROVAL in its final ~~e~~ Chair: Supervisory Committee ~£ta~ 1. Chapman ABSTRACT The resultant spectra from equivalent-linear and nonlinear methods of site response analysis on three soft and deep soil sites were compared for high levels of ground shaking in the urbanized area of the Wasatch Front near Salt Lake City, Utah. Site response methods were performed in accordance with a guidance document prepared for UDOT (Bartlett 2004) and a research document in preparation for publication in Earthquake Spectra (Bartlett et al., 2008). Findings indicate that nonlinear site response analysis more appropriately models the behavior of soft soils subject to high levels of ground shaking. Formal ground shaking predictions are provided for the North Interchange of Legacy Parkway for rupture scenarios including rupture of the Weber, Brigham, and Salt Lake City segments of the Wasatch Fault, and an additional scenario to model a 475-year event. Guidance and recommendations for accelerometer instrumentation of subsurface soil profiles are provided for the North Interchange of Legacy Parkway. aI., TABLE OF CONTENTS 1.2 Objectives and scope 3 2 DESCRIPTION OF SITE RESPONSE CODES 7 2.1 Equivalent-linear method 7 2.2 Nonlinear methods 8 3 SITE RESPONSE METHODOLOGY 10 3.1 Profile development 10 3.1.1 1-80 profile from Bartlett 2004 12 3.1.2 1-80 profile from Bartlett et al., 2008 12 3.1.3 Legacy Parkway profiles 12 3.2 Generation of spectrum compatible time histories 14 3.2.1 Time histories from Bartlett 2004 16 3.2.2 Time histories from Bartlett et al., 2008 16 3.2.3 Legacy Parkway time histories 17 3.3 Deconvolution analysis 17 3.3.1 Bartlett 2004 18 3.3.2 Bartlett et al., 2008 18 3.3.3 Legacy Parkway analysis 18 3.4 Convolution analysis 19 3.4.1 Bartlett 2004 19 3.4.2 Bartlett et a l , 2008 19 3.4.3 Legacy Parkway analysis 20 3.5 Time history processing and filtering 20 ABSTRACT ............................................................................................................................. iv LIST OF TABLES .................................................................................................................. vii LIST OF FIGURES ............................................................................................................... viii ACKNOWLEDGMENTS ........................................................................................................ x 1 INTRODUCTION ................................................................................................................ 1 1.1 Background ............................................................................................................... 1 1.2 Objectives and scope ................................................................................................. 3 2 DESCRIPTION OF SITE RESPONSE CODES .................................................................. 7 2.1 Equivalent-linear method .......................................................................................... 7 2.2 Nonlinear methods .................................................................................................... 8 3 SITE RESPONSE METHODOLOGY ............................................................................... 10 3.1 Profile development ................................................................................................ 10 3.1.1 1-80 profile from Bartlett 2004 ........................................................................... 12 3.1.2 1-80 profile from Bartlett et aI., 2008 .................................................................. 12 3.1.3 Legacy Parkway profiles ..................................................................................... 12 3.2 Generation of spectrum compatible time histories ................................................. 14 3.2.1 Time histories from Bartlett 2004 ....................................................................... 16 3.2.2 Time histories from Bartlett et aI., 2008 ............................................................. 16 3.2.3 Legacy Parkway time histories ........................................................................... 17 3.3 Deconvolution analysis ........................................................................................... 17 3.3.1 Bartlett 2004 ........................................................................................................ 18 3.3.2 Bartlett et aI., 2008 .............................................................................................. 18 3.3.3 Legacy Parkway analysis .................................................................................... 18 3.4 Convolution analysis ............................................................................................... 19 3.4.1 Bartlett 2004 ........................................................................................................ 19 3.4.2 Bartlett et aI., 2008 .............................................................................................. 19 3.4.3 Legacy Parkway analysis .................................................................................... 20 3.5 Time history processing and filtering ..................................................................... 20 3.5.1 Bartlett 2004 20 3.5.2 Bartlett et a l , 2008 21 3.5.3 Legacy Parkway data 21 4 COMPARISON OF EQL AND NL METHODS 22 4.1 Bartlett (2004) 22 4.2 Bartlett et al. (2008) 27 4.3 Summary for Bartlett (2004) and Bartlett et al. (2008) 28 4.4 Legacy Parkway site response analysis 29 4.5 Comparison of equivalent-linear and nonlinear results 30 4.5.1 Equivalent-linear 38 4.5.2 Nonlinear 39 4.6 Summary of Legacy ground response evaluations 40 5 A PRIORI GROUND MOTION SCENARIOS 44 6 PLACEMENT OF DOWNHOLE ACCELEROMETERS 53 7 DISCUSSION 57 APPENDIX 59 vi '........................................................................................................ aI., .............................................................................................. ............................................................................... .... ....... ............................................................ ... .................. ....................................................................................... ................................................................................................ ............................... .. ......... .................................................................. .............................. .... ........ ..................................................................................... ............ ............................................................................................................. ................................................. ................................................................. .............................................. ..................................................... ................................................................ ............................................................................................................................. REFERENCES ....................................................................................................................... 61 VI LIST OF TABLES Table Page 1: Summary of earthquake time histories 15 2: Summary table of spectral values for Bartlett 2004 and Bartlett et a l , 2008 29 3: Summary table of spectral values for the Legacy Report 41 4: Summary table of spectral values for the a priori ground response predictions 52 5: Spectral values for the a priori ground response predictions 52 6: Shallow interpreted profile for North Interchange of Legacy Highway 54 ..................................................................... aI., ........... ......................................... ....... .................................... ................... LIST OF FIGURES Figure Page 1: Location map of Interstate 80 and Interstate 15 Interchange in Salt Lake County, Utah 4 2: Location map of the North Interchange of Legacy Parkway, Interstate 15, and Highway 89 in Davis County, Utah; and the South Interchange of Legacy Parkway and Interstate 215 in Salt Lake County, Utah 5 3: Shear-wave velocity profiles for site response analysis 4: Results of the 5km deconvolution / convolution EQL analysis and the 200 m convolution EQL analysis for the best-estimate 1-80 Interchange Deep Profile 1 23 5: Results of the 2 km NL deconvolution/convolution and 200 m convolution NL analysis for the best-estimate (i.e., mean) 1-80 Interchange Profile 26 6: Results of the EQL site response analysis for the South Interchange of Legacy Parkway for the rupture of the Weber Segment 31 7: Results of the EQL site response analysis for the North Interchange of Legacy Parkway for the rupture of the Weber Segment 32 8: Results of the NL site response analysis for the South Interchange of Legacy Parkway for the rupture of the Weber Segment 33 9: Results of the NL site response analysis for the North Interchange of Legacy Parkway for the rupture of the Weber Segment 34 10: Results of the NL site response analysis for the North Interchange of Legacy Parkway for the rupture of the Salt Lake City Segment 35 11: Results of the NL site response analysis for the North Interchange of Legacy Parkway for the rupture of the Brigham City Segment 36 12: Results of the NL site response analysis for the North Interchange of Legacy Parkway for the 475- year return period scenario 37 13: Weighted mean comparison of the NL and EQL site response analysis for the South Interchange of Legacy Parkway for the rupture of the Weber Segment 42 ............................................................................................................... ................................. ........................................... 11 I ....................................................................................... ................... Segment.. ......................................... ofthe Segment.. ......................................... ofthe Segment.. ......................................... Segment.. ......................................... .............................. ................................ ........................................ ......................................................................................................... 14: Weighted mean comparison of the NL and EQL site response analyses for the North Interchange of Legacy Parkway for the rupture of the Weber Segment 43 15: A priori prediction of the NL response for the North Interchange of Legacy Parkway for the rupture scenario of the Weber Segment (Mw 7.0, Rrup 0.7 km) of the Wasatch Fault Zone based on spectra with directivity effects 45 16: A priori prediction of the NL response for the North Interchange of Legacy Parkway for the rupture scenario of the Salt Lake Segment (Mw 7.0, Rrup 18.6 km) of the Wasatch Fault Zone based on spectra with directivity effects 46 17: A priori prediction of the NL response for the North Interchange of Legacy Parkway for the rupture scenario of the Brigham City Segment (Mw 7.0, Rrup 39.8 km) of the Wasatch Fault Zone based on spectra with directivity effects 47 18: A priori prediction of the NL response for the North Interchange of Legacy Parkway for the rupture scenario of the 475-year event (Mw 6.79, Rrup 12.0 km) of the Weber segment of the Wasatch Fault Zone 48 19: Comparison of a priori predictions of the NL response for the North Interchange of Legacy Parkway for relevant rupture scenarios 49 20: Recommended borehole accelerometer placement, shallow shear-wave-velocity profile, peak horizontal acceleration (PGA) profile, and geologic interpretation of soil layering for North Interchange of Legacy Parkway 55 ix ......................................................................................................... .................................................................................. .................................................................................. ................................................................... ofthe .................................................................................................. .................................................... ...................................... ACKNOWLEDGMENTS This thesis and technical report was made possible by funding from the Utah Department of Transportation (UDOT). Funding for this thesis is greatly appreciated. I thank my committee chairman, Dr. Steven F. Bartlett, whose guidance and support has made this thesis possible. I recognize Dr. Robert B. Smith and Dr. James C. Pechmann who both provided great insight into the seismological portions of the thesis. I thank my parents for unending encouragement and support throughout my life. I lovingly thank my dear wife Julianna for her devoted support, encouragement, patience, and love. 1 INTRODUCTION 1.1 Background The recommended load and resistance factor design (LRFD) guidelines for the seismic design of highway bridges (MCEER/ATC-49a,b) include procedures for the development of design response spectra using either a general procedure, which is fully developed in the MCEER text, or a site-specific procedure for which general requirements are set forth. The criteria that specify when the site-specific procedure should be used include cases where site-specific analysis is required (Site Class F soils profiles), when the bridge is considered to be an important structure, the site is within 10 km of a known active fault where site conditions may produce near-fault ground effects, or when requested by the owner. However, MCEER/ATC-49 provides very little guidance on the specifics of the deterministic site-response analysis; this is accommodating because allows the methodology to be adapted as the state of practice advances and to incorporate local studies or practice. This also allows changes to the methodology as the geological conditions, population distribution, and project needs require. For example, current attenuation relations are based on generic western U.S. rock profiles that are particularly adapted for conditions in California. These rock profiles differ greatly from the soft soil/rock profiles common in Utah (basin and range/extensional regime), and INTRODUCTION MCEERI MCEERlATC-it 2 incorporation of additional methods in the site response methodology is recommended to account for this large variation of geologic conditions. The MCEER/ATC-49 guidance does not prescribe specific methods to account for these differences, allowing the use of updated methods as the state of practice develops. A very thorough guidance for site-response analysis for deep-soil sites was developed to aid practitioners in performing site response analysis that includes a deconvolution/convolution methodology (Bartlett 2004). However, this document is based on using equivalent linear techniques, which may not be completely reliable for very high levels of strong motion on soft soils sites. The purpose of the Bartlett (2004) report is to provide design guidance to UDOT for performing site-specific ground response analysis and developing design spectra at bridges sites founded on soft or deep soil sites (i.e., NEHRP site class D and E soils). It is applicable where the ground response and design spectra require modification for soil nonlinearity and local rock effects. The guidance addresses site characterization, analysis of deep soil profiles, generation of spectrum compatible time histories (including adjustments for near-fault effects, rotation of time histories to principal components, and advanced spectral matching), linear and equivalent-linear (EQL) deconvolution analysis, EQL convolution analysis, calculation of site-specific amplification factors, and the development of enveloping design spectrum. A summary of Bartlett 2004 is in preparation for Earthquake Spectra (Bartlett et al. 2008) that includes the following major modifications: incorporation of the Next Generation Attenuation (NGA) relations to develop the target spectra, modification of the filtering of earthquake time histories from that used in Bartlett (2004), and the use of nonlinear (NL) code during the convolution analysis to MCEERJ spectra, modification of the filtering of earthquake time histories from that used in Bartlett (2004), and the use of nonlinear (NL) code during the convolution analysis to 3 overcome potential artificial amplification near and after the fundamental period of the soil profile and to reduce errors inherent in the EQL code. 1.2 Objectives and scope The purpose of this document is to employ the guidance of Bartlett (2004) and provide further explanation to the methodological revisions found in Bartlett et al. (2008). It also compares the results of the EQL method with those of the NL method for site response analysis at the 1-80 Interchange in Salt Lake County, Utah as shown in Figure 1. This report is further supplemented with additional EQL and NL analyses from two deep soil sites along the Legacy Parkway alignment in Davis County, Utah as shown in Figure 2. The Legacy analyses are based on the soil profiles of the North Interchange (Legacy, I- 15, and Highway-89) and the South Interchange (Legacy and 1-215), and the maximum credible earthquake (MCE) on the Weber Section of the Wasatch Fault Zone. However, the Legacy target spectra are mean, or 50t h percentile, spectra in contrast to the percentile spectra used in both the UDOT and Spectra papers. The former are used to provide a "best estimate" of the expected strong ground motion at the Legacy sites for time-domain structural modeling purposes, whereas the latter were developed as examples of how to develop design spectra using the requirements found in MCEER/ATC-49. Additional information is provided herein to fulfill contractual requirements of UDOT research PIC Number UT05.702 and UDOT Project Number 5H05433H. These requirements are to provide a priori ground motion predictions for the North Legacy Parkway bridge site including four rupture scenarios along the Wasatch Fault Zone. l­IS, 50th 85th of how to develop design spectra using the requirements found m MCEERlATC-49. FIGURE 1: Location map of Interstate 80 and Interstate 15 Interchange in Salt Lake County, Utah 4 5 FIGURE 2: Location map of the North Interchange of Legacy Parkway, Interstate 15, and Highway 89 Davis County, Utah; and the South Interchange of Legacy Parkway and Interstate 215 Salt Lake County, Utah Great Salt Lake ofthe in in 6 In addition, guidance and recommendations for the placement of free-field accelerometers beneath the North Legacy Parkway Bridge and a downhole strong ground motion array are also provided to fulfill UDOT obligations. 2 DESCRIPTION OF SITE RESPONSE CODES 2.1 Equivalent-linear method The guidance provided in Bartlett 2004 employs one-dimensional EQL code to develop the site-specific response spectra. Kramer (1996) summarizes the EQL method, its basic theory, implementation and other considerations. The commercial EQL code used in Bartlett 2004, known as PROSHAKE (EduPro Civil System, Inc.), was developed from the computer program SHAKE (Schanbel et al. 1972; Idriss and Sun 1992). PROSHAKE and its graphical user interface (GUI) front and back ends were developed for the 1991 version of SHAKE (Idriss and Sun 1992), which is also available from the Earthquake Engineering Research Center at the University of California at Berkeley, but without a GUI. PROSHAKE is a commercially available, heavily validated version of SHAKE 91 that was recoded in Fortran with a Visual Basic Shell. In addition, EDUSHAKE is a freeware noncommercial version of PROSHAKE with significant restrictions that allow students and practitioners to become familiar with the program and user interface before the purchase of a commercial license for use in practice. The Bartlett (2004) guidance selected EQL ground response analysis for the following reasons. The EQL method is relatively straightforward and has distinct computational advantages. In addition, there is also a reasonable amount of geotechnical test data that support the implementation of the EQL method. Further, engineering GUT. PROS HAKE 8 practitioners are familiar with this method and have applied it in practice for approximately 30 years. In addition, practitioners will likely select commercial software with a GUI for reasons of legal liability and ease of use, making this a significant advantage of the EQL method, as currently constituted in PROSHAKE, or other commercial versions. However, the EQL method has some significant disadvantages (Bartlett 2004) which include (1) numerical instability with soft profiles as the peak shear strain approaches the soil's shear strength, (2) artificial amplification near the fundamental period of the soil column, (3) potential deamplification at other periods, (4) frequency domain methods which cannot incorporate effective stress methods and liquefaction, and (5) very little active development of the code. 2.2 Nonlinear methods There are numerous nonlinear methods that vary in complexity in terms of their respective stress-strain relations and ability to perform coupled effective stress analyses (Kramer 1996). The guidance provided in Bartlett et al. (2008) employs one-dimensional NL code to develop site-specific response spectra using guidelines contained in MCEER/ATC-49. Direct numerical integration of the equation of motion in the time domain allows the use of any soil model with updated soil properties at each time step. The stress-strain behavior of soils can be more realistically modeled with NL codes since any soil model can be used along with the equation of motion, allowing the NL method to be expanded as new soil models are developed. In addition, NL (time domain) models can be formulated in terms of effective stresses to include pore pressure models and the PRO SHAKE, fundamental frequency MCEERlATC-any soil model can be used along with the equation of motion, allowing the NL method to be expanded as new soil models are developed. In addition, NL (time domain) models can be formulated in terms of effective stresses to include pore pressure models and the 9 evaluation of liquefaction. The NL method is currently under active development in comparison to the EQL method. However, most implementations of the NL code for one-dimensional site response do not include a GUI; this disadvantage discourages the widespread use of NL methods. In addition, a principal disadvantage of NL methods includes the complexity of advanced soil models (i.e., Cam Clay, Hyperbolic, Hypo- Plastic) and their many variations. This complexity and recent development of many new constitutive models leads to the emergence of additional parameters that are neither well understood nor well developed and may also require advanced geotechnical testing to be performed. Bartlett et al. (2008) recommend the program Deepsoil for NL one-dimensional site response analysis on soft or deep soil sites subject to high levels of strong motion. Deepsoil was developed at the University of Illinois by Hashash, Park and Tsai (Hashash and Park, 2001). Deepsoil features both EQL analysis in the frequency domain and NL analysis in the time domain. The modified hyperbolic model (Matasovic 1993) was extended in Deepsoil to incorporate confining pressure into the soil model. This allows for a decrease in material damping and shear modulus degradation as confining pressure increases. Often NL parameters are difficult to obtain and often require advanced laboratory testing; however, Deepsoil provides a curve matching utility to fit extended modified hyperbolic model parameters to shear modulus and damping degradation curves that are commonly employed in the EQL method. These curves are widely available in geotechnical literature and vary according to soil or rock type, density, plasticity, and gradation, etc. one­dimensional Hypo­Plastic) mcreases. 3 SITE RESPONSE METHODOLOGY A brief summary of the site response methodology used for Bartlett (2004), Bartlett et al. (2008), and the Legacy Parkway Study is provided in this section. The site response methodology of each paper is substantially the same as that discussed in Bartlett (2004); however, small changes were made in Bartlett et al. (2008) and in this study for the Legacy Parkway to more appropriately analyze the dynamic response of soft/deep soil profiles. Relevant portions of Bartlett (2004) were reproduced herein with permission. 3.1 Profile development The first step in a ground response analysis is the development of a site-specific geotechnical profile of the soil column using appropriate dynamic properties. Typically, a 1-D soil column, extending from the ground surface to bedrock, or to a very dense material, is adequate to capture first-order site response characteristics. For this study, site-specific soil and rock profiles were developed for each site as shown in Figure 3. For all analyses, the shallow profiles (0 to 30 m) for each site were estimated using geotechnical boring logs and (CPT) shear-wave velocity measurements. The properties of the intermediate (30 to -100 m) and deep (-100 up to 5 km) profiles vary somewhat and were developed, as described below. METHODOLOGY I-~ 100 (~I 00 11 FIGURE 3: Shear-wave velocity profiles for site response analysis o 250 500 750 1000 1250 1500 1750 -------.... .... \ \ \ , , \ \ \ .... -- "'- - - .... .... .... .... ...... ..... ...... ... \ , \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ , \ , \ , , \ \ \ \ \ \ ------- -\' \ - -, \ \ \ L--___ l- - -1-80/1-15 Interchange --North Legacy Interchange - - - South Legacy Interchange ----- u.S. Western Rock Profile \ , \ \ , \ \ , \ , \ \ , \ \ , \ , , \ , \ , I \ I \ , , \ , \,,,, ,,,, , , ,, 2000 +-~~~~~~~-r~~~-+~~~~~~~~~~~-'~ o 500 1000 1500 2000 2500 3000 Shear Wave Velocity, (m/s) 12 3.1.1 1-80 profile from Bartlett 2004 The intermediate and deep profiles in Bartlett (2004) were based on regional seismological reports, geophysical surveys, and other ground motion modeling studies (e.g., Wong et al. 2002; Wong and Silva 1993; Murphy 1989; Hill 1988). A Vs 3 0 of 208 m/s was measured for the I-15/1-80 Interchange. Equivalent-linear soil properties were modeled in soils to a depth of 350 m, and semiconsolidated sediments were modeled linearly to a depth of 5 km. Refer to the Appendix and Bartlett (2004) for additional data and technical basis for the 1-80 profile. 3.1.2 1-80 profile from Bartlett et al., 2008 In Bartlett et al. (2008), the EQL soil properties were replaced with NL (modified hyperbolic) soil properties and the model depth was reduced from 5 km to a depth of 2 km. The revised depth of the model was considered to be sufficiently deep and occurs at a depth where velocities from the site-specific profile reasonably match the generic western U.S. profile (Figure 3). The NL soil parameters were matched to the EQL modulus degradation and damping curves as described in Section 2.2. Modified hyperbolic curves and parameters are provided in the Appendix of this report 3.1.3 Legacy Parkway profiles The intermediate portions of the profiles for the North and South Interchanges of Legacy Parkway compiled in this report are based on deep well logs available in the area. The South Interchange of Legacy Parkway is located in one of the deepest sediment basins along the Wasatch Front with depth to bedrock ranging from 840 m to 900 m Vs30 mls 1-u.13 according to the constrained inversion of gravity data by Radkins (1990). Radkins also reports the depth of the boundary between unconsolidated sediments and semi-consolidated sediments, as estimated by Arnow (1981), at approximately 700 m. This represents an exceedingly deep soil profile when compared to other sites in the adjacent Salt Lake and Davis Counties where sediment depths probably do not exceed 200 m. The soils in the North Interchange are shallower than those found in the South Interchange. In the North Interchange, semiconsolidated sediments are encountered at about 250 m below the surface (Radkins 1990); depth to bedrock is estimated at about 700 m below the surface. Additional data supporting the Legacy profiles can be found in the Appendix. Values of VS3o were measured for the North and South Interchanges of Legacy Parkway of 191 and 188 m/s, respectively. For comparison purposes, EQL and NL soil properties were modeled in soils from the surface to a depth of 250 m for the North Interchange and from the surface to a depth of 700 m for the South Interchange. One case was done using EQL properties for these depth intervals and then the analysis was repeated using NL properties in these intervals. The semiconsolidated sediments were modeled to a depth of 2 km for both locations. Both the NL and EQL cases were based on using modified hyperbolic soil parameters, which is a user specified option in Deepsoil. When this option is used, modified hyperbolic soil parameters are used to provide continuous functions for the shear modulus degradation and damping curves, but the analysis is still done using the EQL method. The modified hyperbolic soil parameters were obtained by matching the semi­consolidated Vs30 mis, usmg 14 appropriate EQL modulus degradation and damping curves, as described in Section 2.2. Modified hyperbolic curves and parameters are provided in the Appendix. 3.2 Generation of spectrum compatible time histories Recorded time histories were selected among candidate time histories with similar geologic settings and earthquake characteristics. Near-field records from earthquakes with comparable Mw and distance were used for rock or stiff soil conditions (i.e., NEHRP site class B or C). A summary of the time histories that were used in each report is shown in Table 1. To incorporate fault directivity effects, it is recommended that the candidate acceleration time histories be rotated to find their principal components, and these principal components should be used in the spectral matching process. Because the candidate time histories selected in Table 1 were selected to represent near-field motions (i.e., fault directivity with strong velocity pulses in the fault-normal component), it is important that the horizontal components of the selected motions be transformed into their principal components so that these can be aligned with the direction of fault directivity. The major and minor principal components are the directions that best correlate with the fault-normal and fault-parallel directions, respectively. Mw TABLE 1: Summary of earthquake time histories Time History Fault / Type Surface Distance Magnitude (-) (km) (Mw) Cape Mendocino, 1992 Cascadia / Thrust 7 7.0 Erzincan Turkey, 1992 North Anatolian / Strike-Slip 4 6.7 Imperial Valley, 1979 Imperial / Strike-Slip 13 6.5 Northridge, 1994 Northridge / Reverse 23 6.7 Superstition Hills, 1987 Superstition Hills / Strike-Slip 6 6.5 Forward directivity effects were calculated using fault and site parameters that produced the maximum acceleration increase from the Sommerville et al. (1997) model. The forward directivity direction is perpendicular to the fault trace and should be applied in that direction. For bridges that are oblique or parallel to the fault, the directivity effect may be somewhat less, but it is important to capture the maximum directional effect. To do this, we developed two target spectra for each site, one that has the maximum directivity effect (fault-normal spectrum) and one that has no increase for fault directivity (fault-parallel spectrum). Most acceleration time histories, when taken at face value without modification, do not provide a very good match to the target spectrum; thus they must be scaled, adjusted or matched to the target design spectrum. Spectrum compatible time histories are acceleration time histories that have been matched to a target acceleration response spectrum using numerical techniques. The general objective of spectral matching is to generate a design acceleration time history that approximately achieves a mean-based fit to the target spectrum (NUREG CR-6728). An additional aim is to achieve an acceleration time history that does not have significant gaps in the Fourier amplitude 15 Fault! (-) ( -) Ian) Cascadia! Anatolian! Imperial! Northridge! Hills! 6.S 16 spectrum, but is not biased too high with respect to the target spectrum. An accelerogram that exceeds the target spectrum at most frequencies may overdrive a site soil column or structure where nonlinear response is of interest (NUREG CR-6728). To minimize modification of the phase characteristics of the input time histories, the spectral matching for each report was performed using the RSPMATCH software developed by Arahamson (1992). RSPMATCH adjusts the initial accelerogram iteratively in the time domain to achieve compatibility with the target spectrum. This method preserves the overall phasing characteristics and the time-varying (i.e., non-stationary) frequency content of the ground motion (Somerville, 1998a). 3.2.1 Time histories from Bartlett 2004 The earthquake time histories were matched to mean, outcropping rock target spectrum based on the Abrahamson and Silva (1997) attenuation relationship. However, the spectral matching and response analysis of Bartlett (2004) was performed prior to the release of MCEER/ATC-49, which has a different requirement for the target spectrum. MCEER/ATC-49 requires the input spectrum to be an 85 percentile spectrum, which corresponds to a mean plus one standard deviation value. Target spectra for all analyses are shown in the Appendix. 3.2.2 Time histories from Bartlett et al., 2008 The earthquake time histories in Table 1 were matched to an 85t h percentile, outcropping rock target spectrum based on the log-mean of Boore and Atkinson (2007), Campbell and Bozorgnia (2007), Chiou and Young (2007), and Spudich et al., (1999) RSPMA TCH non­stationary) MCEERJATC-MCEERJ 85th aI., 85th aI., attenuation relations. (Other NGA relations by Abrahamson and Silva and Idriss were not available at the time this work was completed and were not used in developing the target spectra herein. However, they should be used in conjunction with other NGA relations in developing the target spectrum for future evaluations.) 3.2.3 Legacy Parkway time histories For the "best" estimate analysis done for the Legacy Parkway (Section 1.2), the earthquake time histories were matched to a 50t h percentile, outcropping rock target spectrum based on the log-mean of Boore and Atkinson (2007), Campbell and Bozorgnia (2007), and Chiou and Young (2007) attenuation relationships. 3.3 Deconvolution analysis Deconvolution analysis involves the computation of outcropping bedrock motion from a surface motion. The deconvolution analysis is necessary to fully account for the characteristics of the shallow crust Vs profile at the candidate site. The shallow crustal rock Vs profile in the Salt Lake Valley is significantly different from that of the average western U.S. rock Vs profile (Boore and Joyner, 1997), as shown in Figure 3. These marked differences in the shallow crustal Vs profiles can produce significant differences in the outcropping rock motion for the Salt Lake Valley when it is compared with a site having a rock profile more similar to the "average western U.S. rock profile." To correct for these differences, a deconvolution analysis followed by a convolution analysis was performed. Refer to Bartlett (2004) and the Appendix for additional details on the western U.S. rock profile and the deconvolution analysis. 17 50th V s V s V s differences performed. Refer to Bartlett (2004) and the Appendix for additional details on the western U.S. rock profile and the deconvolution analysis. 3.3.1 Bartlett 2004 The spectrally matched time histories were deconvolved down to a depth of 5 km to a point where the generic western U.S. Vs profile and the site-specific Vs profiles are reasonably matched (Figure 3). The deconvolution analysis was performed using PROSHAKE using EQL methods for the shallow weathered outcropping rock and linear methods for the underlying rock. 3.3.2 Bartlett et al., 2008 The spectrally matched time histories were deconvolved down to a depth of 2 km to a point where the generic western U.S. Vs profile and the site-specific Vs profiles are sufficiently matched (Figure 3). The deconvolution analysis was performed using PROSHAKE using EQL methods for the shallow weathered outcropping rock and linear methods for the underlying rock. The spectrally matched time histories for the Legacy Sites were also deconvolved down to a depth of 2 km to a point where the generic western U.S. Vs profile and the site-specific Vs profiles are sufficiently matched (Figure 3). The deconvolution analysis was performed using PROSHAKE using EQL methods for the shallow weathered outcropping rock and linear methods for the underlying rock. 18 3.3.3 Legacy Parkway analysis of2 site­specific 3.4 Convolution analysis Convolution analysis evaluates the spectrally matched time histories as modified by the response of the soil layers in the site-specific soil profile. During this stage of the site response analysis, careful attention must be given to the level of strain expected the soft soil layers near the surface. The advantages and disadvantages of EQL and NL site response methods as outlined Section 2 can significantly affect the results of the site response analysis. 3.4.1 Bartlett 2004 The deconvolved time histories were convolved to the surface through the 5 site-specific soil profile. The convolution analysis was performed using PROSHAKE using EQL methods for the upper 350 m of the soil profile. Refer to Bartlett (2004), Section 3.1 of this report, and the Appendix for additional details on the site-specific profile and the convolution analysis. 3.4.2 Bartlett et al., 2008 The deconvolved time histories were convolved to the surface through the truncated 2 site-specific soil profile. The convolution analysis was performed using Deepsoils v2.6 using NL methods (modified hyperbolic soil properties) for the upper 350 al., Appendix for additional details on the site-specific profile and the convolution analysis. 19 in in km at., km m of the soil profile. Refer to Bartlett et aI., (2008), Section 3.1 of this report, and the 20 3.4.3 Legacy Parkway analysis The deconvolved time histories were convolved to the surface through the 2 km site-specific soil profile. The convolution analysis was performed using Deepsoils v2.6 for both EQL and NL methods. Modified hyperbolic soil properties were used for both EQL and NL methods for the upper 250 m of the soil profile for the North Interchange and 700 m for the soil profile of the South Interchange. Refer to Bartlett et al. (2008), Section 3.1 of this report, and the Appendix for additional details on the site-specific profile and the convolution analysis. 3.5 Time history processing and filtering The time history records used in the site response analysis were obtained from the PEER database. Acceleration time histories from the PEER repository have already been processed and filtered appropriately for use in site response analysis. However, the spectral matching process does introduce drift into the processed record, which must be corrected. Baseline correction of this drift is important if the spectrally matched time history is to be used in analyses where displacement is to be predicted from the analysis (Bartlett 2004). It is less important if only the accelerations or forces are to be obtained. 3.5.1 Bartlett 2004 Following the spectral matching process the time histories were baseline corrected for drift using the computer program BASELINE.EXE using a least squares inversion using a 4t h degree polynomial. The records were also filtered using a band-pass filtering 4th 21 Butterworth filter to remove unwanted noise above 15 Hz and below 0.14 Hz using the program Seismosignal (2004). addition, the deconvolution process introduced high frequency spikes into the time histories which were again filtered with a 15 Hz low-pass Butterworth filter to remove the high frequency spikes (Bartlett 2004). 3.5.2 Bartlett et aL 2008 Following the spectral matching process, the time histories were corrected for baseline drift using a least squares inversion of a 4 t h degree polynomial and filtered using a band-pass Butterworth filter to remove unwanted noise above 15 Hz and below 0.14 Hz using the program Seismosignal (2006). No additional filtering was performed after the deconvolution analysis. 3.5.3 Legacy Parkway data Following the spectral matching process the time histories were corrected for baseline drift using a least squares inversion of a 4 t h degree polynomial and filtered using a band-pass Butterworth filter to remove unwanted noise above 15 Hz and below 0.14 Hz using the program Seismosignal (2006). No additional filtering was performed after the deconvolution analysis. In al., 4th 4th 4 COMPARISON OF EQL AND NL METHODS In this section, the EQL spectra from each site will be compared to the NL spectra using the level of peak ground acceleration (PGA), value of the spectral peak and corresponding period of vibration and the overall shape of the response spectra. All of the spectra under consideration in this report were generated using the same input time histories. (It should be noted, however, that the target spectral values in Bartlett et al. (2008) between periods of 0.5 and 2.5 seconds are slightly larger than those in Bartlett (2004) because the former were developed using 85t h percentile values from the NGA relations and the later were developed using mean values from the Abrahamson and Silva (1997) attenuation relation.) 4.1 Bartlett (2004) The one-dimensional site response analyses documented in Bartlett (2004) were performed using the EQL code (PROSHAKE). Figure 4 shows the results for spectra with fault-normal and fault-parallel directivity effects for the 5 km deconvolution/convolution analysis and for the 200 m convolution analysis for fault-normal directivity effects. The results are for the best estimate (mean) soil profile (Bartlett 2004). peak: peak: 85th fault­normal 2.00 1.75 1.50 1.25 od • l-H | 1.00 1oo3 < 1 0.75 -f-> O <u 0.50 0.25 0.00 / \ / \ / \ / \ / \ -B- 5 km Deconvolution/Convolution, Fault ••- 5 km Deconvolution/Convolution, Fault Normal Component 200 M Convolution, Fault Normal Component - - Target Rock Spectrum 0.01 0.1 Period of Vibration, (s) 10 FIGURE 4: Results of the 5km deconvolution / convolution EQL analysis and the 200 m convolution EQL analysis for the best-estimate 1-80 Interchange Deep Profile 1 ~---------------------------.----------------------------.---------------------------~ ,-o..n.. '-' !::f .-0 ta I-< 1.00 Q) Q) u u < ].. ... 0.75 u Q) 0- r:/) 0.50 / ;' ---..,.." / / / / / / / / / I I I I I I I " " , ,, , \ \ \ \ \ \ --e- Parallel Component - ----- , , 1 , , , , , , " " " " best­estimate tv W The mean spectrum for the 5 km deconvolution/convolution analysis with fault-normal directivity effects (Figure 4) has a pga of 0.5 g, a peak acceleration of 1.0 g between 0.8 and 1.7 seconds, and a gradual and linear decay thereafter. For the fault-parallel directivity case, the spectral results are similar to the fault-normal values with a pga value of 0.5 g and a peak value of 1.1 g at a corresponding period of vibration of 0.9 seconds. The spectrum remains above 1.0 g out to a period of 1.8 seconds, although these results are less flat than those of the previous analysis, the spectral values only decay 0.1 g between 0.9 seconds and 1.8 seconds, where the principal decay begins. In short, when compared to the input rock motion (Figure 4) the EQL results show a significant deamplification of the short-period spectral values, a large shift in the fundamental period and amplification of the long-period response. These changes compared to the original input spectra are typical of EQL analyses for deep soil sites. MCEER/ATC-49 allows for a simple convolution analysis, where the input spectrum is assigned into a NEHRP site class C soil as an outcropping rock motion. Site Class C sites have Vs values that range from 360 m/s to 760 m/s. However, for this analysis, a specific value of about 600 m/s was used based on western U.S. rock conditions from Boore and Joyner (1997). The Boore and Joyner (1997) rock Vs profile has an average Vs value of 618 m/s in the upper 30 m of the profile, which is the mean VS3o value for rock sites in western North America and approximates the average rock Vs value at sites used to develop the current empirical attenuation relations for this region. Thus, if one chooses to perform simple convolution analysis using MCEER/ATC-49b guidance, it is recommended that the soil model extend to a depth where a Vs value of 24 fault­normal fault­parallel ofEQL MCEERI Vs mls mls. mls u.Vs Vs mls V s30 Vs MCEERlATC-guidance, it is recommended that the soil model extend to a depth where a V s value of 25 about 600 m/s is first encountered. For the I-15/1-80 site, this corresponds to a depth of about 200 m. The 200 m convolution analysis was conducted for the earthquake time histories with fault-normal directivity effects (Figure 4). The short period part of the spectrum begins with a pga of 0.6 g and reaches a peak value of 1.2 g at a period of 0.6 seconds. After the peak, the long-term response decays fairly linearly and slowly. The results of the 5 km deconvolution/convolution analysis and the 200 m convolution analysis can also be compared in Figure 4. As mentioned above, the deconvolution/convolution spectrum exhibits relatively linear features with a flat top between 0.8 and 1.7 seconds and slow linear decay; the 200 m deconvolution spectrum peaks much more quickly at a period of 0.6 seconds and has a peak spectral value that is 20 percent larger than the former analysis. However, the EQL modeling for this site suggests that a simple 200 m convolution analyses, as allowed by MCEER/ATC-49, may somewhat underestimate the long period ground motion for deep sedimentary basins, such as the Salt Lake Valley, when compared with a deep (2 km) deconvolution / convolution EQL analysis (Figure 4). Thus a simple 200 m convolution analysis is not recommend for developing design spectra because it does not appear to capture long-period effects. For the best-estimate soil profile and the case with fault directivity, the spectral acceleration values for the 2 km deconvolution / convolution analysis are somewhat higher at a period beginning at about 1 s (Figure 4). In addition, it appears that the spectral values of the 2 km deconvolution / convolution analysis are somewhat lower at shorter periods. 1-MCEERI about 1 s (Figure 4). In addition, it appears that the spectral values of the 2 deconvolution / convolution analysis are somewhat lower at shorter periods. 2.00 0.00 0.01 / \ / \ / \ / -B- -•- 2 km Deconvolution/Convolution, Fault 200 M Convolution, Fault Normal 0.1 1 Period of Vibration, (s) 10 FIGURE 5: Results of the 2 km NL deconvolution/convolution and 200 m convolution NL analysis for the best-estimate (i.e., mean) 1-80 Interchange Profile ,-... OJ) '-" ~::r ..0... ~ I-< -V V U u <t: ".'.§.. u v 0.. r:/J ~--------------------------~----------------------------.---------------------------~ 1.75 +----------------------------4-------/~_~,--------~ / , / , / \ / \ / \ 1.50 +--------------+--i-----~\----t I \ 1.25 1.00 0.75 --.... / 0.50 / ,/ / / / / / / / / / I \ / , , --e-- 2 km Deconvolution/Convolution, Fault Parallel Component --Normal Component --Component - - -. Target Rock Spectrum , , , \ , , , , " " " , 0.25 r--------I--------I--~'~,~. ~ ~~~ ............... -- 0.00 +-------~----~--~~~~~~--------~--~--~~--~~~+-------~----~~--~~~~~ tv 0\ 27 4.2 (2008) The one-dimensional EQL site response analyses documented in Bartlett et al. (2004) were repeated using full NL code (Deepsoil v 2.6). Figure 5 shows the site response results for fault-normal and fault-parallel spectra for the 2 km deconvolution/convolution analysis, the fault-normal spectrum for the 200 m convolution analysis, and the comparison of the fault-normal spectra for both the deconvolution/convolution analysis and the simplified 200 m convolution analysis. The results of the NL analysis exhibit more variability (i.e., greater spread) in the response values from the different input ground motions when compared with the results tendency for the soil to react nonlinearly to the different input motions because the damping and shear modulus parameters are updated for each time-step of the earthquake motion. The mean spectrum for the 2 deconvolution/convolution analysis with fault-normal directivity effects is shown in Figure 5. The mean spectrum has a pga value of 0.41 g, a very rounded peak of 1.1 g corresponding to a period of vibration of 0.8 seconds, with a slow decay thereafter. Figure 5 also shows results with fault-parallel directivity effects. The pga and spectral peak are similar to those of the fault-normal analysis, although the spectral shape is somewhat changed. The pga of 0.36 g is followed by steep and approximately linear growth to a sharp peak of 1.2 g at a period of vibration of 0.8 seconds with gradual decay thereafter. The 200 m convolution analysis was conducted using the fault-normal earthquake time histories as shown in Figure 5. The steep short period part of the spectrum begins Bartlett et al. companson of the EQL analysis. Reasons for increased variability in the NL results may include the km fault­normal with a pga value of 0.42 g and reaches a peak value of 1.23 g at a period of 0.8 seconds. After the peak, the longer period response decays fairly linearly and more quickly than the full deconvolution/convolution results. The 2 km deconvolution/convolution analysis and the 200 m convolution analysis can also be compared in Figure 5. This figure shows that the spectral shapes are more similar than the EQL analysis (Figure 4). As mentioned above, the NL deconvolution/convolution spectrum exhibits a rounded peak at 0.8 seconds and slow decay at longer periods. The 200 m NL deconvolution spectrum also peaks at a period of 0.8 seconds with a peak spectral value 12 percent larger than the former analysis. However, because the 200 m convolution analysis ignores the presence of a deep sedimentary basin, it still has the potential to underestimate the long-period response as previously discussed and is not recommend for deep soil sites. 4.3 Summary for Bartlett (2004) and Bartlett et al. (2008) A summary of the information above from Bartlett (2004) and Bartlett et al. (2008) is presented in Table 2. The pga values for the EQL method are between 0.1 g (25%) and 0.2 g (50%) larger than those of the NL method. Interestingly, the peak spectral values for the EQL method are between 0.0 g (0%) and 0.1 g (10%) lower than those of the NL method. The period of vibration that corresponds to the spectral peaks for the EQL method was reported as a range of values for some cases, if the spectral shape is relatively flat within that range. 28 TABLE 2: Summary table of spectral values for Bartlett 2004 and Bartlett et al., 2008. Analysis Type / Parameter Deconvolution/Convolution 200 m Convolution AnPaalyrsaims eTtyepr e Fault Normal Fault Parallel Fault Normal EQL NL EQL NL EQL NL Pga, Spectral peak (g) 1.1 1.1 1.2 Spectral Peak Period (s) Compared to the original rock spectra, the results of the NL site response analysis show deamplification of the short-period spectral values, a moderate shift in the fundamental period, and moderate amplification of the long-period response. These modifications to the original spectra are typical of NL analyses on deep soil sites; however, the changes are less pronounced using NL methods than using EQL methods. 4.4 Legacy Parkway site response analysis Additional ground response analyses were performed at the South and North Interchanges of the Legacy Parkway to evaluate the potential ground shaking resulting from rupture of the Weber-Davis County segment of the Wasatch fault. The evaluations for this event were done using both EQL and NL methods so that a comparison of the techniques could be made. Additional rupture events were evaluated for the North Interchange of the Legacy Parkway that include: rupture on the Salt Lake City and Brigham City segments of the Wasatch fault and a 475-year return period event. These analyses were done using NL site response methods and upper, mean and lower bound soil profiles. The South Interchange of the Legacy Parkway connecting to 1-215 is located approximately 2 kilometers west of the Wasatch Range near the Salt Lake / Davis County aI., pga, (g) 0.5 0.4 0.5 0.4 0.6 0.4 1.0 l.l 1.2 1.2 0.7-1.7 0.8 0.9 0.8 0.6 0.8 29 I 30 line. The North Interchange of the Legacy Parkway connecting to 1-15 and Highway 89 is located approximately 2 kilometers west of the Wasatch Range in Farmington, Utah as shown in Figure 2. 4.5 Comparison of equivalent-linear and nonlinear results One-dimensional site response analyses for the North and South Interchanges of Legacy Parkway were performed using the EQL and NL codes implemented in Deepsoil. In order to more closely compare the EQL and NL codes, the modified hyperbolic model was used for shear modulus degradation and damping formulations for both analyses (Section 3.1.3). Figures 6 to 9 show the site response results for a rupture of the Weber Segment of the Wasatch Fault Zone for the North and South Interchanges of Legacy Parkway. NL site response results for alternative rupture scenarios along the Wasatch Fault Zone (Salt Lake City Segment, Brigham City Segment, and 475-year return period) are included for comparison in Figures 10 to 12. The EQL spectral values are generally greater than the NL spectra for both interchanges (Figures 6 through 12). Both the EQL and NL spectra for the Legacy Parkway exhibit a significant shift in the predominant period from approximately 0.2 in the input rock target spectrum, to approximately 0.5 sec in the NGA spectrum to between 0.9 and 1.4 sec in the EQL and NL spectra. 3 od • i-H oo < o GO 1.25 -- 1.00 -- 0.50 0.25 -H- Upper Profile, Fault-Parallel Upper Profile, Fault-Normal Mean Profile, Fault-Parallel Mean Profile, Fault-Normal Lower Profile, Fault-Parallel -•- Lower Profile, Fault-Normal Weighted Average - • - Rock Target Spectrum 0.00 0.01 0.1 1 10 Period of Vibration, (s) FIGURE 6: Results of the EQL site response analysis for the South Interchange of Legacy Parkway for the rupture of the Weber Segment 1.50 ~------------------------~--------------------------~------------------------~ ,-.... ~ s:::f o -B- ~ Nonnal -B- ~ Nonnal -B- ~ Nonnal - --NGA " .~ 0.75 / _ - - Q) - - . " " g / / ~ / ~ / / ~ .-.- / ~ t-~~~--~·--~------------17~------~~~r---~~~--~~~~~------------1 0.. -- . r/J " " 1.50 1.25 -- 1.00 O 10.75 oo < 10.50 OH 00 0.25 0.00 -B- Upper Profile, Fault-Parallel -•- Upper Profile, Fault-Normal -B- Mean Profile, Fault-Parallel -•- Mean Profile, Fault-Normal • Lower Profile, Fault-Parallel -•- Lower Profile, Fault-Normal Weighted Average NGA - • - Rock Target Spectrum •1 - -§ -e e-• • _j i i i i i i 0.01 0.1 1 10 Period of Vibration, (s) FIGURE 7: Results of the EQL site response analysis for the North Interchange of Legacy Parkway for the rupture of the Weber Segment -e- ------ -e- ------ -e- -. ------ --/ '\ -- - . / / " " ofthe od % oo < ou 00 1.00 0.75 0.50 0.25 0.00 0.01 X \ Upper Profile, Fault-Parallel Upper Profile, Fault-Normal Mean Profile, Fault-Parallel - Mean Profile, Fault-Normal - Lower Profile, Fault-Parallel - Lower-Profile, Fault-Normal - Weighted Average - NGA • ~ Rock Target Spectrum 0.1 1 10 Period of Vibration, (s) FIGURE 8: Results of the NL site response analysis for the South Interchange of Legacy Parkway for the rupture of the Weber Segment r-... OJ) '-" d' ....0.... .. ~ \l) V u u ~ ].. ... u \l) 0.. r/) 1.50 .--------------------------.--------------------------.-------------------------~ 1.25 -+---------------+---------------i _. _. / / .-. - / / '\. / / / /' / ,...- - '\. -A- -.-Nonnal -A- -.-Nonnal -A- -.-Nonnal ----10 - - o . I-I 11oo30 .75 < 8 0.50 0.00 -B -a -B Upper Profile, Fault-Normal Mean Profile, Fault-Parallel Mean Profile, Fault-Normal Lower Profile, Fault-Parallel H- Lower Profile, Fault-Normal - Weighted Average - • ~ Rock Target Spectrum \ / \ 0.1 1 10 Period of Vibration, (s) FIGURE 9: Results of the NL site response analysis for the North Interchange of Legacy Parkway for the rupture of the Weber Segment ,-., ~ I=:~ 1.50 1.25 1.00 - -B- Upper Profile, Fault-Parallel ---B- ---B- --- --NGA - . - Spectrum -. / '\ / , / , '.g ~0.75 +-----------------------~-;------~~----~~~~--~~~----------------------~ Q) u u < ~ -- / - .-' ~0.50 +---_-_- -.-~---~------------r-~----~~------~~------~~--~~~~--------------~ 0.. C/1 0.25 0.01 1.00 0.75 -B- Upper Profile, Fault-Parallel -•- Upper Profile, Fault-Normal -B- Mean Profile, Fault-Parallel -«- Mean Profile, Fault-Normal -B- Lower Profile, Fault-Parallel -•- Lower Profile, Fault-Normal • Weighted Average NGA g0.50 FIGURE 10: Results of the NL site response analysis for the North Interchange of Legacy Parkway for the rupture of the Salt Lake City Segment ,---------------------------,---------------------------,---------------------------, -B- - -B- - -B- - - Weighted Average d' o --.~ ~ 0.50 +---------------------------~--------------------------~------------------------~ Q) u u <t: S t il) ~ r:/J ", ", /--- 0.25 t----------:;,L-~::IrJi:~tp:.-__::m;;;z::::!=~~~-----------l -------- --- 0.01 Period of Vibration, (s) 0.1 1 10 ofthe 1.00 0.75 -e-• Upper Profile, Fault-Parallel -•- Upper Profile, Fault-Normal -B- • Mean Profile, Fault-Parallel -•- • Mean Profile, Fault-Normal -B- Lower Profile, Fault-Parallel -«- • Lower Profile, Fault-Normal • Weighted Average NGA g 0.50 O O Period of Vibration, (s) FIGURE 11: Results of the NL site response analysis for the North Interchange of Legacy Parkway for the rupture of the Brigham City Segment -B- Upper Profile, Fault-Parallel --- -B-Mean Profile, Fault-Parallel --- Mean Profile, Fault-Normal -B- ---Lower Profile, Fault-Normal ,-b..I.), - Average '-" d' --00.g I-< ~ Q) uu -~ ..u~.... ~ 0.. C/) 0.25 ------ 0.00 0.01 0.1 1 10 1.00 0.75 .2 § 0 0oo) <: PH GO 50 0.25 0.00 -B- Upper Profile, Fault-Parallel -•-Upper -B- Mean Profile, Fault-Parallel - •- Mean Profile, Fault-Normal -B- Lower Profile, Fault-Parallel ••-Lower Weighted Average - 0.01 0.1 1 10 Period of Vibration, (s) FIGURE 12: Results of the NL site response analysis for the North Interchange of Legacy Parkway for the 475-year return period scenario -8- Upper Profile, Fault-Parallel --Upper Profile, Fault-Normal -S- Mean Profile, Fault-Parallel ___ Mean Profile, Fault-Normal -8- Lower Profile, Fault-Parallel --Lower Profile, Fault-Normal ~ OJ) - Weighted Average '-' ~~ --NGA ..0... ~ M 0.50 -(]) (]) uu <t: '."..§.. u (]) 0.. ifJ 0.00 -t-__ --'---_-'------'-----'--....L.......I----'--+ __ ---'--_---'------'------'-----'--....t........L......+ __ -----'-_---'--"~~~ ... 38 4.5.1 Equivalent-linear Figure 6 shows the EQL results for the South Interchange (mean profile) below compared to the input target rock spectrum and the mean NGA relations using the shear wave velocity of the mean profile (191 m/s). The NGA relations (Boore and Atkinson (2007), Campbell and Bozorgnia (2007), and Chiou and Youngs (2007)) match well with the EQL results at short periods (less than 0.05 seconds) and at long periods (greater than 2 seconds) and exceed the EQL results at other periods by up to a factor of two. EQL spectra for the deconvolution/convolution analysis with directivity for the South Interchange are shown in Figure 6. For the mean shallow profile, fault-normal component, the important spectral parameters include a PGA of 0.27 g followed by a peak value of 0.78 g corresponding to a period of vibration of 1.3 seconds. Figure 6 also shows results for the fault-parallel component. The peak ground acceleration of 0.29 g is followed by a peak value of 0.73 g at a corresponding period of vibration of 1.4 seconds. Figure 7 gives the EQL results for the North Interchange (mean profile) below compared to the input rock target spectrum and the mean NGA relations using the shear wave velocity of the mean profile (188 m/s). The results of the EQL analysis for the mean profile, fault normal component exceed the NGA relations (Boore and Atkinson (2007), Campbell and Bozorgnia (2007), and Chiou and Youngs (2007)) at periods less than 0.08 seconds and longer than 0.6 seconds and fall below the NGA relations by as much as 70 percent between 0.08 and 0.6 seconds. EQL spectra for the deconvolution/convolution analysis with directivity effects for the North Interchange are shown in Figure 7. For the mean profile, fault-normal component, the average spectral parameters include a PGA of 0.50 g, a peak value of 1.0 effects 39 g corresponding to a period of vibration of 0.9 seconds, and slow decay thereafter. Figure 7 also shows results for the fault-parallel component. The peak ground acceleration of 0.37 g is followed by a peak value of 0.92 g at a corresponding period of vibration of 0.9 seconds. 4.5.2 Nonlinear Figure 8 gives the NL results for the South Interchange (mean profile) below compared to the input rock target spectrum and the mean NGA relations using the shear wave velocity of the mean profile (191 m/s). The NGA relations (Boore and Atkinson (2007), Campbell and Bozorgnia (2007), and Chiou and Youngs (2007)) exceed the NL results by 70 percent at pga, as much as 100 percent between 0.1 and 1 second, and matches reasonably well after 3 seconds. NL spectra for the deconvolution/convolution analysis with directivity for the South Interchange are shown in Figure 8. For the mean profile, fault-normal component, the average spectral parameters include a PGA of 0.16 g and a peak value of 0.48 g at a period of vibration of 1.3 seconds. Figure 8 also shows results for the fault-parallel component. The peak ground acceleration of 0.20 g is followed by a peak value of 0.50 g at a corresponding period of vibration of 0.9 seconds. Figure 9 gives the NL results for the North Interchange below compared to the input rock target spectrum and the mean NGA relations using the shear wave velocity of the mean profile (188 m/s). The NGA relations (Boore and Atkinson (2007), Campbell and Bozorgnia (2007), and Chiou and Youngs (2007)) exceed the NL results by 35 mls). percent at pga, as much as 60 percent between 0.1 and 1 second, and matches reasonably well after 1 second. NL spectra for the deconvolution/convolution analysis for the North Interchange with directivity effects are shown in Figure 9. For the mean profile, fault-normal component, the average spectral values include a pga value of 0.25 g and a peak value of 0.73 g corresponding to a period of vibration of 1.2 seconds. Figure 9 also shows results for the fault-parallel component. The peak ground acceleration of 0.25 g is followed by a peak value of 0.63 g at a corresponding period of vibration of 0.9 seconds. The results of the NL site response also show deamplification of the short-period spectral values and a moderate shift in the fundamental period when compared to the input rock target spectrum. These modifications to the original spectra are typical of NL analyses on deep soil sites; however, the changes are less pronounced using NL methods than the same analysis using EQL methods. 4.6 Summary of Legacy ground response evaluations The NGA relations do not generally match the results of the Legacy site response analysis as described above; however, the shapes of the NL spectra correspond more closely to the NGA relations than those of the EQL spectra. A summary of the information above from the Legacy Interchange analyses is presented in Table 3. The values of peak ground acceleration for the EQL method are between 0.09 g (45%) and 0.25 g (100%) larger than those of the NL method. Similarly, the peak spectral values for the EQL method are between 0.23 g (62%) and 0.30 g (68%) larger than those of the NL method. 40 I 41 TABLE 3: Summary table of spectral values for the Legacy Report Analysis Type / Parameter North Interchange Fault Normal Fault Parallel South Interchange Fault Normal Fault Parallel EQL NL EQL NL EQL NL EQL NL Pga 0.5 0.25 0.37 0.25 0.27 0.16 0.29 0.20 Spectral peak (g) 1.0 0.73 0.92 0.63 0.78 0.48 0.73 0.50 Period (s) 0.9 1.2 0.9 0.9 1.3 1.3 1.4 0.90 There is a marked difference between the results of the NL and the EQL analyses. The NL spectra exhibit broad rounded spectral shapes and lower spectral values compared with those of the EQL analysis that tend to have more narrow peaks and greater variations in the results (Figures 13 and 14). The differences between the EQL and NL results for the sites analyzed in this study indicate that it may be difficult to fully characterize the differences between the methods based on just three sites. Variations in the soil profile from site to site can be significant. Thus it is difficult to isolate the differences in spectral parameters from the differences due to changes in the profile and input ground motions. However, from a modeling standpoint, NL analyses are preferable to EQL techniques and are recommended for design and evaluation purposes. pga (g) 1.25 •39 d .2 1oo3 0.75 ^ 0.50 2 o 0.00 0.1 1 Period of Vibration, (s) FIGURE 13: Weighted mean comparison of the NL and EQL site response analysis for the South Interchange of Legacy Parkway for the rupture of the Weber Segment 1.25 .,--------------.-------------.,.-------------, -Non-Linear Weighted Mean - - Equivalent-Linear Weighted Mean 1.00 +-------------------------~--------------------------~------------------------~ /-" II \ ~ / \ ~0.75 +-------------------------~------------------~------~----_r------------------~ § / ~ / ~ ~ / 8 / ~0.50 +----------------------4--------~~--~~------4-----~~~----------~ ..~... .,r (.) Q) 0- r./) 0.25 i----------9----------+-----~---___l 0.00 +-----~~--~~~~~~~------~-~~-~~~~------~--~--~~~~-Y 0.01 1 10 1.25 -3B do 2 2 00 0.25 0.00 1 Period of Vibration, (s) FIGURE 14: Weighted mean comparison of the NL and EQL site response analyses for the North Interchange of Legacy Parkway for the rupture of the Weber Segment --Non-LinearWeighted Mean - - Equivalent-LinearWeighted Mean 1.00 +---------------------------+---------------------------+-------------------------~ ,,-... ~ 0.75 +---------------------------+---------------------------+-------------------------~ r:£ o .~ I-< Q) Q) u u < 0.50 +----------------------+------------------~~ .. ~----~------------~ ] t) Q) 0.. r/l +-------------------------~~~~----------------------+-------------~~~------~ 0.01 0.1 10 5 A PRIORI GROUND MOTION SCENARIOS An instrument array, consisting of bridge, free-field and downhole strong motion sensors is planned for the North Interchange of the Legacy Parkway. UDOT requested that the deployment of the array should be accompanied by formal predictions of the level of ground shaking expected at the site. The estimates should be made a priori, because postearthquake evaluations will be biased because the measured results are known. A priori estimate are beneficial because they can be used to judge the accuracy and reasonableness of ground response analyses. In addition, the subsurface response predicted from the models can be used to select the placement of the downhole accelerometers in the subsurface strata. In contrast to the ground response analyses performed in the previous section, the predicted response spectra developed in this section (Figures 15 to 19) are based on the weighted mean results of the NL site response analysis. To determine the weighted mean spectra a weighting of 0.3 for the upper bound, 0.4 for the mean, and 0.3 for the lower bound spectra were applied to the spectral values. Where significant differences were found between the fault-normal and fault-parallel spectra, the weighted mean spectra were slightly adjusted to capture the near-fault effects and favor the fault-normal response. For example, the spectral values in Figures 14 and 17 were slightly increased near the spectral peaks to favor the fault-normal response spectrum. SCENARIOS 0.5 0.3 0.0 i i i J ! ! 1_ 0.01 0.1 1 10 FIGURE 15: A priori prediction of the NL response for the North Interchange of Legacy Parkway for the rupture scenario of the Weber Segment (Mw 7.0, Rrup 0.7 km) of the Wasatch Fault Zone based on spectra with directivity effects 1.0 ~--------------------------.---------------------------.---------------------------, 0.8 +---------------------------~--------------------------;---------------------------~ ~ on '-' Ii .0- ~ I-< -<1) <1) (.) (.) -<t: ..S... (.) <1) 0. V1 Period of Vibration, (s) 1.0 0.8 3B co 1 j) 1oo3 < -t-> o <u OH If! 0.5 0.3 0.0 0.01 0.1 Period of Vibration, (s) 1 10 FIGURE 16: A priori prediction of the NL response for the North Interchange of Legacy Parkway for the rupture scenario of the Salt Lake Segment (Mw 7.0, Rrup 18.6 km) of the Wasatch Fault Zone based on spectra with directivity effects .-------------------------.------------------------.------------------------~ +------------------------+------------------------r---------------------~ --O--J-) '--' f;::f ..0.. . ~ CI) Q) u u -~ -~ u CI) 0.. [/J effects 1.0 0.8 3 do 1 1oo3 < •a 00 0.5 0.3 0.0 0.01 0.1 Period of Vibration, (s) 1 10 FIGURE 17: A priori prediction of the NL response for the North Interchange of Legacy Parkway for the rupture scenario of the Brigham City Segment (Mw 7.0, Rrup 39.8 km) of the Wasatch Fault Zone based on spectra with directivity effects ~ ~ ~ ~ effects 1.0 0.8 3 do 1 1oo3 •<-»a-> o oo 0.5 0.3 0.0 0.01 0.1 Period of Vibration, (s) 1 10 FIGURE 18: A priori prediction of the NL response for the North Interchange of Legacy Parkway for the rupture scenario of the 475-year event (Mw 6.79, Rrup 12.0 km) of the Weber segment of the Wasatch Fault Zone 4^ 00 ~------------------------.------------------------.------------------------~ +-------------------------~-----------------------+------------------------~ ,-.... OJ) '--' ~~ 0 .~ Q) V <) <) ~ ".'.§... <) Q) 0.. ifl ofthe 1.0 0.8 OJJ ^-/ do 1 S 0.5 CD O O <u a GO 0.3 -" Weber Segment Scenario - *475 - Year Return Period Scenario Weber Segment • - Salt Lake City Scenario • - Brigham City Scenario 0.0 0.01 0.1 1 10 FIGURE 19: Comparison of a priori predictions of the NL response for the North Interchange of Legacy Parkway for relevant rupture scenarios - Scenario - -475 --- Salt Lake City Scenario - " /, ------... --- -... " ..,.,-.--._.-- ......... " ........ ._._.-._.-- -" Period of Vibration, (s) 50 The North Interchange of Legacy Parkway, which links the parkway with 1-15 and US-89 in Farmington, Utah, has been selected for instrumentation by Utah State University (USU) (Figure 2). A priori NL ground motion estimates for three rupture scenarios along the Wasatch Fault Zone are provided in this report including ruptures of the Brigham City, Weber, and Salt Lake City Segments. An additional probabilistic scenario for a 475-year return period was requested by UDOT and is considered using seismic deaggregation available from the USGS National Strong Ground Motion program. The spectrum in Figure 15 shows the a priori estimate of ground shaking for the rupture (Mw = 7.0, Rrup = 0.7 km) of the Weber Segment of the Wasatch Fault Zone. The weighted mean spectrum was increased by 0.07g (11%) at a period of vibration of 1.3 seconds to favor the near-fault effects of the fault-normal component that were not well represented in the weighted mean (see the spectra values in Figure 9 between 0.7 and 3.0 seconds). The predicted spectral parameters include a pga value of 0.25 g and a peak value of 0.72 g corresponding to a period of vibration of 1.2 seconds. A summary of key values along with a full table of spectra values is provided below in Tables 4 and 5. The spectrum in Figure 16 shows the a priori estimate of ground shaking for the rupture (Mw = 7.0, Rrup = 18.6 km) of the Salt Lake City Segment of the Wasatch Fault Zone. The weighted mean spectrum was not modified because the near-fault effects were well represented in the weighted mean (Figure 10). The predicted spectral parameters include a pga value of 0.11 g and a peak spectral value of 0.31 g corresponding to a period of vibration of 0.5 seconds. 11 %) 51 The spectrum in Figure 17 shows the a priori estimate of ground shaking for the rupture (Mw = 7.0, Rrup = 39.8 km) of the Brigham City Segment of the Wasatch Fault Zone. The weighted mean spectrum was not modified because the near-fault effects were well represented in the weighted mean (Figure 11). The predicted spectral parameters include a pga value of 0.08 g and a peak spectral value of 0.20 g corresponding to a period of vibration of 0.3 seconds. The spectrum in Figure 18 shows the a priori estimate of ground shaking for the 475-year return period rupture (Mw = 6.79, Rrup = 12.0 km) of the Weber Segment of the Wasatch Fault Zone. The weighted mean spectrum was increased by 0.03g (7%) at a period of vibration of 0.6 seconds to favor the near-fault effects of the fault normal component that were not well represented in the weighted mean (see the spectral values in Figure 12 between 0.3 and 1.0 seconds). The predicted spectral parameters include a pga value of 0.15 g and a peak spectral value of 0.45 g corresponding to a period of vibration of 0.6 seconds. A summary of key values along with a full table of spectral values is provided in Tables 4 and 5. Figure 19 shows the predicted spectra for the four rupture scenarios for the North Interchange of Legacy Highway. These spectra represent a best-estimate of the mean seismic response that can be expected at the North Interchange of Legacy Highway but are not suitable for design because they do not have the conservatism in the analysis required by MCEER/ATC-49. Tabulated values for each spectrum are provided in Table 5. MCEERlATC-52 TABLE 4: Summary table of spectral values for the a priori ground response predictions Analysis Type / Parameter Intensity Measure Level and Rupture Scenario Maximum Credible Earthquake (MCE) 475-Year Weber Salt Lake City Brigham City Weber Pga (g) 0.25 0.11 0.08 0.15 Spectral peak (g) 0.72 0.31 0.20 0.45 Period (s) 1.2 0.5 0.3 0.6 TABLE 5: Spectral values for the a priori ground response predictions Analysis Type / Parameter Intensity Measure Level and Rupture Scenario Maximum Credible Earthquake (MCE) 475-Weber Salt Lake City 0.01 0.25 0.11 0.08 0.15 0.02 0.25 0.11 0.08 0.15 0.05 0.25 0.12 0.08 0.16 0.08 0.26 0.16 0.12 0.20 0.1 0.28 0.18 0.13 0.22 0.2 0.35 0.26 0.19 0.31 0.3 0.43 0.29 0.20 0.36 0.5 0.55 0.31 0.20 0.44 0.8 0.65 0.27 0.16 0.42 1.0 0.70 0.24 0.14 0.35 1.5 0.69 0.18 0.10 0.28 2.0 0.52 0.12 0.07 0.21 3.0 0.31 0.07 0.03 0.11 5.0 0.12 0.02 0.01 0.03 8.0 0.03 0.01 0.0 0.01 10 0.02 0.0 0.0 0.01 pga (g) (s) Maxim um 47S-47S-Year Brigham City Weber (g) (g) (g) (g) O.ot 6 PLACEMENT OF DOWNHOLE ACCELEROMETERS Instrumentation of UDOT bridges and the underlying soil profile can provide valuable information on the structural response of bridge/soils systems. The addition of downhole seismic arrays of accelerometers to the structural instrumentation can provide important insight into the nature of the ground response and is interaction with the foundation and structure. Downhole accelerometer arrays allow seismic energy and deformation to be monitored as they propagate vertically through the soil media. Seismic energy can be significantly modified by propagation through soft, horizontally layered soil strata. Unfortunately, these effects are poorly understood because of the dearth of downhole arrays, and further instrumentation and research is needed in this area. Because the North Interchange of Legacy Highway is located within a kilometer of the Wasatch Fault Zone, a successful recording of a large magnitude event using a downhole, free-field and bridge seismic array will provide priceless data to the earthquake research community. The design of a downhole array should be conducted in connection with a site response analysis and formal predictions of the expected free-field response at the instrumentation site. During the site response analysis, inspection of the vertical propagation of seismic response may also indicate areas of high impedance contrast between major geologic sediment beds. Accelerometers should be placed above and below such high impedance interfaces in the site-specific profile. One free-field ACCELEROMETERS free­field free-54 TABLE 6: Shallow interpreted profile for North Interchange of Legacy Highway Soil Type Total Unit Weight Density Shear Wave Velocity Depth Impedance Relfection Coefficient (-) (kN/m3) (kg/m3) (m/s) (m) (kO) (-) Silty Sand Gravel Lean Clay Silty Sand Gravel Silty Sand Gravel Fat Clay Gravel Clayey Sand - accelerometer at the surface with a minimum of three additional accelerometers at depth is adequate to capture the effects of the local sedimentary soil layers on the transmission of seismic energy. The spectral results and interpreted profile from the site response analysis can be used to determine instrument locations in the site-specific profile. Table 6 shows the shallow interpreted profile for the North Interchange of Legacy Highway that was developed during the site response analysis. Among the best indicators of the high contrast boundaries are impedance contrast (reflection coefficient), shear wave velocity, and the results of the site response analysis. Figure 20 shows the recommended instrument locations, the shallow shear wave velocity profile, peak ground acceleration profile from the results of the site response analysis, and the geologic interpretation of major sediment beds based on cone penetration testing and boring data. Figure 20 shows the measured data and predicted results to enable easy placement of the instruments. m3) {m3} {s} {m} {Idl} H 19 979 160 4 157 0.077 21 1142 160 7 183 -0.072 20 989 160 9 158 -0.016 19 958 160 12 153 0.292 22 1244 225 13 280 -0.008 22 1223 225 15 275 0.008 22 1244 225 20 280 -0.284 20 1040 150 22 156 0.229 22 1244 200 25 249 -0.0427 21 1142 200 30 228 55 5 -- 10 -- 15 -- a. 20 -- 25 30 35 Peak Horizontal Acceleration, (g) 0.05 0.1 0.15 0.2 0.25 -I 1-• 1 1 1 0.3 Recent Alluvial Deposits Bonneville Lacustrine Deposits T Interbedded * Deposits f Cutler Lacustrine Deposits Interbedded Interglacial Deposits Reflection Coefficient I nstrument Location PGA Profile -0.4 -0.2 0.8 0.35 0.0 0.2 0.4 1.0 Shear Wave Velocity, (m/s) FIGURE 20: Recommended borehole accelerometer placement, shallow shear-wave velocity profile, peak horizontal acceleration (PGA) profile, and geologic interpretation of soil layering for North Interchange of Legacy Parkway o o +------+------+- ---+------~------~-----+-------+ 0 / 5 / '" 10 "- ~ ---- - • Interglacial / -- 15 '-E" • Instrument -E- / '-" ..c ....... ..c 0.. ....... <!) 0.. Q / --PG A <!) Q .... 20 25 • 30 L-____ ~ ______ ~ ____ ~ ______ ~ ____ ~ ______ ~ ____ __L 35 0.6 56 I recommend one free-field accelerometer at the surface, a second in the lean clay-layer of the Bonneville lacustrine deposits, a third and fourth in the gravel layers of the interbedded interglacial deposits, a fifth in the fat clay layer in the Cutler lacustrine deposits, and a possibly a sixth located in the clayey sand layer in the lower interbedded interglacial deposits. These locations meet the criteria described above and are expected to provide valuable data in the case of a seismic event in the area. clay layer 7 DISCUSSION The 1-80 and Legacy Highway NL ground response analyses are not easily comparable. The 1-80 spectra were developed using target spectra, which are appropriate for design purposes. The Legacy Highway spectra were primarily developed as "best-estimate" predictions at the bridge locations for structural response evaluations. Such large variations in amplitude of the target spectra and their corresponding input motions can create differing effects when convolved to the surface using the NL or EQL methods. When the EQL and NL results are more directly compared, where the input motion and soil profile do not vary, a more reasonable comparison and interpretation can be made. The 1-80 site and its analyses have the stiffest of the considered profiles and also the most severe earthquake loading. For this case (see Table 2), the pga and peak spectral acceleration correspond well between the two methods; however, a very large disparity is documented between the period of vibration that corresponds to the peak spectral acceleration. The significant variation in shape is clearly seen in Figures 4 and 5. As the soil profile becomes increasingly soft, the EQL analysis is expected to have more numerical difficulty calculating the large levels of shear strain that develop in soft layers. This appears to hold true in the results of the site response analysis for both Legacy Parkway sites. Table 3 shows the disparity between the NL and EQL results for the Legacy sites. The results of the EQL analysis are generally between 0.07 and 0.25g or 35 to 100 percent higher than those of the NL. The large disparity is also seen in the full best­estimate" 58 spectra in Figures 6 to 9. It is important to note that for these figures, the NL and EQL analysis are identical in every respect except for the calculation method: NL (shear modulus and damping values updated at every time step), and EQL (one values or shear modulus and damping used for the entire time history). These results suggest that greater emphasis can be placed on the results of the NL analysis because the disparity between the two methods is likely a result of incompatible shear modulus and damping parameters used by the EQL method. The strain-compatible EQL parameters, which do not vary during the EQL analysis, do not appear to correctly model the behavior of the soft soil layers. Use of the NL method of site response analysis is generally recommend for sites in the along the Wasatch Front where deep soil basins and very soft soil deposits exhibit NL behavior that is more accurately modeled with NL methods. However, to guard against potential unconservatism in design spectra, it is recommended that a "bounding" design spectrum be developed, as discussed in Bartlett (2004). This bounding spectrum should envelope all NL results, results from NGA relations and the minimum spectral shape for deterministic analyses given in MCEER/ATC-49. MCEERlATC-AAPPPPEENNDDIIXX Table of Contents The following page is a table of contents for the CD. Geologic and geotechnical data folder Maps, logs, and data used as reference for creation of the site-specific profiles. Soil and rock profiles Figures, tables, and material properties of the site-specific profiles Target spectra Target spectra for the site-specific profiles and rupture scenarios Site response spectra Resultant spectra from the spectral matching process and deconvolution analysis. Ground motions and profiles Electronic version of the original, rotated and spectral matched, and deconvolved ground motions and Deepsoil profiles for each site-specific profile and rupture scenario. ofthe ofthe REFERENCES Abrahamson, N.A. (1992). Non-stationary spectral matching, Seismological Research Letter, Vol. 63, No.l. Abrahamson, N.A., and Silva, W.J. (1997). Empirical response spectral attenuation relations for shallow crustal earthquakes: Seismological Research Letter, Vol. 68, p. 97- 127. American Association of State Highway and Transportation Officials (AASHTO), (2007). LRFD Bridge Design Specifications, Washington, D.C. Arnow, T., (1981). 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