Presentation is loading. Please wait.

Presentation is loading. Please wait.

2009 ODOT Geo/Hydro/HazMat Conference Geotechnical Aspects of ODOT Seismic Bridge Design Jan Six P.E. ODOT Bridge Section.

Similar presentations


Presentation on theme: "2009 ODOT Geo/Hydro/HazMat Conference Geotechnical Aspects of ODOT Seismic Bridge Design Jan Six P.E. ODOT Bridge Section."— Presentation transcript:

1 2009 ODOT Geo/Hydro/HazMat Conference Geotechnical Aspects of ODOT Seismic Bridge Design Jan Six P.E. ODOT Bridge Section

2 2009 ODOT Geo/Hydro/HazMat Conference Seismic Design Standards ODOT Geotechnical Manual AASHTO Guide Specifications for LRFD Seismic Bridge Design ODOT Bridge Design & Drafting Manual

3 2009 ODOT Geo/Hydro/HazMat Conference When is a Site Specific Response Analysis Needed? What does a Ground Response Analysis consist of? How is liquefaction and lateral spread quantified? How are these results used in design? When is liquefaction mitigation needed? Topics

4 2009 ODOT Geo/Hydro/HazMat Conference Hazard Analysis vs. Ground Response Analysis When is a Site Specific Response Analysis Needed? Site Specific Analysis ?????

5 2009 ODOT Geo/Hydro/HazMat Conference Seismic Hazard Analysis When is a Site Specific Response Analysis Needed? Probabilistic seismic hazard analysis (PSHA) or Deterministic seismic hazard analysis A deterministic hazard analysis (DSHA) involves evaluating the seismic hazard at a site for an earthquake of a specific magnitude occurring at a specific location, considering the attenuation of the ground motions with distance. The DSHA is usually conducted without regard for the likelihood of occurrence.

6 2009 ODOT Geo/Hydro/HazMat Conference Probabilistic Seismic Hazard Analysis (PSHA) When is a Site Specific Response Analysis Needed? Focuses on the spatial and temporal occurrence of earthquakes, and evaluates all of the possible earthquake sources contributing to the seismic hazard at a site with the purpose of developing ground motion data consistent with a specified uniform hazard level. Quantifies the uncertainties associated with the seismic hazard, including the location of the source, extent and geometry, maximum earthquake magnitudes, rate of seismicity, and estimated ground-motion parameters. Produces a uniform hazard acceleration response spectrum based on a specified uniform hazard level or probability of exceedance within a specified time period (i.e., 7% probability of exceedance in 75 years).

7 2009 ODOT Geo/Hydro/HazMat Conference Seismic Hazard Analysis When is a Site Specific Response Analysis Needed? Site specific hazard analysis are typically not performed on routine ODOT projects. Only if new information on new or existing sources was uncovered and documented. The 2002 USGS Probabilistic Seismic Hazard Maps are typically used.

8 2009 ODOT Geo/Hydro/HazMat Conference Usually done to either: 1.Develop acceleration response spectra (ARS) or 2.For liquefaction analysis When is a Site Specific Response Analysis Needed? Ground Response Analysis

9 2009 ODOT Geo/Hydro/HazMat Conference AASHTO General Procedure usually adequate Use 2002 USGS Seismic Hazard Maps to obtain bedrock PGA, S 0.2 and S 1 for 500 and 1000 yr return periods Determine soil site class designation (A – F) Develop Response Spectra When is a Site Specific Response Analysis Needed?

10 2009 ODOT Geo/Hydro/HazMat Conference General Procedure for determining Response Spectrum When is a Site Specific Response Analysis Needed? Use the program: SeismicDesignUtility_2002.mde

11 2009 ODOT Geo/Hydro/HazMat Conference A site-specific ground motion response analyses should be performed if any of the following apply (AASHTO): The site consists of Site Class F soils, as defined in Article 3.4.2.1. The bridge is considered critical or essential according to Article 4.2.2, for which a higher degree of confidence of meeting the seismic performance objectives of Article 3.2 is desired. When is a Site Specific Response Analysis Needed?

12 2009 ODOT Geo/Hydro/HazMat Conference AASHTO 3.4: If the site is located within 6 mi of a known active fault capable of producing a magnitude 5 earthquake and near fault effects are not modeled in the development of national ground motion maps, directivity and directionality effects should be considered as described in Article 3.4.3.1 and its commentary. When is a Site Specific Response Analysis Needed? AASHTO 3.4.3.1 For sites located within 6 mi of an active surface or shallow fault, as depicted in the USGS Active Fault Map, near-fault effects on ground motions should be considered to determine if these could significantly influence the bridge response. Near–Fault Effects

13 2009 ODOT Geo/Hydro/HazMat Conference AASHTO 3.4 definition: An active fault is defined as a near surface or shallow fault whose location is known or can reasonably be inferred and which has exhibited evidence of displacement in Holocene (or recent) time (in the past 11,000 yr, approximately). Use USGS Quaternary Fault database to determine if fault is considered active (<15ka) and for description of fault characteristics. When is a Site Specific Response Analysis Needed? Near–Fault Effects

14 2009 ODOT Geo/Hydro/HazMat Conference Directivity effects that increase ground motions for periods greater than 0.5 sec if the fault rupture propagates toward the site, and Directionality effects that increase ground motions for periods greater than 0.5 sec in the direction normal (perpendicular) to the strike of the fault. AASHTO 3.4.3.1: These effects are significant only for periods longer than 0.5 sec and normally would be evaluated only for essential or critical bridges having natural periods of vibration longer than 0.5 sec. When is a Site Specific Response Analysis Needed? Near–Fault Effects

15 2009 ODOT Geo/Hydro/HazMat Conference Currently no ODOT classification of essential or critical bridges. All bridges considered subject to near fault effects if criteria is met. Ground Response Analysis typically not required. Currently researching procedures to use for modifying general response spectrum. When is a Site Specific Response Analysis Needed? Near–Fault Effects

16 2009 ODOT Geo/Hydro/HazMat Conference Site Class F soils, as defined in Article 3.4.2.1: Peat or highly organic clays, greater than 10 ft in thickness, Very high plasticity clays (H > 25 ft with PI > 75) Very thick soft/medium stiff clays (H >120 ft), When is a Site Specific Response Analysis Needed?

17 2009 ODOT Geo/Hydro/HazMat Conference When is a Site Specific Response Analysis Needed? Evaluation of Liquefiable Soil Conditions (vs. Simplified Methods, when FOS liq 1.0) Very deep soil deposits or thin (<40 – 50 feet) soil layers over bedrock. Obtain better information for evaluating lateral deformations, near surface soil shear strain levels or deep foundation performance. Obtain ground surface PGA values for abutment wall or other design. A site-specific ground motion response analyses should be considered if any of the following apply:

18 2009 ODOT Geo/Hydro/HazMat Conference Ground Response Analysis Primary uses: Developing Site Specific Design Acceleration Response Spectra (ARS) Developing ground motion data for use in liquefaction evaluation When is a Site Specific Response Analysis Needed?

19 2009 ODOT Geo/Hydro/HazMat Conference Evaluates the response of a layered soil deposit subjected to earthquake motions. One-dimensional, equivalent-linear models are commonly utilized in practice. What does a Ground Response study consist of?

20 2009 ODOT Geo/Hydro/HazMat Conference What does a Ground Response study consist of? This model uses an iterative total stress approach to estimate the nonlinear elastic behavior of soils. Modified versions of the numerical model SHAKE (e.g., SHAKE2000, ProSHAKE, SHAKE91) are routinely used to simulate the propagation of seismic waves through the soil column

21 2009 ODOT Geo/Hydro/HazMat Conference Output consists of: acceleration response spectra at ground surface or at depths of interest, time histories at selected depths in the soil profile, plots of ground motion parameters with depth (e.g., PGA, maximum shear stress and shear strain), induced cyclic shear stresses in individual soil layers, which may be used in liquefaction analysis. What does a Ground Response study consist of?

22 2009 ODOT Geo/Hydro/HazMat Conference Earthquake Source Characterization (deaggregation of uniform seismic hazard) Earthquake Source Characterization (deaggregation of uniform seismic hazard) Develop input ground motions (time-histories) Develop input ground motions (time-histories) Develop soil profile and dynamic properties for soil model Develop soil profile and dynamic properties for soil model Run program and develop response spectrum from output Run program and develop response spectrum from output Acceleration Response Spectra Development Steps What does a Ground Response study consist of?

23 2009 ODOT Geo/Hydro/HazMat Conference Develop Uniform Hazard Spectrum from 2002 USGS Seismic Hazard maps (target bedrock spectrum) Develop Uniform Hazard Spectrum from 2002 USGS Seismic Hazard maps (target bedrock spectrum) Use the deaggregation information from the 2002 USGS Seismic Hazard database to obtain information on the primary sources that affect the site. Use the deaggregation information from the 2002 USGS Seismic Hazard database to obtain information on the primary sources that affect the site. Review USGS deaggregation data to: Review USGS deaggregation data to: Determine and characterize primary seismic sources Determine and characterize primary seismic sources Determine magnitude (M) and distance (R) of each source Determine magnitude (M) and distance (R) of each source Earthquake Source Characterization Design Response Spectra from Ground Response Analysis

24 2009 ODOT Geo/Hydro/HazMat Conference Earthquake Source Characterization Design Response Spectra from Ground Response Analysis All seismic sources (M-R pairs) that contribute more than about 5% to the hazard in the period range of interest should be considered. All seismic sources (M-R pairs) that contribute more than about 5% to the hazard in the period range of interest should be considered. Scale (or spectrally match) earthquake time histories to the target spectrum Scale (or spectrally match) earthquake time histories to the target spectrum

25 2009 ODOT Geo/Hydro/HazMat Conference Earthquake Source Characterization Design Response Spectra from Ground Response Analysis 2002 USGS PSHA maps

26 2009 ODOT Geo/Hydro/HazMat Conference Earthquake Source Characterization Design Response Spectra from Ground Response Analysis USGS Web Site:http://earthquake.usgs.gov/research/hazmaps/ Custom Mapping Analysis Tools

27 2009 ODOT Geo/Hydro/HazMat Conference Design Response Spectra from Ground Response Analysis Earthquake Source Characterization (Deaggregation)

28 2009 ODOT Geo/Hydro/HazMat Conference Design Response Spectra from Ground Response Analysis

29 2009 ODOT Geo/Hydro/HazMat Conference 2475 year Period = 0 sec Period = 0.1 sec Period = 0.2 sec Period = 0.3 sec Period = 0.5 sec Period = 1 sec Period = 2 sec PGA = 0.3923 SA = 0.784 SA = 0.9313 SA = 0.8206 SA = 0.6283 SA = 0.3284 SA = 0.1531 SUMMARY STATISTICS Cont. (%) R (km) M Cont. (%) R (km) M Cont. (%) R (km) M Cont. (%) R (km) M Cont. (%) R (km) M Cont. (%) R (km) M Cont. (%) R (km) M Mean Values --29.76.760.82--24.76.510.87--30.76.780.92--37.27.030.95--55.67.571.05--61.37.731.07--70.57.91.18 Modal Values --7.56.63-0.24--7.76.63-0.05--88.591.42--88.591.29--88.591.03--88.590.95--88.590.94 Gridded Modal 6.40888.59 1 - 2 1 - 25.5437.66.63 0 - 1 6.90988.59 1 - 2 1 - 29.49788.59 16.1388.59 16.988.59 16.9688.59 Principle Sources (contributions >10%) WUS shallow gridded 54.179.55.960.7962.589.85.850.8454.08105.970.946.5110.16.080.9130.5210.16.240.9626.4111.76.35121.514.16.461.14 Wash-Oreg faults 22.559.86.74-0.0719.849.66.720.1221.929.76.720.122.579.76.730.1119.049.56.750.2417.829.96.750.3215.4610.96.750.53 M 9.0 Subduction 13.039891.54--------13.8298.291.5217.9598.991.428.710091.1432.8210191.0634.910291.04 M 8.3 Subduction ------------------------12.3899.38.31.9421.121028.31.7522.341038.31.7527.231088.31.72 Individual fault hazard details (contributions >1%) Grant Butte Fault 1.3417.86.21.941.4917.96.21.91.3417.76.21.881.6917.66.21.871.1617.86.21.961.2118.16.21.91.3816.86.21.9 Helvetia Fault 1.0315.76.380.72--------1.0615.56.380.781.0315.36.390.86------------------------ Portland Hills Fault Char. 6.568.36.96-0.42--------6.088.26.96-0.27-------------------------------- Portland Hills Fault 138.46.72-0.2311.318.26.71-0.0812.298.36.72-0.112.318.36.72-0.0710.658.36.730.139.618.46.730.27.768.36.740.4 877 Portland Hills Fault --------5.518.16.95-0.21--------6.438.26.96-0.295.828.36.96-0.145.578.36.97-0.14.848.36.970.06 Earthquake Source Characterization Design Response Spectra from Ground Response Analysis

30 2009 ODOT Geo/Hydro/HazMat Conference 2475 year Period = 0 sec Period = 0.1 sec Period = 0.2 sec Period = 0.3 sec Period = 0.5 sec Period = 1 sec Period = 2 sec PGA = 0.3923 SA = 0.784 SA = 0.9313 SA = 0.8206 SA = 0.6283 SA = 0.3284 SA = 0.1531 SUMMARY STATISTICS Cont. (%) R (km) M Cont. (%) R (km) M Cont. (%) R (km) M Cont. (%) R (km) M Cont. (%) R (km) M Cont. (%) R (km) M Cont. (%) R (km) M Mean Values --29.76.760.82--24.76.510.87--30.76.780.92--37.27.030.95--55.67.571.05--61.37.731.07--70.57.91.18 Modal Values --7.56.63-0.24--7.76.63-0.05--88.591.42--88.591.29--88.591.03--88.590.95--88.590.94 Gridded Modal 6.40888.59 1 - 2 1 - 25.5437.66.63 0 - 1 6.90988.59 1 - 2 1 - 29.49788.59 16.1388.59 16.988.59 16.9688.59 Principle Sources (contributions >10%) WUS shallow gridded 54.179.55.960.7962.589.85.850.8454.08105.970.946.5110.16.080.9130.5210.16.240.9626.4111.76.35121.514.16.461.14 Wash-Oreg faults 22.559.86.74-0.0719.849.66.720.1221.929.76.720.122.579.76.730.1119.049.56.750.2417.829.96.750.3215.4610.96.750.53 M 9.0 Subduction 13.039891.54--------13.8298.291.5217.9598.991.428.710091.1432.8210191.0634.910291.04 M 8.3 Subduction ------------------------12.3899.38.31.9421.121028.31.7522.341038.31.7527.231088.31.72 Individual fault hazard details (contributions >1%) Grant Butte Fault 1.3417.86.21.941.4917.96.21.91.3417.76.21.881.6917.66.21.871.1617.86.21.961.2118.16.21.91.3816.86.21.9 Helvetia Fault 1.0315.76.380.72--------1.0615.56.380.781.0315.36.390.86------------------------ Portland Hills Fault Char. 6.568.36.96-0.42--------6.088.26.96-0.27-------------------------------- Portland Hills Fault 138.46.72-0.2311.318.26.71-0.0812.298.36.72-0.112.318.36.72-0.0710.658.36.730.139.618.46.730.27.768.36.740.4 877 Portland Hills Fault --------5.518.16.95-0.21--------6.438.26.96-0.295.828.36.96-0.145.578.36.97-0.14.848.36.970.06 Period = 0.1 sec SA = 0.784 Cont. (%) R (km) M --24.76.510.87 --7.76.63-0.05 5.5437.66.63 0 - 1 62.589.85.850.84 19.849.66.720.12 -------- -------- 1.4917.96.21.9 -------- -------- 11.318.26.71-0.08 5.518.16.95-0.21 Period = 2 sec SA = 0.1531 Cont. (%) R (km) Me --70.57.91.18 --88.590.94 16.9688.59 1 - 2 1 - 2 21.514.16.461.14 15.4610.96.750.53 34.910291.04 27.231088.31.72 1.3816.86.21.9 -------- -------- 7.768.36.740.4 4.848.36.970.06 Earthquake Source Characterization Design Response Spectra from Ground Response Analysis

31 2009 ODOT Geo/Hydro/HazMat Conference Most Significant Contributors to Seismic Ground Motion Hazard Design Response Spectra from Ground Response Analysis 0 – 0.5s period: Shallow Crustal 0.5 – 2s period: Subduction Zone Mega-Thrust Earthquake Source Characterization In areas where the hazard has a significant contribution from both the Cascadia Subduction Zone (CSZ) and from crustal sources, both earthquake sources need to be included in the analysis and development of a site specific response spectra.

32 2009 ODOT Geo/Hydro/HazMat Conference Selection of Time Histories Design Response Spectra from Ground Response Analysis considering tectonic environment and style of faulting (subduction zone, Benioff zone, or shallow crustal faults), seismic source-to-site-distance, earthquake magnitude, duration of strong shaking, peak acceleration, site subsurface characteristics, predominant period, spectral shape

33 2009 ODOT Geo/Hydro/HazMat Conference Selection and Scaling of Time Histories Design Response Spectra from Ground Response Analysis AASHTO (2009) allows two options for the selection of time histories to use in ground response analysis. The two options are: a) Use a suite of 3 response-spectrum-compatible time histories with the design response spectrum developed enveloping the maximum response, or b) Use of at least 7 time histories and develop the design spectrum as the mean of the computed response spectra.

34 2009 ODOT Geo/Hydro/HazMat Conference Design Response Spectra from Ground Response Analysis Use at least three (3) spectrum-compatible time histories, representing the seismic source characteristics. Used for single primary source sites Match the selected time-histories to the target spectrum using response spectrum matching techniques. Develop the design response spectrum by enveloping the caps of the resulting response spectra. Selection and Scaling of Time Histories

35 2009 ODOT Geo/Hydro/HazMat Conference Selection and Scaling of Time Histories: Design Response Spectra from Ground Response Analysis Sites with multiple primary sources Difficult to match time histories from every source to the entire target spectrum (gives unrealistic results) Use a collection of time histories that include at least three (3) ground motion records representative each primary source (typically subduction zone events and shallow crustal earthquakes) Scale the records associated with each primary source so that the average of the records closely matches the target spectrum in the period range of significance. Develop the mean spectrum for each primary source Design response spectrum is developed as an envelope with minor reductions in the spectral peaks (mean + one standard deviation).

36 2009 ODOT Geo/Hydro/HazMat Conference Four earthquake records based on PSHA deaggregation, deterministic specta Two Shallow Crustal (SC-1, SC-2) Two Subduction Zone (CSZ-1, CSZ-2) EarthquakeStationDirectionMagnitudeDistance SC-1 Northridge, CA Santa Monica City Hall 360 deg. 6.7 18 km SC-2 Northridge, CA Santa Monica City Hall 90 deg. 6.7 18 km CSZ-1 Michoacán, MEX La Union 90 deg. 8.1 83.9 km CSZ-2 Michoacán, MEX Zihuatenejo 90 deg. 8.1 132.6 km Scaling of Time Histories Design Response Spectra from Ground Response Analysis

37 2009 ODOT Geo/Hydro/HazMat Conference Scaling to get the geometric mean matched to period range of predominate hazard contribution Scaling of Time Histories Design Response Spectra from Ground Response Analysis

38 2009 ODOT Geo/Hydro/HazMat Conference Once the time histories have been scaled or spectrally matched, they can be used directly as input into the ground response analysis programs to develop response spectra and other seismic design parameters. Five percent (5%) damping is typically used in all site response analysis. Scaling of Time Histories Design Response Spectra from Ground Response Analysis

39 2009 ODOT Geo/Hydro/HazMat Conference Select bent location Develop input parameters dependent on type of analysis, total or effective stress (nonlinear) dependent on type of analysis, total or effective stress (nonlinear) Shear wave velocity profile Shear wave velocity profile static and dynamic soil properties static and dynamic soil properties Site Characterization Design Response Spectra from Ground Response Analysis

40 2009 ODOT Geo/Hydro/HazMat Conference Total Stress Analysis SHAKE91 Computer Program (Shake2000, Proshake) SHAKE91 Computer Program (Shake2000, Proshake) One Dimensional Wave Propagation Theory One Dimensional Wave Propagation Theory Vertical Propagation of Shear Waves Vertical Propagation of Shear Waves Equivalent Linear Analysis Equivalent Linear Analysis Design Response Spectra from Ground Response Analysis Effective Stress, Nonlinear Analysis D-MOD, DESRA Computer Program D-MOD, DESRA Computer Program One Dimensional Wave Propagation Theory One Dimensional Wave Propagation Theory Vertical Propagation of Shear Waves Vertical Propagation of Shear Waves Models pore water pressure generation Models pore water pressure generation Models nonlinear soil degradation Models nonlinear soil degradation

41 2009 ODOT Geo/Hydro/HazMat Conference Design Response Spectra from Ground Response Analysis

42 2009 ODOT Geo/Hydro/HazMat Conference Design Response Spectra from Ground Response Analysis

43 2009 ODOT Geo/Hydro/HazMat Conference Design Response Spectra from Ground Response Analysis

44 2009 ODOT Geo/Hydro/HazMat Conference Design Response Spectra from Ground Response Analysis

45 2009 ODOT Geo/Hydro/HazMat Conference Liquefaction Assessment from Ground Response Analysis Preliminary Screening Liquefaction Assessment not required if: The bedrock PGA (or Acceleration Coefficient, As) is less than 0.10g, The ground water table is more than 75 feet below the ground surface, The soils in the upper 75 feet of the profile have a minimum SPT resistance, corrected for overburden depth and hammer energy (N 60 ), of 25 blows/ft, or a cone tip resistance qc of 150 tsf. Liquefaction Assessment Procedures (AASHTO 6.8 and GDM Section 6.5.2.2)

46 2009 ODOT Geo/Hydro/HazMat Conference Preliminary Screening (cont.) Liquefaction Assessment not required if: All soils in the upper 75 feet are classified as cohesive, and Have a PI 18. Note that cohesive soils with PI 18 may still be very soft or exhibit sensitive behavior and could therefore undergo significant strength loss under earthquake shaking. This criterion should be used with care and good engineering judgment. Liquefaction Assessment Procedures (AASHTO 6.8 and GDM Section 6.5.2.2) Liquefaction Assessment from Ground Response Analysis

47 2009 ODOT Geo/Hydro/HazMat Conference Simplified (empirical-based) Procedures (Seed & Idriss and others) Simplified (empirical-based) Procedures (Seed & Idriss and others) Limited to depths of about 50 feet Limited to depths of about 50 feet Total stress ground response analysis methods, used to obtain parameters for use in simplified procedures Total stress ground response analysis methods, used to obtain parameters for use in simplified procedures Limited to low to moderate cyclic strain and moderate peak accelerations Limited to low to moderate cyclic strain and moderate peak accelerations Effective stress, nonlinear ground response analysis methods are used to obtain pore pressure ratio to assess liquefaction potential Effective stress, nonlinear ground response analysis methods are used to obtain pore pressure ratio to assess liquefaction potential More sophisticated analysis, requires peer review More sophisticated analysis, requires peer review Liquefaction Assessment Procedures (AASHTO 6.8) Liquefaction Assessment from Ground Response Analysis

48 2009 ODOT Geo/Hydro/HazMat Conference Simplified Procedures (Seed & Idriss and others) Simplified Procedures (Seed & Idriss and others) Limited to depths of about 50 feet Limited to depths of about 50 feet Stress reduction factor (r d ), becomes Stress reduction factor (r d ), becomes highly variable and uncertain with depth Liquefaction Assessment Procedures Liquefaction Assessment from Ground Response Analysis

49 2009 ODOT Geo/Hydro/HazMat Conference Simplified Procedures (Seed & Idriss and others) Liquefaction Assessment Procedures Cyclic Resistance Ratio (CRR) Liquefaction Assessment from Ground Response Analysis

50 2009 ODOT Geo/Hydro/HazMat Conference Earthquake Source Characterization Earthquake Source Characterization Identify primary sources contributing to the hazard Identify primary sources contributing to the hazard Attenuate PGA from primary source(s) to site (given M-R pairs) Attenuate PGA from primary source(s) to site (given M-R pairs) Develop soil profile and dynamic properties for soil model Develop soil profile and dynamic properties for soil model Apply soil amplification factors to obtain surface PGA for use with simplified procedures Apply soil amplification factors to obtain surface PGA for use with simplified proceduresOR Perform ground response analysis Perform ground response analysis total stress or total stress or effective stress, nonlinear analysis effective stress, nonlinear analysis Ground Response Analysis for Liquefaction Assessment Liquefaction Assessment from Ground Response Analysis

51 2009 ODOT Geo/Hydro/HazMat Conference 2475 year Period = 0 sec Period = 0.1 sec Period = 0.2 sec Period = 0.3 sec Period = 0.5 sec Period = 1 sec Period = 2 sec PGA = 0.3923 SA = 0.784 SA = 0.9313 SA = 0.8206 SA = 0.6283 SA = 0.3284 SA = 0.1531 SUMMARY STATISTICS Cont. (%) R (km) M Cont. (%) R (km) M Cont. (%) R (km) M Cont. (%) R (km) M Cont. (%) R (km) M Cont. (%) R (km) M Cont. (%) R (km) M Mean Values --29.76.760.82--24.76.510.87--30.76.780.92--37.27.030.95--55.67.571.05--61.37.731.07--70.57.91.18 Modal Values --7.56.63-0.24--7.76.63-0.05--88.591.42--88.591.29--88.591.03--88.590.95--88.590.94 Gridded Modal 6.40888.59 1 - 2 1 - 25.5437.66.63 0 - 1 6.90988.59 1 - 2 1 - 29.49788.59 16.1388.59 16.988.59 16.9688.59 Principle Sources (contributions >10%) WUS shallow gridded 54.179.55.960.7962.589.85.850.8454.08105.970.946.5110.16.080.9130.5210.16.240.9626.4111.76.35121.514.16.461.14 Wash-Oreg faults 22.559.86.74-0.0719.849.66.720.1221.929.76.720.122.579.76.730.1119.049.56.750.2417.829.96.750.3215.4610.96.750.53 M 9.0 Subduction 13.039891.54--------13.8298.291.5217.9598.991.428.710091.1432.8210191.0634.910291.04 M 8.3 Subduction ------------------------12.3899.38.31.9421.121028.31.7522.341038.31.7527.231088.31.72 Individual fault hazard details (contributions >1%) Grant Butte Fault 1.3417.86.21.941.4917.96.21.91.3417.76.21.881.6917.66.21.871.1617.86.21.961.2118.16.21.91.3816.86.21.9 Helvetia Fault 1.0315.76.380.72--------1.0615.56.380.781.0315.36.390.86------------------------ Portland Hills Fault Char. 6.568.36.96-0.42--------6.088.26.96-0.27-------------------------------- Portland Hills Fault 138.46.72-0.2311.318.26.71-0.0812.298.36.72-0.112.318.36.72-0.0710.658.36.730.139.618.46.730.27.768.36.740.4 877 Portland Hills Fault --------5.518.16.95-0.21--------6.438.26.96-0.295.828.36.96-0.145.578.36.97-0.14.848.36.970.06 Period = 0 sec PGA = 0.3923 Cont. (%) R (km) M --29.76.760.82 --7.56.63-0.24 6.40888.59 1 - 2 1 - 2 54.179.55.960.79 22.559.86.74-0.07 13.039891.54 -------- 1.3417.86.21.94 1.0315.76.380.72 6.568.36.96-0.42 138.46.72-0.23 -------- Earthquake Source Characterization Liquefaction Assessment from Ground Response Analysis

52 2009 ODOT Geo/Hydro/HazMat Conference Earthquake Source Characterization Three Primary Sources for consideration Shallow Crustal Shallow Crustal Gridded (random) Gridded (random) Subduction Zone Subduction Zone For the crustal and gridded sources, review the individual fault details to select fault characteristics (M, R, fault mechanism, etc.) most relevant to the hazard. Liquefaction Assessment from Ground Response Analysis

53 2009 ODOT Geo/Hydro/HazMat Conference Summary of Magnitude, Distance and PGA (1000-yr return period) Magnitude and Distance pairs represent weighted averages of the individual sources Attenuate PGA from Source to Site SourceMagnitudeDistance, (km) Depth, (km) Crustal6.728.410.5 Subduction9.09820 Liquefaction Assessment from Ground Response Analysis

54 2009 ODOT Geo/Hydro/HazMat Conference Shallow Crustal: Shallow Crustal: Boore et al. (1997) Boore et al. (1997) Abrahamson and Silva (1997) Abrahamson and Silva (1997) Sadigh et al. (1997) Sadigh et al. (1997) Spudich et al., 1999, Spudich et al., 1999, Campbell and Bozorgnia (2003). Campbell and Bozorgnia (2003). Cascadia Subduction Zone: Cascadia Subduction Zone: Youngs et. al. (1997) Youngs et. al. (1997) Sadigh et al. (1997) Sadigh et al. (1997) Ground motion attenuation relationships used in 2002 USGS PHSA Liquefaction Assessment from Ground Response Analysis

55 2009 ODOT Geo/Hydro/HazMat Conference Attenuate PGA from Source to Site Liquefaction Assessment from Ground Response Analysis

56 2009 ODOT Geo/Hydro/HazMat Conference Attenuate PGA from Source to Site Liquefaction Assessment from Ground Response Analysis

57 2009 ODOT Geo/Hydro/HazMat Conference Summary of Magnitude, Distance and PGA (1000-yr return period) SourceMagnitudeDistance, (km) Depth, (km)PGA rock Crustal6.728.410.50.38 Subduction9.098200.09 Magnitude and Distance pairs represent weighted averages of the individual sources Attenuate PGA from Source to Site Liquefaction Assessment from Ground Response Analysis

58 2009 ODOT Geo/Hydro/HazMat Conference Select bent location Develop input parameters dependent on type of analysis, total or effective stress (nonlinear) dependent on type of analysis, total or effective stress (nonlinear) shear wave velocity profile shear wave velocity profile static and dynamic soil properties static and dynamic soil properties Site Characterization Liquefaction Assessment from Ground Response Analysis

59 2009 ODOT Geo/Hydro/HazMat Conference Total Stress Analysis SHAKE91 Computer Program (Shake2000, Proshake) SHAKE91 Computer Program (Shake2000, Proshake) Calculate cyclic shear stress ratio (CSR) with depth Calculate cyclic shear stress ratio (CSR) with depth Calculate cyclic resistance ratio (CRR) with depth Calculate cyclic resistance ratio (CRR) with depth FOS against liquefaction equals (CRR/CSR) FOS against liquefaction equals (CRR/CSR) Effective Stress, Nonlinear Analysis Used in areas of high accelerations and high cyclic shear strains Used in areas of high accelerations and high cyclic shear strains D-MOD, DESRA or other computer Program D-MOD, DESRA or other computer Program Calculates pore pressure ratio, Ru, with depth in soil profile Calculates pore pressure ratio, Ru, with depth in soil profile Determine where Ru 0.80 – 0.90 for liquefaction Determine where Ru 0.80 – 0.90 for liquefaction Liquefaction Assessment from Ground Response Analysis

60 2009 ODOT Geo/Hydro/HazMat Conference Selection of Time Histories use at least: 3 motions representative of subduction zone events and 3 motions representative of subduction zone events and 3 motions appropriate for shallow crustal earthquakes 3 motions appropriate for shallow crustal earthquakes Scaled to the bedrock PGA determined from attenuation relationships Scaled to the bedrock PGA determined from attenuation relationships Liquefaction Assessment from Ground Response Analysis

61 2009 ODOT Geo/Hydro/HazMat Conference Shake Analysis; Peak Acceleration Liquefaction Assessment from Ground Response Analysis

62 2009 ODOT Geo/Hydro/HazMat Conference CSR(Shake) vs. CSR Simplified Procedure Liquefaction Assessment from Ground Response Analysis

63 2009 ODOT Geo/Hydro/HazMat Conference Shake Analysis; FOS Against Liquefaction Subduction Zone Liquefaction Assessment from Ground Response Analysis

64 2009 ODOT Geo/Hydro/HazMat Conference Subduction Zone Shake Analysis; FOS Against Liquefaction Liquefaction Assessment from Ground Response Analysis

65 2009 ODOT Geo/Hydro/HazMat Conference Shake Analysis; FOS Against Liquefaction Subduction Zone Liquefaction Assessment from Ground Response Analysis

66 2009 ODOT Geo/Hydro/HazMat Conference Crustal EQs Shake Analysis; FOS Against Liquefaction Liquefaction Assessment from Ground Response Analysis

67 2009 ODOT Geo/Hydro/HazMat Conference Crustal EQs Shake Analysis; FOS Against Liquefaction Liquefaction Assessment from Ground Response Analysis

68 2009 ODOT Geo/Hydro/HazMat Conference Crustal EQs Shake Analysis; FOS Against Liquefaction Liquefaction Assessment from Ground Response Analysis

69 2009 ODOT Geo/Hydro/HazMat Conference FOS Against Liquefaction Liquefaction Assessment from Ground Response Analysis FOS < 1.1 » Liquefaction (also indicates the potential for liquefaction- induced ground movement (lateral spread and settlement). FOS between 1.1 and 1.4 » reduced soil shear strengths due to excess pore pressure generation. FOS > 1.4 » excess pore pressure generation is considered negligible and the soil does not experience appreciable reduction in shear strength.

70 2009 ODOT Geo/Hydro/HazMat Conference Crustal and Subduction Zone EQs DMOD Analysis; Liquefaction Assessment Liquefaction Assessment from Ground Response Analysis

71 2009 ODOT Geo/Hydro/HazMat Conference Use deepest liquefaction depth with UHS Design Response Spectra (from either AASHTO General Procedure or Ground Response Analysis) Use deepest liquefaction depth with UHS Design Response Spectra (from either AASHTO General Procedure or Ground Response Analysis) Design Response Spectrum cannot be lower than 2/3 rd of spectrum from the AASHTO General Procedure Design Response Spectrum cannot be lower than 2/3 rd of spectrum from the AASHTO General Procedure Recommendations

72 2009 ODOT Geo/Hydro/HazMat Conference Lateral Spread Assessment Residual shear strengths are used in liquefiable layers, Typically dont use K h or K v (de-coupled analysis), If FOS < 1.0; Flow failure If FOS 1.0; Deformation Analysis Use conventional limit equilibrium analysis to assess slope failure potential

73 2009 ODOT Geo/Hydro/HazMat Conference Lateral Spread Assessment Empirically-based displacement estimates for lateral spreading (Youd et al. (2002), Newmark-type analyses using acceleration time histories generated from site-specific soil response modeling. Simplified charts based on Newmark-type analyses (Makdisi and Seed, 1978) Methods to estimate the magnitude of seismically induced lateral slope deformation include:

74 2009 ODOT Geo/Hydro/HazMat Conference Lateral Spread Assessment Simplified procedures based on refined Newmark-type analyses (Bray and Travasarou 2007, Saygili and Rathje 2008) Simplified charts based on nonlinear, effective stress modeling (Dickenson et al, 2002) Two-dimensional numerical modeling of dynamic slope deformation. Methods to estimate the magnitude of seismically induced lateral slope deformation include:

75 2009 ODOT Geo/Hydro/HazMat Conference Lateral Spread Assessment Several of these methods should be used as appropriate, and engineering judgment applied to the results, to determine the most reasonable range of predicted displacements

76 2009 ODOT Geo/Hydro/HazMat Conference How are these results used in design? Liquefaction effects include: reduced axial and lateral capacities and stiffness in deep foundations, ground settlement and possible downdrag effects lateral spread, global instabilities and displacements of slopes and embankments, loads transferred to foundation piles and shafts from lateral displacements

77 2009 ODOT Geo/Hydro/HazMat Conference How are these results used in design? Bridge Approach Fills: Assess performance requirements (no-collapse & serviceability) Global stability Settlement Allowable deformation and foundation damage

78 2009 ODOT Geo/Hydro/HazMat Conference Designer has two options: Use passive resistance Dont use passive resistance If using presumptive values in AASHTO the longitudinal passive soil pressure shall be less than 0.70 of the value obtained using the procedure given in Article 5.2.3 Abutment Resistance for Seismic Loads

79 2009 ODOT Geo/Hydro/HazMat Conference Abutment Resistance for Seismic Loads Presumptive P p (AASHTO 5.2.3)

80 2009 ODOT Geo/Hydro/HazMat Conference Abutment Resistance for Seismic Loads Presumptive P p

81 2009 ODOT Geo/Hydro/HazMat Conference Abutment Resistance for Seismic Loads Passive soil pressure less than 0.70 of the value obtained using presumptive method = no Agency Approval Required Passive soil pressure greater than 0.70 of the value obtained using presumptive method = Agency Approval Required

82 2009 ODOT Geo/Hydro/HazMat Conference How are these results used in design? Bridge Foundations (Extreme Limit State I): Loss of strength due to liquefaction generally assumed to be concurrent with the peak loads in the structure Unless nonlinear effective stress analysis is performed.

83 2009 ODOT Geo/Hydro/HazMat Conference How are these results used in design? Bridge Foundations (Extreme Limit State I): For bridge sites where liquefaction occurs bridges should be analyzed and designed in two configurations as follows: Nonliquefied Configuration: no liquefaction occurs, using the ground response spectrum appropriate for the site soil conditions in a nonliquefied state. Liquefied Configuration: The structure as designed in the nonliquefied configuration should be reanalyzed assuming that the layer has liquefied and the liquefied soil provides the appropriate residual resistance for lateral and axial deep foundation response analyses consistent with liquefied soil conditions The design spectrum should be the same as that used in a nonliquefied configuration.

84 2009 ODOT Geo/Hydro/HazMat Conference How are these results used in design? Bridge Foundations Spread Footings: Not recommended over liquefiable soils unless ground improvement provided Piles & Drilled Shafts: Tips located below deepest liquefiable layer Friction resistance in liquefiable layer not included in Extreme Event I state loading case Provide modified soil parameters for modeling p-y curves in liquefied soil layers (dont use built-in DFSAP program option for estimating liquefied lateral stiffness parameters) Provide estimates of downdrag loads due to liquefaction settlement

85 2009 ODOT Geo/Hydro/HazMat Conference How are these results used in design? Bridge Foundations Piles & Drilled Shafts (cont.): Assess effects of lateral spread deformations on deep foundations and the ability of the pile/shaft foundation to resist these loads ATC/MCEER reports: Recommended LRFD Guidelines for the seismic design of bridges (Design Examples & Liquefaction Study Report); MCEER/ATC 49-1/49-2. Determine if mitigation is necessary

86 2009 ODOT Geo/Hydro/HazMat Conference Earthquake Resisting Elements not permitted Full plastic hinging of pile foundations under seismic loads is not permitted (BDDM)

87 2009 ODOT Geo/Hydro/HazMat Conference Mitigation is required when the bridge performance requirements cannot otherwise be met. Design deviations can be considered by the Bridge Section All mitigation designs are to be reviewed by the Bridge Section When is liquefaction mitigation needed?

88 2009 ODOT Geo/Hydro/HazMat Conference Performance Requirements (New Bridges ) 1000-year No-Collapse Criteria Under this level of shaking, the bridge and approach structures, bridge foundation and approach fills must be able to withstand the forces and displacements without collapse of any portion of the structure. If large embankment displacements (lateral spread) or overall slope failure of the end fills are predicted, the impacts on the bridge end bent, abutment walls and interior piers should be evaluated to see if the impacts could potentially result in collapse of any part of the structure. Slopes adjacent to a bridge or tunnel should be evaluated if their failure could result in collapse of a portion or all of the structure. When is liquefaction mitigation needed?

89 2009 ODOT Geo/Hydro/HazMat Conference Performance Requirements (New Bridges ) 500-year Serviceability Criteria Under this level of shaking, the bridge and approach fills, are designed to remain in service shortly after the event (after the bridge has been properly inspected) to provide access for emergency vehicles. In order to do so, the bridge is designed to respond semi-elastically under seismic loads with minimal damage. Some structural damage is anticipated but the damage should be repairable and the bridge should be able to carry emergency vehicles immediately following the earthquake. This holds true for the approach fills leading up to the bridge. When is liquefaction mitigation needed?

90 2009 ODOT Geo/Hydro/HazMat Conference Performance Requirements (New Bridges ) 500-year Serviceability Criteria (cont.) Approach fill settlement and lateral displacements should be minimal to provide for immediate emergency vehicle access for at least one travel lane. For mitigation purposes approach fills are defined as shown on Figure 6- 12. As a general rule of thumb, an estimated lateral embankment displacement of up to 1 foot is considered acceptable in many cases as long as the serviceable performance criteria described above can be met. Vertical settlements on the order of 6 to 12 may be acceptable depending on the roadway geometry and anticipated performance of the bridge end panels. When is liquefaction mitigation needed?

91 2009 ODOT Geo/Hydro/HazMat Conference Performance Requirements (New Bridges ) 500-year Serviceability Criteria (cont.) These displacement criteria are to serve as general guidelines only and engineering judgment is required to determine the final amounts of acceptable displacement that will meet the desired criteria. It should be noted that these estimated displacements are not at all precise values and may easily vary by factors of 2 to 3 depending on the analysis method(s) used. The amounts of allowable vertical and horizontal displacements should be decided on a case-by-case basis, based on discussions and consensus between the bridge designer and the geotechnical designer and perhaps other project personnel. When is liquefaction mitigation needed?

92 2009 ODOT Geo/Hydro/HazMat Conference When is liquefaction mitigation needed? BDDM Section 1.1.10.6 & GDM Appendix 6C

93 2009 ODOT Geo/Hydro/HazMat Conference Mitigation Zone at Bridge Approaches When is liquefaction mitigation needed?

94 2009 ODOT Geo/Hydro/HazMat Conference Thank You For Your Attention


Download ppt "2009 ODOT Geo/Hydro/HazMat Conference Geotechnical Aspects of ODOT Seismic Bridge Design Jan Six P.E. ODOT Bridge Section."

Similar presentations


Ads by Google