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Site-Specific Risk-Targeted Ground Motion Procedures Jorge F. Meneses, PhD, PE, GE, D.GE, F.ASCE Carlsbad, California consulting engineers and scientists AEG Inland Empire Chapter Continuing Education Series May 31, 2014

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Overview Site-specific procedures Risk coefficient NGA Relationships Deaggregation Examples Performance Based EE Summary Outline

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Source, Path and Site

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Evaluating Seismic Hazard and Ground Motions

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2103 CBC, , 1616A.1.3 “For buildings assigned to Seismic Design Category E and F, or when required by the building official, a ground motion hazard analysis shall be performed in accordance with ASCE 7 Chapter 21, as modified by Section 1803A.6 of this code.” SITE-SPECIFIC STUDY

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Structures on Site Class F sites (T s > 0.5 seconds) At least 5 recorded or simulated horizontal ground motion acceleration time histories (MCE R spectrum at bedrock) Site Response Analysis Seismic Hazard Analysis Seismically isolated structures (S 1 0.6) Structures with damping systems (S 1 0.6) A time history response analysis of the building is performed (ASCE 7-10, Section , p.67) SITE-SPECIFIC STUDY (cont’d)

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SITE RESPONSE ANALYSIS (ASCE 7-10, Section 21.1, p.207) Ground Surface Rock base

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SITE-SPECIFIC GROUND MOTION PROCEDURE (Sections 21.2, 21.3, and 21.4) Probabilistic ground motion Method 1: Uniform-hazard GM * Risk Coefficient Method 2: Risk-targeted probabilistic GM directly Deterministic ground motion 84 th -%ile GM, but not < 1.5F a or 0.6*F v /T MCE R = Min (Prob. GM, Det. GM) All GMs are max-direction spectral accelerations (S a )

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Risk coefficient: C R T ≤ 0.2 s; C R = C RS (Figure 22-17) T ≥ 1.0 s; C R = C R1 (Figure 22-18) 0.2 s ≤ T ≤ 1.0 s; C R linear interpolation of C RS and C R1 Risk coefficient

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Risk Coefficient

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SITE-SPECIFIC GROUND MOTION PROCEDURE Prob MCE R Det MCE R MCE R Spectrum DESIGN Spectrum SITE-SPECIFIC DESIGN SPECTRUM General DESIGN Spectrum General MCE Spectrum Site CoordSite Class 1% Prob. of collapse 50 yr (direction of max horiz resp) Lesser of PSHA and DSHA 2/3 MCE Spectrum > 80% General Design Spectrum 84 th percentile (direction of max horiz resp) (Sections 21.2, 21.3, and 21.4)

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SITE-SPECIFIC GROUND MOTION PROCEDURE Deterministic Lower Limit (DLL) on MCE R Spectrum 1.5 F a 0.6 F a Sa = 0.6 F v /T 0.08 Fv/Fa0.4 Fv/Fa TLTL Period (seconds) Sa (g) Sa = 0.6 F v T L /T 2 (Section , p. 209)

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Attenuation Relationships Several types of ground motions parameters can be calculated from a recorded EQ time history. But what do you do if you want to estimate what the ground motion parameters are going to be from an earthquake that hasn’t happened yet?

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Attenuation Relationships ANSWER: Use the data that we’ve collected so far and fit equations to them for predicting future ground motions. These equations are often called attenuation relationships.

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Attenuation Relationships Distance from Source Ground Motion Parameter Initial relationships were just based on Magnitude (M) and Distance (R), but equations become much more complex as researchers looked for ways to minimize data scatter.

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Attenuation Relationships Modern attenuation relationships have terms that deal with such complexities as: 1) Fault type 2) Fault geometry 3) Hanging wall/Foot wall 4) Site response effects 5) Basin effects 6) Main shock vs. After shock effects Pretty complex …. Hard to do by hand!!

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Attenuation Relationships Ideally, every geographic area that experiences EQs would have its own set of attenuation relationships. WHY? Not enough recorded data! Scatter in the data could be minimized! …But we can’t really produce site-specific attenuation relationships for places other than those that have a lot of frequent earthquakes. WHY? So we start combining earthquake records from geographically different areas with the assumption that the ground motions should be similar despite the differences in location. Ergodic Assumption

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Three NGA projects: For active crustal Eqs (California, Middle East, Japan, Taiwan,…): NGA-West For subduction Eqs (US Pacific Northwest and northern California, Japan, Chile, Peru,…): NGA-Sub Stable continental regions (Central and Eastern US, portion of Europe, South Africa,…): NGA-East NGA=Next Generation “Attenuation” Relations

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Attenuation Relationships (GMPEs) For crustal faults in the Western US and other high- to moderate- seismicity areas, most professionals currently use: Next Generation Attenuation Relationships (NGAs) NGA West 1: 5 separate research teams were given the same set of ground motion data and were asked to develop relationships to fit the data. Their results were published in Abrahamson & Silva -Chiou & Youngs -Campbell & Bozorgnia -Idriss -Boore & Atkinson (rock only)

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NGA-West 1: 2008 NGA-West 2: 2014 NGA-West Data setNo. EQsNo. RecSa TypeDamping (%) Periods (sec) NGA-West 11733,551AR, GMRotI NGA-West ,331AR, RotDnn AR= as-recorded

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Rotate horizontal components, at each period compute: RotD50 = 50 percentile RotD100 = max RotD00 = min RotDnn RotD50 is the main intensity measure PGA, PGV and Sa at 21 periods: 0.01, 0.02,……,5, 7.5, 10 sec No GMPE for PGD

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Applicable magnitude range: –M ≤ 8.5 for strike-slip (SS) –M ≤ 8.0 for reverse (RV) –M ≤ 7.5 for normal faults (NM) Applicable distance range: –0 – 200 km (preferably 300km) NGA West-2 ranges of applicability

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ParameterASBSSACBCYI Magnitude MwMw MwMw MwMw MwMw MwMw Top of rupture Z tor Style of faulting RV, NM, SS Dip Yes Downdip fault width Yes Closest distance to rupture R rup Hor. dist. to surface proj. R jb Hor. dist. Perpendicular to strike R x, R y RxRx RxRx Hanging wall model Yes(R jb )Yes V s30 (760m/s)V s30, (S j )V s30 V s30 ≥450 Depth to Vs Z 1.0 Z 2.5 Z 1.0 Hypocentral depth H hyp Vs30 for reference rock (m/s) 1, ,1001,130 Horizontal NGA-West 2 GMPEs parameters

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Abrahamson-Silva-Kamai (ASK) Boore-Stewart-Seyhan-Atkinson (BSSA) Campbell-Bozorgnia (CB) Chiou-Youngs (CY) Idriss (I) NGA West 2 Five models

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NGA Distance Notations

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More on distances Geotechnical Services Design Manual, Version 1.0, 2009, Caltrans Development of the Caltrans Deterministic PGA Map and Caltrans ARS Online, 2009, Caltrans

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NGA Soil vs. Rock NGA equations don’t have a “trigger” for soil or rock. They just rely on the V S30, which is the average shear wave velocity in the upper 30 meters of the ground. V S30 (m/s) Type Site Class > <180 Hard Rock Firm Rock Soft Rock Regular Soil Soft Soil A B C D E

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NGA West 2 Excel spreadsheet

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2013 CBC, Section 1803A.6 Geohazard Reports The three Next Generation Attenuation (NGA) relations used for the 2008 USGS seismic hazard maps for Western United States (WUS) shall be utilized to determine the site-specific ground motion. When supported by data and analysis, other NGA relations, that were not used for the 2008 USGS maps, shall be permitted as additions or substitutions. No fewer than three NGA relations shall be utilized 2008 USGS Boore and Atkinson (2008) Campbell and Bozorgnia (2008) Chiou and Youngs (2008)

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Not an average velocity in upper 30 m Ratio of 30 m to shear wave travel time What is V s30 ? (Stewart 2011)

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Not an average velocity in upper 30 m Ratio of 30 m to shear wave travel time What is V s30 ? (Stewart 2011)

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Not an average velocity in upper 30 m Ratio of 30 m to shear wave travel time Emphasizes low V s layers What is V s30 ? (Stewart 2011)

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Seismic Source Interpretation from PSHA Results Deaggregation: Break the probabilistic “aggregation” back down to individual contributions based on magnitude and distance. Provides: - Mean M,R: weighted average - Modal M,R: Greatest single contribution to hazard

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Risk-Targeted MCE R Probabilistic Response Spectrum C RS = C R1 = 0.906

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Deterministic MCE R Response Spectra

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Site-Specific MCE R Response Spectrum

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Design Response Spectrum

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Site-Specific Response Spectra at Ground Surface

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Site-specific MCE geometric mean (MCE G ) PGA PROB MCE G PGA The probabilistic geometric mean PGA shall be taken as the geometric mean PGA with a 2% PE in 50 years DETERMINISTIC MCE G PGA Calculated as the largest 84 th percentile geometric mean PGA for characteristic earthquakes on all known active faults. Minimum value 0.5 F PGA (F PGA at PGA=0.5g) SITE-SPECIFIC MCE G PGA Lesser of probabilistic and deterministic MCE G PGA ≥ 0.80 PGA M (Section 21.5)

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SITE-SPECIFIC GROUND MOTION PROCEDURE Site-specific Probabilistic MCE R (1% probability of collapse in 50 years) METHOD 1 C R * Sa (2% PE 50 year) METHOD 2 From iterative integration of a site-specific hazard curve with a lognormal probability density function representing the collapse fragility C R = risk coefficient (from maps) T ≤ 0.2s C R = C RS T ≥ 1.0s C R = C R1 0.2s < T < 1s Linear interp C RS and C R1 (i.e., probability of collapse as a function of Sa) Collapse fragility with a)10% Prob. of collapse; b)logarithmic std dev of 0.6 (Section )

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PSHA Review….. Risk is computed using a. Do you remember the concept of probabilistic seismic hazard analysis? All possible magnitudes are considered - contribution of each is weighted by its probability of occurrence All possible distances are considered - contribution of each is weighted by its probability of occurrence All possible effects are considered - each weighted by its conditional probability of occurrence Basic equation: All sources and their rates of recurrence are considered All sources and their rates of recurrence are considered Performance-Based Earthquake Engineering Probabilistic framework

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Pacific Earthquake Engineering Research Center (PEER) developed a probabilistic framework for considering the engineering effects from EQ ground motions: Intensity measure, IM Engineering demand parameter, EDP Damage measure, DM Repair Cost Lives Lost Down Time Pile Deflection Cracking Collapse Potential FS liq Lateral Spread Settlement Story Drift PGA PGV I A CAV Decision variable, DV Performance-Based Earthquake Engineering

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P[D > 3.0 | PGA=0.3g] P[ D > 1.0 | PGA=0.3g] P[D > 2.0 | PGA=0.3g] 0.3g Example of Fragility curves P[D > d i | PGA] 3.0cm 2.0cm 1.0cm PGA EDP = Displacement = D IM = PGA Fragility Curves

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The PEER performance-based framework incorporates seismic hazard curves and fragility curves. Convolving a fragility curve with a seismic hazard curve produces a single point on a new hazard curve!! Seismic hazard curve for IM (from PSHA) Fragility curve – EDP given IM Fragility curve – DM given EDP Fragility curve – DV given DM Risk curve – DV vs DV Fragility Curves and Seismic Hazard Curves

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Hazard curve PGA P[D>d i | PGA] PGA D proportional to sum of thick red lines Fragility curve for D > 2.0cm Fragility Curves and Seismic Hazard Curves

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Hazard curve PGA IM PGA D proportional to sum of probabilities Fragility curve D D Seismic hazard curve for Displacement Fragility Curves and Seismic Hazard Curves D=2.0cm PGA P[D>d i | PGA]

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Risk-targeted ground motions (Luco 2009)

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Risk-targeted ground motions (Luco 2009)

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Risk-targeted ground motions - Example

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Summary of differences ASCE 7-05ASCE 7-10 NameMCEMCE R Probabilistic GMs (objective) Uniform hazard (2%-in-50 yr Pr. of Exc.) Risk targeted (1%-in-50 yr Pr. of Collapse) Deterministic GMs1.5*median84%-ile (approx. 1.8*median) GM parameterGeometric mean, S a Maximum direction, S a USGS web toolJava ground motion parameter calculator Seismic design maps web application Average S DS 0.73g0.72g Average S D1 0.38g0.40g (Luco 2009)

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Contact Jorge F. Meneses, PhD, PE, GE, D.GE, F.ASCE (760) For further information

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