asce 7-10 site based response spectra.pdf

7/25/2019 ASCE 7-10 SITE BASED RESPONSE SPECTRA.pdf

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ASCE 7-10

Required Procedures for

Determining Site-SpecificResponse Spectra

C. B. Crouse

URS Corporation

November 22, 2013

C.B. Crouse 2013


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ASCE 7-10; Ch.21

Site-Specific Ground Motion

C.B. Crouse 2013


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2008 USGS SS and SI Maps in ASCE 7-10

a

a

H1

H2

t

t

1 d.o.f.

H1

H2

Acc.

in

H2

direction

(g)

Acc. in H1direction (g)

Max Sa

C.B. Crouse 2013


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Ground-Motion Prediction Equations Compute

Geometric Mean = Sa1 * Sa2

AccelerogramHorizontal Components

a

a

H1

H2

t

t

Response Spectra

H1

H2

Sa

Sa

Sa1

Sa2

Ti

Ti

T

T

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Geomean Sa vs Max Sa

1.0

T (sec)

Bedrock Response Spectra

Sa

x 1.1

x 1.3

Based on:

Max Sa

Geomean Sa

C.B. Crouse 2013


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Adjustment of Site-Specific

Geomean Sa for Max Direction Sa

ASCE 7-10

Supplement

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Sect. 21.2.3: Site-Specific MCER

SaM(T) = min[SaProb (T), SaDet (T)]

Site-Specific Ground Motion Procedures

Ch. 21 of ASCE 7-10: Risk-Targeted MCE (MCER)

Sect. 21.2.1: Probabilistic MCER SaProb

Sect. 21.2.2: Deterministic MCER SaDet

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ASCE 7-10: Two Methods for Probabilistic MCER

Method 2 (Exact) in Sect. 21.2.1.2

Use Risk Integral Equation

Required for foreign sites

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Probabilistic MCER

Risk Integral

where

Pf = 1% probability collapse in 50 yrs

P(a) = probability of exceeding spectral acceleration

in 50 yrs

Pf (a) = probability of collapse given spectral

acceleration

Pf = P(a) dadPf(a)

da

0

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Probabilistic MCER

Risk Integral

Fragility Function

(log normal distribution)

stand. dev., = 0.6

Hazard Curve

From PSHA

Pf = P(a) dadPf(a)

da

0

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Probabilistic MCER (Actual Calc.)

Risk Integral becomes:

Fragility Function

(log normal distribution)

stand. dev., = 0.6

Hazard Curve From PSHA

(Annual Exceedance Freq.)

Hf = H(a) dadPf(a)

da

a2

a1

Annual

Collapse Freq.

C.B. Crouse 2013


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Calculation of aMCER is Iterative

Assume aMCER = 2475-yr a

Compute Hf

Adjust aMCER or

Repeat until Hf0.000201

Convert aMCER from geomean to max. direction

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Method 1 (Approx.) in Sect. 21.2.1.1

Compute 2% in 50 yr Sa from PSHA Convert from geomean to max direction motion

Multiply by risk coefficients, CR(T)

CRS & CR1 from USGS web site (detailed report)

ASCE 7-10: Two Methods for Probabilistic MCER

CR =aMCER from Method 2

2475-yr a

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Deterministic MCER

1. Identify Controlling

Faults

2. Postulate MMAX foreach Fault

3. Use same GMPEs &

weights in PSHA

84th Percentile

Sa(T)

median + 1

C.B. Crouse 2013


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Example: MMAX for SAF

MMAX = weighted average MMAX for each fault

rupture scenario

Use USGS MMAX assigned for its

Deterministic MCER

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Selection on MMAX (Characteristic Earthquake)

San Andreas Fault

Source: Time Life Books

Highly Unlikely

M 8.5 (??)

Less Likely?

M 8 (1525?)

Likely

M 7.8 (1857)

C.B. Crouse 2013


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Uncertainty in MMAX for Given Rupture Scenario

Source: Hanks & Bakun (2008)C.B. Crouse 2013


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Deterministic MCER

Use Envelop Sa

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Deterministic MCER

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Site-Specific MCER SaM

SaM = min[SaProb (T), Sa

Det (T)]

Sa = SaM 0.8 x Sa

Design Response Spectrum (Sect. 21.3)

Figure 11.4-1

(Sect. 11.4.5)

23

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Clarification

Site-Specific Sa from Sect. 21.3 used to compute

R.S. and R.H. earthquake loads

SDS & SD1 from Sect. 21.4 are for determiningSeismic Design Category, forces on

non-structural components and ELF analysis.

C.B. Crouse 2013

asce 7-10 site based response spectra.pdf

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