Site Coefficients, F , F , and F , Proposed for ASCE 7-16

Site Coefficients, Fa, Fv, and FPGA,

Proposed for ASCE 7-16

C.B. Crouse AECOM

February 11, 2015

2015 BSSC Colloquium

Proposed New Site Coefficients, Fa & Fv

Fa

Fv


Existing Fa & Fv in ASCE 7-10

> 20 yrs old

Finalized at 1992 USC Workshop

Based on:

1989 Loma Prieta ground motion data

Numerous generic site response analyses

Judgement


Proposed Fa & Fv for ASCE 7-16

Based on statistical analysis of NGA West 2 database (104 records)

3-yr PEER study – J. Stewart, PI

12-person project team

Fa & Fv = 1.0 for B/C boundary (VS30 = 760 m/s)


Proposed vs. Existing Fa

≥ 10%

≥ 10%

New

Site S s ≥ 1.5 Class Proposed ASCE Proposed ASCE Proposed ASCE Proposed ASCE Proposed ASCE Proposed

A 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 B 0.9 1.0 0.9 1.0 0.9 1.0 0.9 1.0 0.9 1.0 0.9 C 1.3 1.2 1.2 1.2 1.2 1.1 1.2 1.0 1.2 1.0 1.2 D 1.6 1.6 1.4 1.4 1.3 1.2 1.2 1.1 1.0 1.0 E 2.4 2.5 1.7 1.7 1.3 1.2 1.1 0.9 1.0 0.9 0.8

S s < 0.25 S s = 0.5 S s = 0.75 S s = 1.0 S s = 1.25

1.1


Proposed vs. Existing Fa

≥ 10%

≥ 10%

New

S s ≥ 1.5 Proposed ASCE Proposed ASCE Proposed

0.8 0.8 0.8 0.8 0.8 0.9 1.0 0.9 1.0 0.9 1.2 1.0 1.2 1.0 1.2 1.2 1.1 1.0 1.0 1.1 0.9 1.0 0.9 0.8

S s = 1.0 S s = 1.25 Site Class

A B C D E

1.1


Default Site Class in Sect. 11.4.2

Triggered when geotech firm does not determine site class, but knows it is not Site Class E or F

ASCE 7-10: Site Class D is default

Reason: Fa & Fv were largest for Site Class D

ASCE 7-16: Site Class D is still default but Fa ≥ 1.2


Proposed vs. Existing Fv

≥ 10%

≥ 10%

New

Site S 1 ≥ 0.6 Class Proposed ASCE Proposed ASCE Proposed ASCE Proposed ASCE Proposed ASCE Proposed

A 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 B 0.8 1.0 0.8 1.0 0.8 1.0 0.8 1.0 0.8 1.0 0.8 C 1.5 1.7 1.5 1.6 1.5 1.5 1.5 1.4 1.3 1.4 D 2.4 2.4 2.2 2.0 2.0 1.8 1.9 1.6 1.8 1.5 1.7 E 4.2 3.5 3.3 3.2 2.8 2.8 2.4 2.4 2.2 2.4 2.0

S 1 < 0.1 S 1 = 0.2 S 1 = 0.3 S 1 = 0.4 S 1 = 0.5

1.5


Proposed vs. Existing Fv

≥ 10%

≥ 10%

New

S 1 ≥ 0.6

Proposed ASCE Proposed ASCE Proposed 0.8 0.8 0.8 0.8 0.8 0.8 1.0 0.8 1.0 0.8 1.5 1.4 1.3 1.4 1.9 1.6 1.8 1.5 1.7 2.4 2.4 2.2 2.4 2.0

S 1 = 0.4 S 1 = 0.5 Site Class

A B C D E

1.5


Equations for Fa & Fv in Commentary

( )( ){ }{ }

( )3030exp 0.00638 min ,760 360 / 2.3 0.1

exp 0.727ln 0.2298 ln760 0.1exp 0.00638 400

s ssa

V SVF − − − + = − − − ×

( )( ){ }{ }

( )30 130exp 0.00756 min ,760 360 / 0.7 0.1

exp 1.03ln 0.118 ln760 0.1exp 0.00756 400

ssv

V SVF − − − + = − − − ×

PGA

PGA


Design Response Spectrum (Sect. 11.4.5) Figure 11.4-1

SDS > SD1


How to Draw DE Spectrum When SD1 > SDS


SD1 > SDS

When: SM1 > SMS

S1 ∙ FV > SS ∙ Fa

> FV

Fa SS

S1

Where: High Ground Motion Areas in CA on Site Class E


Option Selected

Set SDS = SD1

Example ELF “Design Spectrum” based on ASCE 7-16 (proposed) Site Factors M8.0 earthquake ground motions at RX = 8.5 km, Site Class D/E

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0.1 1.0 10.0

Spec

tral A

ccel

erat

ion

(g)

Period (seconds)

MCEr - BC (Vs,30 = 2,500 fps)

MCEr - DE (Vs,30 = 600 fps)

Design DE (Vs,30 = 600 fps)

ELF DE (Vs,30 = 600 fps)

ASCE 7-16 (Revised)Fa = 0.9 = (1.0 + 0.8)/2Fv = 1.85 = (1.7 + 2.0)/2

Ts = 0.85s

Conservative

Non-Conservative

Ground Motion ValuesSDS = 2/3FaSs = 2/3 x 0.9 x 1.56g = 0.94gSD1 = 2/3FvS1 = 2/3 x 1.85 x 0.70g = 0.86g

ELF “Design Spectrum”Cs x (R/Ie) = min[SDS, SD1/T]

From C. Kircher



Proposal for Adjustment Factors, Ca, on Fa and Cv, on Fv

T > 1 sec

Site classes D & E

High seismic areas only (?)

(?)

(?)


Two Proposed Options (ASCE 7-16)

Option 1

SMS = CaFaSs

SM1 = CVFVS1

Option 2

Require Site-Specific Study (Ch. 21) for Certain Cases

Replaced by multipoint Sa for ASCE 7-21


Proposed Site Coefficients, FPGA, for PGA

Revise FPGA table in Sect. 11.8.3 of ASCE 7-10 for liquefaction & stability evaluations of soil

≥ 10%

≥ 10%

New

Site PGA ≥ 0.6 Class Proposed ASCE Proposed ASCE Proposed ASCE Proposed ASCE Proposed ASCE Proposed

A 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 B 0.9 1.0 0.9 1.0 0.9 1.0 0.9 1.0 0.9 1.0 0.9 C 1.3 1.2 1.2 1.2 1.2 1.1 1.2 1.0 1.2 1.0 1.2 D 1.6 1.6 1.4 1.4 1.3 1.2 1.2 1.1 1.0 1.1 E 2.4 2.5 1.9 1.7 1.6 1.2 1.4 0.9 1.2 0.9 1.1

PGA < 0.1 PGA = 0.2 PGA = 0.3 PGA = 0.4 PGA = 0.5

1.1


Equation for FPGA in Commentary

( )( ){ }{ }

exp 0.00701 min ,760 360 0.1exp 0.604ln 0.150 ln760 0.1exp 0.00701 400

ssPGA

vv PGAF − − − + = − − − ×


Conclusions

New Fa, Fv, FPGA will likely be in ASCE 7-16

Site-specific study (Ch. 21) will be required for certain cases

Documents

Site Coefficients, F , F , and F , Proposed for ASCE 7-16