2015 BSSC Colloquium
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
2015 BSSC Colloquium
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)
2015 BSSC Colloquium
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
2015 BSSC Colloquium
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
2015 BSSC Colloquium
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
2015 BSSC Colloquium
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
2015 BSSC Colloquium
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
2015 BSSC Colloquium
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
2015 BSSC Colloquium
SD1 > SDS
When: SM1 > SMS
S1 ∙ FV > SS ∙ Fa
> FV
Fa SS
S1
Where: High Ground Motion Areas in CA on Site Class E
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
2015 BSSC Colloquium
2015 BSSC Colloquium
Proposal for Adjustment Factors, Ca, on Fa and Cv, on Fv
T > 1 sec
Site classes D & E
High seismic areas only (?)
(?)
(?)
2015 BSSC Colloquium
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
2015 BSSC Colloquium
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
2015 BSSC Colloquium
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 − − − + = − − − ×