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c onsulting engineers and scientists. Updates on Ground Motion and Geotechnical Data Requirements in the 2013 CBC Jorge F. Meneses, PhD, PE, GE, D.GE, F.ASCE Carlsbad, California. AEG Inland Empire Chapter Continuing Education Series May 31, 2014. Outline. Overview Design earthquakes - PowerPoint PPT Presentation
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Updates on Ground Motion and Geotechnical Data Requirements in the 2013 CBCJorge F. Meneses, PhD, PE, GE, D.GE, F.ASCECarlsbad, California
consulting engineers and scientists
AEG Inland Empire Chapter Continuing Education SeriesMay 31, 2014
• Overview • Design earthquakes• Maximum direction• Risk-targeted• General procedure• Examples• Geotechnical Requirements• Summary
Outline
Building Code Cycle
2012
NEHRP 2009 ASCE 7-10 IBC 2012
(Effective January 1, 2014)
Source, Path and Site
Evaluating Seismic Hazard and Ground Motions
Some definitions
• Definitions– Hazard: a phenomenon that has the potential to cause
damage– Risk: the probability that damage will occur
• In general, it is accepted that Earthquake Hazard cannot be avoided
• Hence, the philosophy behind building codes is to “mitigate risk”– We can’t avoid earthquakes, so we will build structures
that can withstand earthquakes
• Key concept: acceptable risk
MCER
The most severe earthquake effects considered by ASCE 7-10 determined for the orientation that results in the largest maximum response to horizontal ground motions and with adjustment for targeted risk
(ASCE 7-10, Chapter 11, p.60)
RISK-TARGETED MAXIMUM CONSIDERED EARTHQUAKE (MCER) GROUND MOTION
RESPONSE ACCELERATION
MCEG
The most severe earthquake effects considered by ASCE 7-10 determined for geometric mean peak ground acceleration and without adjustment for targeted risk
The MCEG PGA adjusted for site effects (PGAM) is used for evaluation of liquefaction, lateral spreading, seismic settlements, and other soil related issues.
MAXIMUM CONSIDERED EARTHQUAKE GEOMETRIC MEAN (MCEG) PEAK
GROUND ACCELERATION
(ASCE 7-10, Chapter 11, p.60)
Orientation of Maximum Response (Max. direction)
Maximum direction
Geomean and maximum Sa
(Whittaker et al 2009)
Landers, Joshua Tree
Loma Prieta, LGPC
DUZCE, BOLU
Directivity Effects on Ground Motions
Comparison of various models SaRotD100/SaRotD50
(Shahi and Baker 2013)
• Ground motion values contoured on maps incorporate factors to adjust from a geometric mean to the maximum response regardless of direction
• These factors are 1.1 for 0.2 second spectral response acceleration (SS) and 1.3 for 1.0 second spectral response acceleration (S1)
Maximum Response
(ASCE 7-10, Figures 22-1 through 22-6)
General procedure
• Use mapped values and tables from code
• USGS Seismic design maps web application
Seismic Ground Motion Values
(ASCE 7-10, Chapter 11, p.65-66)
SS, S1
Fa , Fv
SMS, SM1 SDS, SD1
Site Class B
Site Classification
(ASCE 7-10, Chapter 20, p.204)
Site Coefficient Fa
Site class
Mapped risk-targeted MCER Sa at short second
Ss ≤ 0.25 Ss = 0.50 Ss = 0.75 Ss = 1.0 Ss ≥ 1.25
A 0.8 0.8 0.8 0.8 0.8
B 1.0 1.0 1.0 1.0 1.0
C 1.2 1.2 1.1 1.0 1.0
D 1.6 1.4 1.2 1.1 1.0
E 2.5 1.7 1.2 0.9 0.9
F Site-specific study required
(Chapter 11, p.66)
Site Coefficient Fv
Site class
Mapped risk-targeted MCER Sa at 1 second
S1 ≤ 0.1 S1 = 0.2 S1 = 0.3 S1 = 0.4 S1 ≥ 0.5
A 0.8 0.8 0.8 0.8 0.8
B 1.0 1.0 1.0 1.0 1.0
C 1.7 1.6 1.5 1.4 1.3
D 2.4 2.0 1.8 1.6 1.5
E 3.5 3.2 2.8 2.4 2.4
F Site-specific study required
(Chapter 11, p.66)
SDS = 2/3*SMS=0.946
SD1 =2/3*SM1
=0.454
SS
S1
SM1=Fv*S1
To=0.10 TS=0.48
Sa = SDS (0.4+0.6 T/To)
PGA = 0.4 SDS = SDS/2.5
PGA = 0.378g
SAN DIEGO SITESITE CLASS C (Fa = 1.0, Fv = 1.3)
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Period (seconds)
Sp
ectr
al A
ccele
rati
on
(g
)MCER Site Class B
MCER Site Class C
DE = 2/3 MCER
5 percent damping
Sa = SD1/T
To = 0.2 SD1/SDS
Ts = SD1/SDS
*Fa= SMS
Risk Category of Buildings
Use or occupancy of buildings and structures Risk category
Buildings and other structures that represent a low risk to human life in the event of failure I
All buildings and other structures except those listed in Risk Categories I, III, and IV II
Buildings and other structures, the failure of which could pose a substantial risk to human life III
Buildings and other structures designated as essential facilities. Buildings and other structures, the failure of which could pose a substantial hazard to the community
IV
(Chapter 1, p.2)
Seismic Design Category based on S1
Value of SDS
Risk category
I or II or III IV
S1 ≥ 0.75 E F
S1 < 0.75 See following tables
(Chapter 11, p. 67)
Seismic Design Category based on SDS
Value of SDS
Risk category
I or II or III IV
SDS < 0.167 A A
0.167 ≤ SDS < 0.33 B C
0.33 ≤ SDS < 0.50 C D
0.50 ≤ SDS D D
(Chapter 11, p. 67)
Seismic Design Category based on SD1
Value of SDS1
Risk category
I or II or III IV
SD1 < 0.067 A A
0.067 ≤ SD1 < 0.133 B C
0.133 ≤ SD1 < 0.20 C D
0.20 ≤ SD1 D D
(Chapter 11, p. 67)
Seismic design category D through F
For liquefaction studies
PGAM = FPGA PGA
PGAM = MCEG PGA adjusted for site effectsPGA = Mapped MCEG PGAsFPGA = Site coefficients (see table)
(ASCE 7-10, Section 11.8.3.2, p.68-69)
Site coefficient FPGA
Site class
Mapped MCEG PGA
PGA ≤ 0.1 PGA = 0.2 PGA = 0.3 PGA = 0.4 PGA ≥ 0.5
A 0.8 0.8 0.8 0.8 0.8
B 1.0 1.0 1.0 1.0 1.0
C 1.2 1.2 1.1 1.0 1.0
D 1.6 1.4 1.2 1.1 1.0
E 2.5 1.7 1.2 0.9 0.9
F Site-specific study required
(ASCE 7-10, Chapter 11, p.68)
Location of three selected sites
Rose Canyon-Newport-Inglewood Fault Zone
Coronado Bank Fault Zone
San Diego Trough Fault Zone
http://geohazards.usgs.gov/designmaps/us/application.php
Comparison of design response spectra
0 0.5 1 1.5 2 2.5 3 3.5 40
0.2
0.4
0.6
0.8
1
1.2
ASCE 7-05
ASCE 7-10
Period (seconds)
Des
ign
Spec
tral
Acc
eler
ation
s (g
)
Site 1Site Class D
Site 2
0 0.5 1 1.5 2 2.5 3 3.5 40
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
ASCE 7-05
ASCE 7-10
Period (seconds)
Des
ign
Spec
tral
Acc
eler
ation
s (g
)
Site 2Site Class C
Site 3
0 0.5 1 1.5 2 2.5 3 3.5 40
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
ASCE 7-05
ASCE 7-10
Period (seconds)
Des
ign
Spec
tral
Acc
eler
ation
s (g
)
Site 3Site Class E
Site 2
Site Class E? Watch out!
Site Class E?
Site Class E? SM1 > SMS !
Comparison of SDS
(Luco 2009)
Comparison of SD1
SDS – Southern California
(OSHPD 2012)
SDS – Northern California
Maxima and Minima Values for California
MaximaSs = 3.73 gS1 = 1.28 g
MinimaSs = 0.204 gS1 = 0.107 gSDS = 0.22 gSD1 = 0.17 g
Seismic design category D through F
For seismic lateral earth pressures:
The determination of dynamic seismic lateral earth pressures on foundation walls and retaining walls supporting more than 6 feet (1.83m) of backfill height due to design earthquake ground motions
(2013 CBC, Section 1803A.5.12, p. 177)
Seismic design category D through F
An assessment of potential consequences of liquefaction and soil strength loss, including, but not limited to:
- Estimation of total and differential settlement- Lateral soil movement- Lateral soil loads on foundations- Reduction in foundation soil-bearing capacity and lateral soil
reaction- Soil downdrag and reduction in axial and lateral soil reaction
for pile foundations- Increases in soil lateral pressures on retaining walls
(2013 CBC, Section 1803A.5.12, p. 177)
Seismic design category D through F
Discussion of mitigation measures such as, but not limited to:
- Selection of appropriate foundation type and depths- Selection of appropriate structural systems to accommodate
anticipated displacements and forces- Ground stabilization- Any combination of these measures and how they shall be
considered in the design of the structure
(2013 CBC, Section 1803A.5.12, p. 177)
Geotechnical Peer Review (DSA-SS and DSA-SS/CC)
When alternate foundations designs or ground improvements are employed or where slope stabilization is required, a qualified peer review by a California-licensed geotechnical engineer, in accordance with Section 3422, may be required by the enforcement agency. In Section 3422, where reference is made to structural or seismic-resisting system, it shall be replaced with geotechnical, foundation, or ground improvement, as appropriate.
(2013 CBC, Section 1803A.8, p. 178)
Retaining Walls – Design lateral soil loads
Retaining walls shall be designed for the lateral loads determined by a geotechnical investigation in accordance with Section 1803A and shall not be less than eighty percent of the lateral soil loads determined in accordance with Section 1610A.
(2013 CBC, Section 1803A.8, p. 178)
Table 1610A.1 Lateral Soil Load
(2013 CBC, Section 11610A, p. 87)
Contact
Jorge F. Meneses, PhD, PE, GE, D.GE, F.ASCE
(760)795-1964
For further information