c onsulting engineers and scientists

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


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


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


(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



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


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)


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)


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

[email protected]

(760)795-1964

For further information

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