Seismic Design - Introduction

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SEISMIC DESIGN - INTRODUCTION 1

SEISMIC DESIGN - INTRODUCTION

Dr. Ajit C. Khanse, Ph. D.

Agenda

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Seismic Design Introduction

SDC & Design

Structural failures

Plate Tectonics

Seismicity

Fault Rupture

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WORLD SEISMICITY: 1900 – 2013

Seismicity refers to the geographic and historical distribution of earthquakes. The dots represent the epicenters of significant earthquakes. It is apparent that the locations of the great majority of earthquakes correspond to the boundaries between plates.

Mw ≥ 7.0

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Volcanic arcs and oceanic trenches partly encircling the Pacific Basin form the so-called Ring of Fire, a zone of frequent earthquakes and volcanic eruptions.

RING OF FIRE

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The Earth is made up of a dozen major plates and several minor plates. Tectonic plates are constantly on the move. The fastest tectonic plate constantly races

along at 6” per year while the slowest plates crawl at less than1” per year [USGS]

PLATE TECTONICS

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CONTINETAL DRIFT

www.tectonics.caltech.edu

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SAN ANDREAS FAULT, CA

The Pacific Plate (western side of San Andreas fault) is moving horizontally in a northerly direction relative to the North American Plate (eastern side of fault)

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RUPTURE PROPAGATION With Compliments from Prof. Krishnan, Caltech

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EARTHQUAKE MAGNITUDE Earthquake magnitude M, is a measure of the kinetic energy released by an earthquake.

Due to limitations in the ability of some recording instruments to measure values above a certain amplitude, some of these magnitude scales tend to reach an asymptotic upper limit. To correct this, the moment magnitude, Mw, scale was developed.

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EFFECTS OF EARTHQUAKE

1) Ground Shaking

2) Permanent Ground Deformation

3) Liquefaction (a) Sand Boils

(b) Lateral Spreading Landslides

(c) Graben and Horst

4) Basin Effect

5) Tsunami

6) Landslides

7) Structural Destruction

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PROGRESSIVE COLLAPSE, Mw = 7.9 With Compliments from Prof. Krishnan, Caltech

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GROUND SHAKING RESULTING IN STRUCTURAL FAILURE The reverse-oblique fault line crosses the largest concrete gravity 石岡 Shigung dam in Taiwan. The eastern 80 % of the dam is uplifted by about 33 ft and the western part by about 10 ft. At fault-line, the concrete dam wall was cut off and 23 ft difference appeared in the elevation.

The 1999 Chi Chi, Taiwan Earthquake, Mw = 7.6 www.infra.kochi-tech.ac.jp/

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PERMANENT GROUND DEFORMATION

The 1999 Chi Chi, Taiwan Earthquake, Mw = 7.6 Ref: kyoto-u.ac.jp

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SOIL LIQUEFACTION describes a phenomenon whereby a saturated soil substantially loses strength and stiffness in response to earthquake shaking or other sudden change in

stress condition, causing it to behave like a liquid.

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A SAND BOIL is sand & water that come out onto the ground surface during an earthquake as a result of

liquefaction at shallow depth.

. .

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Lateral spread or flow are terms referring to landslides that commonly form on gentle slopes and that have rapid fluid-like flow movement, like water.

LIQUEFACTION: Lateral Spreading Landslides

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LIQUEFACTION: Lateral Spreading

Lateral spreading in the

soil beneath the roadway

embankment caused the

embankment to be pulled

apart, producing the large

crack down the center of

the road. (REF: USGS)

The 1964 Alaska Earthquake, Mw = 7.9

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BASIN EFFECT – I

Epicenter was 220 miles away from Mexico City. Estimated 35,000 people

died in Mexico City, where 412 multistory (8 to 25 floors) buildings collapsed completely and another

3,124 were seriously damaged. (USGS)

21-story, steel-frame building 15-story reinforced concrete building

8-story RC building The 1985 Michoacán (Mexico) Earthquake, Mw = 8.3

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BASIN EFFECT – II

The 1985 Michoacán (Mexico) Earthquake, Mw = 8.3

Characteristics of the soil profiles

• Extremely soft, saturated surface clays • At some places Plasticity Index ≈ 300 • Friction angles as low as, ϕ = 5-15o

Zone Depth

(ft)

Eff. Vs

(ft/s)

Predominant

period (s)

Transition 43 285 0.6 Lake 125 250 2.0

Deep Lake 185 200 3.4

Dynamic characteristics of Soil deposits play vital role

[Aviles and Perez-Rocha 1998] Map of seismic zonation and isoperiod curves (in sec) of Mexico City

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BASIN EFFECT – III

The 1985 Michoacán (Mexico) Earthquake, Mw = 8.3

Source-averaged basin amplification is period-dependent,

with the highest amplifications occurring for the longest

periods and greatest basin depths.

Relative to the very-hard rock reference structure, general

maximum amplification is about a factor of 8. At Mexico

city (1985 Michoacán earthquake), seismic motion was

amplified up to a factor of 60 compared to the bedrock. [Aviles and Perez-Rocha 1998]

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Earthquake Magnitude vs Tsunami Intensity (1896 – 2005)

Earthquake Magnitude

REF: USGS

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TSUNAMI 津波 Seismic Sea Waves

Tsunamis are ocean waves caused by large earthquakes & landslides that occur near or under the ocean.

Generated when thrust faults associated with convergent or destructive plate boundaries move abruptly, resulting in water displacement, owing to the vertical component of movement involved.

Sumatra and the Andaman Islands are part of an island arc. REF: USGS

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Details of Tsunami Generation

REF: USGS

Tsunami generation from an inter-plate thrust fault

The displacement of rock surrounding the inter-plate thrust

Diagram of tsunami splitting, soon after generation

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USGS The 2004 Mw =9.2 Sumatra Earthquake: Rupture Propagation

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LANDSLIDES Landslide north of Fort Funston, San Mateo Coast, CA

The 1989 Loma Prieta Earthquake

Landslides occur due to ground shaking alone or shaking-caused dilation of soil materials, which allows rapid infiltration of water. REF: USGS

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LANDSLIDE MITIGATION

The hazard from landslides can be reduced by

avoiding construction on steep slopes and existing landslides

stabilizing the slopes. Slope stability is increased when

a retaining structure &/or the weight of a soil/rock berm are

placed at the toe of the landslide.

when mass is removed from the top of the slope.

When ground water is prevented from rising in the landslide

mass.

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TUNNEL DESTRUCTION

2004 Niigata Earthquake, Japan

1995 Kobe Earthquake, Japan

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‘There is not a fiercer hell than the failure in a great object’ – Keats

LOMA PRIETA 1989, Mw=6.93 KOBE, JAPAN 1995, Mw= 6.9

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FEW Q&A Q: There are no faults in the Central and Eastern United States (CEUS). Earthquakes are rare. Is seismic design mandatory?

• An intraplate earthquake occurs in the interior of a tectonic plate,

which could be due to unknown causative fault buried inside a plate.

• Recall Load Combinations of AASHTO 2010 & ASCE 7-10.

• Site-specific investigation of Seismic Design Category (SDC)

determines the type of design procedure.

Q: Traditionally unreinforced concrete liner has been provided in some cases – is it acceptable?

AASHTO 2010 has no comment. ACI 318-14 Ch. 18 on ‘Earthquake

Resistant Structures’ does not allow unreinforced concrete. Further, the

ovaling deformation may induce considerable tensile hoop forces.

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FEW Q&A

Q: Since liner in rock is anchored to rock, the tensile hoop forces in liner are apparent during ovaling response. Do we have these for liner in soil?

Liner in Soil

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FEW Q&A


Liner in Soil

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FEW Q&A


F = m.a

Forces due to motion,

Liner in Soil

T

T

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SEISMIC DESIGN CATEGORY (SDC)

There are various correlations of the qualitative Modified Mercalli Intensity (MMI) with quantitative characterizations of ground-shaking limits for the various SDCs.

MMI V No real damage SDC A 0 < SM1 <0.1g MMI VI Light nonstructural damage SDC B 0.1g < SM1 < 0.2g MMI VII Hazardous nonstructural damage SDC C 0.2g < SM1 < 0.3g MMI VIII Hazardous damage to susceptible structures SDC D 0.3 < SM1 < 1.12g MMI IX Hazardous damage to robust structures SDC E SM1 > 1.125g

[§11.6, ASCE 7-10]

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MCER 1-second spectral response acceleration parameter, SM1 (%g)

Map with associated regions of Seismic Design Category, assuming Site Class D conditions

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SEISMIC DESIGN CATEGORY (SDC)

[ASCE 7-10, AASHTO 2010]

Seismic Design Category (SDC) depends upon Topographic location,

Site soil class,

Occupancy (risk) category,

Deterministic design spectral response parameter at short

period SDS and that at 1-sec period SD1.

The design requirements depending upon SDC:

SDC A: No seismic design. Certain provisions shall be met.

SDC B & C: Analytical closed-form analysis procedure.

SDC D, E & F: The finite-element or finite-difference numerical

modelling approach.

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LOAD CASE EXTREME EVENT - I

[AASHTO 2010]

• Designed to withstand seismic ground motions with a

Return Period of 2,500 years, corresponding to 2%

probability of exceedance in 50 years.

• Values from Maximum Considered Earthquake (MCER)

shall be used for Load Case Extreme Event I.

The recurrence interval, or Return Period (RP), is the

average time span between earthquake occurrences.

In 1100

TRPPE

For PE = 2 and T = 50 years, RP ≈ 2,500 years

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LOAD CASE EXTREME EVENT - I

[AASHTO 2010]

, site-specific, deterministic

http://earthquake.usgs.gov/designmaps/us/application.php

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RESPONSE SPECTRA

Response spectra establish the ground motion shaking intensity level and are used for deriving other ground motion parameters, e.g., PGA / SM1 is used to find PGV, shear strain, etc.

Response spectra are used as target spectra for generating design ground motion time histories for refined numerical analysis

Minimum three points are required to establish Response Spectra

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LOAD CASE EXTREME EVENT - II

[AASHTO 2010]

area-specific, probabilistic http://geohazards.usgs.gov/hazards/apps/cmaps

A 'realistic design basis earthquake',

typically taken as occurring once in a

period equal to about three times the

design life (3 x 100).

For CEUSA, the Return Period of

500 years i.e., 10% probability of

exceedance in 50 years.

The values for site class B are

obtained from USGS hazard maps.

Values for other soil class are

derived from Ch. 11 of ASCE 7-10

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LOAD CASE EXTREME EVENT - III

[AASHTO 2010]

area-specific, probabilistic, all soil types

http://geohazards.usgs.gov/hazardtool/application.php

The Extreme Event III and

Construction Strength I combination

should consider “a smaller

earthquake as a static load” to be

combined with other loads

A Return Period of 10 years i.e.,

99% probability of exceedance in 50

years

The values for all site classes for

any probability are obtained from

USGS hazard maps.

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SEISMIC DESIGN TOOL – WORLDWIDE

http://earthquake.usgs.gov/hazards/designmaps/wwdesign.php

Salah Bey Cable Bridge, Constantine, Algeria

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SIMPLIFIED PROCEDURE FOR SDC B & C:

Ovaling/Racking Deformation of Circular/Rectangular c/section to

Vertically Propagating Shear Waves

Axial/Curvature Deformation Along Tunnel Due to Traveling Waves

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SIMPLIFIED PROCEDURE FOR SDC B & C:

The values of "Peak Gravitational Acceleration (PGA)" and "Maximum spectral response at 1-s period (SM1)" are obtained from the site-specific, deterministic hazard analysis from USGS.

SM1 is used to calculate the shear wave peak particle velocity Vs of soil

Using closed-form analytical equations, the free-field shear strain, γ at the required depth is evaluated from PGA and Vs, separately.

Bending moments and axial hoop forces are evaluated from γ using closed-form equations.

Seismic forces are added to static loads with appropriate load factors.

Ch. 13 of AASHTO 2010

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FE NUMERICAL PROCEDURE FOR SDC D, E & F:

(A) Pseudo-Static Seismic Coefficient Deformation Method for

(a) underground structures buried at shallow depths,

(b) when the subsurface conditions are not highly variable,

nor ground stability is a concern,

(c) simple and non-critical structures,

(d) low seismic area

(B) Dynamic Time History Analysis:

In a dynamic time history analysis, the entire soil-structure

system is subject to dynamic excitations using ground motion

time histories as input at the base of the soil-structure system

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DYNAMIC TIME HISTORY ANALYSIS using Plaxis

Tunnel of any shape can be modeled

Dynamic Load input options:

1) Simple sinusoidal wave

2) Any time-dependent force

3) Earthquake Time History

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SOIL STRUCTURE INETRACTION (SSI)

The response of a structure to

earthquake shaking is affected by

interactions between three linked

systems:

1) the structure,

2) the foundation, and

3) the geologic media underlying

and surrounding the foundation. [Fig. from H. Allison Smith & Wen-Hwa Wu, 1997]

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FLUID STRUCTURE INTERACTION (FSI)

Femarnbelt Immersed Tube Tunnel, Denmark Offshore structures

http://www.tunneltalk.com/Femarn-Crossing-Jan13-Femarnbelt-RFQ-attracts-24-international-companies.php

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Thank You! Q?

“Earthquake effects on structures

systematically bring out the mistakes

made in design and construction,

even the minutest mistakes” –

Newmark and Rosenblueth

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DESIGN STANDARDS (1) AASHTO Technical Manual for Design & Construction of Road Tunnels –

Civil Elements 2010

(2) FHWA-NHI-11-032, LRFD Seismic Analysis and Design of Transportation

Geotechnical Features and Structural Foundations, 2011

(3) FHWA-HRT-05-067 Seismic Retrofitting Manual for Highway Structures: Part

2 – Tunnels, Retaining Structures, Slopes, Culverts & Roadways, 2005

(4) ASCE/SEI 7-10 Minimum Design Loads for Buildings and Other Structures

(5) AASHTO LRFD Bridge Design Specifications, 6th Edition, 2014

(6) AASHTO LRFD Seismic Bridge Design, 2nd Edition, 2011

(7) AISC 341-10 Seismic Provisions for Structural Steel Buildings, 2010

(8) ACI 318-14 Building Code Requirements for Structural Concrete & Commentary

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MCER = Risk-targeted Maximum Considered Earthquake Ground Motion. Design response spectrum shall be determined by dividing ordinates of MCER response spectrum by 1.5.

FEW NOTATIONS & DEFINATIONS

CR = risk coefficient; see Section 21.2.1.1 CRS = mapped value of the risk coefficient at short periods as defined by Figure 22-3 CR1 = mapped value of the risk coefficient at a period of 1 second as defined by Figure 22-4 SSD = mapped deterministic, 5 percent damped, spectral response acceleration parameter at short periods as defined in Section 11.4.1 SSUH = mapped uniform-hazard, 5 percent damped, spectral response acceleration parameter at short periods as defined in Section 11.4.1 S1D = mapped deterministic, 5 percent damped, spectral response acceleration parameter at a period of 1 second as defined in Section 11.4.1 S1UH = mapped uniform-hazard, 5 percent damped, spectral response acceleration parameter at a period of 1 second as defined in Section 11.4.1

SS = 5 percent damped, spectral response acceleration parameter at short periods as defined in Sec. 11.4.3 S1 = spectral response acceleration parameter at a period of 1 second as defined in Section 11.4.3 SaM = the site-specific MCER spectral response acceleration at any period SMS = the MCER, 5 percent damped, spectral response acceleration parameter at short periods adjusted for target risk and site-class effects as defined in Section 11.4.3 SM1 = the MCER, 5 percent damped, spectral response acceleration parameter at a period of 1 second adjusted for target risk and site-class effects as defined in Section 11.4.3

[Sec. 11.2, 11.3, ASCE 7-10]

Presentation Title

DESIGN RESPONSE SPECTRA

54

for TS ≤ T ≤ TL (Eq. 11.4-10)

for T > TL (Eq. 11.4-11)

SDS = ⅔.Fa.CRS.SSUH or ⅔.Fa.SSD, lesser. (Eq. 11.4-1, 11.4-2, Table 11.4-1)

00

0.4 0.6 ( .11.4 9) DSaTS for T T EqST

SD1 = ⅔.Fv.CR1.S1UH or ⅔.Fv.S1D, lesser. (Eq. 11.4-3, 11.4-4, Table 11.4-2)

[Sec. 11.4, ASCE 7-10] Response Spectra

Seismic Design - Introduction

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