Earthquake Resistant Design Codes in Japan 2000

JAPAN SOCIETY OF CIVIL ENGINEERS

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January,2000

JAPAN SOCIETY OF CIVIL ENGINEERS

EARTHQUAKE RESISTANT DESIGN CODES OF CIVIL ENGINEERING STRUCTURES IN JAPAN

1.

KEY CONCEPTS FOR EARTHQUAKE RESISTANT DESIGN OF CIVIL ENGINEERING

STRUCTURES

AFTER

THE

1995

HYOGOKEN-NANBU

EARTHQUAKE 2.

1996 SEISMIC DESIGN SPECIFICATIONS OF HIGHWAY BRIDGES JAPAN ROAD ASSOCIATION

3.

SEISMIC DESIGN FOR RAILWAY STRUCTURES RAILWAY TECHNICAL RESEARCH INSTITUTE, JAPAN

4.

EARTHQUAKE RESISTANT DESIGN OF PORT FACILITIES BUREAU OF THE PORTS AND HARBORS, IvuNISTRY OF TRANSPORT

5.

BASIC PRINCIPLES OF SEISMIC DESIGN AND CONSTRUCTION FOR WATER SUPPLY FACILITIES JAPAN WATER WORKS ASSOCIATION

6.

RECOMMENDED PRACTICES FOR EARTHQUAKE RESISTANT DESIGN OF GAS PIPELINES JAPAN GAS ASSOCIATION

THE JAPAN SOCIETY OF CIVIL ENGINEERS

THE PUBLICATION COMMITTEE OF EARTHQUAKE RESISTANT DESIGN CODES OF CIVIL ENGINEERING STRUCTURES IN JAPAN

Chairman:

Masanori Hamada

(r#iseda Unievrsity)

Key Concepts for Earthquake Resistant Design

Members:

Shigeki Unjo

(Public Works Research Institute, Ministry of Construction)

Highway Bridges

Akihiko Nishimura

(Railway Technical Research Institute, Japan)

Railway Structures

Tatsuo Uwabe

(Port and Harbor Research Institute, Ministry ot Trensport)

Port Facilities

Seiji U ne

(Japan Water Works Association)

Water Supply Facilities

Hiroyuki Yamakawa Gas Pipelines

(Japan Ges Associetion)

1. KEY CONCEPTS FOR EARTHQUAKE RESISTANT DESIGN OF CIVIL

ENGINEERING STRUCTURES AFTER THE

1995 HYOGOKEN-NANBU

EARTHQUAKE

1.1

Lessons from The 1995 Hyogoken-nanbu (Kobe) Earthquake

1- 1

1.2

Key Concepts for Earthquake Resistant Design

1- 4

1.3

Technical Subjects for Revision of Earthquake Design Code

1- 6

1.4

Diagnosis and Reinforcement of Existing Structures

1- 7

1.5

Future Innovations of Design Codes and Research Subjects

1- 8

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

1. KEY CONCEPTS FOR EARTHQUAKE RESISTANT DESIGN OF CIVIL ENGINEERING STRUCTURES AFTERTHE 1995 HYOGOKEN-NANBU EARTHQUAKE the causative fault system with a length of 40km,

1.1 Lessons from The 1995 Hyogoken-nanbu (Kobe) Earthquake At 5:46AM of January 17, 1995, a highly urbanized area of western Japan was jolted by an earthquake with a magnitude of M=7.2. This earthquake affected an extensive area containing major cities, Kobe and Osaka and their surrounding satellite cities which constitute the industrial, commercial and cultural center of western Japan. The areas most heavily damaged by this earthquake extends in a belt-shaped zone along

Table 1.1

particularly the zones identified as JMA intensity scale VII (equivalent to MMI=X). They extend over the entire east -west length of the most densely populated part of Hanshin (meaning Osaka-Kobe) metropolitan region.. Three million

people in this region were seriously affected. A free-field ground acceleration (pGA) exceeded 800cmfs 2 in Kobe city and its response spectrum was over 2000cmfs 2 at a damping coefficient of 0.05. Table.Ll shows loss of human lives, and a

A Summary of Damage Caused by the 1995 Kobe Earthquake (1995 Kobe Earthquake)

Human*

Death: 6306 Missing: 2

Housing and Buildings

Totally collapsed houses:

Injured: 41,527

100,300

Half and partially collapsed houses:

214,000

3,700

Buildings:

Railway:

32

Bridges **

Road (Hanshin Expressway):

Embankment and Landslides

Embankment:

427

Landslides: 367

Water

Customers without service:

1.2 million

Restoration time: 40 days

Gas

Customers without service:

857,000

Restoration time: 85 days

Electricity

Customers without service: Outage of electric power: Restoration time:

2.6 million 2836Mw 7 days

Telecommunication

Customers affected by Switchboard Malfunction: Damaged Cable Line: 19,300

Economic Impact

Private properties: Transportation facilities: Lifelines: Others: Grand total:

*

Toll by Fire Defense Agency May 21, 1995

**

Collapsed and Extensively Damaged

1-1

67

¥6.3 ¥2.2 ¥0.6 ¥0.5 ¥9.6

235,000

trillion trillion trillion trillion trillion

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

summary of structural and functional disaster by

been· incorporated into design codes. This is one

the Kobe earthquake to houses and buildings,

of the technical subjects that the earthquake

bridge, lifeline facilities and so on.

showed needs to be promptly studied and

The first point to note about damage to civil

implemented.

engineering structures is that elevated highway bridge piers were completely destroyed. Although there had been RC bridge piers damaged by earthquakes in the past, this was the first experience of total collapse in Japan. Most of the seriously damaged

piers

were

designed

in

accordance with pre-1980 earthquake resistant design codes. The piers of concrete structures having low ductility and low ultimate strength, were shear-fractured, resulting in such major failures. Damage to RC piers designed

Figure 1.3

in

Buckling of A Steel Pier of A

Bridge (1995 Kobe Earthquake)

conformance with the current earthquake resistant design codes after 1980 was not so severe as to result in bridge collapses.

Damage to large underground structures, such as subway structures has also become a focus ofattention. The severest dainage was caused at a subway station in the downtown of Kobe city, which is of box-type

RC structure,

where

reinforced concrete columns were shear- fractured and an upper floor deck slab collapsed along with the overburden soil. Severe damage to other underground subway stations was also reported. Besides subway tunnels, which were constructed Figure 1.2 Elevated

by the cut-and-fill method, many mountain

Collapse of Bridge Piers of A

tunnels

Highway Bridge (1995 Kobe

of railway and highway were also

damaged due to large ground motion in the near

Earthquake)

field of the earthquake fault.

Another point to note is the damage to steel

Another. typical characteristic of damage to civil infrastructures caused by the Kobe

bridge piers. Many steel bridge piers buckled.

earthquake is collapses and large displacements of

Most steel structures were designed by a method

quay walls. Numerous collapses of revetments and

where stresses in steel structural members fell

quay walls had been reported in past earthquakes,

within an elastic region. The characteristics of

but most of them had not been designed to

plastic deformation of steel structures had not

withstand soil liquefaction and had been decaying.

1-2

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

This was the first time when recently constructed

of the Shinkansen (bullet trains) shocked not only

quay walls were largely displaced by several

civil engineers, but also the general public. RC

meters or collapsed. All the damaged quay walls

bridge piers were shear-fractured and collapsed,

had been constructed using concrete caissons. The

and

result of the investigation into cause of the

earthquake struck 14 minutes before service hours,

damage to quay walls said that soft clay of the sea

no human life was lost. A serious issue has

bed largely amplified the earthquake motion and

surfaced of how to assure the safety of high speed

girders

fell.

Fortunately,

because

the

the foundation ground of the caissons, which had been constructed by replacing the original sea bed of soft

clay with

liquefiable gravel

sand,

weathered granite, also liquefied besides the filled ground behind the quay walls.

Figure 1.5

Soil Liquefaction of An Artificial

Island in Kobe (1995 Kobe Earthquake)

trains, including Shinkansen, against earthquakes caused by inland faults directly below them. Figure 1.4

Large Movement of Concrete

Soil liquefaction was extensively caused in

Caisson Quay walls (1995 Kobe Earthquake)

the artificial islands and alluvial low lands in Kobe and its neighboring areas, which resulted in a significant damage

However, it should be noted that all the

facilities. Most of the artificial islands in Kobe

survived. The construction of earthquake resistant

area was reclaimed from the sea by weathered

quay walls has been promoted nationwide, mainly

granite which contained large cobbles and fine

in major ports and harbors, through the lessons

contents. This revealed a need of revision of the

leamed from the damage to quay walls in Akita during

the

1983

and

structures of lifeline systems, and many port

so-called earthquake resistant quay walls mostly

Harbor

to buried pipes

method to evaluate the liquefaction potential of

Nihonkai-Chubu

gravel sand with fine contents.

earthquake. The earthquake resistant quay walls,

The ground behind the quay walls moved

which were designed by adopting a higher seismic

several meters towards the sea, resulting from the

load than that for conventional quay walls, were

large displacement of quay walls. These lateral

constructed to withstand liquefaction.

ground movement damaged the foundation piles

Damage to RC elevated railway bridge piers

of bridges, buildings and industrial facilities.

1-3

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

Furthermore,

large

ground

strain

due

to

factor was that the earthquake struck early in the

liquefaction-induced ground movement ruptured

morning. If the earthquake had struck a few hours

buried pipes of lifeline systems such as gas, water,

later during the rush hour, the results would have

electricity and sewer. A great number of breakages

been much more tragic. Another factor was that

of buried pipes resulted in the out of service to

dawn broke over the disaster-stricken area after

numerous customers during a long period. These

the earthquake. The daylight aided the evacuation

liquefaction-induced ground displacement had not

of victims and the rescue of people trapped under

been taken in the consideration in the earthquake resistant design codes before the 1995 Kobe

collapsed houses. If the earthquake had struck at midnight, the death toll would have been much

earthquake.

greater. It is highly important to investigate into the

causes of damage to the structures and to apply the results in future preventive measures against earthquakes, but we should also pay our full attention on the above-mentioned hidden lessons.

1.2

Figure 1.6

Key Concepts for Earthquake Resistant Design. The JSCE (Japan Society of Civil Engineers) organized a Special Task Committee of Earthquake Resistance of Civil Engineering Structures ill March 1995, about two months after the Kobe earthquake, to discuss various subjects, such as what an earthquake resistant capability of civil engineering structures should be in the future through the lessons from the Kobe earthquake. The committee first discussed whether the strong earthquake motions that had occurred in Kobe area should be taken into account in the future earthquake resistant design of civil engineering structures. According to researchers on active faults, in Japan the return period of the activity of the earthquake fault is 500 to 2,000 years. Assuming that the return period of the fault activity is 1,000 years and the service life of civil engineering structures is about 50 years, a probability that the structures would undergo such strong earthquake motions as those observed at the Kobe earthquake during the serviceable life is

Fall of A Bridge Girder due to

Movement of its Foundation Caused by Liquefaction-Induced Ground Displacement

When we learn the lessons from the Kobe earthquake, we should keep in mind the fact that some conditional factors mitigated the disaster. For one example had the earthquake struck the Shinkansen (bullet train) traveling on elevated railway bridges one hour later, it would have run off the rails and caused disastrous train accidents. The same can be said of the collapse of subway stations. Concrete slabs along with their overburden soil collapsed onto subway tracks. If subway trains had been stopped there or had smashed into the collapsed sections, additional serious damage would have resulted. There were other factors that contributed to lessening the secondary damage. One important

1-4

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

only five percent. The subject of the discussions by the JSCE committee was how to treat great

Level IT ground motion should be taken into

disasters with such low probability of occurrence.

account in the earthquake resistant design is

One of the reasons why JSCE said that the

The JSCE proposed two key concepts for

shown in Figure 1.7. This figure is a list of the

earthquake resistant design of civil engineering structures based on the discussions by the

damaging earthquakes in the last century in Japan and the numbers of casualties, and shows that

committee. Those are two levels of ground

inland earthquakes of magnitude 7 and larger such

motions for earthquake resistant design and so

as the Kobe earthquake, which are surrounded by

called performance-based design.

squares in the figure, occurred 8 times and have a

JSCE said that the resistance of civil

probability of occurrence that can not be neglected in terms of reformation of the design codes.

engineering structures against future earthquakes should

be

examined

by

taking

into

Figurel.7

the

also

shows

that

the

inland

consideration such strong earthquake motions as

earthquakes such as the Kobe earthquake resulted

observed during the Kobe earthquake in addition

in a greater number of causalities in comparison

to the ordinary earthquake motions that have thus

with the plate boundary earthquakes in the pacific ocean, if the 1923 Kanto and the 1900

far been used for earthquake resistant design.

Sanriku-Tsunami earthquake are excepted. In

These two earthquake motions are respectively called Level I and Level IT ground motions. Name of Earthquake Kumamoto

M

5.8

D ate

0

1889. 7.28

~

8.0

1891.10.28

Tokyo

6.7

1894. 6.20

Shonai

6.8

1894.10.22

Sanriku Tsun.

7.1

1896. 6.15

Rikuu

7.0

1896. 8.31

Gono

6.4

1909. 8.14

Akita·-Senpoku

5.9

1914. 3.15

Ch!iiwa-Bay

6.0

1922.12. 8

Great Kanto

7.9

1923. 9. 1

ita-t'Tafima

6.5

1925. 5.23

ita Tango

7.5

1927. 3.7

ita Izu

7.0

1930.11.26

Sanr-iku Tsun.

8.3

1933. 3. 3

Oga-Hanto

7.0

1939. 5.1

~

7.4

1943. 9.10

Tonankai

8.0

1944.12.7

lMikawa

I

Nanka!

IFukui

I

7.1

1945. 1.13

8.1

1946.12.21

7.3

1948. 6.28

Tokecbf-oki

8.1

1952. 3. 4

Chile EQ Tsun.

8.5

1960. 5.23

Niigata

7.5

1964. 6.16

Tokachr-oki

7.9

1968. 5.16

Izu Hanto-roki

6.9

1974

Izu-Oshima

7.0

1978. 1.14

Miyagiken-·oki

7.4

1978. 6.12

Nihonkat--Chubu

7.7

1983. 5.26

INagano-Seibu I 6.8

1984. 9.14

5. 9

Kushiro-oki

7.8

1993. 1.15

Hokkaido SI:

7.8

1993. 7.12

Hyogoken S

7.2

1995. 1.17

~

~

1000

Casualties 2000 3000

(H, Kem!)da Kyoto

4000

5000

20 7273

31 209

1900

~ ~O

these two earthquakes, the main causes of the loss

~-------------~~~

41 94

~ C;;;65······ ..·..···..·················J~~!'~!·

~ 1------------

2925

~

r- 272

" ••••••••• ---..

P

;;::

~ r------

18~6

·1961

...................... 144J

3769

29

1'-196a... -i-as

t:::

3064

27

26 52

-

.

InlandE.Q. ••••••• ' Plate Boundary (in Pacific Ocean) E.Q. _ - _ Plate Boundary (Tsunami)

30 25 28 104 29

~ 2.

230

6308"

2000

Figure 1.7

Damaging Earthquakes and Number of Causalities in Last Century in Japan (c=J: Inland Earthquakes)

1-5

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

of human lives were the aftermath fire and the

determined by considering the following items;

tsunami, respectively.

i) effects of collapse of structures on human life

However, JSCE's recommendation does not

and survival, ii) effects on rescue and ambulance

mean that all structures should be designed and

operations and restoration activities immediately

constructed to sustain Level II earthquake motions.

after earthquakes, iii) effects on civic life after

It states that the earthquake resistant capability,

earthquakes, iv) effects on economic activities

namely performance level of a structure should be

after earthquake, and v) effects on reconstruction

determined by comparing the importance of the

works.

structure with the probability of occurrence of the

The above-mentioned key concepts proposed

design earthquake motion. For instance, against

by JSCE were adopted in the National Disaster

earthquake motions having

a probability of

Prevention Program in Japan which was newly

occurrence once or twice during the service life of

revised after the Kobe earthquake and were

structures, e.g. Level I earthquake motions, the

strongly referred for the revision and development

earthquake resistant design should stipulate that

of the earthquake resistant design codes.

the deformation of structure falls within an elastic limit and that any residual deformation does not

1.3

remain after the design earthquake. In contrast to

Technical

Subjects

for

Revision

of

this, against very rare earthquake motions, e.g.

Earthquake Design Code The adoption of the JSCE-proporsed key

Level II earthquake motions, the performance

concepts for earthquake resistant design raised

level of a structure should be changed according

following technical subjects to be resolved for the

to

code developments.

the

importance

of

the

structure.

The

performance of structures after an encounter with

i) Determination of Level II earthquake ground

the design earthquake motion can be varied for an example

as

functional, iii)

follows;

and

ii) Evaluation of elasto-plastic behaviors and

ii) slightly damaged but functional,

ultimate strength of structures against the

heavily damaged

repairable,

i)

non-damaged

motion.

and

Level II ground motion.

unfunctional, but

iv) collapsed and unrepairable.

iii) Evaluation of residual deformation of earth

structures such as embankments, retaining

The degree of importance of a structure is

Probability of occurrence of

Importance of structure

design earthquake motion

I

~

I

Earthquake resistant capability (Performance Level) of structure Figure 1.8

Determination of Performance Level (Earthquake Resistant Capability)

1-6

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

walls and quay walls.

behaviors of steel structures in plastic region. The of

same can be said of the ultimate strength of buried

comparatively stiffer soil against Level II

steel pipes of lifeline systems. If large ground

ground motion v) Effects of liquefaction-induced large ground

strain due to liquefaction-induced lateral ground

iv)

Evaluation

of liquefaction

January, 2000

potential

flow is incorporated into the earthquake resistant design of buried pipes, strains of the pipes will

displacement. How to determine the Level II ground motion

reach a plastic region. But a small amount of data

was one of the most important subjects in the

has

development of the design codes. There were

characteristics in a plastic region and ultimate

following three kinds of ideas;

strength of buried pipes.

been

accumulated

on

the

deformation

i) Adoption of the maximum ground motion

Further, evaluation of the and ductility of

recorded during past earthquakes including the

earth structures, e.g. embankments, revetments,

Kobe earthquake.

retaining walls, and quay walls, is another subject

ii) Statistical approach of recorded and calculated

which needs research and development. These above-mentioned technical subjects

ground motion.

have been progressively carried out after the Kobe earthquake and the outcomes of the researches

iii) Numerical Analysis of ground motion directly from the design earthquake fault.

was applied for the revision and the development

The first idea was introduced for the seismic

of the design code.

design specifications of highway bridges (Chapter 2) and the Level II ground motion was determined

steel structures has been generally made by the

1.4 Diagnosis and Reinforcement of Existing Structures Although the future earthquake resistant design of civil engineering structures will be based on the concepts described above, an additional problem is diagnosis and reinforcement of existing structures. In large Japanese cities, such as Tokyo and Osaka, there are countless civil engineering structures similar to those damaged in the Kobe area by the Kobe earthquake. Some of them, e.g. highway bridges, Shinkansen lines, subways, and quay walls, were constructed earlier or have decayed more than those damaged in the Kobe area. The earthquake resistant reinforcement of these structures becomes an inevitable problem if disaster preventive measures are taken by

allowable stress method. That is, the design is

predicting that earthquakes of a similar scale of

made, not in a plastic region beyond an elastic

the Kobe earthquake will hit these cities.

based on the ground motions recorded during the Kobe earthquake. The second idea was adopted in the revision of the design codes for the railway facilities (Chapter 3) water facilities and gas supply facilities (Chapters 4, 5). The third idea where the :design ground motion was numerically calculated from the fault movement was also adopted for the railway facilities and gas supply facilities. The adoption of the Level II design ground motion raised another Technical subjects. One is how to estimate the behaviors of the structures in the plastic region and their ultimate strength. For an example, the earthquake resistant design of

Therefore, reinforcement of concrete piers of

region. Research has hardly been done on the

1-7

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

highways and railways and concrete columns of

more detailed investigations in future.

subways has been carried out by jacketing the

i) Dynamic failure mechanism of steel and

existing

concrete

with

steel

casting

concrete structures due to severe earthquake

additional concrete, and the other methods while

ground motion, eg Level II ground motion,

the effectiveness of those reinforcements was

shall be investigated through static and

confirmed by loading teats in the laboratory.

dynamic loading tests of structural members

However, the diagnosis and the reinforcement of

and large size structural models. Outcomes of

the foundations of bridges and buildings against

these studies are expected to give significant

the

information to

liquefaction-induced

plates

large

ground

displacement has hardly been conducted.

establish

new

earthquake

resistant design method against extremely

As is clear from the damage caused by the

severe earthquake ground motion.

Kobe earthquake, most critical and urgent issue is

ii) Mechanisms of large deformation and failure of

the reinforcement of structures on reclaimed lands,

foundations against strong earthquake ground

for instance the Tokyo Bay and the Osaka Bay

motion and large ground deformation shall be

areas, where in most of cases no soil improvement

investigated, and effective countermeasures for

has been taken against soil liquefaction, and a

foundations against liquefaction and its induced

huge number of buildings, bridges, and lifeline

large ground displacement are required to be

facilities already exist there. It is urgently required

developed.

to develop technologies of soil improvement of

iii) Mechanisms of occurrence of static large

existing artificial grounds.

ground deformation due to liquefaction shall

In addition, because reinforcement should be

be studied by large scale shaking table test.

undertaken in a proper order, it is also necessary to develop a basic idea to decide the priority of

Studies on properties of perfectly liquefied soil is essential for development of a rational

reinforcement.

method

The

previously

mentioned

for

estimation

of

the

ground

importance level of structures may be referred to

displacement. Furthermore, large scale shaking

in deciding the priority of the reinforcement. That

table test on liquefaction-induced ground

is, the effects of structures on human life and

displacement is

survival and on rescue and ambulance operations

mechanism.

and

restoration

activities

immediately

expected

to

clarify the

iv)Reasonable techniques are expected to be

after

developed for diagnosis and reinforcement of

earthquake, as well as other effects:

existing

structures

Furthermore,

1.5 Future Innovations of Design Codes and

including

foundations.

proper technology

shall be

developed for the soil improvement of existing

Research Subjects Most of earthquake resistant design codes for

liquefiable ground.

civil engineering structures have been revised or newly developed under the JSCE's key concepts and based on the outcomes from the researches after the Kobe earthquake. However, the following technical subjects remains unresolved and needs

1-8

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

REFERENCES 1)

Japan Society of Civil Engineers: Proposal on Earthquake Resistance for Civil Engineering Structures, 1996

2)

Hamada, M.: Seismic Code Development for Civil

Infrastructures

Hyogoken-nanbu

after

(Kobe)

Proceedings of the 5

th

the

1995

Earthquake,

U.S. Conference on

Lifeline Earthquake Engineering, TCLEE, Monograph No.16, pp922-929, 1999 3)

Japan

Road

Association:

Design

Specifications of Highway bridges, Part I Common Part, Part IT Steel Bridges, Part ill Concrete Bridges, Part IV Foundations, and Part V Seismic Design, 1996

4)

Seismic Design Code for Railway Structures, published by MARUZEN, Oct., 1999. (in Japanese) 5) Japan Water Works Association: Seismic Design and Construction Guidelines for Water Supply Facilities, 1997

1-9

2. 1996 SEISMIC DESIGN SPECIFICATIONS OF HIGHWAY BRIDGES

JAPAN ROAD ASSOCIATION 2.1

Introduction

2- 1

2.2

Damage Features of Bridges in The Hyogo-ken Nanbu Earthquake

2- 1

2.3

Basic Principle of Seismic Design

2- 3

2.4

Design Methods

2- 4

2.5

Design Seismic Force

2- 6

2.6

Evaluation of Displacement Ductility Factor of a Reinforced Concrete Pier

2- 7

2.6.1

Evaluation of Failure Mode

2- 7

2.6.2

Displacement Ductility Factor

2- 7

2.6.3

Shear Capacity

2- 8

2.6.4

Arrangement of Reinforcement

2- 9

2.6.5

Two-Column Bent

2- 11

Evaluation of Displacement Ductility of a Steel Pier

2.7

2- I I

2.7.1

Basic Concept

2- 11

2.7.2

Concrete Infilled Steel Pier

2- 12

2.7.3

Steel Pier without Infilled Concrete

2- 12

2.8

Dynamic Response Analysis

2- 13

2.9

Menshin Design

2- 14

2.9.1

Basic Principle

2- 14

2.9.2

Design Procedure

2- 15

2.9.3

Design of Menshin Devices

2- 15

2.10

Design of Foundation

2- 17

2.11

Design Against Soil Liquefaction and Liquefaction-Induced Ground Flow

2- 17

2.11.1 Estimation of Liquefaction Potential

2- 17

2.11.2 Design Treatment of Liquefaction for Bridge Foundations

2- 17

2.11.3 Design Treatment of Liquefaction-induced Ground Flow for Bridge Foundations 2- 18 2.12

Bearing Supports

2- 18

2.13

Unseating Prevention Systems

2- 19

2.14

Concluding Remarks

2- 20

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

2.1996 SEISMIC DESIGN SPECIFICATIONS OF HIGHWAY BRIDGES JAPAN ROAD ASSOCIATION 2.1 Introduction Highway bridges in Japan had been considered safe even against extreme earthquake such as the Great Kanto Earthquake (M7.9) in 1923, because various past bitter experiences have been accumulated to formulate the seismic design method (Kawashima (1995)). Large seismic lateral force ranging from O.2g to O.3g has been adopted in the allowable stress design approach. Various provisions for preventing damage due to instability of soils such as soil liquefaction have been adopted. Furthermore, design detailings including the unseating prevention devices have been implemented. In fact, reflecting those provisions, number of highway bridges which suffered complete collapse of superstructures was only 15 since 1923 Great Kanto Earthquake. Based on such evidence, it had been regarded that the seismic damage of highway bridges had been decreasing in recent years. However, the Hyogo-ken nanbu Earthquake of January 17, 1995, exactly one year after the Northridge, California, USA, earthquake, caused destructive damage to highway bridges. Collapse and nearly collapse of superstructures occurred at 9 sites, and other destructive damage occurred at 16 sites (Ministry of Construction, 1995a). The earthquake revealed that there are a number of critical issues to be revised in the seismic design and seismic strengthening of bridges in urban areas. After the earthquake the "Committee for Investigation on the Damage of Highway Bridges Caused by the Hyogo-ken nanbu Earthquake" (chairman : Toshio IWASAKI, Executive Director, Civil Engineering Research Laboratory) was formulated in the Ministry of Construction to survey the damage and clarify the factors which contributed to the damage. On February 27, 1995, the Committee approved the "Guide Specifications for

Reconstruction and Repair of Highway Bridges which suffered Damage due to the Hyogo-ken nanbe Earthquake," (Ministry of Construction 1995b) and the Ministry of Construction noticed on the same day that the reconstruction and repair of the highway bridges which suffered damage in the Hyogo-ken nanbu earthquake should be made by the Guide Specifications. It was decided by the Ministry of Construction on May 25, 1995 that the Guide Specifications should be tentatively used in all sections of Japan as emergency measures for seismic design of new highway bridges and seismic strengthening of existing highway bridges until the Design Specifications of Highway Bridges was revised. In May, 1995, the "Special Sub-Committee for Seismic Countermeasures for Highway Bridges" (chairman Kazuhiko KAWASHIMA, Professor of the Tokyo Institute of Technology) was formulated in the "Bridge Committee" (chairman : Nobuyuki NARlTA, Professor of the Tokyo Metropolitan University), Japan Road Association, to draft the revision of· the Design Specifications of Highway Bridges. The Special Sub-Committee drafted the new Design Specifications of Highway Bridges, and after the approval of the Bridges Committee, the Ministry of Construction released it November 1, 1996. This chapter summarizes the damage feature of highway bridges by the Hyogo-ken N anbu earthquake and the new Design Specifications of Highway Bridges issued in November 1996. 2.2 Damage Features of Bridges in The Hyogo-ken Nanbu Earthquake Hyogo-ken Nanbu earthquake was the first earthquake which hit an urban area in Japan since the 1948 Fukui Earthquake. Although the magnitude of the earthquake was moderate (M7.2), the ground motion was much larger

2-1

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

than anticipated in the codes. It occurred very close to the Kobe City with shallow focal depth. Damage was developed at highway bridges on Routes 2, 43, 171 and 176 of the National Highway, Route 3 (Kobe Line) and Route 5 (Bay Shore Line) of the Hanshin Expressway, the Meishin and Chugoku Expressway. Damage was surveyed for all bridges on National Highways, Hanshin Expressways and Expressways in the area where destructive damage occurred. Total number of piers surveyed reached 3,396 (Ministry of Construction, 1995a). Fig.2.1 shows Design Specifications referred to in design of the 3,396 piers. Most of piers (bridges) which suffered damage were designed according to the 1964 Design Specifications or older Design Specifications. Although the seismic design methods have been improved and amended several times since 1926 based on damage experience and progress of bridge earthquake engineering, only a requirement for lateral force coefficient was provided in the 1964 Design Specifications or older Specifications. 1980 Design Specifications

January, 2000

or no damage). Substructures of the Route 3 and Route 5 were designed with the 1964 Design Specifications and 1980 Design Specifications, respectively. It should be noted in this comparison that the intensity of ground shaking in terms of response spectra was smaller at the Bay Area than the narrow rectangular area where JMA Seismic Intensity was vn (equivalent to Modified Mercalli Intensity of X-XI). The Route 3 was located in the narrow rectangular area while the Route 5 was located in the Bay Area. Keeping in mind such difference of ground motion, it is apparent in Fig.2.2 that about 14% of the piers on Route 3 suffered As or A damage while no such damage was developed in the piers on the Route 5. A

s

B

o

1990 Design Specifications (a) Route 3

(b) Route 5

Fig.2.2 Comparison of Damage Degree between Route 3 and Route 5 (As: Collapse, A : Nearly Collapse, B : Moderate Damage, C : Damage of . Secondary Members, D : Minor or No Damage)

1971 Design Specifications

Although damage concentrated on the bridges designed with the older Design Specifications, it was thought that essential revision was required even in the recent Design Specifications to prevent damage against destructive earthquakes such as the Hyogo-ken nanbu earthquake. The main points requiring modifications were; (1) it was required to increase lateral capacity and ductility of all structural components in which seismic force is predominant so that ductility of a total bridge system be enhanced. For such purpose, it was required to upgrade

1964 or Older Design Specifications

Fig.2.1 Design Specifications Referred to in Design of Hanshin Expressway Fig.2.2 compares damage of piers on the Route 3 (Kobe Line) and Route 5 (Bay Shore Line) of the Hanshin Expressway. Damage degree was classified as As (collapse), A (nearly collapse), B (moderate damage), C (damage of secondary members) and D (minor

2-2

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

the "Check of Ductility of Reinforced Concrete Piers," which has been used since 1990, to a "Ductility Design Method," and to apply the Ductility Design Method to all structural components. It should be noted here that "check" and "design" is different; the check is only to verify the safety of a structural member designed by other design method, and is effective only to increase the size or reinforcements if required, while the design is an essential procedure to determine the size and reinforcements, (2) it was required to include the ground motion developed at Kobe in the earthquake as a design force in the Ductility Design Method, (3) it was required to specify input ground motions in terms of acceleration response spectra for dynamic response analysis more actively, (4) it was required to increase tie reinforcements and to introduce intermediate ties for increasing ductility of piers. It was decided not to terminate main reinforcements at mid-height for preventing premature shear failure, in principle, (5) it was suggested to adopt multi-span continuous bridge for increasing number of indeterminate of a total bridge system, (6) it was suggested to adopt rubber bearings for absorbing lateral displacement between a superstructure and substructures. It was

important to consider correct mechanism of force transfer from a superstructure to substructures, (7) it was suggested to include the Menshin design (seismic isolation), (8) it was required to increase strength, ductility and energy dissipation capacity of unseating prevention devices, and (9) it was required to consider the effect of lateral spreading associated with soil liquefaction in design of foundations at the site vulnerable to lateral spreading.

2.3 Basic Principle of Seismic Design Table 2.1 shows the seismic performance level provided in the revised Design Specifications in 1996. The bridges are categorized into two groups depending on their importance; standard bridges (Type-A bridges) and important bridges (Type-B bridges). Seismic performance level depends on the importance of bridges. For moderate ground motions induced in the earthquakes with high probability to occur, both A and B bridges should behave in an elastic manner without essential structural damage. For extreme ground motions induced in the earthquakes with low probability to occur, the Type-A bridges should prevent critical failure, while the Type-B bridges should perform with limited damage .

Table 2.1 Seismic Performance Levels

Importance of Bridges Type of Design Ground Motions

Type-A (Standard Bridges)

Type-B Equivalent (Important Static Lateral Bndges) Force Methods

Ground Motions with Prevent Damage High Probability to Occur Ground Motions with Low Probability to Occur

Type-I (Plate Boundary Earthquakes) Type-II (Inland Earthquakes)

Design Methods

Seismic Coefficient Method

Dynamic Analysis Step by Step Analysis or

Prevent Critical Damage

2-3

Limited Damage

Ductility Design Method

Response Spectrum Analysis

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

In the Ductility Design Method, two types of ground motions must be considered. The first is the ground motions which could be induced in the plate boundary-type earthquakes with magnitude of about 8. The ground motion at Tokyo in the 1923 Kanto Earthquake is a typical target of this type of ground motion. The second is the ground motion developed in earthquakes with magnitude of about 7-7.2 at very short distance. Obviously the ground motions at Kobe in the Hyogo-ken nanbu earthquake is a typical target of this type of ground motions are called as Type-I and Type-Il ground motions, respectively.

(

Start

January, 2000

The recurrence time of the Type-IT ground motion may be longer than that of the Type-I ground motion, although the estimation is very difficult.

2.4 Design Methods Bridges are designed by both the Seismic Coefficient Method and the Ductility Design Method as shown in Fig.2.3. In the Seismic Coefficient Method, a lateral force coefficient ranging from 0.2 to 0.3 has been used based on the allowable stress design approach. No change was introduced since the 1990 Specifications in the Seismic Coefficient

)

Design for

Principal Loads

Seismic Design by Seismic Coefficient Method

>--~

:heck the Safety by Dynamic Response Anal sis

Unseating Prevention Devices

Seismic Design by Dynamic Response Analysis (Type I and II Ground Motions

Seismic Design by Ductility Design Method (Type J and II Design Force) Check the Safety by Dynamic Response Analysis (Type I and II Ground Motion)

I End

Fig.2.3

Flowchart of Seismic Design

2-4

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

OR = CR (jJ. R-l) (l-r) a y jJ. R = 1/2 {(he' W /Pai+ l ]

(5) (6) in which R = residual displacement of a pier after an earthquake, Ra = allowable residual displacement of a pier, r = bilinear factor defined as a ratio between the first stiffness (yield stiffness) and the second stiffness (post-yield stiffness) of a pier, CR = factor depending on the bilinear factor r, jJ. R = response ductility factor of a pier, and y = yield displacement of a pier. The a aa should be 11100 of a distance between the bottom of a pier and a gravity center of a superstructure. In a bridge with complex dynamic response, the dynamic response analysis is required to check the safety of a bridge after it is designed by the Seismic Coefficient Method and the Ductility Design Method. Because this is only for a check of the design, the size and reinforcements of structural members once determined by the Seismic Coefficient Method and the Ductility Design Methods can only be increased if necessary. It should be noted however that under the following conditions in which the Ductility Design Method is not directly applied, the size and reinforcements can be determined based on the results f a dynamic response analysis as shown in Fig.2.3. The conditions when the Ductility Design Method should not be directly used include: (1) principle mode shapes which contribute to

Method. In the Ductility Design Method, assuming a principle plastic hinge formed at the bottom of pier as shown in Fig.4(a) and the equal energy assumption, a bridge is designed so that the following requirement is satisfied. Pa > he W (1) where he

khe = -.fZjJ.a-1 = Wo--c» Wp

a

a

a

(Z)

W (3) in which, Pa = lateral capacity of a pier, he = equivalent lateral force coefficient, W = equivalent weight, kne = lateral force coefficient, jJ. a = allowable displacement ductility factor of a pier, Wu = weight of a part of superstructure supported by the pier, Wp = weight of a pier, and cp = coefficient depending on the type of failure mode. The cp is 0.5 for a pier in which either flexural failure or shear failure after flexural cracks are developed, and 1.0 for a pier in which shear failure is developed. The lateral capacity of a pier Pa is defined as a lateral force at the gravity center of a superstructure. In the Type-B bridges, residual displacement developed at a pier after an earthquake must be checked as (4) R< aa where

a

January, 2000

a

Principal Plastic Hinge

(a) Conventional Design

(b) Menshin Design (c) Bridge Supported by A Wall-type Pier

Fig.2.4 Location of Primary Plastic Hinge

2-5

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

most cases excessive. Therefore if a foundation has sufficiently large lateral capacity compared with the lateral seismic force, the foundation is designed assuming a plastic hinge at the foundation and surrounding soils as shown in Fig.2A(e),

bridge response are different from the ones assumed in the Ductility Design Methods, (2) more than two modes significantly contribute to bridge response, (3) principle plastic hinges form at more than two locations, or principle plastic hinges are not known where to be formed, and (4) response modes for which the equal energy assumption are not applied. In the seismic design of a foundation, a lateral force equivalent to the ultimate lateral capacity of a pier Pu is assumed to be a design force as h p = Cdf PuIW (7) in which hp = lateral force coefficient for a foundation, Cdf = modification coefficient (=1.1), and W = equivalent weight by Eq.(3). Because the lateral capacity of a wall-type pier is very large in transverse direction, the lateral seismic force evaluated by Eq. (7) becomes in

2.5 Design Seismic Force Lateral force coefficient he in Eq.(2) is given as he = cz : heO (8) in which cz = modification coefficient for zone, and is 0.7, 0.85 and 1.0 depending on zone, and heo = standard modification coefficient. Table 2.2 and Fig.2.S show the standard lateral force coefficients heo for the Type-I and the Type-Il ground motions. The Type-I ground motions have been used since 1990 (1990 Specifications), while the Type-Il ground motions were newly introduced in the 1996

Table 2.2 Lateral Force Coefficient heo in the Ductility Design Method (a) Type-I Ground Motions Lateral Force Coefficient fuco

Soil Condition Group I

2J hco=0.876T / for T > 1.4

fuco=0.7 for T < 1.4

(stiff) Group II (moderate) Group III (soft)

fueo=1.51TI/J (fueo > 0.7) for T 0.18 I/J beo=1.51T (beo > 0.7) for T 0.29

<

<

fueo=0.85 for 0.18

< T < 1.6

fueo=1.0 for 0.29

< T < 2.0

fueo=1.16T2/J for T> 1.6 fueo= 1.59T2/3 for T> 2.0

(b) Type-Il Ground Motions Lateral Force Coefficient fueo

Soil Condition Group I (stiff) Group II

fueo=4.46T/J for T

< 0.3

heo=3.22T for T

Group III

hco=2.38T

(soft)

for T

for 0.3

/J

< 0.4

(moderate)

beo=2.00

heo=1.75 for 0.4 ~ T

/3

< 0.5

< T < 0.7

< 1.2

beo=1.50 for 0.5

2-6

< T < 1.5

beo=1.24T

4/J

for T> 0.7 beo=2.23T4/J for T> 1.2

beo=2.57T'3 for T> 1.5

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

u

2.5

.Y

....., c a;

2

I I

U u- et> y) Lp(h - Lp/2) (10) in which et> y = yield curvature of a pier at bottom, et> u == ultimate curvature of a pier at bottom, h == height of a pier, and Lp == plastic hinge length of a pier. The plastic hinge length is given as

a

a

a

2-7

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

and a = 0.2 and j3 = 0.4 for a rectangular pier), and p s = tie reinforcement ratio defmed as

Lp= 0.2h - O.lD (O.lD < Lr < 0.5D) (11) in which D is a width or a diameter of a pier. The yield curvature ¢ y and ultimate curvature ¢ u in Eq.(10) are evaluated assuming a stress-strain relation of reinforcements and concrete as shown in Fig.2.6. The stress (J' e - strain t: e relation of concrete with lateral confinement is assumed as Ee

e

e{l _

1 n

~)n-l} C

ee

(0 < C e < e cc ) Edes( c e - c cc) (c cc < e e < E cu) (12) Ee e ee n= (13) Ee E ee - (J' ee in which a cc = strength of confined concrete, Ee = elastic modules of concrete, e cc = strain at maximum strength, and Edes = gradient at descending branch. In Eq.(12), (J' cc, C ee and Eses are determined as a ee = (J' ek + 3.8 a p s (J' sy (14) (J'e=

[

ee -

C

ee = 0.002+0.033 j3

P s (J' sy (J' ek

Edes = 11.2

(15)

(J' ek 2

(16) p s (J' sy in which (J' ek = design strength of concrete, (J' sy = yield strength of reinforcements, a and j3 = coefficients depending on shape of pier ( a =1.0 and j3 =1.0 for a circular pier,

Stress

Stress (}s

=

4Ah

< 0.018 (17) sd in which Ah = area of tie reinforcements, s = space of tie reinforcements, and d = effective width of tie reinforcements. The ultimate curvature ¢ u is defmed as a curvature when concrete strain at longitudinal reinforcing bars in compression reaches an ultimate strain e eu defined as for Type I ground motions C ee C ell = ( 0.2 (J' ee C ee + Edes for Type II ground motions (18) It is important to note here that the ultimate strain c eu depends on the types of ground motions; the c eu for the Type-II ground motions is larger than that for the Type-I ground motions. Based on a loading test, it is known that a certain level of failure in a pier such as a sudden decrease of lateral capacity occurs at smaller lateral displacement in a pier subjected to a loading hysteresis with more number of load reversals. To reflect such a fact, it was decided that the ultimate strain e eu should be evaluated by Eq.(18), depending on the type of ground motions. p

0.80' cc

s

O'c

I

- - - - --

_____ L

_

I

I I I

I I

Strain e,

I

I I

I I

r

£cu

(b) Concrete

(a) Reinforcing Bars

Fig.2.6 Stress and Strain Relation of Confined Concrete and Reinforcing Bars

2-8

Strain E.c

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

Table 2.3

January, 2000

Safety Factor a in Eq.(9)

Type of Bridges

Type-I Ground Motions

Type-II Ground Motions

Type-B

3.0

1.5

Type-A

2.4

1.2

Table 2.4

Modification Factor On Scale Effect for Shear Capacity Shared by Concrete Effective Width of Section d (m)

Coefficient

d ;;:;; 1

1.0

d::::3

0.7

d::::5

0.6

~

0.5

d

10

Therefore, the allowable ductility factor u a depends on the type of ground motions; the u a is larger in a pier subjected to the Type-IT ground motions than a pier subjected to the Type-I ground motions. It should be noted that the safety factor a in Eq.(9) depends on the type of bridges as well as the type of ground motions as shown in Table 2.3. This is to preserve higher seismic safety in the important bridges, and to take account of the difference of recurrent time between the Type-I and the Type-IT ground motions.

Ce

:::: width and height of section, Aw :::: sectional area of tie reinforcement, (J' sy:::: yield strength of tie reinforcement, = angle between vertical axis and tie reinforcement, and a = spacing of tie reinforcement. The modification factor on scale effect of effective width, Ce, was based on the experimental study of loading tests of beams with various effective height and was newly introduced in the 1996 Specifications. Table 2.4 shows the modification factor on scale effect.

e

2.6.4 Arrangement of Reinforcement Fig.2.7 shows suggested arrangement of tie reinforcement. Tie reinforcement should be deformed bars with a diameter equal or larger than 13 mm, and it should be placed in most bridges at a distance of no longer than 150mm. In special cases such as the bridges with pier height taller than 30m, the distance of tie reinforcement may be increased at height so that pier strength should not be sharply decreased at the section. Intermediate ties should be also provided with the same distance with the ties to confine the concrete. Space of the intermediate ties should be less than 1m.

2.6.3 Shear Capacity Shear capacity of reinforced concrete piers is evaluated by a conventional method as Ps :::: Sc + Ss (19) Sc :::: 10 Cc Ce Cpt reb d (20) Ss > Aw a sy d (sin e +cos e) (21) 10 x 1.1Sa in which Ps :::: shear capacity, Sc :::: shear capacity shared by concrete, Ss :::: shear capacity shared by tie reinforcements, t: c = shear stress capacity shared by concrete, Cc = modification factor for cyclic loading (0.6 for Type-I ground motions, 0.8 for Type-II ground motions), Ce = modification factor for scale effect of effective width, Cpt :::: modification factor for longitudinal reinforcement ratio, b, d

2-9

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

~~

u

u

u

u

u

p

(

(

~

~~

~

(b) Semi-square Section

(a) Square Section

(c) Circular Section (d) Hollow Section Fig.2.7. Confinement of Core-concrete by Tie Reinforcement

n

Lp

Lp

r:

o--6--r--o---(c)}-+----------j-- T2), in which Ti and T2 represent the natural period of the two adjacent bridge systems. 2) The clearance at an expansion joint LE is

evaluated as LE = us + LA (43) in which UB = design displacement of men shin devices (cm) by Eq.(35), and LA = redundancy of a clearance (generally -+- 1.5cm).

Table 2.9 Modification Coefficient for Clearance

c. TIT,

CB

CB

o ~~ TlTl < 0.1 0.1 ~ ~ TIT, < 0.8

-V2

0.8 ~ ~ T(I\ ~ 1.0

1

1

2.14 CONCLUDING REMARKS The preceding pages presented an outline

motion records prevented to seriously evaluate the validity of recent seismic design codes is

2-20

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

N anbu Earthquake, 1995

important. The Hyogo-ken nanbu earthquake revealed that history of strong motion recording is very short, and that no near-field records have yet been measured by an earthquake with magnitude on the order of 8. It is therefore essential to have enough redundancy and ductility in a total bridge system. It is hoped that the revised Seismic Design Specifications of Highway Bridges contributes to enhance seismic safety of highway bridges. ACKNOWLEDGMENTS

Drafting of the revised version of the "Part V Seismic Design" of the "Design Specifications of Highway Bridges" was conducted at the "Special Sub-committee for Seismic Countermeasures for Highway Bridges" and was approved by the Bridge Committee, Japan Road Association. The first and other authors of this paper served as chairman and executive members in the Special Sub-committee. The authors thank ail members of the Special Sub-Committee and the Bridge Committee. REFERENCES 1) Japan Road Association Design Specifications of Highway Bridges, Part I Common Part, Part II Steel Bridges, Part ill Concrete Bridges, Part IV Foundations, and Part V Seismic Design, 1996 2) Kawashima, K.: Impact of Hanshin/Awaji Earthquake on Seismic Design and Seismic Strengthening of Highway Bridges, Report No. TIT/EERG 95-2, Tokyo Institute of Technology., 1995 3) Ministry of Construction: Report on the Damage of Highway Bridges by the Hyogo-ken N anbu Earthquake, Committee for Investigation on the Damage of Highway Bridges Caused by the Hyogo-ken Nanbu Earthquake, 1995 4) Ministry of Construction: Guide Specifications for Reconstruction and Repair of Highway Bridges Which Suffered Damage due to the Hyogo-ken

2-21

3. SEISMIC DESIGN FOR RAILWAY STRUCTURES

RAILWAY TECHNICAL RESEARCH INSTITUTE, JAPAN 3.1

Basic Principles of Seismic Design for Railway Structures

3- 1

3.2

Setting of Design Earthquake Motions

3- 3

3.3

3.2.1

Setting of Earthquake Motions for Bedrock

3- 3

3.2.2

Setting of Design Earthquake Motions on the Ground Surface

3-11

Seismic Performance of Structures 3.3.1

Setting of Seismic Performance Levels for Structures

3.3.2

Consideration on the Damage Levels of Member, the Stability Levels of Foundation as well as their Limit Values

3-13

3-13

3-14

3.4

Concept ofImportance Degree of Structure

3.5

Evaluation of Surface Ground and Calculation of Displacement and Stress ofStructure3-17

3.6

3.7

3-17

3.5.1

Evaluation of Surface Ground

3-17

3.5.2

Calculation of Responses of Structures

3-24

Safety (Seismic Performance) Checking of Structures

3-25

3.6.1

Checking Damage Levels of Members

3-27

3.6.2

Checking Stability Levels of Foundation

3-27

3.6.3

An Example of Safety Checking of Pile Foundation

3-27

Conclusions

3-29

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

3. SEISMIC DESIGN FOR RAILWAY STRUCTURES RAILWAY TECHNICAL RESEARCH INSTITUTE, JAPAN 3.1

totally and the other side with only cracks in

Basic Principles of Seismic Design for Railway Structures

columns. This situation with different damage pattern might be mainly due to the difference in

A new code, "Seismic Design Code for

dynamic behavior of the surface ground, which

Railway Structures" (in Japanese), drawn up by

was inferred through the dynamic analysis by

Railway Technical Research Institute, has been

considering both the properties of structures

published recently, which reflects the recent

and ground.

advances in earthquake engineering'{ In the code

@As to the damage of cut and cover tunnel, both

some new thought for seismic design have been

bending and shear stresses occurred in columns ,

adopted by drawing the lesson of the Hyogoken-

but since the shear strength was lower than that

Nanbu Earthquake of January 17, 1995 that

of bending which is same as the case of

caused the devastating damage including the

viaducts, the shear failure occurred and caused

large-scale cave-in of many railway structures. In

the collapse under the weight of overburden.

order to introduce a methodology for the seismic

The

design that can effectively prevent reappearance

the following causes of the damage are inferred damage

reconnaissance

@The necessary to

and

following

use

dynamic

analysis

methods and consider the dynamic behavior of

analysis".

surface

CDMany of the structures damaged possessed the a

horizontal

design

ground

in

response

analysis

of

structures.

seismic capacity that was designed by only considering

the

®Evaluating the safety of members by considering the failure modes of structures

mechanism has been conducted. As the results, the

indicate

CDTaking inland earthquakes into account

Nanbu Earthquake, elucidation of the damage

on

above

procedures are important to seismic design.

of the kind of damage happened in the Hyogoken-

based

facts

Moreover, the level of design earthquake

seismic

motion has become dramatically large because of

coefficient of 0.2. However, the acceleration

consideration

level of the Hyogoken-Nanbu Earthquake was

of

the

inland

earthquakes.

Generally the return period of the intense

far over such a design level and caused the

earthquake may be several hundred years long.'

large damage.

Therefore, it is reasonable to abandon the elastic

®Viaducts of the Shinkansen that suffered serious damage including the collapsing of

design method and adopt the performance-based design method in which the seismic performance

structures, were originally designed to be less

of structures is evaluated and the damage of

safety against shear loads than bending loads.

structure is allowable in some extend, but never

This imbalance aggravated the damage degree

the collapse.

of the structures. This was partly due to the

Seismic design of a railway structure should

fact that allowable stress against shear force

therefore be carried out

was set larger in the design code of those days.

following

@Some situation of the damage showed a great

procedures.

according to the Firstly,

from

the

viewpoint of damage control, the degree of

gap in the damage degree between two

damage to a structure (seismic performance)

adjoining viaducts, where one side collapsed

should be identified. Secondly, the responses of 3-1

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

the surface ground are analyzed by inputting the

resulting from an earthquake should be made to

design earthquake motion in the base ground.

satisfy

Thirdly, the response waves of the surface

Which performance the structure should be

ground are inputted to the structure and the

endowed

responses of the structure are analyzed. Finally,

importance of the structure.

the

seismic

with

performance

basically

objective.

depends

on

the

As the reasons described above, in order to

basing on the obtained responses of the structure the seismic performance can be checked.

check the seismic performance properly, a

There are two types of design earthquake

dynamic analysis method for calculating the

motion are determined in this code. One is the

responses of a structure is generally adopted in

so-call L1 earthquake motion, which has a

seismic design.

recurrence probability of a few times during the

analysis method is also used depending on the

service life of the structure. .The other is L2

type of structure.

earthquake motion with high intensity, which is

design for bridges or viaducts based on the

caused by a near-land-large-scale interplate

approaches above is shown in Fig.3.1.1.1.

However, some times a static The procedure of seismic

earthquake or an inland earthquake near to the

As what indicated in the figure, there are two

Comparing with Ll earthquake, the

types of approaches can be used for the seismic

structure.

occurrence probability of L2 earthquake is low.

design. One is the simplified method (nonlinear spectrum method) that can be easily applied for

For the earthquake motions, by considering the of the

the calculation of the responses of a structure by

foundations, the seismic performance of a

i) selecting the soil profile type based on site

structure is set to 3 grades corresponding to the

geological conditions; ii) using the demand yield

presumed levels of repair or reinforcement that

strength spectrum that is calculated with the

may be required following an intense earthquake.

earthquake motion corresponding to the soil

In the seismic design, responses of a structure

profile type selected. The other is the detailed

damage of members

and

stability

Setting input earthquake motion

Selection of Ll , L2 earthquake motions (Spectrum I, Spectrum II)

Selection of earthquake motions according to Soil Profile Type

Evaluation of surface ground

Simplified dynamic analysis (Nonlinear spectrum method)

Calculation of responses of structures

Examination of seismic performance

Members : Damage Level Foundation; Stability Level

Fig.3.1.1.1 Procedure of seismic design for bridges or viaducts

3-2

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

method (time-history dynamic analysis method)

may happen in most areas of Japan. Consequently,

with which the time history of responses of the

the motion due to this type of earthquake is also

ground and structure can be analyzed detailed.

covered by Spectrum I, therefore this spectrum is

For

a

common

structure,

spectrum method is suitable.

the

nonlinear

regarded as the minimum earthquake motion to be

However if a

verified in the seismic design.

®

structure can not be modeled as a system with

SpectrumII : acceleration spectrum based

single degree of freedom, as described later, the

on the statistic analysis of the earthquake data

detailed analysis method should be applied to.

recorded in the past inland earthquakes caused

In the following pages, major procedures for

by active faults.

@ Spectrumill:

the seismic design, such as the setting of design

also

representing

the

of

motions caused by active inland faults, but based

displacements and stresses of structures, and the

on the analysis of the active faults, if such a

checking of structural safety are described.

model of active fault is available.

3.2

motion from the 3 types above is a difficult, but

earthquake

motions,

the

analysis

Setting of Design Earthquake Motions

3.2.1

important task in the seismic design, because the

Setting of Earthquake Motions for

presumed earthquake may be affected by a great

Bedrock

amount of uncertainty. (1) Types

and

Determination

of

Design

It

Spectra

is

desirable

to

determine

the

design

earthquake motion for a specific site according to

As what described previously, in order to

the risk factors such as the return period of

consider the effects of surface ground to the

earthquake from certain seismic faults. However,

responses of a structure, either LIar L2

the return period of earthquake related to an

earthquake motion is set on the surface of

inland active fault is not accurate enough at

bedrock.

present, when compared with the service life of

Ll earthquake motion has about the same level

structure. Therefore, an extreme event associated

as the acceleration spectrum corresponding to the

with an inland active fault should be taken into

high quality ground that used to be adopted in

account, unless it is evident that the fault will not

the allowable stress design. The maximum value

move during the life of structure.

of

the

response

acceleration

is

250

To determine the design earthquake motion of a

gal

site, the geological and seismological information

corresponding to the damping coefficient of 5 %.

on inland active faults, historical activities of

L2 earthquake motion is classified into the

earthquakes

around

spectrum

earthquakes

near

interplate

carefully'). A general flowchart is given in

following 3 types.

CD

SpectrumI

corresponding

acceleration to

the

near-land

the land

site must

and

interplate

be

analyzed

Fig.3 .2.1.1.

earthquakes of magnitude 8.0 and epicenter

There are a number of ways to define the design

distance of 30 to 40 kilometers. In addition, the inland active fault, which will

earthquake motion. The design earthquake motion

cause an earthquake of magnitude less than 6.5, is

is defined below by the response spectra of

difficult to be found since its size is not big

acceleration on a free surface of bedrock, the

enough to reach the ground surface. According to

shear wave speed of which is over 400m/s. The

the historical earthquakes, this type of earthquake

choice of bedrock is to avoid the influences from 3-3

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

local effects of specific site on the ground motion,

objective response spectra of acceleration and

such as the amplification due to the soft surface

modeling the phases to reflect the non-stationary

soil and irregular topography of ground. The

property of earthquake motions.

influence due to geological conditions is very

Which spectrum should be used as the design

remarkable, as recognized in seismic records, and

earthquake motion depends on the results of

can be evaluated by calculating the responses of

investigation of inland active faults. There could

surface soil using a proper numerical model of

be three possibilities shown following from the

surface ground with the design earthquake motion

investigation (Fig.3.2.1.1).

as the incident motion. A corresponding artificial

The first (the left route in Fig.3.2.I.1), if there is

seismic wave can be generated by adjusting

no active fault near the site, the earthquake motion

Fourier amplitudes of the wave according to the

of Spectrum I is to be used as design earthquake

T No

Doubtful

Analysis with source model?

No

Yes, Computation of ground motions

Determine local seismic risk factor

,

,I

,

Spectrum I modified by risk factor

Determination of spectrum ill

Determine local seismic risk factor

~-----'

,

Speetrum Il attenuated with distance

Spectrum TI modified by risk factor

I

Compared with odified spectrum

,

,

Artificial wave

I

c? Fig.3.2.1.1 General flowchart to determine the design earthquake motion

3-4

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

motion after modified by the risk factor of the

with each other. Hence, the design earthquake

area.

motion is Spectrum IT modified by the risk factor

The second (the middle route in Fig.3.2.1.1),

of the area.

there are cases where one or more active faults

(2)Near-Source Earthquake Motions Induced by Inland Active Faults

existing near the site. When the parameters of seismic source for the faults can be properly decided, the design earthquake motion can be

There are still many problems to be solved

determined by the fault analysis with source

when using a seismic source model of fault to

model (Spectrum III). Otherwise, the earthquake

predict the earthquake ground motion at a site for

motion of Spectrum IT attenuated according to the

the purpose of seismic design, such as the

distance between the fault and site, will be used as

distribution of the asperity on the fault plane, the

the design earthquake motion. Because the power

start point of rupture, etc.

of the motion decreases as the distance between

uncertainties of it, it is effective to evaluate the earthquake

motion

To consider these

near inland

fault

from

attenuated results of Spectrum IT and III should be

statistical analyses of near-source strong seismic

compared with that of Spectrum I modified by the

records

risk factor of the area, then the larger one will be

summarized is a method to determine Spectrum IT

taken as the design earthquake motion.

based on strong seismic records.

The third (the right route in Fig.3.2.1.1), there

observed

in

recent

years.

Below

are sites where the existence of active fault is very

1) Seismic records Table 3.2.1.1 shows the list of records observed

doubtful and difficult to confirm due to very deep

in recent earthquakes in the United States and

sedimentary deposit, or there exists a complex

Japan, Hyogoken-Nanbu (1995,M7.2), Coyote

tectonic structure beneath the site, such as the

Lake (1979, MS.9), Loma Prieta (1989,M7.1),

Kanto area in Japan where three plates encounter

Landers (1992, M7.5) and Northridge (1994,

Table 3.2.1.1 Near-source seismic records from recent earthquakes "S

]

Max. Ace. (gal)

tU LL

r!:::

Ol

No

-""

Ol

::::>

""0

'" 0-

£;

ffi

.8

Ol

3

Name of seismic record NS

EW

W

~

....J

Ol ""0

3

'5> c

0 ....J

'-' o

Ol

c.. c> .>, c; .c ro

-05 C._

Ol""O Cij

>

'5 0-

UJ

2 3 4

Hyogoken-

5

Nanbu

Ol

o c ro

05 0 05 Ol

'"

a

_

Ol

>

Ol

c 0

:.=

Soil condition

ro

-2:

""OOl C en

::::>.0

eo

at the position of seismometer

o

0

U

679.8

302.6

135.208

11.64

3.24

GL-83

Vs=450 (m/s)

86.0

109.3

134.783

32.75

27.08

GL·100

Vs=460 (m/s)

293.9

319.8

135.442

34.57

24.65

GL-97.0

Vs=455 (m/s)

272.0

306.5

135.240

14.99

6.90

GL·9.5

0.5m (240m/s) layeroverVs=590 (m/s) Vs=780m/s

185.3

200.4

135.427

38.03

25.03

GL-30

6

445.9

425.3

135.296

20.00

12.38

GL-33

Layerof N=18 aboveGL-45

7

683.6

600.9

135.344

29.93

16.88

GLO.O

N over63, 1.5m surfacelayerwith N=5

16.52

7.53

GLO.O

Vs=300m/s, 4msurface layerVs=200m/s

1.0

GLO.O

Rock

12.19

GLO.O

Limestone

8 9 10

Coyote Lake Loma Prieta

11 12 13

::;]

Landers

510.7

584.2

135.250

314.6

408.8

121.484

433.1

401.5

122.06

18.01

426.6

433.6

121.572

26.56

12.21

GLO.O

Franciscan Sandstone

268.3

278.4

116.314

16.90

10.79

GLO.O

Shallow alluvium over granite bedrock

GLO.O

Northridge

GLO.O

3-5

Thin alluvium oversiltstone

IRock

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

4000

2000

1000 800

---.

600

'"2 400 eo -\

-,

I

ss

Fig.3.2.1.4 compares the statistical results based 2D

on the seismic records of USA and Kobe. They 10

0.2

0.1

satisfactorily agree with each other for the period

0.3

0.4

0.5 0.6 0.7 OBO.g 1 Pedodfsec) 2

4

5

up to 1.0 second. For the period longer than 1.0

Fig.3.2.1.4 Comparison of the statistical results

second, the records at Kobe give larger response

based on the seismic records in USA

spectra This difference would be a major cause

and Kobe, respectively

of larger deviation of total statistical results in the long period range.

4000

Meanwhile, it can also be

2000

found that the statistical results become smoother

~

V' 1000 800

as the number of records increases.

600

The attenuation function based on CDF is also

400

used, where the distance of destination is taken as

200

2lan. The point of 2km from fault is the place

100

---

I

1'--.. i J--.....

rt- I

~

I

_oo-ou

_OO_IIHA -OO-11lUl

This can be easily verified through the attenuation

-OQ-11HA. _OO_11Wl

_CXi_lJlU..

-oo-1.ltlB

-!'-ss.,..s

function given above, where the depth of a fault

_1"_llol'lW _~'l"':lltS

-J,(-I4f38W

center is assumed as 10km from the ground aa

(1.: Unit (m)

feature of the damage was a large settlement at the apron in an order of 1.0 to 1.5m, and the cais-

FigA.2.2 Cross section and deformation of a quaywall at Kushiro port (West port District No.2 West quaywaIl-9m)

son wall inclined toward the sea by 1.6 degree. Maximum horizontal displacement at the top of the caisson was lAm. Observed was 0.22g of maximum acceleration in Akita port. There was 4-3

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

The 1995 Hyougoken-Nambu earthquake

- - - before - - after

Gravity type quaywalls in Kobe port slid to

+2.37

offshore side 1m to Sm and subsided 1m to 2m,

r,---~~~-------~~~r------­

subsidence behind the quaywalls of 3m to 4m due

I

\

I

~\

_

\7±O.

to the lateral deformation of the quaywall as indicated in Fig A .2.3. As shown in this figure, a caisson wall was put on loosely deposited decom-

Tie Rod 1=11.0

E E

~

0 0

tti

"S-

c::

posed granite. A peak acceleration of 0.55g at a

~

Ol

s: Ul

depth of GL-32m was recorded at the Port Island

~~

vertical seismic array site in Kobe port.

FigA.2A Cross section of a sheetpile bulkhead in Yamanoshita Revetment in Niigata port T:'.: C .rlgUlC '"t • .L . .J ~l'"

_L

snows a

........:

1:'

(.;1U::;::; ::;C(.;l.!UH Ul

.....L

_

anouier

sheetpile bulkhead in Yamanoshita wharf Con-

Alluvial Clay Layer

Backfillin Sand for Replacing Clay Layer

struction of this wharf was completed about one year before the earthquake. The earthquake resistance design of the wharf was carried out using the design seismic coefficient of 0.12. As seen in

Sand Drain

'V-34.00~-36.00

Unil(m}

the figure, no appreciable damage was observed, except for a local sinking of the fill behind the

FigA.2.3 Cross section and deformation of a quaywall in Kobe port (RC-5, Rokko Island -14m)

anchor plate.

4.2.2 Sheetpile bulkheads The 1964 Niigata earthquake Tie Rod

The majority of quaywalls in Niigata port were sheetpile bulkheads. A typical damage of the sheetpile bulkheads was their swelling and tilting toward the sea. This type of damage was observed mostly in bulkheads with poor anchor resistance. In such cases, the swelling of bulkheads was accompanied by a horizontal shear at a joint

FigA.2.5 Cross section of a sheetpile bulkhead

of the top concrete and the upper end of sheet-

in Yamanoshita wharf in Niigata port

piles. The 1968 Tokachi-oki earthquake

A cross section of a sheetpile bulkhead in

As shown in FigA.2.6, the Konakano No.1

Yamanoshita Revetment is shown in FigA.2A. A characteristic feature of the damage was an over-

quaywall in Hachinohe port was heavily damaged

all settlement. A face line of the walls swelled

by the earthquake. The walls tilted 5 degrees and

more or less toward the sea and some of the top

swelled toward the sea by O.6m at maximum due

concrete blocks sank completely under the water.

to insufficient anchor resistance. Tension cracks in the direction parallel to the face line and set4-4

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

tlement in an order of several 10cm occurred in

January, 2000

The 1973 Nemuro-hanto-oki earthquake

the backfill surface. The maximum acceleration

As shown in FigA.2.8, the sheetpile bulkhead

of the earthquake was observed to be 0.26g in

was severely damaged by the earthquake. Ac-

this district.

cording to the investigation after the earthquake, the tie rods were not cut and the damage was es-

- - - l:efore

-after

timated to have been caused by the decrease of anchoring capacity due to the seismic effect. - _. before aIler

L - 068.0 I~~

H.WL+~ ~itf

LWL ±O.ro

15.0

__ . [+250 :::

1

1\

TIe Rod

Tumbuclde

""

Tlrrber Pile I

]~

-5.0

s:

-4.5

FigA.2.6 Cross section of a sheetpile bulkhead in Konakano No.1 quaywaII in Hachinohe port

\

~

VV

FigA.2.8 Cross section of a sheetpile bulkhead

in Hanasaki port

The sheetpile bulkhead with batter anchor piles, the quaywall of Kitahama pier in Hakodate

The 1983 Nipponkai-chubu earthquake

port, was damaged by the earthquake as shown in

The severe damage occurred on the sheetpile bulkhead at Ohama NO.2 wharf of -10m depth.

FigA.2.7. The fixation point of sheetpiles and anchorpiles was broken and the face line of the

Typical features of damage in the quaywall were

quaywall swelled toward the sea by 59cm at

a large settlement at the apron and a tilting of the

maximum.

coping. Through the investigation after the earth- - - before - - after

quake, the sheetpile damage was summarized as

+3.00 HWL +1.04 ~ , L WL ± O.00 "1\\~:;:Ll:u"

shown in Fig.4.2.9. These damages were estimat+2.73

ed to be caused mainly by liquefaction of the backfilling sand.

+2.0 -7.00

LWL

~

±o.oo

-12.00 -14.50

-

-10.0 -1.lV..t.?;t--

Fig.4.2.7 Cross section of a sheetpile bulk-

Fig.4.2.9 Cross section of a sheetpile bulkhead

head in Kitahama pier in Hakodate port

at Ohama No.2 pier in Akita port 4-5

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

4.2.3 Pile supported piers

January, 2000

Composite breakwaters consisting of concrete

The 1964 Niigata earthquake

caissons and the foundation rubble in Kobe port

The severe damage was observed on the tres-

suffered damage as shown in Fig.4 .2.12. These

tle type quaywalls at Rinko district in Niigata

breakwaters were constructed on loose decom-

port. The ground having consisted of very loose

posed granite, which was filled into the area after

sandy alluvial layer, a typical feature of damage

the excavation of the original alluvial clay layer.

in this area was a large settlement. The quaywall

TIle breakwater settled about 1.4 to 2.6m through

shown in FigA.2.10 sank completely under the

the earthquake. The horizontal displacements of

water.

the breakwater, however, were less than tens of em. The mode of deformation suggests that the

+2.40 l7

caisson was pushed into the rubble foundation and the rubble was also dragged down and

+0.00

pushed into the loose deposit beneath it.

-1.50

- - - before -after

II II II II II

,

FigA.2.10 Cross section of a trestle type pier in B Berth in Niigata port -·16.7

The 1995 Hyogoken-Nambu earthquake FigA.2.11 Cross section and deformationlfailure of a pile supported pier at Kobe port

A pile supported pier suffered damage at Takahama wharf in Kobe port. The horizontal residual displacement of the pier ranged from 1.3 to 1.7m. A typical example of the cross section and deformation of the pile supported pier is

before -afler

shown in FigA.2.ll. As shown in this figure, the

.g L.W.L

pier was constructed on a :firm foundation deposit consisting of alternating layers of Pleistocene clay and sandy gravel. The steel piles having a ....

diameter of 700mm buckled at the pile heads exClay

cept for the piles located most landward. A crack

.... -!-'~s

Backfill Soil, after Excavating Clay Layer

...........

///

......

E

~

..------;--

~P'"

l

'/

'I

!\

'-"'1\

!

,

~.->J~

,J:r If' Iti'f

i

!

i

i

Shear stress

0 0

10

-r: (Him')

20

,

a;:a... o.,

i\\

Ii

~'::J

"",~

!

:;.;0

?J;

-,

1"< \7

QI

.!

(

'

z

b:

~1.0r----.....

In this equation, several corrections are included as listed

-c

u

in followings.

1=

'" o '" u

(1).Stress condition correction: The stress conditions

~ 0.5

between at site( Ko) and

13

in the triaxial cell(isotropic

;;:

~

5

"' '"

01 0

--'--

-'-

5

10

-'--__---',

(2).Type of Input motion correction: The applied stress

15

condition

20

FINE CONTENT (BELOW 0.075I11m) ('To)

between at

a site high/low degree of

irregularity of input motion(impact type/vibration type)

Fig. 4.6.3 Reduction facto!" for critical STP-N value

and in case case of cyclic triaxial test(harmonic).

based on the fine content.

Impact type input motion

C, =0.55

Vibration type input motion C, =0.7 The two corrected equivalent N values are plotted in 0.5

Fig.(4.6.2) with acceleration and the zone to which c

a soil layer belongs is determined as follows. In

l2;:> 0.4

the case that the (N+ D N) is inside of the zone ] , the

o f::: -c 0.3 p::

soil layer belongs to the zone 1 . In the case that the

CI) CI)

(N+ D N) is inside ofthe zone II, the soil layer belongs

~ 0.2 f~------':"'_----6 Rrnaxtvibration type) ' " CI)

to the zone II . In the case that the (N+ D N) is inside ofthe zone III or N, and the

(N\5

0.1

/0.5 is outside ofthe

N, the soil layer belongs to the zone ill. In the N, and the (N)65 / 0.5 is inside of the zone N, the soil layer belongs to the zone N. zone

O!:-:-----'-----:-'::-~--:-:':-::------:-:-:!

0.1

case that the (N+ 6.N) is inside of the zone ill or

N value is calculated by Eqs.(4.6.5) and (4.6.6). The

10 20

100

1000

NUMBER OF CYCLES NI

Fig. 4.6.4 Correction of Rmax

Case3: The plasticity index is not less than 20 and the fine content is not less than 15%. A corrected equivalent

Undrained Cyclic Triaxial Test Results

Applied stress ratio L max =

T"max / (5'

I'

is calculated by

seismic response analysis. The liquefaction potentiahsafetyfactorjf'., is given as,

corrected equivalent N value is plotted in Fig.(4.6.2) with an equivalent acceleration and the zone to which a soil layer belongs is determined.

(4.6.8)

4.6.3 Undrained Cyclic Triaxial Test and seismic response analysis (Sensitive assess method)

In case ofF L < 1.0, the soil layer should liquefy.

When the liquefaction potential cannot be determined from the grain size distribution and SPT N value,

Reference:(the text mentioned above is revised in 1998 )

liquefaction prediction is made by performing undrained

POIi and Harbour Research Institute ed., 'Handbook on

cyclic triaxial tests using undisturbed soil samples. The

Liquefaction

index of a degree of liquefaction strength R max of a soil

Balkema, 1997.

4-24

Remediation

of

Reclamimed

Land',

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

4.7 Seismic Design of High Seismic Resistant Quaywalls 4.7.1

Evaluation of seismic performance of high seismic resistant facilities.

(1) In the design process of high seismic resistant facilities, it is requested that their seismic performance should be evaluated for a level-2 ground motion to assure that their seismic resistance is satisfactory. (2) Seismic performance should be evaluated by appropriately modeling the soil and the structure of the facility, with a method which is appropriate for the particular type of the structure.

January, 2000

the earthquake is presented, should be useful for the judgement. It should be noted, however, that these tables cannot be applied to a quaywall with cranes because the stability or the function of the cranes is not addressed in Tables 4.7.1 and 4.7.2. In the case of the 1995 Hyogoken-Nanbu earthquake, some of the caisson quaywalls with a normalized deformation (lateral residual displacement I height of the quaywall) of over 10-20% was temporary repaired and offered for immediate use just after the earthquake. . Related information for

seismic resistant quaywalls. 4.7.2 Design Seismic coefficient ofhigh seismic resistance facilities

Ground motion which is used for the evaluation of seismic performance should be determined with response analysis of the ground in principle.

(1) When pseudo-static design is applied to high seismic resistant quaywalls, the design seismic coefficient should be determined by a global judgement base on the seismic coefficient determined by EqAA.l with importance factor 1.5, by following equations for which peak ground acceleration should be calculated with ground response analysis for level-2 ground motion, and by other appropriate methods. 1. If a is smaller than or equal to 200Gal, Kh=a/g (4.7.1) 2. If a is larger than 200Gal, x, =(113) X ( a Ig)(lJ3) (4.7.2) Here, Kh is horizontal seismic coefficient, a is peak ground acceleration at free surface and g LS the acceleration of gravity.

Explanation (1) Evaluation of the residual deformation of high seismic resistant facilities, which is based on a earthquake response analysis, is required for the purpose of verifying that they will sustain their intended functions after a level-2 ground motion. The reason is that, for the examination of the stability of the structure or the soil for a large ground motion such as a level-2 ground motion, conventional pseudostatic method is not sufficient. (2) The judgement whether the high seismic resistant facilities will sustain their intended functions based on the results of earthquake response analysis should be based on the combined considerations on the stability of the structure after the earthquake, the functions and the difficulty of restoration work. Although the allowable residual deformation should be defined for this judgement, it is not easy to specify the allowable deformation at the present state of knowledge. Tables 4.7.1 and 4.7.2, in which the possibility of temporal use just after

Explanations (1) When the design seismic. coefficient can be accurately determined by investigating regional seismic activity, characteristics of ground motion, site response, ete., it is preferable to use this design seismic coefficient instead of the value designated here. For example, when the design ground

4-25

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

Table 4.7.1 Allowable residual deformation from the viewpoint of availability i

Type of structure.

Depth of water

'Available: N at available

Amount of deformation

I II

Gravity quay wan

Sheet-pile quay wall

More than 7.5m

Less than 7.5m

More than 1.5m

Less than 7.5m

o -30cm

o -20cm

o-30cm

o -20cm

30-l00cm

20-S0cm

30-S0cm

20-30cm

Table 4.7.2 Allowable residual displacement from functional point ofview

Subsidence of whole apron Main structure

20-30cm 3- 5

Inclination

0

20-30cm

Irregularity of the horizontal displacement offace line Irregularity of subsidence Apron

Gap between apron and backyard: Inclination

normal: 3-5%

3 -lOcm 30-70cm

reverse: 0%

(5) From the experience of significant damage at Kobe Port during the 1995 Hyogoken-Nanbu earthquake, minimum design seismic coefficient for high seismic resistant facilities should be 0.25 if the site is ill a near-source region. (6) When it is desired, seismic resistant qua walls should be designed for level-2 ground motion with a method other than pseudo-static method such as earthquake response analysis. In this case, it is necessary to make sure that seismic resistant facilities will sustain their structural stability for level-I ground motion.

motion is determined based on the information regarding regional seismic activities or based on strong ground motion observations or when seismic response analysis of the structure is conducted, design seismic coefficient can be determined based on these results. (2) In the design of high seismic resistant facilities. target earthquake has to be selected from earthquakes including hypothetical earthquake in the disaster prevention plan set by local government. (3) One way of calculating peak ground acceleration at free surface is to use multiple reflection model for the response analysis of the ground. (4) Refer to the reference 1) and 2) for the details ofEq.4.7.1 and Eq.4.7.2.

Related information (1) Level-2 ground motion for high seismic

4-26

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

Regional seismic coefficient, XF'actor for subsoil condition >< Importance factor O. 5)

Requirement of performance

I I

Ground motion

; Seismic coefficient

I Size of earthquake

I

I

I Type and parameters of structure,

soil improvement, function of facility Selection of target earthquake

I-

I

, (Near-source or not?) Cross section of the facility

-

I

PGA at bedrock

Assessment of liquefaction and mitigation

l-

I

Selection of waveform

Examination of residual, deformation for level-2 ground motion

r--

I

Earthquake response analysis of ground

Detailed design

Figure 4.7.1 Design process of high seismic resistant facilities

£rom another fault, these faults should be considered as one long fault m the determination of magnitude. If there is difficulty in the application of EqA.7.3, the magnitude 7.2 can be used, which is the same as the 1995 Hyogoken-Nanbu earthquake. (b) Following equation" can be used to determine peak ground acceleration at engineering-oriented bedrock. Log lOAsMAC=O.53M . -loglO(X+O.0062 x lOo.53~ - O.00169X+O.524. (4.7A) Here, A SMAC is the peak ground acceleration measured with SMAC-type accelerograph (Gal), M is the magnitude, X is the closest distance from the fault to the site (km). The relation is shown in Fig.4.7.2. If the dip angle of the fault

resistant facilities (a) If hypothetical earthquake is not designated in the regional disaster prevention plan or if the hypothetical earthquake in the disaster prevention plan is not appropriate for determining level-2 ground motion, it is recommended to select an earthquake which brings the largest ground motion to the site among earthquakes in the past and hypothetical earthquakes on active faults. Magnitude of hypothetical earthquake on active faults can be estimated with following equation. Log1oL=O.6M-2.9. (4.7.3) Here, L is the length of the fault (kID) and M is the magnitude. Sometimes several active faults are closely located to each other in the fault map. In such cases, if one fault is within 51an 4-27

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

0;

Q. ;(,

5-14

HGtlRfS~3+

.

($ElSMICMOT!ON LJ-:V'l::L2)

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

equivalent with factors which are used

(K' hOI) and (K hOl) shall be derived using Table

for

5.3.4.

calculating

seismic

equivalent horizontal

intensity

"Road

in

Bridge

Specifications. " This is defined

as

follows:

The standard horizontal seismic

intensity at the objective depth may be derived by linear interpolation between K hOl and K'hOI' 2. The design horizontal seismic intensity, when applying Seismic Motion Level 1, shall be

D

determined as follows:

= J5

hJh

1) The design horizontal seismic intensity at ground surface

=

D 17

't'lTL

1

s;

~1+417

at the base ground surface

VVUC>1C>

h = attenuation coefficient (%)

s;

=durability ratio

=

Cz

'

K'hOi

Where:

The structural characteristic factors

C; Region-specific correction factor. Values are 1.0-0.7.

(Cs) can only be used for seismic motion Level 2.

Cz ' K hOI

2) The standard horizontal seismic intensity

_

7]

=

They cannot be applied to

seismic motion Level 1 anti-seismic construction design.

3) When considering the vertical design seismic intensity (KVI ) K Y1

5.3.4 Seismic Intensity Used in Anti-Seismic

=

K h/2.

Design by the Seismic Intensity Method

·.·rAJHES,3L4 ·STANDARlJHORlZ0f4i1;j\n.SlEtSMlCIN1""Et4Sfl')'{UEVEDll

for Buried Structures

DEsIG1'j'.·.BiX·.1fJ3,$••$EISMlY.·.INTlU-iSIlT'Y·••METH0D

WH1£ff.jS·.TJSED•. FnR't$i$ .•$tJE~D$TRtle'TURA:E

(Seismic Motion Levell) GROIl'1>J"DTi:PB

1. When

anti-seismic

design

for

buried

structures is carried out using the seismic intensity method, seismic

intensity

the standard horizontal shall

be

determined

employing the standard horizontal seismic intensity (K' hOI) at the base ground level assumed for the design and the ground surface seismic intensity (K hOI)'

The values of

5-'15

..... $TAh1)AiRril-to~6NS1AlmAlU)ffd~f1jtf

CLASSJElCATlom

SmlSM1CIh'1'ENSlT'i': •.• .•

.•....·N$l'm"· . .

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

When the buried structures are designed by the

3. If there is possible amplification of seismic

seismic intensity method, the standard horizontal

motion due to such irregularities of the ground

seismic intensity which will act on the buried

as tilted ground surface, the design seismic

structure can be considered as the standard

intensity shall be increased by 1.2 times at

horizontal seismic intensity at the center of the

maximum.

gravity of the structure. Also for the underground standard horizontal

Similar to seismic motion Level 1, the

seismic intensity will be assumed that it will

design horizontal seismic intensity, which acts

change linearly between the base ground of the

on buried structures, may be acceptably

anti-seismic

derived using linear interpolation at the

design

and

ground

surface.

Therefore, it will be obtained the value at the

structure's center of the gravity.

center of the gravity of structure by the linear

design horizontal seismic intensity Kh2 is not

interpolation.

necessarj when considering the structural

Here the

characteristic factor. 5.3.5 Design Seismic Intensity Used in Anti-

tAaH15.35

Seismic Intensity Method for Buried

DESIGNfORHORlZONTAI..>SElSMIG.. rNTENSITY

Structures

{S£lSMiCM01'lONLEVU2JWJ:liCHU$ED FOR mJRISD$t~VC:nJltAL. hEsl(iN(SE1SMIC tN'Tt~i$nY

METHOD

(Seismic Motion Level 2) 1. In the case anti-seismic design for an Buried 't'fPR dMJUND

·t1C0NSESFECTRUMfORCONSTRUGT1QUI]E$fOW·

intensity. TG : the natural period(s) for the surface layer

i$El$~tlC

M01'JON·LKVE:L2'l

of the ground. K 'h1: the design horizontal seismic intensity at

foundation

ground

surface where

the

5.3.7 Seismic Intensity Used in Design of

design is based (Refer to 5.3.4 Seismic

Buried Structures by

Intensity Used in Anti-Seismic Design by

Displacement Method

the Seismic Intensity Method for Buried

the Response

(Seismic Motion Level 2)

Structures (Seismic Motion Levell)) Similar to the case of Seismic Motion Levell,

H: the thickness of surface ground layer (m) response

like Buried structures, anti-seismic design of

displacement amplitude is taken into account,

structures whose response characteristics during

the following formula is used:

an earthquake are chiefly affected by displacement

ill

the

1 U v =-U 2 h

case

the

vertical

of surrounding ground, the response displacement

5-17

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

method shall principally be used.

January, 2000

foundation and rock bed surface observations

Cross-sectional force, stress and strain, etc.

within 20 km from the Hyogo fault.

Figure

working on the structures shall be computed

5.3.3 represents the velocity response spectrum

based on the displacement or deformation.

obtained

The ground displacement amplitude generated

spectrum of the ground surface.

under Seismic Motion Level 2 is derived by

judgment was added.

the following formula at the distance x(m)

different kinds of values - 200 cm/s (upper

from the ground surface.

limit) and 70 cm/s (lower limit) - as the

U'; (x)

2

(5.3.5)

acceleration

response

Engineering

Figure 5.3.3 shows two

The system was

modeled with one degree of freedom for natural periods above 0.7(s).

Where,

U; (x): the horizontal displacement amplitude ground surface.

Each of these values is

compatible to a probability not exceeding 90% and 70%.

The desigu value is increased or

decreased within the scope of the upper limit

Sy: seismic motion velocity response spectrum (cm/s)

the

maximum response velocity.

1lX

I

= 7r 2 S; To cos 2H

from

and the lower limit, according to significance rank of the structure.

[See Figure 5.3.3]

To: the natural period(s) for the surface ground layer. H : the thickness of the surface ground layer (m)

When

the

ground

vertical

response

displacement amplitude Uv is considered, the formula is:

1 U =-U 2 h y

If there is possible amplification of seismic

motion due to such irregularities of the ground as tilted ground surface, the design seismic intensity shall be increased by 1.2 times at

r

10

FA'1'tiJLAiL l"B.RIOD(n:;){flFOR•.S.tJf\.f,....c·~:GR0lJND rPUNDATI0N

maximum.

These records were from the 1995 Hyogoken Nanbu earthquake. These records took into account five wave forms obtained from ground

5-18

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

5.3.8 Seismic Motion Input Used in Design

Soil surveys here include all surveys related to topography,

Using the Dynamic Analysis

January,2000

geology,

ground,

and

soiL

Generally, less damage due to earthquakes is The seismic waves used for dynamic analysis

found on good ground, that is firm and uniform

must fit the founding ground surface velocity

ground.

response spectrum is shown in Figure 5.3.3, the

be required to be built on such stable ground.

ground surface acceleration response spectrum is

The following are not good ground conditions:

Therefore, water works facilities must

observed in the vicinity of inland faults such as

CD ®

ones caused by the 1995 Hyogo-ken Nanbu

@ Slopes;

earthquake.

@ Different soil layer interfaces;

shown in Figure 5.3.1, or the seismic waves

Sliding; Mountainous slope toes and slope shoulders;

@ Weak ground; When selecting seismic wave observation sites for dynamic analysis against seismic motion Level 2, the ground types for the sites must be well considered.

@ Reclaimed ground;

(J) Ground subject to fluidization or lateral floating during an earthquake.

In particular, whether or not the

observed seismic wave response spectrum is similar to the design response spectrum in Figure

5.3.1 must be check. The maximum value of the

1. Survey using existing records Rough soil conditions at the facility construction site can be studied. 2. Common soil survey

inputted seismic wave for dynamic analysis must be for a ground surface that is 6,000 - 7,000 cm/s"

Study of required items for construction

and 400 - 600 cm/s 2 against the first ground type,

planning and

second ground type, and third ground type.

facilities will be conducted.

earthquake resistance of

3. Survey of dynamic properties of soil

Similarly, the base ground must be 400-500 cm/s".

The physical properties of soil 5.4 Geotechnical Surveys, Ground Displacement,

represented by the N value.

are

Cohesion, C,

and the internal friction angle 1>, are for

and Ground Distortion

static behaviors.

However, the velocity

effect of stress to the constants of the

5.4.1 Primary Subjects of Geotechnical Survey

ground and the effects of stress during an For

anti-seismic

design

of water supply

earthquake must be discussed.

For these

facilities, geotechnical survey at locations, where

studies, the following constants shall be

construction works are situated, depending on the

determined.

importance of the facilities.

5-19

EARTHQUAKE RESISTANT DESIGN CODESIN JAPAN

1) Modulus of dynamic distortion;

January, 2000

The geotechnical survey methods shall be based

2) Attenuation coefficient;

on the following:

3) Dynamic poison ratio;

1. Follow the standard or criteria which are set

4) Dynamic shear strength.

forth in the Japan Industrial Standard (JIS)

4. Survey of dynamic physical properties of

or the Japan Geology Society (JGS) for

the ground

various survey and laboratory test.

1) Velocity of elastic wave;

2. In principle, measurements shall be actually

2) Ground predominant period; and

conducted for dynamic soil constants and

3) Other.

dynamic physical properties of the ground. When it is impossible to do so, they may be obtained from the results of other surveys.

5.4.2 Methods of Geotechnical Survey

Vfu-lOliS

test-methods and soil Constants related

to ground and soil are shown in Table 5.4.1.

o

01

~.

iO fJ

i

10 .10

o

o Jh7Klli/OR.BODY StAWIC'1'ESTS UNIJl...'t.J'AL.C(tMPRESSI0t'i SMfPtt"1C•.'l'E);.r·· ·.·.Tlo:;sT'l"~lA.."{lAX. . CDM:?RESSrO.NTh:S't~ •. DlRECtSflEAroNGT$tirt ..... ·lixiNA.lV!lC'l'Rb\XIAt

.",.",_.."-_ _....;..

j

. COMPR~S$!ON'T:m$T .

i

··.·PYNi>H;nON

ntlrt:H1I'B0M GThOlJ:ND S'l;JE'

GEMEHAtllJN

f'AC~m}

SCOP2bF$AJ:'WtYRAT!t'}j"'L

'~=-,,~---'---;""'-+~

January, 2000

,.;..,.:.........=-"f-..---~-+=-"=-"~.-.-+-- . . . . . ~........., . . . . . _=-"~

5.5 Soil Pressure During an Earthquake 5.5.1 General

For anti-seismic design of structures attached to the earth, the soil pressure during an earthquake shall be determined according to the following: 1. The horizontal soil pressure during an earthquake must be derived by the MononobeOkabe soil pressure formula. 2. In case vertical seismic intensity for the surcharge

load

during

an

earthquake,

the

surcharge load must be multiplied by (1 +Kv ) . 5.5.2 Calculation of Horizontal Soil Pressure During on Earthquake For calculation of the horizontal soil pressure during an earthquake, the cohesiveness of soil, if

5.5.3 Calculation of Vertical Soil Pressure During an Earthquake

any, shall be taken into account. The vertical soil pressure on buried pipeline 1.

Soil

calculation.

classification

for

earth

pressure

For soil classification and for

must be calculated taking into account, the influence of lateral friction, if any.

various numerical soil values of earth pressure, refer to Table 5.5.1.

5-23

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

5.5.4

External

Pressure

due

to

Lateral

5.5.5 Buoyancy Generated by Soil Liquefaction

Spreading ill case the liquefaction resistance coefficient,

On the ground, which may be subject to lateral

FL , refer to Explanation of 5.4.3 (Soil Liquefaction

spreading due to liquefaction, anti -seismic design

and Lateral Spreading) of soil surrounding such

of foundation structures must be carried out with

buried structures as pipeline is smaller than 1.0,

consideration to the external force caused by such

the safety of the structure in regard to buoyancy

spreading.

In this case, the influence of inertia

shall be examined.

force from the super-structure and the base Specific gravity of fluidized soil is 18 - 20

structure don't have to be considered.

kN/m3 (1.8 - 2.0 X 10-3 kgf/cnr'). Great concern about the external pressure

If the actual

specific gravity includes the content volume or

created by lateral ground flow exists, especially, with regards to water works facilities built on

it will become smaller than this value and the

suspect ground.

buried structure will have a tendency to balloon.

Anti -seismic structural design

The upper portion of the non-fluidization layer,

must consider earth and flow pressure. It is shown in the experiments that fluidization

the weight of the road surface pavement materials,

flow pressure (which acts on the buried structure)

and the shearing resistance will usually block out

in the liquefied ground layer is below 30% of the

the

total load pressure.

(Niigata earthquake, etc.) illustrate that floating up

The lateral flow of the external pressure is

floating

up.

However, past examples

bad broken pipelines or manholes.

Careful

examination is necessary.

stated in Figure 5.5.1.

5.6

Hydrodynamic

Pressure

During

an

Earthquake and the Water Sloshing

5.6.1

Hydrodynamic

Pressure

During

an

design

of

Earthquake For

anti-seismic

construction

structures that come into contact with water, dynamic water pressure during an earthquake must be considered.

5-24

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

Structures which contact water (such as a dams,

January, 2000

sloshing is induced during an earthquake.

The

water tanks, etc.) and are subject to an earthquake

effects of sloshing bring about overflow or impact

must be considered.

pressure against the roof.

These structures receive

dynamic water pressure during an earthquake.

Whether such sloshing cause damage, or not, it

The action of dynamic water pressure during an

depend on the close relationship between the

earthquake must take into account two factors: (1)

natural period of water sloshing in the tank and

whether free surface water is present and (2)

the periodic characteristic of the seismic motion.

whether the complacability of the water can be

The sloshing of water inside of the tank shall be

ignored.

checked by following methods.

Dynamic water pressure action created during an earthquake can be dived into two factors: (1) inertial action which interacts proportionality with

a: Response spectrum method based on the potential theory. b: n wave response method. c: Response spectrum method based on the

secondary dynamic water pressure generated by free surface water oscillation. inertial

force

of

dynamic

Generally, the water

pressure

interaction is more significant and, therefore, will be taken into account by the design.

potential theory. However, when the competent seismic wave has

inputted,

dynamic

response

analysis

is

acceptable.

The action

of surface water oscillation is a supplemental issue

5.7 Safety Check

for dynamic analysis. The complacability of water, with regards to

5.7.1 Combination of Loads

structures like water tanks and water intake towers in water works facilities, can be ignored without creating

problems.

However,

for

Structure safety in anti-seismic calculations

pipeline

must be checked by combining the normal load

structures, the complacability of water must be

(dead weight and live load at ordinary times) and

considered. It is not, an excessive load for the

seismic effects.

design may result. 5.7.2 Safety Check of the Structures Fabricated with Steel, Concrete, etc.

5.6.2 Water Sloshing For anti-seismic design of water tanks, water

For safety checks of structures fabricated with concrete, steel bars, structural steel pre-stressed

sloshing must be considered when necessary.

concrete(pC) etc., the following related standards For water tanks with free

surface water,

5-25

must be used.

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

Specifications for Highway Bridges (Japan

characteristics is summarized in Table 5.7.1.

Road Association);

Concrete

For

either the seismic motion Level 1 or seismic

Standard

Specifications

motion Level 2, the pipeline component stress will

(Japan

Society of Civil Engineers);

not exceed the allowable stress of the pipe materials.

Iron Sluice Valve Technology Standard (Iron Sluice Valve & Pipe Society).

With jointed pipeline structures under

live loads and under ordinary conditions, the jointed component expansion capacity will not exceed the maximum expansion capacity of the

5.7.3 Safety Check of Pipeline in their Anti-

design.

Seismic Calculations

This is the main point for anti-seismic

checking. As a general rule, safety of pipeline during an earthquake must be checked with consideration to

With safety checks against seismic motion

I the strength and flexibility of the pipeline.

under live loads, must basically be below yield point stress for the pipe component material.

A pipeline structure for a water works facility varies in types.

Distortion, which corresponds with the yield point

If roughly categorized, the

following two types would emerge:

stress, is: Here, most of

1. Jointed pipeline structures -

E

=

(J

IE

= 2,400/2,100,000 = 0.11 %

After field condition are completely considered,

the flexibility is dependant on the joint. Here, most

appearances seem better, since distortion of the

of the flexibility is dependent on material the pipe

pipe component is below 23t/D (%) (about 0.15 -

is made of.

0.20)% and the anti-seismic capability can be

2. Continuous pipeline structure -

The anti-seismic calculation method

for the direction of principal buried pipelines is

checked.

described in this edition of the guidelines.

the diameter of the pipe.

Anti-seismic

Level 2, the distortion of the component, even

This method is

considering the stationary free load, is below

based on the behavior of the pipeline. behavior

is generated

through

the

46tID (%) (about 0.3 - 0.4)%.

This relative

capability can be checked.

displacement of pipeline and the ground. The pipelines, which possess the characteristics of (1), are represented by ductile iron pipe.

The

pipeline which possess the characteristics of (2) are represented by steel pipe.

With seismic motion

the

ability is checked using

response displacement method.

Here, t is the pipe thickness and D is

The basic concept

of the safety check on pipelines with these

5-26

The anti-seismic

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

5.7.4 Safety Check of the Foundation Ground in its Anti-Seismic Calculations

January, 2000

so that no plastic yield shall occur until the structures have reached te critical state. 3. For the anti-seismic design based on the

As a general rule, safety of the foundation

critical state, an appropriate safety factor

ground in anti-seismic calculations must be

must be employed with reference to the

checked in accordance with "Supporting Ground

critical displacement.

and Allowable Bearing Force".

5.7.5 Safety Check of Foundation, Earthen and Retaining

wall

in

Anti-Seismic

Calculations As a general lule, safety check of foundation,

earthen structures, and retaining wall in antiseismic

calculation

accordance

with

must

be

"Anti-Seismic

checked

in

Calculation

Methods for Foundations" and "Anti-Seismic Calculation Methods for Earthen Structures and Retaining Wall".

5.7.6 Safety Check in Anti-Seismic Calculations in Consideration of Critical State under Seismic Motion Level 2 Safety check in anti-seismic calculations in consideration of critical state must be carried out using the following rules: 1. Based on the results of proper analyses or testing the anti-seismic safety of structures must be checked with reference to the critical state found in such analysis and testing. 2. In anti-seismic design based on the critical state, tenacity of structures must be secured

5-27

6. RECOMMENDED PRACTICES FOR EARTHQUAKE RESISTANT DESIGN OF GAS PIPELINES (DRAFT)

JAPAN GAS ASSOCIATION 6.1

Introduction

6- 1

6.2

High-Pressure Gas Pipelines

6- 1

6.3

6.4

6.2.1

Basic Policy on Earthquake-Resistant Design

6- 1

6.2.2

Earthquake-Resistant Design against Seismic Motions of Level 1

6- 3

6.2.3

Earthquake-Resistant Design against Seismic Motions of Level 2

6- 4

Medium- and Low-Pressure Gas Pipeilnes

6-17

6.3.1

Basic Policy on Earthquake-Resistant Design

6-17

6.3.2

Earthquake-Resistant Design Procedure

6-17

6.3.3

Design Ground Displacement

6-17

6.3.4

Ground Condition

6-19

6.3.5

Pipeline Capability to Absorb Ground Displacement

6-20

6.3.6

Allowable Strain and Allowable Displacement

6-22

Appendix

6-24

6.4.1

Earthquake-Resistant Design ofHigh-Pressure Gas Pipeline

6-24

6.4.2

Improvement of Earthquake Resistance of Pipelines

6-29

6.4.3

Block System of Pipeline Networks

6-29

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

6.RECOMMENDEDPRACTICESFDREARrHQUAKE-RESfSTANTDESIGNOFGASPIPELINES (DRAFT) JAPAN GAS ASSOCIATION 6.1 Introduction

Design of High Pressure Gas Pipelines, be-

The presently used "Recommended Practices

cause its official issue may be after the publi-

for Earthquake-Resistant Design of Gas Pipe-

cation of the English version, it is hoped to

lines" was established as the recommended

recognize it as based on a "Draft" of the revised

practices for earthquake-resistant design of

recommended practice.

high-pressure gas pipelines

(See Appendix

The presently used Recommended Practices

6.4.1.) and medium- and low-pressure gas

for Earthquake-Resistant Design of Gas Pipe-

pipelines in March 1982, after the Miyagiken-

lines has not been revised in the medium- and

Oki Earthquake (June 1978),

low-pressure gas pipelines section, since it has

The Hyogoken-N anbu Earthquake occurred in January 1995.

been confirmed that the recommendations

Since the earthquake far

therein

are

reasonable

for

earthquake-

exceeded conventional theory, the Central Dis-

resistant design, judging from the results of

aster Prevention Council reviewed its Basic

investigation of the Hyogoken-Nanbu Earth-

Plan for Disaster Prevention and the Japan

quake.

Society of Civil Engineers presented a proposal. These actions showed the necessity for and

6.2

concept of containing the recommended prac-

6.2.1

.tices for the earthquake-resistant design of

High-Pressure Gas Pipelines Basic Policy on EarthquakeResistant Design

(1) Basic Concept of Earthquake-Resistant

important structures in methods of design for seismic motions of a higher level, level 2 seis-

Design

mic motions, which correspond to the shocks

For the earthquake-resistant design, two

generated by the Hyogoken-Nanbu Earth-

levels of seismic motions are assumed to se-

quake in the Kobe District.

cure the earthquake-resistant performance

The gas utilities are also now revising the Recommended

Practices

for

specified for the respective levels of seismic

Earthquake-

motions in principle.

Resistant Design of Gas Pipelines in the high-

(Description)

pressure gas pipelines section, mainly for the

(a) The Basic Plan for Disaster Prevention of

purpose of improving the resistance of high-

the Central Disaster Prevention Council

pressure gas pipelines to seismic motions of

was reviewed based on the Hyogoken-

level 2, especially in the concept of design in-

Nanbu Earthquake which occurred on

put seismic motions. This revision is aimed at

January 17,

achieving a more carefully-formulated respon-

that the earthquake-resistant design of

se to advanced seismic needs worldwide in the

structures, facilities, etc. to be constructed

light of technological findings since the pre-

in the future shall not suffer any serious

sently used Recommended Practices were established 17 years ago.

1995, and it now stipulates

loss of function even should general seismic

Regarding this re-

motions with a probability of occurring once

vised edition of Recommended Practice for

6-1

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

or twice within the service life of the pipeline occur,

January, 2000

(Description)

and shall not have any serious

(a) Seismic Motions of Level 1, and Earth-

influence on human life even should a

quake-Resistant

higher level of seismic motions of low prob-

Them

ability occur, due to an inland type earth-

Seismic motions specified in the previous

(b) For the earthquake-resistant design of gas

Recommended Practices

equipment, two levels of seismic motions

for

Earthquake-

resistant design of High Pressure Gas Pipe-

and considering the influ-

lines (March 1982).

ence of structures, facilities, etc. on -human

[Earthquake-Resistant Performance]

life, the influence on relief activities and on the prevention of secondary disasters,

against

[Seismic Motions]

quake or trench type huge earthquake.

are assumed,

Performance

The earthquake-resistant performance re-

and

quired for the seismic motions of level 1 is

the influence on economic activities, gas equipment must have earthquake-resistant

such that "Operation can be resumed imD:1e-

performance suitable for its respective

diately without any repair." based on the Re-

kinds and degree of importance.

port of the Committee for Preventing Seismically Caused Gas Disasters.

(c) Based on the above basic concept; earth-

(b) Seismic Motions of Level 2, and Earth-

quake-resistant design is performed to secure the earthquake-resistant performance

quake-Resistant

required for the two levels of seismic mo-

Them

tions, as described in the following chapter. (2) Seismic Motions to be Assumed for

Performance

against

[Seismic Motions] A proposal concerning the seismic standard,

Design, and Earthquake-Resistant

etc. of the Japan Society of Civil Engineers

Performance

presents concrete images as "seismic motion

The seismic motions to be assumed for de-

near the hypocenter fault of an earthquake

sign, and the earthquake-resistant perfor-

caused by any internal strain of a plate of

mance required of them are shown in Table

magnitude 7 class (hereinafter called an in-

6.2.1.

land type earthquake)" and "seismic motion

Table 6.2.1

Seismic Motions to be Assumed for Design General seismic motions Seismic with a probability of motions occurring once or twice of during the service life of level 1 gas pipeline are assumed.

Eart hquake- Resistan t Performance Operation can be resumed immediately without any repair.

Very strong seismic motions due to an inland type earthquake or trench type earthquake likely to occur at a low probability rate during the service life of gas pipeline are assumed.

The pipeline does not though leak. deformed.

Seismic motions of leve12

in the hypocenter region by a large-scale in-

Seismic Motions and EarthquakeResistant Performance

ter-plate earthquake occurring near land (hereinafter called a trench type earthquake)",

and the present "Recommended

Practices" assumes the seismic motions of these two earthquake types; inland type earthquake and trench type earthquake. Further, even if there -is no active fault found in the existing documents, there is a possibility that an inland type earthquake may occur.

6-2

Thus, it was decided to adopt a

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

concept that a lower limit level is set when

March 1982)*.

seismic motions are assumed.

propagationvelocity of seismic motion", the

[Earthquake-Resistant Performance]

value stated in "Apparent wavelength of

However, for the "apparent

The earthquake-resistant performance re-

seismic motion" is used, and for the "ground

quired for the seismic motions of level 2 is

spring constants in the axial direction ofthe

such that "the pipeline does not leak, though

pipe and in the transverse direction of the

deformed." based on the Report of the Com-

pipe",

mittee for Preventing Seismically Caused

of ground" are used.

the values stated in "Confining force

Gas Disasters.

* See Appendix 6.4.1.

(3) Evaluation of Earthquake-Resistance

(Description)

Since seismic motions repetitively forcibly

For earthquake-resistant design against

displace the pipeline, the fatigue damage at

seismic motions of levell, Recommended Prac-

a very low frequency caused by them is

tices for Earthquake-Resistant Design of High

evaluated for earthquake-resistant design,

Pressure Gas Pipelines* (Japan Gas Association, March 1982) is applied.

When the ground of the planned pipeline is likely to be greatly deformed by liquefac-

However, the following portions among the

tion, etc., it must be examined adequately.

latest results of research concerning the earthquake-resistant design, especially among

(Description) The method for evaluating earthquake-

the findings obtained after the 1995 Hyogo-

resistance was decided, considering that seis-

ken-Nanbu Earthquake inclusive should also

mic motions have the following characteristics:

be applied, in view of their nature, to the.

a) the loads are short-term ones, and

earthquake-resistant design against seismic

b) since the strains (or relative displacements)

motions of level 1.

So, for the following val-

caused in the ground by seismic motions are

ues stated in the 1982 Recommended Practices,

repetitively applied to the pipeline, the loads

those stated in the present Recommended

are periodically displacement-controlled, and

Practices are used. (1) "Apparent propagation velocity of seismic

also in reference to the concepts of existing

motion" in "Design seismic motion"

standards(ASME Sec. III, etc.) which specify

(2) "Ground spring constants in the axial di-

these loads.

rection of the pipe and in the transverse di6.2.2

Earthquake-Resistant Design

rection

of the

pipe"

in

"Earthquake-

against Seismic Motions of Levell

resistant design of straight pipe in uniform

The earthquake-resistant design against

ground", "Earthquake-resistant design of

seismic motions of level 1 is performed ac-

straight pipe in roughly varying Ground"

cording to the Recommended Practices for

and "Earthquake-resistant design for bend

Earthquake-resistant design of High Pres-

and tee".

sure Gas Pipelines (Japan Gas Association,

6-3

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

6.2.3

Earthquake-Resistant Design

plying the design seismic motion II stated

against Seismic Motions of Level 2

in "[E] Design seismic motion II" by the

(1) Entire Flow of Earthquake-Resistant

seismic zone coefficient stated in "[G]

Design

Seismic zone coefficient" is used as the

(a) The procedure for setting the design seis-

design seismic motion.

mic motion is shown in Fig. 6.2.1.

3) When it has been concluded that the exis-

(b) The earthquake-resistant design flow

tence of any active fault is unknown: . The seismic motion obtained by multi-

based on the set design seismic motion is

plying the design seismic motion I stated

shown in Fig. 6.2.2. (2) Setting of Design Seismic Motion

in "[D] Design seismic motion I" by the

[A] Procedure and Method for Setting

seismic zone coefficient stated in "[G] Seismic zone coefficient" is used as the

Design Seismic Motion I, II and III

design seismic motion.

The design seismic motion is set as follows based on "[B] Investigation of active

(Description)

fault" and "[C] Judgment as to existence of

(1) The seismic motion of level 2 to be applied

active fault".

for design is set using any of the three kinds

1) When it has been concluded that the ex-

of seismic motion described below based on

istence of any active fault is positive:

the conclusion as to whether the existence

· The seismic motion obtained by multi-

of any active fault is positive or negative.

plying the design seismic motion I stated

Design seismic motion I: Seismic motion

in "[D] Design seismic motion I" by the

decided for the inland type earthquake

seISmIC zone coefficient stated in "[G]

based on the observation records of

Seismic zone coefficient" is used as the

Hyogoken-Nanbu Earthquake

design seismic motion.

Design seismic motion II: Seismic motion

· Alternatively if fault analysis can be per-

decided for the trench type earthquake

formed, the seismic motion calculated ac-

based on past earthquake observation

cording to the fault analysis stated in "[F]

records

Design seismic motion III" is used as the

Design seismic motion III: Seismic motion

However, if the

based on analytical decision for the in-

calculated design seismic motion is smal-

land type earthquake by modeling the

ler than the seismic motion obtained ac-

hypocenter fault and using the hypocen-

cording to the procedure of 2), the seismic

ter parameter and the information on

motion of 2) is used as the design seismic

the ground and physical properties of

motion.

propagation routes

design seismic motion.

(2) If it is concluded that the existence of any

2) When it has been concluded that the existence of any active fault is negative:

active fault likely to greatly affect the

· The seismic motion obtained by multi-

planned pipeline is positive,

6-4

it can be con-

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

sidered to analytically calculate the seismic

(3) When it has been concluded that the exis-

motion by modeling the hypocenter fault

tence of any active fault is negative, it is re-

and using the. fault parameter and the in-

quired to take only the trench type earth-

formation onthe ground and physical prop-

quake into consideration, and the design

erties of propagation routes (this method is

seismic motion is set using the design seis-

called fault analysis).

mic motion II for the trench type earth-

However, presently

the data necessary for analysis and the

quake.

analytical method are not sufficiently es-

(4) When it

has been concluded that the exis-

Therefore, the design seismic

tence of any active fault is unknown, the

motion is set by using the design seismic

design seismic motion is set using the

motion I decided based on the observation

above-mentioned design seismic motion I,

records of Hyogoken-Nanbu Earthquake,

from the viewpoint of obtaining conserva-

one of the recent largest inland type earth-

tive results for design, since it cannot be

quakes, or by fault analysis.

concluded that there is no active fault.

tablished.

Investigation of active fault near the design site (B)

Positive

Negative

No Design seismic motion II (E)

Design seismic motion I (D) Yes

Selection of seismic zone coefficient (G)

Selection of seismic zone coefficient (G)

Corrected design seismic motion II

Corrected design seismic motion I

Design seismic motion ill (F)

Decision of design seismic motion

* 1) If the design seismic motion III is smaller than the corrected design seismic motion II, the corrected design seismic motion II is used as the design seismic motion. Fig. 6.2.1

Design Seismic Motion Setting Flow

6-5

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

Fig. 6.2.2

Earthquake-Resistant Design Flow for High Pressure Gas Pipelines against Seismic Motions of Level 2

Design Seismic Motion I or II (set based on earthquake observation records)

Design Seismic Motion III (set by fault analysis)

.Natural Period of Ground of Surface Layer

4.H :EVsjOH j :T=-=-, V s = - - ' - - -

.Ma:cimum Velocity in the Ground of

v, H H ; Thickness of ground of surface layer (m)

ied depth of gas pipeline): v

V s ; Shear wave velocity in the ground of surface layer (m/s)

Maximum ground displacement: Uh

I r Elastic wave survey xC""", Sand L Clay Estimate from N value -.:::::::::: Sand Clay

Surface Layer at Design Site (at bur-

0.7 E . 0.6 0.7 E • 0.85 0.7 E • 6NO.2! 07 E12 • NO·078

.Apparent Wavelength of Seismic Motion :L=V·T V;Apparent propagation velocity of seismic motion

(2.5,800)

V (rn/s)

.Apparent Horizontal Propagation Velocity of Wave: V a. Apparent propagation hodograph

(0.15, 100)

b. Calculation of simple phase velocity c. Detailed analysis (Haske] matrix method, etc.)

T (s)

To calculate according to any of a, band c.

.Ground Displacement of Surface Layer 1tZ

.Ground Strain

. T· Sv : cos-

aa

V (cm/s)

(0.1, 8.0)

v ; Seismic zone

f ~7,50) (0.7, 100)

(0.1, 4.0)

coefficient z ; Buried depth of pipeline (m) Sv; Standard response velocity (cm/s)

T (s)

.

.Ground Strain of Uniform Ground :

E Gl=2 1t X

UhlL

•

Ground

Strain

of Irregular

Shallow

Ground: EG2= IE G12+ EG/ E G3: Ground strain caused by irregular shallow ground

(* *)

6-6

No

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

Design of Straight Pipe

Ground strain due to (*) or (**)

January, 2000

Design of Bend and Tee

Ground displacement due to (*) or (**)

E G

.Strain Transfer Coefficient

Uh

.Displacement Transfer Coefficient a * = q* • aa q* ; Coefficient considering sliding

between pipe and ground Relative displacement between pipe q. Coefficient considering sliding between

and ground : 6. = (1- a *) .

pipe and ground

Al =

~

KI E'A

~

; Ground spring constant in axial direction of pipe

• Strain of Pipe caused by earthquake E p = a • E G (a • E G < E y)

=

.Strain of Bend or Tee during Earthquake

(ex • E G ~ e y) E y; Yield strain of pipe material :

Ep

Uh

In the case of irregular shallow ground, the value at or near the place where the bend or tee is installed is used.

E B,T= f3

EG

E B,T=

B,T •

6. (f3 B,T~ 1.27 E y)

C· f3B,T ·6.(f3 B ,T > L

27 E

y)

f3 B,T ; Coefficient of conversion C ; Plastic state correction factor

.Allowable Strain : Allowable strain of straight pipe, bend and tee 3%

No

Examination of Design Modification

6-7

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

[B] Investigation ofActive Fault

January, 2000

(Description)

For investigation of any active fault, the

(1) The conclusion as to whether the existence

information concerning the position, prob-

of any active fault is "positive", "negative" or

ability, activity; etc. of any inland active fault

"unknown" can be made in reference to Ta-

likely to produce large seismic motions to the

ble 6.2. Table 6.2.2

planned pipeline is collected from existing

existence of any active fault is "positive",

documents.

"nezative" or "unknown" ....

(Description)

Conclusion "Positive"

(1) For any inland active fault, basically, the active faults belonging to probabilities I and II of "Active Faults in Japan (New Edition)" are investigated for comprehensive evaluation also in reference to the active fault list

"Negative"

stated in "Investigation and Observation Plan for Foundations Relating to Earthquakes",

Criterion for concluding that the

the earthquakes assumed in the

regional disaster prevention plan and other findings in the latest investigation and re-

"Unknown"

search results. (2) If any active fault found as a result of active fault investigation is found not to be imminent in activity and not to act during the service life of the pipeline,

it can be ex-

Criterion · It is judged that "The existence of any active fault likely to produce large seismic motions is positive." Fig. 6.2.3 shows the relation between the distance from an active fault and the magnitude of an earthquake. · It is judged that "The existence of any active fault likely to produce large seismic motions is negative." Fig. 6.2.3 shows the relation between the distance from an active fault and the magnitude of an earthauake. · It is not confirmed that there is no active fault in a plain covered with a thick sedimentary layer. ·A complicated earth structure is formed with boundaries of three plates gathering underground, as in the metrooolitan area.

(2) The boundary line of Fig. 6.2.3 is obtained

cluded from the investigation.

by calculating the weak ground conditions

[C] Judgment as to the Existence of Active

with a ground surface velocity of 64 cmls as

Fault

the boundary on the conservative side.

If

Whether the existence of any active fault

the shortest distance from the active fault

likely to give large seismic motions to the

concerned to the planned pipeline and the

planned pipeline is "positive", "negative" or

magnitude of the earthquake likely to be

"unknown" is concluded by taking the fol-

caused by the active fault exist on the left

lowing into consideration:

side of the boundary line,

(1) Distance of the planned pipeline from the

face velocity caused at the planned pipeline

the ground sur-

when the active fault aets is larger than 64

active fault

cm/s.

(2) Magnitude of earthquake estimated from

If they exist on the right, the ground

surface velocity is smaller than 64 em/s.

the length ofthe active fault

The surface ground velocity of 64 cm/s was obtained by converting 50 cm/s, which is the

6-8

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

response velocity of design seismic motion II

January, 2000

(Description)

caused by the trench type earthquake speci-

(1) The design seismic motion I was decided by

fied in "Design seismic motion II", into the

obtaining the velocity response spectrum on

ground surface velocity (50 x 4J 7[

= 64,

4J 7[:

the seismic base rock (engineering under-

coefficient for converting the response of

ground base rock) based on 16 observed

single-degree-of-freedom system into the re-

waves of two horizontal components at the

sponse of continuum).

hypocenter region and nearby (within 10 km from the active fault) eight sites of the

8

I I I I I II II

I

I

L

"Positive' I

I

I I I I

I

the non-excess probability.

[E] Design Seismic Motion II _.

~ .

I

o

I

Th~ _d~Sign seismic motion II is shown in

l!'lg.

(j.~.5. 300

.

~s

I

J0

20

30

40 .7-;50)

The shortest distance from an active fault, d (km)

0

Fig. 6.2.3 Criterion for concluding whether the existence of any active fault likely to produce large seismic motions is positive or negative

V (O.l.U

3 0.1

(3) As an example of the methods for estimating

Fig. 6.2.5

proposes the following formula:

V

The design seismic motion I is shown in

~

c~'e _ Co >

design

Course,

tion (December 1996) . Earthquake-resistant design (draft), Design Standard and Description of Railway Structures, Etc. (November 1998)

3Or--+-74--+++f+H--+-+-+-I v

[F] Design Seismic Motion III

~er; ~

Earthquake-resistant

Highway Bridge Specifications and Descrip-

II II

c-,

"'r

Velocity response spectrum of as-

ence to the two spectra.

[D] Design Seismic Motion I

a>

'.0

half of the design seismic motion I, in refer-

by Meteorological Agency

B

2.D

(1) The design seismic motion II was set at one

M : Magnitude of an earthquake specified

-.;

J.O

(Description)

L: Length ofthe active fault

c -

0.:5

sumed trench type earthquake

LoglOL = a.6M - 2.9

o>

0.2

Natural period of ground of surface layer T (5)

the magnitude of an earthquake, Matsuda

Fig. 6.2.4.

considering

I

I

I

5

I

Hyogoken-Nanbu Earthquake,

11111 11111 11111 1111I

I I I

I I

'Negative" .

I I

VI

,I

I

I

1.-1"

I

6

,

I I

{O.1.I.Q

I

The design seismic motion III is calculated

,

I 0..3

I

I 1.0

1.0

5.0

by fault analysis.

Natural period of ground of surface layer T (5)

Fig. 6.2.4 Velocity response spectrum of

(Description)

assumed inland type earthquake

(1) If the seismic motion calculated by fault

6-9

I

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

analysis is smaller than the corrected design

January, 2000

(Description) Fig. 6.2.6 shows the zone classification map

seismic motion II caused by the trench type earthquake at the planned pipeline, the cor-

for the seismic zone coefficient.

rected design seismic motion II is used as

(3) Ground Displacement and Ground Strain of Surface Layer

the design seismic motion.

[A] Natural Period of Ground of Surface Layer

[G] Seismic Zone Coefficient (1) The zone classification is the same as the classification specified in the Recommended

Practices

for

The basic natural period of ground of surface layer is obtained from the following formula:

4- H

Earthquake-

T=~

where

Vs

Resistant Design of High Pressure Gas

T: Natural period of ground of surface layer(s) H: Thickness of ground of surface layer

Pipelines (Japan Gas Association, March 1982).

n ~

(2) The seismic zone coefficient is the value

(=

Vs : Shear wave velocity in the ground of surface layer (rn/s)

Table 6 2 3 Seismic Zone Coefficient Seismic Zone Coefficient

Special A Zone

1.0

A Zone

0.8

B or C Zone

0.7

[

_

Vs; Shear wave velocity of

n

"" Vs - H

f;::

j

j

~:

j-th layer (mJs) Thickness of j-th layer

H

Special A Zone

m o .

§

Fig. 6.2.6

.

(m)

j=l

stated in Table 6.2.3 for each zone. Zone Classification

-_.

LH j)

AZone

BZone CZone

Zone Classification for Seismic Zone Coefficient

6-10

(m)

J

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

of Section 6.2.3 (2) [D]

[B] Apparent Wavelength of Seismic Motion

The apparent wavelength of seismic mo-

T: Natural period of ground of surface layer(s)

tion in the direction along the ground surface is obtained from the following formula:

z : Buried depth of pipeline (m) H: Thickness of ground of surface layer (m)

L= V' T

where L : Apparent wavelength of seismic motion in the direction along the

(2) When design seismic motion II is used, it

is obtained from the following formula:

ground surface (m)

U

V: Apparent propagation velocity of seismic

motion (m/s)

=~. Jr

h

2

T' v· S

VII

(T)' cos (

JrZ )

2H

where SVII(1): Response velocity of design

T: Natural period of ground of surface layer(s)

seismic motion II (cm/s), according to

The apparent propagation velocity of seismic motion is obtained from Fig. 6.2.7.

Fig. 6.2.5 of Section 6.2.3 (2) [E]

3000

II III

! Ii

2000

I,

1000

I I I I 1111

I

i

u,I .

I

!

500

!

,

i. : II

I

I

I

! i I!! I . /

I

/

I

!

!

I

i

i I ! 10

I

! I

I

Viii'!

II

I i

'

; I

/11 I

i III1

: !,:

1=(0.15,1~

,

!

50

I

0.5

0.2

1.0

II

I

,,

2.0

: 5.0

Natural period of ground of surface layer, T (s)

Fig. 6.2.7

Apparent propagation velocity of

(3) When design seismic motion III is used, the ground displacement of the surface layer at the buried position of the pipeline

of Uniform Ground The ground strain of surface layer in the case of uniform ground is obtained as follows: (1) When design seismic motion I is used, it is obtained from the following formula:

seismic motion [C] Ground Displacement of Surface Layer The ground displacement of surface layer

E G1

where

=V

E G1 :

is obtained as follows: obtained from the following formula: h

=~. Jr 2

•

E GIO •

1rZ) cos( 2H

Ground strain of surface layer in the case of uniform ground

(1) When design seismic motion I is used, it is

U

snecified for (1) - ...- - " ,.

[D] Ground Strain of Surface Layer in the Case

I

I

Hrf~ HI'l --- -- -

is directly calculated.

i

I

0.1

i

I

i

200

100

I I !

'rnp ntnpr i'lvmhnli'l - - - - - - - - - - -oJ ----- - - -

T' v· S. (T)' cos ( r I

JrZ )

2H

where U;,: Ground displacement of surface layer (em) v: Seismic zone coefficient, according to Sec-

tion 6.2.3 (2) [G] SVI(T): Response velocity of design seismic

v: Seismic zone coefficient, according to 6.2.3 (2) [G] E GIO :

Ground strain of surface layer of

design seismic motion I in the case of uniform ground, according to Fig. 6.2.8 (2) When design seismic motion II is used, it is obtained from the following formula: E Gl

=V

•

E GIlD •

1rZ) cos ( 2H

motion I (cm/s), according to Fig. 6.2.4 where

E GIlD:

Ground strain of surface

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

(4) Ground Strain ofIrregular Shallow

layer of design seismic motion II in the case of uniform ground, according to Fig.

Ground

6.2.9

In the case of irregular shallow ground, a

.§ "

0; __

ground strain larger than that in the uniform 1.0

,

U)~

,

:::~

.~] " r"

:::o

,.~

- '" -

rJJ '"

::

(0.1.0.102

-=

~

g

.:l .-

o

~

o:E

\Qj.o:~i

L..-ri !'N..,! I

,

,

0.0 2

,

,

I

,

i

iii

!

i

i

i I i ! ! !!! , Ii i ! i ! t i i !!

I

! ! i i1

I

j

I i

i ! ! !

! i

i

into account for earthquake-resistant design.

[Description

i

I

i

1

!

i

i

I I

!

i

J

Ground Strain of Irregular

(a) The ground strain caused in irregular shallow ground is calculated by superimposing the ground strain of uniform ground on the ground strain caused by inclined seismic

I

! ! ! ! ! 11 _'----'-....o.........I I I 0.01.-1-1---'---'---'---'---'-............._ 0.1 0.2 0.5 1.0 2.0 5.0

base rock.

Natural period of ground of surface layer, T (5)

Fig. 6.2.8

1J

Shallow Ground

,,

, !

!

ground can happen, and this must be taken

, !

I

i

!

I

,

, ,

i ii ,ii !i ! !~ ! i i ..... I i i i i i Ii , I (2..S.1i.16j I I ! i ! !! l i i

i

0.05

-=~

rJJ _.5

, I l1

OJ

'00

i

nVCQr-°.

~~

,

i

'. , ! lA

~

~ ,~ -g ~ c 0.1

,, , ,,

!

0.5 0

:l 0

~ E » .... 0.20

.~

January, 2000

Ground strain of surface layer

where

of design seismic motion I in the case of

cG2

=.J

g2 G1

cG3

=n

-0.3 (%)

E

+ c 2G3

G1: Ground strain of uniform ground,

according to 6.2.3 (3) [D] "Ground strain

uniform ground

of surface layer in the case of uniform , .~"'g 0.50 0;

Restriction of Soil

--.. --.. --.. --.. -+ --..

I

Pipe

I

Fig. 6.3.2 : Ground Displacement Input for Ground Conditions I, II, and IDa

~

O"v

__-

. . AE

~----=-_

1

Fig. 6.3.3: Bilinear Elastoplastic Model of Steel Material

Ground Displacement

--v> c.... ~

Ground Restraint Force --..-+-+-+--..-+

~

'-:

~~r--;:;U-----:=-----r-------------~

.3

:r.;

I >:?i

Fig. 6.3.4 : Ground Displacement Input on Piping Fixed at One End in Ground Condition IDb

~~-------------r""

-~~-.--.~--- ..-.... -..

--_ ....... - .......... -_ ..... - .. --- .... -_., I,

.............................................. .. ..'I

Fig. 6.3.5: Ground Displacement Input in Transverse Direction Under Ground Condition I, II, or ID a

6-21

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN

January, 2000

1 : Moment of inertia of cross-section (mm 4)

the plastic limit and the reduced elastic

k : Reduced coefficient of subgrade reaction

modulus (E) applied when calculating the

(Nzmm")

material's ability to absorb ground displace-

ii) Piping with localized drop in strength

ment, which depends upon the material, are

against bending moment (steel pipe with

shown below. 1) Steel pipe: Allowable strain .... £0=3 [%]

screwed joint) Llv=

.fie

4

Jr

EI

/

~4EI --M kD

Reduced elastic modulus

.... E =3.0X 104 [N/mm2J

0

2) Ductile cast-iron pipe : Allowable strain.... £0=2 [%]

Where, M o : Mome.it atthe location of localized drop in strength (N . mm)

Reduced elastic modulus

E : Elastic modulus (N/mm~

.... E =3.0 X 104 [Nzmm'']

The capability to absorb ground displace-

3) Polyethylene pipe : Allowable strain .... £0=20 [%]

ment when the pipe is fixed to structure under Ground Condition J:Ifu, as in Fig. 6.3.6, is

Reduced elastic modulus

displacement that the pipe can absorb when

.... E =3.0 X Hf [N/mmZ]

displacement concentrates at the border of

When, however, reduced elastic modulus is

the structure and ground.

inapplicable for steel or ductile cast-iron pipe,

(3) Capability of 3-D piping to Absorb

Young's modulus that is within the range of

Ground Displacement (Llu)

elasticity is applied.

The capability of 3-D piping system comprised oflow - pressure service and internal

Steel pipe: 2.1 x lOS [Nzmm']

pipes under Ground Condition I, Il , or ma

Ductile cast-iron pipe: 1.6 X lOS [N'mnr'] Coefficient A used to determine the tan-

is ground displacement that the piping can

gent modulus (AE ) used to calculate elastic-

absorb at the displacement shown in Fig.

ity of steel pipe is founded upon the following:

6.3.7.

--1 =7.1 X 10-3

The absorption capability of a 3-D piping

(2) Allowable Displacement for Mechanical

system buried under Ground Condition Illb

Joints and Expansion Fittings

and fixed at one end to a structure is ground

Standard displacement for expansionjoints

displacement that can be absorbed when the ground displacement shown in Fig. 6.3.4 is

such as mechanical and flexible joints for

applied.

connecting pipes in ways other than welding is the official value specified under JIS or

If no nominal

6.3.6 Allowable Strain and Allowable

other equivalent standards.

Displacement (1) Allowable Strain in Pipe Material (£0)

value is found, it is determined as the displacement that removes airtightness or inflicts serious damage or deformation upon a ma-

and Elastic Modulus (E) The Allowable strain (£0) that is set over

jor part of the joint.

6-22

EARTHQUAKE RESISTANT DESIGN CODES IN JAPAN January, 2000

................. "..f.

.

V

6.v

Fig. 6.3.6 : Ground Displacement Input in Transverse Direction for Piping Fixed at One End Under Ground Condition ill b

Location of Ground Displacement Input

Pwad

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