seismic performance of seismically isolated buildings at the 2011 great east japan earthquake

7/28/2019 Seismic Performance of Seismically Isolated Buildings at the 2011 Great East Japan Earthquake

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12th WORLD CONFERENCE ON SEISMIC ISOLATIONENERGY DISSIPATION AND ACTIVE VIBRATION CONTROL OF STRUCTURES

SEISMIC PERFORMANCE OF SEISMICALLY ISOLATEDBUILDINGS AT THE 2011 GREAT EAST JAPAN EARTHQUAKE

Taiki Saito1, Masanori Iiba1, Koichi Morita1,

Tatsuya Azuhata2 and Namihiko Inoue2

1 Building Research Institute, 1 Tatehara, Tsukuba, Japan

2 National Institute of Land, Infrastructure and Management, 1 Tatehara, Tsukuba, Japan

ABSTRACT

The 2011 earthquake off the Pacific coast of Tohoku, also known as the Great East JapanEarthquake with a magnitude 9.0 (Mw) occurred at 14:46 for the local time on Friday, 11March 2011 in Japan. The earthquake triggered destructive tsunami waves which causedextensive damage to the coastal areas in Tohoku region. On the other hand, building damagedue to earthquake ground motion was limited and buildings designed by the current standardperformed quite well except damage to nonstructural elements such as drop of ceiling panels,falling down of furniture, scatter of contents in shelves. The seismically isolated buildings

showed excellent performance without any severe damage even to nonstructural elements insuperstructure. However, some damage to isolation dampers and expansion joints wereobserved. This paper introduces some cases to explain seismic performance of seismicallyisolated buildings.

1. INTRODUCTION

Reflecting high consciousness of earthquake risks in Miyagi Prefecture and nearby

areas in Tohoku region, Japan, there are many seismically isolated buildings

(hereinafter referred to as SI buildings) have been constructed in those areas. After

the 2011 Great East Japan Earthquake, an investigation team consisted by the

members from NILIM (National Institute of Land, Infrastructure and Management)

and BRI (Building Research Institute) was dispatched to the disaster areas on June

1st and 2nd to examine performance of SI buildings and ask persons in charge of the

buildings about the structural damage. In total, 16 SI buildings in Miyagi Prefecture

and 1 building in Yamagata Prefecture were investigated. Table 1 shows the list of

SI buildings investigated. The list contains the JMA (Japan Meteorological Agency)

seismic intensity (from 0 to 7) near the building. Most buildings in the list suffered

severe ground motion with the intensity more than 6 lower.


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Table 1 List of SI buildings investigated on June 1st and 2nd in 2011

Usage Structural type

and number of

floors

Existence

of scratch

board

Existence

of

earthquak

e record

JMA Seismic

Intensity at the

nearest

observatory

A Office SRC, 9F+B2F 6 lower

B Warehouse S, 1F 6 lower

C Condominium RC, 14F 6 lower

D Condominium RC, 12F 6 lower

E Condominium RC, 15F 6 lower

F Condominium RC, 10F 6 lowerG Hospital RC, 6F 6 lower

H Office RC, 18F +B2F 6 lower

I Hotel RC,12F 6 upper

J Fire Station S, 3F 6 upper

K Hospital RC, 5F 6 upper

L Fire Station RC, 3F 6 lower 6 upper

M Hospital S, 6F 5 upper

N Fire Station RC, 3F 5 upper - 6 lower

O Hospital RC, 4F 6 lower

P Hospital RC, 10F 4

Q Hospital SRC, 4F 5 upper

(SRC: steel reinforced concrete, RC: reinforced concrete, S: steel)

2. PERFORMANCE OF SI BUILDINGS

2.1 SI building (A)

(1) Building information

The SI building (A) is a reinforced concrete office building with 9-story

super-structure and 2-story basement, located in Miyagino-ward in Sendai-city

(Figure 1). The building was retrofitted by using base isolation technique putting

isolation devices on the top of columns in B1F. The floor plan has the 26.4 m 54m rectangular shape and 44 high-damping rubber bearings (HRBs) are installed.

(2) Building performance during earthquake

Observation results are summarized as follows:

a) According to the person in charge of the building, no furniture was turned overand no structural damage was observed.

b) However, some damage was observed at the cover-panels of fire protection andthe expansion joints near the boundary between isolated and non-isolated floors


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(Figure 2). It seems that parts of expansion joints were not well operated due tothe large displacement of SI floor during earthquake.

c) The ground surrounding the building partially subsided around 10 cm.

(a) Overview of the building (b) Sign board to warn about seismic gap

Figure 1 SI building (A) RC office building -

(a) Damage to the panel (b) Damage to the expansion joint

Figure 2 Damage near the boundary between isolated and non-isolated floors

(3) Earthquake motion records

This building has accelerometers at B2F, 1F and 9F (top floor). Also, there is a

scratch board in B1F to record the displacement of isolation floor. Furthermore,there is an accelerometer installed by JMA in the basement of an adjacent building.

The maximum acceleration values of these accelerometers at main shock are listed

in Table 2.

From the trace on the scratch board installed on the SI floor (Figure 3), the

maximum displacement was estimated as around 18 cm at the Main Shock (on

March 11, 2011) and around 10 cm at the aftershock (on April 7, 2011) (Figure 4).


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Table 2 Maximum acceleration values

Location

Direction

Horizontal

X(EW)

[gal]

Horizontal

Y(NS)

[gal]

Vertical Z

[gal]

Basement of

adjacent building317.9 409.9 251.4

B2F (below SI) 250.8 289.0 234.9

1F (above SI) 143.7 120.5 373.7

9F 169.9 141.7 523.9

Figure 3 Scratch board installed on the SI floor

(a) Trace at the Main Shock on 3/11 (b) Trace at the Aftershock on 4/7

Figure 4 Trace of movement of SI floor during earthquake


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2.2 SI building (B)


The SI building (B) is a one-story steel warehouse constructed in 1996, located in

Miyagino-ward in Sendai-city (Figure5). The building height is 30 m. There are 20

HRBs (with diameter 850 mm) and 4 HRBs (with diameter 800 mm) arranged in the

basement with 51.6 m 31.7 m rectangular shape.

Figure 5 SI building (B) Steel warehouse -


Since the building is located near the Sendai-Shiogama bay, Tsunami reached the

building and the SI floor was submerged under water. The building also suffered thedamage to outer walls by the collision of floating debris (Figure 6). Observation

results are summarized as follows:

a) According to the person in charge of the building, other warehouses nearby hadtrouble of cargo-shift or collapse of stuff by the earthquake. On the contrary,

this SI warehouse had no such trouble at all. Since this warehouse is a freezer,

water entered in the freezer space was frozen after the earthquake. Also it took

16 days to remove the water from the SI floor.

b) Tsunami height was estimated around 4.0 m from the trace of water on the wall(Figure 7) and damage situation of nearby buildings (Figure 8). There is no

information about the direction and impact force of Tsunami.

c) The ground was excavated in North-East corner of the building around 1.0 mdepth, probably because of the water flow from the building at the moment ofTsunami (Figure 9).

d) Form visual inspection, there was no harmful scratch or inflation of the rubberof HRB, however, severe rust was observed at the steel plates and bolts (Figure

10).


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Figure 6 Damage due to floating debris Figure 7 Trace of tsunami water

Figure 8 Tsunami damage Figure 9 Excavation of ground

Figure 10 HRB device at the basement


From the trace on the scratch board in the SI floor, the maximum displacement was

estimated as around 21 cm at the Main Shock (Figure 11).


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Figure 11 Trace of movement of SI floor on the scratch board

2.3 SI building (C)


The SI building (C) is a 14-story reinforced concrete building used for

condominium, located in Miyagino-ward in Sendai-city (Figure 12). The building

has the U-shape plan and the corners of the building are separated by expansion

joints. There are 24 NRBs, 8 Lead dampers, and 13 U-shape steel dampers installed

in the SI floor.

(a) Overview of the building (b) Sign board to warn about seismic gapFigure 12 SI building (C) RC condominium building



a) According to the person in charge of the building, no furniture was turned overand no structural damage was observed inside of rooms. However, the damage

to the expansion joint was observed.

b) Drop of the ceramic tiles on outer wall (Figure 13) and shear crack on the wall


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2.4 SI building (L)


The SI building (L) is a 3-story reinforced concrete building used for Fire Station,

located in Tome-city (Figure18). The following SI devices are installed in the

basement with L-shape plan; 61 m in the East-West direction and 58 m in the

North-South direction:

- 34 lead rubber bearings (LRB) (6 with diameter 650 mm and 28 with diameter700 mm)

- 11 elastic-sliding bearings (6 with diameter 500 mm and 5 with diameter 600mm)

- 8 U-shape steel dampers-

(a) Overview of the building (b) Sign board to warn about seismic gapFigure 18 SI building (L) RC Fire Station building



a) According to the person in charge of the building, no furniture was turned overand no structural damage was observed.

b) Because of the movement of SI floor during earthquake, the bolts of steeldampers became loose and the paint on the dampers was peeled off widely. Also

a large amount of residual deformation of steel was remained (Figure 19).


From the scratch board in the SI floor, the maximum displacement was estimated asaround 40 cm in the North direction (Figure 20). This displacement was also

confirmed from the trace of scratch found at the expansion joint outside of the

building.


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(a) Peeling off of paint (2) Deformation of steel

Figure 19 Deformation of U-shape steel damper

(a) 40cm in the North direction (b) 15cm in East and 22cm in West

Figure 20 Trace of movement of SI floor on the scratch board

2.5 SI building (M)


The SI building (M) is a 6 story steel building with one story basement used for

hospital, located in Ishinomaki-city (Figure 21). Lower part of the building up to

second story has the 100 m 100 m square plan and higher part has 100 m 25 m

plan. The following SI devices are installed in the basement:- 6 natural rubber bearings (NRB) with diameter 1000 mm- 16 laminated rubber with diameter 1000 mm with U shape steel dampers- 16 U shape steel dampers- 74 elastic sliding dampers (30 with 400 mm diameter, 25 with 600 mm

diameter, 11 with 800 mm diameter and 8 with 900 mm diameter)



E W

N

S


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a) According to the person in charge of the building, up-down shaking happenedtogether with horizontal shaking during earthquake. On the 6

thfloor, contents

inside of the rooms such as refrigerators and shelves are moved or turned over,

and the fire protection steel door moved to open and hit against the ceiling by

vertical shaking causing the damage to the lamp covers. In all floors, PC

monitors turned over.

b) In the penthouse, anti-vibration rubber of a power generator was moved and thebottom part of a water tank was broken.

c) Because of the movement of SI floor during earthquake, the bolts of the steeldampers became loose and the paint on the dampers was peeled off (Figure 22).

d) The ground surrounding the building subsided around 20 cm.

(a) Overview of the building (b) Sign board to warn about seismic gapFigure 21 SI building (M) Steel hospital building


From the trace on the scratch board in the SI floor, the maximum displacement was

estimated as around 25 cm in the West direction (Figure 23). This displacement was

also confirmed from the trace of movement of the sliding bearing (Figure 24).

Figure 22 Peeling off of paint and loose of the bolts of U-shape steel dampers


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seismic performance of seismically isolated buildings at the 2011 great east japan earthquake

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