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Behavior of base isolation buildings under long period earthquake ground motions
Taiki SAITO
Professor, Dr. of Engineering
Toyohashi University of Technology, Japan
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Objectives
• Under a huge earthquake, seismically isolated buildings have a large displacement and a lot of repetitions at isolated layers.
• Mathematical models of isolators under multi‐
cycle motions based on experimental data are implemented in the frame analysis software, “STERA_3D”.
• Earthquake response analyses of existing two seismically isolated buildings are conducted adopting new models. E‐defense shaking table test
under long‐period ground motion
(NHK Special. 2016.11)
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Objectives
• Under a huge earthquake, seismically isolated buildings have a large displacement and a lot of repetitions at isolated layers.
• Mathematical models of isolators under multi‐
cycle motions based on experimental data are implemented in the frame analysis software, “STERA_3D”.
• Earthquake response analyses of existing two seismically isolated buildings are conducted adopting new models. High Damping Rubber Bearing (HDRB)
Reduction of
Equivalent Stiffness
CK
Reduction of
Equivalent Damping
Ch
(by T. Nishimura et.al. 2013)
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High Damping Rubber Bearing (HDRB)
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Reduction factor
0.98
Ch
0.96
CK
0.94
Equivalent Damping
0.92
0.9
Equivalent Stiffness
0.88
(by T. Nishimura et.al. 2013)
0.86
0
5
10
15
20
25
Energy/Volume (N/mm2)
Element Model in STERA_3D
Modified Bilinear Model
30
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Lead Damper (LD)
(kN)
Reduction of strength
(mm)
±200m 30cycles
(by T. Nishimura et.al. 2011, 2012)
Lead Damper (LD)
Reduction factor
(by T. Nishimura et.al. 2011, 2012)
Energy (kNm)
Element Model in STERA_3D
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Elastic Sliding Bearing (ESB)
Reduction of strength
(by S. Minewaki et.al. 2012)
84 cycles
4 sets
84 cycles
Elastic Sliding Bearing (ESB)
Increment of temperature with dissipated energy
Change of friction coefficient
(by S. Minewaki et.al. 2012)
Element Model in STERA_3D
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STERA 3D software http://www.rc.ace.tut.ac.jp/saito/software‐e.html
Developed by T. Saito
3D‐Frame analysis software
Modal analysis
Nonlinear push‐over analysis
Nonlinear earthquake response analysis
RC, SRC, Steel, Masonry
Base isolation devices
Response control devices
Free download
Tutorial video on YouTube
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Objectives
• Under a huge earthquake, seismically isolated buildings have a large displacement and a lot of repetitions at isolated layers.
• Mathematical models of isolators under multi‐
cycle motions based on experimental data are implemented in the frame analysis software, “STERA_3D”.
• Earthquake response analyses of existing two seismically isolated buildings are conducted adopting new models. 13
Target buildings
Building 1
Building 2
City
Toyohashi
Toyohashi
Usage
Condominium
Condominium
Story
18 story
21 story
Height
56m
68m
Structure
RC
MRF + shear wall
RC
MRF
Isolation devices
NRB, ESB
Lead damper
HRB
Oil damper
NRB: Natural Rubber Bearing
ESB: Elastic Sliding Bearing
HRB: High damping Rubber Bearing
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Isolation Floor (Building 1)
Device type No.
NRB
ESB
Lead Damper
Consider reduction of strength under cyclic loading
NRB: Natural Rubber Bearing
ESB: Elastic Sliding Bearing
Lead Damper
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Isolation Floor (Building 2)
HRB
Oil damper
Consider reduction of strength under cyclic loading
HRB: High damping Rubber Bearing
Oil Damper
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STERA_3D Models
Natural Period ⇒2.063sec
Building 1
Natural Period ⇒3.115sec
Building 2
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Earthquake Input
Toyohashi
Nagoya
Simulated earthquake of Nankai‐trough earthquake
MW = 8.7
(by MLIT)
Osaka
gal(cm/s2)
Hamamatsu site (+Standard Deviation)
Hamamatsu
max = 1069 gal
s
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Building 1
Isolation Floor
without reduction
with reduction
Story shear (kN)
12000
8000
4000
12% increment
0
‐4000
‐8000
‐12000
‐60
‐40
‐20
0
20
40
Story displacement (cm)
60
Isolation Devices
LD (Lead Damper)
El Centro NS (50kine)
1200
1200
800
800
400
400
0
0
‐400
‐400
ESB (Elastic Sliding Bearing)
Force (kN)
40
Force (kN)
30
20
5% reduction
‐800
10
0
‐10
‐1200
‐40
‐20
0
20
40
60
‐60
‐40
‐20
0
20
40
15% reduction
‐30
cm
‐1200
‐60
‐20
35% reduction
‐800
60
Ordinary ground motion Long period ground motion
cm
‐40
‐60
‐40
‐20
0
20
40
60
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Building 2
Isolation Floor
without reduction
with reduction
6% increment
Story shear (kN)
10000
5000
0
‐5000
‐10000
‐50
‐25
0
25
50
Story displacement (cm)
Isolation Devices
HDRB (High Damping Rubber Bearing)
Force (kN)
800
OD (Oil Damper)
800
400
400
0
0
‐400
Equivalent damping
‐800
‐50
‐400
9% reduction
5% reduction
Equivalent stiffness cm
‐25
0
25
Force (kN)
50
cm
‐800
‐50
‐25
0
25
50
Conclusions
• Under a huge earthquake, seismically isolated buildings have a large displacement and a lot of repetitions at isolated layers under long period ground motions.
• Strength deterioration of isolation devices under multi‐cycle input motions is considered in the frame analyses of existing buildings.
• By considering strength deterioration, displacement of isolation floor increased 6‐12%.
References
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Takuya Nishimura et al., “Experimental Study on Multi‐cyclic Characteristics of Devices for Seismic Isolation against Long Period Earthquake Motions: Part 7‐ Lead Damper”, AIJ Annual Convention, Architectural Institute of Japan, 2011, pp.667‐668 (in Japanese)
Takuya Nishimura et al., “Study on Multi‐cyclic Modeling of Devices and Response Evaluation for Seismic Isolation against Long Period Earthquake Motions: Part 5‐Modeling of Lead Damper and Seismic Response Analyses”, AIJ Annual Convention, Architectural Institute of Japan, 2012.9, pp.383‐384 (in Japanese)
Takuya Nishimura et al., “Practical Response Evaluation Method for Seismic Isolation System against Long Period Earthquake Motions ‐ Part2‐ High‐Damping Rubber Bearing and Lead Damper”, AIJ Annual Convention, Architectural Institute of Japan, 2013, pp.767‐768 (in Japanese)
Shigeo Minewaki et al., “Study on Multi‐cyclic Modeling of Devices and Response Evaluation for Seismic Isolation against Long Period Earthquake Motions : Part 2‐Modeling of Low Friction Bearing and Viscous Damper”, AIJ Annual Convention, Architectural Institute of Japan, 2012, pp.377‐378 (in Japanese)
Masanori Iiba, Ichiro Nagashima, Hiroshi Hibino, Yasuo Takenaka, Akihiro Kondo, Keiji Nakanishi, Masaaki Saruta, Masashi Yamamoto, Shigeo Minewaki, Tatsuya Azuhata and Namihiko Inoue , “Research on Characteristics of Isolators and Dampers under Multi‐cyclic Earthquake Motions and Effects on Response of Seismically Isolated Buildings”, Published by Building Research Institute, National Research and Development Agency, Japan, 2016.4 (in Japanese)