seismic hazard and state of the art seismic design practice in … 0... · 2019. 9. 4. · seismic...
TRANSCRIPT
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Current Seismic Design Practice in Korea and Engineering Implications of Recent M5.8 Gyeong-Ju Earthquake
4 6 8-0.5
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0.5
4 6 8 10-0.5
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0.5
6 8 10 12-0.5
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Cheol-Ho LeeDept. of Arch. and Arch. Engrg., Seoul National University
Introduction to Earthquake Engineering and Dynamics of Building Structures_ 1
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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I. Introduction
II. Ground Shaking for Seismic Design of Building Structures in Korea
III. Brief Summary of Current Seismic Design Practice in Korea
IV. Preliminary Engineering Analysis of 2016 M 5.8 Gyeong-JuEarthquake
VI. Summary and Conclusions
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
Outline of Presentation
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Kobe EQ, Japan (1995.1.17)
* M = 6.9
* Casualties 6,000
* Economic loss
200 trillion USD
Ji Ji EQ, Taiwan(1999.9.21)
* M = 7.7,
* Casualties 2415
* Taiwan’s economic basis
severely shaken
Northridge EQ, Calif.
(1994.1.17)
* M = 6.7
* Casualties 57
* Economic loss 22 trillion USD
“Some recent strong EQ events and Losses”
Sichuan EQ, China (2008.5.12)
* M= 8.0
* Casualties and loss 70,000
Christ Church, NZ
(2011.2.22)
* M = 6.3
* Shallow epicenter (5km)
East Japan Great EQ (2011.3.11)
* M = 9.0
* Casualties 15, 000
* Catastrophic tsunami
* Hukushima nuclear power plant
explosion due to tsunami
* Strongest since 1900 in Japan
Haiti EQ (2010.1.12)
* M= 7.0
* Casualties 100,000
* More than 250,000
dwellings damaged
Nepal EQ(2015.4.25)
* M= 7.8
* Casualties and injuries 210,000
* Economic loss
50% Nepal’s GDP
Tainan EQ, Taiwan (2016.2.6)
* M= 6.4
* Casualties 117
Kumamoto EQ (2016.4.15)
* M= 7.0
* Casualties 49
* Shallow epicenter (10km)
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
I. Introduction
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Date 2008.6.14 2008.5.12
Magnitude
(16 times difference in energy)
7.2 8.0
Focal depth (km) 10 19
Casualties/losses/injuries 10/12/ 231 69,180/17,406/
374,431
Notes:
* Drastic difference in terms of casualties/losses/injuries
* Seismic provisions often exist in seismically fragile
countries (apparently very stringent)
* Effective seismic design down to the grass root level is
critically important
Seismic hazard (or activity)
Casualties/losses/injuries
Comparison of Iwate (Japan) and Sichuan (China) EQs in 2008
“The critical importance of implementing seismic design effectively down to the grass root level”
Average expectation
Seismically fragile
countries
Seismically
well-prepared
countries
“Our hopeful positioning should be here”
“The core of seismic resilience: effective implementation of seismic design and the emergency management and recovery actions”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
“The First Defense Line”
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Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
II. Ground Shaking for Seismic Design of Building Structures in Korea
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“Infrequent but large earthquakes can occur at the faults within the plate (intraplate earthquakes); for example, Tang-San M 7.8 EQ in 1976, China”
• Set to account for “infrequent but large earthquakes” probable in low-to-moderate intraplate EQ regions (like Korea and eastern US…)
• Infrequent but large EQs: so called MCEs (max. considered earthquakes) for building structures with 2400-year return period
• We don’t care about more stronger shaking beyond 2400-year EQ (or we don’t care about geological scale EQs).
• DBE (Design Basis Earthquake) in Korea• = (2/3)*MCE • = approx. 1000 year EQ
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
Design Basis Earthquake (DBE) in Korea
Intraplate EQs
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Possible Standard Seismic Performance Levels
DBE MCE
BSO (Basic Safety Objective) for general bldg. structures (Importance Class= 2) implied in 2016 KBC
(Korean Building Code)
(70yr EQ) (200yr EQ) (1000yr EQ)(2400yr EQ)
OperationalImmediate Occupancy Collapse PreventionLife Safety
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
Significant structural and non-structural damage permitted, able to resist after-shocks, generally costly repair needed to re-occupy
Lateral stiffness and strength almost lost and barely supporting gravity load, very dangerous for after-shocks
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Brief Review of Seismic Hazards in Korea
• Instrumental EQ data collected since late 1970’s_ now fairly dense strong motion instrumentation arrays managed by the government agencies
• A fairly long historical EQ data including 600-year good records in Cho-Sun Dynasty
• Engineering quantification of such historical EQ data: very important especially for low-to-mid seismicity regions like Korea because of lack of more reliable instrumental EQ data
• Huge uncertainties inevitable to quantification of historical EQ data_ the importance of engineering seismic design to overcome such uncertainties involved
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Seismic Hazard from Historical Earthquakes_ dominant
Historical earthquake data in Korea
Period Total no. of quakes No. of quakes with MMI> VII
Total
0
0
*
1 (2 / 3) [Gutenberg-Richiter 1956]
log( ) 0.5 [Gutenberg-Richiter 1956]
log( ) 0.014 0.3 [Trifunac-Brady 1975]
MMI M
M MMI
MMI PGA
PGA MMI
PGA MMI
*
(1/3)
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
• Korean peninsular seismically active during the 15th
~18th century; seismic loading in KBC governed bythe historical earthquakes
• Max. historical MMI (Modified Mercalli Intensity)~ VIII~IX
• Empirically converted M~ 6.2
• Thirteen (13) M6.2 quakes in our history
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“MMI Rating= VIII”
An Example of MMI Rating from a Historical Record (1518)
• Different rating possible among different evaluators • Tends to be conservative because local extreme damage is extrapolated to wider areas (Bolt 1978)
“Thundering sound heard; people not able to stand up well ; castle walls fell down…”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Large Events AD 27 and 89 Events (Baek Jae Dynasty, 2000 years ago)
Note that no epicenter information is reported at all
“How to locate the epicenter needed for seismic hazard analysis?”
“Nominally assign the epicenter to the ancient capital location when no epicenter information is reported_ one of the intensity rating rules often used”
Then, where is the location of the ancient capital?; NamhanSansung or Mongchon Tosung or else where?
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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KMA official historical EQ report (2012)(KMA= Korea Meteorological Agency)
Rated MMI (not JMA scale)-- VIII
Rated MMI (not JMA scale)-- VIII~IX
“M~ 6.2”Based on very empirical MMI0-M conversion
Construction quality 2000 years ago: worse or better than the 1930’s ?
Recall: MMI rating is based on the building construction quality of 1930’s US west coast practice
Assigned to Mongchon Tosung area; surely, this would artificially increase the seismic hazard of downtown Seoul
“Based on the very brief damage description”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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0
0
*
1 (2 / 3) [Gutenberg-Richiter 1956]
log( ) 0.5 [Gutenberg-Richiter 1956]
log( ) 0.014 0.3 [Trifunac-Brady 1975]
MMI M
M MMI
MMI PGA
PGA MMI
PGA MMI
*
(1/3)
Another huge uncertainties in empirical conversion formula among MMI-M-PGA
widely used
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
MMI (epicenter) M
MMI PGA
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Recorded maximum accelerations vs.
reported intensities for the period
1933-1943
Recorded maximum accelerations Vs. reported intensities for the period
1933-1954
“Log scale”
Recorded PGA vs.
Reported MMI
(Ambraseys 1974)
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
MMI PGA Conversion
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Recorded maximum accelerations vs.
reported intensities for the period
1933-1973
Gutenberg-Richter 1956
“Log scale”
“Log scale”
“Already 10 times different!”
What if for 1933-2016?
Recorded PGA vs. Reported
MMI (Ambraseys 1974) Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
Recorded PGA vs.
Reported MMI
(Ambraseys 1974)
MMI PGA Conversion
Accept over- or under-estimation of historical seismic hazards
All these uncertainties should be absorbed in seismic design
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Hazard Map in KBC (NEMA 2013)
2400 year return period
• Incorporates the historical seismic hazards and prepared through the consensus of the domestic representative seismologists, and should be respected and conformed by the law.
• The EPA of 2400-year EQ (MCE, for general building structures) thus obtained: about 0.22g
• The DBE (design basis earthquake) is defined in KBC (Korean Building Code) as (2/3) of MCE in order to take into account of the infrequent but large EQs in low to moderate seismicity of Korea
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
High uncertainties involved should be admitted
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Comparison with Japanese Design Spectrum (in terms of PSV spectrum_ soft rock site)
Japanese traditional “dual spectrum approach” highly evaluated personally
Japanese 500yr EQ (for ultimate strength)
Japanese 50yr EQ (for serviceability)
Korea:13,000yr EQ5,000yr EQ1500yr EQ
• DBE in KBC slightly stronger than Japanese serviceability EQ by about 10% or more
• Japan is seismically real strong DBE= 1000yr EQ
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“EQ ground motion: a stochastic (random) process: high variability in amplitude, strong motion duration and frequency contents”
No same EQs occur even at the same site
Response spectra from three EQs at the same site (Imperial valley station, southern Calif.)
• Factors on the details of EQ ground motions:
1. local site conditions; only available usually
2. hypocentral distance,
3. source mechanism,
4. wave transmission path geology, etc.
All from southern California
Base shear
Structural period
Usually unknown
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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III. Brief Summary of Current Seismic Design Practice in Korea
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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“Avoid socio-economically unacceptable elastic design,,and permit damage strategically; resist strong EQswith cyclic ductility Engineering Compromise inmodern seismic design
Strength demand for no damage or elastic response
Actual strength supply= 1/8~1/1.5
저층건물
고층건물
지진하중/ 건물자중
“Averaging, smoothing_ highly variable in fact
“Socio-Economic Reasons”
Base shear ratio
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
• Possibility of strong EQs, whether DBE or MCE, very low for a nominal useful life of buildings (say 50 years) but could be catastrophic once they occur
Adopted the R-factor approach similar to the US practice but in modified form with considering our design and construction practice
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• One thing sure as a result of the reduction: strong EQs would drive building structures beyond elastic range, or would demand seismic energy dissipation
• Control the seismic behavior reliably only through design, not by analysis which has to base very uncertain input
• The capacity design concept has to be resorted to which ensures stable seismic energy dissipation irrespective of the details of EQ ground motions usually known to us
• Now well established after the 1994 Northridge EQ and incorporated in KBC seismic provisions since 2009.
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
“Control yield mechanism by design, not by analysis, and provide ductile details at the predetermined locations”
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Brief History of Seismic Design in Korea
• Enacted for the buildings more than six-story high since 1988 because of the 1978 Hong-Sung EQ that caused some un-negligible damage and now about to enforce seismic design for all new construction
• Large-size cyclic testing started since late 1990’s, meaning researchers in Korea started to appreciate the importance of experimental evidence for reliable seismic design
• Now large-size testing active for academic and commercial purposes
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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The early full-scale testing setup by Lee, CH and Park, JW (1997)
Lee et al. (2001)
Cyclic testing conducted for some proprietary connection and its field
application (Lee and Park et al. 2011)
-400
0
400
-300 0 300
Beam tip displacement (mm)
Beam
tip
forc
e (
kN
)
aa
a
Test
Analysis
• Nice large-size testing labs in some universities and public/private institutes
• Even PBSD is tried for some important building projects or to circumvent prescriptive R factor approach
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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An example of nonlinear dynamic analysis input for seismic performance evaluation
“De-aggregation of seismic hazard at the site may be used to select candidate input motions”
An 80-story high-rise building located at soil condition SD
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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KBC design spectrum
“Our seismic design force level is not low at all in fact when the soil and/or importance factor is involved; especially for long-period (tall building) structures”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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IV. Preliminary Engineering Analysis of 2016/9/12 M5.8 Gyeong-Ju Earthquake
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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•Gyeong-Ju Quake M= 5.2/5.8, 09/12/2016
The first (pre-) shock: ML 5.2, 19:44The main shock: ML 5.8, 20:32Focal depth: 13km (relatively deep)
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
The 912 Gyeong-Ju EQ, strongest ever recoded instrumentally, has strongly shaken the south-eastern part of Korean peninsular and drove us into panic
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Magnitude reported
11.8 1.5
16.05 1.5
0 0
log( ) 11.8 1.5 ; 10 ( ) (1)
(2 / 3) log( ) 10.7; ( ) 10 ( ) (2)
L
W
M
L
M
W
E M E ergs
M M M seismic moment dyne
The main shock: ML 5.8Focal depth: 13km
The main shock: Mw 5.36Focal depth: 15km
(per Prof. YH Kim, SNU)
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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22 km
8 km5.9 km
Three accel. records near the epicenter available
“SB (MKL, DKJ) or SC (USN) soil condition speculated”
SC (USN)
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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USN-NS
Processed Time Histories and Spectra(prepared by CH Lee, JH Park, SY Kim and TJ Kim)
But strong motion duration (SMD) is very short, just about 3 seconds; or damage potential is weak.
Apparent PGA is as high as 0.39g
Nyquist freq.= 25 Hz
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
Ground motion maxima ratio (stiff soil site)PGA: PGV: PGD= 1g: 1.22 m/sec: 0.91m (Calif. EQ)
PGA: PGV: PGD=1g: 0.16 m/sec: 0.015 m (GJ USN EQ)
“1/8 and 1/60”
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4 6 8-0.5
0
0.5
4 6 8 10-0.5
0
0.5
6 8 10 12-0.5
0
0.5
Nyquist freq.= 25 Hz
MKL USN
DKJ
PGA= 0.39gPGA= 0.26g
PGA= 0.09g
Arias
Intensity
(m/s)
PGA
(g)
0.18 0.257
0.70 0.351
0.05 0.092
MKLUSNDKJ
“Apparent PGA is a weak damage indicator”
“EPGA~ 0.18g (진앙지 부근)”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
“Amplitude, strong motion duration and frequency contents should considered all together”
-
10-1
100
101
102
10-4
10-3
10-2
10-1
100
Frequency (Hz)
Magnit
ude (
g2-H
z)
Kyung-Ju 2016-MKL.HGN (raw)
Kyung-Ju 2016-MKL.HGN (filtered)
Kyung-Ju 2016-USN.HGN (raw)
Kyung-Ju 2016-USN.HGN (filtered)
Kyung-Ju 2016-DKJ.HGN (raw)
Kyung-Ju 2016-DKJ.HGN (filtered)
Fourier Amplitude Spectrum
“Energy was concentrated in high frequency band over 10 Hz; these high frequencies can not excite multi-story building structures effectively”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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MKL-EW
33
Design Sa = 0.37g at 0.3 sec for site class S_B
Design Sa = 0.15g at 1.0 sec for site class S_B
Pseudo-acceleration Response Spectrum
“Damage of short-period structures (1~3 story buildings) with poor or brittle construction highly probable as really observed”
“Damage of building structures of average construction with periods longer than 0.3~0.4 sec. difficult to occur”
Comparison of elastic spectral acceleration caused by 912 Geong-JuEQ with KBC (SB) spectrum
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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EPGA (effective peak ground accel.)
“Apparent PGA by high frequency pulse not damaging”
“Repetitive (effective) PGA in SMD more damaging and meaningful”
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0 0.5 1 1.5 2 2.5 30
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8Spectra in a single direction
KBC 2016 SB
MKL E-W
MKL N-S
USN E-W
USN N-S
DKJ E-W
DKJ N-S
MKL E-W MKL N-S DKJ E-W DKJ N-S
EPGA (g) 0.1706 (S_B) 0.184 (S_B) 0.0436(S_B) 0.0993 (S_B)
4 6 8-0.5
0
0.5
4 6 8 10-0.5
0
0.5
6 8 10 12-0.5
0
0.5(per KBC 2016)
EPGA (effective peak ground accel.)
MKL(near epicenter)
DKJ
PGA= 0.26g
PGA= 0.09g“EPGA~ 0.18g (near epicenter)”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
“1000yr EPGA~ 0.15g”
PGA= 0.26g -- EPGA= 0.18g (70%)MKL(near epicenter)
교수님,
적분 시 수치를 다르게 집어 넣어서 틀린 값이 나왔었습니다.아래 값이 ePGA입니다.
MKL.KG.BGE = 0.1533gMKL.KG.BGN = 0.1639gUSN.KS.BGE = 0.2925gUSN.KS.BGN = 0.1918gDKJ.KG.BGE = 0.0386gDKJ.KG.BGN = 0.0839g
그전 값에 비해 10%가량 낮은데, 전에 지반조건을 이리저리 다르게하다 보니 다소 오차가 있었던 것같습니다.
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Comparison with 1940 El Centro strong motion record
0 10 20 30 40-0.4
-0.2
0
0.2
0.4
Time, sec
Accele
rati
on
, g
El Centro 1940 S00E
Kyung-Ju 2016 USN.HGN
Comparison of two time histories; El Centro
1940 S00E and Kyung-Ju 2016 USN
El Centro 1940 S00E record_ one of the representative strong motion records most frequently used among researchers worldwide
M Epicentraldistance
(km)Comp
PGA (g)
PGV (m/s)
PGD (m) Site
Imperial Valley 5/18/1940, El Centro site 6.9 11.5 S00E 0.348 0.335 0.109 Alluvium
30 times stronger than Gyoeng-Ju EQ
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• Demands more for very stiff and brittle structures (with ductility capacity less than 2) • Strength supply required by Geong-Ju USN is much lower for the velocity and
displacement regions
10-1
100
101
0
0.2
0.4
0.6
0.8
1
Period Tn , sec
f y/w
=A
y/g
El Centro 1940 S00E
Kyung-Ju 2016 USN.HGN
=1
8
4
2
1.5
8
4
2
1.5
1
Constant Ductility Spectrum
Yield base shear (divided by building weight)
0.2 sec
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
-
0 5 10 15 20 25 30
-100
-75
-50
-25
0
25
50
75
100
Time, sec
No
rmali
zed
dis
pla
cem
en
t u
/uy
El Centro 1940 S00E
Kyung-Ju 2016 USN.HGN
Yield base shear ratio
fy= 5% W (bldg. weight)
When building period is as short as 0.1sec
Ductility demand ~ 90
Ductility demand~ 12
0 5 10 15 20 25 30-60
-40
-20
0
20
40
60
Time, sec
Norm
ali
zed d
ispla
cem
ent
u/u
y
El Centro 1940 S00E
Kyung-Ju 2016 USN.HGN
Ductility demand~ 7
Ductility demand ~ 60
Yield base shear ratio
fy= 10% W (bldg. weight)
-
0 5 10 15 20 25 30
-4
-2
0
2
4
Time, sec
No
rmali
zed
dis
pla
cem
en
t u
/uy
El Centro 1940 S00E
Kyung-Ju 2016 USN.HGN
fy= 5% W (bldg. weight)
When building period is 1.0 sec (say, 10-story bldg.)
DD~ 4
“Elastic”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
-4 -2 0 2 4
-2
-1
0
1
2
Normalized displacement u/uy
No
rmali
zed
rest
ori
ng
fo
rce
f S/f
y
El Centro 1940 S00E
Kyung-Ju 2016 USN.HGN
“Elastic”
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Failures reported
VI StrongFelt by all, many frightened. Some heavy furniture moved; a few insta
nces of fallen plaster. Damage slight.
VII Very strongDamage negligible in buildings of good design and construction; slig
ht to moderate in well-built ordinary structures; considerable damage
in poorly built or badly designed structures; some chimneys broken.
Intensity Shaking Description/Damage
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
• Most of average buildings successfully resisted the EQ without any significant structural damage and casualties
• Most of failures occurred in low-rise non-engineered/poor construction and corresponded to the MMI V~VII damage
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Show window shattered Typical corner cracking at
opening
Failure in an already poor (non-engineered) construction
Unreinforced block wall fallen down
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Damage observed in a 3-story RC Building (Ulju, Ulsan)_ ceiling and brick wall failure
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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• One of the well-known seismic failure modes observed in a Buddhist temple: so called “short-column” shear failure
• Never imagined to see….in Korea
“Virtually devoid of hoops”
The most impressive failure mode_ “short-column” shear failure
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
“Two-way shear test”
-
• Similar short-column shear damage in the piloti column
• Found on September 30 (2 weeks later)• More close investigation needed for
possible structural damage unrevealed yet
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Some observations and probable reasons for relatively less seismic damage of building structures in the 912 Gyeong-Ju EQ
1. Apparent magnitude of PGA is a weak damage indicator2. The epicenter was relatively deep (approx. 13~15 km)3. Surface soil layer is generally shallow (about 20 m-deep) and the bedrock motion is
not much amplified4. Energy concentrated in high frequency band over 10 Hz; these high frequency can
not attack building structures with long periods effectively 5. The strong motion duration was very short; 6. Because of the reasons above, damage was mostly restricted to short-period
structures (1~3 story buildings) with non-engineered/ poor or brittle construction.
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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M 6.2 EQ near Pyung-Yang in 1952 or “during Korean War”
• Known during the technical meeting between south and north Korean seismologists for the KEDO program (supporting program for north Korea’s NPP) once promoted but now halted
• Seismic design is one of the top priority issues in any nuclear power plant construction
• The information following is based on the presentation made by Drs. TS Kang and MS Jeon (former KIGAM researchers) at the EESK symposium last year: “Seismological evaluation of major earthquakes in Korean peninsular and seismic safety of building and civil structures”, Feb. 23, 2016
• The occurrence of this major EQ was not well recognized probably due to the turmoil during the war, but… < 1952 평양 인근 지진의 진앙 (USGS) >Epicenter location
reported by USGS
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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• Date and Time
• 1952-03-19 09:04:18 (UTC)
• 1952-03-19 18:04:18 (Local Time)
• Epicenter (USGS)
• 38.872N, 125.834E
• Nearby cities
• Chung-HWA: 3 km
• Pyung-Yang: 19 km
• Sariwon: 41 km
• Focal depth : 35.0 km (estimate; appear to be rather deep, less damaging)
• Magnitude reported by various researchers based on measured records: M= 6.2~6.5
RUSSIA_ Rustanovich et al.(1963): M=6.3
CHINA_中国国家地震局科技情報中心(1987) Ms=6.5
Yuche Li (2001): M=6.5
JAPAN_Ishikawa et al.(2008): Md=6.5
USA_ USGS Mw 6.3
KOREA_ Kang (2011) Mw 6.2
(Ishikawa et al., 2008)
1952
19781978
1936
2004
1980
20071996
1982
SOURCE: the presentation made by Drs. TS Kang and MS Jeon at the EESK symposium last year: “Seismological evaluation of major earthquakes in Korean peninsular and seismic safety of building and civil structures”, Feb. 23, 2016
“100 or 1000 times more meaningful than historical EQs since this is instrumental”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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V. Summary and Conclusions
• i) The very high uncertainties associated with modern engineering seismology should be and can be absorbed through the engineering means like the capacity design principle.
• ii) The capacity design method, underlying domestic design codes since KBC2009, should be faithfully implemented down to the grass level (or from design to construction) through the participation of structural engineers well equipped with seismic deign.
• iii) The 912 Gyeong-Ju EQ has effectively invalidated the misbelief among many people, even structural engineers, that only weak EQs around M~5 would occur in Korea.
• iv) However, the overall damage caused by the Gyeong-Ju EQ was minor compared to the magnitude because the strong motion duration was short and the seismic energy was mainly concentrated in the high frequency range, thus causing seismic damage mostly in low rise and/or poor building construction.
• v) PGV and PGD observed in the 912 Gyeong-Ju EQ were much lower, compared to the ground motion maxima ratio in California, thus causing much less spectral demand in the velocity and displacement regions
• vi) It is speculated that the 912 Gyeong-Ju EQ records may represent typical characteristics of EQs in Korean peninsular; relatively short strong motion duration dominated by high-frequencies. However ductility demand can be substantial for short-period structures even with a yield base shear ratio as high as 10% building weight
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vii) Further extensive studies from the perspective of both seismic design and engineering
seismology are warranted to identify the damage potential factors inherent in the strong EQs
expected to strike our building structures.
viii) The increase of the seismic force level, in spite of 1952 Pyung-Yang and 2016 Kyung-Ju
EQs, is not needed. Seismic capacity against strong EQs lies in well-implemented seismic
design, or ductility design rather than strength or stiffness design.
ix) Proper and cost-effective measures should be taken to salvage poorly constructed and inherently brittle low-rise buildings. Nonstructural damage which may cause injuries as well as malfunctioning due to typical larger amplitude of motion of the upper part of high-rise buildings should be properly addressed.
x) The 912 Gyeong-Ju EQ should be considered as the Early Warning EQ for Korea. All the
lessons learned from this EQ should be reflected in future actions, technological and
institutional, to establish seismically resilient Korea in a socio-economically acceptable way.
xi) We do not live in southern California nor in Japan. Over-threatening of seismic hazard
without clear physical/scientific evidences can lead to the abuse of our valuable national
resources.
END OF PRESENTATION
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Analysis of Structural Damage Observed in the 2016 Gyeongju and 2017 Pohang Earthquakes in Korea
Introduction to Earthquake Engineering and Dynamics of Building Structures_ 2
Cheol-Ho LeeDept. of Arch. and Arch. Engrg., Seoul National University
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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I. Introduction
II. Brief review of 2016 Gyeongju EQ
III. Comparative analysis of damage potentials
IV. Some notes on the 2017 Pohang EQ damage
V. Conclusions
Outline
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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I. Introduction
• The 2016 Gyongju EQ M5.8_ the first modern damaging instrumental EQ in seismic history of Korea
• Effectively invalidated our misbelief
• The epicenter_ the impact widespread and profound
• Thought to be a rare event
• A big surprise_ M5.4 Pohang EQ occurred just one year later; much more damaging in spite of its lower magnitude M5.4.
Primary objective_ provide probable explanations and reasons for the more severe damage observed in the 2017 Pohang EQ.
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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“Provided strong ground motion records for the first time and enabled meaningful engineering analysis to be started in Korea”
II. Brief review of 2016 Gyeongju EQ damage and its engineering impact
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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The most severe damage reported
Damage in non-structural elements prevalent
School building damage reported_ minor and just several cases
Damage observed
The overall damage caused by the 2016 Gyeongju earthquake_ minor,mostly nonstructural
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Probable reasons for the relatively minor damage in the 2016 M5.8 Gyeongiu EQ:
The strong motion duration was very short.
Seismic energy was concentrated in the high frequency band over 10 Hz; the surface soil layer in Korea is generally shallow (about 20 m-deep or less) and the bedrock motion is not much amplified
Thus, damage was mostly restricted to low-rise (1 or 2 story high) non-engineered and poor construction.
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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The impact of the 2016 Gyeong-ju EQ
• The 2016 Gyeongju EQ effectively invalidated the misbelief among many peoplethat only weak EQs around M5 would occur in Korea.
• This earthquake has made Korean government and people admit that earthquake isa real and effective threat.
• The Earthquake Disaster Mitigation Task Committee formed on Sep. 22, 2016 by theMinistry of Public Safety and Security and the experts from academia andprofessional societies: proposed short-term and long-term actions and measures tobe taken
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Recommended major measures and actions
1. Overall re-evaluation of governmental EQ emergency management plans2. Enforcing seismic design to all the new housing and small-sized buildings 3. Modernization of seismic codes for some facilities in civil and infra side 4. Improvements of strong motion instrumentation program and early warning system 5. Earthquake response manuals for various purposes and sectors 6. Seismic retrofit for public and private buildings accelerated/encouraged 7. Long-term large-scale investigation of faults and construction of active fault map8. Re-checking seismic safety of NPPs, major industrial facilities and historical buildings 9. Earthquake-preparedness education and drills for the public 10. EQ-related man power and budgets in the government much expanded
(about 100 expects newly hired by the government) 11. Establishment of earthquake refuge facility and rescue system 12. Laws and regulations revision if needed for enhancing national seismic safety, etc.
The major beneficiaries from the Gyeong-ju EQ: the seismologists group; four-stage 20-year project to construct comprehensive fault map under way.
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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III. Comparative analysis of damage potentials
Source: KIGAM (Korea Institute of Geoscience and Mineral)
ML5.8 (MW 5.4), Focal depth: 13km ML5.4 (MW 5.4), Focal depth: 4km
2016 Gyeongju EQ 2017 Pohang EQ
Real Time Shake Map (PGA)
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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: Piloti building damage observed in the 2017 Pohang earthquake
Building damage much more severe in the Pohang EQ
: The most serious damage reported in the 2016 Gyeongju earthquake
Damage in the Phang EQ
• Direct damage cost_ 50 million USD (5 times GJ EQ)
• Recovery cost_ 150 million USD (10 times GJ EQ)
• No. of completely-damaged housing_ 331
• No. of Half-damaged housing_ 228• No. of slightly-damaged housing_
25,362
• Public facility damage_ 27 million USD
• School building damage_ 13 million USD
• Seaport damage_ 2.4 million USD• Cultural heritage damage_ 1.4
million USD
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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ML 5.8 (MW 5.4)
Focal depth: 13km
ML 5.4 (MW 5.4)
Focal depth: 4km
Gyeongju Pohang
Focal Depth_ shallow vs. deep
Shallow EQs produce structurally destructive surface waves more.
“One probable explanation for the more severe damage in Pohang EQ”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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SD soil site
Pohang EQ
Gyeongju EQ
Rock-site recording stations (KIGAM/KMA, dense)
Free-field recording stations (Min. of Public Administration and Security, sparse/difficult to access)
SC soil site
USN
PHA2
Rock
Soil
6 Records Measured Yellow box
White box
* Gyeongju USN and Pohang PHA2 records measured on Sc and SD soil site at about 8km epi-central distance_ the most strong and meaningful for engineering analysis
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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20
d2
T
AI a t t
g
Summary of ground motion characteristics from the 2017 Pohang and 2016 Gyeongju earthquakes
Earthquake 2017 Pohang 2016 GyeongjuStation CHS HAK DKJ PHA2 MKL USN
Epi-distance, km 25 23 28 9 5.9 8Soil condition SB SB SB SD SB SCComponent EW NS EW NS EW NS EW NS HGE HGN
PGA, g 0.018 0.014 0.023 0.035 0.017 0.036 0.131 0.189 0.285 0.351
EPGA, g 0.010 0.012 0.020 0.028 0.006 0.018 0.073 0.098 0.151 0.189
EPGA/PGA 0.547 0.864 0.871 0.807 0.371 0.498 0.555 0.517 0.530 0.538
IA, m/s 0.002 0.002 0.005 0.007 0.002 0.004 0.080 0.158 0.225 0.675
D5-75, sec 6.000 3.650 3.600 1.500 5.750 1.600 0.900 1.400 0.760 1.890
D5-95, sec 16.150 15.800 11.700 8.550 20.150 9.900 2.950 2.450 1.800 10.130
• 2 time in EPA• 4 times in IA• Longer SMD
“Gyeongju USN much stronger”
USN
PHA2
2018 SEEBUS, Kyoto University, Japan, November 2-3
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: Comparison of the 2017 Pohang and 2016 Gyeongju earthquakes
Frequency spectra Response spectra
Black line_ Gyeongju recordsRed line_ Pohang PHA2
“High frequency contents over 10 Hz dominant”
“Spectral peak occurred around 2 Hz”
Gyeongjurecords
Pohang PHA2
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Record SI (m/s×s)
USNEW 0.1873
NS 0.1196
PHA2EW 0.2319
NS 0.4442
𝑆𝐼 = න0⋅1
2.5
𝑆𝑣 𝜉,𝑇 ⅆ𝑇
Spectrum Intensity(defined by Housner)
* The area under the pseudo-velocity spectrum with periods between 0.1 and 2.5sec _ related to the elastic strain energy absorbed by almost all the building structures
* The best scalar measure for evaluating comprehensive damage potential of a ground motion
Pseudo-velocity= elastic strain energy-equivalent velocity
“4 times larger value”
𝐸𝑠, 𝑚𝑎𝑥 =1
2𝑚𝑠𝑣
2
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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μ=1
1.5
2
4
8
1
1.5
2
4
8
1
1.5
2
4
8
1
1.5
2
4
8
Comparison of constant ductility Spectrum
5% damping
USN
PHA2
El Centro
Mexico City
• The base shear demand of Gyeongju USN is very high only for very stiff and brittle structures, and becomes almost null in the velocity region.
• PHA2 record is still demanding for mid-period range
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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IV. Some notes on the 2017 Pohang EQ damage
Source: AIK (2018). a study of damage prevention strategies for earthquake-vulnerable building structures including piloti construction: a report submitted to the Ministry of Land, Infrastructures and Transport.
• Major damage concentrated_ Heung-hae and Jang-sung dong, northern Pohang part, within 10km epi-central distance
• Low-rise piloti housing buildings in Jang-sung dong severely damaged
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Taiwn
Southern Calif.
“Relevant Keywords”
• Vertical irregularity• Horizontal irregularity• Torsion• Design/construction errors
Japan 2017 Pohang earthquakeKorea
Piloti building failure_ always warned after any damaging EQ but always repeats itself in next EQ everywhere
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Critical design error revealed in damaged piloti structures at Jang-Sung dong
(US approach adopted since 2009 KBC)
“The amplified seismic load combination to supplement current elastic-analysis based R factor approach, or to estimate probable force demand on critical elastic elements at M point”
“M point”
• The amplified seismic load combination for the transfer elements and piloti columns not required before 2009,
• Neglected in design after 2009 in spite of the relevant provisions enforced in KBC 2009
𝜴 = 𝟐. 𝟓
“This load combination not considered in design at all”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Other errors or deficiencies revealed
• Severely eccentric core (staircase structure)
• Non seismic details_ missing cross ties, 90-degree hooks
• Insufficient hoop rebars• and others….
“Damaging earthquakes always reveal design and construction errors hidden”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Epicenter
Jang-sung dong site_ 3km away from epicenter
: Data base on Geotechnical Information Portal System, Korea.
: PGA attenuation observed in Gyeongju EQ (KIGAM 2016)
Generation of Jang-sung dong ground motions for nonlinear dynamic analysis (AIK 2018)
AIK (2018): a study of damage prevention strategies for earthquake-vulnerable building structures including piloti construction: a report submitted to the Ministry of Land, Infrastructures and Transport, Korea.
“Three measured rock motions as seeds”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Base shear level exerted on Jang-Sung dong pilotibuildings
Gyeongju USN_ SC soil, 8km epi. distance
Jang-Sung Dong (avg)_ SD soil, 3km epi. distance
Pohang PHA2_ SD soil, 9km epi. distance (it’s fair to scale up PHA2 by 1.25 for motion at Jang-Sung dong considering attenuation)
Range of “elastic” period of damaged piloti buildings at Jang-Sung dong
“The base shear level exerted on the pilotibuildings_ only 0.50g”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Comparison with Sylmar record
Korean records_ moderate tremors in a stable continental region (SCR), much less damaging than strong interplaterecords like Sylmar
Sylmar record
Gyeongju
Pohang
“Level of base shear_ 3.0 g”
Range of “elastic”period of damaged low-rise piloti housing at Jang-Sung dong
Sylmar NS record from the 1994 Northridge EQ, M6.7, 16km hypo-distance, site class D (deep alluvium over rock)
“Level of base shear_ 0.50g”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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A case study_ seismic vulnerability of a low-rise piloti housing_ seriously damaged Crystal Villa
• No amp. seismic load applied in design
• Severely eccentric core (staircase) • Non seismic details_ missing cross
ties, 90-degree hooks• Insufficient hoop rebars• and others….
• Commercial code ETABS used
• Medelling_ as-built conditions_ ASCE 41 (hinge parameter etc)_ ACI 318 (shear strength)
• Input_ original PHA2 record having freq. contents as given by the nature
• Bi-directional input 3D analysis
All design/construction errors and deficiencies:
“Hoop spacing too wide”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Wall_ fiber elements and elastic shear spring Simple DCR analysis
“All the columns modelled as brittle in shear_ Condition III”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Name DCR(= Vu/Vn)
C1 1
C2 1
C3 0.86
C4 0.96
C5 0.32
C6 0.83
C7 0.11
C8 0.59
C9 0.09
C10 0.58
[Column shear DCR]
Name DCR(=Vu/Vn)
W1 1.22
W2 1.06
W3 1.47
W4 0.91
[Wall shear DCR]
80% PHA2 Intensity
= Column failure in shear
uy,max=9.58 mm
[1st story displacement time history_ Y-axis]
Max. SDR= 0.37%
At 80% PHA2 intensity, the columns farthest from the core started to fail in shear
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Name DCR(=Vu/Vn)
C1 1
C2 1
C3 1
C4 1
C5 0.42
C6 1
C7 0.14
C8 0.75
C9 0.11
C10 0.73
Name DCR(=Vu/Vn)
W1 1.50
W2 1.34
W3 1.84
W4 1.24
100% PHA2 intensity
[Column shear DCR]
[Wall shear DCR]
= column shear failure
Wall cracking observed
Column shear failure predicted
Column shear failure reported (AIK 2018)
C2
C1
C4
C3
C6
[1st story displacement time history_ Y-axis]
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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[Column shear responses]
C2 C4
C1 C3
Predominantly bi-axial
Predominantly uni-axial
100% PHA2 intensity
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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* Shear hinge parameters calculated per ASCE 41-13
Name DCR(=Vu/Vn)
C1 1
C2 1
C3 1
C4 1
C5 0.76
C6 0.87
C7 0.30
C8 0.60
C9 0.09
C10 0.59
Name DCR (=Vu/Vu)
W1 0.71
W2 0.70
W3 0.81
W4 0.67
“Wall_ cracked, but shear demand less than ultimate strength”
= Column shear failure predicted
100% PHA2 analysis with including wall nonlinearity in shear
Including wall nonlinearity did not affect the overall column shear failure pattern.
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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C2
C1
C4
C3
C2
C1
C4
C3
As a result of adding wall nonlinearity in shear, the bi-axial behavior weakened
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Source: KIGAM (Korea Institute of Geoscience and Mineral)
KIGAM Report (2018)on Large-Scale Soil Condition Survey Results in Pohang Area
Sedimentary soil thickness
Landfill thickness Weathered rock
thickness Sedentary deposit
thickness
Depth to bedrock Vs30 Site period (Tg)
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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The fatal piloti building damage at Jang-Sung dong was a result of unfortunate marriage of bad structure and bad soil.
The severely damaged Jang-Sung dong area_ a spot of deeper alluvium with resulting longer ground period and low shear wave velocity
Jang-sung dong
Jang-sung dong
Jang-sung dong
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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2017 Pohang EQ (ML5.4, MW5.4)
2016 Gyeongju EQ (ML5.8, MW5.4)
Well-known among geotechnicians and geologists:• Gyeongju_ generally rocky (granite) region• Pohang_ largely of sedimentary area (sea about
10 million years ago)
Overall Ground Soil Conditions of the Two Cities
Much more extensive damage in the Pohang EQ more easily understandable when considering urban-scale soil conditions
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2018 Hualian Earthquake
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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Gyeongju?
Pohang?
From Gyeongju?
From Pohang?
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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: Geographical distribution of characteristic ground period (estimate per microtremor)
“No. of stories of collapsed buildings:11~12
Characteristic ground period:
0.8~1.2 sec
“Several piloti multi-story buildings collapsed”
High correlation between the characteristic ground period and the fundamental period of collapsed piloti buildings
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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“Almost the same phenomenon occurred at two different places of this globe”
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU
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V. Summary and Conclusions
This studied comparatively analyzed the damage potentials of the two recent Gyeongjuand Pohang EQ based on simple frequency and time domain analysis of measured ground motions.
Some seismo-geotechnical perspectives were also presented to better understand the more severe damage observed in the Pohang EQ in spite of its apparent lower magnitude than the Gyeongju EQ
The 2017 Pohang earthquake clearly showed that fatal damage to poorly engineered and constructed piloti buildings is highly probable, when subsoil is soft, the epicenter is close, and the hypocenter is shallow, although the earthquake is just moderate (M 5+) and of short duration.
Steel Structures & Seismic Design Lab, Dept. of Arch and Arch Engrg, SNU