1 Structural Responses – Structural Responses – Preliminary Results and Preliminary Results and Observations Observations PEER GMSM Program Workshop, Richmond CA, October 29, 2007 PEER GMSM Program Workshop, Richmond CA, October 29, 2007 Curt B. Haselton, PhD, PE Curt B. Haselton, PhD, PE Assistant Professor Assistant Professor California State University, Chico California State University, Chico And other members of PEER GMSM Working Group And other members of PEER GMSM Working Group
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1 Structural Responses – Preliminary Results and Observations PEER GMSM Program Workshop, Richmond CA, October 29, 2007 Curt B. Haselton, PhD, PE Assistant.
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Higher prediction again associated with higher collapse
rate.
CMS methods (and POC): 0/28
Inelastic methods: 3/28
POC = 0.019
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Overview of Structural Response ResultsOverview of Structural Response Results Results summary by method classification for Building C (median MIDR/POC):
Sa(T1) and UHS methods results in highly variable predictions which tend to be
larger than the POC.
Methods that match the CMS agree well with the POC.
CMS Proxy methods and Inelastic methods:
On average, results in response 15% higher than the POC.
This seems to also come with a higher collapse rate.
**These observations are an average or all methods in the class; some of the
individual methods have predictions nearly the same as the POC.
Sa(T1) UHS CMS *Proxy (i.e. ε) Inelastic
Median: 1.48 1.26 1.01 1.15 1.14
c.o.v.: 0.34 0.23 0.20 0.30 0.19
Minimum: 1.07 0.91 0.76 0.79 0.76
Maximum: 2.74 2.07 1.51 1.88 1.58
* With methods 57 and 58 removed.
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Overview of Structural Response ResultsOverview of Structural Response Results Comparison of results for Buildings A and D
Sa(T1) methods: Tend to over-predict response, predictions depend
on spectra shape and contributions of inelastic and higher-mode
responses.
Matching CMS: Predictions close to POC in all cases.
Proxy methods: Consistent at 10% above the POC.
Inelastic methods: 15% above the POC for frame buildings (C and A),
and right at POC for shear wall (Building D).
Median(MIDR/POC)Building T1
(sec)Sa(T1) UHS CMS
*Proxy (i.e. ε)
Inelastic
Building C (20-story RC frame) 2.63 1.48 1.26 1.01 1.15 1.14
Building A (4-story RC frame) 1.00 1.48 -- 1.05 1.05 1.17
Building D (12-story RC wall) 1.20 1.17 -- 0.94 1.09 1.00
* With methods 57 and 58 removed. Averages: 1.38 1.26 1.00 1.10 1.10
With Sa(T1) scaling, we scale all of the spectra to the
UHS at a given period. This causes predictions to be
highly variable and depend on:
The spectral shape of the record bin, as compared to the
UHS.
The period used for scaling.
These items affect the shape of the spectrum away
from T1, which affect inelastic response.
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A Detailed Look at Results of A Detailed Look at Results of
Building Code-Based Record Building Code-Based Record
SelectionSelection
PEER GMSM Program Workshop, Richmond CA, October 29, 2007PEER GMSM Program Workshop, Richmond CA, October 29, 2007
Jack W. Baker, PhDJack W. Baker, PhD
Assistant ProfessorAssistant Professor
Stanford University Stanford University
And other members of PEER GMSM Working GroupAnd other members of PEER GMSM Working Group
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IBC (ASCE 7-05) building code IBC (ASCE 7-05) building code requirementsrequirements
From ASCE 7-05, section 16.1.3.1:
“Each ground motion shall consist of a horizontal acceleration history, selected from an actual recorded event”
“obtained from records of events having magnitudes, fault distance, and source mechanisms that are consistent with those that control the maximum considered earthquake.”
“The ground motions shall be scaled such that the average value of the 5 percent damped response spectra for the suite of motions is not less than the design response spectrum for the site for periods ranging from 0.2T to 1.5T “
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Number of ground motionsNumber of ground motions
From ASCE 7-05, section 16.1.4:
“If at least seven ground motions are analyzed, the design member forces … and the design story drift … is permitted to be taken respectively as the average of the … values determined from the analyses”
“The probabilistic MCE spectral response accelerations shall be taken as the spectral response accelerations represented by a 5 percent damped acceleration response spectrum having a 2 percent probability of exceedance within a 50-yr. period.”
Here we use the +2 σ response spectrum at all periods, to facilitate comparison and since that has a ~2% probability of exceedance, given the scenario magnitude and distance.
The 150%-of-median deterministic cap is ignored here to allow comparison with other results.
33
Selection approachSelection approach
Start with the NGA ground motion library (7038 horizontal components)
Eliminate records not meeting specified criteria (e.g., magnitude and distance ranges)
Select the 28 records that most closely matched the target spectra after scaling
If the average of the 28 spectra fell significantly below the target spectrum, perform some additional minor scaling
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Case 1 (Method Tag 9980)Case 1 (Method Tag 9980)No M/R/Mech. Restrictions
No filter frequency restriction
7038 records available
10-1
100
101
10-2
10-1
100
101
Period [s]
Sp
ect
ral a
cce
lera
tion
[g]
Scaled response spectra, T1 = 2.63s
0.2 T1 1.5 T1
3510
-110
010
110
-2
10-1
100
101
Period [s]
Sp
ect
ral a
cce
lera
tion
[g]
Scaled response spectra, T1 = 2.63s
Case 2 (Method Tag 9981)Case 2 (Method Tag 9981)No M/R/Mech. Restrictions
Restricted filter frequencies
3454 records available (50%)
3610
-110
010
110
-2
10-1
100
101
Period [s]
Sp
ect
ral a
cce
lera
tion
[g]
Scaled response spectra, T1 = 2.63s
Case 3 (Method Tag 9982)Case 3 (Method Tag 9982)6.5 < M < 7.6
No Dist./Mech. Restrictions
1122 records available (16%)
10-1
100
101
10-2
10-1
100
101
Period [s]
Spe
ctra
l acc
eler
atio
n [g
]
Scaled response spectra, T1 = 2.63s
Set #4
3710
-110
010
110
-2
10-1
100
101
Period [s]
Sp
ect
ral a
cce
lera
tion
[g]
Scaled response spectra, T1 = 2.63s
Case 4 (Method Tag 9983)Case 4 (Method Tag 9983)0 < R < 30 km
No Mag./Mech. Restrictions
856 records available (12%)
3810
-110
010
110
-2
10-1
100
101
Period [s]
Sp
ect
ral a
cce
lera
tion
[g]
Scaled response spectra, T1 = 2.63s
Case 5 (Method Tag 9984)Case 5 (Method Tag 9984)Strike slip events only
No Mag./Dist. Restrictions
978 records available (14%)
3910
-110
010
110
-2
10-1
100
101
Period [s]
Sp
ect
ral a
cce
lera
tion
[g]
Scaled response spectra, T1 = 2.63s
Case 6 (Method Tag 9985)Case 6 (Method Tag 9985)6.5 < M < 7.6,
0 < R < 30 km
Strike slip events only
Target spectrum not always exceeded
132 records available (2%)
4010
-110
010
110
-2
10-1
100
101
Period [s]
Sp
ect
ral a
cce
lera
tion
[g]
Scaled response spectra, T1 = 2.63s
10-1
100
101
10-2
10-1
100
101
Period [s]
Sp
ect
ral a
cce
lera
tion
[g]
Scaled response spectra, T1 = 2.63s
Case 7 (Method Tag 9986)Case 7 (Method Tag 9986)6.5 < M < 7.6
0 < R < 30 km
Strike slip events only
Target spectrum exceeded
132 records available (2%)
4110
-110
010
110
-2
10-1
100
101
Period [s]
Spe
ctra
l acc
eler
atio
n [g
]
Scaled response spectra, T1 = 2.63s
10-1
100
101
10-2
10-1
100
101
Period [s]
Spe
ctra
l acc
eler
atio
n [g
]
Scaled response spectra, T1 = 2.63s
Case 8 (Method Tag 9975)Case 8 (Method Tag 9975)6.5 < M < 7.6
0 < R < 30 km
Strike slip events only
Max scale factor = 4
132 records available (2%)
4210
-110
010
110
-2
10-1
100
101
Period [s]
Spe
ctra
l acc
eler
atio
n [g
]
Scaled response spectra, T1 = 2.63s
10-1
100
101
10-2
10-1
100
101
Period [s]
Spe
ctra
l acc
eler
atio
n [g
]
Scaled response spectra, T1 = 2.63s
Case 9 (Method Tag 9976)Case 9 (Method Tag 9976)
10-1
100
101
10-2
10-1
100
101
Period [s]
Spe
ctra
l acc
eler
atio
n [g
]
Scaled response spectra, T1 = 2.63s
Set #4
6.5 < M < 7.6
0 < R < 30 km
Strike slip events only
Max scale factor = 2
132 records available (2%)
4310
-110
010
110
-2
10-1
100
101
Period [s]
Sp
ect
ral a
cce
lera
tion
[g]
Scaled response spectra, T1 = 2.63s
10-1
100
101
10-2
10-1
100
101
Period [s]
Sp
ect
ral a
cce
lera
tion
[g]
Scaled response spectra, T1 = 2.63s
Case 10 (Method Tag 9989)Case 10 (Method Tag 9989)6.5 < M < 7.6
0 < R < 30 km
Strike slip events only
Max one record per event
9 records available (0.1%)
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10-1
100
101
10-2
10-1
100
Period (s)
Sa
(g)
M = 7.5, R = 30 kmM = 6.5, R = 10 km
ObservationsObservations
Are the magnitude/distance/mechanism restrictions needed?
We know they affect spectral shape, but we are already specifying a target spectral shape
Median response spectra from events with differing magnitudes and distances
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ObservationsObservations
Are scale factor restrictions needed?
They don’t seem to have an effect. Again, this may result from the target spectrum requirement
Note that no such restriction is given in the code
Is the one-record-per-event restriction needed?
It doesn’t seem to have an effect, and severely limits the available number of records
Note that no such restriction is given in the code
46
ObservationsObservations
Is the filter frequency limitation needed?
Presumably over-filtered motions will not match the design spectrum, so the target spectrum should ensure we have records with proper filtering (assuming that 0.2T to 1.5T are the only periods we need to worry about)
Note that no such restriction is given in the code
0 5 10 15 20 25 300
1000
2000
3000
4000
5000
6000
7000
Maximum usable period [s]
Nu
mb
er
of r
eco
rd c
om
po
ne
nts
ava
ilab
le
47
ConclusionsConclusions
Responses seem to be controlled by the target spectral shape, rather than the other selection criteria
This suggests that the choice of the target spectrum is a more important consideration than the choice of additional criteria
Benefit of the additional criteria: more “insurance” that you have appropriate record properties
Disadvantage of the additional criteria: a reduced number of records to chose from, meaning that you will not be able to match the target spectrum as closely