10NCEE
Tenth U.S. National Conference on Earthquake Engineering
Frontiers of Earthquake Engineering
July 21-25, 2014
Anchorage, Alaska
SEISMIC TESTING OF NON-STRUCTURAL
COMPONENTS AND ASSESSMENT OF
THE PRESCRIBED RESPONSE SPECTRUM
S.M. Takhirov1, A. Gilani2, and L. Tedesco3
ABSTRACT
The current US building code specifies seismic certification by means of shake table tests of
nonstructural components. A brief review of current status of non-structural testing in the United
States by means of shake tables is presented. A key feature of the evaluation is the use of a
prescribed required response spectrum. The required spectral accelerations are based on certain
assumptions on spectral amplification over building’s elevation. To date no study has been
conducted to assess the applicability of the prescribed standard for buildings of various heights,
construction material, and lateral load resisting framing. To address this issue, strong motion data
from the database of recorded earthquakes was utilized. Based on these records, an empirical
estimate of spectral amplification was developed which is crucial for development of required
response spectra for seismic evaluation testing of non-structural components by means of shake
table testing. The buildings considered in the study have permanently installed strong motion
instrumentation or were studied by temporarily installed high-sensitive instrumentation used for
monitoring ambient vibration. The paper employs a number of floor responses recorded in a
number of buildings during low level ambient vibrations or earthquakes. The paper focuses on
specifics of floor spectra recorded during (1) ultra-low amplitude (ambient vibration) tests, (2)
low, and (3) high level seismic excitations. As anticipated, the spectral acceleration is largely
amplified at the resonant frequencies of buildings. In many cases the floor spectra are
significantly greater than the test spectra currently prescribed for use in tests of non-structural
components.
1
NEES Site Manager, PEER, University of California Berkeley, Richmond, CA 94804
Senior Associate, Miyamoto International, West Sacramento, CA, 95691
3
Senior Manager, Ceiling Systems, USG Corporation, Chicago, IL 60661
2
Takhirov SM, Gilani A, and Tedesco L. Seismic testing of non-structural components and assessment of the
prescribed response spectrum. Proceedings of the 10th National Conference in Earthquake Engineering, Earthquake
Engineering Research Institute, Anchorage, AK, 2014.
10NCEE
Tenth U.S. National Conference on Earthquake Engineering
Frontiers of Earthquake Engineering
July 21-25, 2014
Anchorage, Alaska
Seismic Testing of Non-structural Components and Assessment of
the Prescribed Response Spectrum
S.M. Takhirov1, A. Gilani2, and L. Tedesco3
ABSTRACT
The current US building code specifies seismic certification by means of shake table tests of
nonstructural components. A brief review of current status of non-structural testing in the United
States by means of shake tables is presented. A key feature of the evaluation is the use of a
prescribed required response spectrum. The required spectral accelerations are based on certain
assumptions on spectral amplification over building’s elevation. To date no study has been
conducted to assess the applicability of the prescribed standard for buildings of various heights,
construction material, and lateral load resisting framing. To address this issue, strong motion data
from the database of recorded earthquakes was utilized. Based on these records, an empirical
estimate of spectral amplification was developed which is crucial for development of required
response spectra for seismic evaluation testing of non-structural components by means of shake
table testing. The buildings considered in the study have permanently installed strong motion
instrumentation or were studied by temporarily installed high-sensitive instrumentation used for
monitoring ambient vibration. The paper employs a number of floor responses recorded in a
number of buildings during low level ambient vibrations or earthquakes. The paper focuses on
specifics of floor spectra recorded during (1) ultra-low amplitude (ambient vibration) tests, (2)
low, (3) moderate and (4) high levels of seismic excitations. As anticipated, the spectral
acceleration is largely amplified at the resonant frequencies of buildings. In many cases the floor
spectra are significantly greater than the test spectra currently prescribed for use in tests of nonstructural components.
Introduction
Non-structural components and equipment consist of many elements and as such are difficult to
analyze numerically. To assess their seismic performance earthquake simulation testing can be
used. Such technique was used by many manufacturers of non-structural components and
equipment in the United States to characterize performance of their products during earthquakes.
Seismic evaluation of non-structural components and equipment is based on prescribed required
response spectra. This paper discusses the existing prescribed response spectra and prescribed
amplification parameters and compares them to that obtained from acceleration records of real
buildings. The comparison is conducted for different excitation levels varying from very low –
noise level excitation to very high seismic excitation that causes inelastic deformation of a
1
NEES Site Manager, University of California Berkeley, Richmond, CA 94804
Senior Associate, Miyamoto International, West Sacramento, CA, 95691
3
Senior Manager, Ceiling Systems, USG Corporation, Chicago, IL 60661
2
Takhirov SM, Gilani A, and Tedesco L. Seismic testing of non-structural components and assessment of the
prescribed response spectrum. Proceedings of the 10th National Conference in Earthquake Engineering, Earthquake
Engineering Research Institute, Anchorage, AK, 2014.
building.
Review of Current US-Practice on Non-Structural Testing
Code requirements in the United States
The current edition of the International Building Code (IBC) [1] and its referenced documents
address the seismic requirements for suspended ceilings. Both design and installation issues are
addressed in the document. The IBC [1] assigns seismic design categories (SDCs) A through F to
buildings. The SDC for a structure depends on its occupancy, the underlying soil conditions, and
the site-specific seismic hazard intensity. For structures located in Categories D to F, the code
mandates prescriptive installation requirements, as summarized in [2]. For seismic force
calculations, the IBC [1] and the ASCE/SEI 7-10 [3] treat the suspended ceiling system as a nonstructural component (NSC) and specify seismic force from:
(Eq.1)
Fp
( R p / I p )W p
z
 [ 0.4a p ( 1  2 )] S DS  ( 1.6 )S DS
h
where Fp is the seismic force, Wp is the unit weight of the ceiling; Ip is the importance factor;
Rp, is the response modification factor, ap accounts for the response amplification; and SDS =
2/3FaSS designates the short-period (0.2-sec) spectral acceleration for the design earthquake
(10% probability of occurrence in 50 years). The z/h factor accounts for the amplification of the
response along the building height. The code assumes an inverted triangular distribution that is
capped at 1.6. Although not explicitly stated, such amplification would not exist in the vertical
direction because the building’s columns are stiff along their axes and thus do not amplify the
vertical component of the earthquake at the top of the columns.
In the United States, the code explicitly allows earthquake simulator (shake table) testing
to be performed in lieu of the analytical procedure of (Eq.1). As an example, such an approach
was used to assess the performance of the code-prescribed ceiling installation and the USG®
seismic clip [4]. In the United States, shake table testing must follow the requirements of a test
and qualification document such as the ICC-ES AC156 [5]. The ICC-ES AC156 uses the seismic
force of (Eq.1) to develop the required response spectrum (RRS) with the following assumptions:
(a) components with a frequency of greater than 16.7 Hz are considered rigid without
amplification of acceleration; and (b) components with a frequency of less than 16.7 Hz are
considered flexible with a maximum amplification of spectral acceleration. Thus (Eq.1) can be
expressed in terms of the required spectral acceleration for flexible and rigid components
respectively as:
(Eq.2) ARIG = 0.4SDS(1+2z/h) ≤1.2 SDS and AFLX = SDS(1+2z/h) ≤1.6SDS
Typical required response spectra in horizontal excitation and the code prescribed
spectral amplification are presented in Figure 1.
3.5
1
1
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
3
Elevation, z/h
Spectral acceleration, g
2.5
2
1.5
1
0.5
SS=3.0g - ground
SS=3.0g - roof
0
0
1
10
10
Frequency, Hz
0
1
1.5
2
2.5
3
Spectral amplification of AFLX
0
1
1.5
2
2.5
3
Spectral amplification of ARIG
(a)
(b)
Figure 1. Typical required response spectra in horizontal direction (a) and code prescribed spectral
amplification (b).
Empiric Floor Spectral Accelerations
Ultra-low excitations
Spectral amplifications of building vibrations due to ambient noise are very important for
expensive equipment sensitive to low level vibrations. MRI and CT scanners are representative
examples of such vibration sensitive equipment and instruments. A significant engineering effort
is required for vibration reduction at the site by means of advanced vibration control and
engineering design to identify and control vibration sources. A capability to estimate the amount
of transmitted energy and vibration amplification throughout elevation of the building is crucial
for vibration reduction.
This paper discusses the results of the ambient vibration study of the Berkeley Public
Library [6]. From earthquake engineering point of view this level of vibrations can be considered
as ultra-low with peak accelerations in the order of 0.005g or so. The study represents one of the
typical cases where ultra-low vibrations of a building caused by passing traffic, contraction noise
and other ambient excitations, are investigated. As is commonly done in ambient vibration
studies, one level of the building (the roof of the building, in this case) was taken as a reference
level. At least four velocimeters were installed on both the reference level as well as the current
level under investigation. Therefore, in each set of records there are recorded velocities of
specific levels of the building in reference to the roof which are differentiated to deliver
accelerations at the instrument locations. At each building elevation, two out of four instruments
recorded vibration in the east-west direction at the opposing sides of the building, whereas the
remaining two recorded vibration in the north-south direction. The recorded accelerations for
each direction were averaged to remove any torsional component of vibration. The peak
accelerations obtained from the data were below 0.005g.
Spectral amplifications were derived by dividing the floor spectra by the spectra at the
basement elevation. The building had 4 elevations above the basement including the roof. The
spectral amplifications for these elevations in ‘soft’ (translational) and ‘stiff’ (longitudinal)
directions of the building are presented in Figure 2a and Figure 2b, respectively. One of the main
goals of this ambient vibration study was to estimate the resonant frequencies of the building.
The buildings’ resonant frequency in transverse direction was lower than its frequency in the
longitudinal direction. This was expected, as this difference is correlated with greater stiffness of
the building in the longitudinal direction. As anticipated, the spectral amplifications in
longitudinal directions were less than those of the building in the transverse direction: an
amplification of 15 at the roof elevation in the transverse direction versus an amplification of
about 12.5 in the longitudinal direction.
Floor to basement spectral ratio (Sf/Sb) in north-south direction
Floor to basement spectral ratio (Sf/Sb) in east-west direction
16
16
Roof
3rd floor
2nd floor
1st floor
14
12
Spectral ratio, g/g
Spectral ratio, g/g
12
10
8
6
10
8
6
4
4
2
2
0
10
0
10
Frequency, Hz
1
Roof
3rd floor
2nd floor
1st floor
14
0
10
0
10
1
Frequency, Hz
(a)
(b)
Figure 2. Spectral amplification at ultra-low excitation levels: a) north-south (more flexible direction), (b)
east-west (more rigid direction).
Floor spectral acceleration in the same building during low and moderate level earthquake
excitations
This section presents a comparison between the recorded spectral amplification throughout a
buildings elevation during low and moderate levels of ground excitations caused by two different
earthquakes. The same building was studied to investigate the differences in amplification at
these two levels of excitations. The building studied is located in Burbank, California, U.S.A.
and its shaking was recorded during the 1994 Northridge and the 2011 New Hall earthquakes.
This is a ten-story residential building with precast concrete shear walls in lateral and
transversal directions. The building design is dated back to 1974. It was instrumented in 1980
with 16 accelerometers on 4 levels in the building (CSMIP station #24385). The filtered
acceleration records from [7] were used in the study. The building’s plan has 1:2.9 aspect ratio
with the longitudinal direction coinciding with 2700 direction of the accelerometer orientation.
The 00 direction of the accelerometer orientation represents the transverse direction of the
building. To avoid any beating effect associated with possible coupling between translational and
torsional motions and low damping [8, 9], accelerations in transverse directions were averaged.
Figure 3a presents the spectral amplification at many elevations of the building in respect
to the first level in longitudinal direction. The spectra amplification peaked at the first frequency
of the building in this direction and it was close to 10 at the roof level. The amplifications at the
first resonance frequency of the building at the roof level are consistent for both levels of
earthquake excitations, but the amplifications for lower excitations were consistently higher. A
noticeably lower resonant frequency is also observed at higher level which is most likely related
to some inelastic performance of the building. Spectral amplification at moderate level was close
to 7.5. Figure 3b shows big difference in ground excitation recorded for these two earthquakes at
the 1st level. The similar conclusion was made regarding the building’s amplification in the
transverse direction, although the amplification in this direction was much higher for low level
excitation (about 14) and was about the same (right below 7) for moderate level as shown in
Figure 4a. Figure 4b shows 1st level spectra calculated for both low and moderate excitations in
transverse direction.
Longitudinal direction
Longitudinal direction
14
Spectral amplification
10
8
6
4
0.8
0.6
0.4
0.2
2
0
N
NH
1
Spectral acceleration, g
Roof@N
Roof@NH
8th Floor@N
8th Floor@NH
4th Floor@N
4th Floor@NH
12
1.2
0
0
1
10
10
0
1
10
Frequency, Hz
10
Frequency, Hz
(a)
(b)
Figure 3. (a) Amplification of floor spectra relative to that of first level and (b) spectra of 1st floor
accelerations recorded during low New Hall (NH) and moderate Northridge (N) earthquake excitations
(Burbank, CA in longitudinal direction).
Transverse direction
Transverse direction
14
Spectral amplification
10
8
6
4
0.8
0.6
0.4
0.2
2
0
N
NH
1
Spectral acceleration, g
Roof@N
Roof@NH
8th Floor@N
8th Floor@NH
4th Floor@N
4th Floor@NH
12
1.2
0
1
10
10
Frequency, Hz
0
0
1
10
10
Frequency, Hz
(a)
(b)
Figure 4. (a) Amplification of floor spectra relative to that of first level and (b) spectra of 1st floor
accelerations recorded during low New Hall (NH) and moderate Northridge (N) earthquake excitations
(Burbank, CA in transverse direction).
Analysis of the building’s transfer function during both of these excitations showed that
the first resonance frequency has slight shift toward lower frequencies.
Amplifications in same building during two different moderate level earthquake excitations
This section presents a comparison between the recorded spectral amplification over the
elevation of a building during high level ground excitations caused by two different earthquakes.
The building located in Pasadena, California, U.S.A. is studied based on excitations produced by
the 1991 Sierra Madre and 1994 Northridge earthquakes.
This is a nine-story commercial building with reinforced concrete slab-column system
providing moment resistance in lateral and transversal directions and beam-column system at the
core of each floor. The building design is dated back to 1963. It was instrumented in 1989 by 15
accelerometers installed on 5 levels of the building (CSMIP station #24571). The filtered
acceleration records from [7] were used in the study. The building’s plan has 1:2.5 aspect ratio
with the longitudinal direction coinciding with 1800 direction of the accelerometer orientation.
The 900 direction of the accelerometer orientation represents the transverse direction of the
building with the lowest natural frequency.
To avoid any beating effect associated with possible coupling between translational and
torsional motions and low damping [8, 9], accelerations in transverse directions were averaged
where possible.
The ratios of the spectra recorded at the second, fifth and roof levels of the building in
respect to the basement level in longitudinal direction are presented in Figure 5a. The spectra
estimated for the basement floor are presented in Figure 5b. The spectral amplifications over
elevation of a building are consistently concentrated around the first resonance frequency in this
direction, which is estimated at 0.7 Hz. The spectra amplification curves for each level are about
the same for both earthquake excitations despite the fact that the ground level acceleration
spectra have completely different shapes as shown in Figure 5b. The amplification of the spectra
at the second resonance frequency (estimated as 2.7 Hz) is less dramatic and slightly greater than
2. The peak acceleration at the roof level during the 1991 Sierra Madre earthquake is amplified
by a factor slightly less than 2. Since spectral accelerations are about the same at resonant
frequency of the building, the spectral amplification is about the same during both earthquakes.
The spectra at the roof level are amplified by more than 10 times relative to that at the ground
(basement) level in both cases.
Longitudinal direction
Longitudinal direction
12
Spectral amplification
10
8
6
4
2
0
N
SM
1
Spectral acceleration, g
Roof@N
Roof@SM
5th Floor@N
5th Floor@SM
2nd Floor@N
2nd Floor@SM
0.8
0.6
0.4
0.2
0
1
10
10
Frequency, Hz
0
0
1
10
10
Frequency, Hz
(a)
(b)
Figure 5. (a) Amplification of floor spectra relative to that of first level and (b) spectra of ground
floor accelerations during two moderate level seismic excitations: Sierra Madre (SM) and Northridge (N)
EQs (Pasadena, CA: longitudinal direction).
The ratios of the spectra recorded at the second, fifth and roof levels of the building in
respect to the basement level in transverse direction are presented in Figure 6a. The spectra
estimated for the basement floor are presented in Figure 6b. The spectral amplifications over
elevation of a building are consistently concentrated around the first resonance frequency in this
direction, which is estimated at 0.46 Hz. The spectra amplification curves for each level are
about the same for both earthquake excitations despite the fact that the ground level acceleration
spectra have completely different shapes as shown in Figure 6b. This can be explained by the
fact that the spectral accelerations at the resonant frequency were about the same in case of both
earthquakes. The amplification of the spectra at the second resonance frequency (estimated as
1.6 Hz) is less dramatic and close to 2. The peak acceleration had minimal amplification from
basement to roof. The spectra at the roof level are amplified by more than 8 times relative to that
at the ground (basement) level in both cases.
Transverse direction
Transverse direction
12
Spectral amplification
10
8
6
4
2
0
N
SM
1
Spectral acceleration, g
Roof@N
Roof@SM
5th Floor@N
5th Floor@SM
2nd Floor@N
2nd Floor@SM
0.8
0.6
0.4
0.2
0
1
10
10
Frequency, Hz
0
0
1
10
10
Frequency, Hz
(a)
(b)
Figure 6 (a) Amplification of floor spectra relative to that of first level and (b) spectra of ground
floor accelerations during two moderate level seismic excitations: Sierra Madre (SM) and Northridge (N)
EQs (Pasadena, CA: transverse direction).
Amplifications in same building during design level earthquake excitations
This section presents spectral amplification in a building subject to high level of seismic
excitation which exceeds a design level earthquake. For this purpose a seven-story reinforced
concrete building located in Van Nuys, California, U.S.A. was selected. The building was
located approximately 7 km from the epicenter of the 1994 Northridge earthquake. This is a
seven-story commercial building with interior concrete column-slab frames and exterior concrete
column-spandrel beam frames as a lateral force resisting system. The building design is dated
back to 1965 and it was instrumented in 1980 by 16 accelerometers installed on 5 levels of the
building (CSMIP station #24386). The filtered acceleration records from [7] were used in the
study. The building’s plan has 1:2.75 aspect ratio with the longitudinal direction coinciding with
900 direction of the accelerometer orientation. The 3600 direction of the accelerometer
orientation represents the transverse direction of the building.
The building sustained extensive damage during the Northridge earthquake [10]. There
was extensive cracking in beams and beam to column connections. The most serious damage
occurred at the top of some columns in the south frame of the fourth floor.
To access spectral amplification of the building the same procedure was followed. The
accelerations in transverse directions were averaged to avoid noticeable beating effect associated
with coupling between translational and torsional motions and low damping [8, 9].
The ground spectra in both lateral and transverse directions are presented in Figure 7a.
Since the spectral shapes are about the same the excitations in both directions had about the same
frequency content. The roof spectral amplification is shown in Figure 7b which shows two well
isolated spectral peaks associated with resonant frequencies of the building. Spectral
amplifications in longitudinal and transverse directions are shown in Figure 8a and Figure 8b,
respectively.
Ground floor spectra
Roof spectra
2.5
2.5
Longitudinal
Transverse
Longitudinal
Transverse
2
Spectral acceleration, g
Spectral acceleration, g
2
1.5
1
0.5
0
1.5
1
0.5
0
0
1
10
10
0
1
10
Frequency, Hz
10
Frequency, Hz
(a)
(b)
Figure 7. (a) Ground floor spectra and (b) roof spectra calculated for Van Nuys building during
Northridge EQ.
Longitudinal direction
Transverse direction
4
4.5
Roof
3rd Floor
2nd Floor
3.5
3.5
Spectral amplification
Spectral amplification
3
2.5
2
1.5
1
3
2.5
2
1.5
1
0.5
0
Roof
3rd Floor
2nd Floor
4
0.5
0
1
10
10
Frequency, Hz
0
0
1
10
10
Frequency, Hz
(a)
(b)
Figure 8. Spectral amplification in longitudinal (a) and transverse (b) directions estimated for Van
Nuys building during Northridge EQ.
The spectral amplifications of this building are much less than those presented earlier. At
the roof level the spectral amplification is about 3.8 in longitudinal direction and about 3.2 in
transverse direction. This big difference in spectral amplifications between this level and lower
levels of excitation can be explained by extensive inelastic deformations of the building during
the earthquake.
Summary of results
1
1
0.8
0.8
Elevation, z/h
Elevation, z/h
A summary of peak floor acceleration’s amplification and spectral amplification for all buildings
studied is presented in Figure 9. All amplifications are presented in respect to z/h ratio depicted
in Figure 10. The amplifications of peak floor accelerations shown in Figure 9a are well
enveloped by the amplification specified by the AC156 document [5], although the latter
amplification might be too conservative for high level excitations as it was noticed earlier [11].
Based on discussion provided above and the plots in Figure 9b, it can be concluded that
the spectral amplification greatly depends on level of excitation. In general, lower excitations
produce higher spectral amplifications, since the energy of seismic excitation is not dissipated by
any non-linear effects in the structure. All peaks of spectral accelerations exceed the spectral
amplification specified by AC156 document [5]. In addition to excitation level, other major
parameters can have significant contribution to spectral amplification: design of lateral force
resisting system, soil conditions, number of stories, design concept (base isolated versus fixed
base), geometric shape of the building and so on.
0.6
0.6
0.4
0.4
0.2
0.2
0
0.5
AC156
High
Moderate
1
1.5
2
Spectral amplification of ARIG
2.5
3
0
AC156
Ultra-low
Low
Moderate
High
2
4
6
8
10
Spectral amplification of ARIG
12
14
(a)
(b)
Figure 9. Amplification is presented as function of z/h ratio: (a) amplification of ARIG and (b) peaks of
spectral amplifications (b).
Figure 10. Amplifications are presented in respect to z/h ratio.
Conclusions
The results presented here show that spectral amplification is excitation dependent. Depending
on building’s construction details, spectral amplification has a tendency to be higher at ultra-low
excitations with a much higher amplification than that is currently anticipated by the code. With
excitation level increasing, the spectral amplification has a tendency to decrease, but the cases
presented here still demonstrate higher spectral amplification than the one prescribed by the
code. A more detailed study is required to further investigate this issue and develop a new code
requirement. The future study will be based on a statistical analysis of a large dataset of
instrumented buildings throughout the world.
Acknowledgments
The financial support of USG Corporation to this project is kindly appreciated.
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