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Comparison of Codal Provisions on Pounding between Adjacent
Buildings
by
Chenna Rajaram, Pradeep Kumar Ramancharla
in
International Journal of Earth Sciences and Engineering
Report No: IIIT/TR/2012/-1
Centre for Earthquake EngineeringInternational Institute of Information Technology
Hyderabad - 500 032, INDIAMarch 2012
www.cafetinnova.org
Indexed in
Scopus Compendex and Geobase Elsevier, Chemical Abstract
Services-USA, Geo-Ref Information Services-USA
ISSN 0974-5904, Volume 05, No. 01
February 2012, P.P. 72-82
Comparison of Codal Provisions on Pounding between Adjacent
Buildings
CHENNA RAJARAM and RAMANCHARLA PRADEEP KUMAR Earthquake Engineering Research Centre International Institute of Information Technology
Gachibowli, Hyderabad 500 032, India
Email: rajaram.chenna@research.iiit.ac.in; ramancharla@iiit.ac.in
Abstract: Pounding between adjacent structures is commonly observed phenomenon during major earthquakes
which may cause both architectural and structural damages. Generally most of the existing buildings in seismically
moderate regions are built without codal provisions. In the event of earthquake, pounding may cause considerable
damage and leads to collapse of the colliding structures if the separation distance is insufficient. The aim of this
paper is to study the impact of first collision according to the codal provisions for five different earthquakes. For this
purpose we considered two buildings and the same were idealized as linear single degree of freedom oscillators.
Separation distance between buildings is provided accoding to codal provisions of various countries and the
buildings are subjected to different ground motions of PGA ranging from 0.22 g to 0.88 g. Later impact force due to
collision is calculation and the results were analyzed.
Keywords: Pounding, separation distance, ground motion.
Introduction:
Pounding is the phenomena of collision between
adjacent buildings or different parts of the same
building during strong vibrations. It may cause either
architectural or structural damage and may lead to
partial or complete collapse of the structure. Reported
case studies of pounding are as follows: During Loma
Prieta earthquake (Kazuhiko kasai et.al., 1997) (M7.1)
occurred on 17 October 1989 over 200 structures were
affected to pounding. These structures were located
around 90 km away from the epicentre. A ten storied
building experienced pounding with an adjacent five-
storey building and they were separated by about 4 cm.
In 1999, the chi-chi earthquake (Jeng-Hsiang Lin et.al.,
2002) in central Taiwan structural pounding events were
also observed after the earthquake. Many structural
failure examples resulted from seismic pounding due to
inadequate building separation distance. The Sikkim
earthquake (Hemant B Kaushik et.al., 2006) caused
pounding damage (see figure 1.1) to a nine storey
masonry infill RC frame hostel building at Sikkim
Manipal Institute of Medical Sciences (SMIMS)
Tadong, Gangtok. In the proposed study it is planned to
first review the codal provisions across the world and
later study the impact for between the structures
following these provisions.
Figure 1.1: Pounding Damages at the Ends of the Two
Wings took Place at all the Floor Levels
Literature Review:
Pounding is one of the recent topics of interest in the
research community. Many investigations have been
carried out on pounding damage during previous
earthquake events. Stavros A Anagnostopoulos (1988)
studied the pounding of several adjacent buildings in a
block due to strong earthquakes. Each structure is
modeled as a SDOF system and pounding is simulated
using impact elements. The parametric investigation of
this problem showed that the end structures experience
more response than the interior structures. Maison and
Kasai (1992) studied pounding between 15-storey and
8-storey buildings. They assessed the influence of
building separation, relative mass, and contact location
on the impact force. Van Jeng et.al, (1992) developed
spectral difference method (Double Difference
Combination rule) to estimate the required separation to
preclude pounding. This was based on response
spectrum approach. This method is useful not only for
the assessment of pounding but also for studying the
problems involving relative displacement. Filiatrault
et.al, (1995) proposed pounding mitigation techniques.
They suggested separation distance to deal with
pounding. Solutions were either filling the gaps between
the buildings with a material or by connecting them
with bumper walls.
Review on Codal Provisions:
Most of the world regulations for seismic design do not
take into account the pounding phenomenon. Among of
the ones who do consider it, do not provide specific
rules that must be followed. Some codes are exceptions
to this. Among the exceptions are the codes of
Argentina, Australia, Canada, France, India, Indonesia,
Mexico, Taiwan and USA. These codes specify a
minimum separation distance between adjacent
buildings. In some cases this depends only on the
maximum displacements of the each building. Being in
some cases the simple sum of the displacements of each
building (eg., Canada and Israel) and in other cases a
small value that may be either a percentage of previous
one or a quadratic combination of the maximum
displacements (eg., France). In other cases the
separation distance is made dependent on the building
height (eg., Taiwan), in some cases a combination of
two rules is implemented and in others there is even a
minimum gap size which varies between 2.5 cm (eg.
Argentina) and 1.5 cm (eg., Taiwan). In some cases
these values depend on the type of soil and seismic
action.
According to International Building Code (IBC-2003)
all the structures shall be separated from adjoining
structures. If the adjacent buildings are on the same
property line, the minimum separation distance simply
follows SRSS rule and if they are not located on the
same property line (adjacent buildings separated by
property line) simply follows the sum of maximum
displacements of the structures. In 2006 version there is
no such type of codal provision on building separation.
Uniform Building Code (UBC-1997) also follows the
same codal provisions.
According to Federal Emergency Management Agency
(FEMA: 273-1997) pounding may be presumed not to
occur whenever the buildings are separated at any level
i by a distance greater than or equal to si. The value of si
need not exceed 0.04 times the height of the buildings
above grade at the zone of potential impacts.
NBC-PERU E.03 states that every structure should be
separated from other close structures a minimum
distances to avoid contact during strong ground
motions. This minimum distance not be lower than 2/3
of the sum of the maximum displacement of adjacent
blocks. ASCE 7-05 states that all portions of the
structure shall be designed and constructed to act as an
integral unit in resisting seismic forces unless separated
structurally by a distance sufficient to avoid damaging
contact under total deflection as determined in section
12.8.6. Separation distance between two structures
depends on deflection amplification factor and
importance factor.
In India, codal provision on pounding phenomenon was
included in the current revision of IS: 1893-2002. It
recommends that the separation between two adjacent
units or buildings shall be separated by a distance equal
to the amount response reduction factor (R) times the
sum of the calculated storey displacements to avoid
damage of the two structures when the two units deflect
towards each other. When the two buildings are at the
same elevation levels, the factor R may be replaced by
R/2. This clause assumes only two dimensional
behaviors of building i.e., only translational pounding,
but no torsional pounding. But in reality torsional
pounding tends to be more realistic than uni-directional
pounding during real ground motions. The basic
drawback in our codal provisions is that it uses linear
methods only.
From the observation of all codal provisions it is seen
that most of the codal provisions follow SRSS method
only. The minimum separation distance is not only
depending on the response of the structure but also
various factors like importance factor, amplification
factor etc. The details of codal provision for different
countries are as shown in Table 1. This case study deals
about the collision force of first impact of the structure
by using linear impact models. The response considered
is in translational direction only and not consider in
torsional direction.
Minimum Separation between Buildings:
For studying pounding between adjacent structures
numerically, we considered two buildings as shown in
figure 1.2. These buildings were idealized as two
equivalent linear single degree of freedom (SDOF)
systems. The two buildings are referred hereafter as
Building 1 and Building 2 and are separated by a
distance δ between them. The two buildings have
lumped masses m1 = 11400kg, m2 = 6410kg, equal
stiffnesses k = 45000kN/m and equal damping ratios ζ.
Let u1 (t) and u2 (t) are independent responses of
Building 1 and Building 2.
Table 1: Building Separation Distance between Two Adjacent Structures from Different Country Codal Provisions
S No. COUNTRY FORMULA
1.
INDIA
IS-1893:2002
Clause 7.11.3
R times the sum of the calculated storey displacements as per
clause7.11.1. When floors levels of two similar adjacent units or
buildings are at the same elevation levels, factor R in this
requirement may be replaced by R/2.
2.
INTERNATIONAL
BUILDING CODE – 2003 &
UNIFORM BUILDING
CODE – 1997
)δ+(δ=δ 2M22M1M --(Adjacent Buildings located on the
same property line)
(Clause 1620.4.5 in IBC 2003 & Clause 1633.2.11)
3.
FEDERAL EMERGENCY
MANAGEMENT AGENCY
– 273-1997
The value of ‘Si’ calculated by the equation need not exceed 0.04
times the height of the buildings above grade at the zone of
potential impacts.
2
i2i1i Δ+Δ=S 2
(Clause 2.11.10)
4. NATIONAL BUILDING
CODE-PERU E.030-2003
The minimum will no. be lower than 2/3 of the sum of the
maximum displacements of the adjacent blocks nor lower than
S=3+0.004(h-500)
(h and s in centimeters)
S> 3 cms
(Clause 3.8.2)
5. ASCE/SEI – 7- 05 I
δC=δ xed
x
(Clause 12.12.3)
S = Separation distance (in cms)
h = Height of structure (in cms)
R = Response reduction factor
δM = Separation distance between two structures
δM1 and δM2 = Peak Displacement response of adjacent structures 1 & 2
Cd = Total deflection amplification factor
δmax = Maximum elastic displacement that occurs anywhere in a floor from the application of design base shear to
the structure.
I = Importance factor for seismic loading
(a) Real model of SDOF systems (b) Idealized model of SDOF systems
Figure 1.2: Idealized Model of SDOF Systems
The governing differential equation of motion of SDOF
system is expressed as follows:
(t)um=(t)uk+(t)uc+(t)um giiiiiii (1)
Where, i denotes the building under consideration. For
the purpose of studying the collision between the
buildings we considered SE component of El-Centro
ground motion (see Figure 1.3b) whose PGA is 0.348 g.
Also for find the response of building to earthquake
ground motion, we considered newmark’s approach.
Figure 1.3: Ground Motions
Now if another building (say Building 2) is placed
adjacent to Building 1, what is the minimum distance
between the buildings can be checked by the following
condition:
δ(t)u(t)u 21 (2)
If the above condition satisfies then collision occurs.
For the purpose of finding the minimum gap between
two buildings, we considered different time periods for
Building 2 ie., 0.075, 0.10, 0.125, 0.15, 0.175, 0.20,
0.225 and 0.25sec. The peak of relative response of
adjacent buildings gives the minimum separation
distance between them. The minimum separation
distance between two adjacent structures is as shown in
Figure 1.5. From this figure it can be observed that as
the time period of the structure increases, minimum
distance is increasing to avoid pounding and for the two
structures with same time period, there is no need to
provide any separation distance because these buildings
will vibrate in phase and does not collide at any point of
time. However, this situation is not realistic because it is
very difficult to construct two structures with same
natural period. Also, it can be observed from the figure
that the minimum separation distance is getting
saturated when time period of building 2 is increasing
say beyond 1 sec.
Figure 1.4: Minimum Space Provided between Two
Structures having different Dynamic Properties
Case Study:
For the purpose of studying the impact force by
providing minimum separation distance between
buildings, we selected Building 1 with time period 0.1
sec time period and varied time period of Building 2 i.e,
0.075, 0.1, 0.15, 0.2 sec. Also for the purpose of doing
time history analysis we selected five earthquake
records, viz., Loma-Prieta earthquake, Elcentro
earthquake, Parkfield earthquake, Petrolia earthquake
and Northridge earthquake. The records were selected to
observe the pounding behaviour for wide range of
predominant frequencies. Characteristics of the selected
ground motions are given in Table 2.
When both the buildings are subjected to ground
motion, collision may take place and during collision
usually energy transfer from one building to another
building is a natural phenomenon. Due to this energy
transfer, both the structures behave differently due to
either loss of energy or gaining energy. There are
different impact models available for calculation of
impact.
Table 2: Details of Ground Motion Data
For example linear spring model, Kelvin model
(Susender Muthukumar et.al., 2004) are linear models.
Hertz model and hertz damp model are nonlinear
models. In linear spring model, energy loss during
impact is not considered for calculating the impact
force. The contact force during impact is taken as,
0221 δuuδ);u(uk=F 1kc
0; 0 21 <δuu= (3)
Kelvin approach takes into account damping also. The
calculation of collision force according to Kelvin model
is as follows,
022121 δuu);uu(c+δ)u(uk=F 1kkc
0; 0 21 <δuu= (4)
The damping co-efficient ck can be related to the
coefficient restitution e by equating energy loss during
impact.
2
kkm+m
mmk=c
1
212ξ22 ln
ln
e)(+π
e=ξ (5)
For the purpose study we considered Kelvin model. For
the calculation of impact force between two structures
stiffness of the spring, kk is assumed as 4378 MN/m.
The co-efficient of restitution, e = 0.6 is assumed and it
is defined as the ratio of the relative velocities of the
bodies after collision to the relative velocities of the
bodies before collision.
Results & Discussion:
Lomaprieta earthquake occurred in 1989 having a
magnitude of 6.9 and PGA value of 0.22 g (see figure
1.3a). The duration of this ground motion is 9.58 sec
according to trifunac and broady calculation.
In this study structures having time period range from
0.075 sec to 0.2 sec with an interval of 0.025 sec has
taken. Structure having time period 0.1 sec is kept
constant and others are varying and the minimum
separation distances are calculated from above codal
provisions. As the structures time period increases, the
response of the structure is also increases for a given
ground motion and damping. According to NBC Peru
codal provision the minimum separation distance is very
less compared to other codal provisions, because the
minimum separation distance is 2/3 of the sum of
maximum displacements of adjacent blocks. According
to IBC, UBC and FEMA follows SRSS rule and this
value is higher than Peru codal provision. According to
INDIA and ASCE codal provisions the minimum
separation distance is high compared to others. But
ASCE codal provision deals importance factor also.
This importance factor is based on occupancy category
(Ref table 1.1 from ASCE: 7-05). In table 3 the
minimum separation distances according to ASCE codal
provision are for occupancy category I or II, III and IV
respectively. The predominant time period range (0.41-
1.61 sec) is not presented in this case and there is no
impact of the structures. Hence the collision force is
zero for all the structures.
Table 3: Details Of Lomaprieta Ground Motion Record Having Amplitude Of 0.22 G, Duration 9.58 Sec And
Predominant Time Period 0.41-1.61 Sec
Elcentro earthquake (see figure 1.3b) occurred in 1940
having a magnitude of 7.1 and PGA value of 0.348 g.
The duration of this ground motion is 24.44 sec
according to trifunac and broady calculation.
In this study structures having time period range from
0.075 sec to 0.2 sec with an interval of 0.025 sec has
taken. Structure having time period 0.1 sec is kept
constant and others are varying and the minimum
separation distances are calculated from above codal
provisions. The impact force is calculated according to
Kelvin model approach. For the structures having time
period 0.1 and 0.075 sec the amount of impact is 20.58
MN by providing the minimum separation distance
0.012 m according to IBC, UBC and FEMA. According
to NBC Peru the minimum separation distance is 0.011
m, but the impact is 25 MN. As the minimum space
between the structures decreases the amount of impact
increases, but this impact occurs at the same time even
the separation distance decreases. For the structures
having same time period, no need to provide minimum
space between them. Because both structures response
is same. For the structures having time period 0.1 and
0.15 sec, the amount of impact is 26.28 MN by
providing the minimum separation distance 0.028 m
according to IBC, UBC and FEMA. According to NBC
Peru the minimum separation distance is 0.024 m, but
the impact is 1.31 MN. For these structures even though
the minimum separation distance decreases, the amount
of impact is also decreases. Because this impact not
occurs at the same time, it happens before occurrence of
that time. For the structures having time period 0.1 and
0.2 sec, the amount of impact is 42.92 MN by providing
the minimum separation distance 0.056 m according to
IBC, UBC and FEMA. According to NBC Peru the
minimum separation distance is 0.044 m, but the impact
is 96.36 MN. The amount of impact depends on
response of the structures at particular time, minimum
space between the structures and velocity of the
structures. Even though the predominant time period
range (0.45-0.87 sec) is not presented, there are
collisions for the structures. If the predominant time
period range structures are present, the collision will be
more. As the time period of the structures near to the
predominant time period range, the response of the
structures are more and the impact, damage are more
and finally may lead to collapse of the structure. In
some cases variation of impact takes place as shown in
table 4 for all the structures according to NBC Peru
codal provision.
Table 4: Details of Elcentro Ground Motion (S00E) Record Having Amplitude of 0.348 g, Duration 24.44 Sec and
Predominant Time Period Ranges From 0.45-0.87 Sec.
Parkfield earthquake (see figure 1.3c) occurred in 1966
having a magnitude of 6.0 and PGA value of 0.43 g. The
duration of this ground motion is 6.76 sec according to
trifunac and broady calculation In this study structures
having time period range from 0.075 sec to 0.2 sec with
an interval of 0.025 sec has taken. Structure having time
period 0.1 sec is kept constant and others are varying
and the minimum separation distances are calculated
from above codal provisions. For the structures having
time period 0.1 and 0.075 sec there is no collision and
for the structures having same time period also there is
no collision. For the structures having time period 0.1
and 0.15 sec the amount of impact is 38.98 MN by
providing the minimum separation distance 0.03 m
according to IBC, UBC and FEMA. According to NBC
Peru the minimum separation distance is 0.026 m, but
the impact is 56.5 MN. In this case the impact occurs at
the same time, when the distance between two
structures reduced. For the structures having time period
0.1 and 0.2 sec, the amount of impact is 58.70 MN by
providing 0.07 m according to NBC Peru codal
provision. Even though the predominant time period
range (0.30-1.2 sec) is not presented, there are collisions
for the structures. But if the predominant time period
structures present, the impact is more. According to
NBC Peru codal provision, for the structures having
time period 0.1 and 0.15 sec the impact is 56.5 MN and
with 0.2 sec the impact is more than with 0.15 sec. For
the structures having time period 0.1 and 0.15 sec there
is collision when the provided minimum space is 0.03
m, but if the structure changed to 0.15 to 0.2 sec there is
no collision according to IBC, UBC and FEMA,
because the provided space is more. For the structures
having time period 0.1 and 0.2 sec, the amount of
impact increases from 56.5 to 58.7 MN according to
NBC Peru codal provision and the details are as shown
in table 5.
Table 5: Details of Parkfield Ground Motion Record Having Amplitude of 0.430 g, Duration 6.76 sec and
Predominant Time Period 0.3-1.20 Sec
Petrolia earthquake (see figure 1.3d) occurred in 1992
having a magnitude of 7.2 and PGA value of 0.662 g.
The duration of this ground motion is 48.74 sec
according to trifunac and broady calculation. In this
study structures having time period range from 0.075
sec to 0.2 sec with an interval of 0.025 sec has taken.
Structure having time period 0.1 sec is kept constant and
others are varying and the minimum separation
distances are calculated from above codal provisions.
The minimum separation distance for the structures 0.1
and 0.075 sec is 0.03 m according to NBC Peru codal
provisions and the amount of impact is 6.13 MN.
Remaining for all structures there is no impact
according to following codal provision minimum
separation distance as shown in table 6.
Table 6: Details of Petrolia Ground Motion Record Having Amplitude of 0.662 g, Duration 48.74 sec and
Predominant Time Period 0.50-0.83 Sec
Northridge earthquake (see figure 1.3e) occurred in
1994 having a magnitude of 6.70 and PGA value of
0.883 g. The duration of this ground motion is 8.94 sec
according to trifunac and broady calculation. In this
study structures having time period range from 0.075
sec to 0.2 sec with an interval of 0.025 sec has taken.
For the structures having time periods 0.1 and 0.075 sec
the minimum separation distance is 0.035 m according
to NBC Peru codal provision, the amount of impact is
1.314 MN which is very less compared to other impacts,
because the structures are come closer and touch each
other during vibration. For the structures having same
time period (0.1 sec) having no impact. For the
structures having time period 0.1 and 0.15 sec has no
impact. For the structures 0.1 and 0.2 sec time period
the minimum separation distance is 0.23 m according to
IBC, UBC and FEMA. The amount of impact is 56.5
MN. Now the separation distance is reduced from 0.23
to 0.178 m according to NBC Peru codal provision. The
amount of impact is 43.8 MN. In this case even though
the separation distance is reduced the amount of impact
is also reduced, because the time of collision is not
same, which occurs before when the separation distance
is 0.23 m (see table 7).
Table 7: Details of Northridge Ground Motion Record Having Amplitude of 0.883 g, Duration 8.94 Sec
Conclusions:
From the above observations, the duration of strong
motion increases with an increase of magnitude of
ground motion. As the PGA value increases, the
minimum separation between the structures also
increases.
The separation distance between the two structures
decreases, the amount of impact is increases, which is
not applicable in all cases. It is only applicable when the
impact time is same. It may also decreases when
separation distance decreases, which leads to less
impact time.
At resonance condition the response of the structure
is more and may lead to collapse of the whole structure.
In this case even though the predominant time period
range is not present, the impact occurs, but this impact
is more when the predominant time period structures
present.
For Petrolia earthquake, the magnitude and duration
of ground motion are more, but there is very slight
collision happens.
For Elcentro earthquake, the PGA value and
duration are slightly less than Petrolia earthquake, but
the collision is significant. The minimum separation
distances are different in both cases and less in Elcentro
earthquake.
For Parkfield earthquake, magnitude and duration
are less and predominant time period structures are near
to the existing structures. Hence collision happens.
For Northridge earthquake which are less
magnitude and duration than Parkfield, the collision is
more because of resonant frequencies. The amount of
impact is not only depending on response and velocity
of the structure but also magnitude and duration of
earthquake.
Among all the Indian and ASCE codal provisions
having no pounding between adjacent structures for
different earthquakes data and spacing. Majority of
maximum pounding happens for NBC-PERU codal
provision, because it has least spacing between the
structures among all the codal provisions.
For IBC, UBC and FEMA codal provisions
pounding happens almost structures having different
dynamic properties when El-Centro ground motion is
given to the structures. This happens for moderate
earthquakes.
From the all above observation, the duration of
strong motion increases with an increase of magnitude
of ground motion. As the PGA value increases, the
minimum separation distance is also increases between
the structures.
References:
[1] International Building Code, IBC-2003,
International Code Council, INC
[2] Indian standard criteria for earthquake resistant
design of structures, part-1 general provisions and
buildings, IS:1893-2002, Bureau of Indian
standards, New Delhi.
[3] Federal Emergency Management Agency (FEMA),
NEHRP Guidelines for the seismic rehabilitation of
buildings, FEMA:273-1997,WashingtonD.C., USA.
[4] Uniform Building Code, UBC-1997, Volume-2,
Structural Engineering Design Provisions,
International Conference of Building Officials,
California.
[5] National Building Code- PERU, Technical Standard
of Building E.030, Earthquake Resistant Design.
[6] American Society of Civil Engineers for Minimum
Design Loads for Buildings and Other Structures,
ASCE/SEI 7-05, USA
[7] Andre Filiatrault and Pierre Wagner., Analytical
prediction of experimental building pounding,
Earthquake Engineering and Structural Dynamics,
August 1995, Vol. 24, Issue 8, pp. 1131-1154.
[8] Bruce F. Maison and Kazuhiko Kasai., Dynamics of
pounding when two buildings collide, Earthquake
Engineering and Structural Dynamics, 1992, Vol.
21, Issue 9, pp. 771-786.
[9] Hemant B Kaushik, Kastubh Dasgupta, Dipti R
Sahoo and Gayatri Kharel., Performance of
structures during the Sikkim earthquake of 14
feb.06, Current Science, August 2006, Vol. 91, No.
4, pp. 449-455. [10] Jeng-Hsiang Lin and Cheng Chiang Weng., A study on
seismic pounding probability of buildings in Taipei
metropolitan area, Journal of the Chinese Institute of
Engineers, 2002, Vol. 25, No. 2, pp. 123-135.
[11] Kazuhiko kasai and B.F Maison., Building
pounding damage during the 1989 lomaprieta
earthquake, Engineering Structures, 1997, Vol. 19,
No. 3, pp. 195-207.
[12] Stavros A. Anagnostopoulos., Pounding of
buildings in series during earthquakes, Earthquake
Engineering and Structural Dynamics, 1988, Vol.
16, pp. 443-456.
[13] Susender Muthukumar and Reginald Desroches.,
Evaluation of impact models for seismic pounding,
Proceedings of Thirteenth World Conference on
Earthquake Engineering,August2004, paper No.235
[14] Van Jeng, Kazuhiko Kasai and Bruce F. Maison., A
Spectral Difference Method to Estimate Building
Separations to Avoid Pounding, Earthquake
Spectra, May 1992, Vol. 8, Issue 2, pp. 201-223.
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