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.