ABSTRACT

It has been widely seen that when earthquake occurs
it causes large and intense shaking of the ground. So the building or the
structure of any shape, size or of any height will experience the motion at its
base.The level of damage caused by earthquake on a structure depends on the intensity
of release of stain energy and the duration of shaking. The amplitudes are
largest with respect to the large earthquake and the duration of shaking
generally increases with the size of earthquake.  When two adjacent building vibrates out of
phase the collision occures due to the insufficient sepration or gap this
phenomenon is known as  pounding of
building. This paper includes the study of pounding between adjacent building
with same or different properties. Lump mass 
sytem is considered using MDOF system. In this time history analysis is
carried out using  past earthquake
of  Imperial valley.

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I.                   
INTRODUCTION

 

Investigation of past studies had illustrated the
damages caused due to earthquake. Earthquake is a sudden shaking of earths
surface due to the release of strain energy in large amount, due to this sudden
shaking buildings or structures experiences initial force due to which partial
or collapse or fully collapse condition occur. But when the buildings are
adjacent to each other and due to insufficient separation the collision takes
place which results more damage in the structure. The phenomenon where building
displaces out of phase and collides with each other, this is known as pounding
of building. But the level of damage caused by earthquake on a structure
depends on the amplitude and the duration of shaking. The amplitudes are
largest with respect to the large earthquake and the duration of shaking
generally increases with the size of earthquake.

As per Indian standard 1893:2002 the structure is
said to be sway when the lateral displacement is more than the 0.004 times the
height of structure above the ground. This displacement causes the high torsion
and moment in the structure. The effect due to lateral displacement becomes
more critical when the two structures are placed adjacent to each other without
providing insufficient gap. The effect experienced by both the structure is
known as pounding effect.

 

The powerful 2001 Bhuj earthquake has
been most dominating earthquake in the last five decades in India. Reinforced
concrete building suffered the heaviest damage during the earthquake because of
poor design and construction practices and pounding of adjacent structure was
evident at Ajodhya apartment in Ahmadabad with significant damages.

 

TYPES
OF POUNDING

1.      
Floor
to column pounding:

This
type of pounding occurs in some adjacent buildings in which the floor levels
are not in the same heights. Therefore when shaking with different phases
occurs, the floor of one building hits the column of another, and causes
serious damages which can lead to fracture of the columns of storey. This type
is the most dangerous impact that can result in sudden destruction of the
building. The separation of two building is kept according to IS 4326.

 

2.      
Adjacent
buildings with greatly differing mass:

Since
adjacent buildings may differ in the structural system of floors and in their
application, they have different mass which causes different phase
oscillations, since the lighter building tolerates more intensive response.

 

3.      
Buildings
with significantly differing total heights:

When
two structures with different heights are adjacent, because of different
dynamic properties, the short structure hits the adjacent one, which results in
floor shearing in higher levels of impact part.

 

4.      
End
buildings of a row when all the buildings have similar properties:

This
type of impact is usually seen in buildings, which are built completely the
same. In this type of impact, some similar buildings that oscillate similarly,
in strong earthquake, hit the last building in the series and causes serious
displacement in the pounded building. Existence of same shape of the vibration
in some building and height momentum lead to last building has intensive
responses.

 

FACTORS
AFFECTING POUNDING

1.      
Soil conditions

2.      
Building heights and relative difference
between heights

3.      
Separation between adjacent buildings

4.      
Lateral load resisting structural
system.

5.      
The peak ground acceleration of the
earthquake at location of building.

6.      
The material of construction.

7.      
Type of induced vibrations.

8.      
Damping mechanism.

9.      
The lateral eccentricity and twisting
motion ,if any

 

II.                 
LITERATURE
REVIEW

Amruta
Sadan and Tapashetti(2014):

In this journal author
analyzed a three dimensional reinforced concrete moment resisting frame
buildings with open ground floor in SAP2000 to observe pounding and also Time
History Analysis is carried out taking data of Elcentro. Author also said that
since gap between the buildings cannot be increased to accommodate the relative
movement of both the buildings, the relative displacement can be reduced by
providing additional stiffness i.e. By bracings, shear wall and by combined
action, to accommodate out of phase movement under provided gap and also Shear
walls are provided to reduce the lateral displacements in the buildings, here
they have replaced masonry wall with RC wall. They also provided information
that to improve seismic response FVD is provided as a diagonal brace as it
substantially increases the damping within the structure and also provides
additional stiffness and strength and energy dissipation capacity during strong
winds and moderate earthquakes.

 

M.A. Somwanshiand M.A. Bhokare,2017): This
study considers the simple case of collision between two buildings with floors
at the same height. They also stated that If by increasing the distance of the
two buildings still pounding occurs, this increase of distance increases the
responses and by using impact absorbing material, the acceleration response of
structures was   reduced which can be
very important, especially for non-structural elements also Connecting the
structures at a floor level reduced the responses. In this author has focused
on lighten the seismic pounding effects between buildings and measures to
reduce this effect. . The viscous damper and elastic spring can reduce the
structural response. They have also described that elastic spring itself can
limit the pounding force. By connecting the structures at a floor level reduced
the response of adjacent structure. Connecting the two buildings at more than a
level did not improve very much the responses of the structures.

 

Puneeth Kumar and S Karuna,(2015):

 In this study to observe pounding between
adjacent buildings, separated by an expansion joint were subjected to gravity
and dynamic loading and were analyzed by using Sap2000. After analyzing they
resulted that displacement of buildings with bracings is reduced 50% than
buildings when compared with bare frame and also was the same case with shear
wall.In this author
concluded that during strong earthquakes, adjacent buildings without proper
separation gap are affected by pounding. 
When author comparing all the cases of study, adjacent buildings with
same floor level, different floor level and set back, out of phase movement was
greater than expansion joint which created 
impact force adjacent buildings, with different dynamic properties,
vibrated out of phase leading to pounding damage.  The maximum response (displacement) was more
in taller buildings than the shorter one. They also concluded that Buildings
with shear wall are more effective than with bracings.

 

M.
Abdel-Mooty and H. Al-Atrpy (2009): In this paper author
studied the factors affecting seismic pounding of adjacent buildings were
identified and critically examined. The formulation and modeling of pounding
phenomenon was introduced. Parametric study on seismic pounding phenomenon was
conducted to examine the effects of various factors on seismic pounding. They
calculated Pounding forces by using software SAP 2000 where nonlinear gap
elements between the adjacent building floors were used to calculate pounding
forces. They concluded that variation in the stiffness of the gap element has
negligible effect on the calculated pounding forces but the size of the gap
significantly affect the calculated forces and their frequency of occurrence.
They also concluded that pounding forces depends very much on the
characteristics of the earthquake records and the dynamic characteristics of
the adjacent buildings. They stated that effect of earthquake record is not
limited to just the value of force; it affects the frequency of hits and also
Pounding forces increases as the difference in the structural systems in the adjacent
buildings increases. They said that largest pounding forces occur when there is
a difference in height of the adjacent buildings due to the whiplash effect.
Highest values of pounding forces occur near the top of the building. In
generally pounding forces decreases as the separation distance increases. However,
very small separation distance may prevent the build-up of momentum of the
moving masses thus reducing the impact forces. 
They observed that the number of pounding hits consistently decreases as
the separation distance increases.

 

M
phanikumarand J D Chaitanya Kumar (2015):

In this thesis the factors
affecting seismic pounding of adjacent buildings were identified and c
examined. Parametric study on seismic pounding phenomenon was conducted to
examine the effects of various factors on seismic pounding. They calculated
Pounding forces acting on structure by using commercial software packages like
ETABS, where nonlinear gap elements between the adjacent building floors are
used to calculate pounding forces. Based on the observations from the analysis
results, they concluded that Compared to the linear dynamic analysis the storey
displacements of the two adjacent buildings increased 90 to 95% with non-linear
dynamic analysis. They also mentioned that there is no pounding between two
adjacent buildings when it is analyzed by linear dynamic analysis because the
displacement are very small, but there is a pounding effect when it is analyzed
by non-linear dynamic analysis because the displacements increased largely.
They concluded that it is necessary to carry out non-linear dynamic analysis to
know the actual response of the structure. The displacements of the buildings
decreasing gradually by introducing shear walls over brick infill walls at
suitable locations. From this we can say that the minimum seismic gap can be
reduced by introducing shear walls when the separation distance available is
less. In this the pounding forces are decreasing by 10 to 15% between two
adjacent buildings as the separation distance is increasing with a variation of
10 mm gradually. So, it can be said that the pounding effect can be decreased
with increasing separation distance. They said that pounding forces are also
decreases gradually between two adjacent buildings by introducing shear walls
at suitable locations compared to fully brick infill walls. So, that pounding
effect can be mitigated by introducing shear walls over brick infill walls.

 

III.              
CONCLUSION:

                From the above literatures
it can be concluded that the building with lighter mass are prone to the most
intensive response. When the mass and stiffness of both buildings are same they
oscillate in the same phase and so there is no overlap, hence no pounding but
if the stiffness is kept same and masses are changed then pounding is observed.