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.