Seismic Strengthening of RC Structures

This assignment delves into the topic of seismic strengthening of Reinforced Concrete (RC) structures. It examines various techniques employed to enhance the seismic resistance of these structures, with a particular emphasis on the use of exterior shear walls and novel shape memory alloy dampers. The analysis draws upon relevant research papers and standards to provide a comprehensive understanding of the subject.

ENGINEERING PROJECT
EARTHQUAKE VIBRATION CONTROL USING MODIFIED FRAME SHEAR WALL

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ABSTRACT
Earthquake is a serious and extreme disaster, which makes even larger and
stronger buildings and infrastructure as vulnerable. The eventual result would be
the rehabilitation of these buildings and infrastructure, which are vulnerable in
nature. As the technology has been progressing, there are various technologies
developed to improve the strength of the buildings and infrastructure, in
earthquake prone regions. The present study gives insight of the new technology
and technique to strengthen the infrastructures and structures, with exterior shear
walls. The mission of the new technology is to protect the lives of the people and
increase the monetary losses.

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Contents
EARTHQUAKE VIBRATION CONTROL USING MODIFIED FRAME SHEAR
WALL..............................................................................................................................................5
INTRODUCTION...............................................................................................................5
LITERATURE REVIEW.....................................................................................................6
EARTHQUAKE..........................................................................................................................6
SHEAR WALLS.........................................................................................................................7
EVALUATION....................................................................................................................8
SEISMIC EVALUATION...........................................................................................................8
STRUCTURAL FEATURES......................................................................................................8
EARTHQUAKE AND MODIFIED FRAMED SHEAR WALL.............................................12
EARTHQUAKE AND BUILDING PERFORMANCE...........................................................13
IMPORTANT STUDIES...........................................................................................................13
PERFORMANCE DURING EARTHQUAKE.................................................................17
CONCLUSION..................................................................................................................17
REFERENCES..................................................................................................................18

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EARTHQUAKE VIBRATION CONTROL USING MODIFIED FRAME SHEAR WALL
INTRODUCTION
The earthquakes occurred in the past have either completely collapsed the
buildings or left many of them and experience various kinds of damages, structures
made by the reinforced concrete. There have been various kinds of investigations
carried out, on the strength of the structures and buildings, against the capability to
withstand to the normal to severe earthquake. Some of the structural deficiencies
discovered with the reinforced concrete made buildings are poor quality concrete,
weak columns, splice lengths that are inadequate, incomplete considerations of the
design and short column behaviour. Eventually, as attempts to minimize the
structural deficiencies, various building codes are introduced and developed.
Lateral stiffness, required ductility and strength are lower compared to the ones,
imposed by the modern codes of buildings developed. Since these structures
possess low ductility, these structures are more prone to the demand of the large
displacement, because of the deficiencies in the lateral strength and stiffness.

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Figure: Collapsed Building in Bhuj Earthquake
LITERATURE REVIEW
EARTHQUAKE
When the earthquake is occurred , vibrations of the earth surface generate
strong waves and disturb the buildings and infrastructure present on the surface of
the earth. The loss of life does not happen directly, because of the earthquake
directly, but because of the disturbing structure that are built, with no knowledge
and safety against the earthquake force. Hence, there is an increasing need of
understanding of the earthquake behaviour and relative construction methods for
earthquake resistant buildings.

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SHEAR WALLS
Shear walls act as strong structural systems, offering strong and lateral
stability, against the earthquake, wind loads and many other lateral loads, to the
structures. Usually, construction of the structural systems is done by the timber or
plywood unreinforced masonry, reinforced concrete and reinforced masonry. The
reinforced masonry is further divided, into shear wall frames, coupled shear walls,
staggered walls and shear panels. These shear walls are modified in various
techniques and methods for varied applications. (Venkatasairamkumar, 2014)
The objective of using the shear walls is to provide more resistance to the
most of the lateral loads portion, in the structures’ bottom portion and provides
better support through the framed element of the top structures portion. The top
structure portions and their strength is necessary for wider range, small story,
medium to high rise buildings. Most of the basements present in the world are
used, generally, for garages, offices or parking and top floors are usually, allocated
for the purpose of residence.
The behaviour of the shear walls depends ultimately, on the material used,
thickness of the shear wall, length of the wall, positioning of the wall, in the frame
of building and several factors, such as the reinforcement, based on the provisions
of the code.

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EVALUATION
SEISMIC EVALUATION
The study of the existing buildings strengthening, based on the seismic
evaluation is conducted. The study has emphasized on the identification of the
risky buildings most vulnerable components and retrofit of the same, so that the
risk of complete or partial collapse can be worked out to decrease. Though this
evaluation does not stop or control the earthquake, but the performance of the
building cna be increased, by strengthening the buildings, when earthquakes are
occurred. In technical aspects, the word strengthening refers to retrofitting and
practically, seismic performance improvement (Durgesh & Rai, N.D.)
STRUCTURAL FEATURES
The gravity and lateral system of load resisting has reinforced concrete slabs
and walls. When the shear walls are considered, the major difference is that it is a
main vertical structural element having a resisting dual role, with the lateral loads
and gravity loads. The thickness of the wall varies in between 14 to 50 cm and is
based on the age of the building, total number of stories and requirements of
thermal insulation. Most often, the shear walls are constructed as continuous,
throughout the height of the building. But, there are some walls which are
discontinued, at the basement level or street front, so that parking spaces or

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commercial spaces can be allowed. It is also usual that the layout of the wall is
symmetrical, according to, minimum of one axis of symmetry, when the plan is
considered. Most often, the floor slabs are cast-in-situ flat slabs and however,
precast hollow-core slabs also do exist. The thickness of the slabs does vary in
between 12 cm, as in previous USSR and to 22 cm, when hollow-core slabs are
considered in Kyrgyzstan, etc. Support of buildings is done by mat foundations or
concrete strip and the mat foundations are commonly used for the buildings having
the basements. Usually, modifications of structures are less common, for this kind
of construction.
The seismic forces are the basic code requirement to design and build the
shear wall buildings. It depends on the country specific seismic design provisions
and method of analysis. For instance, when a Chilean seismic code is considered, it
prescribes a coefficient of base shear, for the buildings of shear wall of 5 to 6.7%
and it depends over the seismic zone. According to Canadian seismic requirements
and Chilean requirements, the maximum drift of lateral story would be limited to
0.0002, when the regular buildings are considered and it would be 0.0005, when
the Colombian seismic code is considered.

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Figure: Typical shear wall building plan, in Chile and Romania
The requirements of reinforcement are according to the specific code
requirements of each country. In most of the cases, the reinforcement of the wall
has two distributed reinforcement layers, both vertical and horizontal, throughout
the wall. And bars of vertical reinforcement are provided, close to the openings of
window and door and at the barbells or as boundary elements, called as, end zones
of the wall, as well.
When the Romania shear wall buildings are considered, they consist of the
walls that are lightly reinforced, having one 12 mm diameter layer for vertical bars
and 8 mm for the horizontal bars. The spacing of reinforcement for walls varies in
between 25 cm to 15 cm, respectively, in transverse and longitudinal direction.
There are boundary elements for the transverse shear walls, at the end of facade.
When Canada seismic requirements are considered, the classification of
National Building Code is done for shear wall buildings, into the wall system of
ductile and nominally ductile, having its factor of force modification, R to have 2

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and 3.5 values, respectively. For all kinds of the shear walls, both vertical and
horizontal distributed reinforcement would be required, with the ratio of 0.25%.
When the ductile shear walls are considered, there is an area of 0.25% of the wall
and at least 4 bars are needed, for each fo the end zone.
In the instance of the Chile, the reinforced concrete structures design has to
be performed based on the code, ACI1318-95. The design of the shear wall does
not require considering and following its specific clauses, referring to the boundary
elements design of the structural walls. In coupling beams, confinement
reinforcement is also used, but rarely, for the vertical bars, at the diagonal bars or at
the ends of the wall. Here, a cover with reduced reinforcement is allowed.
The shear walls having perforated with the openings would be considered as
coupling walls, and act as cantilevered walls that are isolated and connected with
the beams of coupling and it is called lintels or spandrel beams, designed for shear
effects and bending effects. The function of these beams is to act as fuses and have
its applications in seismic energy dissipation, when it is designed as a ductile
manner. Coupling beams are designed, having its diagonal reinforcement, for
ensuring the strong and effective ductile seismic response. Joining of the
reinforcement bars together is done, through lap splices or welding.
Cladding of exterior shear walls is done, in stucco, backed by the cold-farm
masonry or steel framing veneer, panels of glazing or steel or precast.

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EARTHQUAKE AND MODIFIED FRAMED SHEAR WALL
Global structure strengthening is an effective and economical strategy of
rehabilitation and where as seismic evaluation refers to the performance that is
acceptable, because of the overall strengthened structure. This unacceptable
performance can be identified, during the occurrence of global inelastic onset
behaviour, at ground levels shaking, which are lesser substantially, compared to the
design levels of the code. The ground motion threshold value can be raised
possibly, by the introduction of additional strength to this resisting system of lateral
force. Braced frames and shear walls are considered as the important elements,
made use for the same purpose. However, sufficient stiffness has to be assured,
compared to the building, supplementing. It demands the design to have all the
lateral resistance of the structure. It is needed, when it is desired, since the existing
members possess, inelastic strength at very little value. When a new structural
system is added to the building that exists, would change the complete building’s
dynamic behaviour automatically to a considerable extent, when earthquake is
occurred. The choice of the size and number of the elements added and type of the
element depends on the existing building’s vulnerability and also on the building’s
functional layout. Shear walls can possibly provide the earthquake resistance,
needed for the building structure, which is the most significant part, because of the
lateral strength and greater stiffness.

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EARTHQUAKE AND BUILDING PERFORMANCE
There are close to six severe earthquakes of more than 8.0+ degree and have
been eminent during the nineteenth century. These major and extreme loss
earthquakes have taught significant lessons to the society and to the governments.
Here, only a small number of buildings made with reinforced concrete are
subjected and affected to these eminent earthquakes.
IMPORTANT STUDIES
There has been an important study conducted for the epoxy grouted dowels
guidelines in the projects of seismic strengthening. The existing concrete structures
are to be used either to improve the seismic performance of the structures, towards
stronger existence in the future or to rebuild the buildings with enough strength, in
the earthquake regions, after the earthquakes are occurred. The strength of the
buildings can be bettered, by adding a new steel member or adding a new concrete,
to the structures existing. The best choice is the epoxy grouted dowels, because of
the ease fo the epoxy resins installation and improved strength of the same. Creep
concern is precluded, for the dowels short term loading, from the seismic loading.
As the concrete mass is used to grout the dowels, enough insulation would be
needed for the epoxy protection, from the sources of heat, like fire (Wylli, 1988).
Another study has been conducted by National Research Council of Canada,
with the objective of exploring and developing the building structures seismic

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upgrade guidelines. The fact discovered is that most of the buildings, in Canada,
India and many other earthquake prone areas, are built with the older technology
and were built with hardly any understanding and knowledge of resistance of
earthquake. Eventually, these buildings are now found to be unsafe, when checked
their strengths, against the present building codes. Hence, the code requirement can
be justified, only for the new buildings. It is because, attempt to evaluate the
existing buildings demand huge cost, for upgrade of the existing buildings and the
heritage value would be easily destructed. Hence, a new set of procedures are
developed as alternatives, by NRC and have published, in the Seismic Evaluation
of Existing Building Guidelines. These guidelines are presently known and
referred as ‘Guidelines for Seismic Evaluation’ (NRC, Canada, 1995).
The guidelines emphasize the use of the shear walls. These shear walls
usually are made up of reinforced masonry, reinforced concrete, steel or plywood
on studs. The new system is guided to place wither in the interior of the building,
as interior walls or also as exterior walls, or in the form of bracing. It is also seen
as buttresses, outside the building. (NRC, Canada, 1995)
The study has been advanced with the recent retrofit of RC shear wall. The
reinforced concrete shear walls are considered to provide better stiffness, lateral
strength and better capacity of energy dissipation and so give better resistance
against the lateral loads that are occurred from the wind loading or earthquakes.

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Hence, these RC shear walls have given better and wider applications in the
buildings both in medium to high-rise, covering both residential and commercial
purpose buildings.
The RC shear walls have gone through various modifications, in the aspect
of their design, in the past decades. So, they are presently have the capability to
adopt for both the new construction and strengthen the older constructions. The
modern principles of capacity design and performance evaluation methods adopted
are the major and significant advances, worth noting in the earthquake engineering
advancement. So, an opportunity has been found to develop and enhance the
seismic performance of the older buildings, by adopting the modern technology of
adopting the RC shear walls. Hence, RC shear walls are found to match the need of
the new seismic design techniques, based on the performance (Galal & El-Sokkary,
2008). The modern technology makes use of various retrofit techniques, with the
help of various kinds of materials, like concrete, shape memory alloys, steel, fiber-
reinforced polymers, all adopted, differently with different techniques of retrofit,
towards upgrading the existing building seismic resistance.
A massive destructive earthquake in Turkey has taken lives of many
residents and caused huge loss of infrastructure and buildings. The study conducted
on the strength of the buildings, have revealed the fact that these buildings and
reinforced concrete have no enough rigidity and strength, to withstand the

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earthquakes. Hence, the loss of the lives and property are recorded to be huge. The
method of strengthening that could have been used in these kinds of RC buildings
is the RC shear walls or infill walls application, in the buildings’ frame openings.
An attempt was made to retrofit these buildings, which are in unsafe
conditions, since these buildings were in heavy risk conditions. However, people
were not ready to rehabilitate easily, their buildings. So, easier methods were
explored fro application, without vacating these buildings, to strengthen these
structures. The application method for retrofit is the external shear wall
application. These shear walls made of reinforced concrete and applied on the
structures’ external surface.
The retrofit technique made use of total 7 test samples, in the geometrical
scale of ½ and 1/3rd and the retrofitting technique performance is analyzed. The
technique involved the shear wall, leaning over the frame, from the strengthening
techniques and application of external shear wall building. The design includes
some space, between the external shear wall and frame, by connecting the
elements, through coupling beam (Kaltakci et al, 2010).
Another study has been conducted on the RC building seismic strength,
through exterior shear wall. Seismic loadings were simulated, through the two
stories framed model structures testing, under cyclic lateral sway, reversed and
imposed. The study has reported the findings that the shear walls implemented to

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the system of structure has shown greater improvement to the bare frame capacity,
as anticipated (Kaplan et al. 2011).
PERFORMANCE DURING EARTHQUAKE
The type of building is the earthquake resistance consideration. Most of the
reports show the good behaviour, during the past earthquakes. These buildings’
unfavourable earthquake performance is because of the construction quality that is
inadequate and was in Moldova case. Other factors are inadequate detailing and
amount in wall reinforcement and wall density in longitudinal direction and lateral
confinement lack within the walls and the elements of boundary.
The possible deficiencies that could affect the seismic performance,
adversely, for this kind of construction are soft-story mechanism, reduced density
of wall and their effects.
CONCLUSION
Earthquake either damages the structures of the building or collapses
completely and the result is based purely on the kind of construction and its
strength. The important factor that influences the result is the reinforcement
concrete. The performance of the building is also influenced by the severity of the
earthquake. Shear walls are considered to be an important factor that can be
controlled with the specification of the building code. The specification of the
building code varies for each region, according to the seismic affect and possibility

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in the same region. The objective is to increase the lateral loads portion resistance
for the structures. Seismic evaluation is done for each zone to develop the building
code and according to it, structural features are defined and followed, in each
region. Earthquake affects and influences can be better controlled with the
modified framed shear walls, according to the possibility and severity of
earthquake in each region. There have been many studies conducted for the shear
wall design and presented.
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Kaltakci, M. Y., Ozturk, M. and Arslan, M. H. 2010. “An Experimental
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