Strengthing of damaged structure

Strengthing Of Damaged Structure, D.Monica, Mrs.B.Lavanya, M.Tech, Journal Impact Factor (2015):
9.1215 (Calculated by GISI) www.jifactor.com
www.iaeme.com/ijciet.asp 92 editor@iaeme.com
1
M.E, Construction Engineering and Management
Sree Sastha Institute of Engineering & Technology
Chembarambakkam, Chennai-600123
2
Assistant Professor,
Sree Sastha Institute of Engineering & Technology
Chembarabakkam, Chennai-600123
ABSTRACT
The construction activity in India has been increasing geometrically without matching
increase in the availability of quality inputs, in terms of materials and skilled workmen. The gap
between the quality planned and the quality achieved continues to widen. The factors contributing to
damages/distress due to various causes including leakage/seepage have, thus, become intrinsic right
from the construction stage.
This project is conduct to assets the existing condition of structure of cooling tower present in
CPCL site in Chennai and find out causes for the failure of the structure. Select suitable method of
repair and protection strategy. Post retrofitting evaluation of the structure is done.
I. INTRODUCTION
Concrete construction is generally expected to give trouble free service throughout its
intended design life. However these expectations are not realized in many constructions because of
structural deficiency, material deterioration, unanticipated overloading or physical damage.
Premature material deterioration can arise from a number of causes the most common being when
the constructions specifications are violated or when the facility is exposed to harsher environment
than those expected during the planning and design stage. Physical damage can also arise from fire,
explosion, as well as from restraint both internal and external against structural movement. Expect in
extreme case, most of the structure require restoration to meet its functional requirement by
appropriate repair technique.
In my project i use different techniques along with micro concrete to strength the defective
parts of the structure. The success of a repair or rehabilitation project depends on the specific plans
designed for it. Concrete Structures: Protection, Repair and Rehabilitation provides guidance on
evaluating the condition of the concrete in a structure, relating the condition of the concrete to the
underlying cause or causes of that condition, selecting an appropriate repair material and method for
STRENGTHING OF DAMAGED STRUCTURE
D.Monica1
, Mrs.B.Lavanya, M.Tech2
Volume 6, Issue 6, June (2015), Pp. 92-99
Article ID: 20320150606009
International Journal of Civil Engineering and Technology (IJCIET)
© IAEME: www.iaeme.com/Ijciet.asp
ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316 (Online)
IJCIET
© I A E M E

any deficiency found, and using the selected materials and methods to repair or rehabilitate the
structure
II. AIM
The main aim of my project is to convert sick building to healthy building by using advance
techniques.
III. SCOPE OF STUDY
• Ascertaining the present state of the building.
• Establishing the repair/ strengthen techniques.
• Preparation of repair program.
• Determining the required target condition.
• Re-check and inspection.
IV. METHODOLOGY
Study of literature related to repair and rehabilitation of structure.
List out causes of damage and failure occur in the structure.
List out the alternative solutions.
Site visit and analyses of structure health condition.
Find the strength of the structure by different testing techniques.
Prepare the detailed report about the damage occur in the structure.
Select the suitable repairing techniques.
Apply the remedial measures to be suggested and recheck the work done whether it regain its
strength or not.
Conclusions, recommendations and suggestions for future study.
A. Method of Surveying
Before any repair or rehabilitation work is taken up, the cause of damage and the extent of
damage to the structure must be ascertained. This aspect is often disregarded with the result that
further repairs have to be carried out within a short time. Sometimes the cause of damage or
deterioration is obvious, but careful investigation of a deteriorated structure is essential. The
investigation of the causes of the damages to the structure is largely a matter of gathering
information by visual observations, studying records and asking questions, supplemented by a
certain amount of laboratory and field testing and finally interpreting the information thus collected.
B. Investigation Questions
Investigations should cover defects relating to materials, construction, design or other
aspects. All observed signs of damage must be analyzed to determine their cause. The following
questions should be answered:
• How long have signs of damage been noticed?
• Have the signs changed with time?
• Was the assumed loading and the design (including specifications) complete and correct?
• Were there any special occurrences, omissions during construction?
• Could some defects have been overlooked or unknown?

Only after thorough investigation and analysis any evidence of damage may be removed.
During the repair itself, further information can be obtained and should be taken into consideration
for necessary adjustment to the analysis, repair plan and its execution.
C. Analysis of Result
The analysis of results of condition survey, detailed investigation and structural assessment
should enable the engineer to know:
• Whether there is a risk of failure of the damaged structure.
• Whether damages have established or likely to propagate further with time and repeated
loading.
• Whether or not an economically effective repair plan can limit or contain damages and enhance
the effective service life of a structure.
• Degree of urgency required in implementing a repair plan because of advanced stage of
damage.
D. Selection of Repair
The data from the investigations form the basis of decision regarding selection of an
appropriate repair or rehabilitation plan out of the following available options:
• Total replacement in case the damages are found to be too extensive and the cost of repair is
prohibitive.
• Partial replacement and repair based on the severity of localized damages in the structure.
• Extensive rehabilitation and/or strengthening.
• Minor repairs
V.COOLING TOWER
A. Background
The structure selected to retrofit is cooling tower at CPCL site in Chennai (manali). It is the
old structure of height upto 15m and the damage is occurring due to ageing of the structure. The
main objective of this project is to repair the structure under the working condition. The cracks and
water leakage occur in the structure leads to spalling and deterioration of the structural member. The
spalling of concrete make the reinforcement to exposed to atmosphere and severe corrosion occur.
Fig.1 cooling tower

The non-destructive test is carried out and found out that the structure is safe and need only
repair and rehabilitation and the structure is strong enough to withstand the loads.
B. Distress Observed
Since the building was very old and located in moisture atmosphere, the water leakage and
reinforcement corrosion was the major issues. There were leakages in the side wall through the
cracks occur. The corrosion of reinforcement leads to spalling of concrete.
Fig.2 damage occur in structure
VI. SELECTION OF MATERIAL AND METHOD
The repair materials that used in should meet the following characteristics:
• Be durable and protect reinforcement.
• Be dimensionally stable to avoid loss of contact between the old and new materials due to
shrinkage.
• Provide good bond between the new and old materials, including bond between steel and
concrete elements.
• Be able to develop adequate resistance at early ages, especially if the capacity of a damaged
element had to be restored rapidly.
The properties of repair materials had to be similar to the existing material properties to avoid
creating overstresses in the old material. The elastic modulus and time or temperature effects on the
materials had to be compatible with existing materials to avoid problems under high stresses,
sustained loads, or temperature changes. In the case where new concrete was used to repair an
element, the new concrete compressive strength was at least equal to the existing concrete strength.
However, the difference in strength had to be given special consideration to avoid failure and
crushing in the lower strength materials. Some comments regarding specific material are included in
the following sections.
VII. REHABILITATION AND RETROFITTING METHOD
The decision to repair or replace a structure or its component can be taken only after
consideration of likely service life of the structure established based on the technical and economical
evolutions. The decision based on preliminary investigation to carry out the repair, proper diagnosis,
identification and extent of distress in structural members has to be correctly assessed. A detailed
methodology should developed, which include
• Method of repair
• Repair material

VIII. REHABILITATION OF COOLING TOWER
1. Site Investigation
In the site investigation the physical condition of the structure is analyzed. The structure is to
retrofit is cooling tower which is always in contact with the water and present in the industrial zone.
The structure is too old and loses its strength due to ageing and it not maintained properly. It is a
single building of height up to 15- 17m.
2. Visual Inspection
Visual inspection of a structure is the most effective qualitative method of evaluation of
structural soundness and identifying the typical distress symptoms together with the associated
problems. By visual inspection it is found that the structure is severely damaged on outside but the
strong enough to hold the load and only retrofitting is required. There was a leakage occur
throughout the crack formedand the reinforcement is exposed to atmosphere and corroded.
3. NDT Test
Non-destructive test is available to determine in-situ strength and quality of concrete. The
non-destructive test like rebound hammer and soundness test is done to found the health condition of
the structure.
The rebound hammer test with low value represent the weak portion of the concrete as
compare to high value. The soundness test is done to analyzing the sound by hitting the concrete
surface. While hitting the surface the good concrete produce bold sound and dull sound produce by
weak concrete.
4. Causes for the Failure
The major cause for the failure of the structure is due to ageing and poor maintained. The
structure is fully contact with water, so the alternate occurrence of wetness and dryness occur which
leads to the formation of cracks. Due to crack formation and the moisture atmosphere the steel
reinforcement get corroded. The corrosion of reinforcement leads to spalling of concrete and make
the concrete surface weak.
5. Suitable Repair Technique
The repair technique is selected according to the requirement and environmental condition.
At first the weak concrete should be removed by chipping process. The severe damaged
reinforcement should be replaced and additional shear connector is provided. To avoid corrosion the
reinforcement is coated with primer.
Since the structure is in working condition and it is in contact with water surface it has to
gain its strength as soon as possible and should have less pores to reduce the possibility of crack
formation for this polymer based micro concrete is used. The bonding agent is used for better
bonding of new one with old concrete.
6. Step by Step Procedure to Carry Out Repair
A. General Requirement
Initial safety measures have to be taken before carried out the work. Proper instruction and
working procedure should be explained to the workmen for the proper execution of work. The
require amount material in proper quantity and quality should bought early and stored in safe place.

B. Propping and Supporting Structure
Since the structure is in working condition proper supporting should be given for the safety of
the structure. The prop was planned in such a manner that each prop should temporally relieve the
load of the slab contributing to the dilapidated column. The estimated load on each prop was 120KN.
C. Chipping of Unsound and Weak Concrete
The unsound and weak concrete should be removed. To reduce the vibration on the structure
power driven percussion type or pneumatic chisel is used. The debris should be removed.
Fig.3 after chipping
D. Cutting Reinforcement Bar
The corroded and fully damaged reinforcement should be cut and removed. The removal of
reinforcement should be done carefully without damaging the existing structure.
E. Inserting New Bar and Shear Key Bar
The hole is drilled on the surface using power drilling up to minimum depth of 150 mm and
up to 200 mm. the reinforcement is fixed in the position using welding and epoxy. The reinforcement
bar is coated with the primer NITOZIN as anti-corrosion agent.
Fig.4 inserting reinforcement

F. Bonding Coat
The bonding coat is to be applied on the existing concrete surface the bonding agent preferred
was NITOBOND EP. It has more overlay time, high bond strength and act as a barrier coat for the
migration of chloride ions.
Fig.5 applying bonding agent on surface
G. Micro Concrete
Micro concrete is polymer based cementitious material mostly used for repair of damaged
reinforced concrete element, particularly where access is restricted and where the vibration of the
placed material is difficult. It can able to gain strength of 60N/mm2
.
The cube is done on the micro concrete with the ratio of 2:1(micro concrete power, aggregate
of size 12mm) and water is added. The cube teat is done at the age of 12 days with 4 samples gives
average strength of 50N/mm2
. Finally curing is done.
7. Post Retrofitting Evaluation
Retrofitting evaluation is done by making a cube with pieces from old concrete and micro
concrete mix and it is tested.
IX. CONCLUSION
From the above study it is noted that with advance techniques for rehabilitation of structure
can able to regain its strength higher than that it deserved. By using micro concrete we can able to
regain the original strength within the short duration than the construction of new structure and more
economical. It also increases the life time of the building.
REFERENCE
1. Alcove, S. M., “rehabilitation of RC Frame Connections using Jacketing”, Tenth World
Conference on Earthquake Engineering, Madrid, Spain, 19-24 July, 1992
2. Baja S, Sengupta B, 2005 Review of classical water-cement ratio for present day high
performance concretes and need for further research.

3. Choppola, L. 2000. Concrete Durability and Repair Technology. ENCO Engineering and
Concrete Spresiano (TV).
4. David, E., C. Djelal and F. Buyle-Bodin, 1998. Repair and Strengthening of Reinforced
Concrete Beams Using Composite Materials. 2nd Int. PhD Symposium in Civil Engineering,
Budapest.
5. Dr. Suchita Hirde and Ms. Minakshi Jagtap, “Retrofitting of Damaged Industrial Buildings”
International Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 4, 2013,
pp. 267 - 277, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.
6. Mohammed J. Abed, K. Nasharuddin, M. A. Alam, Zakaria CM, and Moatasem M. Fayyadh,
“Damaged RC Beams with Circular Web Opening Repaired Using Different Configurations
of Bonding Steel Plate” International Journal of Civil Engineering & Technology (IJCIET),
Volume 3, Issue 2, 2012, pp. 70 - 83, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.

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