Innovative Ductile Fiber Reinforced CementiousComposites for Structural Applications
(Materials, Analysis, Design & Industrial Scope)
Prof. Shamsher Bahadur Singh, Ph.D., PDF, PE (Mich., USA)
Civil Engineering Department
Birla Institute of Technology and Science, Pilani -333031
E-mail: [email protected]; [email protected]
Web: (http://discovery.bits-pilani.ac.in/Homepage/disciplines/civil/sbsingh/sbsingh.htm)
Brief Bio-data
S.B. Singh is an ICI member and Professor &Head of Civil Engineering Department at BirlaInstitute of Technology and Science (BITS), Pilani.His current areas of research are development ofdesign guidelines for Fiber Reinforced Polymer(FRP) reinforced prestressed concrete structures inparticular and composite structures in generalincluding nonlinear finite element modeling. He hasbeen Indian Team Leader for prestigious UKIERIcollaborative research project on sustainableconcrete Infrastructure. He is also member ofvarious committee and serving as editorial boardmember of various Journals. Currently, he isrepresenting BITS Pilani on committee of Ireland-India Concrete Research Initiatives (IICRI).
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Content
(1) Fiber Reinforced Polymers (FRP) – Analysis, Design and
Applications
~ Scope for composite manufacturing industries
~ Scope for structural engineering Consulting companies
~ Scope for engineering construction companies
~ Scope for structural repair and rehabilitation companies
(2)Engineered Cementitious Composites (ECC) (Ductile
Concrete) – Applications
~ Scope for concrete industry
Fiber Reinforced Polymers (FRP) (Analysis, Design and Applications)
Introduction - Time Line
World War II : The evolution of FRP materials started.1960s- The combination of high strength, high stiffness, less density and lowcost FRP materials such as boron, aramid and carbon were commercializedfor air travel and space exploration
1970s :The cost of FRP materials continues to decrease and the aggressive infrastructural renewal has started
Late 1980s and 1990s :The funding agencies encouraged research for FRP materials for infrastructure development
2000 onwards : Many projects have been successfully completed and structures are performing efficiently as demonstration projects
Ref: (ACI 440-96)
FRP Materials:Introduction
Fiber Reinforced Plastics(FRP) is a compositematerial comprising apolymer matrix reinforcedwith fibers
Fibers are usuallyfiberglass, carbon, oraramid, while the polymeris usually an epoxy,vinylester or polyesterthermosetting plastic
High tensile strength to weight ratio
Non-corrodible characteristics
Chemically inert properties
Non-sensitive to magnetic effects
But, linear elastic behavior till rupture
Ref: (ACI 440-07)
Scope for Composite Manufacturing Industries
FRP Products
Ref: (ACI 440-07)
Composite Fabrication Hand Lay-up
Ref: (ACI 440-96)
Fibers in the form of unidirectional mats, fabric or braid are cut and laid up to produce laminate
For small quantities of complex and/or high quality parts. Very labor-intensive and thus expensive
Until recently, even high volume parts for aerospace applications were produced by this process
This process has been partially automated. Woven or Non-woven fabric are used with this process
Produces laminates with relatively higher fiber volume fractions (50-60%) and low void contents (1-2%). Used to make fly rods and most golf club shafts
Filament Winding
Ref: (ACI 440-96)
Fibers are pulled from single or multiple continuous fiber - spools and passed through a resin bath
The primary advantage of the filament winding process is high processing speed (i.e., up to 700 lbs of material/hr) -resulting in a low cost. In spite of higher capital costs, cost of filament wound parts can be one third of that of hand lay-up
Examples:
Rocket motor casings
Pressure vessels
Light poles
Oil pipes
Aircraft fuselages
Pultrusion
Ref: (ACI 440-96)
Continuous fiber reinforcement is impregnated with resin by passing through a resin bath. The impregnated fibers are pulled through a forming die, consolidated, cured, cooled quickly, and cut to length; all as a continuous automated process
Production speeds are usually two to four feet per minute
Pull forming which allows changing cross sections and fabrication of curved parts.
Examples:
I-beams, Rebar
Prestressing strand
Twisted cables
Automotive shafts
Development of Ductile Fiber Reinforced Polymer (DFRP)
Development of Ductile Fiber Reinforced Cementitious Composite (DFRCC)
Investigation on various strengthening patterns applied to masonry structures
Development of design guidelines
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INTRODUCTION AND CHARACTERISTICS OF FRP
FRP is a special type of two-component composite material consisting of high-strength fibers embedded in a polymer matrix.
High tensile strength ( can reach upto 3000 MPa)
Low density ( 1800 kg/m3)
High modulus (300-400 GPa)
Resistant to corrosion
Good dimensional stability (extremely low coefficient of thermal expansion)
Outstanding fatigue characteristics
Electromagnetic neutrality
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THEN
WHY GO
FOR
HYBRID FRP ??
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Lack of Ductility
Current FRP bars behave linearly
elastic till rupture
No early warning of
failure
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In Hybrid FRP Bars :
The proposed hybridrebar consists of differenttypes of fibers which failat different strains duringthe load history of therebar, thereby allowing agradual failure of therebar.
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REDUCTION OF COST
Carbon fibers have high ultimate tensile strength but are very expensive. In order to make the FRP reinforcements economically viable, it is fabricated by combining with other cheap fibers such as glass fibers and/ or metallic fibers. Glass fibers have UTS less than carbon but are much cheaper than carbon fibers.
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Deliverables Planned at BITSPilani
Development of Low cost FRP Manufacturing Techniques
Development of Viable Anchorage Systems for Tensile Tests of FRP Specimens
Development of Ductile FRP Rebars, fabrics and Plates
Development of Precast DFRCC Wall Panels and Plates/Strip
Development of Design Approach for FRP Strengthened Masonry Structures (Beams and Columns)
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Methodology
Stage 1: Develop Ductile Fiber Reinforced Polymer (FRP) rebars, fabrics, Ductile Fiber Reinforced CementitiousComposite (DFRCC) wall panels, plates and examine their mechanical properties for structural applications
The project has been planned to be executed in four stages as described herewith.
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Methodology (Contd..)
Stage 2: Investigate the behavior of masonry columns externally strengthened using newly developed ductile FRP rebars, fabrics and DFRCC plates in compression and flexure.
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Methodology (Contd..)
Stage 3: Examine thebehavior of masonry wallsexternally strengthenedusing newly developedductile FRP rebars,fabrics and DFRCCplates in compressionand flexure.
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Methodology (Contd….)
Stage 4: Preparation of technical papers, Submission of research findings and Completion of Report
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Fabrication of Hybrid FRP BarsFRP bars with a diameter of 10 mm were designed and made by hand lay-up process.
Six types of bars were manufactured.
Carbon FRP
Glass FRP
Hybrid- 70% glass & 30% carbon
Hybrid- 50% glass & 50% carbon
Hybrid- 60% glass & 40% carbon
Hybrid- 80% glass & 20% carbon
Bars having a length of 2.4 m and a nominal diameter of 10 mmwere manufactured with 76 longitudinal fiber ribbons and Epoxy wasused as resin. Hardener dose of 7% by weight was added to Epoxyfor acquiring sufficient strength, hardening and curing purpose inwinter season.
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Tensile Testing of Bars
Tensile testing was done on Universal Testing Machine
The length of specimen is taken as 600 mm.
Anchors were prepared for these specimen to ensure proper grip. Anchors were prepared with mild steel pipes with 20mm diameter & 200mm length and attached to the
specimen using epoxy.
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Uni-axial Tensile Strength
CharacteristicsS. No. FRP Type Diameter, mm
(Area, mm2 )
Failure Load, kN Tensile
Strength, MPa
1 CFRP 8 (50.27) 51.54 1025.4
2 GFRP 9 (63.62) 32.26 507.1
3 Hybrid FRP
(30% CFRP
plus 70%
GFRP)
9 (63.62) 43.23 679.4
Tensile strength of the hybrid FRP bar (30%CFRP and 70% GFRP) is 66.3% of carbon FRP bar and 170% of the strength of steel(400MPa).Thus, it could be concluded that the fabricated hybrid bar possess reasonable strength (>400 MPa) while maintaining the benefits of composite characteristics.
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Beam Specifications
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Grooving of Beams
Mounting of NSM FRP Bars
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Mix Proportion of DFRCC Beams made of ECC
Cement Silica
Sand
Fly-Ash Water Plasticizer PVA fiber
452 kg/m3 452 kg/m3 452 kg/m3 199 kg/m3 9.03 kg/m3 20 kg/m3
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Flexural Testing of NSM Hybrid FRP Reinforced ECC Beams
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60% GFRP- 40% CFRP
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Flexural Response of DFRCC Beams (ECC Beams)
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Achievements
Development of FRP fabrication Equipment for
processing with hand
Development of Tensile Anchor
Systems
Development of Ductile Hybrid FRP System and DFRCC
Beams
Demonstration of Effectiveness of Hybrid FRP System for low cost DFRCC
Beams
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Scope for Structural Engineering
Consultancies
Prestressing with FRPs
FRP materials exhibit several properties including high tensile strength, which make them suitable for the use as structural reinforcement and prestressingtendons
FRP tendons for prestressing is the ability to configure the reinforcement to meet specific performance and design objectives
FRP tendons may be configured as rods, bars, and strands and characteristics of an FRP tendon are dependent on fiber and resin properties, as well as manufacturing process
FRP tendons are produced from a wide variety of fibers, resins, shapes, and sizes. Especially carbon fibers, however, are recommended for prestressingapplications, since glass fibers have poor resistance to creep
Tensile stress-strain behavior of various reinforcing fibers and tendons
Ref: (ACI 440-4R-04)
General Design Considerations
Allowable stresses in FRP tendons are limited to 40 to 65% of their ultimate strength due to stress-rupture limitations
During the overall design a prestress level of 40 to 50% of the tendon strength is selected as initial stresses and service stresses are checked
If the section is sufficient, the flexural design is over. Otherwise, it is prescribed to increase the number of tendons rather than stress level in tendons
Nonprestressed FRP rods can be used to increase the strength
Typical cross-sections for DT-beam bridge with bonded and unbonded tendons
Ref: Grace and Singh (2003): ACI Structural Journal
Cross-sections for Box Beam bridgewith bonded and unbonded tendons
Ref: Grace, Singh, Mathew, Shenouda (2004), PCI Journal
Design and Analysis of FRP Prestressed Beams
Design approach
1. Balanced
Section
2. Reinforcement
Ratio
3. Cracking
Moment
4. Flexural
Capacity
a. Strains and
stresses in
tendons
b. Internal
forces in the
section
c. Nominal
moment
capacity
Ref: Grace and Singh (2003): ACI Structural Journal
Experimental Studies and Validation of Design Approach
Ref: Grace and Singh (2003): ACI Structural Journal
Full Scale test of Double Tee Beams
An experimental study was conducted in Lawrence Technological
University (LTU), Michigan, USA
A special purpose computer program was developed to compute the overall
response of the beams such as deflections, strains, cracking loads,
and post-tensioning forces.
The design equations and the accuracy of the nonlinear computer
program were validated by comparing the analytical results with
experimental results from a full-scale Double-Tee (DT) test beam
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Load Vs. Deflection Response
Ref: Grace and Singh (2003): ACI Structural Journal
Energy Ratio Based Ductility Index
Ref: Grace, Singh, Mathew, Shenouda (2004), PCI Journal
Scope for Engineering Construction Companies
Successful Deployment of CRRP PrestressingTechnology
Bridge Street Bridge, Southfield,MI,USA(First vehicular FRP
prestressed bridge in USA)
Bridge Street Bridge, City of Southfield, Michigan,USA( Construction Site)
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Scope for Structural Repair and Rehabilitation Companies
An experimental study:
Examined the efficiency of the CFRP plates in strengthening of the RC beams.
All flexural specimens loaded to a predetermined cracking load to simulate a deficient structure. Strengthened with CFRP plates using the proper epoxy adhesive. Specimens were then loaded to failure.
Significantly improved the load carrying capacity of the beams. Debonding of the plates and concrete shear failure were failure modes in all of the strengthened beams
Strengthening In Flexure
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Strengthening of Negative Moment Regions of RC Beams
An experimental study:
The first strengthening of beams was designed to fail in flexure, while the second dealt with strengthening of beams designed to fail in shear
Figure shows failures in some of tested beams by debonding of the plates
The maximum stress experienced in the CFRP plates was observed to be 52% of their ultimate load carrying capacity for the beams designed to fail in flexure and 28.5% for the beams designed to fail in shear
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Shear Strengthening
An experimental study:
The strengthening of beams in shear was dealt with using three different lay-ups (45°, 0°/90°, and 0°/90°/45°) of CFRP fabric sheets on the beams
A total of four beams were tested while the fourth beam was unstrengthened and served as the control beam.
It was also noted that there exits a critical value of shear force up to which there is no appreciable strain in the beam
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Shear Strengthening
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Scope for Concrete Industry (Engineered Mortar/Precast/Ready-mix)
Engineered Cementitious Composites
(Ductile Concrete)
~ Introduction~ Precast Products
~ Micromechanics Based Design of ECC~ Structural Response of FRP/Steel reinforced
ECC beams
How ECC differs from FRC ?How ECC differs from FRC ?
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Precast ECC Products
ECC Ductile plate ECC conoe
Extrusion of a 100mm ECC-pipe
Research Significance
+
=
Brittle FRP materials
Ductile ECC
High flexural strength & Ultra-high ductility
of
structures
Design Approach
Fiber Reinforced Plastics (FRP)Reinforced
Engineered CementitiousComposite (ECC) beam
Verification of Present Analytical Models
Flexural load vs. deflection response has been evaluated analytically
A special purpose computer program was developed
Computer program incorporates the tensile strain hardening behavior of PE-ECC and considers its tensile load carrying capacity
Strain controlled approach
WeightedaverageofYoung’smodulus / Numerical integration of the curvature
Comparison of Load vs. Deflection Curves Beam-GRE16
The curtailment of the simulation is governed by rupture strain
of GFRP bars
Difference in peak
load = 13.1%
Difference in
deflection = 1.6%
Experimental Investigation on ECC
Demonstration of DFRCC as Strengthening Structural Material
Effect of DFRCC Plastic Hinge
Length
Effect of Thickness of
External DFRCC Layer
Response of RC Frames
strengthened with DFRCC
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Beam Design
Over Reinforced Beam
Under Reinforced Beam
Loading Pattern
Effect of DFRCC Plastic Hinge Length & Thickness of DFRCC Layer
Effect of Plastic Hinge Length
Effect of ECC Layer Thickness
Response of RC Beams Strengthened with DFRCC Plastic Hinges
In the present study, a number of parameters such as
Compressive strength of DFRCC
Compressive strength of concrete
Length of plastic hinge
Load span of control beams and load span of strengthened beams
were maintained different for each beam specimen so as to incorporate the
diverse effects of materials and geometry. The load versus deflection
response, the applied load was normalized with a parameter. Normalized
Load Parameter is given below
XParameter
loadAppliedY
,
spanOverall
spanLoad
spanOverall
lengthhingePlastic
f
fXParameter
ecc
ck 1,'
'
Response of RC Over-Reinforced Beams
Strengthened with DFRCC Plastic Hinges
ORPH 600 Load capacity= 6.34 times of the control beam
ORPH 400 Load capacity=4.24 times of the control beam
ORPH 200 Load Capacity= 2.85 times of the control beam
Failure of RC Over-Reinforced Beams Strengthened with DFRCC Plastic Hinges
Ultimate failure of all over reinforced
beams (ORPH 200, ORPH 400 and ORCB) was governed by flexural compression except ORPH 600.
Ultimate failure of ORPH 600 was governed by
one single flexural crack at tension side
Response of RC Under-Reinforced Beams Strengthened with DFRCC Plastic Hinges
URPH 600 Load Capacity= 4.83 times of control beam
URPH 400 Load capacity =1.72 times of control beam
URPH 200 Load Capacity= 1.55 times of control beam
Failure of RC Under-Reinforced Beams Strengthened with DFRCC Plastic Hinges
Ultimate failure of all UR beams was governedby flexural tension. Beams URPH 200 andURPH 400 exhibited multiple microcracks atECC plastic hinge zone.
But beam URPH 600 did not show multiple cracks and its failure was similar to beam ORPH 600 with one single crack at tension side.
Response of RC Beams Strengthened with DFRCC Layer
In the present study, a number of parameters such as
Compressive strength of concrete
Thickness of DFRCC Layer
Load span of control beams and load span of strengthened beams
were maintained different for each beam specimen so as to incorporate the
diverse effects of materials and geometry. The load versus deflection
response, the applied load was normalized with a parameter. Normalized
Load Parameter is given below
MParameter
loadAppliedY
,
spanOverall
spanLoad
depthOverall
LayerECCofThickness
f
fMParameter
ecc
ck 1,'
'
Response of RC Under-Reinforced Beams Strengthened with DFRCC Layer
URLY 70 (Load capacity= 8.31 times of control beam)
URLY 50 (Load capacity=5.37 times of control beam)
Failure of RC Under-Reinforced Beams Strengthened with DFRCC Layer
Ultimate failure of allUR beams occurreddue to flexuraltension accompaniedby yielding of internalsteel rebars.
Unlike under reinforced ECC strengthened plastic hinge beams, the under reinforced layered ECC beams have not shown microcracks.
The failure was governed by a single flexural crack at the tension side.
Response of RC Over-reinforced Beams Strengthened with DFRCC Layer
ORLY 70mm (Load capacity =8.45 times of control beam )
ORLY 50mm (Load capacity=5.71times of control beam)
Failure of RC Over-Reinforced Beams Strengthened with DFRCC Layer
Ultimate failure of allOver-reinforcedstrengthened beamsoccurred due tocrushing of concreteat Compression side
Applications of DFRCC in RC Frames as Strengthening Material
Steel Reinforced DFRCC FramesTotal of Steel reinforced DFRCC
frames (6 Nos.)
Category I – 3 Nos. (Detailed as per IS 13920-2002)
Category II – 3 Nos. (Detailed as per IS 456-2000)
Fully DFRCC
Fully Concrete
Both DFRCC & Concrete
Frame Design Following IS 13920-2002
Frame Design Following IS 456-2000
Loading Pattern
Load vs. Deflection Response for IS 13920-2002 Frames
33 % More load carrying capacity & 2 times more ductile
21.8 % More load carrying capacity & less ductile*
Load vs. Deflection Response for IS 456-2000 Frames
0
6
37.2 % More load capacity & 1.5 times more ductile
27.2 % More load capacity & 2.8 times more ductile
Category Frame Yield
deflection,
mm
Ultimate
deflection,
mm
Ductility
factor
Failure
mode
1 CON 13920 6.36 11.77 1.85 Flexural compression
and moderately brittle
DFRCON
13920
6.93 8.06 1.16 Flexural tension and
local failure
DFR 13920 4.52 17.08 3.78 Flexural tension with
multiple micro cracks
and highly ductile
2 CON 456 4.49 5.44 1.21 Flexural compression
and highly brittle
DFRCON
456
4.35 14.65 3.37 Flexural tension and
highly ductile
DFR 456 6.0 11.11 1.85 Flexural tension with
multiple micro cracks
and ductile
CONCLUSIONS
Fiber Reinforced Polymers are potential constructionmaterials and they give lot of scope for various industries likeComposite, Structural Consultancies, ConstructionCompanies, Repair & Rehabilitation Companies andConcrete industries.
These materials always need performance based designapproaches for better exploitation of the material strengthand economy.
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CONCLUSIONS (Contd..)
NSM hybrid FRP rods provide a promising reinforcing technique to enhance theflexural capacity of ductile fiber reinforced cementitious composites (DFRCC) beamsfabricated with engineered cementitious composites (ECC) materials with significantwarning and cost effectiveness based on replacement of carbon fibers with low costglass fibers without compromising the strength of DFRCC beams. Among the varioustested beams, the strengthened ones showed an increase in capacity ranging from42% to 53% over the control beam, which demonstrates the effectives of NSM FRPbars for rehabilitation of beams under flexural loading. Moreover, it also exhibits thecost effectiveness by incorporating the hybrid configuration of FRP systems.
However, it appears that the bond strength between FRP bars and the beamis of critical importance for the effectiveness of this technique. Maximumstrength of FRP rods could not be achieved due to bond failure. Therefore, allthe different compositions show somewhat similar results. Hence, it may bepoint of future research to find the solution for preventing the debondingmode of failure of NSM bars reinforcing ECC beams
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CONCLUSIONS (Contd..)
Experimental study conducted on framedstructures has provided additionalconfidence to use DFRCC as potentialstrengthening material in RC structures
Further research programme of this project will focus ondeveloping hybrid FRP systems with improved ductileresponse and its applications for strengthening the masonrybeams, columns and walls for developing low cost masonrystructural elements. Moreover, a design approach will also bedeveloped to design the FRP reinforced ECC beams andmasonry structures (beams and columns).
CONCLUSIONS (Contd..)
Generalized stress-strain relationships are developed for PE-ECC in tension and compression. Using developed stress-strain relationships, a unified design approach is presented for flexural strength prediction of FRP reinforced PE-ECC beams.
Design equations derived herein predict the balanced ratio, depth of neutral axis section, moment carrying capacity which are in close agreement with experimental results available in literature. Close agreement between analytical and experimental results shows the robustness of the developed stress-strain models.
In general, for a specific size configuration, it is observed that for a given load, deflection is higher for the lower reinforcement ratio.
CONCLUSIONS (Contd..)
Conventional definition of section being under-reinforced or over-reinforced based on balanced ratio is not consistent with experimental results for ECC beams. Hence, more experimental investigations are required to investigate the correlation between flexural crushing strain and crushing strain from uni-axial test
Acknowledgements
DST – New Delhi (ECC Project)
CSIR- New Delhi (PostbucklingStrength of Laminated Composite
Plates)
UGC – New Delhi (NSM Project)
Aditya Birla Group Companies
&
UKIERI Research Collaboration
KK Birla Academy Projects, BITS-Pilani
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