retrofitting of buildingppt
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240 million houses stock according to 2000 census
85 90 % houses are masonry houses
Stone masonry, Block masonry, Brick masonry
No standardized procedure/ no code
Differs from structure to structure
Depends upon seismic zone
Structural Engineering expert
Structural drawings/ soil data
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Houses not designed to resist earthquakes
People don't know what to do ?
Whether their houses are earthquake safe ?
How strong they are ?
How to make them earthquake safe ?Buildings can be upgraded by minor interventions Seismic Retrofitting
What level of Seismic Retrofitting ?
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Earthquake intensity
Structural configuration and components
Structural condition
Geological condition
Foundation capability
Non-structural components
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Difficulty in estimating the earthquakeparameters, intensity.
Influence of site condition microzonation.
Difficulty in estimation of insitu strength of
materials.
Analytical methods are either unreliable or toocomplex.
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Before the retrofitting to identify the deficiency
After the retrofitting to estimate the adequacyand effectiveness
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Detailed layout (plan and elevation)
Detail of foundation and soil
Structural drawings
Detail of codes used/ design calculations
Vulnerability assessment
If found deficient -retrofitting is done
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Natural frequencies of vibration of the structure
Frequency content of ground motion
Type of local soil and type of foundation
Strength of building material used
Care taken in its detailing for energy absorption
Care taken in construction
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Damage on masonry buildings start from corner separation
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Number of unsafe buildings is alarming
Non-engineered buildings
Faulty original design lack of lateral resistingelements: frames, shear wallsChanges in Codal practicesInadequate detailing of reinforcement
Extensions, Alterations and EncroachmentIncrease in load due to usagePoor and deficient constructionLack of regular maintenance
Degradation of building material/ Corrosion
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Integral box action
Integrity of various components Roof to wall
Wall to wall at corners
Wall to foundation
Limit on openings
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Integral box action
Integrity of various components Roof to wall
Wall to wall at corners
Wall to foundation
Limit on openings
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Many buildings with soft storey collapsed due tofailure of columns at joints in soft storey
The failure occurred due toLack of strength &stiffness of soft storey
strong beam-weak column behaviour of momentresisting frame
lack of ductility due to poor detailing
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Soft storey
Floating columns
In-plane and out-of-plane irregularity
Asymmetric configuration
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Strengthening ExistingMembersReinforcedConcrete Jacketing, Overlay &UnderlaySteel Plate Bonding and Jacketing, Steelsection caging; FRP Plate Bonding and Jacketing
Adding New MembersShearwallsFramesBracingsButtresses
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Conventional cast-in-place concrete
High-strength concrete using shrinkage
compensating admixture
Ferro-cementShotcrete (gunite)
Polymer concrete
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ResinsResin concreteGroutsGluing metal sheets on concreteWelding of new reinforcement
Gluing fibre-reinforced plastic (FRP) sheets onconcreteComposite reinforcing bars
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Fibre reinforced composite
Latest technique in structural rhabilitation
ACS comprises of uni-directional or bi-directional
woven reinforcing fabric saturated with speciallyformulated epoxy matrix
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Quick and easy application procedure results in timeand cost saving
Flexibility of application makes it suitable forapplication on member with any shape or profile
Causes no destruction or disturbance to existing
concreteIt can be used in space constrained areas
No heavy machinery or equipment is required
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It is light weight and easy to install causing nodistress to the member being strengthened
It increases the strength and ductility; enhancesaxial, shear, flexural and tensile capacities
No appreciable increase in member size or deadload
It does not corrode and inhibits further corrosion
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Increasing the size of ground storey columns by jacketing
Addition of RC walls at ground floor
Steel bracings at ground storey
Use of energy dissipating devices such as yieldingbracing or viscous dampers
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Option 1:
Detailed non-linear dynamic analysis to
ensure the deflection of the groundstorey columns to be within safe limits
Option 2: Increased lateral stiffness of the groundstorey to avoid soft storey effect
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The size of the ground storey beams and columns is increased to have the stiffness of theground storey comparable with upper storeys
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The ground storey should be provided with shear walls to increase the stiffness at groundstorey
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THE RESPONSE OF THE STRUCTURE IS
MODIFIED TO REDUCE THE EARTHQUAKEFORCES AND DISPLACEMENTS
STRATEGIES ARE:
1. REDUCTION OF MASS2. BASE ISOLATION3. ENERGY DISSIPATION
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Generally required for large masonry buildings, excavationsare made around the foundations of the building and thebuilding (in piecemeal fashion) is separated from the
foundationsSteel or reinforced concrete beams replace the connectionsto the foundations, while under these, layered rubber andmetal isolating pads replace the material removed, these inturn are attached below to new or existing foundations.
These allow the ground to move while the building,restrained by its inertial mass, remains relatively static.
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Lead rubber bearing
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Directly Increases The Structure DampingLarge relative displacements are required foreffective damping.
More effective in frame structures with large
window openings, than in shear wall buildings.
Sometimes braced frames are required formounting.
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Large Number Seismically Deficient Buildings -QuickAssessment Method
Upgradationof existing buildings is huge job andshould be taken up on buildings importance basis
Government alone cannot do it
Techniques of retrofitting and strengthening shouldbe applied
Techo-financing -tax exemption incentives
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Thank You for your patient hearing