EARTHQUAKE An earthquake (also known as a quake, tremor or temblor)is the result of a sudden release of energy in the Earths crustthat creates seismic waves. The seismicity, seismism or seismic activity of an arearefers to the frequency, type and size of earthquakesexperienced over a period of time.
INTRODUCTION• Seismic retrofitting of constructions are vulnerable to earthquake. Most of the Indian building stock is vulnerable to seismic action even if located in areas that have long been considered of high seismic hazard. In the past thirty years moderate to severe earthquakes have occurred in India at intervals of 5 to 10 years. Such events have clearly shown the vulnerability of the building stock in particular and of the built environment in general• Aim is to focus on a few specific procedures which may improve the state-of-the-art practice for the evaluation of seismic vulnerability of existing reinforced concrete buildings and for their seismic retrofitting by means of innovative techniques such as base isolation and energy dissipation.
SEISMIC RETROFITTING To provide existing structures with more resistance toseismic activity due to earthquake Includes strengthening of weak connections found in theroof to wall connections, continuity ties, shear walls and roofdiaphragm.
NEED FOR SEISMIC RETROFITTINGTo ensure the safety and security of a building,employees, structure functionality, machinery andinventoryEssential to reduce hazard and losses from non-structuralelementsPredominantly concerned with structural improvement toreduce seismic hazard
SIX MORE REASONS TO SEISMIC RETROFIT Marketability of the building is improved The risk of injury and legal litigation is reduced Earthquake coverage Lenders Insurance companies Tenants
METHODS FOR SEISMIC RETROFITTINGConventional Strengthening MethodsTraditional Methods of seismic retrofittingRetrofit of structures using innovative materialsBase IsolationSupplemental Energy Dissipation and Structural Control
CONVENTIONAL STRENGTHENING METHODSConventional retrofitting method include addition of newstructural elements to the system and enlarging the existingmembers. Methods such as Addition of post cast shear walls Additional foundation to support the shear walls to be constructed around the stairs Concrete jacketing of a column Addition of column members to vertical irregularities
TRADITIONAL METHODS OF SEISMIC RETROFITStructural designMass reduction
Seismic Retrofitting by Mass Reduction (removal of storey)
RETROFIT OF STRUCTURES USING I N N O VAT I V E M AT E R I A L S High Performance Concrete High Performance Steel Fibre Reinforced Plastic
BASE ISOLATION Placing flexible isolation systems between the foundationand the superstructure. Provides safety against collapse. Also used in the seismic retrofitting of historic structureswithout imparting their architectural characteristics byreducing the induced seismic forces.
S U P P L E M E N TA L E N E R G Y D I S S I PAT I O N AND STRUCTURAL CONTROL Cost efficient retrofitting strategy compared to base isolation isinstallation of supplemental energy devices in structures as a meansfor passive or active structural control Objective of structural control is to reduce structural vibrationsfor improved safety and serviceability under wind and earthquakeloadings
Other methods used for seismic retrofit are: Carbon fiber retrofit Mending Application of Reinforced Sheets Aramid Fiber Retrofitting System Precast Retrofit Shear Wall System Pitacolumn Method Tufnes Method Outer-frame brace Taisei Anchor-less Retrofit system
I N N O VAT I V E A P P R O A C H E S Stiffness reduction Ductility increase Damage controlled structures Composite materials Active control
ADVANCED METHODS SDOF equivalent systems Storey force-displacement (Push over analysis) Seismic Resistance in terms of effective Peak GroundAcceleration(PGA)
Table 4: Relative Seismic Resistance R (%) of the Retrofitted Building Seismic Zone Transverse Direction Longitudinal Direction Original Building 43 66 High Seismicity Building + Walls 75 60 SR+W 135 135 Original Building 60 92Medium Seismicity Building + Walls 104 84 SR+W 189 189 Original Building 100 153 Low Seismicity Building + Walls 174 140 SR+W 315 315
Table 5: Seismic Vulnerability V (%) of the Retrofitted Building Seismic Zone Transverse Direction Longitudinal Direction Original Building 57 34 High Seismicity Building + Walls 25 40 SR+W 0 0 Original Building 40 8Medium Seismicity Building + Walls 0 16 SR+W 0 0 Original Building 0 0 Low Seismicity Building + Walls 0 0 SR+W 0 0
Table 6: Seismic Over-resistance OR (%) of the Retrofitted Building Seismic Zone Transverse Direction Longitudinal Direction Original Building 0 0 High Seismicity Building + Walls 0 0 SR+W 35 35 Original Building 0 0Medium Seismicity Building + Walls 4 0 SR+W 89 89 Original Building 0 0 Low Seismicity Building + Walls 74 40 SR+W 215 215
Table 8: Angular Inter-storey Drifts (%) at Limit Base Displacement Direction First Storey Second Storey Third Storey Fourth StoreyTransverse 0.09 0.18 0.20 0.19Longitudinal 0.20 0.16 0.12 0.07
CONCLUSION This paper considers the retrofitting of buildings vulnerable toearthquakes and briefly discuss about the traditional, conventionaland innovative methods of seismic retrofitting. In conclusion it is hoped that the material presented in this paperwill be useful in understanding of the earthquake engineeringproblems and of seismic retrofitting