Seismic retrofit of building structures
- 1. SEISMIC RETROFIT OF BUILDING STRUCTURES
- 2. EARTHQUAKE An earthquake (also known as a quake, tremor or temblor) is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time.
- 5. 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.
- 6. SEISMIC RETROFITTING To provide existing structures with more resistance to seismic activity due to earthquake Includes strengthening of weak connections found in the roof to wall connections, continuity ties, shear walls and roof diaphragm.
- 7. NEED FOR SEISMIC RETROFITTING To ensure the safety and security of a building, employees, structure functionality, machinery and inventory Essential to reduce hazard and losses from non-structural elements Predominantly concerned with structural improvement to reduce seismic hazard
- 8. 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
- 9. METHODS FOR SEISMIC RETROFITTING Conventional Strengthening Methods Traditional Methods of seismic retrofitting Retrofit of structures using innovative materials Base Isolation Supplemental Energy Dissipation and Structural Control
- 10. CONVENTIONAL STRENGTHENING METHODS Conventional retrofitting method include addition of new structural elements to the system and enlarging the existing members. 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
- 11. Addition of post cast shear walls
- 12. TRADITIONAL METHODS OF SEISMIC RETROFIT Structural design Mass reduction
- 13. Seismic Retrofitting by Mass Reduction (removal of storey)
- 14. 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
- 15. BASE ISOLATION Placing flexible isolation systems between the foundation and the superstructure. Provides safety against collapse. Also used in the seismic retrofitting of historic structures without imparting their architectural characteristics by reducing the induced seismic forces.
- 17. 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 is installation of supplemental energy devices in structures as a means for passive or active structural control Objective of structural control is to reduce structural vibrations for improved safety and serviceability under wind and earthquake loadings
- 18. 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
- 19. 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
- 20. Damage controlled structures = + Global structure Primary structure Damping system
- 21. ADVANCED METHODS SDOF equivalent systems Storey force-displacement (Push over analysis) Seismic Resistance in terms of effective Peak Ground Acceleration(PGA)
- 30. 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 92 Medium Seismicity Building + Walls 104 84 SR+W 189 189 Original Building 100 153 Low Seismicity Building + Walls 174 140 SR+W 315 315
- 31. 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 8 Medium Seismicity Building + Walls 0 16 SR+W 0 0 Original Building 0 0 Low Seismicity Building + Walls 0 0 SR+W 0 0
- 32. 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 0 Medium Seismicity Building + Walls 4 0 SR+W 89 89 Original Building 0 0 Low Seismicity Building + Walls 74 40 SR+W 215 215
- 33. Table 8: Angular Inter-storey Drifts (%) at Limit Base Displacement Direction First Storey Second Storey Third Storey Fourth Storey Transverse 0.09 0.18 0.20 0.19 Longitudinal 0.20 0.16 0.12 0.07
- 35. CONCLUSION This paper considers the retrofitting of buildings vulnerable to earthquakes and briefly discuss about the traditional, conventional and innovative methods of seismic retrofitting. In conclusion it is hoped that the material presented in this paper will be useful in understanding of the earthquake engineering problems and of seismic retrofitting
- 36. SUBMITTED BY R.Gopinath V.Umapathi
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