Seismic_Retrofitting_in_Nepalese_Buildin.pptx

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1. SEISMIC RETROFITTING In Nepalese Buildings Presented by: Sujit Bhandari 065/BCE/128 At : Pulchowk Campus, Lalitpur On : January 2012

2. What is Seismic Retrofitting? Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity , ground motion, or soil failure due to earthquakes. Seismic retrofitting is achieved by the inclusion of structural improvements that may prevent the building, people, and the equipment from damage by seismic waves. 2

3. Seismicity in Nepal Most part of the country is seismically active. The history of earthquakes in Nepal suggests every hundred years a significant earthquake strikes. We have faced great Earthquake in 1934 A.D. & 1988 A.D. Recent earthquakes in neighboring countries suggest the risk of earthquake in Nepal. 3

4. Seismicity Map of Nepal Photo Courtesy:National Seismological Centre 4

5. In Nepal … More than 80% of non-engineered structures are vulnerable to earthquake , from mud houses in villages to the moderately large buildings in cities . Buildings lack both strength and ductility because of inferior masonry quality, lean frames, and lack of reinforcements . With their number increasing, the reinforced concrete non-engineered frame buildings in the urban areas of Nepal are unsafe against large impending earthquakes . Nepal’s urban areas face a rapidly growing threat due to the widespread use of improperly reinforced concrete frame building structures. 5

6. Reinforced cement concrete building system: Weak joints of elements Load bearing system of stone in mud: No bands, vertical bars Building of load bearing system: No bands, vertical bars Existing Buildings in Nepal 6

7. Out of Plane Failure Out of Plane Toppling Failure in Nepalese Buildings 7

8. Lack of Bonding Between Walls Lack of Vertical Reinforcement Failure in Nepalese Buildings(contd.) 8

9. More Reasons for Retrofitting The risk of injury and life loss is reduced. Marketability of a building is improved. Earthquake damage can be reduced. The original structure is retained , so a good point for historical and architectural buildings. Building can be used during retrofitting . So, can be used for schools, hospitals, public places. 9

10. Retrofitting Methods Methods Description Polypropylene (PP) Meshing Encasing masonry walls with a mesh constructed of polypropylene strapping Wire Meshing Similar to pp-meshing, but using a steel wire mesh Column Jacketing Addition of external steel around the column Splint and Bandages Addition of steel members and concrete at strategic locations of the building Bracing Additional of diagonal members connecting two vertical members 10

11. Wall Jacketing For masonry infill walls, jacketing can take the form of: shotcreting – the application by spraying a thin layer of concrete onto the face of the brickwork. Reinforcement may or may not be attached to the brickwork before spraying; prefabricated reinforced concrete panels attached, normally, with dowels through the brickwork; steel plates or fiber composite sheets glued/bonded onto the brickwork; or steel strip bracing attached to the brickwork using either through-bolting or some form of chemical bonding agent. 11

12. Wire Meshing in Walls 12

13. PP Meshing After plastering 13 Addition of Polypropylene wires around the walls and columns Ductility and strength is increased PP Meshing

14. PP Meshing Total installation cost was less than 5% of the total construction cost. Project was a collaboration between Oxford University, Tokyo University, Nepal Engineering College, Khwopa Engineering College, the IIT - Bombay and the NSET, Nepal. 14 Thimi (2008-2009)

15. Cross Wall and Buttress Cross Wall Buttress Buttress can give extra strength and resistance against horizontal loads to walls. 15

16. Corner Stitch Stitch are provided at corners to provide connection between walls. 16

17. Splint and Bandages Splint and Bandages are provided at strategic locations like corners, around openings. 17

18. Micro Concrete Work of Splints and Bandage at Sill Level and Placement of New Windows Drilling of Slab for Continuation of Reinforcement Bars for Splints TRI- NAGAR HIGHER SECONDARY SCHOOL BUILDING DHANAGADHI MUNICIPALITY, KAILALI, NEPAL Splint and Bandages 18

19. Steel Bracing The brace connection should be adequate against out-of-plane failure and brittle fracture Center line should pass through the centers of the beam-column joints. Bracing Types 19

20. Steel Bracing Steel diagonal braces (Angle or channel steel profiles) can be added to existing concrete frames 20

21. Column jacketing RC jacketing involves installing new longitudinal and transverse reinforcement as well as concrete Increase both flexural strength, shear strength and ductility 21

22. Column RC Jacketing Chipping and Drilling of Holes Insertion of dowel bars Addition of extra bars should be such that it should be monolithic with the existing column The grade of new concrete should be 5M greater than the grade of existing column 22

23. Column Steel Jacketing • Steel angle profiles placed at each corner of the existing reinforced concrete member connected together as a skeleton with transverse steel straps. • Another way is by providing steel encasement (Complete covering of existing member with thin plates) • Increases its shear strength, • Improves deficient lap splices and • Increases ductility through confinement. 23

24. Increase size of the footing and micro-pile Enlarge the strip footing below the masonry or concrete wall Provide/connect beam/footing below the new shear wall Provide driven piles Provide new raft foundation (when severely insufficient and addition of new floors ) Enhance the foundation soil by grouting Foundation Strengthening 24

25. Foundation Strengthening Enlarging Strip Footing Enlarging Pad Footing 25

26. Retrofitting Methods Selection of Retrofitting Method depends on earthquake intensity at that place, strength of existing building and on use and importance of building. Most practically feasible and economically viable methods in Nepal are wall jacketing and introduction of shear walls or bracing. It is advisable for buildings of 2 to 4 stories high to adopt wall jacketing as a strengthening measure to improve their resistance to large earthquakes. For buildings above 4 stories, shear wall can be provided at required intervals. 26

27. Present Status Awareness raising meetings and workshops are being organized by different governmental and non-governmental organizations like National Society for Earthquake Technology-Nepal (NSET), Center for Resilient Development(CORD) . School Earthquake Safety Program (SESP) run by Nepal Government with aid from UN agencies. Trainings held by governmental bodies to implement the National Building Code. Seismic Evaluation of Blood banks, Hospitals, schools of Nepal. Seismic Retrofitting in different buildings has been done and is being carried out. 27

28. Retrofitted Buildings Schools under SESP: Bhuwaneshwory Lower Secondary School, Nangkhel Gadgade , Nagarkot Upayogi , Sirutar And other more than 50 schools, many in progress. French School, Lazimpat Tri- nagar higher secondary school building , Dhanagadhi municipality, kailali Fire brigade building , Pokhara sub- metropolitan city, kaski And many others 28

29. What to do? Awareness trainings, workshops, and orientations to community people, policy makers, technicians, masons and engineers. Building Code has to develop guidelines for existing structures and implement practical measures to safeguard these buildings. Retrofitting is the best method for existing structures with public importance, so has to be done in public buildings like Hospitals, Blood Banks, Schools, Commercial Buildings , etc. 29

30. Limitations Less development in retrofitting technology Extra Cost involved Less aware clients towards the earthquake risk (towards seismic retrofitting) Lack of suitable standards and codes for retrofitting 30

31. Table Model Analysis of Non-Retrofitted and Retrofitted Model Photo courtesy: NSET 31 Retrofitting Works!!!

32. Lastly, Earthquakes, as such, do not kill people. It is the falling buildings that do! 32

33. References Shrestha , Hari Darshan;Pribadi Krishna S.; Kusumastuti , Dyah ; Lim, Edwin .Manual on Retrofitting of existing vulnerable school bulidings-assesment to retrofitting. Part 1 and 2.Save the children,CQTA,CDM -ITB www.wikipedia.com NSET; The Kathmandu Valley Earthquake Risk Management Action Plan , NSET, Kathmandu,1999 Training and Workshop papers, Nepal Government; UNDP Humagai,Ram Sharan;Pandey,Bishnu H . Implementation of Demonstration Education Project, UNESCO CCT Initiative 33

34. Thank You! 34