unit-5 retrofitting.pptx B.Arch Vth year

B.Arch_DRA_ RETROFITTING

1. AR17B9.1E DISASTER RESISTANT ARCHITECTURE Seismic Strengthening of building BY Ar. Sudeshwar Kumar Associate Professor VCAP-Visakhapatnam Ar. Sudesh 7/9/2024 1

2. INTENT Seismic Strengthening and retrofitting techniques of building:- Ar. Sudesh 7/9/2024 2

3. Introduction Ar. Sudesh 7/9/2024 3 Earthquake creates great devastation in terms of life, money and failures of structures. Earthquake Mitigation is an important field of study from a long time now. Seismic Retrofitting is a collection mitigation techniques for Earthquake Engineering. It is of utmost importance for historic monuments, areas prone to severe earthquakes and tall or expensive structures.

4. Ar. Sudesh 7/9/2024 4 Some of the most significant disasters in the last hundred years caused by earthquake results a loss of about 2,03141 human lives, besides damage to property and infrastructure. Around 60% of the country’s landmass is prone to moderate, high or severe earthquake risks. North- east experiences earthquake of average magnitude >6.0 every year which causes huge losses to property. Introduction

5. Ar. Sudesh 7/9/2024 5 Introduction

6. DEFINITION OF RETROFITTING Ar. Sudesh 7/9/2024 6 Ter m s ar e assoc i at e d to ret ro f i tt i n g w i t h a marg i nal difference like Repair, Strengthening, Remolding , Rehabilitation, Reconstruction, Re-engineering etc. The most common definitions of Retrofitting are To upgrade the earthquake resistance up to the level of the present day codes by appropriate techniques (IS 13935: 1993) Increasing the seismic resistance of a damaged building is called retrofitting. ( Tomazevic , 1999) It is an upgrading of certain building system, such as mechanical, electrical, or structural, to improve performance, function, or appearance (Newman, 2001). It is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes.

7. Ar. Sudesh 7/9/2024 7 Need of Retrofitting The buildings have been designed according to a seismic code, but the code has been upgraded in later years . Bui l d i ngs des i gne d t o mee t t h e mode rn se i smic code s , but deficiencies exist in the design and /or construction . Essential buildings must be strengthened like hospitals, historical monuments and architectural buildings . I m por t ant bui l dings whose s ervice is assumed t o be essential even just after an earthquake . Bui l d i ngs, the u se o f wh i ch has c han g ed through the years . Buildings that are expanded renovated or rebuilt . Earthquake damaged buildings

8. Concepts of Retrofitting Ar. Sudesh 7/9/2024 8 Up gradation of the lateral strength of the structure Increase in the ductility of structure Increase in strength and ductility

9. Ar. Sudesh 7/9/2024 9 Consideration in Retrofitting of Structures Retrofitting principally depends on the horizontal and vertical load resisting system of the structure and the type of materials used for parent construction . It also relies on the technology that is feasible and economical . The understanding of mode of failure, structural behaviour and weak and strong design aspects exercise considerable influence on selection of retrofitting methods . Usually, retrofitting method is aimed at increasing the lateral resistance of the structure .

10. Ar. Sudesh 7/9/2024 10 Consideration in Retrofitting of Structures cont.... Avoid an irregular stiffness distribution in the retrofitted structure . It is suggested that the design of retrofitted schemes should be based on drift control rather than on strength consideration alone . The use of three-dimensional analysis is recommended to identify and locate the potential weakness of the retrofitted building .

11. Ar. Sudesh 7/9/2024 11 Structural Damage due to Lack of Deformation Due to limited amount of ductility and the inability to redistribute load . The mos t co m mo n region s o f fa ilure in an existi n g reinforced concrete frame are

12. Ar. Sudesh 7/9/2024 12 Quality of Workmanship and Materials There are numerous instances where faulty construction practices and lack of quality control have contributed to the damage The faulty construction practices may be like, lack of amount and detailing of reinforcement as per requirement of code particularly when the end of lateral reinforcement is not bent by 135 degrees as the code specified Many buildings have been damaged due to poor quality control of design material strength as specified, spalling of concrete by the corrosion of embedded reinforcing bars, porous concrete, age of concrete, proper maintenance etc.

13. Ar. Sudesh 7/9/2024 13 Classification of Retrofitting Techniques There a r e tw o way s to enh a n c e th e seism i c capacity of existing structures Structural-level approach of retrofitting Global modifications to the structural system Member level approach or local retrofitting Inc rease o f th e ducti l ity o f c ompone n t s w i t h ade q uate capacities to satisfy their specific limit states

14. Ar. Sudesh 7/9/2024 14 Classification of Retrofitting Techniques

15. Ar. Sudesh 7/9/2024 15 Structural Level (or Global) Retrofit Methods Conventional Methods Add i ng New Shear Wal l s i n to/onto the Existing Frames Adding Steel Bracing into/onto the Existing Frame Adding Infill Walls into/onto the Existing Frames Non-Conventional Approach Seismic Base Isolation/ Supplemental Damping Devices Global Retrofit Methods

16. Ar. Sudesh 7/9/2024 16 Adding New Shear Walls Fr e quen t ly us e d f or re t r of i t t i ng o f non ductile reinforced concrete frame buildings. The added elements can be either cast ‐ in ‐ place or precast concrete elements. New e l e m ents p r e f e ra b ly b e p l a ced a t t he exterior of the building. Not preferred in the interior of the structure to avoid interior mouldings . In the shear walls, reinforcements are provided vertically in the walls to support the lateral loads and earthquake loads.  Fig: Addit i onal Shear W a l l Global Retrofit Methods (cont....)

17. Ar. Sudesh 7/9/2024 17 Adding New Shear Walls cont.... Technical Considerations De t er m ining the ad e q u a c y o f e x i s t i n g f l oo r and r o o f to c a r r y the seismic forces . Transfer of diaphragm shear into the new shear walls with dowels . Increase in the weight and concentration of shear by the addition of wall, which may affect the foundations

18. Ar. Sudesh 7/9/2024 18 Constructional Considerations To find locations which may align to the full height of the building to minimize torsion It is often desirable to locate walls adjacent to the beam between columns so that only minimum slab demolition is required with connections made to beam at the sides and /of columns The reinforcement has to pass through holes in slabs and around the beams to avoid interference. Wall thickness also varies from 15 to 25cm (6 to 10 inch) and is normally placed externally. Adding New Shear Walls cont....

19. Ar. Sudesh 7/9/2024 19 Adding New Shear Walls cont.... Limitations Increase in lateral resistance but it is concentrated at a few places Increased overturning moment at foundation causes very high uplifting that needs either new foundations or strengthening of the existing foundations Increased dead load of the structure Excessive destruction at each floor level results in functional disability of the buildings Possibilities of adequate attachment between the new walls and the existing structure Closing of formerly open spaces can have major negative impact on the interior of the building uses or exterior appearance

20. Ar. Sudesh 7/9/2024 20 Ste e l br a c ing has a pot e n t ial a dv a n t a g e ov e r o t h er sch e mes f o r t h e following reasons:- Higher strength and stiffness . Opening for natural light can be made easily . Amount of work is less since foundation cost may be minimized The bracing system adds much less weight to the existing structure Most of the retrofitting work can be performed with prefabricated elements and disturbance to the occupants may be minimized Adding Steel Bracing

21. Ar. Sudesh 7/9/2024 21 Adding Steel Bracing - Technical Considerations Technical Considerations Collector’s members are recommended for transferring forces between the frame and bracing system . Careful consideration of connections of strengthening elements to the existing structures and to the foundations have to be consciously designed to ensure proper shear transfer . Local reinforcement to the columns may be needed to bear the increased load generated on them . The epoxies threaded rods have proved to be quite effective in connecting the bracing system to the concrete frame and in transferring the forces .

22. Ar. Sudesh 7/9/2024 22 Adding Steel Bracing - Limitations Limitations Lack o f inf o r mat ion ab o ut t h e s e i s m ic b eha v ior of t h e add e d B racing . Steel bracing system may be sensitive to construction errors or omissions, which cause reduction in member capacity at a section A moderate to high level of skilled labour is necessary for construction, due to the need for member fit-up adjustment and welding Close quality control particularly with respect to welding is essential

23. Ar. Sudesh 7/9/2024 23 Adding Infill Walls It is an effective and economical method for improving strength and reducing drift of existing frames . The addition of masonry infill wall is a viable option for the building, with open ground stories. Infill walls increase strength and stiffness of the building, but do not enhance the ductility. Relatively strong masonry infill may result in a failure of the columns of existing frame The addition of masonry infill wall is a viable option for the building, with open ground stories. Infill walls increase strength and stiffness of the building, but do not enhance the ductility. Column lap splices subjected to large axial force due to frame wall action

24. Ar. Sudesh 7/9/2024 24 Technical Consideration Mode 1: Weak columns, strong beams and strong infill - failure occurs in the columns followed by crushing of infill in the compressive corners Mode 2: Strong columns, weak beams and strong infill - failure occurs in the beam again followed by crushing of infill Mode 3: Strong columns, strong beams and weak infill - failure occurs when corner crushing extends diagonally followed by frame joint failure. Limitations The benefit of retrofitting by infill walls is often limited by failure of splices in existing columns, which act as boundary elements for new infill walls . Adding Infill Walls cont...

25. Ar. Sudesh 7/9/2024 25 Non-Conventional Approach Seismic Base Isolation It is a powerful and relatively cheaper method of seismic rehabilitation of buildings Advantages Bette r p r otec t ion against e arthqu a ke du e to the decreasing of shears Superstructure will need no reinforcement Founda tion sys t em will no t n eed any r e inforcement to resist the overturning moments Least interrupting the building activities, since the work is carried out in the basement Least temporary work is required

26. Ar. Sudesh 7/9/2024 26 Seismic Base Isolation cont.... Process of seismic retrofitting by base isolation in mid storey isolation

27. Ar. Sudesh 7/9/2024 27 Seismic Base Isolation cont.... A typical base isolation system is evolved by the use of rubber bearing located at the base of the building, most often just below the first floor, under columns or shear walls Rubber bearing consists of laminated layers of rubber and steel plates strongly bound together during the vulcanizing process of rubber They are designed with a vertical stiffness, which is usually 300 to 1000 times higher than the horizontal stiffness Such a system increases the first natural period in both the horizontal directions in between the range of 1 to 2.5 seconds and the response acceleration decreases accordingly

28. Ar. Sudesh 7/9/2024 28 Effectiveness of Base Isolation Fig: Comparison Stresses in Z direction for Fixed Base (left) and Isolated Base (right) Seismic Base Isolation cont....

29. Ar. Sudesh 7/9/2024 29 Isolates Building from ground motion Lesser seismic loads, hence lesser damage to the structure. Minimal repair of superstructure. Building can remain serviceable throughout construction. Does not involve major intrusion upon existing superstructure . Advantages of Base Isolation Seismic Base Isolation cont....

30. Ar. Sudesh 7/9/2024 30 Supplemental Damping Devices Use of supplemental damping may be an effective method to resist seismic force The most commonly used approaches to add supplemental dampers to a structure are installing of viscous damper or visco- elastic damper, frictional damper, and hysteretic dampers as components of braced frames

31. Ar. Sudesh 7/9/2024 31 Supplemental Damping Devices cont.... Seismic Dampers are used in place of structural elements, like diagonal braces, for controlling seismic damage in structures. It partly absorbs the seismic energy and reduces the motion of buildings. Types:- Viscous Dampers (energy is absorbed by silicone-based fluid passing between piston-cylinder arrangement), Friction Dampers (energy is absorbed by surfaces with friction between them rubbing against each other), and Yielding Dampers (energy is absorbed by metallic components that yield). Viscous Dampers Friction Dampers Yielding Dampers

32. Ar. Sudesh 7/9/2024 32 Member Level (or Local) Retrofit Methods Jacketing/ Confinement Jacketing is the most oftenly used and one of the most popular methods for strengthening Most common types of jackets are steel jacket, reinforced concrete jacket, fiber reinforced polymer composite jacket, jacket with high tension materials like carbon fiber, glass fiber etc. The main purposes of jacketing are: (i) to increase concrete confinement by transverse fiber/ reinforcement, especially for circular cross-sectional columns, (ii) to increase shear strength Transverse fiber should be wrapped all around the entire circumference of the members possessing close loops sufficiently overlapped or welded in order to increase concrete confinement and shear strength .

33. Ar. Sudesh 7/9/2024 33 Jacketing of Columns

34. Ar. Sudesh 7/9/2024 34 Jacketing of Beams Jacketing of beams is recommended for several purposes as it gives continuity to the columns and increases the strength and stiffness of the structure In jacketing of a beam its flexural resistance must be carefully computed to avoid the creation of a strong beam-weak column system In the retrofitted structure, there is a strong possibility of change of mode of failure and redistribution of forces as a result of jacketing of column, which may consequently cause beam hinging The location of the beam critical section and the participation of the existing reinforcement should be taken into consideration Jacketing of beam may be carried out under different ways the most common are one-sided jackets or 3 and 4-sided jackets The beam should be jacketed through its whole length

35. Ar. Sudesh 7/9/2024 35 Jacketing of Beams cont.... Four sided jacketing Three sided jacketing

36. Ar. Sudesh 7/9/2024 36 Jacketing of Beams cont.... Continuity of longitudinal steel in jacketed beams

37. Ar. Sudesh 7/9/2024 37 Fiber reinforced polymer composite jacket Current research on advanced materials has mainly concentrated on FRP composites. Studies have shown that externally bonded FRP composites can be applied to various structural members including columns, beams, slabs, and walls to improve their structural performance such as stiffness, load carrying capacity, and ductility.

38. Ar. Sudesh 7/9/2024 38 Fiber reinforced polymer composite jacket....

39. Ar. Sudesh 7/9/2024 39 Effectiveness of FRPC as a Retrofitting Material Fig: A 3 - D Model of a Building (a) Wall Stresses before Retrofitting (b) After installation of Ste el W indow frames (c) Addit i onal FRP Re t rofi t t i ng Fig: A Re t rofit Appli c a t ion combining Convention a l and Composites Retrofitting

40. Ar. Sudesh 7/9/2024 40 Conclusion Seismic Retrofitting is a suitable technology for protection of a variety of structures. It has matured in the recent years to a highly reliable technology. But, the expertise needed is not available in the basic level. The main challenge is to achieve a desired performance level at a minimum cost, which can be achieved through a detailed nonlinear analysis. Optimization techniques are needed to know the most efficient retrofit for a particular structure. Proper Design Codes are needed to be published as code of practice for professionals related to this field.

41. Ar. Sudesh 7/9/2024 41 Other techniques for strengthening of building

42. Ar. Sudesh 7/9/2024 42 GROUTING

43. Ar. Sudesh 7/9/2024 43 Other techniques for strengthening of building

44. Ar. Sudesh 7/9/2024 44 Other techniques for strengthening of building

45. Ar. Sudesh 7/9/2024 45 Other techniques for strengthening of building

46. Ar. Sudesh 7/9/2024 46 Disaster Resistant Architecture Write short notes on the following: 1.Causes of earthquake. 2.Seismic waves and its types with suitable sketches. 3.Epicentre and focal point. Assignment-1 Write the following in detail with suitable sketches: 1.Seismic Base Isolation 2.Damping Devices and its type. 3. Classification of Retrofitting Techniques Assignment-2

47. Ar. Sudesh 7/9/2024 47 Disaster Resistant Architecture Write the following in detail with suitable sketches: 1.Seismic Base Isolation 2.Damping Devices and its type. 3. Classification of Retrofitting Techniques Assignment-2

48. Preventing measures for natural disaster. 4 measures ways to prevent natural disasters from becoming human tragedies: Early warning systems for famines. Wonder hunger-products to address malnutrition Giving money directly to the poor so they can help themselves. Mobile technology that informs and empowers citizens.