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Structure Repairs & Rehabilitation In Low Strength Masonry Buildings

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Presentation on theme: "Structure Repairs & Rehabilitation In Low Strength Masonry Buildings"— Presentation transcript:

1 Structure Repairs & Rehabilitation In Low Strength Masonry Buildings
Presentation From TSG

2 Structure Repairs & Rehabilitation
Low Strength Masonry Building is Laid in Fired brick work in clay & mud mortar Random rubble ; Uncoursed, Undressed stone masonry in weak mortars made of cement-sand , lime-sand & clay-mud.

3 Structure Repairs & Rehabilitation
Component Of Low Strength Masonry Building: Foundation Flooring Brick/ Stone Columns Brick Work Stone Masonry Wood Work Slab Slopping Wooden frame Roof Plaster R.C.C. Frame work is not included In low strength masonry building.

4 Structure Repairs & Rehabilitation
Life Of Structure Depend Upon: Geography Of Location Building Material Technology Workmanship

5 Structure Repairs & Rehabilitation
A . Geography Of Location: Type of Strata Water Table Earth Quack, Wind, Cyclone, Flood, Snow Pollutant Land Slide Tree location w.r.t. building

6 Structure Repairs & Rehabilitation
B . Building Materials Cement Lime Fine Sand Coarse Sand Coarse Aggregate Quality of Water Bamboo/Wood Brick Content of free lime in cement; Alkalinity in aggregate; Sulphate in soil & Brick; quality of water w.r.t. salts & defects & water content in wood

7 Structure Repairs & Rehabilitation
C. Technology Architectural Design Structural Design Based On Load Bearing Wall Construction Methods Quality Practices Construction Management Generally Low strength masonry wall is non engineering building as these are neither designed nor supervised by technical persons.

8 Structure Repairs & Rehabilitation
D Workmanship Structural Work Finishing Work Water Proofing Work Development of Drainage (Internal & External) Maintenance Of Building In absence of proper supervision its construction quality rest on skills of masons, carpenters. It does not mean that all these buildings cannot survive disasters.

9 Structure Repairs & Rehabilitation
Building Needs Repairs & Retrofitting Crack & Spalling In Structural Members Crack & Settlement In Flooring Crack & Spalling in Non Structural Members Leakage In Water Supply & Drainage System Redesigning existing structure for nature forces Changed functional requirements Retrofitting is needed to fulfill safety & functional requirement of building. Cracks in building may Be Horizontal, Vertical , Diagonal, and crazy in appearance .sometime cracks are wide at one end & narrow at other end.

10 Structure Repairs & Rehabilitation
Crack & Spalling In Structural Members Cracks Occur Due To Settlement In Foundation Cracks Due To Earth Quack ,Wind Crack Due To Overloading Of Structure Crack Due To Reduction in Load Carrying Capacity of Structure Due To Weathering Crack Due To Improper Design Of Structure Crack due to Poor connection Of Structural Members Resulted From Poor Workmanship

11 Structure Repairs & Rehabilitation
Crack & Settlement In Flooring Due To Improper Plinth Filling In case of black cotton soil in foundation not replaced up to sufficient depth by Good Soil under plinth (For generating enough Counter weight upon black cotton soil) Water Table vary within the Plinth Sub base (this occur in frequent flooding area & near sea soar) Improper curing, Improper laying, Poor Quality of workmanship. Improper design for loading i.e. thickness & type of flooring. There may be many more reasons of cracks or even there may be multiple reasons for a single crack.

12 Structure Repairs & Rehabilitation
Crack & Spalling in Non Structural Members Crack In Plaster Crack In Finishing Crack In Water Proofing Work Vertical cracks in long boundary wall due to thermal movement Or Shrinkage. Crack Induced due to thermal changes, change in moisture content in building material, Chemical Reactions This is broad listing of non structural cracks

13 Structure Repairs & Rehabilitation
Leakage In Water Supply & Drainage It may result from structural cracks & settlement Improper selection of pipe thickness Improper selection of Supports & its spacing to Pipe Improper making Of joints Non Provision for contraction & expansion (Particularly when pipe is passing over different type of long structures) Non Testing of Pipe before & after laying Insufficient soil cover over pipe Masonry work need expansion joint in every 20 meters. This has to be considered while designing piping along such walls. Unattended leakages deteriorate life of structure.

14 Structure Repairs & Rehabilitation
Redesigning existing structure to meet functional requirement as well as forces generated by Nature It is a comprehensive task & require planning which include following Information gathering. Field investigations including details of sub strata, foundation details Type of Existing structure & its members stability Design Data Collection Identification of components required to be strengthened, replaced. Cost Estimates (it is feasible up to 60% of new construction) Method or Procedure to be fallowed. While starting retrofitting we should laid down sequence of activities so that effect of one activity is countered by succsesseding activities.

15 Structure Repairs & Rehabilitation
Crack Investigation Location Profile (vertical, Horizontal, Diagonal) Crack Size throughout length (Width,Depth & length) Thin crack< 1mm Medium Crack >1 to 2 mm Wide Crack > 2 mm Crack may be non-uniform width. i.e. Tapper in width(narrow at one end & wider at other end. ) Static or Live cracks Cracks Investigations are necessary to find out correct solution for effective retrofitting.

16 Structure Repairs & Rehabilitation
Cracks are static or live, is monitored & recorded by “Tell-Tale” method Widening Of Crack Crack in wall Quick setting mortar or Adhesive Marking in Glass Crack in Glass strips Cracks are static or live, is monitored & recorded by “Tell-Tale” method In Sketch 2 ,Marking In both Glass strips is done as soon as strips are fixed on wall. Glass strips of 2 to 3 C.M. in width & 10 to 12 length

17 Structure Repairs & Rehabilitation
These Crack occur around opening due to drying shrinkage & thermal movement in a building resulting weakening in the wall. Vertical cracks over chajja (opening).

18 Structure Repairs & Rehabilitation
Expansion & thickening of roots creating concentration of stress at joints & weak locations such as openings Slide showing effect of vegetation on building

19 Structure Repairs & Rehabilitation
The long horizontal crack resulted due to deflection of slab and lifting up of edge of the slab, combined with horizontal movement in the slab due to shrinkage.

20 Structure Repairs & Rehabilitation
This Cracks are due to pull exerted on the wall by the slab because of drying shrinkage and thermal contraction this pull results in bending of the wall which causes cracking at a weak section, that is, at the lintel or sill level of the window openings. Such cracks generally occurs when windows and room spans are very large. This cracks can be avoided by providing slip joints at slab supports on the walls. This slide showing slip joints

21 Structure Repairs & Rehabilitation
Construction Details Of Bearing Of R.C.C. Roof Slab Over a Masonry Wall Concrete Fillet Brick tiles or Cement mortar with chequer grove finish 12 mm Gap ,3/4 filled with Mastic Compound First Course Of parapet masonry is thicker than the wall By half Brick Control joints are needed to safe wall while edges reinforcement in top of slabs are needed to overcome partial fixidity of slab due to friction over wall. Slip Joint can be made of two or three layer of tarred paper are placed over plastered surface. 12 mm wide groove in plaster Slip Joint(two or three layer of tarred paper are placed over plastered surface)

22 Structure Repairs & Rehabilitation
Thickness of plaster is to much high & silt content is also Very High Slide is showing Spilling of plaster.

23 Structure Repairs & Rehabilitation
Longer opening & less bearing & deteriorated lintel load capacity exposes diagonal crack which is widened towards corner wall edge.

24 Structure Repairs & Rehabilitation
Vertical crack under window occur when wall have large window opening & little wall space on both side of opening. Difference in stress due to more stress in wall portion adjoining to window & less stressed portion under sill of window results in crack.

25 Structure Repairs & Rehabilitation
Cantilever Chajja not having main bars on upper face

26 Structure Repairs & Rehabilitation When two adjacent walls shake in different directions, their joint at corners comes under a lot of stress. This causes crack at the junction of two walls. In Normal conditions, cracks in this location comes when one of wall expand more than short wall. This is one of slide showing cracks due to earth quacks.

27 Structure Repairs & Rehabilitation When the long wall bends outward or inwards vertically in the middle of its length, this stretching causes tension and causes vertical cracks in the walls.

28 Structure Repairs & Rehabilitation Similarly when the walls bends outward or inwards horizontally in the middle of its height, this stretching causes tension and causes horizontal cracks in the walls. This happens at the base of gable wall.

29 Structure Repairs & Rehabilitation Many times the wall gets pulled from its corners. This results in to tearing of wall in diagonal direction. In the wall if there is a window or a door, then the diagonal crack occur at their corners.

30 Structure Repairs & Rehabilitation Flexural Tension Cracks At Lintel Level Due to Shrinkage & contraction of R.C.C. Slab

31 Structure Repairs & Rehabilitation If the window is very large or if there are many doors and windows in a wall, then it tears even more easily in an earthquake.

32 Structure Repairs & Rehabilitation Many times the roof slides on top of the walls on which it is sitting on

33 Structure Repairs & Rehabilitation
Structural Repairs Load Bearing Walls: PROCEDURE IN NEXT SLIDE CRACK IN BRICK PLACING OF RCC BLOCK AFTER CUTTING HOLE IN B.W. This is a important slide. It is a part of exercise to control expanding cracks (generally more than 1.5 mm).Although it is necessary to find causes & eliminating it for ever.

34 Structure Repairs & Rehabilitation
Repairing Of Crack Due To Structural Cause Replace all cracked bricks Use R.C.C. Stitching Block In Vertical Spacing In Every 5th or 6th Course ( 0.5 meter apart ). Stitching block Width=equal to wall width, Length = 1.5 to 2 bricks, Thick =1 or 2 bricks as per severity of cracks Mortar For Repairs 1:1:6 (1 Cement :1 lime: 6 sand) We have to temporary support the roof before strengthening the wall.

35 Structure Repairs & Rehabilitation
load bearing walls(May be Brick or Stone) have inbuilt deficiency. Each Brick have different strength Thickness of Mortar Joints are not also uniform. Bricks are not perfectly laid horizontally & vertically Opening in walls Improper staggered joints Use of unwanted Brick bats 1. These resulted in cumulative effect & concentration of stress in particular section of wall is more than other section.

36 Structure Repairs & Rehabilitation
Corrective Measures For Load Bearing Wall Building Therefore Shifting of Window, Door ,Inbuilt construction of Almirah should be carried out with due consideration to IS code 13828:1993 Proper Bearing to lintel over brick work to avoid diagonal cracks & it can be done in retrofitting work. It is advisable to keep window width as less as feasible while height can be increased with fixed glass pans on top portion as per slide 41.

37 Structure Repairs & Rehabilitation
Importance Factor(I) Depend Upon Functional Use Of Structures Hazardous Consequences Of Its Failure Post Earthquake Personal needs Historical Value Economic Importance School Building Have “I” value=1.5 We have to identify how much degree of rectification is required based on geographical location.Importance factor for school building decided by IS code is 1.5. Zone I has been merged in Zone II by BIS. Rectification measures “A” & “B” is not suited for school building. “I” value Zone II III IV V 1.5 Building Retrofitting need C D E

38 Structure Repairs & Rehabilitation
Elevation : Distance b1 to b8 changes as per Building Retrofitting Need l1 l2 b8 t 3 h3 b7 b1 b2 b3 b6 2 2 h2 b4 1 2 h2 1 h1 This is elevation showing dimensions required while retrofitting is being carried out as per need of school buildings of different seismic zone. These dimensions should confirm next slide criteria. b5 b4 b5 b4 b4

39 Structure Repairs & Rehabilitation
Table :Size, Position Of Opening In Above Figure Description Building Retrofitting Need/Category A,B,C D `b6 (Minimum) 230 mm 600 mm (b1+b2+b3)/l1 ; (b6+b7)/l2 = 0.46 ( For one Storeyed Building ) 0.42 ( For one Storeyed Building ) `b4 450 mm 500 mm `h3 (minimum) `b8 900 mm 0.37 ( 2 & 3 storeyed (2 & 3 storeyed Building) Building) This is a table for finding type of need for strengthening of a wall having openings.

40 Structure Repairs & Rehabilitation
Strengthening Of Window When Its Position Is Not As Per Table Above Slide No 42. 10 Ø 60 30 75 150 Window 6 150 X X Two Nos HYSD Bars Strengthening of window. there are two band sections depending upon wall thickness . Section X-X

41 Structure Repairs & Rehabilitation
Strengthening Arrangements Recommended For low Strength Masonry Building b = Lintel Bend C = Roof Bend, Gable bend d = Vertical steel at corners & junctions of wall f = Bracing in plan at tie level of Pitched Roofs g = Plinth band For Building of Category ‘B’ in two storey constructed with stone masonry in weak mortar, provide vertical steel of 10 mm dia in both storey. This slide showing meaning of alphabet from “b” to “g” used in next slide

42 Structure Repairs & Rehabilitation
Strengthening Arrangements Recommended For Elements of low Strength Masonry Building Building Category Number Of Storey Allowed Strengthening To Be Provided A One, Two, Three storey `b, c ,f ,g B One & Two Storey Three Storey `b, c, d, f, g C One storey `b, c ,f , g Two & three storey D In this slide Retrofitting need “C” & “D” is useful for school building made of low strength masonry building. For retrofitting of label C & D we have to retrofit by b to g elements.

43 Structure Repairs & Rehabilitation
Seismic wave propagation increases as height of wall/structure increases. Seismic wave expansion pushes bricks of corner of wall out of building. Movement of Seismic wave through joints of similar or dissimilar component of building ,makes joint open, resulting in falling of component of the building.

44 Structure Repairs & Rehabilitation
Possibility For Old Masonry Structures Strength Plinth Belt in lieu of plinth band Lintel level belt in lieu of band Roof level/ gable level band Corner steel Shape, Size & location of Window In Wall Wall length to Height Ratio Cross wall/ Brick Pillar/counter fort

45 Structure Repairs & Rehabilitation Reinforced band on top of gable wall It will reduce bending of gable wall

46 Structure Repairs & Rehabilitation In long walls introduce buttress to strengthen it.

47 Structure Repairs & Rehabilitation
Low Strength Masonry Building Retrofitting For Brick Masonry Structure Height of the building in B.W. shall be restricted to the following. For retrofitting category of building A,B,C up to3 storey with flat roof or 2 storey plus Attic for pitched roof. For category D up to 2 storey with flat roof or one storey plus Attic for pitched roof. where each storey height shall not exceed 3.0 m. Cross wall spacing should not be more than 16 times the wall thickness CONTD. This slide provide details for how much story can be added in existing structure for brick masonry .

48 Structure Repairs & Rehabilitation
3. Minimum wall thickness in brick masonry shall be one brick for one & two storey construction, while in case of three storey, the bottom storey wall thickness is one & half brick. 4. Use brick from kiln only after 2 weeks when work is in summer & 3 week when work in winter. 5. Use leaner mortar preferably also adding lime for repairing cracks in particular& in masonry in general. It can be 1:1:6,1:2:9,1:3:12 as per need. Cement mortar exhibit high shrinkage than cement -lime –mortar. Use brick from kiln only after 2 weeks when work is in summer & 3 week when work in winter. Use leaner mortar preferably also adding lime for repairing cracks in particular& in masonry in general. It can be 1:1:6,1:2:9,1:3:12 as per need.

49 Structure Repairs & Rehabilitation
For Stone Masonry Height of the building in Stone Masonry shall be restricted to the following For retrofitting category of building A,B,—2 storey with flat roof or 1 storey plus Attic for pitched roof .In case cement sand mortar 1:6, the building up to 2 storey plus Attic for pitched roof. 2. For category C,D– 2 storey with flat roof or 2 storey plus Attic for pitched roof with Cement sand mortar or 1 storey plus Attic for pitched roof with lime- sand or mud mortar. CONTD. This slide provide details for how much story can be added in existing structure for stone masonry.

50 Structure Repairs & Rehabilitation
3. Maximum wall thickness in stone masonry shall be 450 mm & preferably 350 mm. , Each storey height shall not exceed 3.0 m and span of walls between cross wall is limited to 5.0m

51 Structure Repairs & Rehabilitation
Cross wall connection In steps SECOND LIFT 600 mm 600 mm This is one of method to leave construction joints in masonry as per code provision You will find next slide in practical. FIRST LIFT

52 Structure Repairs & Rehabilitation Wall to wall joints are to be made by building wall ends in steps form

53 Structure Repairs & Rehabilitation Vertical reinforcement within the masonry in corners increases wall’s capacity to withstand Horizontal cracks due to bending.

54 Structure Repairs & Rehabilitation
In Each Layer Staggered Toothed Joint Y A B X PLAN 230 mm A B Elevation Showing Vertical Joints In Staggered Layer 115 mm This is a second method to leave construction joints in each layer staggered in load bearing walls. 450 mm 230 mm View-X At A-A View- Y At B-B

55 Structure Repairs & Rehabilitation Recommended Longitudinal steel in Reinforcement Concrete Bends
Span of Band Between Cross Wall Building Category “B” Building Category “C” Building Category “D” Building Category “E” In MM No. Of Bars Dia. Φ MM Dia. Φ MM 5 or Less 2 8 10 6 12 7 4 This is a table for recommending longitudinal steel in bends. Spacing Of Tor Ring/Links mm Or mm Bands Thickness vary 75 mm for 2 bars & 150 mm for 4 bars

56 Structure Repairs & Rehabilitation
Steel Profile In Band At Corner & Junction Lap= 50 ф Staggered

57 Structure Repairs & Rehabilitation
Pair of stone with length= ¾ of wall thickness Bonding Elements A. Wood Plank ( 38x38x450 mm) B. R.C.C. Block (50x50x450 & 8 mm) C. 8 or 10 mm Hook or “S” shape bent Bar Plan showing Through Stone Through stone = Bonding Element ≤ 450 ≤ 1200 ≤ 1200 ≤ 1200 Bond Stone if not available then in lieu of this “ bonding elements” like wood plank, R.C.C. Block, “S” hook can be provided. 900 mm For Second Height 600 mm For First Height

58 Structure Repairs & Rehabilitation “S” shaped steel rod placed in a through hole in random rubble wall and fully encased in concrete

59 Structure Repairs & Rehabilitation
Pair of stone with length= ¾ of wall thickness Plan showing Center bar in Casing Casing in every 0.6 m is lifted & M15 or Mortar 1:3 is Compacted around bar. ≤ 450 ≤ 1200 ≤ 1200 ≤ 1200 CL After raising stone masonry of 0.6 m ,casing around the bar is lifted for casting.

60 Structure Repairs & Rehabilitation
Half Split Bamboo Ties To Rafter Brace the Rafter to 50 mm Dia Bamboo (B) Seismic Bend & Rafter should be tied Properly Cross bracings at ends of room X Three Nails 5Ø drilled in member made by splitting bamboo in two part B Provide cross bracing in both gable ends & use three nails instead of two & tie seismic bend to rafter using G.I.wire or suitable mean.

61 Structure Repairs & Rehabilitation Diagonal tying on the upper or underside of the roof Prevents roof from getting distorted and damaged

62 Structure Repairs & Rehabilitation Installing multiple strands of galvanized iron wires pulled and twisted to pretension

63 Structure Repairs & Rehabilitation Vertical steel at corners and junction of walls up to 350 mm thick should be embedded in plinth masonry of foundations, bands, roof slab as per table Nos Of Storey Storey Diameter Of H & D Single HYSD Bar in mm at each critical Section (for above 350 mm, increase bar dia proportionally Category C Category D One Nil 10 Two Top Bottom 12 Three Middle Vertical Steel Reinforcement up to 350 mm thick Low Strength Masonry Walls as per Table

64 Structure Repairs & Rehabilitation
One Brick Thick One & Half Brick Thick Contain One Bar At Centre 3/4B Construction of masonary wall with vertical bar encashing

65 Structure Repairs & Rehabilitation Seismic Belts & closing a opining with pockets made in jams of masonry. Pockets

66 Structure Repairs & Rehabilitation Encasing masonry column in cage of steel rods and encased in micro concrete.

67 Structure Repairs & Rehabilitation Anchoring the roof rafters and trusses with steel angles or other means

68 Structure Repairs & Rehabilitation Weld mesh belt approximately 220mm wide all around the openings and anchored to masonry wall and encased in cement mortar

69 Structure Repairs & Rehabilitation Vertical deformed steel encased in concrete bar from foundation to roof, anchored to both masonry walls at wall junctions with special connectors.

70 Structure Repairs & Rehabilitation Seismic belt in lieu of Seismic Band is made of weld mesh approximately 220mm wide anchored to masonry wall and encased in cement mortar.

71 Structure Repairs & Rehabilitation Use smaller glass panes for windows Prevents the shattering of glass in earthquake and cyclone

72 Structure Repairs & Rehabilitation Anchoring roof to wall &, reducing roof overhangs, prevent the roof from getting blown off

73 Structure Repairs & Rehabilitation Prolonged flooding can weaken the mortar, especially if it is mud mortar, and hence, the wall, causing cracking in walls or collapse.

74 Structure Repairs & Rehabilitation If the ground is sandy in which the foundation is sitting, then high speed flood/surge water can scour the land around and under the foundation of your school, leading to settlement and/or cracking of the wall.

75 Structure Repairs & Rehabilitation Simple erosion of wall near its bottom, or cracking, plaster peeling off and settlement in floor.

76 Structure Repairs & Rehabilitation
Too small Projection Leaking Roof Deficient bearing length of lintels More Than One Story Building Door & Window Opening to large Exposed walls without plaster or Pointing Openings to closer to corner This slide shows one or multiple Causes of failure for low strength masonry structure due to heavy rain or flood Vertical Joint Without Mortar Lack Of foundation & plinth Wall to high & too Long Unbroken joint at corner

77 Structure Repairs & Rehabilitation Extensive cracking of walls caused by differential settlement due to flood

78 Structure Repairs & Rehabilitation High plinth level to avoid entering flood
This slide is being shown for high plinth level construction for flooding area & Jali is there to avoid uplift pressure due to cyclone. In Bihar there is no cyclone therefore need not to provide so much jalli.

79 Structure Repairs & Rehabilitation
Use of pilasters strengthens walls against flowing water If thatch is used, cover with waterproof mud plaster Use band below roof truss/rafter Projected Roof Maxm 0.5 m Opening 1.2 m From Corner Buttress in long wall This Slide shows flood & heavy rain resistant construction features. Waterproof mud plaster or cement plaster Damp proof at Plinth Foundation & plinth Low height wall Maximum 8 times thickness Good bonding Mortar

80 Structure Repairs & Rehabilitation
This Presentation was focused on Low Strength Masonry Buildings therefore for framed structures & rich cement mortar building ,certain slides are in-valid. In next Presentation this balance portion will be highlighted. This Presentation was aiming to provide some technical input to site peoples so that we could point out any doubtful detailing in drawings to Structural/Architectural Designer. It is possible that features of Flood, Heavy Rain fall, Cyclone, earth quack may collide but We have to look priority of our geographical requirement. Thank You

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