Presentation on theme: "Structure Repairs & Rehabilitation In Low Strength Masonry Buildings"— Presentation transcript:
1Structure Repairs & Rehabilitation In Low Strength Masonry Buildings Presentation From TSG
2Structure Repairs & Rehabilitation Low Strength Masonry Building is Laid inFired brick work in clay & mud mortarRandom rubble ; Uncoursed, Undressed stone masonry in weak mortars made of cement-sand , lime-sand & clay-mud.
3Structure Repairs & Rehabilitation Component Of Low Strength Masonry Building:FoundationFlooringBrick/ Stone ColumnsBrick WorkStone MasonryWood WorkSlabSlopping Wooden frame RoofPlasterR.C.C. Frame work is not included In low strength masonry building.
4Structure Repairs & Rehabilitation Life Of Structure Depend Upon:Geography Of LocationBuilding MaterialTechnologyWorkmanship
5Structure Repairs & Rehabilitation A . Geography Of Location:Type of StrataWater TableEarth Quack, Wind, Cyclone, Flood, SnowPollutantLand SlideTree location w.r.t. building
6Structure Repairs & Rehabilitation B . Building MaterialsCementLimeFine SandCoarse SandCoarse AggregateQuality of WaterBamboo/WoodBrickContent of free lime in cement; Alkalinity in aggregate; Sulphate in soil & Brick; quality of water w.r.t. salts & defects & water content in wood
7Structure Repairs & Rehabilitation C. TechnologyArchitectural DesignStructural Design Based On Load Bearing WallConstruction MethodsQuality PracticesConstruction ManagementGenerally Low strength masonry wall is non engineering building as these are neither designed nor supervised by technical persons.
8Structure Repairs & Rehabilitation D WorkmanshipStructural WorkFinishing WorkWater Proofing WorkDevelopment of Drainage (Internal & External)Maintenance Of BuildingIn absence of proper supervision its construction quality rest on skills of masons, carpenters. It does not mean that all these buildings cannot survive disasters.
9Structure Repairs & Rehabilitation Building Needs Repairs & RetrofittingCrack & Spalling In Structural MembersCrack & Settlement In FlooringCrack & Spalling in Non Structural MembersLeakage In Water Supply & Drainage SystemRedesigning existing structure for nature forcesChanged functional requirementsRetrofitting 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.
10Structure Repairs & Rehabilitation Crack & Spalling In Structural MembersCracks Occur Due To Settlement In FoundationCracks Due To Earth Quack ,WindCrack Due To Overloading Of StructureCrack Due To Reduction in Load Carrying Capacity of Structure Due To WeatheringCrack Due To Improper Design Of StructureCrack due to Poor connection Of Structural Members Resulted From Poor Workmanship
11Structure Repairs & Rehabilitation Crack & Settlement In FlooringDue To Improper Plinth FillingIn 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.
12Structure Repairs & Rehabilitation Crack & Spalling in Non Structural MembersCrack In PlasterCrack In FinishingCrack In Water Proofing WorkVertical 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 ReactionsThis is broad listing of non structural cracks
13Structure Repairs & Rehabilitation Leakage In Water Supply & DrainageIt may result from structural cracks & settlementImproper selection of pipe thicknessImproper selection of Supports & its spacing to PipeImproper making Of jointsNon Provision for contraction & expansion (Particularly when pipe is passing over different type of long structures)Non Testing of Pipe before & after layingInsufficient soil cover over pipeMasonry 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.
14Structure Repairs & Rehabilitation Redesigning existing structure to meet functional requirement as well as forces generated by NatureIt is a comprehensive task & require planning which include following Information gathering.Field investigations including details of sub strata, foundation detailsType of Existing structure & its members stabilityDesign Data CollectionIdentification 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.
15Structure Repairs & Rehabilitation Crack InvestigationLocationProfile (vertical, Horizontal, Diagonal)Crack Size throughout length (Width,Depth & length)Thin crack< 1mmMedium Crack >1 to 2 mmWide Crack > 2 mmCrack may be non-uniform width. i.e. Tapper in width(narrow at one end & wider at other end. )Static or Live cracksCracks Investigations are necessary to find out correct solution for effective retrofitting.
16Structure Repairs & Rehabilitation Cracks are static or live, is monitored & recorded by “Tell-Tale” methodWidening Of CrackCrack in wallQuick setting mortar or AdhesiveMarking in GlassCrack in Glass stripsCracks are static or live, is monitored & recorded by “Tell-Tale” methodIn 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 C.M.in length
17Structure 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).
18Structure Repairs & Rehabilitation Expansion & thickening of roots creating concentration of stress at joints & weak locations such as openingsSlide showing effect of vegetation on building
19Structure 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.
20Structure 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
21Structure Repairs & Rehabilitation Construction Details Of Bearing Of R.C.C. Roof Slab Over a Masonry WallConcrete FilletBrick tiles or Cement mortar with chequer grove finish12 mm Gap ,3/4 filled with Mastic CompoundFirst Course Of parapet masonry is thicker than the wall By half BrickControl 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 plasterSlip Joint(two or three layer of tarred paper are placed over plastered surface)
22Structure Repairs & Rehabilitation Thickness of plaster is to much high & silt content is also Very HighSlide is showing Spilling of plaster.
23Structure Repairs & Rehabilitation Longer opening & less bearing & deteriorated lintel load capacity exposes diagonal crack which is widened towards corner wall edge.
24Structure 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.
25Structure Repairs & Rehabilitation Cantilever Chajja not having main bars on upper face
26Structure 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.
27Structure 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.
28Structure 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.
29Structure 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.
30Structure Repairs & Rehabilitation Flexural Tension Cracks At Lintel Level Due to Shrinkage & contraction of R.C.C. Slab
31Structure 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.
32Structure Repairs & Rehabilitation Many times the roof slides on top of the walls on which it is sitting on
33Structure Repairs & Rehabilitation Structural Repairs Load Bearing Walls: PROCEDURE IN NEXT SLIDECRACK IN BRICKPLACING 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.
34Structure Repairs & Rehabilitation Repairing Of Crack Due To Structural CauseReplace all cracked bricksUse R.C.C. Stitching Block In Vertical Spacing In Every 5th or 6th Course ( 0.5 meter apart ).Stitching blockWidth=equal to wall width,Length = 1.5 to 2 bricks,Thick =1 or 2 bricks as per severity of cracksMortar For Repairs 1:1:6 (1 Cement :1 lime: 6 sand)We have to temporary support the roof before strengthening the wall.
35Structure Repairs & Rehabilitation load bearing walls(May be Brick or Stone) have inbuilt deficiency.Each Brick have different strengthThickness of Mortar Joints are not also uniform.Bricks are not perfectly laid horizontally & verticallyOpening in wallsImproper staggered jointsUse of unwanted Brick bats1. These resulted in cumulative effect & concentration of stress in particular section of wall is more than other section.
36Structure Repairs & Rehabilitation Corrective Measures For Load Bearing Wall BuildingTherefore Shifting of Window, Door ,Inbuilt construction of Almirah should be carried out with due consideration to IS code 13828:1993Proper 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.
37Structure Repairs & Rehabilitation Importance Factor(I) Depend UponFunctional Use Of StructuresHazardous Consequences Of Its FailurePost Earthquake Personal needsHistorical ValueEconomic ImportanceSchool Building Have “I” value=1.5We 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” valueZoneIIIIIIVV1.5Building Retrofitting needCDE
38Structure Repairs & Rehabilitation Elevation : Distance b1 to b8 changes as per Building Retrofitting Needl1l2b8t3h3b7b1b2b3b622h2b412h21h1This 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.b5b4b5b4b4
39Structure Repairs & Rehabilitation Table :Size, Position Of Opening In Above FigureDescriptionBuilding Retrofitting Need/CategoryA,B,CD`b6 (Minimum)230 mm600 mm(b1+b2+b3)/l1; (b6+b7)/l2 =0.46 ( For one Storeyed Building )0.42 ( For one Storeyed Building )`b4450 mm500 mm`h3 (minimum)`b8900 mm0.37 ( 2 & 3 storeyed (2 & 3 storeyed Building) Building)This is a table for finding type of need for strengthening of a wall having openings.
40Structure Repairs & Rehabilitation Strengthening Of Window When Its Position Is Not As Per Table Above Slide No 42.10 Ø603075150Window6 150XXTwo Nos HYSD BarsStrengthening of window. there are two band sections depending upon wall thickness .Section X-X
41Structure Repairs & Rehabilitation Strengthening Arrangements Recommended For low Strength Masonry Buildingb = Lintel BendC = Roof Bend, Gable bendd = Vertical steel at corners & junctions of wallf = Bracing in plan at tie level of Pitched Roofsg = Plinth bandFor 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
42Structure Repairs & Rehabilitation Strengthening Arrangements Recommended For Elements of low Strength Masonry BuildingBuilding CategoryNumber Of Storey AllowedStrengthening To Be ProvidedAOne, Two, Three storey`b, c ,f ,gBOne & Two StoreyThree Storey`b, c, d, f, gCOne storey`b, c ,f , gTwo & three storeyDIn 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.
43Structure 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.
44Structure Repairs & Rehabilitation Possibility For Old Masonry Structures StrengthPlinth Belt in lieu of plinth bandLintel level belt in lieu of bandRoof level/ gable level bandCorner steelShape, Size & location of Window In WallWall length to Height RatioCross wall/ Brick Pillar/counter fort
45Structure Repairs & Rehabilitation Reinforced band on top of gable wall It will reduce bending of gable wall
46Structure Repairs & Rehabilitation In long walls introduce buttress to strengthen it.
47Structure Repairs & Rehabilitation Low Strength Masonry Building RetrofittingFor Brick Masonry StructureHeight 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 .
48Structure 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.
49Structure Repairs & Rehabilitation For Stone MasonryHeight of the building in Stone Masonry shall be restricted to the followingFor 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.
50Structure 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
51Structure Repairs & Rehabilitation Cross wall connection In stepsSECOND LIFT600 mm600 mmThis is one of method to leave construction joints in masonry as per code provision You will find next slide in practical.FIRST LIFT
52Structure Repairs & Rehabilitation Wall to wall joints are to be made by building wall ends in steps form
53Structure Repairs & Rehabilitation Vertical reinforcement within the masonry in corners increases wall’s capacity to withstand Horizontal cracks due to bending.
54Structure Repairs & Rehabilitation In Each Layer Staggered Toothed JointY A BX PLAN230 mmABElevation Showing Vertical Joints In Staggered Layer115 mmThis is a second method to leave construction joints in each layer staggered in load bearing walls.450 mm230 mmView-X At A-AView- Y At B-B
55Structure Repairs & Rehabilitation Recommended Longitudinal steel in Reinforcement Concrete Bends Span of Band Between Cross WallBuilding Category “B”Building Category “C”Building Category “D”Building Category“E”In MMNo. Of BarsDia. Φ MMDia.ΦMM5 or Less281061274This is a table for recommending longitudinal steel in bends.Spacing Of Tor Ring/Links mm Or mmBands Thickness vary 75 mm for 2 bars & 150 mm for 4 bars
56Structure Repairs & Rehabilitation Steel Profile In Band At Corner & JunctionLap= 50 ф Staggered
57Structure Repairs & Rehabilitation Pair of stone with length= ¾ of wall thicknessBonding ElementsA. Wood Plank( 38x38x450 mm)B. R.C.C. Block(50x50x450 & 8 mm)C. 8 or 10 mm Hookor “S” shape bent BarPlan showing Through StoneThrough stone = Bonding Element≤ 450≤ 1200≤ 1200≤ 1200Bond 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 Height600 mm For First Height
58Structure Repairs & Rehabilitation “S” shaped steel rod placed in a through hole in random rubble wall and fully encased in concrete
59Structure Repairs & Rehabilitation Pair of stone with length= ¾ of wall thicknessPlan 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≤ 1200CLAfter raising stone masonry of 0.6 m ,casing around the bar is lifted for casting.
60Structure Repairs & Rehabilitation Half Split Bamboo Ties To RafterBrace the Rafter to 50 mm Dia Bamboo (B)Seismic Bend & Rafter should be tied ProperlyCross bracings at ends of roomXThree Nails 5Ø drilled in member made by splitting bamboo in two partBProvide cross bracing in both gable ends & use three nails instead of two & tie seismic bend to rafter using G.I.wire or suitable mean.
61Structure Repairs & Rehabilitation Diagonal tying on the upper or underside of the roof Prevents roof from getting distorted and damaged
62Structure Repairs & Rehabilitation Installing multiple strands of galvanized iron wires pulled and twisted to pretension
63Structure 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 tableNos Of StoreyStoreyDiameter Of H & D Single HYSD Bar in mm at each critical Section (for above 350 mm, increase bar dia proportionallyCategory CCategory DOneNil10TwoTopBottom12ThreeMiddleVertical Steel Reinforcement up to 350 mm thick Low Strength Masonry Walls as per Table
64Structure Repairs & Rehabilitation One Brick Thick One & Half Brick Thick Contain One Bar At Centre3/4BConstruction of masonary wall with vertical bar encashing
65Structure Repairs & Rehabilitation Seismic Belts & closing a opining with pockets made in jams of masonry.Pockets
66Structure Repairs & Rehabilitation Encasing masonry column in cage of steel rods and encased in micro concrete.
67Structure Repairs & Rehabilitation Anchoring the roof rafters and trusses with steel angles or other means
68Structure Repairs & Rehabilitation Weld mesh belt approximately 220mm wide all around the openings and anchored to masonry wall and encased in cement mortar
69Structure Repairs & Rehabilitation Vertical deformed steel encased in concrete bar from foundation to roof, anchored to both masonry walls at wall junctions with special connectors.
70Structure 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.
71Structure Repairs & Rehabilitation Use smaller glass panes for windows Prevents the shattering of glass in earthquake and cyclone
72Structure Repairs & Rehabilitation Anchoring roof to wall &, reducing roof overhangs, prevent the roof from getting blown off
73Structure Repairs & Rehabilitation Prolonged flooding can weaken the mortar, especially if it is mud mortar, and hence, the wall, causing cracking in walls or collapse.
74Structure 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.
75Structure Repairs & Rehabilitation Simple erosion of wall near its bottom, or cracking, plaster peeling off and settlement in floor.
76Structure Repairs & Rehabilitation Too small ProjectionLeaking RoofDeficient bearing length of lintelsMore Than One Story BuildingDoor & Window Opening to largeExposed walls without plaster or PointingOpenings to closer to cornerThis slide shows one or multiple Causes of failure for low strength masonry structure due to heavy rain or floodVertical Joint Without MortarLack Of foundation & plinthWall to high & too LongUnbroken joint at corner
77Structure Repairs & Rehabilitation Extensive cracking of walls caused by differential settlement due to flood
78Structure 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.
79Structure Repairs & Rehabilitation Use of pilasters strengthens walls against flowing waterIf thatch is used, cover with waterproof mud plasterUse band below roof truss/rafterProjected Roof Maxm 0.5 mOpening 1.2 m From CornerButtress in long wallThis Slide shows flood & heavy rain resistant construction features.Waterproof mud plaster or cement plasterDamp proof at PlinthFoundation & plinthLow height wall Maximum 8 times thicknessGood bonding Mortar
80Structure 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