Presentation on theme: "Structure Repairs & Rehabilitation In Low Strength Masonry Buildings Presentation From TSG."— Presentation transcript:
Structure Repairs & Rehabilitation In Low Strength Masonry Buildings Presentation From TSG
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.
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
Structure Repairs & Rehabilitation Life Of Structure Depend Upon: A.Geography Of Location B.Building Material C.Technology D.Workmanship
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
Structure Repairs & Rehabilitation B. Building Materials Cement Lime Fine Sand Coarse Sand Coarse Aggregate Quality of Water Bamboo/Wood Brick
Structure Repairs & Rehabilitation C. Technology Architectural Design Structural Design Based On Load Bearing Wall Construction Methods Quality Practices Construction Management
Structure Repairs & Rehabilitation D Workmanship Structural Work Finishing Work Water Proofing Work Development of Drainage (Internal & External) Maintenance Of Building
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
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
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.
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
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
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.
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
Structure Repairs & Rehabilitation Cracks are static or live, is monitored & recorded by “Tell-Tale” method Crack in wall Quick setting mortar or Adhesive Crack in Glass strips Glass strips of 2 to 3 C.M. in width & 10 to 12 C.M.in length Widening Of Crack Marking in Glass
Structure Repairs & Rehabilitation These Crack occur around opening due to drying shrinkage & thermal movement in a building resulting weakening in the wall.
Structure Repairs & Rehabilitation Expansion & thickening of roots creating concentration of stress at joints & weak locations such as openings
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.
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.
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 First Course Of parapet masonry is thicker than the wall By half Brick 12 mm wide groove in plaster Slip Joint(two or three layer of tarred paper are placed over plastered surface) 12 mm Gap,3/4 filled with Mastic Compound
Structure Repairs & Rehabilitation Thickness of plaster is to much high & silt content is also Very High
Structure Repairs & Rehabilitation Longer opening & less bearing & deteriorated lintel load capacity exposes diagonal crack which is widened towards corner wall edge.
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.
Structure Repairs & Rehabilitation Cantilever Chajja not having main bars on upper face
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.
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.
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.
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.
Structure Repairs & Rehabilitation Flexural Tension Cracks At Lintel Level Due to Shrinkage & contraction of R.C.C. Slab
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.
Structure Repairs & Rehabilitation Many times the roof slides on top of the walls on which it is sitting on
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.
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 5 th or 6 th 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)
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.
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.
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 “I” value ZoneIIIIIIVV 1.5Building Retrofitting needCDEE
h2h2 b5b5 b4b4 b7b7 b8 h2h2 b2b2 h1h1 b5b5 Structure Repairs & Rehabilitation Elevation : Distance b1 to b8 changes as per Building Retrofitting Need b1b1 b4b4 b4b4 b6b6 l1l1 l2l2 b3b3 b4b4 t h
Structure Repairs & Rehabilitation Table :Size, Position Of Opening In Above Figure Description Building Retrofitting Need/Category A,B,CD `b6 (Minimum) 230 mm600 mm (b1+b2+b3)/l 1 ; (b6+b7)/l 2 = 0.46 ( For one Storeyed Building ) 0.42 ( For one Storeyed Building ) `b4450 mm500 mm `h3 (minimum) 600 mm `b8900 mm 0.37 ( 2 & 3 storeyed 0.33 (2 & 3 storeyed Building) Building)
150 Structure Repairs & Rehabilitation Strengthening Of Window When Its Position Is Not As Per Table Above Slide No 42. XX Two Nos HYSD Bars Section X-X Window Ø
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.
Structure Repairs & Rehabilitation Strengthening Arrangements Recommended For Elements of low Strength Masonry Building Building Category Number Of Storey Allowed Strengthening To Be Provided AOne, Two, Three storey `b, c,f,g BOne & Two Storey`b, c,f,g Three Storey`b, c, d, f, g COne storey`b, c,f, g Two & three storey`b, c, d, f, g DOne & Two Storey`b, c, d, f, g
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.
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
Structure Repairs & Rehabilitation Reinforced band on top of gable wall It will reduce bending of gable wall
Structure Repairs & Rehabilitation In long walls introduce buttress to strengthen it.
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. 1.For retrofitting category of building A,B,C up to3 storey with flat roof or 2 storey plus Attic for pitched roof. 2.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.
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.
Structure Repairs & Rehabilitation For Stone Masonry Height of the building in Stone Masonry shall be restricted to the following 1.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 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.
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
Structure Repairs & Rehabilitation Cross wall connection In steps 600 mm FIRST LIFT SECOND LIFT
Structure Repairs & Rehabilitation Wall to wall joints are to be made by building wall ends in steps form
Structure Repairs & Rehabilitation Vertical reinforcement within the masonry in corners increases wall’s capacity to withstand Horizontal cracks due to bending.
In Each Layer Staggered Toothed Joint Y A B X PLAN 450 mm Structure Repairs & Rehabilitation 230 mm 115 mm 230 mm A B View-X At A-A View- Y At B-B Elevation Showing Vertical Joints In Staggered Layer
Structure Repairs & Rehabilitation Recommended Longitudinal steel in Reinforcement Concrete Bends Spacing Of Tor Ring/Links mm Or mm Bands Thickness vary 75 mm for 2 bars & 150 mm for 4 bars
Structure Repairs & Rehabilitation Steel Profile In Band At Corner & Junction Lap= 50 ф Staggered
900 mm For Second Height 600 mm For First Height Structure Repairs & Rehabilitation 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 ≤ 1200 ≤ 450 Pair of stone with length= ¾ of wall thickness
Structure Repairs & Rehabilitation “S” shaped steel rod placed in a through hole in random rubble wall and fully encased in concrete
Structure Repairs & Rehabilitation Plan showing Center bar in Casing Casing in every 0.6 m is lifted & M15 or Mortar 1:3 is Compacted around bar. ≤ 1200 ≤ 450 Pair of stone with length= ¾ of wall thickness CLCL
Half Split Bamboo Ties To Rafter Brace the Rafter to 50 mm Dia Bamboo (B) Seismic Bend & Rafter should be tied Properly Structure Repairs & Rehabilitation X Three Nails 5Ø drilled in member made by splitting bamboo in two part B Cross bracings at ends of room
Structure Repairs & Rehabilitation Diagonal tying on the upper or underside of the roof Prevents roof from getting distorted and damaged
Structure Repairs & Rehabilitation Installing multiple strands of galvanized iron wires pulled and twisted to pretension
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 StoreyStoreyDiameter Of H & D Single HYSD Bar in mm at each critical Section (for above 350 mm, increase bar dia proportionally Category CCategory D One Nil10 Two Top10 Bottom1012 Three Top10 Middle1012 Bottom12
Structure Repairs & Rehabilitation One Brick Thick One & Half Brick Thick Contain One Bar At Centre 3/4B
Structure Repairs & Rehabilitation Seismic Belts & closing a opining with pockets made in jams of masonry. Pockets
Structure Repairs & Rehabilitation Encasing masonry column in cage of steel rods and encased in micro concrete.
Structure Repairs & Rehabilitation Anchoring the roof rafters and trusses with steel angles or other means
Structure Repairs & Rehabilitation Weld mesh belt approximately 220mm wide all around the openings and anchored to masonry wall and encased in cement mortar
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.
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.
Structure Repairs & Rehabilitation Use smaller glass panes for windows Prevents the shattering of glass in earthquake and cyclone
Structure Repairs & Rehabilitation Anchoring roof to wall &, reducing roof overhangs, prevent the roof from getting blown off
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.
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.
Structure Repairs & Rehabilitation Simple erosion of wall near its bottom, or cracking, plaster peeling off and settlement in floor.
Structure Repairs & Rehabilitation Lack Of foundation & plinth Wall to high & too Long Openings to closer to corner Door & Window Opening to large Deficient bearing length of lintels Too small Projection More Than One Story Building Leaking Roof Exposed walls without plaster or Pointing Vertical Joint Without Mortar Unbroken joint at corner
Structure Repairs & Rehabilitation Extensive cracking of walls caused by differential settlement due to flood
Structure Repairs & Rehabilitation High plinth level to avoid entering flood
Structure Repairs & Rehabilitation Foundation & plinth Use band below roof truss/rafter Damp proof at Plinth Buttress in long wall Low height wall Maximum 8 times thickness If thatch is used, cover with waterproof mud plaster Projected Roof Max m 0.5 m Opening 1.2 m From Corner Good bonding Mortar Waterproof mud plaster or cement plaster Use of pilasters strengthens walls against flowing water
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