Structure Repairs & Rehabilitation Presentation From TSG Structure Repairs & Rehabilitation This presentation is not for low strength masonry building. Low Strength Masonry Building is Laid in • a) Fired brick work in clay & mud mortar • b) Random rubble ; Un coursed, Undressed stone masonry in weak mortars made of cement-sand , limesand & clay-mud Structure Repairs & Rehabilitation Type Of Building Construction based On Design & Supervision • Engineered Building (Designed & supervised By Engineer) • Non-Engineered Building (Built by Mason, Carpenters without Input From Engineer) • Semi Engineered Building (Ex. In masonry Building, where Load bearing wall had not been properly designed. Generally It is built by Architect & Contractors without involving Engineer effectively) • Pre- Engineered Buildings (Those Non Engineered building which comply IS 4326,IS 13827, IS 13828 ,IS 13935) Structure Repairs & Rehabilitation Life Of Structure Depend Upon: A. Geography Of Location B. Building Material C. Technology D. Workmanship Structure Repairs & Rehabilitation Categories Of Seismic Damage Damage Categories Extent Of Damage In General Suggested Post Earth Quake Action G1 Slight Non Structural Thin Crack in Plaster, Falling of Damage Plaster bits in limited parts Building Need Not to Vacated., only architectural repairs required. G2 Slight Structural Damage Small crack in walls, Falling of Plaster in large bits over large areas; Damage of non structural Parts like projecting of cornice, kitchen chimney etc.(The load carrying capacity is not reduced appreciably.) Building Need Not to Vacated., Cracks in walls need grouting. Architectural repairs carried out to achieve durability. Seismic strengthening is desirable. G3 Moderate Structural Damage Large & deep Crack in walls; Cracking of walls, columns, piers, & tilting or falling of chimney. (The load carrying capacity of structure is partially reduced.) Building Need to be Vacated for structural restoration & seismic strengthening. Finally Architectural treatment may be carried out. Structure Repairs & Rehabilitation Categories Of Seismic Damage Damage Categories Extent Of Damage In General Suggested Post Earth Quake Action G4 Severe Structural Damage Gaps occur in walls; Inner or outer wall collapse; Failure of ties. Approximate 50% of the main structural elements fail. The building takes a dangerous states. Building has to be vacated. For demolishing or extensive restoration & strengthening work has to be carried out. G5 Collapse A large part of whole of the building collapses. Redesign & construction of Building . This Table is useful for cost deciding estimation for rehabilitation of building. Structure Repairs & Rehabilitation Earthquake Effects on Soils & Foundations & Solutions For Foundations Type “I” Rock Or Hard Soil-Well graded gravel Mixtures with or without clay binder, and clayey sands poorly graded or sand clay mixtures(GB,CW,SB,SW & SC) N>30 Type “II” Medium Soils- All soils N= 10 to 30 & Poorly Graded Sands Or Gravely Sands with Little or No fines (SP) with N>15 Type “III” Soft Soils Other than SP with N < 10. Structure Repairs & Rehabilitation S. Type Of Soil Damaging Effect Of No. Earth quake Earth quack Resisting Feature for foundation 1. 2. Use any foundation type •Use any foundation type •Use tie beams in case of Individual column Foundations 3. a. Type I Hard Type II Medium None •Not much in Zones II & III •Relative Lateral Movement Possible in Zone IV,V Type III Soft Not Much In Zone II Low Water Table Relative Movement Is Possible In Zone III to V Use Any Type of Foundation. & Use plinth bend. Use Plinth beam to connect all type of foundation such as isolated, combined column footings Or provide rafts Or piles as needed for the loads. Structure Repairs & Rehabilitation S.No. Type Of Soil 3. b. Type III Soft Some relative movement Liquefiable with in Zone II high water table Relative Lateral & Vertical movements in Zone III 3c. Black Cotton Soil Damaging Effect Of Earth quake Earth quack Resisting Feature Use Plinth beam to connect isolated Foundations Use piles going to stable soil layer or minimum 10 m length. Driven piles preferable. Liquefaction resulting in tilting/ overturning of buildings & structures likely in zones IV & V Improve the soil to a depth of 7 to 8m or up to stable layer if met earlier,use dynamic compaction or by compaction piles. Use piles going to stable soil layer or minimum 10 m length. Driven piles preferable. Soil not seen to be affected in intensity VII shaking in Latur, Jabalpur earthquakes but effect of ground motion amplified on the buildings Use Plinth beams to connect individual column footings. Use Plinth Band in case of strip foundations. Use of under ream piles preferable Structure Repairs & Rehabilitation Retrofitting is needed for following defects Rectification • • • • • 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 Cracks May Be Horizontal, Vertical & Diagonal Structure Repairs & Rehabilitation Crack & Spalling In Structural Members • Cracks Occur Due To Settlement In Foundation • Cracks Due To Earth Quack ,Wind,cyclone • 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, if it has been not replaced up to sufficient depth by Good Soil under plinth (For generating enough Counter weight upon black cotton soil) • Variation in Water Table within the Plinth Sub base (this occur in frequent flooding area & near sea soar) • Improper curing, Improper laying, Poor Quality of Mortar. • Improper Design for loading i.e. thickness & type of flooring. Structure Repairs & Rehabilitation Crack & Spalling due to Non Structural Reasons • Crack In R.C.C. • Crack In Water Proofing Work • Crack In Brick work • Crack In Plaster • Crack In finishing This cracks occur due to shrinkage, thermal expansion, carbonation, moisture changes in soil, creep, weed. 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 structure) • Non Testing of Pipe before & after laying • Insufficient soil cover over pipe 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 of edge of the slab, It combined with horizontal movement in the slab due to shrinkage. Structure Repairs & Rehabilitation Drying shrinkage and thermal contraction of slab exert a pull on the wall because of 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 Flexural Tension Cracks At Lintel Level Due to Shrinkage & contraction of R.C.C. Slab CRACK ON LINTEL LEVEL Structure Repairs & Rehabilitation Thickness of plaster is too much & silt content is also Very High 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 between wall portion adjoining to window & wall under sill results in crack. 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 CRACK In Normal conditions, cracks in this location comes when one of wall expand more than short wall. Structure Repairs & Rehabilitation Similarly 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 eve level of gable wall. CRACK 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. CRACK 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. Diagonal Crack Structure Repairs & Rehabilitation Make sure there are no hidden conduits within masonry Structure Repairs & Rehabilitation Redesigning existing structure for nature forces It is a comprehensive task & require planning which include following Information gathering. • Field investigations including details of sub strata, foundation details, extent of damage • Type of Existing structure & Design Data Collection • Checking of Members stability • Identification of components required to be strengthened • Cost Estimates (it is feasible up to 60% of new construction) • Then rehabilitation Method or Procedure is decided. 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 Diagonal cracks accompanied by outward tilting of external walls Moderate cracking could be controlled to some extent by providing water- proof apron as shown in a slide. Floor is replaced by brick ballast up to 600 mm depth & relaying base concrete & flooring . When foundation rest on B.C. Soil, drying out is likely to be more at the periphery of the building and less in the inner regions. However in rainy seasons reverse movement is there but cracks remains unclosed fully . Structure Repairs & Rehabilitation Diagonal cracks across the corner of a building affecting two adjacent walls These cracks are due to drying shrinkage of the foundation soil when building is built on shrinkable clay soil and has a shallow foundation Structure Repairs & Rehabilitation Flexible waterproof Apron Around a building to reduce moisture variation in soil under the building Inside This 2.0 m wide apron is generally is made around 0.5 m below G.L. 1 to 2 month after monsoon Outside Tar felt or Alkathene Sheet Lime concrete 100 mm thick laid to slope 1 in 30, Chased 30 to 40 mm into masonry 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 Crack in in Glass Glass strips Glass strips of 2 to 3 C.M. in width & 10 to 12 C.M.in length 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 Settlements Replace all crack bricks Use R.C.C. Stitching Block In Vertical Spacing In Every 5th or 6th Course ( 0.5 meter apart ). Stitching block has fallowing size. Width is equal to wall width, Length is equal to 1.5 to 2 bricks length & Thickness equal to 1 or 2 bricks as per severity of cracks Mortar For Repairs 1:1:6 (1 Cement :1 Lime : 6 Sand) Structure Repairs & Rehabilitation Corrective Measures For Load Bearing Wall Building • Therefore Shifting of Window, creation of more window, Door ,Inbuilt construction of Almirah should be carried out with due consideration to IS code 13935:1993 & as explained in this presentation. • Proper Bearing to lintel over brick work to avoid diagonal cracks & it can be done in retrofitting work. • It is advisable that keep window width as less as feasible while height can be increased with fixed small glass pans on top portion. Structure Repairs & Rehabilitation • Make structure floor, roof lighter as much as possible. • Avoid Un- symmetry of structure as much as possible. For this purpose structure can be divided. • Do Sand Pilling ,Stabilization of weak & sandy soil having high water level. • Proper Connections of building Elements. • Use steel to strengthen load bearing wall as per code requirement. • Provide adequate plinth protection. • Avoid to built Rigid masonry Building resting on rock in Earth Quack porn area. Structure Repairs & Rehabilitation Lateral Supports To Long Wall R.C.C./B.W. Columns Maximum 6m Interval Buttress Maximum 6m Interval Structure Repairs & Rehabilitation • Avoid keeping shallow foundation on Black Cotton Soil. • Use one type of foundation in a whole building to avoid differential settlement. • Physical quality check on material should me periodic. • A.R.C. which is structurally independent from an existing building should be designed & constructed in accordance with the seismic requirements of new structures. Structure Repairs & Rehabilitation • Any existing seismic resistance building if occupied for school building then the building has to be rechecked for seismic resistance for importance factor of 1.5. • Projecting parts like cornices, facia stones, parapets etc. should be avoided as for as possible, otherwise they should be properly reinforced and firmly tied to the main structure Refer IS 1893 CLAUSE -7.12.2 • Ceiling plaster should be avoided as possible. Structure Repairs & Rehabilitation Avoid Cantilever Construction Structure Repairs & Rehabilitation • Whenever one un symmetrical building is divided into two or more building by separation walls, the structure of the divided building up to plinth level is generally monolithic. Refer code IS 4326 5.1 to 5.2 • In load bearing construction even calculations based on code- based seismic coefficients may not indicate tension steel requirements, the reinforcement suggested in the form of seismic bands & vertical steel bars at corners & junction of walls & jambs of openings must be provided since these are safe guard for probable maximum earthquake Structure Repairs & Rehabilitation PROVISION FOR FUTURE EXTENTION Expansion Joint With Twin Columns For Future Extension Structure Repairs & Rehabilitation • Either foundation is kept above maximum water level or keep below natural water level. • In load bearing walls , corrosion resistance precautions should also be taken in ductility detailing of cyclone prone & tsunami prone coastal areas. • IS 456 does not allow R.C.C. below M20 grade Structure Repairs & Rehabilitation • An A.R.C. that is not structurally independent should be designed & constructed such that the entire building conforms to the seismic resistance requirements for new building. The A.R.C. shouldn't increase the seismic force in any structural elements of the existing building by more than 5% unless the capacity of the structural element subjected to the increased force is still in compliance with the IS. Code. The A.R.C. should not decrease the seismic resistance of any structural element of the existing building below that required by the design codes. Structure Repairs & Rehabilitation Importance Factor(I) For Building Depend Upon • Functional Use Of Structure • Hazardous Consequences Of Its Failure • Post Earthquake Personal needs • Historical Value • Economic Importance • School Building Have “I” value=1.5 “I” value 1.5 Zone Building Retrofitting need II III IV V C D E E Structure Repairs & Rehabilitation Strengthening Arrangements Recommended For 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 Structure Repairs & Rehabilitation Strengthening Arrangements Recommended For Masonry Building Retrofittin Number Of Storey g Category A One, Two, Three storey B One & Two Storey Three Storey C One storey Two & three storey D One & Two Storey Strengthening To Be Provided `b, c ,f ,g `b, c ,f ,g `b, c, d, f, g `b, c ,f , g `b, c, d, f, g `b, c, d, f, g Structure Repairs & Rehabilitation Elevation : Distance b1 to b8 changes as per Building Retrofitting l1 Need l2 b8 t 3 b2 b1 2 1 b5 h1 b4 h3 b h2 b4 2 b7 b6 3 b4 2 1 b4 h2 b5 Structure Repairs & Rehabilitation Table :Size, Position Of Opening In Above Figure Description `b5 (Minimum) Building Retrofitting Need/Category C D&E 230 mm 450 mm 0.55 m 0.50m 0.46m 0.42m 0.37m 0.33m 0.45 m 0.56 m `h3 (minimum) 600 mm 600 mm `b8 (Max.) 900 mm 900 mm (b1+b2+b3)/l1 ; (b6+b7)/l2 = shall not exceed ( For one Storey Building ) ( For Two Storey Building ) ( For Three & Four Storey Building ) `b4 Structure Repairs & Rehabilitation For Masonry Structures following features is consideded • Plinth Belt in lieu of Plinth Band (if strata is soft, non-uniform) • Lintel level belt in lieu of lintel band • Roof level/ Eve level/ Gable level band • Reinforcement at corner of wall • Shape, Size & location of Window In Wall • Unsupported Wall length to Height Ratio • Provide Cross wall, Brick Pillar &Buttress in case of long wall more than 6.0 m Structure Repairs & Rehabilitation Elevation : Masonry Building With Limitations t≥ 190 mm ≥40 t t Maximum 3.5 M 20 t Buttress Wall ≤20 t ≤40 t ≤40 t V W D Buttress Can Be Avoided by increasing wall thickness between the cross wall. Structure Repairs & Rehabilitation Masonry Building Retrofitting • Buttress of full height having top width & thickness = Wall thickness ‘t’ and Bottom width = 1/6 of wall height. • Brick Strength shall not be less than 5.0 N/Mm2 for two storey building. • For type “D” retrofitting, Mortar shall be 1:5 (5 MPa) or 1:1 lime :6 sand (3 Mpa) • For type E , Mortar shall be 1:1/4 lime:4 sand (7.5 MPa) or 1:1/2 part lime:4 (6 Mpa) Lime is added only to improve Workability. Structure Repairs & Rehabilitation Height of the load bearing building in B.W. shall be restricted to the following. 1. For retrofitting category ‘B’ & ‘D’ building of 4 storey with flat roof or 3 storey plus Attic for pitched roof. 2. For category E, Building of 3 storey with flat roof or 2 storey plus Attic for pitched roof. Structure Repairs & Rehabilitation • Height of the building in Stone Masonry shall be restricted to the following, where each storey height shall not exceed 3.0 m and span of walls between cross wall is limited to 5.0m 1. For retrofitting category A, B, building of 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. Structure Repairs & Rehabilitation • Minimum wall thickness in brick masonry shall be one brick in one & two storey construction, while in case of three storey, the bottom storey wall thickness should be one & half brick. • Maximum wall thickness in stone masonry shall be 450 mm & preferably 350 mm. Structure Repairs & Rehabilitation • Cross wall connection In steps SECOND LIFT 600 mm 600 mm FIRST LIFT Structure Repairs & Rehabilitation Wall to wall joints are to be made by building wall ends in ladder form A B C • Structure Repairs & Rehabilitation In Each Layer Staggered Toothed Joint A B Y X Plan 230 mm A B Elevation Showing 115 mm Vertical Joints • • • 450 mm View –X At A-A 230 mm View –Y At B-B Structure Repairs & Rehabilitation • Strengthening Of Window When Its Position Is Not As Per Table Above Slide No…….. 60 30 75 6 Ø @ 150 150 X Window Two Nos HYSD Bars Section X-X X Structure Repairs & Rehabilitation • 75 & 150 mm thick band of full width can be Replaced by Composite Band having 2 mm larger dia bar in section ‘A’& ‘B’ as below 100 mm Top Brick Laid While Concrete is Green Section Type A 75 mm 38 mm 75 mm Section Type B Composite Band With Side brick acting also as shuttering also Structure Repairs & Rehabilitation Recommended Longitudinal steel in Reinforcement Concrete Bands Span of Band Between Cross Wall In M Building Category “B” Building Category “C” Dia. Φ MM Building Category “D” No. Of Bars Dia. Φ MM Building Category “E” No. Of Bars Dia. Φ MM No. Of Bars No. Of Bars Dia. Φ MM 5 or Less 2 8 2 8 2 8 2 10 6 2 8 2 8 2 10 2 12 7 2 8 2 10 2 12 4 10 8 2 10 2 12 4 10 4 12 Spacing Of Tor Ring/Links 6 mm @ 150 mm Or 8 mm @ 200 mm Bends 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 Structure Repairs & Rehabilitation Pair of stone with length= ¾ of wall thickness ≤ 450 ≤ 1200 ≤ 1200 ≤ 1200 CL Plan showing Center bar in Casing Casing in every 0.6 m is lifted & M15 or Mortar 1:3 is Compacted around bar. Structure Repairs & Rehabilitation “S” shaped steel rod placed in a damroo shaped through hole in random rubble wall and fully encased in concrete Structure Repairs & Rehabilitation Vertical Steel Reinforcement in Masonry Walls up to 350 mm thick as per Table Vertical steel at corners and junction of walls up to 350 mm thick should be embedded in plinth masonry , foundations, bands &roof slab Nos Of Storey Storey Diameter Of HSD Single HYSD Bar in mm at each critical Section (for above 350 mm, increase bar dia proportionally Category C Category D Category E NIL 10 12 Top NIL 10 12 Bottom NIl 12 16 Top 10 10 12 Middle 10 12 16 Bottom 12 12 16 One -------Two Three Structure Repairs & Rehabilitation 3/4B One Brick Thick One & Half Brick Thick ---Contain One Bar At Centre & M20 or 1:3 Mortar Structure Repairs & Rehabilitation Vertical deformed steel bar from foundation to roof, anchored to masonry walls at wall junctions with special connectors, also connected to the roof at the top and encased in concrete. PROP Structure Repairs & Rehabilitation X Three Nails •5Ø drilled in splited bamboo Cross bracings at ends of room • Half Split Bamboo Ties To Rafter • Bras the 50 mm Dia Bamboo (B) To Rafter • Seismic Bend & Rafter should be tied Properly B Structure Repairs & Rehabilitation In the cyclone prone areas people keep the roof overhangs very small so that during a cyclone its chances of getting blown off are small. Along the coast of Kutchh, in Gujarat this practice is common. Structure Repairs & Rehabilitation Along the Kutchh and Saurashtra coast in Gujarat, roof is anchored to the walls through timber brackets so that it does not get blown off during the cyclonic winds. Structure Repairs & Rehabilitation In long walls introduce pilasters to strengthen it. 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 school, leading to settlement and/or cracking of the wall. Structure Repairs & Rehabilitation Prolonged Flooding can weaken the mortar, especially if it is mud mortar, and causing cracking in walls or collapse. Structure Repairs & Rehabilitation Simple erosion of wall near its bottom, or cracking, plaster peeling off and settlement in floor. Structure Repairs & Rehabilitation Diagonal tying on the upper or underside of the roof Prevents roof from getting distorted and damaged Structure Repairs & Rehabilitation Anchoring roof to wall, reducing roof overhangs and providing roof slope as per local tradition Helps resist uplifting of roof from wall. Also help prevent the roof from getting blown off Structure Repairs & Rehabilitation Seismic belt consisting of Weld mesh in lieu of Seismic Band. It is approximately 220mm wide anchored to masonry wall and encased in cement mortar. 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 Installing multiple strands of galvanized iron wires pulled and twisted for pretension Structure Repairs & Rehabilitation Anchoring the roof rafters and trusses with steel angles or other means Structure Repairs & Rehabilitation Encasing masonry column in cage of steel rods and encased in micro concrete Structure Repairs & Rehabilitation Vertical seismic Belt & filling unwanted opening Joints Structure Repairs & Rehabilitation Retrofitting in Urinal Basins Structure Repairs & Rehabilitation Girls Toilet After Retrofitting Structure Repairs & Rehabilitation Conclusion: The Extent of School Building Repairing Depend upon how well Retrofitting work has been planned at all levels within financial constraint while due consideration has to be given to counter nature destructive forces.