Rehabilitation-and-retrofitting-of-structuresnotes.pdf

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LECTURE NOTES ON

Rehabilitation & Retrofitting of structure

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Department of Civil Engineering

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UNIT-1 INTRODUCTION  Cracks in the building are of common occurrence in a building

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 It is due to exceeding stress in a building components  Causes of the cracks are mainly by increase in live load and dead load, seismic load etc., Classification of cracks

 Structural cracks  Non-structural cracks Structural cracks

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Cracks can be classified into two categories viz.,

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 It arises due to incorrect designs, overloading of structural components  Expenses cracking of foundation walls, beams and columns or slab etc., PHOTO OF STRUCTURAL CRACKS Non structural cracks

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They are due to internal forces developed in materials due to moisture variations, temperature variation, crazing, effects of gases ,liquids etc., They can be broadly classified into vertical, horizontal, diagonal, smoothened cracks PHOTO OF NON STRUCTURAL CRACKS DIRECTION OF THE CRACKS

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 Vertical

 Horizontal  Diagonal  Straight

 Toothed

 Variable and irregular

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WIDTH OF CRACKS It can be measured through instrument and tell-tale signs. The changes in the length of the cracks should be noted. Cracks measuring devices

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CAUSES OF CRACKS Major causes of cracks  Movements of the ground

 Effect of gases, liquids and solids  Effect of changes of temperature

Movements of grounds

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 General causes such as vibrations

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 Over loading

 Due to mining subsidence, land slips, earthquakes, moisture changes due to shrinkable soils. Overloading

 Overloading of the building

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 Overloading of the building parts results in cracks

Overloading forced may be due to

 External ( excessive wind/snow loads)  Internal ( from heavy machinery etc.,)

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Effects of gases, liquids and solids Gases

 Only gases like Co2 (carbon dioxide) is likely to produce cracks.  It causes Carbonation of porous cement products  Leads into an overall shrinkage crazing cracks

Liquids

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 Water is the most commonly used liquid when not taken care it can be hazardous  Construction water i.e., that in the utilization of water during the construction process Effects of water Physical(i.e. due to change in water content)

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Chemical ( directly or indirectly affecting other materials) General vibrations

Vibrations can cause cracks in buildings only when their amplitude of vibrations are high.

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Apart from vibrations caused due to earthquakes, the vibrations caused due to heavy machinery, traffic, sonic booms are also responsible for the occurrence of cracks in buildings. THERMAL MOVEMENT

All materials expand on heat and contract on cool.

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Thermal movement in components of structure creates cracks due to tensile of shear stresses One of the most potent causes of cracking in buildings and need attention GENERAL PRECAUTION TO AVOIDING CRACKS

 Before laying up foundation, the type of foundation to be used should be decided based on the safe bearing capacity of soil.

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 Providing R.C deep beam or an involved T-beam with adequate reinforcements to withstand the stress due to differential ground movements. This method is expensive  Construction operations such as cutting for roads drainages etc., close to the structures should be avoided this will results in reduction of soil moisture with consequent shrinkage of soil beneath the foundation of the structure.

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 In buildings close to the water courses are noticed in many places

PLACING OF CONCRETE Concrete should not be placed in heavy rains unless suitable shelter is provided. To avoid segregation, concrete should not be dropped from a height of more than 1m. Working on freshly laid concrete should be avoided  While placing the concrete in R.C.C members the alignment of formwork should not be disturbed.

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 Concrete should be laid continuously to avoid irregular and unsightly lines.  Internal surface of the forms either steel or wood should have even surfaces and should be oiled so that the concrete may not stick to it MATERIAL QUALITY

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Aggregate should be hard, sound, durable, non-absorbent and capable of of developing good bond with mortar. Water shall be clean and free from alkaline and acid materials and suitable for drinking purposes. TEST TO BE CARRIED OUT

Consistency of concrete should also be tested.

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Slump test to be carried out for the control of addition of water and workability.

A slump of 7.5 to 10cm may be allowed for building work

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LAYING TECHNIQUE AND CURING METHOD

Concrete should be laid in layers and should be compacted while laying with wooden tamping rods or with mechanical vibrators until a dense concrete is obtained After two hours of laying concrete, when the concrete has begun to harden, it shall be kept damp by covering with wet gunny bags or wet sand for 24 hours

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Evaluation of cracks

To determine the effects of cracks in the building. First the cracks location and extent should be noted down for the adopting suitable methods of repair and the future problems due to that cracks. Crack widths should be measured to the accuracy of 0.001 in (0.025mm) using a crack comparator.

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Movements should be recorded with movement sensors. Based on the reports from the location and width the suitable methods is adopted Crack as narrow as 0.002 in can be bonded by the injection of epoxy. Epoxy injection can alone be used to restore the flexural stiffness. For water retaining structure cracks it can be repaired by the autogenous healing. Repairing of cracks

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Routing and sealing. Stitching. Additional reinforcement. Gravity filling

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Grouting Dry packing Polymer impregnation

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Routing and sealing

Routing and sealing of cracks can be used in conditions requiring remedial repair and where structural repair is not necessary. Routing and sealing is used to treat both fill pattern cracks and larger, isolated cracks.

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The sealants may be any of several materials, including epoxies, urethanes, silicones, polysulfide, asphaltic materials, or polymer mortars Process of routing and sealing stitching

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Stitching involves drilling holes on both sides of the crack and grouting in U-shaped metal units with short legs (staples or stitching dogs) that span the crack. Stitching a crack tends to stiffen the structure, and the stiffening may increase the overall structural restraint. The stitching procedure consists of drilling holes on both sides of the crack, cleaning the holes, and anchoring the legs of the staples in the holes, with either a non shrink grout or an epoxy resin-based bonding system

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Figure showing stitching

Additional reinforcements  Conventional reinforcement-Cracked reinforced concrete bridge girders have been successfully repaired by inserting reinforcing bars and bonding them in place with epoxy .  This technique consists of sealing the crack, drilling holes that intersect the crack plane at approximately 90º ,filling the hole and crack with injected epoxy and placing a reinforcing bar into the drilled hole

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Prestressing steel-Post-tensioning is often the desirable solution when a major portion of a member must be strengthened or when the cracks that have formed must be closed. Adequate anchorage must be provided for the prestressing steel, and care is needed so that the problem will not merely migrate to another part of the structure Fig showing additional reinforcements

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grouting

Portland cement grouting-Wide cracks, particularly in gravity dams and thick concrete walls, may be repaired by filling with portland cement grout.

Gravity filling

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This method is effective in stopping water leaks, but it will not structurally bond cracked sections.

Low viscosity monomers and resins can be used to seal cracks with surface widths of 0.001 to 0.08 in. (0.03 to 2 mm) by gravity filling.

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High-molecular-weight methacrylates, urethanes, and some low viscosity epoxies have been used successfully. The lower the viscosity, the finer the cracks that can be filled. Dry packing

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Drypacking is the hand placement of a low water content mortar followed by tamping or ramming of the mortar into place, producing intimate contact between the mortar and the existing concrete. Polymer impregnation

Monomer systems can be used for effective repair of some cracks. A monomer system is a liquid consisting of monomers which will polymerize into a solid.

The most common monomer used for this purpose is methyl methacrylate.

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The procedure consists of drying the fracture, temporarily encasing it in a watertight (monomer proof) band of sheet metal, soaking the fractures with monomer, and polymerizing the monomer conclusion

The discussion on our project mainly focused on the cracks deals with failure due to improper settlement of foundation and poor construction. By the following discussed remedies and instruction what we have concentrated helps to reducing the cracks and move on to the next level in the construction.

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Content 1. Introduction 2. Rehabilitation A. Why Rehabilitation

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B. What Is Rehabilitation 3. Inspection 4. Common Defects And Possible Causes

6. Composite Wraps For Durability 7. Conclusion Introduction

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5. Common Remedies

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Deterioration of reinforced concrete structure due to corrosion of steel is a cause of global concern. The losses due to corrosion every year run in to millions of rupees and any solution to this universal problem of corrosion has a direct bearing economy of the country. It is estimated that about 30 to 40% of steel produce each year is used to replace corroded material.

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Main objective of rehabilitation in the construction industry to reinstate rejuvenate strengthen and upgrade existing concrete structure. Various causes which needs rehabilitation of a building are such as environment degradation, design inadequacies, poor construction practices, lack of maintenance, increase in load, unexpected seismic loading condition in addition to corrosion induced distress. Why rehabilitation

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The chief aim of rehabilitation is to restore a prematurely distressed building back to it’s original standard and to improve the facilities depending upon the needs and the technological advances. In the field of building construction, after rehabilitation the building is expected to give a trouble free service up-to it’s expected life. What is rehabilitation There is basic difference between the words “repair and rehabilitation”. The word repair normally indicates small and petty repairs more or less cosmetic, which are not of structural significance.

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A building is said to require rehabilitation, when structural stability and safety of building and occupant is in danger. Basic advantage of rehabilitation on repair-

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1. Repair building required frequent repair again because these are up to small extent and less durable so the expenditure spent on repair required more. The life of rehabilitated building is comparatively more than that of a repair building and economical too. 2. In repair what we apply is plaster only that does not last long hence leads leakage in pipe line, terrace, therefore there is corrosion in reinforcement of RCC structure but in rehabilitation we can approach the problem by the identification of main culprits responsible for deterioration. Plastering is nothing but the waste of money only. So rehabilitation is effective than repair.

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Causes of distress 1. Design deficiency:

1. underestimation of loads, deflection, shear forces and moments

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2. environmental condition for durability neglected wrongly specifying concrete grade, maximum water to cement ratio and minimum cement content 3. Poor detailing especially at beam and column junction 4. fault analysis and earth quake & wind forces not considered at all

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2. Material deficiency:

a. Poor quality cement b. Poor quality steel

c. Contaminated water

d. Contaminated aggregates

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3. Construction deficiency:

a. inadequate cover of concrete to steel reinforcement b. use of poor quality cover blocks c. poor formwork and staging d. poor preparation of construction joints

4. chemical/environmental attacks:

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a. moisture and chloride attack b. carbonation c. sulphate attacks d. thermal variation, hot and cold cycles

f. biological(insects and fungus) attacks 5. Natural causes:

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a. earth quakes

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e. erosion

b. floods c. fires

a. over loading b. fatigue c. impact 7. Foundation problem-

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6. Mechanical causes-

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a. failure of load bearing strata b. soil consolidation

c. soil shrinkage and swelling d. ground movement

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8. Manmade causesa. blasting

b. poor and no maintenance

Cracks in buildings and it’s components Cracks in column

Cracks in slabs

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Cracks in beam Philosophy of rehabilitation Inspection

1. Preparation of complete defect catalogue

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Systematic detailed inspection is the key to success of any rehabilitation scheme and is done to achieve the following objectives.

2. Evaluate the existing (safety and serviceability) condition of the building and assess the possible rate of future

Items needed during inspection1. Completion drawing for detailing

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3. Decide further course of action

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2. Mason’s tool kit- plumb bob, hammer, chisel, punch etc.

3. Measuring instrument- steel tap, scale, ladder, torch, safety belt etc. 4. Labour 5. Details of repairs Common remedies

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1. Jacketing of column-

Jacketing (provision of additional cross section) is done to strengthen column by removing loose concrete and treating the reinforcement with protection treatment like providing shear anchor of 10mm–12mm diameter with a spacing 20–30cm c/c and then concreting is done (M25). Polymer modified concrete which have good bonding quality and flexural strength, can be used.

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2. Patch repairing by polymer mortar-

Patching is done by removing loose concrete and rust of reinforced. Sometimes extra reinforcement is also provided. after removal of rust a bond coat is applied evenly in order to attain sufficient strength between old concrete and new polymer mortar then polymer mortar is applied which is prepared by weight (one part of polymer latex liquid, 5 part of cement and 15 part of quartz sand). Mortar is applied by hand by pressing it to the damaged or cracked surface. Column jacketing 3. Repairing of toilet block and GI pipe line-

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To avoid leakage problem from toilet, they should be made water proof. for this the seats are broke and cleaned then the surface is applied with suitable polymer coating. After this a coating of 20 mm thick plaster in cm 1:3 with w/c ratio of 0.4 provided. And joints between the seats are sealed with polymer mortar. Pipes which are leaked should be replaced.

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4. GroutingGrouting is used to repair deep structural cracks by injecting grout material like cement grout or resin. It is very effective method for repairing RCC or masonry structure. admixture are added to reduce shrinkage problem of cement grout so that it can reach upto the deepest crack in the structure and fill the pores.

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5. Shotcreting-

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Shotcreting is a technique to achieve better structural capability for walls an other elements. In this method mortar or concrete is conveyed at a high velocity onto a receptive surface by the application of compressed air for moving concrete. the cement, sand mix and water are kept in separate containers, which are connected to a nose pipe. Compressed air is forced into these containers through a motor. FIBER REINFORCED POLYMER COMPOSITE

Fiber reinforced polymer (FRP) is a composite material made by combining two or more materials to give a new combination of properties. It is composed of fiber and matrix, which are bonded.

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In this case, the reinforcing fiber provides FRP composite with strength and stiffness, while the matrix gives rigidity and environmental protection. Formation of Fiber Reinforced Polymer Composite A fiber is a material made into a long filament with a diameter generally in the order of 10 mm.

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The main functions of the fibers are to carry the load and provide stiffness, strength, thermal stability, and other structural properties in the FRP.

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To perform desirable functions, the fibers in FRP composite must have1. High Modulus of Elasticity for use as reinforcement; 2.

High Ultimate Strength;

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Low variation of strength among fibers;

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High Stability of their strength during handling; and

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High Uniformity of diameter and surface dimension among fibers.

Matrix Matrix material is a polymer composed of molecules made from many simpler and smaller units called monomer.

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The matrix must have a lower modulus and greater elongation than those of fibers, so that fibers can carry maximum load. Made from Metal, Polymer or Ceramic Some Ductility is Desirable

USES To strengthen the structures due to:1) Loading Increase

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TYPES OF FRP MATERIALS

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 Increasing the Live Load in warehouses  Increased traffic volume on Bridges

 Installation of Heavy machinery in Industrial Building  Vibrating Structures

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 Change of Building utilization

2) Damage to Structural parts

 Ageing of Construction material  Steel Reinforcement corrosion

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 Vehicle Impact  Fire

 Earthquakes

3) Serviceability Improvement  Decrease of Deformation  Stress reduction in steel reinforcement

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 Crack width reduction 4) Change in Structural System  Removals of walls or columns  Removal of slab section for openings

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5) Design or Construction Defects  Insufficient reinforcement  Insufficient Structural Depth

Low in weight Available in any Length, no joints required Low overall thickness

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Easy to transport

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advantages

Laminate Intersections are simple

Economical application- no heavy handling and installation equipment Very high strength

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High modulus of elasticity

Outstanding fatigue resistance High alkali resistance No corrosion

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conclusion

1. With careful planning and close supervision, expected result can be achieved. 2. We can protect many buildings having historic, cultural, monumental, archeological importance by rehabilitation. 3. Can save lot of money by rehabilitation. 4. Rehabilitation increases the life of building and any type of structure. 5. FRP gives the strength of the structural member.

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UNIT-2 Structure Repairs & Rehabilitation In Low Strength Masonry Buildings •

Structure Repairs & Rehabilitation

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Low Strength Masonry Building is Laid in Fired brick work in clay & mud mortar

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Random rubble ; Uncoursed, Undressed stone masonry in weak mortars made of cement-sand , lime-sand & clay-mud.

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Structure Repairs & Rehabilitation

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Component Of Low Strength Masonry Building: Foundation

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Flooring

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Brick/ Stone Columns

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Brick Work

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Stone Masonry

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Wood Work

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Slab

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Slopping Wooden frame Roof

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Plaster

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Structure Repairs & Rehabilitation

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Life Of Structure Depend Upon: A. Geography Of Location B. Building Material C. Technology

D. Workmanship •

Structure Repairs & Rehabilitation

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A . Geography Of Location: Type of Strata

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Water Table

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Earth Quack, Wind, Cyclone, Flood, Snow

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Pollutant

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Land Slide

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Tree location w.r.t. building

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Structure Repairs & Rehabilitation

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B . Building Materials Cement

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Lime

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Fine Sand

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Coarse Sand

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Coarse Aggregate

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Quality of Water

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Bamboo/Wood

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Brick

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Structure Repairs & Rehabilitation

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C. Technology

Architectural Design

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Structural Design Based On Load Bearing Wall

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Construction Methods

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Quality Practices

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Construction Management

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Structure Repairs & Rehabilitation

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D Workmanship Structural Work

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Finishing Work

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Water Proofing Work

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Development of Drainage (Internal & External)

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Maintenance Of Building

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Structure Repairs & Rehabilitation

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Building Needs Repairs & Retrofitting Crack & Spalling In Structural Members

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Crack & Settlement In Flooring

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Crack & Spalling in Non Structural Members

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Leakage In Water Supply & Drainage System

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Redesigning existing structure for nature forces

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Changed functional requirements

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Structure Repairs & Rehabilitation

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Crack & Spalling In Structural Members

Cracks Occur Due To Settlement In Foundation

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Cracks Due To Earth Quack ,Wind

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Crack Due To Overloading Of Structure

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Crack Due To Reduction in Load Carrying Capacity of Structure Due To Weathering

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Crack Due To Improper Design Of Structure

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Crack due to Poor connection Of Structural Members Resulted From Poor Workmanship

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Structure Repairs & Rehabilitation

Crack & Settlement In Flooring •

Due To Improper Plinth Filling

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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)

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Water Table vary within the Plinth Sub base (this occur in frequent flooding area & near sea soar)

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Improper curing, Improper laying, Poor Quality of workmanship.

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Improper design for loading i.e. thickness & type of flooring.

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Structure Repairs & Rehabilitation

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Crack & Spalling in Non Structural Members Crack In Plaster

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Crack In Finishing

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Crack In Water Proofing Work

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Vertical cracks in long boundary wall due to thermal movement Or Shrinkage.

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Crack Induced due to thermal changes, change in moisture content in building material, Chemical Reactions

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Structure Repairs & Rehabilitation

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Leakage In Water Supply & Drainage

It may result from structural cracks & settlement

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Improper selection of pipe thickness

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Improper selection of Supports & its spacing to Pipe

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Improper making Of joints

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Non Provision for contraction & expansion (Particularly when pipe is passing over different type of long structures)

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Non Testing of Pipe before & after laying

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Insufficient soil cover over pipe

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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.

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Field investigations including details of sub strata, foundation details

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Type of Existing structure & its members stability

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Design Data Collection

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Identification of components required to be strengthened, replaced.

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Cost Estimates (it is feasible up to 60% of new construction)

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Method or Procedure to be fallowed.

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Structure Repairs & Rehabilitation

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Crack Investigation Location

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Profile (vertical, Horizontal, Diagonal)

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Crack Size throughout length (Width,Depth & length)

Thin crack< 1mm

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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

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Structure Repairs & Rehabilitation

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Cracks are static or live, is monitored & recorded by “Tell-Tale” method

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Structure Repairs & Rehabilitation

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Structure Repairs & Rehabilitation

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Structure Repairs & Rehabilitation

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Structure Repairs & Rehabilitation

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Structure Repairs & Rehabilitation

Construction Details Of Bearing Of R.C.C. Roof Slab Over a Masonry Wall •

Structure Repairs & Rehabilitation

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Structure Repairs & Rehabilitation

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Structure Repairs & Rehabilitation

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Structure Repairs & Rehabilitation

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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.

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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.

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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.

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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.

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

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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.

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

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Structure Repairs & Rehabilitation

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Structural Repairs

Load Bearing Walls: PROCEDURE IN NEXT SLIDE •

Structure Repairs & Rehabilitation

Repairing Of Crack Due To Structural Cause •

Replace all cracked bricks

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Use R.C.C. Stitching Block In Vertical Spacing In Every 5th or 6th Course ( 0.5 meter apart ).

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Stitching block

Width=equal to wall width, Length = 1.5 to 2 bricks,

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Mortar For Repairs 1:1:6 (1 Cement :1 lime: 6 sand)

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Structure Repairs & Rehabilitation

load bearing walls(May be Brick or Stone) have inbuilt deficiency. Each Brick have different strength

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Thickness of Mortar Joints are not also uniform.

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Bricks are not perfectly laid horizontally & vertically

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Opening in walls

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Improper staggered joints

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Use of unwanted Brick bats

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Thick =1 or 2 bricks as per severity of cracks

1. These resulted in cumulative effect & concentration of stress in particular section of wall is more than other section. Structure Repairs & Rehabilitation

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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

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Proper Bearing to lintel over brick work to avoid diagonal cracks & it can be done in retrofitting work.

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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.

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Structure Repairs & Rehabilitation

Importance Factor(I) Depend Upon •

Functional Use Of Structures

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Hazardous Consequences Of Its Failure

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Post Earthquake Personal needs

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Historical Value

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Economic Importance

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School Building Have “I” value=1.5

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Structure Repairs & Rehabilitation

Elevation : Distance b1 to b8 changes as per Building •

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Retrofitting

Structure Repairs & Rehabilitation

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Table :Size, Position Of Opening In Above Figure

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Structure Repairs & Rehabilitation

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Strengthening Of Window When Its Position Is Not As Per Table Above Slide No 42.

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Structure Repairs & Rehabilitation

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Strengthening Arrangements Recommended For low Strength Masonry Building b = Lintel Bend

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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

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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 •

Structure Repairs & Rehabilitation

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Seismic wave propagation increases as height of wall/structure increases.

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Seismic wave expansion pushes bricks of corner of wall out of building.

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Movement of Seismic wave through joints of similar or dissimilar component of building ,makes joint open, resulting in falling of component of the building.

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Structure Repairs & Rehabilitation

Possibility For Old Masonry Structures Strength Plinth Belt in lieu of plinth band

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Lintel level belt in lieu of band

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Roof level/ gable level band

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Corner steel

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Shape, Size & location of Window In Wall

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Wall length to Height Ratio

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Cross wall/ Brick Pillar/counter fort

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

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

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Structure Repairs & Rehabilitation

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Low Strength Masonry Building Retrofitting For Brick Masonry Structure •

Height of the building in B.W. shall be restricted to the following.

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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.

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Structure Repairs & Rehabilitation

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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

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•

For Stone Masonry •

Height of the building in Stone Masonry shall be restricted to the following

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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. 2. 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.

•

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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

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Structure Repairs & Rehabilitation

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Cross wall connection In steps

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

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•

•

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

•

Structure Repairs & Rehabilitation

In Each Layer Staggered Toothed Joint

Y A

B

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PLAN

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X

Structure Repairs & Rehabilitation Recommended Longitudinal steel in Reinforcement Concrete Bends

•

Structure Repairs & Rehabilitation

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Steel Profile In Band At Corner & Junction

•

Structure Repairs & Rehabilitation

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or

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Bonding Elements A. Wood Plank

( 38x38x450 mm)

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B. R.C.C. Block (50x50x450 & 8 mm) C. 8 or 10 mm Hook

or “S” shape bent Bar

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Plan showing Through Stone

Through stone = Bonding Element •

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

•

Structure Repairs & Rehabilitation

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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

•

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Half Split Bamboo Ties To Rafter

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Brace the Rafter to 50 mm Dia Bamboo (B)

•

Seismic Bend & Rafter should be tied Properly

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

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•

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

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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

•

Structure Repairs & Rehabilitation

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•

One Brick Thick

One & Half Brick Thick

-------- Contain One Bar At Centre

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

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

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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

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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

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

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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.

TU

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or

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•

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

•

Structure Repairs & Rehabilitation

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

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Structure Repairs & Rehabilitation High plinth level to avoid entering flood

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Structure Repairs & Rehabilitation

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•

Use of pilasters strengthens walls against flowing water •

Structure Repairs & Rehabilitation

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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.

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•

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TU

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Thank You

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UNIT-3 Definition of Corrosion

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Corrosion is the deterioration of materials by chemical interaction with their environment. The term corrosion is sometimes also applied to the degradation of plastics, concrete and wood, but generally refers to metals. Anodic & Cathodic Reactions Effects of corrosion

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The consequences of corrosion are many and varied and the effects of these on the safe, reliable and efficient operation of equipment or structures are often more serious than the simple loss of a mass of metal. Failures of various kinds and the need for expensive replacements may occur even though the amount of metal destroyed is quite small. Underground corrosion

Electronic components

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Buried gas or water supply pipes can suffer severe corrosion which is not detected until an actual leakage occurs, by which time considerable damage may be done.

TU

In electronic equipment it is very important that there should be no raised resistance at low current connections. Corrosion products can cause such damage and can also have sufficient conductance to cause short circuits. These resistors form part of a radar installation.

Corrosion influenced by flow-1

The cast iron pump impeller shown here suffered attack when acid accidentally entered the water that was being pumped. The high velocities in the pump accentuated the corrosion damage. Corrosion influenced by flow – 2

JN

This is a bend in a copper pipe-work cooling system. Water flowed around the bend and then became turbulent at a roughly cut edge. Downstream of this edge two dark corrosion pits may be seen, and one pit is revealed in section. Safety of aircraft

The lower edge of this aircraft skin panel has suffered corrosion due to leakage and spillage from a wash basin in the toilet. Any failure of a structural component of an aircraft can lead to the most serious results.

Influence of corrosion on value

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A very slight amount of corrosion may not interfere with the usefulness of an article, but can affect its commercial value. At the points where these scissors were held into their plastic case some surface corrosion has occurred which would mean that the shop would have to sell them at a reduced price. Motor vehicle corrosion and safety

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The safety problems associated with corrosion of motor vehicles is illustrated by the holes around the filler pipe of this petrol tank. The danger of petrol leakage is obvious. Mud and dirt thrown up from the road can retain salt and water for prolonged periods, forming a corrosive “poultice”. Corrosion at sea

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Sea water is a highly corrosive electrolyte towards mild steel. This ship has suffered severe damage in the areas which are most buffeted by waves, where the protective coating of paint has been largely removed by mechanical action. Aluminium Corrosion

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The current trend for aluminium vehicles is not without problems. This aluminium alloy chassis member shows very advanced corrosion due to contact with road salt from gritting operations or use in coastal / beach regions. Damage due to pressure of expanding rust

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The iron reinforcing rods in this garden fence post have been set too close to the surface of the concrete. A small amount of corrosion leads to bulky rust formation which exerts a pressure and causes the concrete to crack. For structural engineering applications all reinforcing metal should be covered by 50 to 75 mm of concrete.

“Corrosion” of plastics

Not only metals suffer “corrosion” effects. This dished end of a vessel is made of glass fibre reinforced PVC. Due to internal stresses and an aggressive environment it has suffered “environmental stress cracking”.

JN

Galvanic corrosion

This rainwater guttering is made of aluminium and would normally resist corrosion well. Someone tied a copper aerial wire around it, and the localised bimetallic cell led to a “knife-cut” effect. Galvanic corrosion

The tubing, shown here was part of an aircraft’s hydraulic system. The material is an aluminium alloy and to prevent bimetallic galvanic corrosion due to contact with the copper alloy retaining nut this was cadmium plated. The plating was not applied to an adequate thickness and pitting corrosion resulted.

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Galvanic corrosion This polished Aluminium rim was left over Christmas with road salt and mud on the rim. Galvanic corrosion has started between the chromium plated brass spoke nipple and the aluminium rim. Galvanic corrosion

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Galvanic corrosion can be even worse underneath the tyre in bicycles used all winter. Here the corrosion is so advanced it has penetrated the rim thickness.

JN

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Corrosion prevention

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UNIT-4 DAMAGE IN STRUCTURES DUE TO FIRE  DAMAGE IN STRUCTURES DUE TO FIRE

 PART 2: Fire Rating of Structures  PART 3: Phenomenon of Desiccation

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 DAMAGE IN STRUCTURES DUE TO FIRE

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 PART 1: Fire Induced Damages in Structures

 PART 1: Fire Induced Damages in Structures  Part I: Fire Induced Structural Damages

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 Uneven volume changes in affected members, resulting in distortion, buckling and cracking. The temperature gradients are extreme - from ambient 70oF (21oC), to higher than 1500oF (800oC) at the source of the fire and near the surface.  Spalling of rapidly expanding concrete surfaces from extreme heat near the source of the fire. Some aggregates expand in bursts, spalling the adjacent matrix. Moisture rapidly changes to steam, causing localized bursting of small pieces of concrete.

TU

 The cement mortar converts to quicklime at temperatures of 750 oF (400oC), thereby causing disintegeration of concrete.  Reinforcing steel loses tensile capacity as the temperature rises.  Once the reinforcing steel is exposed by the spalling action, the steel expands more rapidly than the surrounding concrete, causing buckling and loss of bond to adjacent concrete where the reinforcement is fully encased.

JN

 Concrete undergoes cracking, spalling, and experiences a decrease in stiffness and strength as the temperature increases.  Concrete has low thermal conductivity, which allows it to undergo heating for longer durations before the temperature increases significantly and damage occurs.  The concrete compressive strength starts decreasing rapidly after its temperature reaches approximately 400°C (750°F).

 At temperatures of around 500oC (932oF), the concrete compressive strength is reduced to 50% of its nominal strength.

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 The tensile yield strength of the steel decreases gradually up to 500 oC (932o F). It is reduced to about 50% of its nominal yield strength at 600 oC (1112oF). This essentially eliminates any factor of safety, which is usually between 1.5 and 2.0.

Stages of deterioration due to Fire  DAMAGE IN STRUCTURES DUE TO FIRE

 PART 2: Fire Ratings of Structures What is Fire Rating?

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 PART 2: Fire Ratings of Structures

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 The steel yield strength decreases more rapidly for temperatures greater than 500 oC (932oF), and failure may be inevitable if temperatures keep increasing while the loading is sustained.

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A fire rating refers to the length of time that a material can withstand complete combustion during a standard fire rating test. Fire testing of building materials and components of buildings -- such as joists, beams and fire walls -- is required in most places by building codes. Other fire tests for things such as appliances and furniture are voluntary, ordered by manufacturers to use in their advertising. Wall and floor safes are examples of products for which fire resistance is a key selling point.

TU

 PART 2: Fire Ratings of Structures What is Fire Rating?

JN

With the required tests, the results are measured in either units of time, because the emphasis is on holding up under fire (literally) long enough for the occupants of a home or building to escape, or by classification designations. This does not mean, necessarily, that the components of every new structure have to be fire tested. In most cases, the fire rating has been already established by testing the product before it is even put on the market.  DAMAGE IN STRUCTURES DUE TO FIRE

 PART 3: Phenomenon of Desiccation  PART 3: Phenomenon of Desiccation  Desiccation is a phenomenon referring to dryness of the material induced by the loss of moisture

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UNIT-5 DISTRESS OF CONCRETE STRUCTURES & THEIR REPAIR TECHNIQUES INTRODUCTION

CATEGORIES OF REASONS DISTRESS OF CONCRETE STRUCTURES

2. AGEING 3. ENVIRONMENTAL EFFECTS 4. INADEQUATE MAINTENANCE

or

1. WEATHERING

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If a building has given about 25v to 30 years of service without much maintenance or repair then it is reasonable to expect that it would need some repair sooner or later.

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5. POOR DESIGNING AND CONSTRUCTION QUALITY

6. CHANGE OF LOADING PATTERN OR NON CONVENTIONAL LOADING ON STRUCTURE 7. WATER LEAKAGE LEADING TO CORROSION OF CONCRETE STRUCTURE CAUSES OF EARLY DETERIORATION OF CONCRETE STRUCTURES

TU

EFFECTS OF CRACKING ON LIFE OR DURABILIY OF STRUCTURE IDENTIFICATION OF DISTRESSED LOCATIONS ON STRUCTURES MATERIALS AND METHODS FOR CRACK REPAIR SOME SPECIFIC REPAIR TECHNIQUE FOR CONCRETE SURFACE ASSESMENT OF QUALITY OF STRUCTURE SOON AFTER ITS CONSTRUCTION

JN

REQUIREMENT FOR TRAINING FOR CONCRETE REPAIR AND CONCRETE WORKERS THANK YOU

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UNIT-6 METHODS OF REPAIRING CONCRETE STRUCTURES

3 Basic symptoms of distress in a concrete structure Cracking, Spalling and Disintegration

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1. INTRODUCTION

or

Reasons for their development may be poor materials, poor design, poor construction practice, poor supervision or a combination

repair of cracks usually does not involve strengthening

2. Repairing cracks

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repair of a structure showing spalling and disintegration, it is usual to find that there have been substantial losses of section and/or pronounced corrosion of the reinforcement

In order to determine whether the cracks are active or dormant, periodic observations are done utilizing various types of telltales

TU

 by placing a mark at the end of the crack

 a pin or a toothpick is lightly wedged into the crack and it falls out if there is any extension of the defect  A strip of notched tape works similarly : Movement is indicated by tearing of the tape

JN

 The device using a typical vernier caliper is the most satisfactory of all. Both extension and compression are indicated

 If more accurate readings are desired, extensometers can be used  Where extreme accuracy is required resistance strain gauges can be glued across the crack

2.1

Types of cracks

•

active cracks and dormant cracks

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the proper differentiation between active and dormant cracks is one of magnitude of movement, and the telltales are a measure of the difference

•

If the magnitude of the movement, measured over a reasonable period of time (say 6 months or 1 year), is sufficient to displace or show significantly on the telltales, we can treat the crack as an active one.

•

If the movements are smaller, the crack may be considered as dormant.

ld

•

Cracks can also be divided into solitary or isolated cracks and pattern cracks

Generally, a solitary crack is due to a positive overstressing of the concrete either due to load or shrinkage

or

Overload cracks are fairly easily identified because they follow the lines demonstrated in laboratory load tests

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In a long retaining wall or long channel, the regular formation of cracks indicates faults in the design rather than the construction, but an irregular distribution of solitary cracks may indicate poor construction as well as poor design Regular patterns of cracks may occur in the surfacing of concrete and in thin slabs. These are called pattern cracks Methods of repairing cracks

1. Bonding with epoxies

TU

Cracks in concrete may be bonded by the injection of epoxy bonding compounds under pressure Usual practice is to

 drill into the crack from the face of the concrete at several locations

inject water or a solvent to flush out the



allow the surface to dry

JN



defect



surface-seal the cracks between the injection



inject the epoxy until it flows out of the adjacent sections of the crack or begins bulge out the surface seals

to



Usually the epoxy is injected through holes of inch deep at 6 to 12 inches centers



Smaller spacing is used for finer cracks

points

about ¾ inch in diameter and ¾

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

The limitation of this method is that unless the crack is dormant or the cause of cracking is removed and thereby the crack is made dormant, it will probably recur, possibly somewhere else in the structure

 Also, this technique is not applicable if the defects are actively leaking to the extent that they cannot be dried out, or where the cracks are numerous

•

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2. Routing and sealing This method involves enlarging the crack along its exposed face and filling and sealing it with a suitable material

or

The routing operation placing the sealant

This is a method where thorough water tightness of the joint is not required and where appearance is not important

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3. Stitching

Concrete can be stitched by iron or steel dogs

A series of stitches of different lengths should be used

TU

bend bars into the shape of a broad flat bottomed letter U between 1 foot and 3 feet long and with ends about 6 inches long The stitching should be on the side, which is opening up first if necessary, strengthen adjacent areas of the construction to take the additional stress

JN

the stitching dogs should be of variable length and/or orientation and so located that the tension transmitted across the crack does not devolve on a single plane of the section, but is spread out over an area In order to resist shear along the crack, it is necessary to use diagonal stitching The lengths of dogs are random so that the anchor points do not form a plane of weakness 4. External stressing

cracks can be closed by inducing a compressive force, sufficient to overcome the tension and to provide a residual compression

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The principle is very similar to stitching, except that the stitches are tensioned; rather than plain bar dogs which apply no closing force to the crack Some form of abutment is needed for providing an anchorage for the prestressing wires or rods 5. Grouting

 cleaning the concrete along the crack  installing built-up seats at intervals along the crack

ld

 same manner as the injection of an epoxy

 sealing the crack between the seats with a cement paint or grout

6. Blanketing similar to routing and sealing

or

 flushing the crack to clean it and test the seal; and then grouting the whole

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applicable for sealing active as well as dormant cracks Preparing the chase is the first step Usually the chase is cut square

The bottom should be chipped as smooth to facilitate breaking the bond between sealant and concrete

TU

The sides of the chase should be prepared to provide a good bond with the sealant material The first consideration in the selection of sealant materials is the amount of movement anticipated and the extremes of temperature at which such movements will occur elastic sealants

mastic sealants

JN

mortar-plugged joints

7. Use of overlays

Sealing of an active crack by use of an overlay requires that the overlay be extensible and not flexible alone Accordingly, an overlay which is flexible but not extensible, ie. can be bent but cannot be stretched, will not seal a crack that is active Gravel is typically used for roofs

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concrete or brick are used where fill is to be placed against the overlay An asphalt block pavement also works well where the area is subjected to heavy traffic Repairing spalling and disintegration

ld

In the repair of a structure showing spalling and disintegration, it is usual to find that there have been substantial losses of section and/or pronounced corrosion of the reinforcement Both are matters of concern from a structural viewpoint, and repair generally involves some urgency and some requirement for restoration of lost strength 1. Jacketing

or

primarily applicable to the repair of deteriorated columns, piers and piles

Jacketing consists of restoring or increasing the section of an existing member, principally a compression member, by encasement in new concrete

W

The form for the jacket should be provided with spacers to assure clearance between it and the existing concrete surface The form may be temporary or permanent and may consist of timber, wrought iron, precast concrete or gauge metal, depending on the purpose and exposure Timber, Wrought iron Gauge metal and other temporary forms can be used under certain conditions

TU

Filling up the forms can be done by pumping the grout, by using prepacked concrete, by using a tremie, or, for subaqueous works, by dewatering the form and placing the concrete in the dry The use of a grout having a cement-sand ratio by volume, between 1:2 and 1:3 , is recommended The richer grout is preferred for thinner sections and the leaner mixture for heavier sections The forms should be filled to overflowing, the grout allowed to settle for about 20 minutes, and the forms refilled to overflowing

JN

The outside of the forms should be vibrated during placing of the grout 2. Guniting

Gunite is also known as shotcrete or pneumatically applied mortar It can be used on vertical and overhead, as well as on horizontal surfaces and is particularly useful for restoring surfaces spalled due to corrosion of reinforcement Gunite is a mixture of Portland cement, sand and water, shot into the place by compressed air

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Sand and cement are mixed dry in a mixing chamber, and the dry mixture is then transferred by air pressure along a pipe or hose to a nozzle, where it is forcibly projected on to the surface to be coated Water is added to the mixture by passing it through a spray injected at the nozzle The flow of water at the nozzle can be controlled to give a mix of desired stiffness, which will adhere to the surface against which it is projected

ld

3. Prepacked concrete

This method is particularly useful for carrying out the repair under water and elsewhere where accessibility is a problem

or

Prepacked concrete is made by filling forms with coarse aggregate and then filling the voids of the aggregate by pumping in a sand-cement grout

Prepacked concrete is used for refacing of structures, jacketing, filling of cavities in and under structures, and underpinning and enlarging piers, abutments, retaining walls and footings Pumping of mortar should commence at the lowest point and proceed upward

4. Drypack

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Placing of grout should be a smooth, uninterrupted operation

Drypacking is the hand placement of a very dry mortar and the subsequent tamping of the mortar into place, producing an intimate contact between the new and existing works

TU

Because of the low water-cement ratio of the material, there is little shrinkage, and the patch remains tight. The usual mortar mix is 1:2.5 to 1:3 5. Replacement of concrete

This method consists of replacing the defective concrete with new concrete of conventional proportions, placed in a conventional manner

JN

This method is a satisfactory and economical solution where the repair occurs in depth (at least beyond the reinforcement), and where the area to be repaired is accessible This method is particularly indicated where a water-tight construction is required and where the deterioration extends completely through the original concrete section Overlays

In addition to seal cracks, an overlay may also be used to restore a spalled or disintegrated surface Overlays used include mortar, bituminous compounds, and epoxies

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They should be bonded to the existing concrete surface Conclusions When repairing cracks, do not fill the crack with new concrete or mortar A brittle overlay should not be used to seal an active crack

ld

The restraints causing the cracks should be relieved, or otherwise the repair must be capable of accommodating future movements Cracks should not be surface-sealed over corroded reinforcement, without encasing the bars

or

The methods adopted for repairing spalling and disintegration must be capable of restoring the lost strength References [1]

Champion, S. Failure and Repair of Concrete Structures. John Wiley & Sons Inc. New York, 1961

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[2] Sidney.M.Johnson. Deterioration, Maintenance and Repair of Structures. Mc Graw-Hill Book Company. New York, 1965. [3] Lee How Son and George C.S. Yuen. Building Maintenance Technology. Macmillan Distribution Ltd. England. 1993.

Thomas H. McKaig. Building Failures.

TU

[4]

Mc Graw-Hill Book Company. New York,

Histories. Oxford & IBH Publishing Co. Pvt.

JN

[5] Jagadish, R. Structural Failures - Case New Delhi.1995.

1962.

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UNIT-7 Repair and Strengthening of Reinforced Concrete Beam-Column Joints: State of the Art CONTENT

ld

1. INTRODUCTION 1.1 RESEARCH SIGNIFICANCE

2. REPAIR AND STRENGTHENING TECHNIQUES FOR BEAM-COLUMN JOINTS

2.2 Removal and replacement 2.3 Concrete jackets 2.4 Reinforced masonry blocks

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2.5 Steel jackets and external steel elements

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2.1 Epoxy repair

2.6 Fiber-reinforced polymeric composites 3. APPENDIX 4. CONCLUSIONS

TU

5. REFERENCES

1. INTRODUCTION

RESEARCH SIGNIFICANCE

2.REPAIR AND STRENGTHENING TECHNIQUES FOR BEAM-COLUMN JOINTS

JN

2.1 Epoxy

repair

2.3 Concrete jackets

Concrete jackets continues… 2.5 Steel jackets and external steel elements 2.6 Fiber-reinforced polymeric composites

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APPENDIX 3. CONCLUSIONS From the literature review on the performance, repair, and strengthening of nonseismically detailed RC beam-column joints presented in this paper, the following conclusions were drawn:

ld

1. The critical nonseismic joint details in existing RC structures have been well-identified as shown in Fig. 1; however, the investigation of their effects on seismic behavior have been limited to testing of isolated one-way joints (no floor slab, transverse beams, or bidirectional loads) to a very large extent, and 1/8and 1/3-scale building models that may not accurately simulate the actual behavior of structural details;

or

2. Epoxy repair techniques have exhibited limited success in restoring the bond of reinforcement, in filling the cracks, and restoring shear strength in one-way joints, although some authors believe it to be inadequate and unreliable.13 The authors believe that injection of epoxy into joints surrounded by floor members would be similarly difficult;

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Conclusion

3. Concrete jacketing of columns and encasing the joint region in a reinforced fillet is an effective but the most labor-intensive strengthening method due to difficulties in placing additional joint transverse reinforcement.

TU

Welding an external steel cage around the joint instead of adding internal steel has also proven effective in the case of a three-dimensional interior joint test. These methods are successful in creating strong column-weak beam mechanisms, but suffer from considerable loss of floor space and disruption to building occupancy; 4. An analytical study showed that joint strengthening with reinforced masonry units can lead to desirable ductile beam failures and reduction of interstory drifts; however, no experimental data are available to validate their performance; Conclusion

JN

5. Grouted steel jackets tested to date cannot be practically applied in cases where floor members are present. If not configured carefully, such methods can result in excessive capacity increases and create unexpected failure modes. Externally attached steel plates connected with rolled sections have been effective in preventing local failures such as beam bottom bar pullout and column splice failure; they have also been successfully used in combination with a reinforced concrete fillet surrounding the joint; 6. Externally bonded FRP composites can eliminate some important limitations of other strengthening methods such as difficulties in construction and increases in member sizes.

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The shear strength of one-way exterior joints has been improved with ±45-degree fibers in the joint region; however, ductile beam failures were observed in only a few specimens, while in others, composite sheets debonded from the concrete surface before a beam plastic hinge formed. Reliable anchorage methods need to be developed to prevent debonding and to achieve full development of fiber strength within the small area of the joint, which can possibly lead to the use of FRPs in strengthening of actual three-dimensional joints; and

ld

Conclusion 7. Most of the strengthening schemes developed thus far have a limited range of applicability, if any, either due to the unaccounted floor members (that is, transverse beams and floor slab) in real structures or to architectural restrictions.

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REFERENCES

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Experiments conducted to date have generally used only unidirectional load histories. Therefore, the research in this area is far from complete, and a significant amount of work is necessary to arrive at reliable, cost-effective, and applicable strengthening methods. In developing such methods, it is important that testing programs be extended to include critical joint types (for example, corner) under bidirectional cyclic loads.

Engindeniz, M.; Kahn, L. F.; and Zureick, A., “Repair and Strengthening of Non-Seismically Designed RC Beam-Column Joints: State-of-the-Art,” Research Report No. 04-4, Georgia Institute of Technology, Atlanta, Ga., Oct. 2004, 58 pp. (available online at http:// www.ce.gatech.edu/groups/struct/reports)

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Repair and Strengthening of Reinforced Concrete Beam-Column Joints: State of the Art. by Murat Engindeniz, Lawrence F. Kahn, and Abdul-Hamid Zureick ,ACI Structural Journal, V. 102, No. 2, MarchApril 2005.

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THANK YOU

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UNIT-8 The Absolutes of Life Some Other Absolutes of Life (other than Death and Taxes)

“So long as structures will keep on getting built, failures will keep on occurring.”

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The Gosain Dictum No. 2

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The Gosain Dictum No. 1

“Failures will keep Forensics Engineers busy for a long time” Primary Causes of Engineering Failures

Design flaws Material failures Overloading

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Deferred maintenance

Combination of all the above

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Gosain and Prasad Observation No. 1

Fear of failure will spur some owners to action! Gosain and Prasad Observation No. 2

An action may be Structural Health Monitoring!

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Some failures are sudden and catastrophic, and some failures just take their time… Structural Health Monitoring (SHM) can be very helpful in serving as an alarm system for preventing both types of failures …………. But what is Structural Health Monitoring? What is Structural Health Monitoring (SHM)? Definition: The process of implementing a distress or damage detection strategy for aerospace, mechanical and civil engineering structures is referred to as Structural Health Monitoring or SHM.

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Not a new concept Has been around for several decades Advances in electronics made it easier to implement. Several non-destructive evaluation (NDE) tools available for monitoring.

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How old is SHM? SHM work goes back almost 80 years. Limited to major structures

Bridges Some early high rises Unique structures

Life-safety issues Economic benefits Performance evaluation

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Significant interest in the past 10 years.

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Dams

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Affordable

Case History from the Past … San Jacinto Monument Built 1936

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La Porte, Texas

San Jacinto Monument Mat Foundation SHM San Jacinto Monument Mat Foundation SHM San Jacinto Monument Mat Foundation SHM San Jacinto Monument Mat Foundation SHM San Jacinto Monument Mat Foundation SHM

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San Jacinto Monument Mat Foundation SHM San Jacinto Monument Mat Foundation SHM San Jacinto Monument Mat Foundation SHM San Jacinto Monument Mat Foundation SHM

1. Modifications to an existing structure, 2. Monitoring of structures affected by external factors,

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3. Monitoring during demolition,

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Objectives of Structural Health Monitoring: Farrar and Worden (2007)

4. Structures subject to long-term movement or degradation of materials, 5. Feedback loop to improve future design based on experience, Objectives of Structural Health Monitoring

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6. Fatigue assessment,

7. Novel systems of construction,

8. Assessment of post-earthquake structural integrity, and 9. Growth in maintenance needs.

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Instrumentation used for SHM 1. Strain gages,

2. Inclinometers,

3. Displacement transducers,

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4. Accelerometers,

5. Temperature gages, 6. Pressure transducers, 7. Acoustic sensors, 8. Piezometers, and 9. Laser optical devices

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Instrumentation used for SHM Most of these sensors can be wirelessly connected. Technology using solar energy is very common in instrumentation. Latest technology even has self powered systems, i.e. no external power required.

Case History 1 Health Monitoring of a Stadium Truss During Erection

Segmented Erection.

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Health Monitoring of a Stadium Truss During Erection

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Some Recent Work…

Monitor strains and stresses at various stages of erection.

Key Challenges

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Verification of predicted behavior was needed

Non-interference with the construction schedule.

No wires were allowed to run from one segment to the other. No main power supply.

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No drilling or welding on to the frame.

Each segment needed to be prepared and instrumented in a narrow 2 day interval. No lift access after erection.

Health Monitoring of a Stadium Truss During Erection

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Instruments

MicroStrain V-Link

4 Strain gauges could be attached to the device. Fully ruggedized for exterior applications.

One laptop with data querying software was sufficient to access all boxes. Low duty cycle can give up to 1 year of battery life.

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Case History 2 Health Monitoring of a Data Center Health Monitoring of a Data Center Health Monitoring of a Data Center

Needed to prevent undesirable vibrations in the data center.

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Key Challenges

Quantify sensitivities of many high-performance computing systems.

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Needed to inform the contractor immediately upon discovery of an issue. Alarm system to alert Walter P Moore and the contractor. Health Monitoring of a Data Center

Pre-construction Testing.

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Instruments

National Instruments dynamic data acquisition system. PCB mG scale accelerometers.

Construction and Operations Time Monitoring

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Instantel Blastmate device. Case History 3

Health Monitoring of a Parking Garage Structure Health Monitoring of a Parking Garage Structure

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Key Challenges

Selection of monitoring location. Selection of types of measurements. Need to operate during power outages. Sensor installation.

Data logger installation.

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Remote communication setup. Alarm system to alert engineer and the client. Instruments Campbell Scientific CR10X logger with DC backup.

Anemometer. Rain gauge.

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Health Monitoring of a Parking Garage Structure

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Inclinometers with temperature sensors.

Health Monitoring of a Parking Garage Structure Case History 4

Health Monitoring of a Bridge Essential to Business Operations

Key Challenges

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Health Monitoring of a Bridge Essential to Business Operations

Installation of inclinometers under girders. Access was difficult.

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Night time installation was preferred.

Installation has to be stopped when a train passed by under the bridge. The whole system needed to be run with solar power. Remote communication setup.

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Alarm system to alert the engineer and the client. Instruments

Campbell Scientific CR1000 logger with solar power. Tilt beams with temperature sensors. Cellular TCP/IP modem facilitates accessing data over the internet Evaluate need

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Discuss the motivation in implementing SHM with the client and the benefits to be accrued Discuss the period of time for monitoring Have a clarity on how the damage or distress is to be defined and measured Select the appropriate instrumentation and data acquisition system

Extract meaningful data Presentation to client in a meaningful and understandable format

Improved hardware. Extensive usage by the industry.

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Reduce the implementation cost.

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Environmental conditions

Implement wireless and self powered technology.

Simplifies installation.

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Facilitates usage even in remote areas.

Insensitive to local power outages.

Estimate potential savings of using SHM.

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Develop models to show potential savings in using SHM vs. periodic physical inspections.

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Deferred Maintenance and SHM

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