design & construction errors- building maintenance and repairs
TRANSCRIPT
DESIGN & CONSTRUCTION
ERRORSHOW IT AFFECTS REPAIR & REHABILITATION
OF STRUCTURES
SRISHTI WAKHLOO B.TECH CE (HONS.) https://in.linkedin.com/in/srishti-wakhloo
BUILDING MAINTENANCE & REPAIRS
CONTENTS■ Introduction■ Design and Detailing Errors
– Causes■ Types of Design Errors■ Construction Errors
– Causes■ Types of Construction Errors■ Effect of Design & Construction Errors on Repair & Rehabilitation■ Conclusion■ References
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INTRODUCTION■ In buildings, repair & rehabilitation become necessary, as some parts
of the building naturally tend to deteriorate & become more defective. This may also happen due to lack of maintenance.
■ Repair: To restore (something damaged, faulty, or worn) to a good condition, for example repair of leakage in buildings, etc.
■ Rehabilitation: To restore something to it’s good or original condition■ Design and construction errors increase the cost and schedule
overruns
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CRAC
KS IN
CO
NCRE
TEBEFORE
HARDENING
DRYING
PLASTIC SHRINKAGE
SETTLEMENT SHRINKAGE
BLEEDING
DELAYED CURING
CONSTRUCTIONAL
FORMWORK MOVEMENT
EXCESS VIBRATIONSUBGRADE
SETTLEMENT
FINISHINGEARLY FROST
DAMAGE
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CRAC
KS IN
CO
NCRE
TEAFTER
HARDENING
UNSOUND MATERIALS
CEMENT
AGGREGATES
EXCESS SILT, MUD & DUST
LONG TERM DRYING
SHRINKAGE
THERMAL
HEAT OF HYDRATION
EXTERNAL TEMPERATURE
JOINTS IN CONCRETE
ELEVATED TEMPERATURE
FREEZING & THAWING
MOISTURE MOVEMENTS
TRANSITION ZONE
BIOLOGICAL
STRUCTURAL DESIGN
DEFICIENCIES
CHEMICAL
SULPHATE ATTACK
ALKALI-AGGREGATE REACTION
ACID ATTACK
SEA WATER
CARBONATION
CHLORIDE ATTACK
CORROSION OF REINFORCEMENT
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DESIGN & DETAILING ERRORS
A deviation from the plans and specificationsResponsibility of owner, designer and contractor
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CAUSES■ Accuracy of drawings■ Number of design omissions and ambiguities ■ Inadequacy within plans and specifications■ Quality of facility
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TYPES OF DESIGN ERRORS
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TYPES OF DESIGN ERRORS1. Inadequate Structural Design2. Poor Design Details
A. Abrupt Changes in SectionB. Insufficient Reinforcement at Corners and OpeningsC. Inadequate Provision for DeflectionD. Inadequate Provision for DrainageE. Insufficient Travel in Expansion JointsF. Incompatibility of Materials G. Neglect of Creep EffectH. Rigid Joints Between Precast UnitsI. Unanticipated Shear Stresses in Piers, Columns, or AbutmentsJ. Inadequate Joint Spacing in Slabs
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1. INADEQUATE STRUCTURAL DESIGN
■ CAUSES– Due to inadequate structural design the
concrete is exposed to greater stress than it can handle or strain in concrete increases more than its strain capacity and fails
■ SYMPTOMS– Spalling of concrete due to high
compressive strength– Cracking of concrete due to torsion and
shear stress■ PREVENTION
– Thorough review of all design calculations– Careful review of rehabilitation methods, if
any
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2. POOR DESIGN DETAILS■ CAUSES
– Localised concentration of high stresses in structural members■ SYMPTOMS
– Cracking of concrete that allows water or chemicals to pass through concrete
– Seepage through structural members– Structural failure
■ PREVENTION– Thorough and careful review of all design calculations
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2A. ABRUPT CHANGES IN
SECTION■ SYMPTOMS
– Cracking because of stress concentrations
■ PREVENTION– Use of relatively thin
sections rigidly tied into massive sections or patches and replacement concrete that are not uniform in plan dimensions
2B. INSUFFICIENT REINFORCEMENT AT CORNERS AND
OPENINGS■ CAUSES
– Increased stress concentration at corners
■ SYMPTOMS– Cracking of concrete
■ PREVENTION– Provide additional
reinforcement in areas where stress concentrations are expected to occur
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2C. INADEQUATE PROVISION FOR
DEFLECTION■ CAUSES
– Loading of members or sections beyond the capacities for which they were designed
■ SYMPTOMS– Cracking of walls or
partitions due to loadings
2B. INADEQUATE PROVISION FOR
DRAINAGE■ CAUSES
– Ponding of water caused by poor attention to details of draining
– Saturation resulting in severely damaged concrete in an area subjected to freezing and thawing
■ SYMPTOMS– Leakage may result in
damage to the interior structure
– Staining and encrustations on the structure
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2E. INSUFFICIENT TRAVEL IN
EXPANSION JOINTS■ CAUSES
– Inadequately designed expansion joints
■ SYMPTOMS– Spalling of concrete adjacent
to the joints■ PREVENTION
– The full range of possible temperature differentials that a concrete may be expected to experience should be taken into account in the specification for expansion joints
2F. INCOMPATIBILITY
OF MATERIALS■ CAUSES
– The use of materials with different properties (modulus of elasticity or coefficient of thermal expansion) adjacent to one another
■ SYMPTOMS– Cracking or spalling as the
structure is loaded or as it is subjected to daily or annual temperature variations
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2G. NEGLECT OF CREEP EFFECT
■ CAUSES– Inadequate provision for
deflections– Neglect of creep in pre-
stressed concrete members may lead to excessive prestress loss
■ SYMPTOMS– Cracking as loads are
applied
2H. RIGID JOINTS BETWEEN
PRECAST UNITS■ SYMPTOMS
– Cracking or spalling■ PREVENTION
– Designs utilizing precast elements must provide for movement between adjacent precast elements or between the precast elements and the supporting frame
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2I. UNANTICIPATED SHEAR STRESSES
IN PIERS, COLUMNS, OR ABUTMENTS
■ CAUSES– Lack of maintenance– Freezing of expansion
bearing assembles causing horizontal loading to be transferred to the concrete elements supporting the bearings
■ SYMPTOMS– Cracking of concrete– Entry of water into the
concrete
2J. INADEQUATE JOINT SPACING IN
SLABS
■ SYMPTOMS– Cracking of slabs-on-
grade
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INSUFFICIENT REINFORCEMENT AT
CORNERS AND OPENINGS
INADEQUATE PROVISION FOR DEFLECTION
INADEQUATE PROVISION FOR DRAINAGE
BLUE TSHUMIABRUPT CHANGE IN
SECTION
INSUFFICIENT TRAVEL IN EXPANSION JOINTS
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CONSTRUCTION ERRORS
Mistakes or inadequacies in a structure's own construction damage it partly or completely
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CAUSES■ May occur due to failure to follow specified procedures and good
practice or outright carelessness■ May not lead to failure or deterioration of concrete■ May have adverse impact on the structure with time
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TYPES OF CONSTRUCTION
ERRORS
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TYPES OF CONSTRUCTION ERRORS
1. Adding Water to Concrete2. Improper Alignment of Formwork3. Improper Consolidation or
Compaction of ConcreteA. Bug HolesB. HoneycombingC. Over-consolidation
4. Improper Curing5. Improper Location of
Reinforcement Steel
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6. Movement of Formwork7. Premature Removal of
Shores or Reshores8. Settling of Concrete9. Settling of the Subgrade10. Vibration of Freshly Placed
Concrete11. Improper Finishing of Flat
Concrete Surface
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1. ADDING WATER TO CONCRETE
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CAUSES EFFECTS
Addition of water to the concrete in a delivery truck to increase slump and decrease pouring or placement effort
• Concrete with lowered strength and reduced durability
• W/c ratio of the concrete increases, the strength and durability will decrease
Water is commonly added during finishing of structural member
Scaling, crazing, and dusting of the concrete
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2. IMPROPER ALIGNMENT OF FORMWORK
■ EFFECTS– Discontinuities on the surface of the concrete
These discontinuities are unsightly in all circumstances Their occurrence may be more critical in areas that are subjected to
high velocity flow of water, where cavitation-erosion may be induced, or in lock chambers where the “rubbing” surfaces must be straight
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3. IMPROPER CONSOLIDATION OR COMPACTION OF CONCRETE
■ EFFECTS– Improper compaction of concrete may result in a variety of
defects, the most common being bug holes, honeycombing, and cold joints
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BUG HOLES HONEYCOMBING OVER-CONSOLIDATION
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These can be reduced by inserting the vibrator more frequently, and as close as possible to the form face without touching the form, and slower withdrawal of the vibrator. Obviously, any or all of these defects make it much easier for any damage-causing mechanism to initiate deterioration of the concrete.
It is usually defined as a situation in which the consolidation effort causes all of the coarse aggregate to settle to the bottom while the paste rises to the surface. If this situation occurs, it is reasonable to conclude that there is a problem of a poorly proportioned concrete rather than too much consolidation.
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These are formed when small pockets of air or water are trapped against the forms. A change in the mixture to make it less “sticky” or the use of small vibrators worked near the form has been used to help eliminate bug holes.
3ABUG HOLES
3BHONEYCOMBING
3COVER-
CONSOLIDATION
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4. IMPROPER CURINGCuring is probably the most abused aspect of the concrete construction process. Unless concrete is given adequate time to cure at a proper humidity and temperature, it will not develop the characteristics that are expected and that are necessary to provide durability.■ SYMPTOMS
– Various types of cracking and surface disintegration– Failure to achieve anticipated concrete strengths, structural
cracking may occur
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5. IMPROPER LOCATION OF REINFORCING STEEL
■ CAUSE– This section refers to reinforcing steel that is improperly located or is not adequately
secured in the proper location■ EFFECTS
– First, the steel may not function structurally as intended, resulting in structural cracking or failure. E.g.is the placement of welded wire mesh in floor slabs. In many cases, the mesh ends up on the bottom of the slab which will subsequently crack because the steel is not in the proper location
– The second type of problem stemming from improperly located or tied reinforcing steel is one of durability. The tendency seems to be for the steel to end up near the surface of the concrete. As the concrete cover over the steel is reduced, it is much easier for corrosion to begin
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6. MOVEMENT OF FORMWORK
■ CAUSE– Movement of formwork during the period while the concrete is
going from a fluid to a rigid material may induce cracking and separation within the concrete
■ EFFECTS– A crack open to the surface will allow access of water to the
interior of the concrete.– An internal void may give rise to freezing or corrosion problems if
the void becomes saturated
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7. PREMATURE REMOVAL OF SHORES OR RESHORES
■ CAUSE– If shores or reshores are removed too soon, the concrete affected
may become overstressed and cracked■ EFFECTS
– In extreme cases there may be major failures
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8. SETTLING OF THE CONCRETE
■ CAUSE– During the period between placing and initial setting of the concrete,
the heavier components of the concrete will settle under the influence of gravity
– This situation may be aggravated by the use of highly fluid concretes ■ EFFECTS
– If any restraint tends to prevent this settling, cracking or separations may result.
– These cracks or separations may also develop problems of corrosion or freezing if saturated
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9. SETTLING OF THE SUBGRADE
■ CAUSE– Settling of the subgrade during the period after the concrete
begins to become rigid but before it gains enough strength to support its own weight
■ EFFECTS– Cracking may also occur– Sags and Humps (Localized Depressions) may occur
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10. VIBRATION OF FRESHLY PLACED CONCRETE
■ CAUSE– Most construction sites are subjected to vibration from various
sources, such as blasting, pile driving, and from the operation of construction equipment. Freshly placed concrete is vulnerable to weakening of its properties.
■ EFFECTS– If subjected to forces, concrete matrix may disrupt during setting
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11. IMPROPER FINISHING OF FLAT CONCRETE SURFACE
A. Adding water to the surface: Evidence that water is being added to the surface is the presence of a large paint brush, along with other finishing tools. The brush is dipped in water and water is “slung” onto the surface being finished.
B. Timing of finishing: Final finishing operations must be done after the concrete has taken its initial set and bleeding has stopped. The waiting period depends on the amounts of water, cement, and admixtures in the mixture but primarily on the temperature of the concrete surface. On a partially shaded slab, the part in the sun will usually be ready to finish before the part in the shade.
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11. IMPROPER FINISHING OF FLAT CONCRETE SURFACE
C. Adding cement to the surface: This practice is often done to dry up bleed water to allow finishing to proceed and will result in a thin cement-rich coating which will craze or flake off easily.
D. Use of tamper: A tamper or “jitterbug” is unnecessarily used on many jobs. This tool forces the coarse aggregate away from the surface and can make finishing easier. This practice, however, creates a cement-rich mortar surface layer which can scale or craze. A jitterbug should not be allowed with a well designed mixture. If a harsh mixture must be finished, the judicious use of a jitterbug could be useful.
E. Jointing: The most frequent cause of cracking in flatwork is the incorrect spacing and location of joints.
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MOVEMENT OF FORMWORK
SETTLING OF CONCRETE SETTLING OF SUBGRADE
IMPROPER FINISHING OF FLAT CONCRETE SURFACE
IMPROPER CURING- PLASTIC SHRINKAGE
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EFFECT OF DESIGN AND CONSTRUCTION ERRORS ON
REPAIR & REHABILITATION
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S.NO. DESIGN ERRORS REPAIR & REHABILITATION TECHNIQUES
1. Inadequate Structural Design
• Plate Bonding Method• RC Jacketing of beams & columns
with RCC• Strengthening by Fibre Reinforced
Polymer (FRP)
2. Poor Design Details• RC Jacketing• Increase in longitudinal
reinforcement
2A Abrupt Changes in Section• Providing struts for span reduction of
beam• Concrete strengthening
2B Insufficient Reinforcement at Corners and Openings
• Installing Ferro-cement plates at corners
• Providing vertical reinforcement at corners, junction of walls
2C Inadequate Provision for Deflection Rebuilding portions of the wall
2D Inadequate Provision for Drainage• Fixing of drainage pipes• Drainage of sloped roof with tiles• Waterproofing• Correction of floor leaks & trapsSRISHTI WAKHLOO B.TECH CE (HONS.) https://in.linkedin.com/in/srishti-wakhloo
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S.NO. DESIGN ERRORS REPAIR & REHABILITATION TECHNIQUES
2E Insufficient travel in expansion joints Repair or replace expansion joints
2F Incompatibility of materials• Grout injection• Concrete ring beams & roof & floor
substitution• Bond coats
2G Neglect of Creep Effect• Bed Joints Reinforcement Technique• Fibre Reinforced Polymer Composite
(CFRP)2H Rigid Joints Between Precast Units Shear Keys/ Mechanical Anchors
2I Unanticipated Shear Stresses in Piers, Columns, or Abutments
• Cutting new expansion joints, jacking structure, isolation bearings, removal of portions of structure
• Providing struts for span reduction of beam
• Reducing dead loads and live loads
2J Inadequate Joint Spacing in Slabs• External stressing• FRP Method• Plate Bonding
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S.NO. CONSTRUCTION ERRORS REPAIR & REHABILITATION TECHNIQUES
1. Adding Water to Concrete• Epoxy Coating (Epoxy Resin +
Hardener)• Polymer Resin based Coating• Shotcrete/ Gunite
2. Improper Alignment of Formwork• Shear Keys• Preformed Foam Gaskets• Cast In Place Foam
3 Improper Consolidation or Compaction of Concrete Fibre Reinforced Concrete
3A Bug Holes Epoxy Resin
3B Honeycombing
• Polymer Modified Cement Mortar (PMM)
• Polyester Putty• Epoxy putty• Emulsified Styrene Butadiene
Rubber(SBR) Polymer
3C Over-consolidation• Polymer Modified Cement Mortar
(PMM)• Polymer Modified Concrete (PMC)• Epoxy Resin
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S.NO. CONSTRUCTION ERRORS REPAIR & REHABILITATION TECHNIQUES
4. Improper Curing
• Elastomeric sealer• ‘Flexible’ epoxy filler• Membrane or special mortar• Strengthening by Fibre Reinforced
Polymer (FRP)
5. Improper Location of Reinforcement Steel
• Introducing new reinforcement bars for structural connections
• Fibre Reinforced Polymer (FRP) for durability
6. Movement of Formwork• Coarse aggregate and grout• Dry-pack• Waterproofing by Acrylic Polymer or
SBR Polymer
7. Premature Removal of Shores or Reshores
• Cutting new expansion joints, jacking structure, isolation bearings, removal of portions of structure
• Caulking for live cracks
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S.NO. CONSTRUCTION ERRORS REPAIR & REHABILITATION TECHNIQUES
8. Settling of The Concrete
• Fusion Bonded Epoxy Powder Coatings (FBEC)
• Cathodic Protection• Chloride Removal• Realkalisation• Epoxy• FRP Strengthening
9. Settling of The Subgrade• Patching with Base Repair• Overlay Patches• Grader Patching
10. Vibration of Freshly Placed Concrete• Fibre Reinforced Concrete (FRC)• Re-concreting• Hardened Cement Paste (HCP)
11. Improper Finishing of Flat Concrete Surface
• Polymer Modified Cement Mortar (PMM) with Bond Coat
• Shotcrete with Finishing Plaster and Water Curing
• Polyurethane Coat
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CONCLUSION■ A structure, if regularly maintained, will not need extensive repair and
rehabilitation and the cost of the same would also go down.■ Design errors' onset is during the stage of planning. These can be
prevented by careful and thorough inspection of drawing at each stage.■ Construction errors' commence during the stage of execution and can
be controlled by inspection, excepting when environmental factors govern the error.
■ Even after the identification of repair/rehabilitation method, it is significant to know the specifications of the materials to be used, so that these can be altered depending upon the need.
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REFERENCES■ http://theconstructor.org/concrete/design-detailing-errors-concrete-constructio
n/8190/■ http://theconstructor.org/concrete/construction-errors-during-concreting-at-sit
e/8184/■ http://nairaproject.com/projects/080.html■ Concrete Problems & Repair Techniques- Professor Khaled A. Soudki, Peng■ CPWD Handbook on Repair & Rehabilitation of RCC Buildings■ Repair & Rehabilitation of Structures- Prof. M. Vijayalakshmi■ WSDOT Maintenance Manual- Chapter 3- Page 3 to 28
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