KTU CE 204 Construction Technology - Module 6

CONSTRUCTION
TECHNOLOGY
Module 6
Fr. Dr. Bennet Kuriakose
Department of Civil Engineering

Syllabus
• Building Failures – General reasons – classification –
Causes of failures in RCC and Steel structures – failure due
to fire, wind and earthquake
• Foundation failure – failures by alteration, improper
maintenance, overloading
• Retrofitting of structural components – beams, columns
and slabs
Department of Civil Engg., SJCET Palai 2

BUILDING FAILURES

Introduction
• Building failure occur when the building loses its ability to
perform its indented function.
• Failure can cause wastage of money, resources, life and
may impart impact on the environment.
Tacoma Narrows Bridge Chernobyl Nuclear Disaster Bhuj Earthquake

Introduction
Shanghai Building Overturn WTC A fire accident
Minneapolis Bridge failure Failure due to landslide

General Reasons (Causes)
1. Improper Structural Design
– Loads need to be estimated carefully and proper design
need to be implemented.
– Can cause due to:
• Errors in load computation
• Errors in modelling
• Errors in theories/ analysis
• Ignorance of repeated or impulsive loads
• Improper choice / misunderstanding of materials
• Ignorance of structural behaviour

2. Improper/ Faulty Construction
– Bad construction practices and improper choice of
materials results in this cause of failure
– Cause due to:
• Improper quality of construction materials
• Improper beam – column joints (steel or concrete)
• Failure to understand the architectural / structural
drawings.
• Ignorance of good engineering practices
• Improper quality control
• Inadequate supervision

3. Foundation Failure
– This can cause due to :
• Poor quality of soil
• Improper design of foundation
• Liquefaction of soil
4. Unexpected / Extraordinary loads
– Ex:
• Natural: Repeated heavy snowfall, Earthquake,
Floods, Hurricane, Tsunami, Landslide
• Manmade: Vehicle impact, unexpected vibration due to
machines, overcrowding

5. Failure by Alteration
– Improper alteration affects the structure and can lead to
failure.
• adding of extra stories of buildings.
• Opening in walls
• Adding extra slabs, beams etc.
– Careful calculations need to be performed before
refurbishment/ alterations
– Temporary supporting system need to be provided
properly
– Check the stability requirements
– Good workmanship and expertise

7. Improper Maintenance
– All the structures will have deterioration on the course of
time, which need to be maintained.
• Concrete can have cracks, corrosion etc.
• Steel can have corrosion.
– If not maintained, will eventually lead to failures.
8. Deliberate Attack
– Terrorist/ antisocial people
9. Bad workmanship
10. Improper selection of materials
11. Compromises in professional ethics

Classification of Failures
A. Classification based on Structural Behaviour
– Structurally, building can fail in the following ways:
1. Strength Failure (structures stresses exceed the
permissible limit. Structure will get yielding, big cracks
leading to collapse, fatigue …)
2. Serviceability/ Functional Failure (structure will not be
fit for its intended use. Ex.: excessive deflection,
excessive crack width, excessive vibration.)
3. Stability Failure (Structure will loose stability. Ex.:
structure buckle, overturn, slide…)

Classification of Failures
B. Classification based on stages of building
1. Construction failure
– Failure during the construction due to improper planning,
supervision, inspection etc.
2. Service Failure
– Mainly due to overloading or fire
3. Maintenance Failure
– Improper maintenance of building – corrosion,
deterioration,
4. Aesthetic Failure
– Rise of dampness, failure of plaster, nonstructural
cracking

Failure in RCC Structures
• RCC structures is most commonly built and can have
different types of failures.
The main causes are:
1. Accidental Loads
– Impact loads of vehicles against bridge pier or walls
– Explosive loads
– Earthquake, flood, tsunami
– Fatigue loads
2. Poor Workmanship
– Unstable formwork
– Misplace/ improper reinforcement

– Improper mix (excessive w/c ratio, aggregates…)
– Error in handling concrete
– Improper curing
3. Unwanted Chemical Reactions
– Acid Attack
– Alkali Attack
– Sulphate Attack
4. Corrosion of Embedded Metals (Rebars)
– When steel corrodes, it occupies greater volume – induce
tensile stress
– Corrosion decreases bonding between rebars and
concrete
– Corrosion decreases the effective cross sectional area of
rebarsDepartment of Civil Engg., SJCET Palai 15

– Prevention:
• Concrete with less permeability
• Adequate cover
• Anticorrosive coated rebars
• Corrosion inhibiting admixtures
• Cathodic protection
– Errors in load computation, modelling, calculation etc.
6. Improper detailing
– Detailing is the process of providing proper reinforcement
and the way with which it is implemented.

7. Freezing and Thawing
– Moisture within concrete freeze to increase the volume,
thereby inducing tensile stress
– Can be reduced by reducing porosity of concrete or
providing air entrained concrete.
8. Shrinkage
– Drying shrinkage and plastic shrinkage causes volume
change and thereby cracking
9. Thermal Stresses
– Due to: heat of hydration, climatic conditions and fire
10. Improper selection of Materials
– Improper selection of ingredients of concrete

Failure of Steel Structures
1. Failure of Connection
– The connections in steel structures are very crucial
– If not properly designed/ deterioration due to corrosion 
failure at joints
– Bolted joint : (a) bolts can shear off (b) plate can tear off
– Welds are brittle and always have a chance of failure

2. Buckling Failure
– Loose of stability of structure
mainly because of compressive
force is called buckling.
– Important types
(a) Global buckling
– Compression buckling of
struts
– Lateral torsional buckling
(b) Local Buckling – certain parts
of the member buckles

3. Fatigue Failure
– Fracture of material because of repeated loading (small
intensity)
– Fatigue fracture is sudden
– Extreme cold enhances steel fatigue failure

4. Corrosion Failure
– Types (a) uniform corrosion (b) pitting corrosion
– Flakes or scales of reddish brown (iron oxide)
– Strength reduces
– Methods to avoid corrosion – Protective coatings,
encasement, sacrificial coatings, galvanisation

5. Fire Attack
– Fire causes:
• Reduction is strength
• Make the steel brittle by changing its microstructure
• Fire induces thermal stresses – gets redistributed into
different components of structure
• If temperature > ~1400 °C steel melts

6. Accidental Loads
– Impact loads of vehicles against bridge pier or walls
– Explosive loads
– Earthquake, flood, tsunami
– Fatigue loads
– Errors in load computation, modelling, calculation etc.

FAILURE DUE TO
EARTHQUAKE

Earthquake

Earthquake - Reason

Characteristics of Earthquake
• PGA (Peak Ground Acceleration) - PGA is equal to the
amplitude of the largest absolute acceleration recorded on
an accelerogram.
• Magnitude (Richter Scale) Measure of energy released
(Quantitative) – same for an earthquake
• Intensity (Mercalli Scale) - Measure of intensity of EQ
(Qualitiative) – different for an earthquake at different places

How Earthquake act?
• Ground acceleration (GA) induce Spectral acceleration (SA)
within the building (both in horizontal directions).
• SA acts with Mass of building at each floor  Inertia Force
(Storey shear)
• Sum of all the storey shears is called Base shear.

Factors Affecting Seismic Failure
1. Magnitude and Intensity of Earthquake
2. Soil conditions –
– some soil amplify the vibrations.
– Saturated sand liquefy upon earthquake
– Building on sloping ground give poor performance
3. Building Configuration
– Setbacks
– Soft Storey
– Floating Columns

4. Size of the building
– too tall, too long or too large in plan
perform badly
5. Adjacency of other Buildings
– Cause pounding during earthquake
– “Pounding”  building hit each
other

Earthquake Resistant Design
The main aspects of Earthquake resistant design or Aseismic
design of structures are:
1. Proper Detailing
– “Detailing” is the way by which reinforcement is arranged
in the structural members.
– If RCC frames are made ductile using “ductile detailing”
principles, the frame performs well in earthquake.

2. Strong Column – Weak Beam Concept
– Columns are made strong and beams weak
– Beams may fail, so that only certain portion of building will
get damage, thereby absorbing energy.
– If columns fail first, may damage the whole building.

3. Avoiding Soft- Storeys
4. Horizontal and Vertical bands in Unframed Buildings
– Provide integrity to the masonry during earthquake

5. Reduce Earthquake effects on Buildings
– Dampers
– Base Isolation

FAILURE DUE TO WIND

Factors Affecting Wind Failure
• Wind exposure increases as height increases
• Wind effects depend on:
1. Direction of wind
2. Velocity of wind
3. Amount of Wind Gust
4. Self weight of building – reduced self weight induce
more forces
5. Height of building
6. Slope of the roof
7. Topography of the site
8. Shape of the building

Factors Affecting Wind Failure
9. Slenderness of building – slender buildings have chance of
vortex shedding effect
• Vortex shedding induce vibration perpendicular to wind
direction (across-wind vibrations)
• Vertex shedding sometimes induce aeroelastic flutter
10. Existence of rain water/ snow on surface of members

Wind Resistant Design
1. Canopies to be avoided
2. Reduce the area of openings (doors and
windows) in a building.
3. Reduce the slope of the pitched roof.
4. Strakes are provided in chimney to avoid
vortex shedding
5. Increase self-weight
6. Do not build a structure on wind
amplification regions (ex. Hilly regions).

FAILURE DUE TO FIRE

Fire
• People die due to burns and asphyxia
• Causes of Fire
– Cooking accidents because of leakage of LPG
– Short circuit in electrical system
– Overheating of appliances
– Inflammable materials in the rubbish

Effects of Fire of Building Materials
1. Stone
– Sandstone withstands moderate fire
– Granite and limestone disintegrate upon fire
2. Bricks
– Bricks normally are not affected by fire.
– In brick masonry, mortar become very weak when
heated up.
3. Steel

Effects of Fire of Building Materials
4. Concrete
– Looses strength beyond 250 degree celcius
– However can resist fire for 60 minutes (of 1000 degree
celcius)
5. Glass
– Borosilicate glass resist high temperatures.
6. Timber
– Will get destroyed because of fire
– Enhances the intensity of fire
– Fire resistant coatings can be provided
7. Plastics
– Most vulnerable to fire, emit poissonous gases upon fire

Protection Against Fire
1. Fireproof Coating for steel
2. Providing minimum thickness of member
3. Increase the cover for concrete
4. Firestop mortar usage
5. Coating with fireproof blankets

FOUNDATION FAILURE

Types/ Causes of Foundation Failure
1. Punching Shear Failure
– In this mode of failure, foundation
fails due to formation of inclined
cracks around the perimeter of the
column.
– The critical section for punching
shear failure is taken at d/2 from the
face of the column
– Additional reinforcement should be
provided to resist punching shear in
case of shear resistance of concrete
with reinforcement provided is not
sufficient.
A. Structural Failure (Overloading)

Types of Foundation Failure
2. Flexural Failure
– The critical section for flexure is
considered at the face of column.
– Flexure failure is resisted by providing
percentage of reinforcement required to
resist the bending moment.
3. One-way shear (Direct shear) Failure
– Foundations in one-way shear failure
fails in inclined cracks at a distance d
from the face of the column
– To avoid one-way shear failure of
foundations, the shear stress at the
critical section of footing should be less
than the shear strength

B. Geotechnical Failure
1. Settlement Failure
– Settlement = elastic (immediate) + consolidation (long
term)
– Tipping and differential settlements create damage to
the structure

2. Liquefaction
– When saturated or partially saturated cohesionless soil is
subjected to vibration, looses all the shear strength and
behaves like liquid.

3. Foundation uplift
– If the structure is subjected to lateral forces, one part of
the structure is subjected to uplift

4. Expansion (swelling) and Heaving
– Some soil expand upon drying. Ex: black cotton soil

C. Failure due to Alteration
• Improper alteration can increase the loading on foundation
• Types:
– Adding extra storeys
– Removing certain load bearing parts (columns, walls etc.)
D. Improper Maintenance
• Corrosion – important structures’ foundation need to be
checked for quality periodically and maintained.
• “Below Ground Corrosion Assessment” (BGCA) system can
be used.

REFURBISHMENT
TECHNOLOGY

Cosmetic Repair
Causes of Deterioration of Concrete
1. Corrosion of rebars
2. Shrinkage cracks
3. Alkali Attack
4. Sulfate Attack
5. Acid Attack
6. Leaching
7. Continuous water splashing (waves or rain)
8. Wear and tear due to continuous vehicle movement
9. Weathering due to freezing and thawing
10.Cracking due to temperature reversals

Cosmetic Repair
• Cosmetic repair does not include structural repairs
• It focuses on surfaces to repair deterioration
• Types:
– basin, sink and bath repairs
– Brick repairs and tinting
– Wooden Cabinets/ door/ furniture repair
– Veneer/ plywood repair
– Ceramic tile repair
– Decorative stone repair
– Marble/granite repair

Retrofitting
• Retrofitting/ Refurbishment Technology is the modification or
upgradation of existing structure to make them more
resistant to loads, especially against earthquake (seismic
retrofit)
• Provides economical solution to lack of strength of a
structure (need not replace the structure)
• Important to small homes, historical monuments etc.
• Performance Objectives:
– Public safety only. The goal is to protect human life,
ensuring that the structure will not collapse
– Structure survivability. The goal is that the structure,
while remaining safe for exit, may require extensive repair
(but not replacement. This is typically the lowest level of
retrofit applied to bridges.

Retrofitting
– Structure functionality. Primary structure undamaged
This is the minimum acceptable level of retrofit for
hospitals.
– Structure unaffected. This level of retrofit is preferred for
historic structures of high cultural significance.
• Classification:
(a) Global (whole structure level): Retrofitting is made to
improve the overall performance of the structure. Ex:
adding shear wall, adding infill wall, base isolation,
adding dampers.
(b) Local (member level): retrofitting is made on a member
so as to arrive at local improvement of performance. Ex:
retrofitting column, retrofitting beam, retrofitting slabs.

Retrofitting of Column
1. Reinforced Concrete Column
(RCC) Jacketing
– Normally opted when global
retrofitting is not viable.
– Cheap and widely used
– Procedure:
• Column face is chipped
• Reinforcement is provided
around the column
• Shotcreting is done over the
column

2. Steel Jacketing
– Steel plates are added on to the existing column.
– Advantages:
• Does not add weight of structure
• No need of curing

3. Fibre Reinforced Plastic (FRP) Jacketing
– Fibre fabric types – Glass Fibre (GFRP), Carbon Fibre
(CFRP), Aramid Fibre (AFRP) or their combinations
– Fabric is pasted on to the column using resin

Retrofitting Beam
1. RCC Jacketing
– Normally opted when global
retrofitting is not viable.
– Cheap and widely used
– Procedure:
• beam face is chipped
• Reinforcement is provided
around the beam, often
drilled into the beam
• Shotcreting is done

Retrofitting Beam
2. Steel Jacketing
– Steel plates are added on to the existing beam.
– Advantages:
• Does not add weight of structure
• No need of curing

Retrofitting Beam
3. FRP Jacketing
– Fabric is pasted on to the column using resin
– Three types:
• Complete Wrapping
• U-Wrapping (3-sides)
• Two sides wrapping

Retrofitting Slab
1. RCC Jacketing
– Two types:
• Jacketing at top – jacked 
chipped  rebars added 
concrete
• Jacketing at bottom – jacked
 chipped  rebars added 
shotcrete

2. Steel Jacketing
– Chipped and steel plates are welded to soffit

3. FRP Jacketing
– Fabric is pasted either to bottom or top

KTU CE 204 Construction Technology - Module 6

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