Fire Damage Assessment Report

Presented by Eng. Jude Aruna Gayan
Based on the
Fire Damage Assessment Report
Submitted by Structural Design Unit –
Defence Head Quarter Complex Project, Sri Lanka

Date: 15th of February 2014
Time: 4.45 PM
Location: Lower Level 02 of Block 06 , Defence Head Quarter Complex
(DHQC) construction site at Akuregoda, Battharamulla
Cause: Electrical leakage in the building (Possible)
Damage: Stored materials and structure of the main tower of Block 06 LL2
and LL1 structural elements
The Incident ...

Fire Damage
• Severity of fire is influenced by three parameters.
Fire load (Quantity, Type And Distribution)
Ventilation (Area, Height, Location)
Compartment (Floor Area, Surface Area, Shape, Thermal Characteristics)
• In building fires, there are two regimes of combustion,
Ventilation controlled fire - Occur where availability of air is limited
Fuel surface controlled fire - Limit is imposed by availability of
combustible materials
The fire at the Block 06 Building could be categorized as
'Ventilation Controlled' type of fire.

• The spread of fire in Block 06 had been controlled due to the lack of
combustible materials at other areas and block work constructions that had
been completed around the fire initiated area.
• The surrounding block works constructed around the fire initiated zone had
concentrated fire in to a limited area, which had controlled the free access of air.
• Remaining debris in affected area shows that, there were combustible materials
such as sponge, rigifoam, safety nets stacked in a confined area of the floor
slab.
• This had caused fire got intensified gravely within a short period of time.

Effect of Fire on Reinforced Concrete
Compressive Strength of Concrete
• Depend on temperatures, mix proportions, Couse aggregate used and loading
conditions at time of exposure.
• Temperatures up to 300 °C do not seriously affect residual strengths of structural
concrete.
• Temperatures greater than
300 °C, Compressive strength
of concrete reduces very rapidly.
• A significant loss in
Compressive Strength of
Concrete when the temperature
reaches up to 500 °C mark.

Approximate
Temperature
Process
100°C
Simple Dilatation / Hydrothermal reactions – loss of chemically bound water
begins.
300°C
Start of temperature loss for siliceous concretes – some flint aggregates
dehydrate.
100 – 400 °C
Critical range for explosive Spallation / above 300 °C, large reduction in
density
400- 500 °C
Decomposition of calcium hydroxide / At 500°C Reduction of 50% of the
concrete strength Ca(OH)2 -----> CaO + H2O
600°C Marked increase in ‘basic’ creep
700°C Dissociation of calcium carbonate
800°C Ceramic binding. Total loss of water of hydration
1200°C Melting starts
Mineralogical Changes In Concrete Caused By Heating
Effect of Fire on Reinforced Concrete cont.…

Elastic Modulus of Concrete
• Elastic modulus of concrete is drastically reduced if heated to temperatures in excess
of 300 °C.
• Elastic deflection due to this effect is not significant in relation to other effects of fire.
Effect of Fire on Reinforced Concrete cont.…
Loss of Bond
• Exposure to high temperatures weaken bond strength of reinforcement bars with
concrete.
• Loss of bond directly affects
crack-width control and consequently
reduce durability of the structure.

Spallation of Concrete
• Spallation involves the breaking off of layers of concrete from the exposed surface at high
and rapidly rising temperatures.
• The main parameter influencing the process is Vapor pressure.
Released from physically and chemically bound water in concrete pores Pressure builds up Lead to spallation
• Three main types of Spallation can be identified.
Explosive Spallation occurs early in the fire and proceeds with a series of disruptions, each locally
removing layers of shallow depth.
Sloughing off / Aggregate Spallation, also occurring in the early stages, involves the expansion and
decomposition of the aggregate at the concrete surface causing pieces of the aggregate to be ejected from
the surface. internal cracking due to different thermal expansion of aggregate and cement paste
Corner Spallation occurs in the later stages of the fire when temperatures are lower. Occurs mainly in
beams and columns, tensile cracks develop at planes of weakness such as the interface between the
reinforcement and the concrete.

Reinforcing Steel
• Steel loses its strength at high temperatures and is usually the reason if Excessive
deflections are observed after a fire.
• Exposure to temperatures less than 600 °C for mild steel has no significant effect in
the yield strength after cooling.
• If temperatures in excess of 700 °C the determination of the strength id critical to
assessment.
• Loss of Ductility may
occur after exposure to high
temperatures.

The assessment could be followed in Two methodologies,
1. Test the fire damaged concrete to directly assess the concrete quality.
2. Estimate the fire severity so as to deduce temperature profiles and hence to calculate the
residual strength of the concrete and the reinforcement.
The first methodology to directly assess the concrete quality.
 Visual inspection
 Non-destructive testing (E.g. rebound hammer, ultrasonic pulse velocity (UPV))
 Destructive Testing (E.g. strength testing of concrete and reinforcement samples)
The second methodology involves three steps to assess the residual strength and the
outcome shall be verified by appropriate testing.
 Evaluation of fire severity – This can be performed based on debris or applying numerical
evaluation methods.
 Determination of temperature profiles – This may be performed applying numerical methods or
simpler calculation techniques
 Assessment of residual strength of the concrete
Assessment Of Fire Damage

Proposed testing methods to determine the fire damage
Test
Location
Test
Type
Test
Method
Information Gained
Colour
changes
Lateral
extent of
damage
Depth of
Damage
Compressive
strength of
undamaged
concrete
Tensile
strength
of r/f
bars
On-Site
Non -
Destructive
Visual inspection √ √ √
Rebound Hammer √
Ultrasonic Pulse
Velocity √
Laboratory Destructive
Core Test √
Reinforcement
test √
Assessment Of Fire Damage cont…

Class of
Damage
Element
Surface Appearance of
concrete
Structural condition
Condition of
Finish
Colour Crazing Spallation
Exposure and condition
of main reinforcement
Cracks
Deflection /
Distortion
0 Any Unaffected or beyond extent of fire
1
Column
Some
peeling Normal Slight Minor
None exposed
None None
Wall
Floor
Very minor exposureBeam
2
Column
Substantial
loss
Pink/red Moderate
Localised to corners
Up to 25% exposed, none
buckled
None None
Wall
Localised to patches
Up to 10% exposed, all
adheringFloor
Beam
Localised to
corners, minor to
soffit
Up to 25% exposed, none
buckled
3
Column
Total loss
Pink/Red
Whitish
grey
Extensive
Considerable to
corners
Up to 50% exposed, not
more than one bar buckled
Minor None
Wall
Considerable to
surface Up to 20% exposed,
generally adhering
Small Not significantFloor
Considerable to
soffit
Beam
Considerable to
corners, sides, soffit
Up to 50% exposed, not
more than one bar buckled
4
Column
Destroyed
Whitish
grey
Surface
lost
Almost all surface
spalled
Over 50% exposed, more
than one bar buckled
Major
Any
distortion
Wall
Over 20% exposed, much
separated from
concrete
Severe and
significant
Severe and
significant
Floor
Beam
Over 50% exposed, more than one
bar buckled
Visual Assessment Go to Slide No 36

More than 25 % R/F
Exposure Condition
More than 50 % R/F
Exposure Condition
Discoloration
Discoloration
Visual Assessment Of Fired Area

Initial Repair Classification
Class of
Damage
Repair
Classification
Repair Requirements
0 Decoration Redecoration if required
1 Superficial Superficial repair of slight damage not needing fabric reinforcement
2 General repair
Non-structural or minor structural repair restoring cover to reinforcement where
this has been partly lost.
3 Principal repair
Strengthening repair reinforced in accordance with the load- carrying requirement
of the member. Concrete and reinforcement strength may be significantly reduced
requiring check by design procedure.
4 Major repair
Major strengthening repair with original concrete and reinforcement written down
to zero strength, or demolition and recasting.

Location Material Conditions
Approximate
Temperature
(°C)
1 Timber Plank(2’*4’) Ignites 240
2 Aluminium Melted 650
4 Piece of concrete No colour change Below 350
5
Steel
Aluminium
Not melted
Melted
1100 - 650
6 Timber plank Ignites 240
8 Piece of concrete Pink colour dots 350
9 Steel Not melted 1100-650
10 Plywood Ignites 240
12
Piece of concrete
PVC
Pink colour dots
Charred
350
500
13 Iron Not melted Below 1100
14
Aluminium
Steel
Melted
Not Melted
1100 - 650
15 Piece of concrete Pink colour dots 350
Survey on Fire Severity
• An assessment of the materials burnt and the
disposition of the fire provide information
about likely temperatures developed and the
duration at any location.
• This Evaluation provides useful guide in
planning more specific examination and
testing for the damage area.

Temperature in fired area was greater than 650°C (Melting temperature of Aluminum), but
should less than 1100°C (Melting temperature of Steel).
Survey on Fire Severity cont…
Aluminum melted
Binding wire not melted Iron piece not melted
Fully burnt timber plank

• Provides a rapid indication of the Compressive strength of concrete.
• The Rebound of an elastic mass depends on the hardness of the surface against which
its mass strikes.
• The rebound is taken to be empirically related to the compressive strength of the
concrete.
• The rebound value is read from a graduated scale and is designated as the rebound
number or rebound index.
• The compressive strength can be read directly from the graph provided on the body of
the hammer.
• The results are significantly affected by :
 Mix characteristics
 Angle of inclination of direction of hammer
 Member characteristics
Test On Structural Element In The Fire Affected Area
Rebound Hammer Test

Graph vs. Rebound Index & Compressive Strength of Concrete
For Good quality / gravel & sand aggregate / Age 14 to 56 days / smooth and dry surfaces

Rebound Hammer – Schematic Diagram

Procedure
• Surface preparation - Using abrasive Stone
 No Plaster
 No Paint or Dust
 No Irregularity / Aggregates
 No spalled surfaces,
• The results of this test on fire-damaged concrete, even on flat surfaces, are somewhat
variable and this is perhaps due to skin hardening effects that appear to occur.
• The survey is carried by dividing the member into well-defined grid points.
• Take the average of about 10 readings
• Should be tested against the Anvil.
Ex: Type N test hammer – Nominal value (79 ± 2)

Interpretation of Results
The rebound reading on the indicator scale has been calibrated by the
manufacturer of the rebound hammer for horizontal impact.
Average Rebound Number Quality of Concrete
> 40 Very good hard layer
30 to 40 Good layer
20 to 30 Fair
< 20 Poor concrete
0 Delaminated

• Requires a Flat Surface and only appropriate for
Unspalled surfaces.
• Can be used to give an indication of Depth Of
Seriously Weakened Concrete.
Ultrasonic Pulse Velocity (UPV) Measurement - Part 4 of BS EN 12504
• Based on the Pulse Velocity Method
• Provide information on the Uniformity Of Concrete, Cavities, Cracks And
Defects, Presence Of Voids, Honeycombing or other discontinuities.
• The pulse velocity in a material depends on its Density And its Elastic
Properties which is related to the quality and the compressive strength of the
concrete.
• It is also applicable to indicate Changes In The Properties Of Concrete, and
in the survey of structures, to estimate the Severity Of Deterioration Or
Cracking.

• The UPV equipment (e.g. PUNDIT)
 Transmitter
 Receiver
 Indicator
• Indicator shows the time for the ultrasonic pulse to
travel from the Transmitter to the receiver through
the concrete.
• The transducer is firmly attached to concrete surface
using a Gel or Grease to vibrate the concrete.
• The pulse velocity can be determined from V = L / T
• The velocity of sound in a concrete is related to the
concrete density & modulus of elasticity. V ~ √E/ρ
V = pulse velocity (km/s)
L = path length (cm)
T = transit time(µs)
E = modulus of elasticity
ρ = density of the concrete

• There are three basic ways in which the transducers may be arranged.
 Opposite faces (Direct transmission)
 Adjacent faces (Semi-direct transmission)
 Same face (Indirect transmission)
Different Test Methods
• Direct transmission is the Most sensitive, and indirect transmission the Least
sensitive.
• Indirect transmission should be used when only one face of the concrete is accessible,
when the depth of a surface defect or crack is to be determined or when the quality of
the surface concrete relative to the overall quality is of interest.

• The results are influenced by;
• Type of cement
• Type and size of aggregate
• Presence of reinforcement
• Moisture condition
• Compaction
• Age of concrete
• Comparatively Higher velocity
indicate Concrete Quality is Good
in terms of density, uniformity,
homogeneity etc.

Concrete Quality Accordingly to Pulse Velocity.
• Uniformity and Relative quality of concrete.
• To indicate the Presence of voids and cracks, and to evaluate the effectiveness of
crack repairs.
• When used to monitor changes in condition over time, test locations are to be
marked on the structure to ensure that tests are repeated at the same positions.
• The Degree of saturation of the concrete affects the pulse velocity.
• The pulse velocity is independent of the dimensions of the test object provided
reflected waves from boundaries
Significance & Use

Core Test
• The most direct method of estimating strength of in-situ concrete is by testing cores cut
from the structure.
• A limited number of test cores were extracted from the fire damaged area to minimize
further damage.
Tensile Test on Reinforcement Steel
• Rebar samples were taken from representative elements of damaged structural members.
• The samples were tested for yield, elongation , ductility and tensile strength.

Structural
Component
Unaffected by fire Affected by fire
Rebound
Hammer
(N/mm2)
UPV Test
(N/mm2)
Core Test
Result
(N/mm2)
Rebound
Hammer
(N/mm2)
UPV Test
(N/mm2)
Core Test
Result
(N/mm2)
Slab 1 53-55 - - 30-33 47.3 -
Slab 2 55-57 51.8 39.1 22-48 51.8 39.7
X Direction
Beam 1
35-44 - - 28-42 42 33.8
Y Direction
Beam 1
46-57 - - 37-46 - -
Column 1 38-48 - - 32-44 - -
Wall 1 37-42 - 40.9 37-39 47.3 35.8
Comparison of Results

Core Test Results
Element Location
Core Test Results
(N/mm2)
W 1 35.8
W 2 40.9
S 6 39.7
S 9 39.1
B 4 33.8

Element Location
UPV test Results
(N/mm2)
B 4 42
W 1 47.3
S 3 47.3
S 6 51.8
S 9 51.8
UPV Test Results

Rebound Hammer Test Results
Tensile Testing
Results

Comparison of damage class according to Visual Inspection with UPV,
Schmidt Hammer and Core Test Results
Visual
Inspection
Class
Structural
Element
UPV Test
(N/mm2)
Core Test (N/mm2)
Rebound
Hammer(N/mm2)
Tensile Strength
of R/F
(N/mm2)
Class 04
S1 - - 35.3 - 55.4 -
S2 - - 38.7 - 49.7 460 - 350
S3 47.3 - 30.1 – 33.0 460 - 350
S4 - - 22.1 -47.9 460 - 350
S5 - - 30.1 – 31.8 350 - 250
S6 51.8 39.7 46.0 - 49.7 > 460
Class 03
B2 - - 46.0 -
B3 - - 22.1 – 37.0 460 - 350
B4 42.0 33.8 28.5 -42.4 > 460
B5 - - 37.0 – 46.0 -
W1 47.3 35.8 37.0 – 38.7 460 - 350
C1 - - 31.8 – 44.1 -
Class 02
B1 - - 35.2 – 42.4 -
B6 - - 35.3 – 44.1 -
B7 - - 37.0 – 44.1 -
B8 - - 38.7 – 40.5 > 460
S7 - - - -
S8 - - - -
Class 01
B9 - - - -
W2 - 40.9 38.7 – 40.5 -
C2 - - 38.7 – 47.9 -
Class 00 S9 51.8 39.1 55.4 – 57.3 -
Slide
No
14

Comparison of final damage class according to Visual Inspection, UPV, Rebound
Hammer, tensile strength and Core Test Results
Final
Damage
Class
Structural
Element
Visual
Inspection
Class
UPV Test
(N/mm2)
Core Test
(N/mm2)
Rebound Hammer
(N/mm2)
Tensile Strength
of R/F
(N/mm2)
Class 04
S2 Class 04 - - 38.7 - 49.7 460 - 350
S3 -do- 47.3 - 30.1 – 33.0 460 - 350
S4 -do- - - 22.1 -47.9 460 - 350
S5 -do- - - 30.1 – 31.8 350 - 250
B2 Class 03 - - 46.0 -
B3 -do- - - 22.1 – 37.0 460 - 350
B8 Class 02 - - 38.7 – 40.5 > 460
Class 03
S1 Class 04 - - 35.3 - 55.4 -
S6 -do- 51.8 39.7 46.0 - 49.7 > 460
B4 Class 03 42.0 33.8 28.5 -42.4 > 460
B5 Class 03 - - 37.0 – 46.0 -
B6 Class 02 - - 35.3 – 44.1 -
B7 -do- - - 37.0 – 44.1 -
W1 Class 03 47.3 35.8 37.0 – 38.7 460 - 350
C1 -do- - - 31.8 – 44.1 -
Class 02
S7 Class 02 - - - -
S8 -do- - - - -
B1 Class 02 - - 35.2 – 42.4 -
W2 Class 01 - 40.9 38.7 – 40.5 -
C2 -do- - - 38.7 – 47.9 -
Class 01 B9 Class 01 - - - -
Class 00 S9 Class 00 51.8 39.1 55.4 – 57.3 -

Final Class of Damage in LL1 of
Block 06

Rectification method for Structural elements
Class of Damage Rectification Methodology Construction Process
Class 00
Slabs Beams, columns and shear walls
Redecoration if required
 Surface cleaning
 Mortar application
Class 01
Superficial repair of slight
damage not needing fabric
reinforcement
 Breaking out damaged area
- Hammer and chisel

Class 02
Non-structural or minor
structural repair restoring cover
to reinforcement where this has
been partly lost.
- Hammer and chisel ( Small areas)
- Electrically or Pneumatically powered
breakers (Large areas)
 Concreting
- Non-Shrinkage, flowable construction grout

Class 03
Slabs
Strengthening repair reinforced in
accordance with the load- carrying
requirement of the member. Concrete
and reinforcement strength may be
significantly reduced requiring check by
design procedure.
 Breaking out the entire damaged slab area
- Electrically or Pneumatically powered
breakers . - Hydro-
demolition
 Connection Reinforcement
- Lapping
- Coupling
- Welding - Not recommended
 Concreting
- Conventional concrete
Beams, columns and shear walls
Strengthening repair reinforced in
accordance with the load- carrying
requirement of the member. Concrete
and reinforcement strength may be
significantly reduced requiring check by
design procedure.
- Hammer and chisel ( Small areas)
- Electrically or Pneumatically powered breakers
(Large areas)
- Lapping
- Coupling
 Concreting
- Non-Shrinkage, flowable construction grout

Strengthening Beams, columns and shear walls of Class 03

Class 04
Slabs
Major strengthening repair with original
concrete and reinforcement written
down to zero strength, or demolition and
recasting.
 Breaking out entire damaged slab area
- Hydro-demolition
- Lapping
- Coupling
 Concreting
- Conventional Concrete
Beams, columns and shear walls
Major strengthening repair with original
concrete and reinforcement written
down to zero strength, or demolition
and recasting.
 Breaking out the entire damaged area
- Lapping
- Coupling
 Concreting
- Conventional Concrete

Repair Methods..
Main process to be undertaken in repair methods of reinforced concrete are
• Removal of damaged or weakened concrete
• Replacement of weakened reinforcement
• Replacement of concrete to to provide adequate structural capacity, durability and
fire resistance.
Surface Cleaning
• Pressure water jetting and in some areas power wire brushing and cementitious Paint
coat were used dependent upon the degree of discoloration.
• Surface cleaning may be required prior to the commencement of any repair works to
enable the clear identification of areas.

Repair Methods..
Breaking Out
• The objectives of breaking out were to remove all the deteriorated concrete and to
deepen the repair area without damage to the concrete and reinforcement that are to
remain in place
• Hammer and chisel, electrically powered breakers were used for breaking out.
• The Braking pattern was determined to avoid any sudden collapse and to un-effect to
the sound concrete.
• Sledgehammer and Chemical blasting were prohibited.

Repair Methods..
Flowable Micro-Concrete and Concrete
• The concrete for section enchasing in structural elements and large filling volumes
were rectified using a Concrete mix of Construction grout and chip concrete with
proportion of 3:1.
• The filling area less than 50 mm were rectified with an Construction grout mortar mix
with specified water cement ratio.

Special Thank to
• Senior Design Eng. S.S.A. Kalugaldeniya
• Senior Design Eng. (Ms). Kalani Sammandapperuma
• Eng. B.A.C. Batepola - In Charge / Site Laboratory

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