INGENIEUR
Stage 1: Preliminary Inspection
● ●
● ●
● ●
Carry out preliminary inspection
Take immediate steps to secure public
safety and the safety of the structure
Prop members that are in a critical
condition
Stage 2: Assessment of Damage
● ●
● ●
Carry out on-site assessment of the
structure to determine the extent of
damage
Decide which elements require further
assessment or cosmetic repairs (e.g.
cleaning, repainting)
Stage 3: Testing and Detailed Assessment
● ●
● ●
● ●
● ●
Break out spalled concrete to determine
depth of fire damage
Carry out laboratory testing of concrete
and reinforcement sample s to
determine their residual strengths and
confirm depth of fire damage
Carry out thermal modelling, where
appropriate, to aid the assessment of
residual strength
Carry out dimensional surveys to
determine the extent of deflections of
beams and slabs and lateral movements
of columns
Stage 4: Design of Repairs to Structural
Elements
● ●
● ●
● ●
● ●
Determine structural capacity of fire-
damaged members using reduced
residual material properties
Decide on extent of demolition
Where repairs are possible, determine
additional concrete and reinforcement
required to reinstate original capacity
Decide on appropriate method of
repair and produce drawings and
specifications
Stage 5: Implement Structural Repairs
● ●
Carry out repair work
Figure 1: Stages in structural assessment and
repair process
6
32
VOL
2018
VOL 76
55 OCTOBER-DECEMBER
JUNE 2013
Concrete changes colour under the
influence of heat. It occurs as a result of the
gradual dehydration of the cement paste and
its transformation within the aggregate. Most
discolorations are associated with oxidation and
carbonation reactions. In many cases of heated
concrete, pink or red discolouration occurs at
temperatures above 300°C. The problem however,
is that colour changes depend on the mineralogy
of the aggregate present in the concrete. It is most
pronounced for siliceous aggregates and less so
for limestone, granite and sintered pulverised fuel
ash. Therefore, not all aggregates undergo colour
changes on heating.
Concrete deformation caused by heat results in
cracking. From 300ºC upwards, micro-cracks begin
to appear throughout the material, while at 530ºC
shrinkage of concrete starts to occur. Moreover,
thermal incompatibility of aggregates and cement
paste causes stress which frequently leads to
cracks, particularly in the form of surface crazing.
In addition, thermal shock caused by rapid cooling
from fire-fighting water may also cause cracks.
Spalling is the breaking off of layers or pieces of
concrete from the surface of a structural element
when it is exposed to high and rapidly rising
temperatures. Usually, two types of spalling occur
during a fire: explosive spalling and sloughing off
of concrete surface layers. Explosive spalling is a
series of pop outs and usually occurs within the first
30 minutes of exposure to fire. A slower spalling
(‘sloughing off’) occurs as cracks form parallel
to the fire-affected surfaces. Spalling is due to
stress induced by the build-up of vapour pressure
in concrete pores, which can be much higher
compared with the tensile strength of the material.
Mechanical properties of concrete such as
strength decrease remarkably once exposed to
fire, and this results in the deterioration of the
concrete. The strength of concrete is commonly
considered to be its most valuable property.
Nevertheless, strength usually gives an overall
picture of the quality of concrete because it is
directly related to the structure of the cement
paste. The residual strengths of dense concrete
after cooling vary depending on the temperature
attained during the fire, mix proportions and
conditions of loading during heating. The
compressive strength of concrete at elevated
temperatures is usually maintained up to 300°C.