A case study on the structural assessment of fire damaged building

Abstract

This paper presents a case study on the structural assessment of building damaged by fire and discussed on the site investigations and test results prior to determine the existing condition of the building. The building was on fire for about one hour before it was extinguished. In order to ascertain the integrity of the building, a visual inspection was conducted for all elements (truss, beam, column and wall), followed by non-destructive, load and material tests. The load test was conducted to determine the ability of truss to resist service load, while the material test to determine the residual strength of the material. At the end of the investigation, a structural analysis was carried out to determine the new factor of safety by considering the residual strength. The highlighted was on the truss element due to steel behaviour that is hardly been predicted. Meanwhile, reinforced concrete elements (beam, column and wall) were found externally affected and caused its strength to be considered as sufficient for further used of building. The new factor of safety is equal to 2, considered as the minimum calculated value for the truss member. Therefore, this fire damaged building was found safe and can be used for further application.

Full text

IOP Conference Series: Materials Science and Engineering
PAPER • OPEN ACCESS
A case study on the structural assessment of fire damaged building
To cite this article: M H Osman et al 2017 IOP Conf. Ser.: Mater. Sci. Eng. 271 012100
View the article online for updates and enhancements.
This content was downloaded from IP address 191.101.95.14 on 08/12/2017 at 02:38

1
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution
of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Published under licence by IOP Publishing Ltd
1234567890
GCoMSE2017 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 271 (2017) 012100 doi:10.1088/1757-899X/271/1/012100
A case study on the structural assessment of fire damaged
building
M H Osman1, N N Sarbini2, I S Ibrahim1, C K Ma2,M Ismail2 and M F Mohd3
1
Forensic Engineering Centre, Institute for Smart Infrastructure and Innovative Construction,
Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, MALAYSIA
2
Depart ment of Structures & Materials, Faculty of Civil Engineering, Universiti Teknologi
Malaysia, 81310 Johor Bahru, Johor, MALAYSIA
3
Malaysia Public Work Department, JKR Head Quarters, 50582 Kuala Lumpur, MALAYSIA
Corresponding author:noornabilah@utm.my
Abstract. This paper presents a case study on the structural assessment of building damaged
by fire and discussed on the site investigations and test results prior to determine the existing
condition of the building. The building was on fire for about one hour before it was
extinguished. In order to ascertain the integrity of the building, a visual inspection was
conducted for all elements (truss, beam, column and wall), followed by non-destructive, load
and material tests. The load test was conducted to determine the ability of truss to resist service
load, while the material test to determine the residual strength of the material. At the end of the
investigation, a structural analysis was carried out to determine the new factor of safet y by
considering the residual strength. The highlighted was on the truss element due to steel
behaviour that is hardly been predicted. Meanwhile, reinforced concrete elements (beam,
column and wall) were found externally affected and caused its strength to be considered as
sufficient for further used of building. The new factor of safety is equal to 2, considered as the
minimum calculated value for the truss member. Therefore, this fire damaged building was
found safe and can be used for further application.
1. Introduction
This paper discussed on the case study of a fire damaged building. The building is made up from
reinforced concrete for the beam, column and wall, while have steel trusses as a main structural
element. In general, the condition i nside the office was affected by the fir e (figure 1). There were a lot
of things that were affected such as partitions, windows, electrical circuit, electrical sockets and
insulations. All the things mentioned were found broken and damaged due to the fire. Effect of fire to
the structural components can be seen from the shaded colour of walls, columns and beams, at all over
the surfaces. On the other hand, the trusses components were also affected by showing rusted steel
appearance all over the surfaces.The structural ass ess ment was aimed to investi gat e the effect of fire t o
the elements inside the building, to investigate the condition of the main structural element due to the
fire (steel trusses) and to recommend overall condition of the building.
In general, reinforced concrete structure performed well under fire [1-3]. Its behaviour as fire
resisting element caused most of fire damaged structure being reused after the fire, provided structural
assessment has been carried out. With sufficient information on the level of fire during the event will
assist the assessment to investigate the existing condition of a building. Effect of fire level to the

2
1234567890
GCoMSE2017 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 271 (2017) 012100 doi:10.1088/1757-899X/271/1/012100
structural element inside the fire damaged building need to be investigated in order to ascertain the
existing capacity and condition.
Several important information in carried out the structural assessment of a fire damaged building
are; types of building elements and materials, point of fire initiated, exposure condition, predicted fire
temperature, duration of fire and other possible data. As structure itself is made up by different other
materials, it made each fire damaged buil ding investigation to become more difficult. In other word,
each investigation will be unique between different fire damaged building incidents. Therefore, it is
very important for investigator to share their experienced wherever they facing such of fire damaged
building investigation.
On the other hand, in reinforced concrete structure, colour changes are normally used to
investigate the temperature of the material exposed to [4-7]. Table 1 is used to determine the level of
temperature exposed to the building elements. Meanwhile, figure 1 shows the flowchart of current
structural assessment of a fire damaged building. The flowchart is determine based on review of
important data that need to be collected in order to ascertain the existing condition of the building
element after exposed to fire.
Figure 1. Interior view of the building
damaged by fire shows most of the
elements inside the building were
affected.
Table 1.Colour changes in concrete at specified range of temperature, T.
Range of temperature, °C Colour Appearance Condition
T < 300
Normal
Normal
Normal
300
≤ T < 600
Pink to red
Surface crazing, cracking and
aggregates pop outs
Sound but strength
may be reduced
600 ≤ T < 950 Whitish
grey
Spalling, exposed of steel
reinforcement and powdered
exist ence
Weak
T
≥ 950
Buff
Extreme spalling
Extreme/severe
Figure 2.Flowchart of a structural assessment.

3
1234567890
GCoMSE2017 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 271 (2017) 012100 doi:10.1088/1757-899X/271/1/012100
2. Site Investigation
2.1. Visual inspection
Visual inspection has been conducted for all elements inside building (figure 3). Through visual
inspection, it was found that there were many damages to the roof due to the fire. There was a few
damages found at the metal sheets which made it not fit for roofing system. The same observation
were found for the foil insulations. It was found that all of the foil insulations were damaged and was
not suitable for use.
The condition of steel purlins was found most affected. These conditions were expected due to the
material properties of steel purlin of which have a strength that is lower compared to the steel truss.
Therefore, the effect of fire will create so much impact to the steel purlin compared to the steel trusses.
General overview on the steel purlins that were corroded on-site was shown in figure 4. Most of the
steel purlins were corroded along their lengths. The most affected steel purlin was found for a purlin
located above the area of fire i nitiated. The steel purlin was heavily buckled and twisted al ong thei r
length.
Figure 3. Plan view of a fire damaged
building shows ten columns (c1 to c10)
and fourteen walls (w1 to w14). Other
elements that were not visible inside the
plan view are two beams spanning from
c5 to c9 and from c11 to c6; and six
steel trusses spanning in between the
beams.
Figure 4. Observation on steel purlins that were affected by fire.
The steel trusses are the main structural elements on-site, as the members carry the roof loads.
Visual inspection shows that all members are affected by the fire. Other than the original colour of
black was brownish in color which was found to be colour of corrosion.In determining the state of the
corrosion; the corroded part was polished using a sandpaper and stiff wire brush to investigate the
STEEL PURLIN

4
1234567890
GCoMSE2017 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 271 (2017) 012100 doi:10.1088/1757-899X/271/1/012100
extent of the depth of the corrosion. After the process, it was found that the condition of the welding at
most of the connections were not satisfactory. An exampl e of the less satisfactory condition that was
found on-site is shown in figure 5(a) is considered as poor quality.
On the other hand, the visual inspection shows that there are many spalling of the plaster on the
surface of the beam. However, the concrete surface beneath the plaster layer is not affected. The
concrete was found not affected due to the appearance and condition that still intact and shows the
original grey in their colour (figure 6). The observation is also shown by column and wall elements.
In general, it can be summarized that reinforced concrete elements inside the building were just
externally affected by the fire. Although comparison of the elements colour and texture to table 1
shows that the elements were experiencing about 600 to 800 °C temperature, nevertheless, only
plastering of the RC elements were affected. In this case, only RC beams were found affected showing
by spalling of the plastering. This proved on the capacity of RC elements in resisting fire as per
mentioned by previous works [1-3]. Meanwhile, the steel purlins and trusses needs to be investigated
in detail due to the confirmation on its behaviour after fire.
(a) Unsatisfactory (b) Satisfactory
Figure 5.Appearance of welding quality at connection.
Figure 6.Physical appearance of the beams
2.2 .Non-Destructive Test
Although the observation from the visual inspection has shown that all RC elements (wall, column and
beam) were just externally affected by the fire, a “Schmidt” rebound hammer test is still been carried
out to ascertain the existing concrete uniformity of the elements. The test is in accordance to ASTM
C805/C805M-13a [8] and was carried out for beam elements on-site due to the occurrence of concrete
spalling. A few points on the beams were selected to carry out the test. In general, the test results show
that the compressive strength for concrete beams are in between 40 ± 4 N/mm
2
, which is considered
as more than adequate.
spalling
Deep
beam
spalling
U
-
channel b eam

5
1234567890
GCoMSE2017 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 271 (2017) 012100 doi:10.1088/1757-899X/271/1/012100
2.3.Load Test
The objective of load test is to ascertain current capacity of trusses on-site (figure 7). Previously, RC
elements have been found externally affected; however, the truss is made up from steel material.
Therefore, further test is needed for the truss elements. Two trusses are selected based on its condition
as the most (Truss 1) and least (Truss 2) affected truss. Full load test was carried out to determine the
truss behaviour due to the loading and unloading process at service load. Loading was applied in 1 kN
increment; and up to maximum service load of 14 kN at point D and E (at the middle of the truss
span). The results for load-deflection relationship for two LVDTs location is shown in figure 8(a).
In general, the deflection relationship have the same curve pattern at LVDTs position (point D and
E) indicating that the loading system and test setup are cl osely symmetrical and aligned. The s ame
pattern was observed for both trusses, during the loading and unloading process. The recorded
deflection at LVDT 1 (point D) and LVDT 2 (point E) was 4.24 mm and 4.79 mm for Truss 1,
respectively. Meanwhile, Truss 2 recorded deflection of 4.06 mm and 4.49 mm at LVDT 1 (point D)
and LVDT 2 (point E), respectively.
Meanwhile, the sustained load test (for service load at 14 kN) was carried out for 24 hours and at
the same time, deflection was recorded at every 30 minutes. Truss 1, the most affected truss was
selected to undergo this sustained load test. The deflection relationship at points D and E is shown in
figure 8(b). The deflection of the truss at LVDT 1 (point D) ranged between 3.51 mm and 4.24 mm,
while LVDT 2 (point E) ranged between 3.96 mm and 4.85 mm. The graph pattern indicates a bit
increasing trend as the load remained sustained on the slabs; at early 8 hours. However, the deflection
became constant after 8 hours from the start of the sustained load.
The full load test and sustained load test results shows that the trusses are still stable and capable
in resisting service load for further used.
Figure 7.Steel trusses on-site
(a) Full load test results (b) Sustained load test results
Figure 8. Deflection relationship during the test
1
st
day 2
nd
day 2
nd
day

6
1234567890
GCoMSE2017 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 271 (2017) 012100 doi:10.1088/1757-899X/271/1/012100
2.4Material Test
The coupon tensile test was carried out on the steel purlins [9]. The test is conducted for the steel
purlin due the observation during visual inspection which found that steel purlins were the most
affected element on-site. This is due to the appearance of the element that was heavily buckled and
twisted compared to the steel trusses. A total of 6 samples that consisted of:3 samples from the most
affected area and 3 samples from less affected area.The average tensile capacity is 341 N/mm2 for
least affected samples, which is 15% less than the design requirements of 400 N/mm2. Meanwhile, the
average tensile capacity is 324 N/mm2 for the most affected samples, which is 19% less than the
design requirements of 400 N/mm2. Therefore, the test results show that the steel purlin was severel y
affected with it yield capacit y reduced at maximum of 19% from the actual capacit y.
3.Structural Analysis
In predicting the current capacity of the steel truss, a structural analysis has been carried out using
STAAD.Pro v8i Analysis Software and in accordance to BS 5950 [10].The values under the design
load and un- factored load were gained fr om the software analysis. Meanwhil e, the design capacity was
calculated based on the actual capacity of the member. Factor of safety, FOS was determined and it
was calculated using equations (1) and (2). The reduce capacity was calculated by considering the
higher temperature that the steel truss was exposed; in a range of 600 to 800 ºC.
Based on an assumption that was made from the literature and investigation, the exposed
temp erature caused t he capacity of the tr uss to drop b y 30% from the actual. It means that, about 30%
of the actual capacity of the truss members were reduced due to the exposure to the fire. This is also
similar to the previous work reported [11]. From their findings, the steel with characteristic strength of
400 to 460 N/mm2 will have a strength loss of about 30% when exposed to a temperature of between
800 to 1000 ºC. Subsequentl y, the coupon tensile strength test of which the steel purlin was made from
the steel with 400 N/ mm2 design strength dropped at about 20% from the strength. Therefore,
assumption on 30% of strength dropped for the steel truss was make sense, although the load test has
already giving unaffected fire condition of a steel truss .After calculation, the FOSnew that was
considering the reduced capacity of each truss members lies between a range of 2 and 64. To the best
knowledge, this will conclude that the steel trusses have enough residual capacity for reused and
further application.
 =
 
 
(1)


=
 
 
(2)
4.Conclusion and Recommendation
The findings of the investigation are:
1) There is no appearance of severe damage for reinforced concrete elements, except for spalling of
mortar screeding found appeared in certain parts of columns and beams. No crack found on the
concrete surface. Strength of concrete beams and columns have been estimated by using Schmidt
rebound hammer test. From the results of the test, it indicates that the strength of concrete is still
unaffected by the fire. It proves the finding of the physical inspection on the appearance of the
concrete surface, i.e. no sign of degradation of strength of concrete in the building structure.
2) From the comparison of colour change on mortar and concrete surface, we can assumed the
building experienced temperature in the range of 600 C to 800 C. This is confirmed with the
occurrence of corrosion on steel truss members which is similar to the occurrence of corrosion on steel
coupon specimen when exposed to fire. From the full-scale loading test, it was found that the steel
trusses are still strong. The maximum deflection of the trusses was very small, i.e in the range of 4
mm, compared to the span of the truss which is 14 m (deflection/span ratio of 1/3500, as compared to
the maximum allowable which is 1/200). The small deflection is also an indication that there is no
structural degradation of the truss members and connections, and proved that they are over-designed.

7
1234567890
GCoMSE2017 IOP Publishing
IOP Conf. Series: Materials Science and Engineering 271 (2017) 012100 doi:10.1088/1757-899X/271/1/012100
5. References
[1] Stanislav Kmet, Michal T and Ivo D 2013 Experimental Diagnostics and Static Assessment of
Fire Damaged Steel Structure Lviv Polytechnic National University Institutional Repository
[2] Emmanuel V R A, Luc R T 2013 Assessment techniques for the evaluation of concrete
structures after fire Journal of Structural Fire Engineering 4(2) 123-129
[3] Narendra K Gosain, Ray F Drexler and Dilip C 2008Evaluation and Repair of Fire-Damaged
Buildings (STRUCTURE Magazine)
[4] Tide R H R 1998 Integrity of structural steel after exposure to fireEngineering Journal 35(1)
26–38
[5] Awoyera P O, Akinwumi I I, Ede A N and Olofinnade M O 2014 Forensic Investigation of Fire-
affected Reinforced Concrete BuildingsIOSR Journal of Mechanical and Civil Engineering
11(4) 17-23
[6] Technical Note - No. 102 ; April 2011. Fire Damaged Reinforced Concrete- Investigation,
Assessment and Repair.
[7] Jiro T and Gregory G Deierlein 2007 Collapse Performance Assessment of Steel-Framed
Buildings under Fires. Report No. 163
[8] ASTM C805/C805M - 13a Standard Test Method for Rebound Number of Hardened Concrete
[9] British Standard Institute. Metallic Materials - Tensile Testing - Part 1: Method of Test at Room
Temperature. London, BS ISO 6892-1. 2009
[10] British Standard Institute. Structural used of Steelwork in Building. London, BS 5950. 2000
[11] Kigha F, Sadeeq J A, Abejide O S 2015 Effects of temperature levels and concrete cove r
thickness on residual strength characteristics of fire exposed reinforced concrete beams
Nigerian Journal of Technology 34(3) 429-437
Acknowledgments
An appreciation goes to all parties that involved directly or indirectly to the completion of this work,
and sponsorship through cost centre no. 14J31.