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Performance of Segmental Post-Τensioned Concrete 

Beams Exposed to High Fire Temperature 
 

H. M. Hekmet 

Department of Civil Engineering 
Al-Farabi University College  

Baghdad, Iraq 

maithem_haider@yahoo.com 

A. F. Izzet 

Department of Civil Engineering 
University of Baghdad  

Baghdad, Iraq 
amer.f@coeng.uobaghdad.edu.iq

 

Abstract—The present study illustrates observations, record 

accurate description and discussion about the behavior of twelve 

tested, simply supported, precast, prestressed, segmental, 

concrete beams with different segment numbers exposed to high 

fire temperatures of 300°C, 500°C, and 700°C. The test program 

included thermal tests by using a furnace manufactured for this 

purpose to expose to high burning temperature (fire flame) nine 

beams which were loaded with sustaining dead load throughout 

the burning process. The beams were divided into three groups 

depending on the precast segments number. All had an identical 

total length of 3150mm but each had different segment number 
(9, 7, and 5 segments), in other words, different segment lengths. 

To simulate genuine fire disasters, the nine beams were exposed 

to high-temperature flames for one hour along with the control 

specimens. The selected temperatures were 300°C (572°F), 500°C 

(932°F), and 700°C (1292°F) as recommended by the standard 

fire curve (ASTM–E119). The specimens were cooled gradually 
at ambient laboratory conditions. The performance of the 

prestressed segmental concrete beams through the burning 

process was described with regard to the beams camber, spalling, 

and occurred deterioration. 

Keywords-burning temperature, fire flame; gradual cooling; 

segmental beam 

I. INTRODUCTION  

Segmental box girder bridges represent one major recent 
development in bridge engineering. This method of 
construction has many advantages like substantial economical 
savings due to the possibility of weather-independent segment 
production, shorter construction periods, simple element 
assembly at job site, replace ability of tendons, the concreting 
and prestressing operations are independent, small light 
segments, the profiling of the main external steel is easier to 
check, and the friction may be reduced [1]. The strength of 
reinforced concrete (RC) and prestressed concrete decreases 
after fire exposure. The basic fire safety objectives are to 
protect life and prevent failure. Following a fire, even if no 
collapse occurs, there is always a possibility of fire-induced 
damage. This research seeks to give an explanation and a 
simplified estimation of fire-induced damages produced in 
precast segmental prestressed concrete (SPC) beams via 
monitoring experimentally the behavior of internally 
prestressed precast concrete segmental beams with selective 

parameters such as segment length, number of joints between 
segments, and the exposure to different burning temperatures. 
Authors in [2, 3] presented the results of nonlinear finite 
element analysis on segmental concrete beams with external 
tendons. Authors in [4] investigated the structural behavior of 
dry joined externally prestressed segmental (EPS) beams under 
combined stresses, i.e. bending, shear and torsion stresses. It 
was found that the presence of torsion in beams reduces the 
vertical load and vertical deflection at the onset of nonlinearity, 
failure load and further, it would alter the failure mechanism. A 
reduction in the load-carrying capacity of EPS beams can be 
compensated by higher pre-stressing and by increasing stirrup 
reinforcement in the joint regions and to ensure serviceability. 
The joints in the supported regions should still be sufficiently 
pre-stressed under service load conditions.  

Previous works dealt with high temperature residual 
mechanical properties of concrete, mild steel and prestressing 
steel and how high temperature residual properties affect the 
ultimate strength of the element. Authors in [5] studied the 
mechanical properties of high-performance concrete (HPC) and 
the normal-strength concrete (NSC) after exposure to high 
temperature. The residual compressive strength was examined 
after the concrete specimens were subjected to a temperature of 
800°C. Authors in [6] compared the strength and durability 
performance of normal and high-strength pozzolanic concretes 
including silica fume, fly ash, and blast furnace slag at high 
temperatures up to 800°C. Authors in [7] reported that concrete 
can suffer large damage when exposed to fire, although it has 
low heat conductivity. Author in [8] stated that concrete 
materials have significant variations, therefore the structural 
fire safety capacity of concrete is very complex. Prestressed 
normal strength concrete (NSC) and high-strength concrete 
(HSC) exposed to fire require constitutive relationships to offer 
active modeling and to meet particular fire performance 
standards for fire-resistant prestressed concrete behavior. In 
this research, formulations were proposed to estimate the 
parameters that affect the behavior of unconfined prestressed 
concrete at high temperatures. Authors in [9] studied the 
mechanical properties of prestressing wires through and after 
the exposure to fire. The results were compared with the 
existing ones from the relevant literature and design codes, and 
empirical formulas were suggested. Researchers concluded that 
although the prior examinations provided beneficial results for 

Corresponding author: H. M. Hekmet



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the mechanical characteristics of prestressing steel at high 
temperatures, the information found was somewhat scattered 
and still inadequate. 

II. SPC BEAMS SET UP 

The experimental program consisted of twelve simply 
supported segmental prestressed concrete beams divided into 
three groups depending on the precast segments number. All 
the SPC beams were selected and designed with 3150, 400 and 
400mm length, depth and width, respectively. The first group 
consisted of SPC beams with 9 segments (350mm segment 
length), the second group with 7 segments (450mm segment 
length), while the last group had 5 segments (630mm segment 
length). Figure 1 shows the schematic shape of the SPC beams 
for each group. Figure 2 demonstrates the details of the two 
opposite contact surfaces of reinforced concrete precast 
segments, which have been used to assemble the SPC beams, 
the first consisted projections as shear connecters (keys), in 
contrast the other consisted pits to engage with the projections. 

 

(a) 

 

(b) 

 

(c) 

 

Fig. 1.  Schematic shape and dimensions of the tested SPC beams: 

(a) Group I, (b) Group II, (c) Group IIII 

The reinforcement details for the three groups are illustrated 
in Figure 3. The deformed 8mm diameter bar of 486 and 
640MPa, its yield stress and ultimate strength, were 
respectively used for the longitudinal and ties reinforcement.  

 
Side view of the shear keys 

 

Precast reinforced concrete segments 

Fig. 2.  Configuration of SPC beam segments (all dimensions in mm) 

 
Fig. 3.  Reinforcement details of segments for each group of the tested 

SPC beams 

The tested SPC beams passed through two stages of 
manufacturing. First, the segments of each beam had been cast 
(using the short line method) and cured, after reaching the 
specified concrete strength of 40MPa, the segments were 
assembled together in groups. After that, eccentric prestressing 
force of 120kN was applied from one end after insertion of low 
relaxation 7-wires strand (12.7mm diameter), grade 270, in the 
plastic tube which had been fixed before casting. The adopted 
prestressing force was selected so that it satisfied the limits of 
the ACI 318M-14 Code. Table I lists the suggested variables. 
Two stages of experimental tests were carried out on the SPC 
beams. 

III. EXPOSURE TO FIRE TEST 

Three SPC beams of each group (with its control 
specimens) were exposed to high temperatures of 300, 500, and 



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700°C while applying uniformly a constant dead load of 
3.22kN/m by using nineteen concrete blocks, 50kg each for 
similar exposure period of 1h after reaching the target 
temperature. After that, all beams were allowed to cool at 
ambient laboratory temperature. The burning stage comprised 
of positioning the SPC beams above their idealized simply 
supported ends, and the deflection due to the constant dead 
load and the camber change due to fire were measured using a 
dial gauge of 0.002mm/div sensitivity. The temperature was 
monitored by a digital thermometer reader with three 
thermocouple sensor wires type K (Nickel-Chromium/Nickel-
Alumel), which can be used at temperatures up to 1100°C. The 
sensors were set at three points with equal distances in the top 
region between the furnace cover and the SPC beam at the mid, 
right and left of the top case of the furnace. The fire flame test 
procedure is illustrated in Figures 4 and 5. 

TABLE I.  SEGMENTAL PRESTRESSED CONCRETE BEAMS 

Burning 

temperature (°C) 

Segment 

length (mm) 

Segment 

number 
Specimen Group 

unburned 350 9 Segments SPC-9-R 

Group I 
300 350 9 Segments SPC-9-300 

500 350 9 Segments SPC-9-500 

700 350 9 Segments SPC-9-700 

unburned 450 7 Segments SPC-7-R 

Group II 
300 450 7 Segments SPC-7-300 

500 450 7 Segments SPC-7-500 

700 450 7 Segments SPC-7-700 

unburned 630 5 Segments SPC-5-R 

Group III 
300 630 5 Segments SPC-5-300 

500 630 5 Segments SPC-5-500 

700 630 5 Segments SPC-5-700 
 

 
Fig. 4.  Furnace schematic shape and burning process 

 
Fig. 5.  Burning process 

IV. RESULTS AND DISCUSSION 

A. Camber at Prestressing Stage 

The effect of the prestressing force, combined with the 
beam self-weight, causes a net upward deflection at the 
midspan of the prestressed beam before superimposed dead and 
live loads are applied. The SPC beams camber was measured 
with a mechanical dial gauge of 0.002mm/div set in the 
midspan of the beam while the prestressing process was 
performed. The results, exhibited in Table II, show a significant 
camber decrease with decreasing number of segments. It 
reveals a decrease percentage in the average camber by 79% 
for SPC beams of 7 segments (Group II) and 62% for SPC 
beams of 5 segments (Group III) compared with the SPC 
beams of 9 segments (Group I). The regular cracks performed 
in the segmental beams are comprehended by the dry joints that 
affect the behavior of camber, due to the high stiffness of 
beams with the small number of joints in the SPC beams with 
less number of segments. 

B. Deflection Due to Superimposed Load 

Nineteen concrete blocks for each specimen were placed 
over the length of the SPC beams during the period of exposure 
to burning temperature. The measured deflections, listed in 
Table II, were set under the beam while these blocks were set 
above the SPC beams. The results show a conflicting relation 
between the deflection and the number of segments composing 
the SPC beam, in other words between the SPC beam stiffness 
and the number of segments. 

TABLE II.  INITIAL PRESTRESSING CAMBER AFTER APPLYING 
SUSTAIN LOAD ON SPC BEAMS 

Group No. 

In
it
ia
l 
p
r
e
s
tr
e
ss
in
g
 

c
a
m
p
e
r
 (
m
m
) 

A
v
e
r
a
g
e
 

p
r
e
s
tr
e
ss
in
g
 

c
a
m
b
e
r
 (
m
m
) 

R
e
s
id
u
a
l 
in
it
ia
l 

p
r
e
s
tr
e
ss
in
g
 

c
a
m
b
e
r
 %

 

S
u
p
e
r
im

p
o
s
e
d
 

lo
a
d
 d
e
fl
e
c
ti
o
n
 

(m
m
) 

N
e
t 
c
a
m
b
e
r
 b
e
fo
r
e
 

b
u
r
n
in
g
 (
m
m
) 

G
ro
u
p
 I
 

SPC-9-R 2.9 

2.9 100 

- - 

SPC-9-300C° 2.8 0.36 2.44 

SPC-9-500C° 3.1 0.36 2.74 

SPC-9-700C° 3 0.36 2.64 

G
ro
u
p
 I
I 

SPC-7-R 2.3 

2.3 79 

- - 

SPC-7-300C° 2.2 0.27 1.93 

SPC-7-500C° 2.4 0.27 2.13 

SPC-7-700C° 2.2 0.27 1.93 

G
ro
u
p
 I
II
 SPC-5-R 1.8 

1.8 62 

- - 

SPC-5-300C° 1.6 0.2 1.4 

SPC-5-500C° 1.8 0.2 1.6 

SPC-5-700C° 1.9 0.2 1.7 

 

C. Thermal Test Results 

The burning process comprised of setting fire until reaching 
the target temperature, then, after an exposure period of 1h to 
the target temperature the fire was turned off and a gradual 
cooling was performed by removing the furnace cover case and 



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lefting the SPC beams with their control specimens in the 
ambient air (lab conditions). 

1) Compressive Strength of Concrete (ƒ′c) 

Authors in [6] reported that there are three testing methods 
available to find the residual compressive strength of the 
concrete at high temperatures: stressed test, unstressed test, and 
unstressed residual strength test. The first two methods opt to 
find concrete strength during high temperatures, while the last 
is excellent for determining the residual properties after 
exposure to high temperature. It was observed that the third 
method gives less strength and is therefore more appropriate 
for obtaining limiting values. This method has been adopted to 
find the residual concrete strength. The test results of 
compressive strength, as shown in Table IIII for the 150mm 
specimens showed reducing in the compressive strength results 
with increasing burning temperature. 

TABLE III.  FIRE EFFECTS ON COMPRESSIVE STRENGTH* 

 
ƒcu 

(MPa) 

ƒ′c
* 

(MPa) 

Average 

residual 

strength % 

ƒ′c
** 

(MPa) 

Residual 

strength 

[8] 

T
e
m
p
e
r
a
tu
r
e
 o
C
 

ambient 42 33.6 100 33.6 100 

300 39 31.2 93 32.1 95.5 

500 28 22.4 67 24.4 72.6 

700 16 12.8 38 13.9 41.4 

* ƒ′c cylindrical compressive strength by using 0.8 converting factor 

** Post fire concrete strength proposed equation by [8] 

 

The loss of strength was characteristically varying 
depending from the burning temperature. Up to 300°C, only a 
small portion of the original strength was lost, about 7%. 
Severe loss in the strength mostly happened within the range of 
500-700°C burning temperature and was 33%-62%, 
respectively. The proposed equations [8] are compared in Table 
III with the test results. It is clear that there is a good agreement 
between the experimental results and the values given by the 
proposed equations. The compressive strength (Figure 6) 
exhibits a rapid decrease above 300°C, due to the dehydration 
of calcium hydroxide in the cement which begins when the 
temperature reaches about 400°C, generating more water vapor 
and also causing an additional significant reduction in the 
physical strength of the material [10]. The residual strength 
exhibits a rapid decrease above 300°C as shown in Figure 7. 

 

 
Fig. 6.  Burning temperature versus compressive strength 

 
Fig. 7.  Burning temperature versus residual strength 

2) Properties of Steel Reinforcement Bars  

Concrete structural properties after exposure to high 
temperature cannot be reversed to the original values. In 
contrast, steel structures usually return approximately to their 
original condition after cooling. This is caused by irreversible 
transformations in the chemical and physical properties of the 
cement itself [10]. Authors in [11] reported that when a 
temperature increment occurs, a significant drop in the value of 
steel yield strength and steel modulus of elasticity emerges. 
However, when the structure is cooled down, reinforcing steel 
properties usually recover the most of their original condition. 
So, real deterioration happens when the reinforcement in some 
structural elements becomes useless due to the failure of bar 
anchorage after exposure to fire. Authors in [12] reported two 
distinguished types of tensile tests of steel at high temperatures 
to find material properties: transient-state and steady-state tests. 
In the transient-state tests, the test specimen is under constant 
load and under constant temperature rise. The heating rate in 
the transient state tests is 20°C/min. Temperature and strain are 
measured during the test. While in the steady-state tests, the 
test specimen are burned up to a definite temperature. A tensile 
test follows. The steady state tests can be carried out either as 
strain or as load controlled. The steady-state test is more 
adequate than the transient-state test and therefore that method 
is more frequently used. The second test method was 
conducted in this research: three reinforcing steel specimens 
were burned at different burning temperatures. After cooling 
stage, tensile tests were carried out. Table IV lists the burning 
effect on the properties of steel reinforcement bars. Mechanical 
properties of the steel reinforcement bars after burning at 
temperature of 300°C were not affected, but a significant drop 
in the value of steel reinforcement properties was observed at 
burning temperatures of 500 and 700°C. 

TABLE IV.  FIRE EFFECTS ON THE PROPERTIES OF STEEL BARS 

 
Yield tensile 

stress (MPa) 

Residual 

yield tensile 

stress % 

Ultimate 

tensile stress 

(MPa) 

Residual 

ultimate tensile 

stress % 

T
e
m
p
e
r
a
tu
r
e
 o
C
 

ambient 486 100 640 100 

300 484 100 630 98 

500 462 95 602 94 

700 379 78 461 72 

 

The percentages of residual yield tensile stress and ultimate 
tensile strength were 95.78 and 94.72% at 500°C and 700°C 

Experimental results 

[8] 

Experimental results 

[8] 



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respectively. The results are in good agreement to the ones 
obtained in [13-15]. 

3) Strand 

The behavior of the prestressing strand is not like that of 
mild steel, where by cooling, the material will restore less 
amount of its original state. The effect of burning on the 
properties of strand is summarized in Table V. The results 
reveal that, the mechanical properties of the strand were not 
affected at burning temperature of 300°C, but at 500°C and 
700°C effects were observed, as was also by other studies. 
Authors in [16] reported the same observation and added that, 
prestressing steel losses almost or all of its non-linear behavior 
at temperatures above 500°C. Authors in [9] reported that the 
prestressing steel properties were more sensitive than 
reinforcing steel bar properties at identical fire temperatures. 
Equations for calculating yield and ultimate residual stress of 
prestressing strand where proposed. The loss percentages of 
79.42% and 76.43% of the residual yield stress and residual 
ultimate tensile strength at temperature 500°C and 700°C were 
observed respectively. They are in good agreement with the 
findings in [9].  

TABLE V.  FIRE EFFECT ON THE PROPERTIES OF PRESTRESSING 
STRAND 

 

Y
ie
ld
 t
e
n
si
le
 

s
tr
e
ss
 (
M
P
a
) 

R
e
s
id
u
a
l 
y
ie
ld
 

te
n
s
il
e
 s
tr
e
ss
 %

 

U
lt
im

a
te
 

te
n
s
il
e
 s
tr
e
s
s 

(M
P
a
) 

R
e
s
id
u
a
l 

u
lt
im

a
te
 t
e
n
s
il
e
 

s
tr
e
s
s 
%

 

[9] 

Residual 

yield % 

Residual 

ultimate % 

T
e
m
p
e
ra
tu
re
 o
C
 

ambient 1720 100 1860 100 100 100 

300 1700 99 1850 99 100 100 

500 1359 79 1414 76 82.7 80 

700 722 42 800 43 47.5 44 

 

4) Camber at Burning and Cooling Stage 

SPC beams of different segment lengths but identical in 
total length were subjected to fire test (Table I). Sustain load 
(3.22kN/m) was applied on the SPC beams simultaneously 
with the exposure to high temperature. The furnace temperature 
was applied as recommended by ASTM–E119. The beams 
passed through three stages within burning and cooling cycle. 
At the first stage, they reached the target temperature of 300˚C, 
500˚C or 700˚C. This took approximately 5, 7 and 12min 
respectively. Then, the temperature was stabilized for 1h. At 
the final and cooling stage, the SPC beams were cooled 
gradually by the ambient air (lab conditions). The effects of the 
three stages on the mid span camber for all beams are 
summarized in Table VI. Camber versus time history for the 
SPC beams of Groups I, II and III are shown in Figures 8, 9 
and 10 respectively. These figures elucidate that, increasing 
burning temperature in the first and second stages lead to steep 
increase in SPC camber, while a gradual camber decreasing in 
the third stage occurs The structure of the prestressed concrete 
beam exhibits upward curvature (camber) due to the eccentric 
prestressing force, which compressed the concrete at the lower 
zone (chord) of the prestressing force position and stretching 

the upper concrete zone (chord). The fire was positioned at the 
base of the furnace towards the lower face of the SPC beam, in 
other words, exposing a concrete beam to high temperature 
under sustain eccentric load led to increase in the deterioration 
in higher camber, despite applying external load. This denotes 
that the effect of temperature was more on concrete than on 
steel reinforcement. The structural response of beams exposure 
to burning can be grouped into three stages as mentioned 
before. In stage 1 (heating stage), concrete and strands are 
subject to very little degradation. The cambers in all SPC 
beams increase gradually and these cambers result from the 
generation of thermal strains caused by high thermal gradients 
that occur in the initial stage of fire exposure. 

 

 

Fig. 8.  Camber vs time for Group I beams at different temperatures 

 

Fig. 9.  Camber vs time for Group II beams at different temperatures 

 

Fig. 10.  Camber vs time for Group III beams at different temperatures 

In the second stage, within the 1h of fire exposure at the 
target temperature, as temperature increased in the internal 
layers of concrete, camber increased significantly caused by 
reduction in thermal concrete strength due to the formation of 
internal hair cracks. The interference of thermal effect into the 
internal layers attributed to concrete’s degradation of strength 
and modulus of elasticity more than that of strand. Then 
camber increased at a higher pace. In addition, camber 
increment is essentially attributed to high creep strains 



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subsequent from high temperatures in concrete which is 
composed of different materials and strands. The value of 
maximum camber at the end of the second stage is shown in 
Table VI. We can see that with increasing burning temperature, 
the maximum camber value of SPC beams increased. At the 
end of stage 2 at 500˚C and 700˚C the maximum camber was 
165% and 335% for SPC beams of 9 segments (Group I), 
compared with that burned at 300˚C. Whereas, it was 181% 
and 388% and 181% and 409% for SPC beams of 7 segments 
(Group II) and beams of 5 segments (Group III) respectively. 
The difference in the behavior (camber) of beams at each group 
is shown in Figures 8-10. The camber (upward deflection) 
increases during the heating period and reaches its maximum at 
the end of stage 2. The upward movement of the SPC beam is 
probably explained by the reduction of concrete’s resistance at 

the location of cracking and spalling, so the residual force in 
the prestressing tendons caused the segmental beams to move 
upwards. It can be seen that at the same burning temperatures 
the deterioration decreases with decreasing number of 
segments. Exposing SPC beams of 7 and 5 segments to 300˚C 
revealed that, the decrease in maximum camber at the end of 
stage 2 was 80% and 64% respectively while for SPC beams 
with 9 segments it was 88%, and 70% for Group II and 93%, 
and 78% for Group III at 500˚C, and 700˚C burning 
temperatures respectively. These comparisons exhibit that 
increased burning temperature increased the camber through 
the exposure period (burning stage), whilst increased segment 
number increased the maximum camber and decreased the 
beam stiffness. 

TABLE VI.  CAMBER AT THE END OF EACH STAGE OF BURNING AND COOLING PROCESS FOR ALL SPC BEAMS 

Group No. 

Initial 

camber 

(mm) 

Heating stage Heat stability for 1 hr Cooling stage 
Final 

camber 

(mm)* 

Residual 

camber 

% 

Duration 

(min) 

Variation 

camber 

(mm) 

Accumulative 

camber 

(mm) 

Duration 

(min) 

Variation 

camber 

(mm) 

Accumulative 

camber 

(mm) 

Duration 

(min) 

Variation 

camber 

(mm) 

I 

SPC-9-R - - - - - - - - - - - 

SPC-9-300C° 2.44 0-5 +0.2 2.64 5-65 +2.0 4.64 65-245 -0.9 3.74 153 

SPC-9-500C° 2.74 0-7 +0.5 3.24 7-67 +3.3 6.54 67-380 -1.9 4.64 169 

SPC-9-700C° 2.64 0-12 +1.0 3.64 12-72 +6.7 10.34 72-520 -4.1 6.24 236 

II 

SPC-7-R - - - - - - - - - - - 

SPC-7-300C° 1.93 0-5 +0.1 2.03 5-65 +1.6 3.63 65-245 -0.7 2.93 152 

SPC-7-500C° 2.13 0-7 +0.3 2.43 7-67 +2.9 5.33 67-380 -1.6 3.73 175 

SPC-7-700C° 1.93 0-12 +0.9 2.83 12-72 +6.2 9.03 72-520 -3.9 5.13 266 

III 

SPC-5-R - - - - - - - - - - - 

SPC-5-300C° 1.4 0-5 +0.07 1.47 5-65 +1.27 2.74 65-245 -0.67 2.07 150 

SPC-5-500C° 1.6 0-7 +0.2 1.8 7-67 +2.3 4.1 67-380 -1.2 2.9 182 

SPC-5-700C° 1.7 0-12 +0.8 2.5 12-72 +5.2 7.7 72-520 -3.4 4.3 253 

* Final camber equals to the sum of initial camber and final camber variation. 

+ sign denotes increased value. 

- sign denotes decreased value. 

At the end of the third stage the camber had a value higher 
than before burning. The ratio between the final camber after 
burning and the initial prestressing camber before burning is 
called the residual camber. The values of the residual camber 
are shown in Table VI. In general, decreasing camber of 
prestressed concrete beams is a sign of increasing losses in 
prestressing force. Increasing camber indicates that 
deterioration could happen in concrete strength whilst the 
prestressing force is not affected. Increased temperature had a 
bad effect on the residual camber, denoting that more 
deterioration occurred. The increased percentage in the residual 
camber for the beams of 9 segments (Group I) was 153%, 
169%, and 236% for burned beams at 300˚C, 500˚C, and 700˚C 
respectively compared to the initial camber before burning. For 
the beams of 7 (Group II) and 5 segments (Group III) it was 
152%, 175% and 266%, and 150%, 182% and 253% for the 
same burning temperatures respectively. Comparing the effect 
with the number of segments shows that the camber increases 
with increasing number of segments. Exposing SPC beams 
composed of 7 and 5 segments to 300˚C decreased the final 
camber at the end of burning and cooling cycle by 78% and 
56% respectively. For SPC beams with 9 segments it was 
decreased by 80%, and 63% for Group II and 82% and 69% for 
Group III, at 500˚C and 700˚C respectively. Figures 11-13 
show the camber difference of beams with different number of 
segments for the tested burning temperatures. 

 

Fig. 11.  Camber-time plot of SPC beams with different segment number 

during burning at 300˚C and cooling cycle 

 
Fig. 12.  Camber-time plot of SPC beams with different segment number 

during burning at 500˚C and cooling cycle 



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Fig. 13.  Camber-time plot of SPC beams with different segment number 

during burning at 700˚C and cooling cycle 

5) Spalling and Cracking Patterns  

During the burning test a distinct network of minor cracks 
occurred in SPC beams exposed to high temperature burning, 
however no main crack was testified. Cracking sounds were 
heard in some of the beams at around 15min after the start of 
the burning test that were mainly caused by spalling. At around 
100ºC, spalling started to appear, surface cracks were noticed 
and continued to develop until the final stage. Figures 14-16 
show an appearance comparison of the beams after the 
exposure to fire. As mentioned before, the SPC beams were 
composed of different number of segments, and the burning 
nozzles were positioned at the lower base of the beams. These 
facts elucidate that due to the irregularity of fire distribution, 
deterioration was noticed at some segments more than others 
and that this difference had marginal effects on the distribution 
of hairline cracks on the beam surfaces. At 300ºC the beams 
exhibited spalling cracks at some regions on the surface of the 
beam depth and at the edges near the fire source (Figure 14). 
Short cracks occurred in all the surfaces of the SPC beams and 
were concentrated in the joint positions between beam 
segments.  

 

 

(a) Specimen spalling at 300ºC 

 

(b) Specimen hairline at 300ºC 

Fig. 14.  Spalling and surface hairline cracks in surface (bottom fiber) of 

specimens near the fire at 300ºC 

At 500ºC the SPC beams have suffered spalling at some 
regions in the surface and edges near to the fire source and 
surface hairline cracks were observed (Figure 15). It is clear 

that the spalling effects at the bottom surface of the beams were 
deeper than those of specimens at 300ºC and the surface 
hairline cracks were more and longer. Hairline cracks at this 
temperature went deeper between segments in the joint 
positions and occurred in the bottom surface at prestressing 
steel position. Naturally, the spalling was observed in the SPC 
beams burned at 700ºC. The map-cracking and separation of 
concrete cover were more and deeper. After cooling, the 
spalling and the network of minor cracks in specimens 
increased as exhibited in Figure 16. 

 

 
(a) Specimen spalling at 500ºC 

 
(b) Specimen hairline at 500ºC 

Fig. 15.  Spalling and surface hairline cracks in surface (bottom fiber) of 

specimens near the fire at 500ºC 

 
(a) Specimen spalling at 700ºC 

 
(b) Specimen hairline at 700ºC 

Fig. 16.  Spalling and surface hairline cracks in surface (bottom fiber) of 
specimens near the fire at 300ºC 

Author in [17] reported that between 100ºC and 200ºC of a 
slow temperature rise, the first effects in concrete will occur 
due to high thermal stresses caused from fast heating and 
pressure caused by moisture evaporation inside the porous 
concrete, which the concrete structure is not able to dissipate. 



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These movements cause the development of cracks and the 
eviction of pieces from the surface layers of the beam material. 
At 300ºC, concrete starts to shrink at a faster rate and surface 
relatively short hairline cracks begin to form. The surface 
moisture evaporates faster than it can be replaced by rising 
bleed water, leading the surface to shrink more than the inside 
concrete. As the internal layers of concrete inhibit the 
shrinkage of the surface layer, stresses grow which exceed the 
concrete’s tensile strength, causing the surface cracks. The 
aggregates start to deteriorate at temperatures between 500ºC to 
700ºC because calcium hydroxide starts to dehydrate at that 
temperature range. Calcium hydroxide is a hydration output of 
most Portland cements, the quantity being dependent at the 
specific cement being utilized. 

V. CONCLUSIONS 

• The camber due to prestressing force decreases with 
decreasing number of segments. The percentage decrease in 
the average camber was 79% and 62% for SPC beams of 7 
and 5 segments compared with beams of 9 segments for 
beams having the same total length and cross section.  

• The fact that the fire was positioned at the base of the 
furnace toward the lower face of the SPC beams, i.e. the 
beams were exposed to high temperature under sustain 
eccentric prestressing force, led to increase in deterioration 
and to higher camber regardless of the applied external 
downward load. This denotes that the effect of temperature 
on concrete was more than that on steel reinforcement. 

• Increasing burning temperature in the first and second 
stages led to steep increase in the SPC camber, while a 
gradual camber decreasing was observed in the third stage 
(cooling stage).  

• For identical SPC beams made up of 9 segments, the value 
of maximum camber at the end of target temperature period 
increased at burning temperature 500˚C, and 700˚C by 
165%,and 335% compared with the one at 300˚C. 
Likewise, it was 181% and 388% and 181% and 409% for 
SPC beams of 7 and 5 segments for the same burning 
temperatures. Correspondingly, the camber at this stage 
compared to the initial value was 182%, 220%, and 354% 
for SPC beams of 9 segments at 300˚C, 500˚C, and 700˚C, 
respectively. Likewise, it was 183%, 236%, and 421% and 
191%, 244%, and 406% for SPC beams of 7 and 5 
segments at the same burning temperatures respectively.  

• Increasing burning temperature had a bad effect on the 
residual final camber at the end of burning and cooling 
cycle, denoting more deterioration occurred. The increase 
percentage in the residual camber for SPC beams of 9 
segments was 153%, 169%, and 236% for burned beams at 
300˚C, 500˚C, and 700˚C respectively compared to the 
initial camber before burning. Whilst, for SPC beams of 7 
and 5 segments it was 152%, 175% and 266%, and 150%, 
182% and 253% for the same temperatures. 

• Comparing the effect of segment number on the residual 
camber of post fire SPC beams, the results show that, 
camber decreases with decreasing number of segments. 

Exposing SPC beams composed of 7 and 5 segments to 
300˚C decreased the final camber by 78% and 56% 
respectively compared to that of 9 segments. It decreased 
by 80% and 63%, and 82% and 69% for SPC beams 
composed of 7 and 5 segments compared to 9 segments at 
500 C, and 700˚C respectively. 

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