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Non-destructive evaluation (NDE) has offered unprecedented utilize for bridge management body to monitor structural health. None of these evaluation methods can provide all the damage information (damage category, quantitative assessment) alone which is required for necessary repair activity and condition rating of structure. In most of the cases, the response of one evaluation method implies the presence of a defect among the multiple defects to which the evaluation method is sensitive. This paper is concerned with the combination of different non-destructive testing to find out the type of damage with the most efficient way. The different response (positive or negative) obtained from each combination and how it confirms the defect is shown through the mathematical set operation. Thus, this study would assist field investigator to ascertain the type of defect which subsequently aids to rate structure based on damage type.
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FACTA UNIVERSITATIS
Series: Architecture and Civil Engineering Vol. 9, No 1, 2011, pp. 11 - 22
DOI: 10.2298/FUACE1101011K
COMBINATION OF NONDESTRUCTIVE EVOLUATIONS
FOR RELIABLE ASSESSMENT OF BRIDGE DECK
UDC 69.01:624.2/.8=111
A.R. Khalim1, D. Sagar1, Md. Kumruzzaman2, A.S.M.Z. Hasan2
1Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia
2Rajshahi University of Engineering & Technology, 6204 RUET,
Talaimari, Rajshahi, Bangladesh
Abstract. Non-destructive evaluation (NDE) has offered unprecedented utilize for bridge
management body to monitor structural health. None of these evaluation methods can
provide all the damage information (damage category, quantitative assessment) alone
which is required for necessary repair activity and condition rating of structure. In most
of the cases, the response of one evaluation method implies the presence of a defect
among the multiple defects to which the evaluation method is sensitive. This paper is
concerned with the combi-nation of different non-destructive testing to find out the type of
damage with the most effi-cient way. The different response (positive or negative)
obtained from each combination and how it confirms the defect is shown through the
mathematical set operation. Thus, this study would assist field investigator to ascertain
the type of defect which subsequently aids to rate structure based on damage type.
Key words: non-destructive evaluation, bridge deck, reliable assessment.
1. INTRODUCTION
There are lots of nondestructive evaluations (NDE) available for concrete inspection,
but, unfortunately a few number is in practical use in deck evaluation. The commonly
used NDE methods for deck evaluation are visual inspection, chain drag, Impact echo,
Ground penetration radar, Infrared thermography and Half-cell potential (Scott et al.
2003). None of these methods can provide all required damage information alone, be-
cause evaluation methods are of different principles (acoustic, electromagnetic, electro-
chemical) that restrict a degree of capability in evaluation addressing different types of
damage in attention. Non-destructive techniques (NDT) can assess the state of health of
structures, but they can only provide an indirect approach to their performances (Brevsse
et al. 2008). Combination of NDE is required because, in majority of cases, response of
one evaluation method does not specify particular damage; rather it provides prediction
Received March 02, 2011
A.R. KHALIM, D. SAGAR, MD. KUMRUZZAMAN, A.S.M.Z. HASAN 12
among a number of defects to which the signal is sensitive. While one evaluation method
fails to screen a particular type of damage, the other could easily identify it. In addition,
the use of third evaluation method can yield quantitative evaluation for the damage. That
is why combination of NDE is recommended by various authors to bring reliability in as-
sessment in conjunction with detailed information of anomaly (Christoph & Streicher
2006). However combination of NDE does not refer to employ all available NDE during
assessment, rather it makes use of combination concerning damage area, type, location,
sensitivity and orientation and find out best combination that is rapid, effective and cover
all the damage types utilizing least number of evaluation methods in application.
There have been controversial experiences gathered by various researchers in evalua-
tion by various methods. Some researchers state that GPR and IR cannot yield ground
truth data as compared to conventional evaluation methods (Chain drag, Half-cell poten-
tial) (Barnes & Trottier 2004) while other reported to have insignificant variation in result
obtained between conventional and comparatively recently developed evaluation methods
like GPR and IR thermography (Cardimona et al. 2001). However, both statements are
factual and the probable cause of the inconsistent experience could be the damage sensi-
tivity to evaluation response, unfavourable environmental condition or lack of monitoring
controlling factors that should have been brought under consideration during the time of
investigation. Combination of non-destructive testing can improve the overall damage
evaluation as the controlling factor for each testing is different from the other. Eventually,
the enrolment of right combination can improve the evaluation with characterization of
defect including the efficient use of the methods.
2. SIGNIFICANCE OF NDE COMBINATION
Last five decades have experienced satisfactory improvement in nondestructive
evaluation methods and several models to predict remaining service life of bridge struc-
tures. Furthermore, several researches reveal the improvement of nondestructive evalua-
tion by combination that improves assessing damage features in deck. The application of
nondestructive evaluation is to do condition rating of structure which implies the degree
of repair or rehabilitation required for safety and longevity of structure. However, several
prediction methods to ascertain remaining life span of structure is significantly related to
reliability of nondestructive evaluation methods that require (prediction methods) infor-
mation of the present damage condition or value of condition rating as an input data. In
fact reliable condition rating and prediction cannot be attained unless a combined ap-
proach of nondestructive evaluations is introduced. The effort provided from one group of
combination (evaluation methods) may differ from evaluation using a different group,
thereby altering the efficiency of damage assessment in structure. Therefore, effective
combined approach of NDE is necessary to categorize the defect inside the bridge deck
and this knowledge would guide the investigator to apply the combination that discrimi-
nates particular damage(s) from defected portion of bridge deck.
Combination of Nondestructive Evoluations for Reliable Assessment of Bridge Deck 13
3. PROBLEM WITH DECK AND EVALUATION
It has been found that the usable life of the bridge deck is only one half of the useful
life of the bridge. The average age of bridges when replaced is 68 years, and the
average length of service of bridge decks before replacement is 35 years (Bettigole
1990). But sometimes this length could be as low as 10 years (Silano 1993). For this
reason, deck slab requires special attention for damage assessment and repair at early
stage. The damages that are common problem in concrete deck are cracking, leaching,
scaling, spalling, corrosion of reinforcement, poor quality concrete, and delaminations
(Yehia et al. 2007).
Unlike other parts of bridge, deck offers some extend of difficulty in evaluation that
are as follows (Rhazi 2001): 1) The concrete slabs are inaccessible to the both sides at the
same time, 2) the asphalt coating may have variable thickness, even within the same deck
(5 cm to up 15 cm) and 3) the thickness of the defects looked for (delamination) is small,
in the order of 1 to 2 mm. Furthermore, some methods require closure of lanes during in-
vestigation operation which urges non-destructive evaluation methods or combination that
are not only effective, but also rapid and cause less or no traffic interruption. Therefore,
closure of bridge lanes and resulting traffic hazard during investigation plays an important
consideration for bridge deck evaluation by non-destructive methods.
4. POTENTIALITY OF EVALUATION METHOD
This section describes the non-destructive evaluation methods potentiality and controlling
factors governing assessment of damage. Although, it has been seen that more than one
method can determine certain damage in same time, one method can prove reliable com-
pared to other including added damage information. A short description of commonly used
evaluation methods are as follows.
4.1. Ground penetration radar
Ground penetration radar relies on electromagnetic wave theory and damage is char-
acterized in terms of dielectric constant that differs from sound concrete. The theory and
working principle of GPR is reported in previous publications [10]. The rapid evaluation
by GPR can be applicable in field at vehicle speed of 72 Km/hr (Bungey 2004) when air
coupled antenna is attached with vehicle. While ground couple antenna is used for
evaluation, then the evaluation can be operated at walking speed of an investigator. This
evaluation method does not require direct contact with the investigation surface. As a re-
sult this method is comparatively rapid. The evaluation result can be presented in 2-D or
3-D view at the end of the evaluation, thus making the method very simple in damage
evaluation. Moreover, the GPR data collection is not adversely affected by traffic noise.
GPR evaluation can be operated with minimum traffic interruption, thus making the
method more popular for bridges with high volume of traffic.
A.R. KHALIM, D. SAGAR, MD. KUMRUZZAMAN, A.S.M.Z. HASAN 14
When dielectric constant of damaged portion alters from sound portion of concrete,
a substantial deflection is observed in reflected signal and thus the presence of damage
is ensured. Reinforcement corrosion, chloride contamination and increase of moisture
in concrete can induce substantial increase of dielectric constant of concrete. The
studies for radar show that radar is quantitatively sensitive to moisture and chloride
conditions associated with delamination and freeze/thaw damage, but cannot directly
sense delamination cracks (Fedaral land highway program 2010). Thus GPR method
cannot directly assess delamination defect, rather it can predict it from the sense that
the area of high chloride contaminated and corroded area possess the high possibility
of delamination crack. Therefore, GPR method is more suitable to detect anomaly in
concrete rather than being more specific in damage category. The use of other evalua-
tion method is required at those defected area to be sure of type of damage inside the
anomaly.
4.2. Infrared thermography
Infrared thermography evaluation method is based on electromagnetic theory and this
method can collect the data in field at the vehicle movement of 16 km/hr (Rhazi 2001).
ASTM D4788 (2006) describes the testing guideline for infrared thermography evalua-
tion. In passive method of infrared thermography the surface of bridge deck is heated by
the sun's infrared radiation, the delaminated areas heat at a faster rate than the adjacent
thicker sound concrete. The fracture plane of the delamination acts as a small insulator
and trapping the heat near the surface. During a summer day, these "hot spots" on the sur-
face are generally 2° C to 5° C warmer than the surrounding solid concrete (Manning &
Masliwec 1990) and those spots are clearly detectable by an infrared camera. Active
method of infrared thermography uses external source of heating to observe the thermal
differences attributed from embedded defects.
The presence of moisture inside concrete has a clear influence on the thermal proper-
ties and thus on the phase image. The phase images provide a deeper probing up to 10-15
cm in relation to the interpretation of the thermograms and to the amplitude images
(Weritz et al. 2005). Studies for infrared thermography show that this technique is capable
of detecting delamination, but is limited in capability when the asphalt cover is large, the
delamination openings are small, and the cracks are deep (Maser & Roddis 1990). An ex-
perimental study conducted by Qader et al. (2008) reports that active infrared thermogra-
phy can identify delamination and void with the maximum depth to be evaluated at 7.62
cm (3 inch) from investigating surface.
4.3. Impact echo
Impact echo method is based on stress wave theory and P wave and R wave gets sole
importance in evaluation. In impact echo method, P wave speed gets the most significant
influence on damage assessed in investigating element and this method is point impact
and point receiving in nature for damage characterizing. The common practice of impact
echo evaluation is to mark the deck slab to grids (typically 1 m × 1 m) and undergo test-
ing by impact echo method on those grids. Being as a point impact and point received
Combination of Nondestructive Evoluations for Reliable Assessment of Bridge Deck 15
method, impact echo is not a rapid evaluation method as compared to electromagnetic
evaluation methods like GPR and IR thermography. Moreover impact echo method is ad-
versely affected by vibration noise provided from traffic activity on bridge. Thus it re-
quires the closure of bridge lane during investigation of decks.
Impact echo method is applicable to assess delamination (Sansalone & Carino
1989; Cheng & Sansalone 1993), void (Pratt & Sansalone 1992), compressive strength
of concrete (Lee et al. 2003), depth of slab. The evaluation of damage by impact echo
method is done in frequency domain analysis. To run the impact echo analysis without
manual interpretation is developed by Das et al. (2009) which would cut short the
overall duration of testing by the method. Impact echo method has negligible influence
at the presence of moisture in concrete (Hamid et al. 2004). The current technology
implementing acoustic techniques, such as the chain drag method and IE, are generally
consistent with results from coring when they are carefully performed (Scott et al.
2003).
4.4. Chain drag
Chain drag method falls within acoustic method which uses dragging of chain over the
concrete surface. When there is discontinuity like delamination or void inside the concrete
the characteristic drummy sound is heard that ensures the presence of defect. The chain
drag testing procedure is explained in ASTM D 4580, 2006. Chain drag method is suit-
able for near surface damage assessment and it is subjective. For convenience, two-person
team allows the tasks of dragging the chains over the deck, clarifying defect boundaries
using a rock hammer (Scott et al. 2003). In spite of being subjective, this method is sim-
ple, easy to operate and cheaper method of concrete testing.
4.5. Half cell potential
Half-cell potential method is an electrochemical method to identify the area where
there is a high probability of active corrosion in the reinforcement inside the bridge
deck. When there is corrosion in bridge deck, the anodic and cathodic zones are
initiates in the rebar, resulting the flow of electron from anode to cathode. The half-cell
electrode probe is placed above the corroded zones and potential in voltage is
recorded. Based on the voltage difference, the corrosion severity of reinforcement is
determined. The result obtained from half-cell potential does not indicate the
delamination defect directly, but it follows that, over time delamination will occur in
those areas in which there is active corrosion. Thus the use of half-cell potential is to
assessment of corrosion severity and probability of delaminarion induced from
corrosion. Test equipment and procedures can be found in ASTM standard C 876,
2006. Table 1. summarizes damage evaluation potentiality by non-destructive methods
commonly applied for bridge deck evaluation.
A.R. KHALIM, D. SAGAR, MD. KUMRUZZAMAN, A.S.M.Z. HASAN 16
Table 1. Assessment of different damages by non-destructive methods.
Evaluation
methods
Damage set
(S) to which
the evaluation
method is
sensitive
Damage/
damage
Parameters
determined
Damage/
damage
parameter to
be assessed
Remarks
Visual
inspection
Crack,
Potholing,
spalling,
Chemical
attack, section
loss
Width of crack,
Damage area
Depth of
crack,
Type of
chemical
attack
Subjectivity in
assessment
Chain drag Delamination,
void
Location of
damage on deck
surface
Depth of
damage
Suitable for near
surface damage,
qualitative assessment
& subjective
Ground
Penetration
Radar
Anomaly that
can be either of
delamination,
void, moisture,
chloride attack
or corrosion in
reinforcement
Depth of the
anomaly, area
of damaged
portion
Type of defect Difficult to
discriminate among
damages
Infrared
thermography
Delamination,
Void,
moisture
damage
Area of
delamination,
void and
moisture
damage
Depth of
damage
mentioned
before,
thickness of
void
Difficult to
discriminate among
damages
Impact echo Delamination,
Void, Crack,
honeycombing
Depth of
delamination,
void and crack
Half-cell
potential
Corrosion in
reinforcement
Corrosion
severity in
reinforcement
5. METHODOLOGY OF NDE COMBINATION
Based on the duration of evaluation, NDE could be divided into two categories. Those
are rapid and comparatively slower methods. While investigating over a bridge deck, the
closure of bridge lane on evaluation demand should also be taken into consideration. The
evaluations which are comparatively fast represent overall damage area of deck. Thereaf-
ter, the slower evaluations should bring under the selected damaged points to be sure or
characterize the types of defect. Although information of damage and their extension are
Combination of Nondestructive Evoluations for Reliable Assessment of Bridge Deck 17
often not fully defined with satisfactory degree, rapid evaluation methods can assess
pathological area in a deck, further investigation (with other evaluation method) of which
disclose damage type with broader information. Some NDE are slow, tedious and make
traffic hazard during testing. Moreover the application of time consuming evaluation is
less preferred option for bridge management body for inconvenience in traffic movement
during investigation. Nevertheless those methods are essentially required for precise char-
acterization of damage. Hence application of those NDE following by the rapid evalua-
tion methods point out area to be investigated by slower NDE, thus making efficient use
of available NDE for a deck.
Most of the evaluation methods are responsive to a number of damages. Thus response of
damage implies prediction of those different types of defects. While the combination is
applied for overall evaluation of damaged area in deck, the combination must be such that
two methods are sensitive to different type of damages. In the stage of rapid screening, the
sensing damaged areas get sole interest. The type of defect within those areas is not im-
portant in this stage of evaluation. Now if the damages under consideration are repre-
sented by universal set U and n number of evaluation methods are employed in assess-
ment then
S
1 U S2 U S3.......U Sn= U (1)
Where S1, S2, S3 and Sn are the damage set to which the evaluation methods E1, E2, E3
and En are responsive respectively. Mathematical operator "U” refer to union of sets. For
a reliable assessment, the sensing of all damages under consideration should be covered
by the rapid evaluation methods employed in this stage.
In the second stage of assessment, the slower evaluations are in use for detail informa-
tion of damage type in the damaged area marked by rapid evaluation methods. Due to
time constraints and traffic hazard during investigation, those methods are not generally
recommended to implement throughout the whole area of a deck. The qualitative infor-
mation obtained from the previous stage can be upgraded to the quantitative information
in this stage. Also, rapid evaluation methods can overestimate the damage inside the deck
and proper selection of evaluation method can ascertain the overestimation of defect.
Now, if the other NDE methods (slower) are employed in evaluation then the combination
could only provide valuable information when the two evaluation methods have some
common damage(s) to be responded during investigation. In this case, either positive or
negative response of the following evaluation method can confirm or predict among the
selected number of defects. Therefore, if two non-destructive testing are involved in
evaluation and, S1 and S2 represents the damage sets to which each evaluation methods are
responsive respectively, then the damages that bring under consideration are S1US2. In
case when there are positive responses by both methods from a defected portion, the most
probable defects within the portion are S1S2. Lastly, in case there is alternating response
from the combination i. e. positive response obtained from one evaluation method
(evaluation method E1), but negative response from the other (evaluation method E2), then
the most probable damage(s) at the selected damage area are S1- S2. However, the nega-
tive response from both evaluation methods refer to no defect that are included in the
damage set S1US2. Table 2 shows the characterization of defect based on the different re-
sponse for evaluation methods.
A.R. KHALIM, D. SAGAR, MD. KUMRUZZAMAN, A.S.M.Z. HASAN 18
Table 2. Assessment of defect type from different combination of NDE.
Type of response Assessment by combination
E1N & E2N The investigation portion does not have any damage that has
been included in set S1 U S2
E1Y & E2Y The investigation portion has damage that has been included
in set S1 S2
E1Y & E2N The investigation portion has damage that has been included
in set S1 - S2
Here E1N refers no response obtained from the evaluation method E1 and E1Y indicates
there is positive response from evaluation method E1. The mathematical operator "U”,
"” and "-" indicate the union, intersection and subtraction by set operation, details of
which can be found in Bourbaki (1968).
6. RESULT OBTAINED FROM DIFFERENT COMBINATION
The damage sets that can be evaluated by evaluation methods are shown in Table 1. As
the capability of some evaluation methods are limited to near surface damage assessment,
the use of other evaluation though get the information throughout the depth of the slab,
the combination is also limited to near surface damages only. IR thermography and chain
drag methods are capable to assess near surface damages. Thus combination with those
methods is concentrated to evaluate at the near surface damages only. In such cases, if
possible, the evaluation by those methods (near surface damage assessment) should be
conducted at both the surfaces (top and bottom) of bridge deck.
The different combination of NDE is discussed with different response as explained in
Table 2. The example of GPR and IR thermography combination is described as follows.
GPR evaluation is sensitive to moisture, chloride attack, corrosion, void and delamination
associated with substantial dielectric increase in concrete. But IR thermography is only
responsive to delamination, void and moisture in concrete. Both the positive and negative
response from this combination is significant to characterize the type (among the types) of
defects in the defected zone. Equation 2 and Equation 3 show the damage set for GPR
and IR methods which is obtained from Table 1. From those equations it is observed that
delamination, void and moisture damages are common in two damage sets. Thus, the
positive response from IR but negative response from GPR would confirm the delamina-
tion defect without the attack of chloride inside the defected area. Because, if there would
have void, moisture or delamination associated with delamination, then there should have
positive response from GPR method and such response uses subtraction of IR thermogra-
phy damage set from GPR damage set as shown in Table 2. Again, positive response by
those two methods would confirm the presence of any defects (void, delamination or
moisture damage) that intersects between these two methods. At the same time it has also
confirmed that there could have no possibility of the defects (those which are not common
to both NDE) chloride attack and corrosion in reinforcement without cracking of concrete
(observing damage sets of GPR and IR thermography). Similarly, the other combination
of NDE and categorization of defects are shown in Table 3. The combination of IE and
Combination of Nondestructive Evoluations for Reliable Assessment of Bridge Deck 19
CD is not effective because both of these NDE methods are assigned to assess delamina-
tion and void only and different or identical response cannot provide any further informa-
tion.
GPR= {Chloride attack, corrosion, void, delamination associated with dielectric increase}(2)
IR={Delamination, void, moisture} (3)
Table 3. Damage evaluation from different NDE combination.
Type of response Confirmation of
damage
Possible damages
GPRY & IRN Corrosion in rebar,
chloride contamination
GPRN & IRY Delamination
GPR & IR
(Combination in
near surface damage) GPRY & IRY Delamination, void,
moisture damage
GPRY & CDN Chloride contamination,
moisture, corrosion
GPRN & CDY Delamination
GPR & Chain drag
(CD)
(Combination in near
surface damage) GPRY & CDY Void or delamination
GPRY & IEN Corrosion in rebar,
chloride contamination,
Moisture damage
GPRN & IEY Delamination
GPR & IE
(Combination
throughout the
depth of slab) GPRY & IEY Void, delamination
IRY & IEN Moisture damage
IRN & IEY Delamination, void
IR & IE
(Combination in
near surface damage) IRY & IEY Delamination/ void
associated with moisture
GPRY, IRN & IEY Void, Delamination
(around bottom rebar mat)
GPRN, IRY & IEYDelamination
(around top rebar mat)
GPR, IR & IE
(Combination
throughout the
depth of slab) GPRY, IRY & IENMoisture damage
The use of half-cell potential method is not shown to have combined in other evalua-
tion method in Table 3. The use of half-cell potential should be brought under evaluation
when it is required to discriminate corrosion damage from other damage. For example,
Table 3 shows the positive response of GPR and negative response from IE indicates the
possible damage of corrosion in rebar, moisture damage or chloride attack in defected
area. Now, when this type of response is obtained form a combination, the use of half-cell
potential can determine whether there is corrosion in rebar or not.
Figure 1 shows the combination of different non-destructive testing usually applied for
bridge deck application.
A.R. KHALIM, D. SAGAR, MD. KUMRUZZAMAN, A.S.M.Z. HASAN 20
Fig. 1. Combination of non-destructive testing to categorized damage in bridge deck.
The methods that fall within the rapid assessment of evaluation are visual inspection,
ground penetration radar and infrared thermography. These three methods are done in
first stage to determine the damaged portion in deck. Although those methods are used for
rapid screening of defect, the different response among those methods within defected
portion has provided additional information of defect type. Then, impact echo and half-
cell potential methods over those pathological areas would discriminate the delamination,
void and rebar corrosion and improve the overall evaluation of bridge deck. The fracture
critical area of the structure elements should provide special attention and those area
should preferably investigated by the slower evaluation methods, although those might not
have any damage mark by slower evaluation methods. Thus right combination of NDE can
determine the damage type in defected zone with minimum duration of lane closure.
Combination of Nondestructive Evoluations for Reliable Assessment of Bridge Deck 21
7. CONCLUSION
The efficient combination of non-destructive evaluation can reduce the duration of
lane closure and identify the type of damage within the damaged area. The right manage-
ment of non-destructive evaluation methods through the effective combination make use
of slower or time consuming evaluation methods to be employed in bridge deck assess-
ment. In this paper the different NDE combination and the damage types addressing the
different response from combination is explained. It is shown, how the damage type is
determined from different response from different combination of evaluation methods.
Especially in bridge deck where duration of investigation restricts the NDE methods that
require prolonged closure of lane, the combination of methods can clarify the damage
type within comparatively less time to spare providing minimum effort by those methods.
Therefore, the assessment of bridge deck with individual damage type would help to rate
the structure element, which subsequently improve overall condition rating of bridge. Fi-
nally, when the type of damage is known, it certainly assists the management body to take
right repair activity after those have been identified. The subsequent paper by the authors
focuses the combined approach NDE methods to calculate evaluation efficiency and how the
condition rating of the structure is normalized based on different evaluation combination.
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KOMBINACIJA NEDESTRUKTIVNIH MTODA ZA POUZDANU
OCENU STANJA NADGRADNJE MOSTOVA
A.R. Khalim , D. Sagar, Md.Kumruzzaman, A.S.M.Z. Hasan
Nedestruktivna ocena stanja (NDE) je našla ogromnu primenu kod osmatranja stanja konstrukcija
mostova. Nijedna od metoda ocene ne može sama da obezbedi sve potrebne informacije o šteti (kategorija
štete, kvantitativna procena) koje su potrebne za neophodne opravke mostova i ocenjivanje stanja
konstrukcija. U većini slučajeva, rezultat samo jedne metode ocene stanja otkriva prisustvo samo jednog
mogućeg defekta, za koje je metoda optimizovana, u mnoštvu drugih. Ovaj rad se bavi kombinacijom
različitih nedestruktivnih ispitivanja u cilju najefikasnijeg otkrivanja vrste oštećenja. Kroz matematički
skup operacija je prikazano kako su različiti rezultati (pozitivni ili negativni) dobijeni iz svake
kombinacije kako se utvrđuju oštećenja. Stoga će ova studija pomoći istraživačima na terenu da utvrde
vrstu oštećenja i da shodno tome daju ocenu upotrebljivosti konstrukcije na temelju vrste oštećenja.
Key words: kombinacija nedestruktivnih metoda, mostovi, puozdana procena.
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