A forensic view to structural failure analysis article

SSRG International Journal of Civil Engineering (SSRG-IJCE) – volume 2 Issue 1 Jan 2015
ISSN: 2348 – 8352 www.internationaljournalssrg.org Page 26
A Forensic View to Structures’ Failure Analysis
K. M. Pathan1
, Sayyad Wajed Ali2
, Shaikh Zubair3
, Aasim Hasan Najmi4
1
Consulting Structural Engineer, Aurangabad (M.S.), India
2
BE (Civil), Deogiri Institute of Engineering & Management Studies, Auranagabad (M.S.), India
3
Assistant Professor; Deogiri Institute of Engineering & Management Studies (M.S.), India
4
M.Sc. Forensic Science, Government Institute of Forensic Science (M.S.), India
ABSTRACT : The study of the structures’ failure
is very much essential. Apart from judicial or
professional necessity, the failure case study is also
essential in learning lessons. With the advancement
of theories and technologies in various
interdisciplinary branches of science, it is now
possible to know the root cause of failures of
various structures. Forensic Engineering is
amongst the examples of such interdisciplinary
science. A systematic study and interdisciplinary
research is carried out in this paper, in structure
failure analysis in view of forensic science.
According to National Crime Record Bureau
(NCRB) many amongst cases are reported of
structure failures and hence, the cases are tackled
by chemical analysis of various building materials
like Cement, Mortar, Concrete, Steel, etc. The
systematic procedure of chemical analysis for these
building materials is carried out and report is
finally submitted to the court. In this paper, the
significance of chemical analysis for Cement and
its various mix products (i.e. concrete, mortar, etc.)
is discussed in advocating the reasons of the
failure.
Keywords - Forensic Engineering, Failure
Investigation, Structure Failures, Chemical
Analysis, Concrete
I. INTRODUCTION
Structural failures and their investigation has
become an active field of professional practice in
which experts are retained to investigate the causes
of failures, as well as to provide technical
assistance to know the root cause. The parties
involved in the litigation of the resulting claims.
Since nearly all structural deficiencies and failures
create claims of damages, disputes and legal
entanglements, Forensic Engineers operate in an
adversarial hence, in addition to their technical
expertise; Forensic Engineers must have at least
some knowledge with the relevant legal processes
and need to know how to work effectively with
claiming parties and judiciary [1].
II. TYPES OF STRUCTURE FAILURES
Failure need not always mean that a structure
collapses. It can make a structure deficient or
dysfunctional in usage. It may even cause
secondary adverse effects [2].
Safety failure: Injury, death, or even risk to people:
Collapse of formwork during concrete
placement
Punching shear failure in flat slab concrete floor
Trench collapse
Slip and fall on wet floor
Functional failure: Compromise of intended
usage:
Excessive vibration of floor
Roof leaks
Inadequate air conditioning
Poor acoustics
Ancillary failure: Adverse affect on schedules,
cost, or use:
Delayed construction
Unexpected foundation problems
Unavailability of materials
Strikes, natural disasters, etc
III. CAUSES OF STRUCTURE FAILURES
Structural failure does not have to be a
“catastrophic collapse”; it may be a “non
conformity with design expectations” or a
“deficient performance”. Collapse is usually
attributed to inadequate strength and/or stability,
while deficient performance or so-called
serviceability problems, and is usually the result of
abnormal deterioration, excessive deformation, and
signs of distress. In short, failure may be
characterized as the unacceptable difference
between intended and actual performance. What
can grow in the design-construction process and in
the use of a structure that may result in immediate
or event failure? A lot! [1]

Negligence: Failure to properly analyze or detail
the design, or disregard codes and standards
Incompetence: Failure to understand engineering
principles or respect the technical limitations of
materials or systems
Ignorance, Oversight: Failure to follow design
documents and safe construction practices
Greed: Short cuts; intentional disregard of industry
requirements and safe practices
Disorganization: Failure to establish a clear
organization and define roles and responsibilities of
parties
Miscommunication: Failure to establish and
maintain lines of communication between parties
Misuse, Abuse, Neglect: Using the facility for
purposes beyond its intended or foregoing
preventive maintenance
IV. WHY FORENSIC ENGINEERING?
When so ever structure fails, there comes what the
reason behind it, so investigator finds out why it
failed. Apart from the legal and professional
necessity to determine the cause of failure, there is
also, the need to learn from it lessons from it that
would enable subsequent designers and builders or
fabricators to avoid the pitfalls of the failed
structure and develop safer alternatives. This
should not result into mass disaster [3].
A. Failure Investigation and Design Process
Fundamentally, structural design requires “an
ability to create a cost-efficient load-bearing
scheme in accordance with a set of „rules‟
prescribed by building codes, for minimal design
cost” [4]. The design process generally commences
with the designer considering a range of design
concepts. Then, by using simplifying performance
assumptions and an iterative process, the designer
produces a single design from what may be many
viable alternatives-that balances various competing
factors such as physical constraints, cost, and
adequate performance.
Design is, therefore, a process of synthesis, which
utilizes assumptions relating to probable loads,
structural behavior, and the capacity of material
properties [4]. These assumptions are conservative
and have been codified over the years to produce
efficient and generally safe structures. To design
structures by attempting to precisely predict the
loads they will carry, how they will behave, and
their material properties would be hopelessly
inefficient and time consuming. Further, actually
attempting to predict these factors to a high level of
accuracy is of questionable value in the design
process, given the unknowns surrounding the
structure‟s construction and the loads it will carry.
Therefore, a key element in the design process is
the management of these unknowns, rather than
their investigation.
The role of this process in the design of new
structures is self evident, but the process also has a
number of important roles to play in the overall
response to structural failure. For example, in
noncatastrophic failures, an engineering design
solution may be required to rectify the failure and
restore the structure to its originally intended
performance, regardless of whether legal
proceedings arise. Likewise, in legal disputes, the
satisfactory settlement of a dispute may depend on
the details of a design engineer‟s solution to
resolve the issue, or, when causation has been
determined, expert testimony may be required to
ascertain whether the engineer that originally
designed the structure did so with the degree of
reasonable skill and care expected of a practicing
engineer, a role for which engineers that typically
utilize the design process are excellently placed
because of their knowledge of standards and
professional engineering practice.
Because of these attributes, an engineer that
typically utilizes the design process also appears
the ideal candidate to determine the cause of
failure. However, an examination of a number of
the key aspects of the design process illustrates the
reason difficulties exist despite the fact that the
engineer may have design experience relevant to
the structure under consideration.
1) Design process objective
The objective of the design process is to identify
and develop engineering solutions, not to determine
causation. Although it is not suggested that design
engineers approach the identification of causation
with a view to developing solutions, many are

simply unfamiliar with the forensic process, and,
consequently, may find themselves falling back-
generally unaware of the transition-on the process
that they typically utilize in their role as designers.
It is, therefore, not surprising that engineers can
gravitate toward providing solutions to rectify the
failure, or rely on determining the cause of failure
in the form of “I wouldn‟t have designed the
structure in this manner, so this must be related to
the cause of failure.”
2) Simplifying performance assumptions and
evidence
The design process creates an appropriate design
solution through the application of simplifying
assumptions, and, where appropriate, errs on the
side of conservatism. In new or remedial design,
this is one of the design process‟s chief strengths,
but in failure investigation, it is a critical weakness.
In failure investigation, the investigator must
determine the actual loads, actual structural
behavior, and actual material properties at the time
of failure, rather than relying on simplifying
performance assumptions. This issue can be further
exacerbated by the sometimes-significant
differences between simplifying performance
assumptions and the performance of structures in
practice. Therefore, the accurate determination of
the cause of failure depends on verifiable evidence
(e.g., a bolt‟s failure surface or the cracking
patterns in concrete members), and while the
collection and analysis of verifiable evidence is
central to failure investigation, it is not an integral
part of the design process.
These limitations affect how an engineer that
typically utilizes the design process approaches
causation investigations. Although determining
causation is a critical objective, the implicit nature
of the design process can naturally move the focus
of the investigation to solution development.
Likewise, the engineer may fail to adequately
collect and interpret physical evidence and instead
rely on simplifying assumptions. These factors
typically combine to frustrate the investigating
engineer and increase the probability that the
failure‟s cause may be identified incorrectly,
potentially leading to repeat failures, inappropriate
rehabilitation strategies, legal challenges, and/or
skewed dispute outcomes.
B. Forensic Process
The key to determining structural causation is the
application of the forensic process, which aims to
objectively identify the technical cause or causes of
failure by using available evidence. Essentially, it
is the application of the scientific method to failure
investigation. Noon (2000) [5], in his text Forensic
Engineering Investigation, states that “a forensic
engineer relies mostly upon the actual physical
evidence found at the scene, verifiable facts related
to the matter, and well-proven scientific principles.
The forensic engineer then applies accepted
scientific methodologies and principles to interpret
the physical evidence and facts.”
The forensic process of collecting evidence,
developing failure hypotheses, testing each
hypothesis against the collected evidence, and
determining the most likely cause of failure, is a
process of analysis, rather than synthesis. The
application of the forensic process is described by
Noon (2000) [5]: “First, careful and detailed
observations are made. Then, based upon the
observations, a working hypothesis is formulated to
explain the observations. Experiments or additional
observations are then made to test the predictive
ability of the working hypothesis.” Noon (2000) [5]
then goes on to say that, “as more observations are
collected and studied, it may be necessary to
modify, amplify, or even discard the original
hypothesis in favor of a new one that can account
for all the observations and data. Unless the data or
observations are proven to be inaccurate, a
hypothesis is not considered valid unless it
accounts for all the relevant observations and data.”
This process avoids many of the pitfalls of
applying a design process alone. The objective of
the process is to identify the cause of failure, and
the process is driven by ruling in or out a failure
hypothesis based on specific evidence and
generally accepted engineering principles, rather
than simplifying assumptions. In other words, the
forensic process relies on understanding how the
structure actually behaved, rather than predicting
how the structure would have behaved based on the
design process. Finally, the separation of evidence
collection from the development of hypotheses, in
conjunction with the rigorous testing of each
hypothesis against the evidence, assists the
investigator to conduct the investigation in a

forensically sound manner, ensuring it will not only
stand up to the scrutiny of engineering peers, but
also, if necessary, to the exacting demands of the
legal system.
V. CHEMICAL ANALYSIS
A. General
The analysis and estimation of different types of
samples collected from the site of the failure; in
forensic science laboratories requires high degree
of skill and expertise. The forensic scientists are
following various methods for the chemical
analysis of these substances in the laboratories. In
this chapter, the chemical analysis methodology for
cement, mortar and concrete is discussed in detail
[6].
B. Sampling
1) Cement
When the sample is drawn from a cement bag, the
details printed on the bag and another marking
thereon should be carefully noted and incorporated
in the forwarding letter. 1 kg sample of cement
should be sent in an airtight plastic jar if available
or it should be securely packed in polythene bag
and then in brown paper to avoid exposure to
moisture. Sampling is done as per the procedure as
laid down in the Indian Standard Procedures of
random sampling.
Sampling of Small Quantities (Less than 12 bags
or packages): When number of bags or other
packages containing the cement bears the same
label on all the packages and are appearing to be
similar, in such cases about 1kg sample of cement
(in an air tight plastic jar) shall be drawn from each
bag and sent for analysis.
Sampling of large Quantities (More than 12 bags
or packages): When number of bags containing the
cement bear the same labels on the packages and
are appearing to be similar, in such cases the
grouping must be done. Each group should contain
about equal no. of bags and 20 percent of sample
weighing 1 kg (in an airtight plastic jar) from each
group shall be drawn into airtight plastic jar and
sent for analysis.
2) Mortar
1-2 Kg of mortar sample accompanied by 1 kg each
of cement and / or lime and sand if available from
the field shall be sent for analysis. Every article
should be independently packed.
3) Concrete
Concrete lumps, about 3-5 kg accompanied by 1 kg
each of cement, sand and aggregate if available
from the field shall be sent for analysis. Every
article should be independently packed.
C. Methods of Analysis
1) Cement
a) Thymolphthalein Test
(Thymolphthalein Indicator 0.1 % in
ethyl alcohol)
Take 100-150 mg of cement sample in a test tube,
add 1-2 ml water and 2 drops of indicator,
development of blue color indicates the presence of
cement, No color indicates that the sample is stone
powder.
b) Heating Test
Take 0.5 gm of sample, heat it for about 20 minutes
on a steel plate.
Change in color: adulterated cement
No change in color: unadulterated cement
c) Performance Test
Make thick slurry of cement with about 1 part of
cement with one part of water and put in an empty
matchbox. The cement gets hardened. The
performance is tested after 24 hours just by
removing matchbox and checking approx. strength
of the cement by fingers, if the block breaks easily,
the setting property is said to be poor. If the block
does not break by fingers, the performance is said
to be good.
d) Acid insoluble
Take 0.5-1.0 gm cement in a 100 ml beaker add 20
ml water to make a paste followed by 5 ml conc.
hydrochloric acid, add 20 ml water, stir, digest on
water bath for five minutes, no lumps should be
formed. Digest further for another 10 minutes, filter
through ashless filter paper till chloride free.
Residue dried in oven and further incinerated in
furnace at 800°C-900°C for 1 hour weigh the
residue, till constant weight. Calculate percent acid
insoluble.

e) Silica
Concentrate filtrate on hot plate to dryness, further
dry completely without charring, then add 20 ml
1:1 Hydrochloric acid and digest on water bath for
10 minutes stir well, and filter on ashless filter
paper till chloride free. Dry the residue
(Precipitated silica) in oven for 1hr and then
incinerate in furnace at 800°C-900°C for 1hr.weigh
the residue, till constant weight. Weight of silica
obtained is noted. (20 % Silica = 100 % cement).
f) Combined Ferric Oxide and Alumina
Concentrate the filtrate to about 200-ml by boiling
then add 2-3 drops of nitric acid to oxidize any
ferrous iron to ferric condition. Add 1-2 grams of
ammonium chloride, stir, and then treat the filtrate
with conc. ammonia solution till smell of ammonia
persists then boil the solution containing the ppts.
of Fe and Al hydroxides for few minute. Filter and
wash the ppt. with hot water. Dry the ppt. in oven
and ignite in platinum crucible till constant weight
at 1050°C to 1100°C. Weigh as alumina and ferric
oxide.
g) Determination of `Calcium` by EDTA
Titration (By Patton Reeder`s
indicator)
Take filtrate from ferric oxide and alumina
determination in 250 ml Vol. flask adjust Vol. to
250 ml. Take out 25ml soln. in titration flask add
50 ml water, 5ml (1:1) glycerol with constant
stirring then add 5ml diethylamine, further add 5-6
pellets of NaOH (pH should be more than 12)
shake well, further add 50 mg of Patton Reeder`s
indicator, shake well and titrate against 0.01M
EDTA solution color change violet to blue.
1ml 0.01 M EDTA = 0.5608 mg of CaO.
(60 % CaO = 100 % Cement) and CaO % = 3
Silica %
Patton Reeder`s Indicator: Grind 10 mg of the
indicator with 10 gm of sodium sulphate (A.R.) and
store in an airtight bottle.
h) Direct Cement % by acid titration
Take 0.5 gm cement in a conical flask add 50ml of
0.5 N HCl, digest on water bath for 30 minutes, add
50 ml water and titrate against 0.5 N NaOH using
phenolphthalein as an indicator. Also, perform a
blank titration. Color change is colorless to pink.
Cement % = 28 × N × Diff. in reading / 3
Where, N= Normality of NaOH
2) Mortar
Mortar is the blend of cement and sand in various
proportions used for various purposes. The mortar
used for brickwork in house walls is generally 1:4
in proportions. For testing of mortar and brick good
piece of mortar, adhering to brick from debris
should be collected.
a) Testing of Mortar
Heat good piece of mortar approximately 200 gms
is heated in oven at 110°C for 15 min. cool and
then weigh. Separate the cement portion from sand
by slowly grinding the lump in iron mortar. (To
separate sand from cement lumps) Sieve the
material and make three fractions as powder, fine
sand and coarse sand. Weigh individually and
record. Take about 5-10 gm of each fraction in
beaker, add 5-10 ml 3.3 N HCl till all the material
is wet with HCl, if required add further 5-10 ml
HCl, to dissolve the material. The cement portion
gets dissolved and sand portion is separated from
cement, digest on water bath for 10 minutes &
filter the liquid through filter paper, wash with
water till chloride free. The filtrate is evaporated
and silica determined as in earlier part, from silica
cement portion in each fraction is determined, from
total weight, weight of sand obtained by
subtracting wt. Of cement and hence the ratio of
cement to sand is calculated. Also % of cement in
the sample is calculated.
b) EDTA Titrations
For filtrate same as cement normally the ratio of
cement: sand used in plastering work is 1:4 (The
ratio used for compound walls and such other work
is 1:6 to 1:8).
3) Concrete
Concrete is a blend of cement, sand and aggregate
in different proportions used for different purposes.
Normally samples from debris selected are pieces
of beams and slabs taken for analysis. About ½ kg
sample is required for analysis dry the piece from
slab/beam in oven at 110°C for 15 minutes, cool
and weigh. Then grind the sample so that cement
particle gets separated from sand and aggregate.
Sieve the bulk with different mesh size sieves, to
separate powder, fine sand, coarse sand and
aggregate. Weigh the fractions so separated

individually. Take about 5-6 gm from powder
fraction and fine sand fraction, about 50-60 gm
from coarse sand and about 100-150 gms of
aggregate fraction for actual silica and calcium
oxide determination. Take all the four fractions as
above in 250 ml beakers; add sufficient quantity of
3.3 N HCl to dissolve the adhering cement
particles. Then digest on water bath for 10-15
minutes and filter. The filtrate so obtained is used
for silica determination.
a) Silica
Filtrate evaporates the filtrate to dryness on hot
plate, dry silica remains in the beaker along with
calcium and aluminium salts. Then add 3.3 N HCl
and digest on water bath for 5 minutes. Filter the
silica through ashless filter paper; wash with water
until chloride free. Dry the silica in oven and
further in furnace at 800°C-1000°C for 2 hours,
Wash the silica so obtained. From silica calculate
the weight of cement obtained in different fractions
(20 % silica = 100 % cement). Each fraction
contains some cement portion and rest being fine
sand, sand and aggregate respectively. Take sand
and fine sand fractions together. Thus calculate the
total cement, total sand and total aggregates present
in the sample, and hence calculate the ratio of
cement: sand: aggregate also calculate the cement
percentage. From filtrate of silica, calculate CaO %
as detailed in cement, from CaO % also calculate
the % cement in each fraction, and hence get the
ratio of cement: sand: aggregate, and also % of
cement in the sample. Compare the results obtained
by silica and CaO.
4) Alternative Method
Keep the sample in the oven for 15 minutes and
then keep them in desiccators for cooling. Weigh
10 gms of sample. Add distilled water and shake
well. Add 20 % HCl and boil the solution. Distilled
water and dilute HCl (i.e., 20 %) should be added
up to 15ml, if required. Add a few drops of conc.
HCl, warm-water/distilled water over the dissolved
residue so that complete CaO dissolves in the
filtrate. Make the solution up to 500 ml after
adding distilled water in the flask. Transfer the
solution after shaking well in the beaker. Pipette
out 10ml of the solution each in 3 beakers in
separately. Add 10-15 ml dilute nitric acid (20 %)
in each beaker. Add 20ml distilled water in each
and boil, add ammonium chloride (nearly 1 ½ - 2
tea spoon) and boil, cool the solution and then add
ammonium hydroxide and boil the solution for the
precipitation to be formed in the IIIrd
group.
Remove the beaker and allow precipitates to settle
down. Filter the solution, make saturated solution
of ammonium oxalate in a beaker and distilled
water nearly 300 ml of solution is formed. Nearly
100 ml each of ammonium oxalate solution are
added in each beaker after filtering the precipitates.
Precipitates as of interfering radical are being
removed in the IIIrd
group. After adding ammonium
oxalate solution, boil the solution for the
precipitates to be formed of CaO. Filter CaO
precipitate.
NOTE: Three separate solutions in beaker are taken
as mean of the titration reading is taken as single
reading gives error. Now, wash the precipitates
with warm water till it is fee from oxalate. Take
few drops of filtrate in a test tube, and CaCl2
solution few drops; if precipitate forms then
solution is not free from Oxalate. Wash till the
residue is free from Oxalate. Keeping the filter
paper carrying the precipitate in the beaker, wash
the filter paper with distilled water so that,
complete precipitates are transferred in a beaker.
Add dilute sulphuric acid as CaO is soluble in
dilute sulphuric acid. Add few drops of
concentrated sulphuric acid if precipitates are not
dissolved in dilute sulphuric acid completely, warm
the solution. Put N/10 KMnO4 in a burette and
titrate it against warm solution at nearly 50-60°C
i.e., till pink color appears. No the initial and final
reading and mean amount of KMnO4 used.
% Calcium Oxide (CaO) = Mean × 1.4
% Cement = CaO % × (100/62)
Assume the pure Cement CaO % = 62
a) Insoluble Residues
Transfer the residue of the previous test in a
beaker. Add 30 ml hot water and 30 ml 2N Na2CO3
solution. Heat the solution below boiling point for
10 minutes. Filter it, wash the residue on the filter
paper with dil. HCl (1:9) and finally with hot water
till the residue is free from chlorides. Ignite the
residue in a tarred crucible at 900-1000°C, cool in a
desiccators and weigh.
b) Check for Chlorides
Take few drops of filtrate and add 2-3 drops of
AgNO3 solution, white precipitates formed

indicates the presence of Chlorides, wash the
residue with hot water till it is free from chlorides.
VI. RESULTS AND DISCUSSIONS
The initial tests like Thymolphthalein test, Heat
test, and Performance test along with percentage of
acid insoluble, calcium oxide and silica data can
allow one to frame a report regarding the cement
percentage with acid insoluble and cement with
non-cementitious material. If stone powder is used
for adulteration the acid insoluble amount for
adulteration percentage but if lime or other material
is used for adulteration then acid insoluble will be
less and calcium oxide will be more, the correct
cement percentage can be assayed from silica
content. The relative standard deviations of 0.44 %
and recovery of 99 % was obtained for EDTA
titration. The relative standard deviations of 0.88
and recovery of 94 % was obtained for silica
determination. Hence the results of the analysis of
cement by the above methods are quite accurate
and reproducible.
VII. CONCLUSION
Finding the root cause/reason of the failure of a
structure requires loyal and delicate experienced
personnel in Structural Engineering as well as in
Forensic Engineering. By performing the chemical
analysis of the samples collected from the scene of
the failure of the structure, one can easily advocate
the fact behind the failure precisely.
The study was successively carried out and
conclusively we can say that, cement is complex
mixture and testing of cement is a difficult task. In
Forensic Context one has to certify whether the
sample is cement or not, and if so, the percentage
of cement in the sample. In case of Mortar and
Concrete the ratio of Cement: Sand and Cement:
Sand: Aggregate is very important, hence selection
of the sample plays an important role. Finally, the
cement content determined by above method
compared with the specifications laid by the
relevant codes may form the basis for reason
behind the failure.
VIII. ACKNOWLEDGEMENT
Firstly, we wish to express our warm sincere thanks to the
Director of Deogiri Institute of Engineering & Management
Studies, Aurangabad (M.S.) Dr. U. D. Shiurkar and Head of
Civil Engineering Department, Prof. G. R. Gandhe, Director of
Government Institute of Forensic Science, Aurangabad (M.S.)
Dr. S.G. Gupta and Head of Department of Chemistry and
Toxicology Dr. R.P. Pawar for encouraging us and providing a
platform to do the necessary works. We would like express our
deep and sincere gratitude to Prof. Naseem Ahmed and Prof.
Javed Khan for reviewing this manuscript. In addition, we are
deeply indebted to all the authors of the references used. Lastly,
we wish to express our gratitude to all those people who have
not been mentioned but helped in the realization of the work in
various ways.
IX. REFERENCE
[1] Robert T. Ratay, Professional practice of forensic
structural engineering, Structure Magazine, July 2007, 50-
53.
[2] Krishnamurthy and Dr. Natarajan, Forensic Engineering in
Structural Design and Construction, CD Preprints of
Structural Engineers World Congress, 2-7 Nov. 2007,
Bangalore, India, 2.
[3] Sean P. Brady, Role of the Forensic Process in
Investigating Structural Failure, Journal of Performance of
Constructed Facilities ASCE, 2012, Forum, 2-6.
[4] Bell, G. R., Engineering Investigating of Structural
Failures, in R. T. Ratay (Ed.), Forensic Structural
Engineering Handbook, 6 (New York: McGraw-Hill,
2000) 6.1, 6.11.
[5] Noon, R. K., Forensic Engineering Investigation (Boca
Raton, FL: CRC Press, 2000) 2, 10.
[6] IS 269 : 1989, Ordinary Portland Cement - Specification,
BIS, New Delhi, 1999.

A forensic view to structural failure analysis article

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