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7/28/2019 Dominguez Lab 8
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Student: Luis Dominguez
A-number: A01834041
Course: Experimental methods in structural
engineering, cee 6050
Professor: Marvin Halling, PhD
Assignment: Lab 8
Date: 04/29/2013
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Team #8: Edyson Rojas, Luis Dominguez, Ivan Quezada
Lab 8: NDT on Slabs
CEE 6050
Experimental MethodsApril 2013
Utah State University
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Table of Contents
Theoretical Background ............................................................................................................................ 4
Impact-Echo NDT Method ................................................................................................................... 4
Weaknesses ................................................................................................................................................. 5
Experiment .................................................................................................................................................. 5
Objectives ................................................................................................................................................ 5
Equipment ............................................................................................................................................... 6
Slabs ..................................................................................................................................................... 6
Spectral Analyzer ............................................................................................................................... 7
Accelerometer ..................................................................................................................................... 7
Impactor (Hammer) ........................................................................................................................... 7
Procedure ................................................................................................................................................ 8Analysis & Report .................................................................................................................................. 9
Conclusion ............................................................................................................................................ 16
Pictures .................................................................................................................................................. 17
References ................................................................................................................................................. 19
Appendix A ............................................................................................................................................... 20
Lab Notes .............................................................................................................................................. 20
Appendix B ............................................................................................................................................... 25
Calculations Tables .............................................................................................................................. 25
Table of FiguresFigure 1, Slab to be analyze ...................................................................................................................... 6
Figure 2, Spectral Analyzer....................................................................................................................... 7
Figure 3, Accelerometer ............................................................................................................................ 7
Figure 4, Hammer ...................................................................................................................................... 7
http://c/Users/Eng.%20Edyson%20Rojas/Google%20Drive/Utah/Spring%202013/Experimental%20Methods%20in%20Structural%20Dynamics/Lab%208/Lab%208%20WriteUp.docx%23_Toc353733846http://c/Users/Eng.%20Edyson%20Rojas/Google%20Drive/Utah/Spring%202013/Experimental%20Methods%20in%20Structural%20Dynamics/Lab%208/Lab%208%20WriteUp.docx%23_Toc353733847http://c/Users/Eng.%20Edyson%20Rojas/Google%20Drive/Utah/Spring%202013/Experimental%20Methods%20in%20Structural%20Dynamics/Lab%208/Lab%208%20WriteUp.docx%23_Toc353733848http://c/Users/Eng.%20Edyson%20Rojas/Google%20Drive/Utah/Spring%202013/Experimental%20Methods%20in%20Structural%20Dynamics/Lab%208/Lab%208%20WriteUp.docx%23_Toc353733848http://c/Users/Eng.%20Edyson%20Rojas/Google%20Drive/Utah/Spring%202013/Experimental%20Methods%20in%20Structural%20Dynamics/Lab%208/Lab%208%20WriteUp.docx%23_Toc353733847http://c/Users/Eng.%20Edyson%20Rojas/Google%20Drive/Utah/Spring%202013/Experimental%20Methods%20in%20Structural%20Dynamics/Lab%208/Lab%208%20WriteUp.docx%23_Toc3537338467/28/2019 Dominguez Lab 8
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Team #8: Edyson Rojas, Luis Dominguez, Ivan Quezada
Theoretical Background
Delamination occurs when the corrosion in the steel rebar induces cracks and the cracks
joined together to cause the concrete cover to separate from the substrate concrete. It results in
the loss of structural strength and facilitates a rapid deterioration of the deck. The delamination
impairs both the appearance and the serviceability of the structure, and repairs can be very
costly. It is estimated that annual maintenance and repair costs related to corrosion for concrete
infrastructure approach $100 billion worldwide. As a corrosion-induced problem, delamination
is of great concern for bridges, and routine inspection is necessary.
Many methods have been developed to detect concrete delamination. These methods
include the conventional chain drag method, impact-echo (the one we will use in this lab),
ultrasonic tests, ground penetrating radar, imaging radar, and infrared thermography. Efforts
have been made to expand, improve, and combine currently available techniques.
Impact-Echo NDT Method
IE is a widely used NDT method, which has been demonstrated to be effective in
detecting delaminations in bare (without asphalt overlay) concrete structures (Sansalone 1996;
Tawhed andGassman 2002; Zhu and Popovics 2007). IE is a mechanical-wave method based on
the transient vibration response of a platelike structure subjected to mechanical impact. The
mechanical impact generates body waves (P waves, or longitudinal waves, and S waves, or
transverse waves), and surface guided waves (e.g., Rayleigh surface waves) that propagate
within the solid material. The multiply reflected and mode converted body waves eventually
set up sets of infinite vibration resonance modes within the solid material (Tolstoy and Usdin1953). The transient time response of the solid structure is measured with a contact sensor (e.g.,
displacement sensor or accelerometer) mounted on the surface close to the impact source. The
Fourier transform (amplitude spectrum) of the time signal will show maxima (peaks) at certain
frequencies, which represent particular resonant modes. Two sets of vibration modes are
relevant to this study, the thickness stretch modes and the flexural drum modes. The thickness
stretch mode family normally dominates the spectral response of a platelike structure that does
not contain any near-surface defects. In that case, the frequency of the fundamental thickness
stretch mode (also called the, IE frequency: ) can be related to the thickness of the plate.
Knowing the P-wave velocity Cp of concrete, the plate thickness D is related to the IE frequency
by:
Where is the correction factor, and ranges from 0.945 to 0.96 for the normal concrete
(Gibson and Popovics 2005) and we are going to use 0.96, D is in inches, Cp is 4100 m/s (need to
convert), and the frequency is in Hertz. The correction factor is based on elastic-dynamic effects
related to a S1 Lamb wave mode with zero group velocity, which depends on the Poissons
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ratio. The thickness stretch mode may also dominate the spectral response when the test is
carried out over a relatively deep defect or delamination. However, the flexural modes tend to
dominate the spectral response when a test is carried out over a shallow (nearsurface) defect or
delamination. These modes normally have much lower frequency than the stretch modes.
Unfortunately, a simple analytical expression that relates the fundamental flexural frequency to
the defect depth has not yet been established because this frequency value depends on the plategeometry, shape, and boundary condition. Despite this problem, IE test data provide valuable
information about the presence of delaminations in concrete plates; areas that show a dominant
response frequency with a relatively low value are likely located above the shallow
delamination defects, although the depth of the defect cannot be directly estimated.
Weaknesses
Data can be difficult to interpret; especially on thick plates or on layered materials(overlays, soil).
Small voids can be missed. Is limited by size of wavelength. Complicated geometries pose difficulties. Flaws beneath sensed flaw must be evaluated from the opposite side.
Experiment
This section will explain the procedure that will be done at the lab, what measurements
to take, what to calculate, and will contain relevant information regarding the experiment.
Objectives
1. Understanding of the Impact-Echo method to detect delamination on slabs.2. Use the IE method to determinate various frequencies values at a given number of
points on a slab.
3. With the obtained frequencies at each point, compute D (depth) at each point. (Depthwill change if theres delamination at that point or not.)
4. Compare the obtained depth with the measurements done in the lab, and calculate thepercentage of error.5. Calculate the area of delamination on the slab based on the calculated depths. Compare
with actual area of delamination and compute the percentage of error.
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Team #8: Edyson Rojas, Luis Dominguez, Ivan Quezada
Equipment
Slabs
Four reinforced concrete plates were constructed in the SMASH Lab. Each concrete platehas the same size, and same layout of #6 steel rebar. All the concrete was placed from the same
ready mix concrete batch in order to achieve similar concrete strengths between specimens. On
each slab, plexiglass sheets were used to simulate the effect of a delamination. Plexiglass is
unaffected by moisture and offers a high strength-to-weight ratio, which is good for preventing
the bonding of concrete above and below it. For the purpose of this experiment we are only
going to analyze one of the delaminated slabs.
For this experiment we are going to analyze just one slab.
Figure 1, Slab to be analyze
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Spectral Analyzer
This piece of equipment is
used to read the data from the
accelerometer and convert it to
frequency as it is displayed on thescreen. The user is then able to find
the frequency values for each point,
each time it is hit with the hammer.
Accelerometer
The accelerometer takes the vibration and transforms it into an
electrical signal which is then sent to the Spectral Analyzer to be
converted into the frequency and time domains.
Impactor (Hammer)
This tool is used to hit the slab at the desired point and
generate waves; the stress waves that propagate within the
structure and are reflected by flaws or external surfaces.
Figure 2, Spectral Analyzer
Figure 3, Accelerometer
Figure 4, Hammer
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Procedure
The procedure for this lab will be the following:
1. Measure the slab and the location of the points that are going to be tested.2. At each point indicated on the slab, the participants of the lab are going to do an
Impact-Echo Test (5 taps) and write down the value of the frequency read on the
Spectral Analyzer.
3. Proceed to compute the depth at each point, and compare it to the onesmeasured in the lab.
4. Based on its value, determine if the calculated depth corresponds to the bottomof the slab or the delamination.
5. Calculate the percentage of error of the value obtained from Impact-Echo incontrast with the measured value.
6. Compute the percentage of delamination of the slab with the actual value of thedelamination. %Delamination=(Adelamination/ASlab)*100.
7. Determine the area of the delamination based only of the information obtainfrom the Impact-Echo and the location of the tested points and calculate the
corresponding percentage of delamination. %Delamination=(Adelamination/ASlab)*100.
8. Calculate the percentage of error of the %Delamination.
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Analysis & Report
Data acquired at the lab.
X Dimension of slab: 9 ft
Y Dimension of slab: 6 ft
Distance between the points in the X direction: 10 in between points and 4 in from the edge
Distance between the points in the Y direction: 6 in between points and 3 in from the edge
Thickness of slab: 5.625 in
Point Frequency (kHz)
1x 18.312 Hz
2x 13.84 Hz
3x 13.84 Hz
4x 14.112 Hz
5x 14.368 Hz
6x 37.984 Hz
7x 35.775 Hz
8x 32.416 Hz
9x 34.496 Hz
10x 38.528 Hz
11x 13.952 Hz
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Team #8: Edyson Rojas, Luis Dominguez, Ivan Quezada
Point Frequency (kHz)
1y 14.48 Hz
2y 14.688 Hz
3y 14.384 Hz
4y 12.128 Hz
5y 14.432 Hz
6y 34.592 Hz
7y 34.336 Hz
8y 32.704 Hz
9y 32.96 Hz
10y 33.632 Hz
11y 34.56 Hz
12y 14.16 Hz
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I started this lab transforming the velocity that the waves can travel in concrete from m/s to in/s.
Using
I was able to calculate de depth of the slab.
0.96
CP (in/s) 161417.3228 in/s
Point Frequency (Hz) Depth (in) Slab or Delamination?
1x 18312 Hz 4.231122486 in Slab2x 13840 Hz 5.598288653 in Slab
3x 13840 Hz 5.598288653 in Slab
4x 14112 Hz 5.49038513 in Slab
5x 14368 Hz 5.392560896 in Slab
6x 37984 Hz 2.039814526 in Delamination
7x 35775 Hz 2.165767015 in Delamination
8x 32416 Hz 2.390187406 in Delamination
9x 34496 Hz 2.246066644 in Delamination10x 38528 Hz 2.011013158 in Delamination
11x 13952 Hz 5.553348263 in Slab
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Point Frequency (Hz) Depth (in) Slab or Delamination?
1y 14480 Hz 5.350850481 in Slab
2y 14688 Hz 5.27507591 in Slab
3y 14384 Hz 5.386562497 in Slab
4y 12128 Hz 6.388548397 in Slab
5y 14432 Hz 5.368647101 in Slab
6y 34592 Hz 2.239833342 in Delamination
7y 34336 Hz 2.256532938 in Delamination
8y 32704 Hz 2.369138789 in Delamination
9y 32960 Hz 2.350737711 in Delamination
10y 33632 Hz 2.30376769 in Delamination
11y 34560 Hz 2.241907262 in Delamination
12y 14160 Hz 5.471773655 in Slab
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In this table we compared the calculated depth based on the frequency measured versus the
actual measures of the slab.
PointDepth (in)
% Error
From IE Measured1x 4.23112249 in 5.625 in 24.78%
2x 5.59828865 in 5.625 in 0.47%
3x 5.59828865 in 5.625 in 0.47%
4x 5.49038513 in 5.625 in 2.39%
5x 5.3925609 in 5.625 in 4.13%
6x 2.03981453 in 2 in 1.99%
7x 2.16576701 in 2 in 8.29%
8x 2.39018741 in 2 in 19.51%9x 2.24606664 in 2 in 12.30%
10x 2.01101316 in 2 in 0.55%
11x 5.55334826 in 5.625 in 1.27%
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PointDepth (in)
% ErrorFrom IE Measured
1y 5.35085048 in 5.625 in 4.87%2y 5.27507591 in 5.625 in 6.22%
3y 5.3865625 in 5.625 in 4.24%
4y 6.3885484 in 5.625 in 13.57%
5y 5.3686471 in 5.625 in 4.56%
6y 2.23983334 in 2 in 11.99%
7y 2.25653294 in 2 in 12.83%
8y 2.36913879 in 2 in 18.46%
9y 2.35073771 in 2 in 17.54%10y 2.30376769 in 2 in 15.19%
11y 2.24190726 in 2 in 12.10%
12y 5.47177366 in 5.625 in 2.72%
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ElementDimension ft
Area ft2
% of
Delamination% of Error
X Y
Slab 9 6 54
Actual
Delamination 4 3 12 22.22%
IE Delamination 3.333 2.5 8.333 15.43% 30.56%
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Conclusion
This experiment taught us a very important way to realize a nondestructive testing of a
concrete slab of any type of structure. We had the chance to perform an impact echo
test on a slab and see for ourselves the relation between the theoretical background we
had acquired so far and the actual values that were obtained and see how close these
were to one another.
My views on this experiment are that the results were pretty close considering some
conditions that might have been a factor in the larger percentage of error that were
obtained in some cases. One of the reasons that could mess with the results might have
been the use of the wax to place the accelerometer on the slab, we could observe that
this was not an easy task and that it required wax which didnt always hold the
accelerometer as straight as we would have liked it to be and this may have presented alittle bit of an issue in the final readings gotten by the machine. Also I think it is
imperative that we understand that the wax, if too much was present between the
accelerometer and the concrete face may have also mess a little bit with the results.
Another reason we get in some cases a really different frequency reading at really close
points might be the way the aggregates are placed on the concrete, since this could
factor in the velocity of the wave through the concrete and therefore in the frequency.
I believe that this experiment could have presented better results if more modern
accelerometers could have been used, if said apparatus could have been placed on the
slab without the use of the wax and maybe just to be on the safe side we could have
performed a different type of test to compare this results.
All in all I think this proved to be an excellent experience for the structural engineer
who may have to practice this test in the future and now they possess important
knowledge about how to go about it.
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Pictures
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References
Seong-Hoon, T., John S. Popovics, M., & Ralf and Jinying Zhu, A. (2012). NondestructiveBridge Deck Testing with Air-Coupled Impact-Echo and Infrared Thermography. Univ
of At - Austin, 1-12.
Shutao Xing, M. W. (2012). Delamination Detection of Reinforced Concrete Decks UsingModal Identification.Journal of Sensors, 17.
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Appendix A
Lab Notes
Dimension of the Slab
Thickness: _______________in
Distance from Surface to Delamination: ______2_________in
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Location of the points to be evaluated
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Frequency readings
Point 1x: ______________KHz Point 7x: ______________KHz
Point 2x: ______________KHz Point 8x: ______________KHz
Point 3x: ______________KHz Point 9x: ______________KHz
Point 4x: ______________KHz Point 10x: ______________KHz
Point 5x: ______________KHz Point 11x: ______________KHz
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Point 6x: ______________KHz
Frequency readings
Point 1y: ______________KHz Point 7y: ______________KHz
Point 2y: ______________KHz Point 8y: ______________KHz
Point 3y: ______________KHz Point 9y: ______________KHz
Point 4y: ______________KHz Point 10y: ______________KHz
Point 5y: ______________KHz Point 11y: ______________KHz
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Team #8: Edyson Rojas, Luis Dominguez, Ivan Quezada
Point 6y: ______________KHz Point 12y: ______________KHz
Appendix B
Calculations Tables
=
Cp (in/s)=
Point
Frequency
(Hz) Depth (in)
Slab or
Delamination?
1x
2x
3x
4x
5x
6x
7x
8x
9x
10x
11x
Point
Frequency
(Hz) Depth (in)
Slab or
Delamination?
1y
2y
3y
4y
5y6y
7y
8y
9y
10y
11y
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12y
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Point
Depth (in)
% ErrorFrom IE Measured
1x
2x
3x
4x5x
6x
7x
8x
9x
10x
11x
PointDepth (in)
% ErrorFrom IE Measured
1y
2y
3y
4y
5y
6y
7y
8y
9y
10y
11y
12y
Element
Dimension
Area
% of
Delamination % of ErrorX Y
Slab -------------------- ---------------
Actual
Delamination
IE
Delamination