ACI Fall 2013 Convention, Blast Blind Predict of Response of Concrete Slabs Subjected to Blast Loading (Contest Winners) - October 22, 4:00 PM - 6:00 PM, C-212 B

1. Olmati P(1), Trasborg P(2), Sgambi L(3), Naito CJ(4), Bontempi F(5)
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
(3) Associate Researcher, Ph.D., P.E., Politecnico di Milano, Email: sgambi@stru.polimi.it
(1) Ph.D. Candidate, P.E., Sapienza University of Rome, Email: pierluigi.olmati@uniroma1.it
(4) Associate Professor and Associate Chair, Ph.D., P.E., Lehigh University, Email: cjn3@lehigh.edu
(5) Professor, Ph.D., P.E., Sapienza University of Rome, Email: franco.bontempi@uniroma1.it
(2) Ph.D. Candidate, Lehigh University, Email: pat310@lehigh.edu
Finite element and analytical approaches for
predicting the structural response of reinforced
concrete slabs under blast loading
Section: Blast Blind Predict of Response of Concrete Slabs Subjected to Blast
Loading (Contest Winners) - October 22, 4:00 PM - 6:00 PM, C-212 B
Chair: Prof. Ganesh Thiagarajan

2. Presentation outline
Introduction1
Finite Element Model2
Analytical Model3
Conclusions4
Questions/References5
1
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3
4
5
2
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu

3. The team - Short bio
3Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
Pierluigi Olmati is in the last year of his Ph.D. in
Structural Engineering at the Sapienza
University of Rome (Italy), with advisor Prof.
Franco Bontempi from the same University and
co-advisor Prof. Clay J. Naito from the Lehigh
University (Bethlehem, PA, USA).
The principal research topic of Mr. Olmati is blast engineering, addressed from
the point of view of FE modeling and probabilistic design. Mr. Olmati spent six
months at the Lehigh University in 2012 studying the performance of insulated
panels subjected to close-in detonations. Recently he was visiting Prof. Charis
Gantes and Prof. Dimitrios Vamvatsikos at the Department of Structural
Engineering of the National Technical University of Athens (Greece), performing
research on the probabilistic aspects of the blast design, and in particular,
developing fragility curves and a safety for built-up blast doors.
Pierluigi Olmati, Ph.D. Candidate, P.E.
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4. The team - Short bio4
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
Patrick Trasborg, Ph.D. Candidate
Patrick Trasborg is in his 4th year of his
Ph.D. in Structural Engineering at Lehigh
University (Bethlehem, PA, USA), with
advisor Professor Clay Naito from the
same University.
The principal research topic of Mr. Trasborg is blast engineering, addressed from
the point of view of analytical modeling with experimental validation. Mr.
Trasborg’s dissertation is on the development of a blast and ballistic resistant
insulated precast concrete wall panel. Currently he is characterizing the
performance of insulated panels with various shear ties subjected to uniform
loading.
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5. The team - Short bio5
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
Luca Sgambi, Associate Researcher,
Ph.D., P.E.
He studied Structural Engineering (1998) and took a 2nd
level Master degree in R.C. Structures (2001) at
Politecnico di Milano. He pursued his studies with a Ph.D.
at “La Sapienza” University of Rome (2005).
At present, he holds the position of Assistant Professor at Politecnico di Milano
and teaches “Structural Analysis” (since 2003) at School of Civil Architecture,
Politecnico di Milano. He is author of 7 papers on international journals and 57
paper on national and international conference proceedings; his research fields
concerning the non linear structural analyses, soft computing techniques,
durability of structural systems.
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6. The team - Short bio6
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
Clay Naito, Associate Professor and
Associate Chair, Ph.D., P.E.
Clay J. Naito is an associate professor of Structural Engineering
and associate chair at Lehigh University Department of Civil
and Environmental Engineering. He received his
undergraduate degree from the University of Hawaii and his
graduate degrees from the University of California Berkeley.
He is a licensed professional engineer in Pennsylvania and California. His research
interests include experimental and analytical evaluation of reinforced and prestressed
concrete structures subjected to extreme events including earthquakes, intentional
blast demands, and tsunamis. Professor Naito is Chair of the PCI Blast Resistance and
Structural Integrity Committee and an Associate Editor of the ASCE Bridge Journal.
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7. The team - Short bio7
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
Franco Bontempi, Professor, Ph.D., P.E.
Prof. Bontempi, born 1963, obtained a Degree in Civil
Engineering in 1988 and a Ph.D. in Structural Engineering in
1993, from the Politecnico di Milano. He is a Professor of
Structural Analysis and Design at the School of Engineering of
the Sapienza University of Rome since 2000.
He spent research periods at the Harbin Institute of Technology, the Univ. of Illinois
Urbana-Champaign, the TU of Karlsruhe and the TU of Munich. He has a wide activity
as a consultant for special structures and as forensic engineering expert.
Prof. Bontempi has a deep research activity on numerous themes related to
Structural Engineering, having developed approximately 250 scientific and technical
publications on the topics: Structural Analysis and Design, System Engineering,
Performance-based Design, Hazard and Risk Analysis, Safety and Reliability
Engineering, Dependability, Structural Integrity, Structural Dynamics and Interaction
Phenomena, Identification, Optimization and Control of Structures, Bridges and
Viaducts, High-rise Buildings, Special Structures, Offshore Wind Turbines.
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8. Presentation outline
Introduction1
Finite Element Model2
Analytical Model3
Conclusions4
Questions/References5
8
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
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9. Finite element for modeling the concrete part of the slab9
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
Image provided by: Lawrence Software Technology Corporation (LSTC). LS-DYNA
theory manual. California (US), Livermore Software Technology Corporation.
Eight-node solid hexahedron element (constant stress solid element)
with reduced integration. Default in LS-Dyna®. Other choices were
prohibitive because computationally expensive.
Hourglass:
Flanagan-Belytschko
stiffness form with
hourglass coefficient
equal to 0,05.
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[image from ANSYS]

10. Finite element for modeling the reinforcements of the slab10
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
The Hughes-Liu beam element with cross section integration.
Tubular cross section with internal diameter much smaller than the
external diameter.
Image provided by: Lawrence Software Technology Corporation (LSTC). LS-DYNA
theory manual. California (US), Livermore Software Technology Corporation.
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11. The finite element mesh11
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
Upper support
Down support
Solid elements: 270,960
Beam elements: 130
Total nodes: 290,6281
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12. Demand12
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
0
10
20
30
40
50
60
0 20 40 60 80 100
Pressure[psi]
Time [msec]
PH-Set 1a
PH-Set 1b
Load 1
Load 2
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13. Material model for the concrete – The Continuous Surface Cap Model13
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
U.S. Department of Transportation, Federal Highway Administration. Users Manual
for LS-DYNA Concrete, Material Model 159.
The cap retract
in function of
the equation of
state.
Material Model 159 – LS-Dyna®
The dynamic increasing
factor affects the failure
surface.
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14. Material model for the concrete – The Continuous Surface Cap Model14
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
U.S. Department of Transportation, Federal Highway Administration. Users Manual
for LS-DYNA Concrete, Material Model 159.
Material Model 159 – LS-Dyna®
Density
2.248 lbf/in4
s2
2.4*103
kg/m3
fc
5400 psi
37 N/mm2
Cap
retraction
active
Rate
effect
active
Erosion none
0
2
4
6
8
0.001 0.1 10 1000
DIF[-]
Strain-rate [1/sec]
Compressive
Tensile
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15. Material model for the rebar– Piecewise Linear Plasticity Model15
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
Material Model 24 – LS-Dyna®
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16. Material model for the rebar– Piecewise Linear Plasticity Model16
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
Material Model 24 – LS-Dyna®
0
20
40
60
80
100
120
140
0 0.05 0.1 0.15 0.2
Stress[kpsi]
Plastic strain [-]
True Stress
Stress
εT= ln 1 + ε
σT= σ eεT
εTp= εT −
σT
E
ε: engineering strain
σ: engineering stress
εT: true strain
σT: true stress
σy: engineering yield stress
σTp= σ eεT − σy
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17. Material model for the rebar– Piecewise Linear Plasticity Model17
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
1
1.2
1.4
1.6
1.8
2
0.001 0.01 0.1 1 10 100
DIF[-]
Strain-rate [1/sec]
US Army Corps of
Engineers,
2008.Methodology
Manual for the
Single-Degree-of-
Freedom Blast
Effects Design
Spreadsheets
(SBEDS).
Cowper and Symonds model for the Material Model 24 – LS-Dyna®
DIF = 1 +
ε
C
1
q
C= 500 [1/s] q=6
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18. Boundary conditions18
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
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19. Boundary conditions19
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
Down support
Upper support
Contact surfaces
Contact
surfaces
Shock load
Gap 0.25”
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20. Boundary conditions20
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
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21. Results – Deflection21
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
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22. Results – Deflection22
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
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23. Results – Crack patterns23
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
33.75 in. (857 mm)
64in.(1625mm)
33.75 in. (857 mm)
64in.(1625mm)
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24. Presentation outline
Introduction1
Finite Element Model2
Analytical Model3
Conclusions4
Questions/References5
24
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
1
2
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4
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25. Analytical Model – Fiber Analysis25
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
Cross Section of Slab
Fiber Analysis of Section
Cross section approximated by dividing into discrete fibers [Kaba, Mahin 1983]
0 0.05 0.1 0.15 0.2
0
50000
100000
150000
200000
0
1500
3000
4500
6000
0 0.01 0.02 0.03
Steel Strain
SteelStress[psi]
ConcreteStress[psi]
Concrete Strain
Conc Data
Mod Popovics
DIF Conc
Steel Data
DIF Steel
A =d *bi
d
d/i
i number of layers
i
b
• Concrete material model approximated
with Popovic’s model
• DIF models same as numerical model
• Correct DIF required iterative processNormal Strength Panel Strengths
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26. Analytical Model – Moment Curvature & Boundary Conditions26
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
-100
0
100
200
300
400
-0.02 -0.01 0 0.01 0.02 0.03
Moment[kip-in]
Curvature [1/in]
• Obtained through fiber-analysis
• Independent of boundary
conditions
Simple-Simple
KLM=0.78
Fixed-Fixed
KLM=0.77
Hinge @ Center
KLM=0.64
Mechanism
KLM=0.66
Boundary conditions change as panel deflects
due to support gap and panel yielding
3"
4"
BLAST LOAD0.25"
BLAST LOAD
SEC A-A
SEC A-A
52"
SEC A-A Deformed
Simple-Simple
KLM=0.78
Fixed-Fixed
KLM=0.77
Simple-Simple
KLM=0.78
Mechanism
KLM=0.66
Normal Strength Panel
High strength panel:
hinging occurs at ends
before center
Normal Strength Panel
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27. Analytical Model – SDOF Approach & Results27
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
Normal Strength Panel Resistance Function
Simple-Simple
KLM=0.78
Fixed-Fixed
KLM=0.77
Hinge @ Center
KLM=0.64
Mechanism
KLM=0.66
0
5
10
15
20
25
30
35
40
0 0.5 1 1.5 2 2.5 3
Resistance[psi]
Deflection [in]
Simp-Simp
0
5
10
15
20
25
30
35
40
0 0.5 1 1.5 2 2.5 3
Resistance[psi]
Deflection [in]
Simp-Simp
Fixed-Fixed
0
5
10
15
20
25
30
35
40
0 0.5 1 1.5 2 2.5 3
Resistance[psi]
Deflection [in]
Simp-Simp
Fixed-Fixed
0
5
10
15
20
25
30
35
40
0 0.5 1 1.5 2 2.5 3
Resistance[psi]
Deflection [in]
Switches to Fixed
Simp-Simp
Fixed-Fixed
0
5
10
15
20
25
30
35
40
0 0.5 1 1.5 2 2.5 3
Resistance[psi]
Deflection [in]
Switches to Fixed
Hinge @ Center
Simp-Simp
Fixed-Fixed
0
5
10
15
20
25
30
35
40
0 0.5 1 1.5 2 2.5 3
Resistance[psi]
Deflection [in]
Switches to Fixed
Hinge @ Center
Hinges @ Ends
Simp-Simp
Fixed-Fixed
0
5
10
15
20
25
30
35
40
0 0.5 1 1.5 2 2.5 3
Resistance[psi]
Deflection [in]
Switches to Fixed
Hinge @ Center
Hinges @ Ends
Simp-Simp
Fixed-Fixed
Simple-Simple
KLM=0.78
Fixed-Fixed
KLM=0.77
Hinge @ Center
KLM=0.64
Mechanism
KLM=0.66
Simple-Simple
KLM=0.78
Fixed-Fixed
KLM=0.77
Hinge @ Center
KLM=0.64
Mechanism
KLM=0.66
Simple-Simple
KLM=0.78
Fixed-Fixed
KLM=0.77
Hinge @ Center
KLM=0.64
Mechanism
KLM=0.66
1
2
3
4
5

28. Analytical Model – SDOF Approach & Results28
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
0
5
10
15
20
25
30
35
40
0 0.5 1 1.5 2 2.5 3
Resistance[psi]
Deflection [in]
Switches to Fixed
Hinge @ Center
Hinges @ Ends
Simp-Simp
Fixed-Fixed
Normal Strength Panel High Strength Panel
0
20
40
60
80
100
120
0
1
2
3
4
5
0 25 50 75 100 125 150
Deflection[mm]
Deflection[in]
Time [ms]
Load 1 Avg Residual
Load 2 Avg Residual
0
10
20
30
40
50
60
70
0
0.5
1
1.5
2
2.5
3
0 25 50 75 100 125 150
Deflection[mm]
Deflection[in]
Time [ms]
Load 1 Avg Residual
Load 2 Avg Residual
Results
0
10
20
30
40
50
60
70
0 0.5 1 1.5 2 2.5 3 3.5 4
Resistance[psi]
Deflection [in]
Switches to Fixed
Hinges @ Ends
Hinge @ Center
Simp-Simp
Fixed-Fixed
1
2
3
4
5

29. Analytical versus Experimental29
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
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30. Presentation outline
Introduction1
Finite Element Model2
Analytical Model3
Conclusions4
Questions/References5
30
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
1
2
3
4
5

31. Upper support
Down support
Conclusions (1)31
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
- Use the symmetry when possible in order to reduce the
computational cost and to improve the quality of the mesh.
- The CSCM (mat 159 LS-Dyna®) for concrete is appropriate for
modeling component responding with flexural mechanism.
- The reinforcements should be modeled by beam elements in order
to be able to carry shear stresses; this is crucial for component with
thin cross section.
- In this case the boundary conditions have a crucial importance.
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32. Conclusions (2)32
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
Simple-Simple
KLM=0.78
Fixed-Fixed
KLM=0.77
Hinge @ Center
KLM=0.64
Mechanism
KLM=0.66
Simple-Simple
KLM=0.78
Fixed-Fixed
KLM=0.77
Simple-Simple
KLM=0.78
Mechanism
KLM=0.66
Cross Section of Slab
Fiber Analysis of Section
- Analytical methods proved accurate when
compared to numerical methods
- Increasing the material strengths of the panel
affected the progression of hinge formation
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33. Conclusions (3)33
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
0
20
40
60
80
100
120
0
1
2
3
4
5
0 25 50 75 100 125
Deflection[mm]
Deflection[in]
Time [ms]
Analytical Numerical
- Analytical methods provide close results to numerical methods. This
is useful for a quick check of results before performing a detailed
design.
- For more detailed analysis, such as crack patterns, numerical
methods are required 33.75 in. (857 mm)
64in.(1625mm)
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34. Presentation outline
Introduction1
Finite Element Model2
Analytical Model3
Conclusions4
Questions/References5
34
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
1
2
3
4
5

35. Questions35
Olmati, Trasborg, Sgambi, Naito, Bontempi
Sapienza University of Rome & Lehigh University
cjn3@lehigh.edu
• Kaba, S., Mahin, S., “Refined Modeling of Reinforced Concrete Columns for Seismic Analysis,”
Nisee e-library, UCB/EERC-84/03, 1984, http://nisee.berkeley.edu/elibrary/Text/141375
• Lawrence Software Technology Corporation (LSTC). LS-DYNA theory manual. California (US),
Livermore Software Technology Corporation.
• U.S. Department of Transportation, Federal Highway Administration. Users Manual for LS-
DYNA Concrete, Material Model 159.
• Olmati P, Trasborg P, Naito CJ, Bontempi F. Blast resistance of reinforced precast concrete walls
under uncertainty. International Journal of Critical Infrastructures 2013; accepted
References
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Placement
• Normal Strength – Numerical Prediction (LS-Dyna) – 1st place
• Normal Strength – Analytical Prediction (SDOF) – 2nd place
• High Strength – Analytical Prediction (SDOF) – 3rd place (unofficial)
• High Strength – Numerical Prediction (LS-Dyna) – Not released