Query optimization and processing for advanced database systems
2016 aci milwaukee_wi_2016_v3
1. Tensile and Flexural Behavior of UHPC under High-
Speed Tensile and Impact Loads
Barzin Mobasher, Yiming Yao, Flavio A. Silva, Vikram Dey
School of Sustainable Engineering and the Built Environment
Ira A. Fulton Schools of Engineering
Arizona State University
Tempe, AZ 85287-5306
ACI Fall Convention, October, 2014, Washington DC
UHPC Behavior under Blast and Impact Load Effects
2. Outline
Introduction
Testing Methodology and Data Processing
Flexural Impact Behavior
Tensile Behavior
Digital Image Correlation (DIC) Method
Analytical Modelling of Flexural Response
Summary
3. Introduction
Desire of energy-efficient, environment
friendly, sustainable, resilient
Ultra-high performance concrete (UHPC)
– 150 Mpa (22 ksi)
– 6% steel fibers
– High strength
– Low permeability
Strength, ductility, impact resistance,
durability, aggressive environmental and
chemical resistance
Thin sections
Complex structural forms
Cast by pouring, injection, extrusion
4. Impact, Blast, Dynamic Events
Cases for dynamic loading:
– blast explosions
– projectiles
– earthquakes
– fast moving traffic
– wind gusts, wind driven objects,
– machine vibrations.
Inherent brittleness and low tensile
strength, dynamic loading can cause
severe damage.
Mechanical properties at high strain
rates for analysis of structural
components.
5. Experimental Program
Materials Weight per
litter, g
Cement-I 832
Microsilica Elkem
971
135
Silica fume 207
Water 166
Sand 975
SAP 29.4
Steel fiber (2.5%) 192
Mix Design
Beam specimen for flexural impact
Dogbone
Specimen
for
tension
Plate
specimen
for
tension
6. High speed testing system at ASU
MTS servo-hydraulic system, rate
up to 14 m/s, load capacity: 90 kN
Dogbone sample Plate sample
7. Impact Test
Impact Test Set-
up
Specimens were tested in both vertical and horizontal
positions with respect to the direction of applied impact
load.
11. Data Processing
Parameters including: force, displacement, stress (average), nominal strain,
strain at peak, strain at failure, work-to-fracture
12. Frequency Analysis and Low-pass filter
Design
100 1000 10000
Frequency (Hz)
0
0.005
0.01
0.015
0.02
0.025
FourierAmplitude(g-s)
Hammer
Raw Signal
Filtered Signal
Modal analysis tests were conducted to identify the predominant
frequencies of the hammer and the test specimens. The predominant
frequency of the hammer is about 5 kHz
0.05 0.052 0.054 0.056 0.058 0.06
Time, sec
-400
-200
0
200
400
600
Acceleration,g
Acceleration of Specimen
h = 50.8 mm
Vertical Direction
Raw Data
Filtered Data
13. Impact Behavior
0 0.02 0.04 0.06 0.08
Time, sec
-400
0
400
800
Acceleration,g
Acceleration of ARG6B
h = 50 mm
h = 200 mm
h = 250 mm
Acceleration and Impact force for UHPC specimens at different drop heights
14. Impact Behavior, continue
Load-deflection variation for UHPC under
different drop heights
H = 50mm H = 250mm H = 500mm
No visible cracking observed at H=50 mm
Cracks at H=250 mm, rebound of specimen
observed
Major cracking and collapse at H=500 mm, no
rebound
15. Drop Height Effects
As H increases from 50 to 500 mm
– Maximum load increases from 5.2kN to 10.1kN, then drops to 8.8kN
– Flexural strength increases from 15.1MPa to 29.2MPa, then decreases to
25.4MPa
– Maximum displacement increases from 0.27mm to 6.13mm
– Absorbed energy increase from 0.6J to 4.3J
17. Strain Rate Effects
As strain rate increases from 25 to 100 s-1
– Tensile strength increases from 15.4 to 26.8 Mpa
– Absorbed energy increases from 3.82 to 10.63 mJ
18. Digital Image Correlation (DIC) Method
Non-contacting optical
measurement
– Developed by Sutton and Bruck
et al. (1983 – 1991)
Advantages
– Full-field deformation
measurement
– Large range of size scales (10-9
to 102 m)
– Large range of time scales (static
to 200 MHz)
– Easy sample preparation and
setup
Template matching -- Minimize
the squared gray value
differences
Subset
Area of
interest
(AOI)
Original subset Deformed subset
F(x,y) G(x’,y’)
x
y
x’
y’
Mapping
21. Flexural Modeling: Stress-strain Model
Tension modelCompression model
Material parameters are described as a multiple of the first cracking tensile strain
(cr) and tensile modulus (E)
22. Stress and Strain Distribution
0 < β < 1 and λ < ω 1 < β < α and λ < ω
α < β < βtu and λ < ω
23. Moment-Curvature Diagram
M
f
f
c
0 < t < tu
k
d
C2
T1
T2
T3
C1
stressstrain Moment curvature
diagram
Incrementally impose 0 < t < tu
Strain Distribution
Stress Distribution
SF = 0, determine k (Neutral axis)
M = SCiyci+ STiyti and f=c/kd
Normalization M’=M/M0 and f’=f/fcr
1 10
kd
c cF b f y dy
1 10
1
kd
c c
c
b
y f y ydy
F
25. Effect of Residual Strength, m
0 4 8 12 16
Normalized top compressive strain,
0
0.1
0.2
0.3
0.4
0.5
Neutralaxisdepthratio,k
m=0.01
m=0.35
m=0.68
m=1.00
m=0.18
= 10
cu = 0.004
tu = 0.015
0 20 40 60
Normalized Cuvature, f'
0
1
2
3
NormalizedMoment,M'
m=0.01
m=0.35
m=0.68
m=1.00
m=0.18
cr
cr
2
=
d
f2
cr cr
1
M = bd E
6
M '( ) = 3
+
m
f
m
M’= 1.910
M’=1.0145
M’= 0.530
M’=2.727
M’=0.03
*tucr
26. Effect of Localization Zone Size, Lp
• Affects the general softening behavior in the post
peak zone
• The simulated residual load capacity is not
sensitive
• Model parameters:
• b=40mm, h=40mm, L=125mm
• E=45GPa, cr=280m, a90, h0.011, m0.021,
tu300, g0.95, 8.33, cu27
~5mm
Localization
Shear
lagUniform
27. Simulation of Experiment Results
• Other model
parameters:
• g0.95, 8.33,
cu27
Drop height
(mm)
E (Gpa) cr (m) m h a tu Lp (mm)
50 35 180 0.11 -0.010 90 280 5
250 45 270 0.02 -0.011 90 300 5
500 42 250 0.06 -0.010 95 500 20
28. Correlation of Tensile and Flexural
Young’s Modulus (E) and cracking strain (cr) increases
Increasing ultimate tensile strain (tu) indicate higher ductility
Larger localization zone Lp implies higher level of localized damage, correlating
to the failure mode
29. Summary
High speed tensile and flexural impact test procedures for UHPC were
developed
Tensile strength over 20 MPa was obtained and the flexural strength
exceeded 25 MPa
Crack and failure behaviours were characterized by means of high
speed images
Digital image correlation (DIC) method was used to determine the
inhomogeneous displacement/strain fields
An optical method of crack width measurement using DIC is proposed
Bilinear parametric model was able to predict the flexural impact
responses