bklast-faa hershey schokker
TRANSCRIPT
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Structural Concrete Innovations:
A Focus on Blast Resistance
Hershey LodgePreconference Symposium17 March 2008
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Blast Overview
Blast can effect structure in multipleway
Air blast
Drag
Ground shock
Primary and secondary fragmentation
Fire
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Blast Loading
Air blast design can be governed by maxpressure, impulse, or combination
Function of size of explosive, standoff distance, and
structure
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Air Blast Loads
Properties of the air blast load afunction of the:
Size and shape of explosive Distance to explosive
Orientation of specimen
Type of blast Free air burst
Ground burst
Contained burst
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Scaled Distance
Convert explosive to equivalent weight ofTNT
Determine scaled distance usingZ = D / W^(1/3)
where Z = scaled distanceW= equivalent TNT weightD = distance between specimenand explosive
Use figures in references (TM5-1300):Structures to Resist the Effects ofAccidental Explosions determine the expected peak pressure and
impulse for determined scaled distance
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ScaledDistance
Figure 2-7TM5-1300
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Types of Cross Sections TM5-1300: 3 types of cross sections
Type I:
Concrete is sufficient to resist compressive component ofmoment
Cover remains undamaged Type II:
Concrete is no longer effective at resisting moment
Equal top and bottom reinforcement
Cover remains in tact Single leg stirrups used to resist shear
Type III:
Equal top and bottom reinforcement
Cover disengages
Lacing used to resist shear
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Example Type II Cross-Section
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Motivation for Innovation inBlast Resistant Concrete
Increased demand for impact andblast-resistant building materials
Need for practical, constructibleoptions
Need for reduction in secondary
fragmentation
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Innovation
Long (3) fibers Increased bond with concrete matrix Length provides crack bridging, spalling resistance,
increased ductility, energy absorption (through long-fiber
pull-out) Coated tape
Mix retains workability (no balling, etc) Can be used with aggregate
Potentially economical
Carbon fiber yarn is waste product from the aerospaceindustry
No special mixers required Lightweight additive reinforcement Precast or cast-in-place
Molds to any shape
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Experimental Program
Mix design development Workability
Static flexural strength
Small and large scale
Ductility
Impact testing
Small beams
Panels Blast Testing
Finite Element Modeling
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Experimental Program
Mix design development 1.5% to 2.5% fiber content (by volume)
Various admixture combinations
Pozzolans (interground SF + GGBFS)
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Preliminary Testing
Mixture Design Avoid balling
Increase workability
Increase fines andcement in mixture
Preliminary StaticTests 6 X 6 X 18 beams
loaded at third points
Flexural Strength = 2112psi
1595
21121887
0
500
1000
1500
2000
2500
B1-2.5 T1-2.5 T2-2.5
FlexuralStress(psi)
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Slab Strips 4 X 12 X 10 slab strips loaded at midspan
Specimens:
2 control specimens with reinforcing mesh
2 fiber reinforced concrete specimens
2 fiber reinforced concrete specimens with mesh
Used to obtain load vs. deflection plot
Useful for obtaining toughness
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Slab Strip Results
Force vs Displacement for Slab Strips
0
0.5
1
1.5
2
2.5
0 1 2 3
Displacement (in)
Force
(K)
Plane 1
Plane 2
Fiber 1
Fiber 2
Fiber + Mesh 1
Fiber + Mesh 2
CompressiveStrength (psi)
TensileStress (psi)
Toughness(lbs-in)
Average Plane + mesh 6151 750 186
Average Fiber 6652 1904 1834
Average Fiber + mesh 6619 2116 2619
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Impact Test Setup
15 ft maximum dropheight
50# weight
Panels 2x2x2
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Impact Testing: PanelsDrop Height at failure
0
20
40
60
80
100
120
140
160
180
1 2 3
D
ropHeight(in
)
Plain FiberWire Mesh
7blows
9blows
7blows
7blows
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Impact Testing: PanelsDrop Height at first cracking (top side)
0
20
40
60
80
100
120
140
160
180
1 2 3
D
ropHeight(in)
Plain FiberWire Mesh
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Impact Testing: Panels(No Steel Reinforcement)
Fiber addition controlled spalling Failure in fiber specimens along weak
plane due to fiber orientation
Plain panel Fiber panel
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Impact Testing: Panels(Steel Reinforcement)
Fiber panel with steel reinforcement didnot fail after repeated blows at top dropheight
Plain panel Fiber panel
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Blast Testing 6 x 6 x 6.5
Heavily reinforced (as per TM5-1300) resist shear failure at supports
evaluate comparison of materials under
full blast design Identical
reinforcement inall specimens
Clear cover to
ties
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Test Setup
Slabs were simplysupported on all
four sides Restraint provided
along two sides toprevent rebound
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Test Setup
TNT suspended atdesired height
Pressure gagesrecord reflectedpressure andincident pressure
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Hit 1: 75# at 6 (scaled range 1.4)
Extensive cracking, some spallingA few hairline cracks
Standard Concrete SafeTcrete
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Hit 2: 75# at 3.2 (scaled range 0.76)
Standard Concrete SafeTcrete
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Hit 2: 75# at 3.2 (scaled range 0.76)
Standard Concrete SafeTcrete
Some concrete loss due to pop out wherereinforcement buckled (3/4 cover)
Concrete rubble within steel cage
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Hit 2: 75# at 3.2 (scaled range 0.76)
Standard Concrete
SafeTcrete
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Summary of Impact &Blast Testing
Much improved workability and dispersionof coated tape fibers
Increased ductility over plain concrete andfurther improved combined with standardreinforcement
Significantly increased flexural strengthunder both static and impact loads
Complete control of spalling in panelsunder impact load
Excellent performance in blast testing
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Potential
Low cost fiber alternative Applications requiring impact and blast
resistance
Protective cladding panels
Structural components: columns, walls
Barriers
Bridge piers
May be used as a replacement for, or incombination with standard reinforcementdepending on application
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Material Properties
Stress-strain curves for material inboth compression and tension needed
for modeling Compression: standard 6 diametercylinders
Tension: dogbone specimens will be
utilized Varied load rates and fiber orientation
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Tensile Properties
New test method fortension in fiber concrete
Difficulties with directtension
Size-effect with long-fibers
Dogbone specimens
32 high, 8 neck width,16 top width
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Concrete Dogbone
Mechanical anchorageswere used to loadspecimen
Anchorage consisted of
5/8, 125 ksi threadedprestressing rod
LVDTs for displacement
Failure occurred indesired region
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Tensile Properties
Increase in energy
dissipation Testing will
determine ifcracking stress isaffected by theaddition of fibers
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Finite Element Modeling
Material model developed from testing
Comparison to field blast test and
instrumented impact testing
Loading
CONWEP (built into LS Dyna)
Gas dynamics model (Lyle Long, AE)
Field data
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Current Work
Continued model refinement Material model
Incorporation of fracture mechanics Contact charges
Application specific testing Durability
Reinforcement and fiber contentvariations
Specification development
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Barrier Application Testing
Use of fibers & polyurea for barriers
Large volume of concrete with smallreinforcement percentage
Reduction in secondary fragmentationneeded
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Wall Testing:Spec Development
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Questions?
Hershey LodgePreconference Symposium17 March 2008