bre/tslab vulcan comparisons - university of...
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25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
Tensile Membrane Action
Peripheral compression
Tensile Area
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
• Rigid – plastic theory with large change of geometry
• Yield line capacity
• Membrane enhancement to yield line capacity
• Panels are horizontally unrestrained
• Vertical support at the boundaries
• Tensile strength of concrete is ignored
BRE – Bailey Method
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
φ
nL
L
l
SS
BRE – Bailey Method
T1
T2
T2’ T2
’
T2
C C
T2 T2
T1
CC
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
• Allowable deflection
( )
8
35.0
2.19
22
12L
E
f
h
lTTv
y×+
−=
α
T2-T1 = 770°C for Time ≤ 90 mins T2-T1 = 900°C for Time > 90 mins
BRE – Bailey Method
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
• Do protected beams provide adequate vertical support?
• Effect of reinforcement ratios on failure
• Effect of tensile strength of concrete
• Effect of edge continuity
Comparison between Vulcan and
BRE – Bailey Method
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
• 9.0m x 6.0m, 7.5m x 9.0m, 9.0m x 9.0m, 9.0m x 12.0m
• S275 beams
• Trapezoidal deck profile
• Normal weight concrete
• Strength (fcu = 40N/mm2, fck = 35N/mm2)
• S500 Reinforcement mesh
• Average mesh position (from top surface) = 45mm
Slab-Panel Properties
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
7.5m x 9.0m Slab-Panel
9.0m
7.5m
Corner vertical supportDifferent protection regimes
and support conditions
A193 Mesh
• Load ratios and limiting temperatures
• Secondary beams = 0.44 and 631°C
• Primary beams = 0.40 and 646°C
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
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Time (min)
Vertical Displacement (mm)60 mins
Span/20
( )8
35.0
2.19
77022
L
E
f
h
lCv
y×+=
oαBRE Limit
( )
8
35.0
2.19
22
12L
E
f
h
lTTv
y×+
−=
αTSLAB
7.5m x 9.0m Slab-Panel
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
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Time (min)
Vertical Displacement (mm)
7.5m x 9.0m Slab-Panel
Bailey - BRE Method
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
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Time (min)
Vertical Displacement (mm)
7.5m x 9.0m Slab-Panel
Vulcan – edge support
Vulcan – corner support
– Generic Protection
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
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Time (min)
Vertical Displacement (mm)
7.5m x 9.0m Slab-Panel
Vulcan – Displacement of slab panel
centre relative to secondary beam
Vulcan – Displacement of slab panel
centre relative to primary beam
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
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Time (min)
Vertical Displacement (mm)
7.5m x 9.0m Slab-Panel
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Time (min)
Vertical Displacement (mm)
Vulcan – Cold Perimeter Beams – Edge
support - Tensile strength of concrete
included
Vulcan – Cold Perimeter Beams –
Edge support - Tensile strength of
concrete ignored
7.5m x 9.0m Slab-Panel
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
• Maximum absolute vertical displacements
• Deflection plots (mesh sizes)
• A142 – Navy blue
• A193 – Red
• A252 – Green
• A393 - Black
• Analytical approaches
• BRE Method – Solid lines
• Vulcan – Broken lines
Main Study
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
Typical slab panel Secondary beam failure Primary beam failure
Type 1
Typical slab panel Secondary beam failure Primary beam failure
Type 2
Proposed Failure Criteria
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
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Time (min)
Maxim
um
Dis
pla
cem
ent
(mm
)
Vulcan Results
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Time (min)M
axim
um
Dis
pla
cem
ent
(mm
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Plastic Failure
9.0m x 6.0m Slab-Panel
Type 2
Type 1
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
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Vulcan Results
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Time (min)M
axim
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Dis
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(mm
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Plastic Failure
9.0m x 12.0m Slab-Panel
Type 2
Type 1
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Vulcan Results
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Time (min)M
axim
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Plastic Failure
9.0m x 9.0m Slab-Panel
Type 2
Type 1
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
• Reinforcement ratios
• 142, 166, 193, 221, 252, 318, 393 (mm2/m)
• Additional ratios for 9.0m x 9.0m slab panel
• 153, 179, 206, 236, 284, 354 (mm2/m)
• Comparison of failure times
Comparison of Failure Times
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
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Time (min)M
axim
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cem
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(mm
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Vulcan failure times BRE failure times
Increasing
reinforcement ratio
Increasing
reinforcement ratio
9.0m x 6.0m Slab-Panel
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
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30
60
90
120
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180
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240
270
140 170 200 230 260 290 320 350 380
Area of Reinforcement (mm2/m)
Failu
re T
ime (
min
)
TSLAB
Span/20
BRE Limit
9.0m x 6.0m comparison
0
30
60
90
120
150
180
210
240
270
140 170 200 230 260 290 320 350 380
Area of Reinforcement (mm2/m)F
ailu
re T
ime (
min
)
TSLAB
Span/20
BRE Limit
9.0m x 12.0m comparison
Failure Times
25-Sep-07 © The University of Sheffield - Structural Fire Engineering Group
Conclusions
• Significant influence of edge support & continuity
• Bailey Method sensitive to mesh size and temperature
• Conservative for
• Smaller mesh sizes
• Larger slab panels
• As ‘collapse’ condition for slab
• Failure criteria - relative or absolute displacements?
• Reinforcement temperatures