Diapositiva 1 - Associazione aicap

Il nuovo quadro normativo sulla progettazione
antincendio delle strutture di calcestruzzo armato
Venerdì 8 febbraio 2008
AICAP – Università di Roma Tre
Meccanica del danno in caso di incendio
prof. ing. Andrea Benedetti
Dip. DISTART, Univ. di Bologna
Viale Risorgimento 2, 40136 BOLOGNA
E-mail: [email protected]
Phase Changes with Fire
• The hot resistance of
concrete depends on
the decomposition of:
• - Tobermoritic GEL
• - Calcium Hydroxide
• - a - b quartz
• The quenched
resistance of the
concrete depends on
the micro cracks
formed by the
cement paste around
the gravel and sand
elements
Merloni production plant fire
DIAVIA Fire (1995)
• La struttura pallettizzata del magazzino ha favorito la
propagazione di un incendio a riscaldamento rapido
• Le pareti tagliafuoco in cartongesso con camera hanno
consentito l’operatività dei locali protetti anche durante l’incendio
• Il calcestruzzo prefabbricato ad alta resistenza ha subito un
danno consistente principalmente per esfoliazione (ploughing)
Damage of Concrete elements
of DIAVIA
• Tutti gli elementi strutturali
sono caratterizzati da
perdite di materia per
esfoliazione con
conseguente esposizione
delle armature
• La presenza di cloro
liberato dalla combustione
della plastica ha innescato
pesanti effetti di corrosione
del ferro
• Gli elementi di bassa
massività (quali quelli di
copertura) presentano
ampi squarci e caduta di
pezzi
Thermal Shock sloughing or
cover detachment
Laboratory Calibration of the NDT
Site Measurements
600 mm
A
B
Avanzamento
carotatrice
B
Velocità Ultrasonore (m/s)
4500
3750
3000
Vus Trasversali carote
Vus Assiali cilindri
2250
0
100
200
300
400
Ascissa nella Carota (mm)
500
600
Resistenza Cilindri (kg/cm2)
A
X
300
200
100
0
• Core Laboratory characterization
–
–
–
–
Transversal ultrasound velocity measurements
Cylinder preparation for cutting
Longitudinal velocity measurement in cut samples
Compression test of the cylindrical samples
Elastic moduli distribution in fire
damaged concrete sections
30
20
10
0
0
10
20
30
40
50
Andrea Benedetti, (1998), “On the ultrasonic pulse propagation into
fire damaged concrete”, ACI Structural Journal, vol. 95-3.
60
70
Path reconstruction by the
minimum travelling time concept
Crack Density
as a measure of
Damage
Spatial
Crack
Distribution
along the
section
thickness
900
800
resistenza cilindrica [kg/cm^2]
Correlation
with the
concrete
disk punch
tests
700
600
500
400
300
200
100
0
0
30
60
ascissa carota [mm]
90
120
Disk Splitting
Tensile Test
• The tensile strength is
temperature and thus
depth dependent
Other Damage Measures (1)
Surface Hardness
Other Damage Measures (2)
Flexural Strength
Other Damage Measures (3)
Dynamic Modulus
Other Damage Measures (4)
Ultrasonic Pulse Velocity
Hot
Concrete
Strength
Schneider U., (1986), “Modeling of concrete behaviour at high temperature”, In: Anchor,
Malhotra, Purkiss, Ed.s: Design of structures against fire, New York, Elsevier, p. 53–69.
Residual
strength
after
cooling
• Residual
Strength is
dependent on
the stress level
during the
thermal cycling
Formulas
for
tangent
modulus
and peak
strength
Time-Temperature-Load
non Holonomic Processes
Evidence of Creep Irreversibility
Thermo Plastic Creep of
Concrete (LITS)
Stress
Profiles
of heated
cylinders
under
axial load
Maximum Restraint Force
During Expansion
Heating test
of a concrete
specimen
confined by
two fixed
distance
plate. The
test shows
the features
of the thermo
plastic
viscous
behavior
Thelandersson Analysis (1)
• The standard thermo elastic analysis is
not able to capture the essence of the
LITS phenomenon
   ( , T )

1 
 ij    kk  ij 
 ij  a T  ij
E
E
x 
x
Ex
 aT
x 
x
Ex
 aT
Thelandersson Analysis (2)
• The LITS effect comes out from coupling of
stress and temperature increase
   ( , , T , T )



1
1 
1
 ij  aT   kk 
 kk   kk T   ij 
 ij 
 ij
E
21
E
22


x
1
x  
 x  a T   xT
Ex 21
 x   cr 
x
Ex
 (a   x )(T  T0 )
Constitutive Models (1)
• Anderberg & Thelandersson
Anderberg Y., Thelandersson S., (1976), “Stress and deformation characteristics of concrete,
experimental investigation and material behaviour model”, Bulletin 54, University of Lund, Sweden
Constitutive Models (2)
• Schneider
Schneider U., (1986), “Modeling of concrete behaviour at high temperature”, In: Anchor, Malhotra,
Purkiss, Ed.s: Design of structures against fire, New York, Elsevier, p. 53–69.
Constitutive Models (3)
• Diederichs
Diederichs U., (1987), “Modelle zur Beschreibung der Betonverformung bei instantionaren
Temperaturen“. In Abschlubkolloquium Bauwerke unter Brandeinwirkung, Technische Universität,
Braunschweig, p. 25–34.
Constitutive Models (4)
• Khoury and Terro
Terro M., (1886), “Numerical modelling of the behaviour of concrete structures”, ACI Structural
Journal 95(2), pp. 183–193.
Comparison of Models (1)
Li L., Purkiss J., (2005), “Stress–strain constitutive equations of concrete material at elevated
temperatures”, Fire Safety Journal, 40, pp. 669–686
Comparison of Models (2)
2 u 0
T
 T 
 (T ) 
 0.021
 0.009 

E0
1000
1000


*
uT
2
Comparison of Models (3)
Comparison of Models (4)
Comparison of Models (5)
Biaxial
limit
surface
for
heated
concrete
Water moisture migration in
concrete during fire
FERRARI
Experience Centre
Fire damages to the Ferrari
Experience Centre
Rate of Heat Release
400,0
300,0
250,0
200,0
RHR Data
150,0
RHR Computed
100,0
50,0
0,0
0
20
40
60
Time [min]
80
100
120
Gas Temperature
Analysis Name:
800
700
600
500
400
Hot Zone
300
Cold Zone
200
100
0
0
Analysis Name:
20
40
60
Time [min]
80
100
120
Two Zone Model of
the fire evolution
350,0
P/C
Beam
Thermal
Analysis
2.5
Coducibility [W/m2°C]
Specific Heat [W/kg°C]
1600
1400
1200
1000
800
200
400
600
800
1000
1200
2
1.5
1
0.5
200
400
600
800
1000
1200
Temperature in the Beam Flange
700,00
T [°C]
600,00
Temperature
profile in the
horizontal
direction at a
depth of 40 mm
t = 3600 s
t = 4500 s
t = 2700 s
500,00
400,00
300,00
200,00
100,00
X [cm]
0,00
0,00
5,00
10,00
15,00
20,00
25,00
30,00
35,00
40,00
45,00
700,00
T [°C]
Temperature
profile in the
vertical direction
at a depth of 40
mm
t = 3600 s
t = 4500 s
t = 2700 s
600,00
500,00
400,00
300,00
200,00
100,00
Y [cm]
0,00
0,00
2,00
4,00
6,00
8,00
10,00
12,00
14,00
16,00
Steel wire Temperature
Web temperature
in the transversal
direction
700,00
T [°C]
600,00
t = 3600 s
t = 4800 s
500,00
400,00
300,00
200,00
100,00
X [cm]
0,00
0,00
2,00
4,00
6,00
400
8,00
10,00
Prestressing
wire
temperature
12,00
T (°C)
1
2
300
3
5
6
9
13
200
7
4
5
8
12
2
4
7
11
1
3
6
10
10
8
11
12
9
13
100
t (sec)
0
0
1000
2000
3000
4000
5000
6000
7000
8000
Light gray
denotes the
section area that
rises up to a
temperature
larger than 500°C
Ultrasonic NDT Tests
46 cm
16 cm
Reduction of the elastic modulus
with the temperature increase
1
Misura tipo A
0.6
0.4
3 f ck ( )
2  c1 ( )
0
0
200
400
Vus ( )
a us 

Vus 0
600
800
17 cm
Ec 0 ( ) 
0.2
m isura tipo C
kE ( )  kc2 ( )
0.8
misura tipo B
x2  x1
x2

x1
ds
k E ( ( s))
Paths used for the
ultrasonic velocity
measurements
0.6
Elastic
Modulus
Distribution
0.5
0.4
0.3
0.2
0.1
0
2.5
5
7.5
10
12.5
15
Elastic modulus distributions along path A
Elastic modulus distributions along path B
Ultrasonic propagation data
4500
4000
3500
3000
2500
2000
1500
1000
500
0
0,00
4500
4000
4000
3500
3000
2500
2000
1500
1000
500
3500
Trave 7
Trave 2
3000
Ttave 3
Trave 7
y = 1755,5Ln(x) - 1413,8
Trave 4
2
Trave 2
2500R = 0,8197
Trave 5
Trave 3
Trave 6
Trave 4
Trave 8
2000
Trave 5
Trave 9
Trave 6
Trave 10
1500 y = 1319,4Ln(x) - 53,658
Trave 8
Best Fit
2
Trave 9
R = 0,7844
y = 440,86Ln(x) + 1818,5
Best Fit
2
1000
Trave 7
Trave 2
Trave 3
Trave 4
Trave 5
R = 0,1894
8,00
0 4,00
500
0,00
4,00
0
0,00
12,00
8,00
16,00
12,00
4,00
8,00
Sezione
A
B
C
20,00
16,00
12,00
Spessore
160
450
120
24,00
20,00
Trave 6
Trave 8
Trave 9
Best Fit
24,00
16,00
aus(2,0)
0,215
0,000
0,531
20,00
24,00
aus MEDIO
0,755
0,669
0,710
aus(22,0)
1,000
1,000
0,794
Comparison between theory
and measurements
Comparison of the strength
reduction in the main section
Calculation of the residual
resisting moment
3500
momento flettente
3000
2500
2000
momento dei carichi
momento resistente
momento danneggiato
momento rinforzato
1500
1000
500
0
0
400
800
1200
ascissa trave
1600
2000
2400
Thanks for Your Attention
Inquiries to:
[email protected]