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THE EXTERNAL THERMAL INSULATION COMPOSITE SYSTEM
A COMPREHENSIVE STRESS STRAIN ANALYSIS
Amilcare Collina
MAPEI S.p.A
4th PORTUGUESE CONFERENCE
ON MORTARS AND ETICS
Coimbra - Portugal March 30, 2012
Gian Piero Lignola
UNIVERSITY OF NAPLES
ETICS STRATIGRAPHY
Ad
hesiv
e Insulation panel
Leveling mortar
Glass net
Leveling mortar
Primer
Finishing
R
en
der
Maso
nry
EXTERNAL THERMAL INSULATION
COMPOSITE SYSTEM
20
16.5
15.9
10.3
5.2
-3.4
-3.9
-5
19 18.8
17.6
16.2
13.9
13.7
-4.5
TEMPERATURE PROFILE WITHIN THE WALL IN WINTER SEASON (°C)
j = 28 W/m2
j = 8 W/m2
TEMPERATURE PROFILE WITHIN THE WALL IN SUMMER SEASON (°C)
50
29.3
29.1
26.4
24.8
23.4
22
26
33.2
39.1
49.4
23.1
26.7
j = 32.8 W/m2
j = 9.4 W/m2
TE = 30
ETICS: A MULTI COMPONENT SYSTEM
COMPONENT REQUIREMENTS
• ADHESIVE
• INSULATING PANEL • LEVELING MORTAR • GLASS GRID • FINISHING
• shear and peel strength
• thermal conductivity, thermal elongation
• adhesion, tensile and compression strength
• polarity, alkali resistance
• water absorption, vapor permeability, aesthetics
COMPATIBILITY
MAPETHERM STRESS ANALYSIS
• WIND
• SELF WEIGHT
• RESTRAINED THERMAL DEFORMATION
THE ADHESIVE IS THE KEY COMPONENT
DUE TO WIND
v cP = -0.4
P1>P P2< P
P2-P = cP*(rv2/2)
DP = - 225 N/m2 s = 0.22 kPa
v = 110 km/h = 30 m/s
P
PEEL STRESS IN THE ADHESIVE
SHEAR STRESS IN THE ADHESIVE
DUE TO SELF WEIGHT
0.9°C
w = (10 kg/m2)*(9.8 m/s2) = 98 N/m2
t = 0.1 kPa
t
ETICS STRESS
0.9°C
lp= 70 m / m°C
Lp = 1250 mm tp = 80 mm Ep = 12 MPa
ta = 4mm Ea= 1200 MPa Ga = 400 MPa
Winkler Type Model
ADHESIVE PEEL STRESS
w
x=0 x=L
Insulating Panel
ka=Ea/ta
3 4
40
12
p p
a
E t wk w
x
cos cosx xw e A x Bsin x e C x Dsin x
43
3 a
p p
k
E t
aaa tEk /
Winkler Type Model
ADHESIVE PEEL STRESS
w
x=0 x=L
Insulating Panel
ka=Ea/ta
Rotation (δw/δx)
Shear Force (proportional to δ3w/δx3)
are zero (symmetry)
Boundary
Conditions
Winkler Type Model
ADHESIVE PEEL STRESS
w
x=0 x=L
Insulating Panel
ka=Ea/ta
Shear Force (proportional to δ3w/δx3)
Total curvature (i.e. δ2w/δx2) sum of elastic
component and thermal component
are zero (condition at free edge)
Boundary
Conditions
12// 3
PPPPel tEtTM D l
-90
-45
0
45
90
135
180
225
270
0 200 400 600
Distance from the center [mm]
Ad
he
siv
e n
orm
al
str
es
s
[kP
a]
-0,3
0
0,3
0,6
0,9
Pa
ne
l T
ran
sv
ers
e
Dis
pla
ce
me
nt
[ mm
]
WINTER
ADHESIVE PEEL STRESS
max 195kPas
-360
-315
-270
-225
-180
-135
-90
-45
0
45
90
0 200 400 600
Distance from the center [mm]
Ad
he
siv
e n
orm
al
str
es
s
[kP
a]
-1,2
-0,9
-0,6
-0,3
0
0,3
Pa
ne
l T
ran
sv
ers
e
Dis
pla
ce
me
nt
[ mm
]
SUMMER
ADHESIVE PEEL STRESS
max 63kPas
Winkler Type Model
ADHESIVE SHEAR STRESS
w
x=0 x=L
Insulating Panel
ka=Ea/ta
SHEAR LAG MODEL
Lp = 1250 mm L= Lp/2 = 625 mm. tp = 80 mm Ep = 12 MPa ta = 4mm Ea= 1200 MPa Ga = 400 MPa lp = 70 m/m°C
Ttt
G
dx
dp
pa
ap
pD ls
s2
2
2
BOUNDARY CONDITIONS
0........
0.......0
p
p
Lx
dx
dX
s
s dx
dt
p
pa
st
ppa
a
Ett
G
Symmetry
Free edge
Winkler Type Model
ADHESIVE SHEAR STRESS
w
x=0 x=L
Insulating Panel
ka=Ea/ta
SHEAR LAG MODEL
Lp = 1250 mm L= Lp/2 = 625 mm. tp = 80 mm Ep = 12 MPa ta = 4mm Ea= 1200 MPa Ga = 400 MPa lp = 70 m/m°C
D
LCh
xChTE ppp
ls 1
LCh
xShTEt pppa
lt D
ppa
a
Ett
G
RELEVANT DT
50°C
29,3°C
CTav 40
Two components:
Zero stress T0=20°C
•Linear thermal expansion DT1=Tav-T0=20°C
•Thermal inflection DT2=(Text-Tint)/2=10°C
SUMMER
SUMMER
DRIVING FORCE
MAX PEEL STRESS
MAX SHEAR STRESS
THERMAL DISTORSION
w DT =-20°C
195 kPa
free edge
winter
-
THERMAL
ELONGATION
s DT = 20°C
- 728 kPa
free edge
summer
WIND
v = 110 km/h
30 m/s
0,22 kPa
distributed
-
SELF WEIGHT
m = 10 kg/m2
w=100 N/m2
- 0,10 kPa
distributed
STRESS IN THE ADHESIVE SUMMARY
STRESS IN THE ADHESIVE
CONCLUSIONS
• MAINLY DUE TO RESTRAINED THERMAL DEFORMATION OF THE PANEL
• WIND AND SELF WEIGHT EFFECTS DEFINITELY NEGLIGEABLE
• MAX SHEAR AND PEEL STRESS AT THE FREE EDGE OF THE PANEL
• CHARACTERISTIC LENGTH OF THE STRESSED ZONE ABOUT 60 mm
STRESS IN THE ADHESIVE
CONCLUSIONS
• THE ONLY SOLICITED PORTION OF THE ADHESIVE IS CLOSE TO THE EDGES OF THE PANEL
• THE OTHER, INNER, PORTION OF THE PANEL IS ALMOST UNLOADED
APPLICATION OF THE ADHESIVE ONLY
ALONG THE PERIMETER OF THE PANEL
NO !!!
SUMMER
BUCKLING ANALYSIS
L=1250 mm.
ETICS SYSTEM UNDER ECCENTRIC LOADING
DUE TO SPOT ADHESIVE APPLICATION
3 2
212
p p
p p p p
E t d yt y t e
dxs s
Eccentricity of the axial load is e and can be assumed equal to half thickness of the panel, tp/2.
cosy A x Bsin x e
3
12 p p p
p p p cr
t
E t L
s s
s
MAXIMUM DEFLECTION AT MID SPAN IN
SUMMER SEASON
0
10
20
30
40
50
60
0 5 10 15 20 25 30
De
fle
cti
on
at
mid
sp
an
[m
m]
Thermal variation, T-Tr [°C]
tp=80mm
Lp/100
Lp/250
tp=120mm
sec 12 2
p p
cr
Ly x e
s
s
MAXIMUM AND MINIMUM AXIAL STRESSES AT MID SPAN IN SUMMER SEASON
-600
-400
-200
0
200
400
600
0 5 10 15 20 25 30 35 40 45
Axia
l str
ess i
n t
he p
an
el
[kP
a]
Thermal variation, T-Tr [°C]
σp,max
σp,min
tp=80mm
tp=120mm
tp=80mmtp=120mm
,max
,min
1 3sec2
p p
p
p cr
s ss
s s
STRESS STRAIN CURVE
SUMMER
BUCKLING ANALYSIS
PANEL FAILURE
17p kPas
,max 112p kPas
DUE TO SPOT APPLICATION OF
ADHESIVE
(i.e. eccentric loading)
CHARACTERISTICS DETERMINING THE ADHESIVE STRESS
• PHISICAL MECHANICAL PROPERTIES - PANEL
YOUNG MODULUS Ep (MPa)
THICKNESS tp (mm)
LINEAR THERMAL ELONGATION COEFFICIENT lp (mm/m°C)
• PHISICAL MECHANICAL PROPERTIES - ADHESIVE
THICKNESS ta (mm)
YOUNG MODULUS Ea (MPa)
SHEAR MODULUS Ga (MPa)
SHEAR AND PEEL STRENGTH (kPa)
SURFACE ADHESION (kPa)
• THERMAL PROFILE
DT MAX BETWEEN PANEL SURFACES (°C)
ADHESIVE APPLICATION GOOD PRACTICE RULES
CONSIDERING • STRESS VALUES • NEED OF PERFECT SURFACE ADHESION
• STRESS DISTRIBUTION
• BUCKLING ISSUE
CONTINUOUS LAYER APPLICATION AND CARE OF PLANARITY
w
x=0 x=Lp/2
Insulating Panel
ka=Ea/ta
CONTINUOUS LAYER APPLICATION OF ADHESIVE
BUCKLING ANALYSIS
3
212
p
cr a p
tF k E
Lateral Buckling is restrained by adhesive
2 a p pk E I
3 4 2
4 20
12
p p
p p a
E t d y d yt k y
dx dxs
Critical load depends on wave number n and length Lp
However a minimum load is given by
CONTINUOUS LAYER APPLICATION OF ADHESIVE
BUCKLING ANALYSIS
3
212 380
3
p
a pa p p
cr
p
tk E
k E tMPa
ts
NO BUCKLING FAILURE
w
x=0 x=Lp/2
Insulating Panel
ka=Ea/ta
ADHESIVE APPLICATION
NO !!!
ADHESIVE APPLICATION
NO !!!
ADHESIVE APPLICATION GOOD PRACTICE RULES
ETICS FAILURE
SPOT APPLICATION
MECHANICAL FIXINGS
CAN MECHANICAL FIXINGS
ALLOW THE SPOT APPLICATION OF THE ADHESIVE?
MECHANICAL FIXINGS
STRESS ANALYSIS
TYPICAL (INCORRECT) SCHEME FOR MECHANICAL FIXINGS ON A PANEL
0.9°C
F2 = 10 mm. Sect. Resistant to shear force S2 = F2h = 800 mm2
F1 = 60 mm. Sect. Resistant to normal force S1 = F12/4 = 2826 mm2
h = 80 mm.
STRESS STRAIN CURVE
ADHESIVE
EXTERNAL WALL
“MECHANICAL FIXINGS”
ADHESIVE SPOT APPLICATION
SUMMER SEASON
SHEAR MODE
RESISTANCE SECTION: 800 mm2
FF
F = 850 N s = F/2S2 = 425/800 = 0.53 MPa = 530 kPa
e >> 10% PS collapse
ADHESIVE
EXTERNAL WALL
“MECHANICAL FIXINGS”
ADHESIVE SPOT APPLICATION
SUMMER SEASON
ATTRITION MODE COMPRESSION PRE-CHARGE
RESISTANCE SECTION: 2826 mm2
f = attrition coefficient = 0.35 F/2f = 425/0.35=1214N s = F/2fS1 = 1214/2826 = 0.43 MPa
= 430 kPa
e >> 10% PS collapse
“MECHANICAL FIXINGS” CONCLUSIONS
• THEY ARE NOT SUITABLE, IN CASE OF FAILURE OF THE ADHESIVE, TO RESTRAIN THE THERMAL DEFORMATION OF THE PANEL
• THEY ARE NOT SUITABLE TO COOPERATE WITH THE ADHESIVE IN RESTRAINING THE THERMAL DEFORMATION OF THE PANEL
• THEIR FUNCTION IS TO AVOID THE FALL DOWN OF THE PANEL IN CASE OF CATASTROPHIC FAILURE OF THE PANEL AND OF THE LEVELING MORTAR
• FOR THIS LIMITED FUNCTION THE GOOD PRACTICE IS THE APPLICATION OF 1- 2 FIXINGS IN THE CENTER OF THE PANEL
“MECHANICAL FIXINGS”
0.9°C NO !!!
“MECHANICAL FIXINGS WITH ADHESIVE IN CONTINUOUS LAYER”
GOOD PRACTICE
0.9°C
WIND CHECK
• WIND FORCE: 225 N/m2 *0.78m2 = 176 N
• SECT. RESISTANT TO FORCE S1 = 2826 mm2
• COMPRESSION STRESS s = 62 kPa
• MATERIAL STRAIN e = 0,5%
ELASTIC DOMAIN OF THE PANEL MATERIAL
SELF WEIGHT CHECK
• SELF WEIGHT FORCE: 98 N/m2 *0.78m2 = 76 N
• SECT. RESISTANT TO FORCE: S2 = 800 mm2
• COMPRESSION STRESS s = 95 kPa
• MATERIAL STRAIN e = 0,8%
ELASTIC DOMAIN OF THE PANEL MATERIAL
STRESS STRAIN CURVE
wind
e = 0,5%
self weight
e = 0,8%
CONCLUSIONS
Most of the temperature gradient lies inside the insulating
panel. This is the main reason for the stress in the adhesive Restrained thermal inflection of the insulating panel leads
to significant peel stress in the adhesive Restrained elongation of the panel leads to relevant
compression stress due to load eccentricity Restrained linear thermal elongation/shrinkage of the
panel leads also to high shear stress in the adhesive High quality adhesive specifically developed for this
application must be used in order to guarantee the long lasting performance of the ETICS system
Mechanical fixings are not suitable to restrain the thermal deformation of the panel in case of adhesive failure
Application of the adhesive in a continuous layer and the care of planarity of the panel are the good practice rules strongly recommended by MAPEI
One mechanical fixing near the center of the panel is sufficient to avoid its fall-down in case of catastrophic failure of the system
obrigado pela vossa atenção