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