Retrofitting of damaged sandwich panels - EPAQ

EASIE Congress 23092011 

Retrofitting of Sandwich Panels 

Actions to return the resistance 

Cladding of sandwich panels 

Paavo Hassinen

Repairing of a wall or roof made of 

sandwich panels 

- Cleaning and painting of the surfaces and 

improving or replacing of the fasteners 

- Repairing of defects 

- Covering the panels with new cladding 

- New architectural appearance of old and new facades 

- Improvement of mechanical and physical behaviour and resistance 

- Extension of the service life of the sandwich panel wall and roof 

EASIE MC, Roma 

September 21, 2011 

2

Returning of resistance of panels 

exposed to blisters or accidential attacts 

Artificial defects 

- simulation of real defects and faults 

Photo; 

Eric Rustemeijer 

Development of repairing actions 

- four different technigues 

- suitability to conditions on site 

B / 1 

R 

Experimental verification 

one circular dent 

- diameter D1 = 200 mm 

- depth d1= 10 mm 

D1 



3

Returning the resistance of panels 

exposed to blisters or accidential attacts 

Photo; Eric Rustemeijer 

Development of repairing actions 

Experimental verification 

Testing of the suitability of the 

techniques on site 



4

Returning of resistance of panels 

Artificial defects in the tests in IsMainz 



5

Wrinkling stress of PU-foam cored sandwich panels before and 

after reparation actions (I, II, III and IV) of artificial defects 

(A, B, C), results by Anton Kull, IsMainz 

1 

Simulation of a wrinkling failure 

Relative wrinkling stress [N/mm²] 

0.90 

0.86 

0.72 

0.74 

0.63 

0.58 

0.54 

0.48 

0.38 

Initial Test 1 

A before repairing 

A after repairing Type I 

A after repairing Type IV 

B before repairing 

B after repairing Type IV 

C after repairing Test 15 Type I 

C after repairing Test 17 Type II 

C after repairing Test 19 Type III 

C after repairing Test 21 Type IV 

1.2 

1 

0.8 

0.6 

0.4 

0.2 

0 



6

Wrinkling stress of PU-foam cored sandwich panels before and 

after reparation actions (I, II, III and IV) of artificial defects 

(D1, D2, E1, E2), results by Anton Kull, IsMainz 

1.2 

1 

1 

Simulation of a local fault 

Relative wrinkling stress [N/mm²] 

0.8 

0.6 

0.4 

0.2 

0 

Initial Test 1 

D1 before repairing 

D1 after repairing Type I 



7 

D1 after repairing Type IV 

D2 before repairing 

D2 after repairing Type I 

D2 after repairing Type IV 

E1 before repairing 

E2 before repairing

Returning the resistance of face layers 

with faults and damages 

- technigues to return the resistance partially 

- full returning of the wrinkling strength is 

a demanding task 

- knowledge about the level of the return is highly 

important in practice 



8

Retrofitting, new to old concept 

Tests at IsMainz and Aalto University 



9

Retrofitting; Cladding based on thin-walled 

purlins and sheetings 

pu-foam cored and steel sheet faced 

ordinary panels, screw fasteners 

Photos: Jessica Kochenbach 



10

Cladding based on thin-walled purlins and 

sheetings 

Wrinkling failure along the plane of the web of Z- and hat profile 


Reduction of the load bearing capacity 



11


sheetings 


Compression failure 

of the profile and face sheet 

Improvement of the load 

bearing capacity 



12


sheetings 

pu-foam cored and steel sheet faced panels, screw fasteners 

1.4 

Relative total load and stiffness 

1.2 

1.0 

0.8 

Relative resistance 

Relative stiffness 

A) Ordinary sandwich panel 

B) Sinusoidal sheet direct 

C) two hat-profiles longitudinal 

D) hat-profiles transverse 

E) Z-profiles transverse 

0.6 

A B C D E 

Resistance and stiffness 

depend on the span 



13


sheetings 

Design using analytical or numerical models 

Shear flexibility of the transverse purlins and fastenings 

Verification of the resistance of the panel, purlins, sheeting 

and fastenings 

Y 

X 

Z 



14

Repair and retrofitting 

Cladding based on additional sandwich panels 

Screw and 

rivet 

fasteners 

EPS foam cored and steel 

sheet faced additional panel 

EPS foam cored and steel 

sheet faced ordinary 

sandwich panel 



15



Load [kN] 

25 

20 

15 

10 

5 

Metal sheet faced additional panel 

Comparison 

between 

experimental 

and 

calculated 

results 

EPS foam cored and steel sheet 

faced additional panel fixed to 

EPS cored and steel sheet faced 

ordinary panel 

Deflection [mm] 

0 

0 5 10 15 20 25 30 35 40 45 50 55 60 

F1b-1, IR2, k500 A1-1 FEM (no cladding) 

FEM (spring IR2 k500) FEM (no slip) FEM (frictionless slip) 



16

Cladding with additional panels 

Flange normal forces 

Steel sheet faced panel + steel sheet faced 

additional panel 

Steel sheet faced panel + 

additional mono panel 

Additional panel: 

uppr face 

lower face 

Original panel: 

upper 

face 

lower 

face 



17

Cladding with additional panels 

Comparison of experimental load-bearing capacity and stiffness 

to those of the ordinary sandwich panel 

2,0 

Sandwich panels covered with additional elements 

2,0 

relative total load 

1,5 

1,0 

0,5 

0,0 

Additional panels 

relative total load 

relative total stiffness 

specimen 

0,0 

A B C D E F G H 

1,5 

1,0 

Additional monopanels 

0,5 

relative total stiffness 

Repeated load 

of 5000 cycles 

no noticeable 

effects 



18


Verification of the resistance of the ordinary sandwich pnel 

and the additional sandwich panel 

Monopanel 

fixed to the 

external face 

Additional thin 

sandwich panel fixed to 

the external face 

Mechanical 

fastening 

Ordinary 

sandwich 

panel 

Three normal forces 

in the faces 

Four normal forces 

in the faces 



19


Visual appearance 

Effect and visibility of the 

fastenings of the 

additional element 



20


Adhesive joints between the cladding 

components 

Benefits 

- fluent flow of stresses without local stress concentrations 

- no holes through the external face of the sandwich panels 

- no visible fastenings in the cladding 

Challenges 

- cleaning and primary coating of the surfaces in contact, 

methods and technique depends strongly on the coatings 

- possible prestress during the hardening of the joint 

- work to be made on site 



21

Product of EASIE project; 

Practical guidelines on cladding and 

repairing of Sandwich panels 

- distributions of the external mechanical pressure load 

- distribution and effects of the temperature on the components of the 

cladding systems and the ordinary sandwich panel 

- local stresses and effects caused by the of self-weight of the additional 

cladding 

- static interactions between the ordinary sandwich panel and the 

additional cladding 

- effects of the local damages 

- long-term effects caused by ageing and repeated loads 

- influence of the cladding on the other properties of the panel such as the 

thermal insulation etc. 

- good practice, including the return of resistance, also 



22

Retrofitting of damaged sandwich panels - EPAQ

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