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Prof. Dr.-Ing. Jörg Lange

Institut für Stahlbau und Werkstoffmechanik, TU Darmstadt, Germany

Core, Structure, Design

Research with Sandwich Panels

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Core Made of Corrugated Cardboard

picture: A. von der Heyden

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• Problems of common core materials:

• Petroleum-based

• Production is energy consumptive

• Recycling difficult and expensive

• Disposal pollutes the environment

Ecological core material for sandwich panels

has to be found…Corrugated Cardboard?

Introduction

Source: polyurethan.isopol.de

Source: cafol.my-icg.de

Source: commons.wikimedia.orgSource: www.ybj-print.com

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Experimental Assessment

• Cardboard is considered to be orthotropic

• Orthotropy due to geometry of corrugations and

due to fibre orientation in paper

• Tests conducted:

• Compression tests

• Tensile test

• Shear tests

• Bending tests

on sandwich beams

• Thermal conductivity

• Controlled climate 20°C, 65 % RH

in different

directions

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Summary

• Corrugated cardboard with regard to bearing properties suitable for

sandwich panels in building industry

• Corrugated cardboard has many advantages in respect of

ecological issues compared to common core materials

Corrugatedcardboard

Polyurethane foam Mineral wool

Density in kg/m³ 100 to 140 35 to 45 90 to 150

Young‘s modulusin N/mm²

3 to 450 2 to 6 3 to 15

Shear modulusin N/mm²

5 to 200 2 to 5 3 to 15

Compressive strengthin N/mm²

0.08 to 1,4 0.1 to 0.15 0.05 to 0.15

Thermal conductivity in W/(m·K)

0.04 to 0.09 0.02 to 0.03 0.03 to 0.05

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Diaphragm Action of Sandwich Panels

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Diaphragm Action of Sandwich PanelsExperimental Assessment

picture: Ch. Kunkel

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Experimental AssessmentExperimental Set-Up for the Diaphragm Action Tests

A

HEB 140

HEB 260

View A

Sandwich Panel

Square tube 40x40

(4 mm)

2,86 m

HEB 260

HEB 260

HE

B 1

40

4,0

5 m

F

HE

B 1

40

C

D

AB

picture: Ch. Kunkel

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Experimental AssessmentResults of the Diaphragm Action Tests

0

2

4

6

8

10

12

14

16

18

20

0 5 10 15 20 25 30 35

Load

in k

N

Displacement of the rig in mm

Diaphragm action (Wall panels dc = 100 mm - 4 x 2,86 m)

Wall panel 100 mmType I - Test 1

Wall panel 100 mmType I - Test 2

Wall panel 100 mm -Hook-and-Loop-Tape -Type I - Test 1

Wall panel 100 mm -Hook-and-Loop-Tape -Type I - Test 2

0

2

4

6

8

10

12

14

16

18

20

0 5 10 15 20 25 30 35

Load

in k

N

Displacement of the rig in mm

Diaphragm action (Wall panels dc = 100 mm - 4 x 2,86 m)

Wall panel 100 mmType I - Test 1

Wall panel 100 mmType I - Test 2

hook-and-

loop-tape}

picture: Ch. Kunkel

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Experimental AssessmentFindings of the Diaphragm Action Tests

• The shear diaphragm action depends on the stiffness of the

connection between panels and substructure.

• The assembly of the fastenings is accountable for the maximum

bearing capacity.

• The connections of the panels via the longitudinal joint

participate in the shear diaphragm action.

How does the longitudinal joint transfer

the load between the panels?

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Experimental AssessmentExperimental Set-Up for the Longitudinal Joint Tests

Load steps of the

horizontal force:

0,5 kN

1,0 kN

1,5 kN

2,0 kN

picture: Ch. Kunkel

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Experimental AssessmentResults of the Longitudinal Joint Tests

Longitudinal joint with standard sealing tape

Sealing tape

picture: Ch. Kunkel

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Experimental AssessmentStrengthening of the Longitudinal Joint

Hook-and-loop-tape (glued with one component polyurethane prepolymer adhesive)

picture: Ch. Kunkel

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Experimental AssessmentResults of the Longitudinal Joint Tests

Longitudinal joint with hook-and-loop-tape

Hook-and-loop-tape

instead of sealing tape

picture: Ch. Kunkel

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• Longitudinal joints effect the bearing capacity of the diaphragm action

→ Integration of the joint in the calculation model

• Improvement by strengthening the joint by hook-and-loop-tape

→ Maximum load up to twice as high

Summary

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ETA

pull-out

pull-over

shear

V

N

Interaction

picture: K. Kilian

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Interaction - Tests

picture: K. Kilian

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Bearing capacity of the sandwich panel

if VE,d

VR,I,d≤ 0,25

NE,d

NR,I,d≤ 1,0

only if VEd is cyclic or deflections are restricted (3 mm)

0,25 <VE,d

VR,I,d≤ 1,00

NE,d

NR,I,d+

VE,d

VR,I,d≤ 1,0

NR,I,d Design value for pull-over

VR,I,d Design value for shear

Bearing capacity of supporting structure

according to

• for steel: EN 1993-1-3:2006

• for aluminum: EN 1999-1-4:2007

• for timber: EN 1995-1-1:2004+A1:2008

NR,II,d Design value of pull-out

VR,II,d Design value for shear

N

Interaction – Recommendation (Bracing)

V

picture: K. Kilian

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Curved Panels

picture: St. Schäfer

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Curved Panels

picture: St. Schäfer

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Curved Panels

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Curved Panels

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Prof. Dr.-Ing. Jörg Lange

Institut für Stahlbau und Werkstoffmechanik, TU Darmstadt, Germany

Core, Structure, Design

Research with Sandwich Panels