adhesive strength of timber joints with unconventional glued-in steel

Adhesive strength of timber joints with

unconventional glued-in steel rods

Kay-Uwe Schober, Michael Drass, Wieland Becker

Conventional applications

with glued-in steel rods GIR advantages GIR disadvantages

• High stiffness

• Fire resistance

• Corrosive

atmosphere

resistance

• Aesthetics

• Stringent quality

control

• High assembling

effort

• Geometrical

restrictions due to

design codes

Unconventional embedding

materials by neglecting

adverse aspects

Introduction

Weak-zone

reinforcement

Apex reinforcement

Innovative application of glued-in rods

Timber-concrete frames Pre-fab assembling joint

Introduction

Introduction


Timber-concrete trusses Pre-fab assembling joint

Introduction

Timber-concrete composite design Corresponding FE-model


Design Code Max. Load Restrictions

German Design Code 18,09 kN

• Bondline length

• Steel grade

• Steel rod diameter

Eurocode 5 19,24 kN

• Bondline length

• Timber density

• Shear stiffness

GIROD 30,07 kN

• Bondline length

• Joint tension

• Slenderness

Riberholt 85,36 kN (brittle)

126,54 kN (ductile)

• Bondline length

• Timber density

• Drill-hole-Ø

• Failure mode

Analytical Investigations

Generally all those approaches deal with:

• Drill-holes are marginal larger than rod diameter

• Steel rods glued-in with epoxy resin or PU adhesives

• Thin adhesive layer between steel and timber

Analyzing larger drill-holes

Modification by admixing dried fillers

Analytical Investigations

Experimental Investigations

Grouting material

-30

0

30

60

90

120

-2 0 2 4 6 8 10e [‰]

fcm [

MP

a]

fctm

[M

Pa]

3.37 MPa 30 MPa 110 Compressive strength

5.45 MPa 5.5 MPa 30 Bending strength

0.64 MPa 30,000 MPa 19,600 Tensile MOE

0.83 g/cm³ 2.4 g/cm³ 2.0 Density

Ratio RC C25/30 EPC Material property

• Fiber orientation (parallel / perp. to grain)

• Drill-hole diameter


1. Test Set-up Push-out

Specimen before testing Specimen after testing


1. Test Set-up Push-out

• Fiber orientation

(parallel / perp. to grain)

• Drill-hole diameter

• Steel rod and steel grade

• Type of ceramic filler


2. Test Set-up Pull-out

• WEVO resin 2c epoxy adhesive

• Bertsche grouting mortar Mineral-bound mortar

• Compono® 100 2c epoxy PC

• UHPC 5-phase concrete


Embedding materials


Test results

Testing parameters

Rod material M 12-10.9 BSt 500 M 12-10.9 BSt 500

Drill-hole diameter [mm] 50 50 50 50 75 75 75 75

Load direction to grain par. perp. par. perp. par. perp. par. perp.

Axial pull-out forces [MN]

WEVO 21.5 27.7 23.4 31.3 11.6 11.3 10.2 10.6

Bertsche 19.6 26.1 20.4 23.2 14.8 17.3 16.0 16.3

CTA 78.6 94.3 69.1 73.4 95.1 96.6 72.9 73.6

UHPC 4.7 5.5 6.7 3.7 9.8 16.1 10.5 9.7

• Increase of load-carrying capacity with a major drill hole diameter

• Higher bearing loads perpendicular to the grain

• Highest bearing load with epoxy pc

• Adhesive failure with mineral-bound mortar, epoxy resin and UHPC

• Cohesive failure with epoxy pc


Test results

3D FE-Model

Orthotropic elasticity of timber

Isotropic elasticity of EPC

Plasticity of Timber

Generalized Hill yield-criterion

Bilinear hardening law

Plasticity of EPC

Yield criterion (William & Warnke)

Multilinear hardening law

Numerical Investigations

2( ) 1 1 expc n n n t

e


What’s going on in the bond line?

Composite Friction model (Xu & Needleman )

Crack propagation and delamination

between EPC and Timber

Loadstep 0 kN Loadstep 68 kN


Push-out tests – Numerical sensitivity studies

Schober, K.U. & Rautenstrauch, K. (2008). WCTE Miyazaki, Japan.

Schober, K.U. et al. (2012). WCTE Auckland, New Zealand.

Model calibration to obtain

the embedding stiffness


Push-out tests – Numerical sensitivity studies


Pull-out tests – Numerical sensitivity studies

2 kN

63 kN

100 kN

delamination

propagation


Pull-out tests – Numerical sensitivity studies

• Composite behavior between timber and proposed epoxy PC

can be assumed as rigid and shear resistant

• Design of composite components and complex 3D assemblage joints

with proposed numerical model is possible

• Good agreement of numerical data and lab tests in

deformation behavior

• Proper description of the damage behavior with the proposed

numerical model, verified by lab tests

• Larger drill-hole diameters cause in higher bondline quality

and neglect missgluing

Conclusions

Outlook

Serero architects Paris

Advanced Manufacturing Technology

„The 21st Century will be built in wood.“

Andrew Waugh, Whaugh-Thistleton Architects, London, UK

Termite Pavillion, PESTIVAL 2009, source: KLH UK

Kay-Uwe Schober

Professor for Timber Structures and Structural Design

Institute of Innovative Structures

Mainz University of Applied Sciences, Germany

[email protected]

Questions

adhesive strength of timber joints with unconventional glued-in steel

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