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State-of-the-art review on timber connections with glued-in steel rods

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Abstract

Adhesive joints have been known and applied for timber structures for decades. Hybrid joints with glued-in rods are nowadays successfully used for both constructing new and strengthening existing timber structures. Since the 1980s the research and development of timber joints with bonded-in rods have been going on, however agreement regarding design criteria for these connections has not been reached. Today, connections with glued-in rods are not included in the European design code. Thus, it is desired to gather the current state of knowledge to enable application in practice of the existing and documented knowledge and experience. This paper summarizes practical and theoretical approaches from research done regarding joints with glued-in steel rods mostly in Europe and published in English, German or Swedish. The review considers manufacturing methods, mechanisms and parameters governing the performance and strength of the joints, theoretical approaches and existing design recommendations.

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Abbreviations

( )r :

Property related to rod

( )w :

Property related to wood/timber

A :

Cross-sectional area (mm2)

B :

Width of the fracture area (mm)

C :

Compliance in energy release rate analysis

D :

Diameter of the drilled hole (mm)

E :

Modulus of elasticity (N/mm2)

F/Fa:

Axial resistance (N), (kN)

Fax,k/Ftk:

Characteristic axial resistance (N), (kN)

F ax,d :

Design axial resistance (N), (kN)

F ax,mean :

Mean axial resistance (N), (kN)

G :

Shear stiffness of adhesive layer (N/mm2)

G c :

Critical energy release rate of the joint (J/m2)

G ekv :

Equivalent shear stiffness

G f :

Fracture energy (J/m2)

G f,s :

Fracture energy in shear (J/m2)

L :

Length of adhesive layer (mm)

P u,k :

Characteristic pull-out strength of a single rod (N), (kN)

R sh :

Design shear strength of wood across the grain (N/mm2)

Ra,d/Rax,d:

Design anchorage capacity (N), (kN)

Ra,k/Rax,k:

Characteristic anchorage capacity (N), (kN)

W :

Work by external loads during crack propagation (J)

T :

Kinetic energy (J)

T g :

Critical temperature, or the glass transition temperature (°C)

b :

Width of the timber member (mm)

d/dnom:

Nominal diameter of a rod/screw (mm)

d/dr/da:

Outer diameter of the rod (mm)

dh/h/D:

Diameter of the (drilled) hole (mm)

e :

Edge distance (mm)

f a :

Mean anchorage strength (N/mm2)

f a,d :

Design anchorage strength (N/mm2)

f a,k :

Characteristic anchorage strength (N/mm2)

f a,u :

Anchorage strength (N/mm2)

f k1,k :

Characteristic value of bond line strength (N/mm2)

f v3 :

Strength parameter (N/mm2)

f v,k :

Characteristic shear strength of the wood (N/mm2)

f v,α,k :

Characteristic shear strength of the wood at the angle α between the rod and grain direction (N/mm2)

f v,mean,b :

Mean shear strength of the bond (N/mm2)

f v,0,mean :

Nominal shear strength of single axially loaded rod bonded in parallel to the grain (N/mm2)

f ws :

Withdrawal parameter for the square root case (N/mm1.5)

f wl :

Withdrawal parameter for the linear case (N/mm2)

k b :

Bar type factor (threaded: 1.0, deformed: 0.8)

k d :

Factor to account for the influence of the rod diameter

k e :

Epoxy factor (Araldite 2005: 0.86–1.17)

k m :

Moisture factor

k mod :

Modification factor for duration of load and moisture content

k s :

Factor to account for the influence of ratio of anchorage length divided by rod diameter

k 1 :

Coefficient due to irregular stress distribution along the bar

k 2 :

Reduction factor taking into account irregular force distribution among multiple bars

l/lg/lad/la/lE/lef:

Glued-in length/effective anchorage length (mm)

l m :

Material length parameter

l geo :

Geometrical length parameter

t/t1/t2:

Member thickness (mm)

a :

Angle between rod and grain direction (°) or (rad)

Φ:

Outer diameter of the rod (mm)

λ:

Slenderness ratio

ϕ:

Elastic strain energy (J)

ρ:

Density of the wood/timber (kg/m3)

ρk :

Characteristic density of the wood/timber (kg/m3)

τ:

Shear stress/shear strength (N/mm2)

τf :

Local bondline shear strength (N/mm2)

τmax :

Maximum shear stress (N/mm2)

ω:

Stiffness ratio of the joint

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Authors and Affiliations

  1. Department of Civil, Mining and Environmental Engineering, Luleå University of Technology, 971 87, Luleå, Sweden

    Gabriela Tlustochowicz

  2. School of Engineering, Linnæus University, Växjö, Sweden

    Erik Serrano

  3. Wood Laboratory, Empa, Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600, Dübendorf, Switzerland

    René Steiger

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  1. Gabriela Tlustochowicz
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  3. René Steiger
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Correspondence to Gabriela Tlustochowicz.

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Tlustochowicz, G., Serrano, E. & Steiger, R. State-of-the-art review on timber connections with glued-in steel rods. Mater Struct 44, 997–1020 (2011). https://doi.org/10.1617/s11527-010-9682-9

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