Steel-to-Timber and Timber-to-Timber Simple Shear Connections
ELZA M. M. FONSECA
Department of Mechanical Engineering,
Polytechnic Institute of Porto,
Rua Dr. António Bernardino de Almeida, 431, 4249-015 Porto,
PORTUGAL
Abstract: - The main objective of this manuscript is to present an analytical procedure of steel-to-timber and
timber-to-timber connections in simple shear, related to the calculated number of dowels needed. These types
of connections need to be assembled by dowel–type fasteners, such as nails, screws, bolts, and dowels. In this
work, the connections are fixed with steel dowels. Timber connections made with dowels are a good choice,
they look great when compared to screw connections and are rigid because have a tight fit while screws have a
loose fit in the hole. Different simplified equations were used to calculate the characteristic load-carrying
capacity in simple shear per fastener. These equations are useful in designing connections in simple shear when
loaded in tensile and allow calculating the number of dowels needed. To obtain the results for discussion,
different parameters were considered: three steel dowel diameters, three applied tensile loads, and three species
in homogeneous glued laminated timber, each one with different densities. The discussion of the results shows
that the number of dowels increases when the diameter decreases, and the material properties have a lesser
dependence on this calculation. Using these simplified equations provides a better and easier understanding of
the factors that can affect the behavior of steel-to-timber and timber-to-timber connections in simple shear. The
key connection point is the shear capacity and ductility behavior of the screw and or dowel element, as
presented in this work.
Key-Words: - Eurocode 5, timber connections, steel dowels, simplified equations, load capacity, strength
material.
Received: April 19, 2024. Revised: October 25, 2024. Accepted: November 12, 2024. Published: December 30, 2024.
1 Introduction
The load-carrying capacity of the connections can
be described by the European Yield Model based on
a plastic limit state analysis. The first researcher
working in this area assumes this model has an ideal
rigid-plastic behavior of the timber and steel dowel,
[1]. This method predicts the strength of a two or
three-member dowel type connection, [2].
Timber-steel connections are fragile members of
structural construction, and the possibility of brittle
failures cannot be avoided in many situations. Both
steel and timber materials behave differently and the
interaction between the elements is even more
complex to analyze.
Many works are presented by some researchers
to study different connections and their capacity due
to different applied boundary conditions. Among
others, some researchers present a numerical
methodology to study an asymmetric multi-bolted
connection preloaded and cyclically exposed to
normal and tangential loads, [3]. Another study by
[4] presents experimental tests about the behavior of
simple supported composite steel-concrete beams
exposed to bending using shear connections,
focused on the use of fiber-reinforced concrete to
reduce the percentage of additional reinforcement in
the concrete dowels.
With the growth concern about climate change,
the use of timber in building construction presents
itself as a solution to this problem. Timber is a
sustainable material when compared with the use of
other materials, requiring only minimum processing
when compared with materials like steel, concrete,
or aluminum. The major justification is related to
the positive contribution to the carbon cycle and the
lowest used energy through its whole process. In
addition, timber can present good mechanical
characteristics, such as strength and density
properties.
Connections have been reported as many
problems as possible in structures related to the
collapse, involving connections dowel-type, [5], [6].
However, most failures occur due to human errors
[5], [6]. Another important issue related to the
physical properties of timber which affects some
failures and consecutively its strength, deformation,
WSEAS TRANSACTIONS on APPLIED and THEORETICAL MECHANICS
DOI: 10.37394/232011.2024.19.17
Elza M. M. Fonseca
E-ISSN: 2224-3429
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and durability is the moisture content, [7]. The
effect of moisture content on the load-carrying
capacity and stiffness of connections has been
demonstrated by researchers, [7], [8], [9].
The main goal of this work is to present
analytical methodologies to predict the safety of
connections in simple shear, determining the load-
carrying capacity and the number of needed dowels
for the connection.
Different constructive connections in a simple
shear, joined by steel dowels will be calculated. This
study brings results to the previous investigations by
the authors [10], looking for the effect of steel
dowels and different materials. The designed
connections were evaluated for different applied
tensile loads parallel to the grain, different dowel
diameters, and different timber material densities.
2 Materials and Methods
The geometric model of the steel-to-timber and
timber-to-timber connections under study will be
calculated according to Eurocode 5, part 1-1, [11],
as represented in Figure 1 and Figure 2. To obtain
the dimensions of the connections it was used the
material properties involved in the study. The main
dimensions of the connection are the width (L),
height (H), the depth (W) obtained by the thickness
of the timber (t1 or t2) and steel plates (ts), the
minimum spacing, and edge/end distances between
the dowels and the plates (a1, a2, a3, and a4,t).
Fig. 1: Steel-to-timber connection
Fig. 2: Timber-to-timber connection
Mechanical properties of timber and steel were
considered for the dimensioning. For timber
members, homogeneous glued laminated specimens
were considered GL24h, GL28h, and GL32h, [9],
[10].
According to the minimum spacing and edge
and end distances given with symbols illustrated in
Figure 1, Table 1 shows the equations that allow the
calculation of these variables. The angle between
the direction of the tensile load and the loaded edge
(or end) is α in the equations presented in Table 1.
Table 1. Calculation of the spacing or edge/end
distance
Spacing or
edge/end
distance
Angle
Minimum spacing
or edge/end
distance
a1
α360°
(3+2+|cos α|) d
a2
α360°
3d
a3,t
α0°
Max(7d; 80 mm)
a4,c
α360°
3d
3 Characteristic Load-Carrying
Capacity Calculation
As reported by some authors, dowelled connections
loaded in tension can fail in different modes:
bearing failure, net tension failure, the split of wood,
shear-out, and group shear-out failure, [12], [13].
These failure mode types depend on joints,
fastener configurations, and the connection
geometry, [12], [13].
In this manuscript, different connections were
designed using the simplified equations from
Eurocode 5, part 1-1 [11] and Eurocode 3, part 1-1,
[14]. To reduce the risk of failure modes, a
minimum edge distance, and end spacing criteria for
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DOI: 10.37394/232011.2024.19.17
Elza M. M. Fonseca
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Volume 19, 2024
the connections, using different dowel diameters,
were considered.
According to the simplified equations from
Eurocode 5, part 1-1 [11], the characteristic load-
carrying capacity per shear plane per fastener, Fv,Rk,
is determined according to equations (1) to (3).
In these equations, the main variables are
related as follows:
Fv,Rk is the characteristic load-carrying capacity in a
simple shear plane per fastener;
fh,i,k is the characteristic embedment strength in the
timber member (i=1, 2);
ti represents the thickness of the timber member
(i=1, 2), respectively the smaller and the middle
timber side member;
d is the dowel or fastener diameter;
My,Rk is the characteristic yield moment of the
fastener, calculated according to the dowel diameter
and the material strength;
is the ratio between the embedment strength of the
members;
Fαx,Rk represents the characteristic axial withdrawal
capacity of the fastener.
Equation 1 is only used for timber-to-timber
connections and fasteners in single shear.
(1)
Equation 2 is used for steel-to-timber
connections in single shear and a thin steel plate as
the outer member.
(2)
Equation 3 is used for steel-to-timber
connections and a thick steel plate in single shear.
(3)
In the study, different parameters were
considered: three dowel diameters (6, 8, and 10
mm), three applied tensile loads Fd (10, 15, and 20
kN), and three materials (GL24h, GL28h, and
GL32h), each one with different densities (370, 420
and 480 kg/m3, respectively).
After the calculated value of Fv,Rk, it is required
to determine the design value of the characteristic
load-carrying capacity Fv,Rd, which is obtained from
equation (4).
(4)
In this equation, two safety factors are
introduced, defined according to Eurocode 5 part 1-
1 [11]. The partial factor for the material property M
is equal to 1.25 for glued laminated timber. The
modification factor, considering the load duration
and moisture content effect kmod was considered
equal to 0.6 for glued laminated timber. With the
obtained design value of the characteristic load-
carrying capacity Fv,Rd it is possible to determine the
number of dowels N according to the applied load
design, using equation (5).
The arrangement of the dowels will be in lines
and columns. The layout between dowels
corresponds to the calculated spacing, resulting
from the equations, according to Eurocode 5 part 1-
1, [11].
(5)
4 Results and Discussion
The results are presented in Figure 3, Figure 4 and
Figure 5, which represent the relation between the
number of dowels depending on the applied load
and the dowel diameter for each type of connection.
For connections timber-to-timber in Figure 3,
there is not a large variation in the number of
dowels for connections with large diameters and any
wood material density. When the use of dowels
decreases in diameter, the variation in the number of
dowels increases.
Figure 4 shows the results for connections steel-
to-timber with thin steel plate, and dowels diameters
8 and 10 mm, the several dowels are very close. The
same behavior is obtained when the steel plate is
thick, Figure 5. For small dowels diameter, in these
connections, a linear increase is verified, also in all
different materials densities used.
In general, the density material does not affect
so much the number of dowels when compared with
the effect of dowel diameter. Nevertheless, the
better the wood, the stronger and stiffer the
connections. The same conclusions were reported
by the authors of this work in previous publications
about connections in double shear, [9], [10]. The
increase in several dowels is significantly
pronounced in connections with small dowel
diameters. Comparing all types of connections,
steel-to-timber with a thick steel plate needs a
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DOI: 10.37394/232011.2024.19.17
Elza M. M. Fonseca
E-ISSN: 2224-3429
158
Volume 19, 2024
higher number of dowels for any type of timber
density. Always for any connection, timber with
high density combined with a higher dowel diameter
needs a lesser number of dowels.
In doweled connection, and according to
Eurocode 5, part 1-1 [11], the dowel diameter
should be greater than 6 mm and less than 30 mm.
This rule does not allow the higher slope to be
verified in the number of dowels when the size
diameter decreases.
Fig. 3: Dowels depend on the applied load in
connections timber-to-timber
Fig. 4: Dowels depend on the applied load in
connections steel-to-timber with a thin steel plate
Fig. 5: Dowels depend on the applied load in
connections steel-to-timber with a thick steel plate
5 Conclusion
A procedure with simplified equations from
Eurocode 5 was presented to assess the dimensions
and the number of dowels of the connections in
simple shear for any applied tensile load.
The main conclusions are listed as follows:
-The number of fasteners increases with load,
according to the use of standards.
-A lower dowel diameter has a higher
pronounced effect on the required number of
fasteners.
-The mechanical effect due to the strength of the
material and its density for GL24h, GL28h, and
GL32h implies the verification that when the
better the wood, the stronger and stiffer the
connections.
Although the current results show interesting
tendencies, further studies are required before useful
outcomes for the implementation.
Recommendations include different load effects and
strength material, and experimental tests to carry out
the same behavior.
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Contribution of Individual Authors to the
Creation of a Scientific Article (Ghostwriting
Policy)
Elza M. M. Fonseca: Conceptualization,
methodology, formal analysis, investigation,
writing—original draft preparation, writing—review
and editing. The author has read and agreed to the
published version of the manuscript.
Sources of Funding for Research Presented in a
Scientific Article or Scientific Article Itself
No funding was received for conducting this study.
Conflict of Interest
The authors have no conflicts of interest to declare.
Creative Commons Attribution License 4.0
(Attribution 4.0 International, CC BY 4.0)
This article is published under the terms of the
Creative Commons Attribution License 4.0
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DOI: 10.37394/232011.2024.19.17
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E-ISSN: 2224-3429
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