Investigation of Grip Type Connection in Timber Structures

This research paper explores the load carrying capacity of grip type connections in timber structures and compares it to other timber connections. It discusses the benefits for stakeholders and the scope of the study. The paper also covers different types of timber connections, forces in grip type connections, and traditional and modern timber connections.

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ENGINEERING RESEARCH PLANNING
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Investigation of grip type connection in Timber structures
Research gap and questions
There are many studies and investigation have been conducted on timber structures. The
investigators exercised on timber-timber connections, steel to timber connections, round timber
connections, timber connections with multiple dowel-type fasteners, connections with glued-in
glass fibre reinforced polymer (GFRP), connections with very high strength steel dowels to find
its failure modes.
In contrast, also researched to improve its load carrying characteristics of connections as well as
whole timber structure performance structurally. The current investigation main concept is to
find out the load carrying capacity of the grip type connection as compared to the load carrying
of other timber connections, which will be discussed in the literature review. At the end of this
research, the experiment results will show and discuss the findings and make a conclusion and
recommendations.
Stakeholder and Benefits
The following people are stakeholders under this research
1. The Timber construction Builders: the connections can be made easier, as a result, the
speed of built increases.
2. Researchers can have scope to further improvements using different shapes and sizes of
connections.
3. Structural Timber production companies: prefabrication of this type of specimens
increases the productivity of structural timber.

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The findings of this research paper will be of great importance to different parties involved in
timber construction. They will be able to understand the load carrying capacity of different
timber connections which will enable them to know which connection to be used in a given
situation.
Scope
Timber is a construction material which is used widely in the construction industry, this is due to
the fact that timber is a renewable resource and at the same time the low energy requirement to
produce timber. The application of timber in the construction industry is likely to grow at a much
faster rate due to current environmental issues of global warming. In structural timber
engineering, connections are the weakest part of the structure, this has been attributed to the non-
linear mechanical behavior and wood anisotropy (Madsen, 2010, p. 237).
There are numerous types of joints in timber structures and the majority of them are
mechanically fastened. The application of dowels, bolts or plates generally induces a reduction
of timber's cross-section jointed areas. Hence timber with large cross sections is necessary to
satisfy the members as well as the joint designs. This thesis will focus on Investigating the grip
type connection in timber structures in order to find out the load bearing capacity, timber
stiffness and bending moments of the Grip-type connection in timber structures (Köhler, 2010, p.
77).
All the connection in building constructed form timber are constructed and designed in a unique
way to transfer the loads from the super structure to the ground below. When analyzing
buildings made from timber it is important to be clear about the forces which are to be resisted

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and at the same time the loads which needs to be transferred to the ground (Thelandersson,
2011, p. 321).
The study will involve carrying out a thorough literature review which will be related to timber
connections and failure modes, preparing specimen with the grip-type connections, the Testing
capacity of the connection under a static load and analyzing the results obtained and making a
conclusion regarding its efficiency. Different types of load which the timber connections are
exposed to will be discussed.
The thesis will also cover different elements which are used in the connection of timber; such as
nails, dowel, bolts, and screws. Their advantages and disadvantages will also be reviewed and
their areas of application will also be discussed. The properties of timber connections i.e.
flexibility, toughness, appearance, and strength will be researched about to determine the
performance of different types of timber connections.
This thesis also discusses the different types of timber connections that exist, whereby the
traditional and the modern ways of connecting timber are discussed. A lot of focus will be on the
grip-type timber connection which is the topic of research. With that different approaches will be
employed in collecting data relevant to the topic of research. Secondary sources such as books,
journals that contains data relevant to the topic of research will be reviewed. Any other
secondary sources which do not contain relevant data related to the topic of research will not be
reviewed since they will result in inaccurate data being collected.
Literature review
Introduction

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The competitiveness of timber structures, relative to other construction materials, may be
established by the efficiency of the connections. Generally, the fastening of timber to timber
demands little design knowledge or skills. In heavy construction of timber structures, timber
joints may require ingenuity and the application of specialized connectors, such as bolts, shear-
plate, nail plates, split rings or the glued-in thread rods. The use of these technologies demands
some design and construction knowledge and skills (Jack Porteous, 2012, p. 418).
Timber connections
Timber joints are very important elements in timber structures since they play a very important
role in determining the stability of the structure. Joinery is part of timber work which involves
joining together different pieces of timber to generate more complex structures. Some of the
timber joints make application of fasteners, adhesives while others make use of wood elements.
The properties of timber joints i.e. flexibility, toughness's, appearance and strength are driven
from the timber and materials involved and the purpose the joint or connection is intended to
serve. Hence, different connection types are used to meet different requirements (Madsen, 2010,
p. 776). There are numerous types of joints in timber structures and the majority of them are
mechanically fastened. The application of dowels, bolts or plates generally induces a reduction
of timber's cross-section jointed areas. Hence timber with large cross sections are necessary to
satisfy the members as well as the joint designs
Forces in grip type timber connections
Structural elements transfer the load of the structure and their own loads via a chain of elements
to the earth. This is normally achieved by designing the connections of timbers members at their
intersection. All the connections in the timber structure are designed to support or transfer a

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specific loading condition or type of loads (Sherwood, 2017, p. 54). To analyze a timber
structure, it is essential to be aware of the forces which need to be resisted , and the loads which
need to be transferred, at each level of the structure in the entire structure, The real character of
a timber connection can be quite complex, to an extent that if all the conditions are
considered, the design of each support would be terribly length and process.
It is normally essential to idealize the behavior of a connection to enable analysis. An approach
is usually taken that is like to a pulley. Mass and friction are in most cases ignored in the
consideration of the behavior of a connection (Simon Aicher, 2014, p. 332). It is very essential to
understand that all of the graphical representations of connections are an idealization of an actual
connection. (Wilkinson, 2015, p. 23).
Traditional timber connections
i) Butt connection
In this type of connection, the end a piece of timber is butted against another piece of timber,
this is considered as the simplest and weakest timber connection. There are three five types of
butt timber connections i.e. T-butt, end-to-end butt, T-lap, edge-to-edge butt, and miter butt
connection.

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(Köhler, 2010, p. 62)
ii) Lap connection
In this type of timber connections, the end of a piece of timber is laid over and then connected to
another piece of timber.
(Köhler, 2010, p. 62)
iii) Bridge connection
This type of timber connection is also referred to as tenon, tongue and fork connection or
open mortise and tenon connection. In this type of connection, the mortise is open on one
side of a piece of timber and then creates a fork-like shape. The mate has a through tenon or a
necked connection. The bridge connection is normally used to join rafters tops, it is also used
in the connection of a scarf joint (Sherwood, 2017, p. 221).

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(Köhler, 2010, p. 62)
iv) dowel joint
The end of a piece of wood is butted against another piece of timbers. In most cases, this is a
reinforced with dowel pins. This connection is easy and quick to build and it is the most
common timber connection used.
(Köhler, 2010, p. 67)
v) Box connection
In this type of timber connection, a corner joint interlocking squares fingers are used.
Receives pressure from two directions (Simon Aicher, 2014, p. 232).
(Köhler, 2010, p. 67)
vi) Dado connection

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This connection is also referred to as a housing connection or a trench connection, a slot is
normally cut across the grains in one piece for another piece which is used to set into.
(Köhler, 2010, p. 67)
Modern timber connections
i) pocket- hole connection
In this type of timber connection, a hidden screw is driven into the joint at an angle.
(Köhler, 2010, p. 67)
ii) Biscuit timber connection
This type of connection involves a wooden oval glued into two-crescent-shaped holes.

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iii) Stitch and glue timber connection
This is a type of timber connection where wood panels are stitched together normally with the
use of copper wires and then they are glued together with epoxy resin.
(Köhler, 2010, p. 67)
Nails, Bolts, Screws, and Dowels
i) Nails
Nails most frequently used fasteners in timber connections and they exist in different cross-
sectional areas and lengths and surface treatment. The most common type of nails used are the
smooth steel wires which in most cases are circular cross-section and they are usually cut from a
wire coil, which have a minimum tensile strange of 600N/mm2 (Jack Porteous, 2012, p. 43). The

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nails are available in a standard range of diameters which are up to 8mm and they can be treated
or plain,
Advantages of pre-drilling
o The use of this method increases the lateral load carrying capacity of timber
o With this method, the amount of slip which occurs is less.
o The spacing between one nail and another may be reduced with this method hence
generating more compact connections.
Disadvantages of pre-drilling
o The method is labor intensive which results in an overall increase in the cost
o Reduces the cross section area of the timber members.
Screws
Timber screws are suitable for the timber to steel connection and timber to panel connection, but
the screws can also be used for timber to timber connections. The screws are normally designed
single shear joints (Simon Aicher, 2014, p. 65).
They are inserted into timber by turning which is normally done by power actuated tools or by
hand.
Dowels
This refers to circular rods of steel or timber which have a diameter of 6mm.
Dowels are normally driven into the marginally or identically undersized holes. The holes must
either be drilled through all the members in operation or be created by CNC machines.

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Timber connections made up of dowels are used in the construction of members which are used
to transmit high forces.
Bolts
Bolts are dowel-type fasteners which have heads and nuts. The bolts are normally ordinary
machines bolts with washers that have a side length of approximately 3D thickness.
(Sherwood, 2017, p. 523)
Embedment Strength test
The embedment strength test for timber ( fh) is the average compressive strength at the
maximum load under the action of a stiff straight dowel:

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(Köhler, 2010, p. 342)
Embedment Strength
The factors below are the most essential parameters that must be considered when considering
the amended strength of the timber.
i) Density

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The embedding strength of any type of wood increase linearly with the increase in density.
ii) Fasteners and hole diameters
The fasteners and whole diameters greatly contribute to the overall embedded strength of any
type of timber. The increase in the fastener diameter results in a decrease in the embedded
strength.
iii) The angle between the grain direction and the load is more critical for the fasteners
with large diameters and this is usually different for the softwood and hardwood timber
iv) Friction and adhesion. The friction and adhesion between the timber and dowel increase
embedded strength of the given timber (Madsen, 2010, p. 38).
Conclusion
In conclusion, Timber joints are very important elements in timber structures since they play a
very important role in determining the stability of the structure. Joinery is part of timber work
which involves joining together different pieces of timber to generate more complex structures.
Structural elements transfer the load of the structure and their own loads via a chain of elements
to the earth. This is normally achieved by designing the connections of timbers members at their
intersection. All the connections in the timber structure are designed to support or transfer a
specific loading condition or type of loads.

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References
Jack Porteous, 2012. Structural Timber Design to Eurocode 5. 4th ed. London: John Wiley &
Sons.
Köhler, J., 2010. Reliability of Timber Structures. 1st ed. Chicago: vdf Hochschulverlag AG.
Madsen, B., 2010. The behaviour of Timber Connections. 4th ed. London: Timber Engineering,
Limited.
Sherwood, G. E., 2017. A Guide for Improved Masonry and Timber Connections in Buildings.
1st ed. Texas: U.S. Department of Commerce, National Bureau of Standards.
Simon Aicher, 2014. Materials and Joints in Timber Structures: Recent Developments of
Technology. 3rd ed. Berlin: Springer Science & Business Media,
Thelandersson, S., 2011. Timber Engineering. 5th ed. Texas: John Wiley & Sons.
Wilkinson, T. L., 2015. Strength of Bolted Timber Connections with Steel Side Members. 2nd ed.
Chicago: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory,

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