Beam To Column Connection Types In Timber Structure Design

image
image

Wood is a natural resource used for many centuries to build buildings, bridges, and various other structures. It is still an important construction material because advances in science and technology have increased our understanding of the material’s behavior. This has helped designers to use timber not just in more efficient and safe manner, but also in a challenging and exciting manner too.

The efficiency of the connections may determine the competitiveness of a timber structure. In wooden structures, beam to column connection types are one of the most important yet least understood components. In a connection, two or more members are connected with one or more mechanical fasteners. It provides continuity to the structural member and strength and stability to the structure.

Here, we will learn everything there is to know about wood beam to column connection in Timber Structure Design.

Wood Beam To Column Connection

What Is Beam To Column Connection In Timber Structure?

According to ‘Arkadiusz Lesko’ (Author of Research Paper Modern Moment Resisting Timber Connections – Theory and Numerical Modelling), Beam Column Connection in timber structure is a junction of beam and column with the usage of connectors and carpentry work in order to ensure mutual cooperation of the beam and the column.

What Are The Different Types Of Beam Column Connections In Wooden Structure?

Types Of Beam Column Connections In Wooden Structure

Wood beam to column connections are classified into two categories –

1) Mechanical Connections:

Mechanical connections are those that attach members to certain types of fasteners. BS EN 1995-1-1 (2004): Eurocode 5[395] (Design of timber structures – Part 1-1: General – Common rules and rules for buildings) provides a number of rules for connections with mechanical fasteners. So before you use it for connection, you should refer to it at least once.

2) Adhesive Connections:

According to ‘RAM S. GUPTA’[396] (Author of Book: Principles Of Structural Design – Wood, Steel, and Concrete), Adhesive connections are those that bind members chemically together under controlled environmental conditions such as that seen in glued laminated timber (GLULAM).

Now, let us discuss mechanical connections in timber building design.

What Are The Different Types Of Mechanical Fasteners Connections?

Mechanical Fastener Connections

Mechanical fasteners connections are constructed using two general fastener types i.e. dowel type fasteners and bearing type fasteners.

1) Dowel Type Fastener Connections:

The nails, screws, bolts and metal connector plates are used in the dowel type fastener connections. Out of them nails, screws and bolts can transmit either lateral load or withdrawal loads (Axial load). Metal connector plates are a special case of dowel-type fasteners because they combine the lateral load actions of dowel fasteners and the strength properties of the metal plates.

Lateral loads are transmitted by bearing stress developed between the connection member and the fastener. Withdrawal loads (Axial load) parallel to the fastener axis transmitted through friction or bearing to the connected materials.

Moving on, let us see different dowel type fastener connections.

a. Nailed Connection

Nails are the most common type of fasteners used in building construction as they can resist lateral loads. There are many variations in types of nails as well as sizes, shapes, coatings, treatments, qualities and finishes.

According to ‘Shashikant K. Duggal’[392] (Author of a book called Earthquake-Resistant Design of Structures), nailed joints are the most common and suitable type of joints for light and medium timber framings up to 15m spans. However, nailed joints require careful attention.

b. Screw Connection

Screws are threaded fasteners with a square or hexagonal head that are placed by turning a wrench into wooden members. According to the United States Department of Agriculture Forest Products Laboratory, screws have lower lateral strength as compared to bolts and are advantageous when an excessive bolt length is required.

Nails and screws are popular types of fasteners that carpenters mostly use in their daily activities. But, which is the best for joining materials together? Click here to know –

c. Bolted Connection

Bolted connections suit the requirements of prefabrication in small and medium-span timber structures for speed and economy in construction. Workshop ease, mass production of components, transport convenience, and reassembly at site of work are some of the advantages of the bolted connection.

Bolts are the most common type of fastener for connections where moderately high lateral strength is required and in tension connections where force is applied parallel to the bolt axis. The standard machine bolts are used for structural connections.

d. Metal Connector Plates

Metal connector plates, also known as metal plate connectors or steel truss plates or truss plates are used extensively in wood trusses. These plates are proprietary products and are generally made of light weight structural quality steel with zinc or zinc-aluminum alloy coatings. Metal connector plate is manufactured to various lengths, widths, and thickness and also designed to transmit lateral loads.

2) Bearing Type Fastener Connection:

Bearing type connections transmit lateral loads only. Bearing-type fasteners, such as shear plates and split ring connectors (also known as Split ring timber connectors, Teco rings or timber rings) transmit shear forces through bearing on the connected materials.

3) Hanger Type Connections:

Hanger-type connections fall between the dowel type fasteners and bearing type fasteners. They generally support one structural member and are connected to another member by a combination of dowel and bearing action.

Selection of a fastener for a specific design application depends on the type of connection and the required strength capacity. However, every connection must be designed and constructed to transmit forces adequately and provide satisfactory performance for the life of the structure without causing splitting, cracking, or excessive deformation of the wood members.

Mechanical fasteners and connectors come in wide range of designs, each with its design requirements developed at different times in history. Some design practices are based on substantial research, some on minimal research, some on the extrapolated study, and some on thumb rules.

Thus mechanical connection design practices in wood structures are fragmented, confusing and contradictory.

Now let’s see how to design wood beam to column connections.

How Are Beam To Column Connected In Timber Structure?

The construction of any structure is typically carried out in different steps of analysis and design. According to ‘Kenneth M. Leet et al’[389] (Author of a book – Fundamentals of Structural Analysis), reinforced concrete structure, steel structure and wooden structure can be analyzed in the same way. If you want to know the relationship of Analysis to design then read here – What is Beam Column Joints in Reinforced Concrete Building?

Design Procedure of Beam Column Connections in Wooden Structure

In wooden structure, the condition of the connectors is critical as to how it will perform. The following are the important requirements regarding to the connectors:

Requirements of Wood Beam to Column Connection:

i) Connectors may be modified in the field unless noted by the manufacturer. Not all modifications are tested by all manufacturers. Contact the manufacturer to verify loads.

ii) The nails specified by the manufacturer should be used to fill all the holes in connectors.

iii) Different environment can cause corrosion of steel connectors. Always evaluate the environment where the connectors will be installed. Connectors are available with different corrosion resistance. Hence contact the manufacturer for availability.

iv) Most wood connections rely on the fasteners to transfer the load from one member to the other. Therefore, the installation and choice of the fasteners is critical to the performance of the connection. The fastener must contain the same corrosion resistance as the connector.

The basic design procedures for wood beam to column connection are similar to those for structural components. For a given wood connection and type of fastener the designer can follow the following basic procedure:

i) Determine the tabulated load for one fastener appropriate for the species group of the connected members.

ii) Apply adjustment factors to the tabulated value to reflect specific applications and conditions of use.

iii) Adjust the modified value for lateral loading conditions other than parallel or perpendicular to grain, when applicable.

iv) Multiply the design load for one fastener by the total number fasteners in the connection and apply a group adjustment factor if justified.

v) Compute the net section and verify the capacity of the members.

vi) Detail the connection to ensure adequate fastener placement and performance.

Summing up, as we discussed, timber structures are joined mainly in two different ways: glue or mechanical fasteners. Glued joints are seldom used as large structural joints since they are brittle in behavior and have the property of decreasing apparent strength with increasing size. Instead, mechanical connections are made of nails, screws, bolts or dowels etc. The advantages of mechanical fasteners are they provide flexible connection and ease of handling in production.

The flexibility in mechanical connections, apart from material properties is dependent on proper fastener placement concerning the grain and load direction. Therefore, in most building codes, there are recommendations regarding minimum spacing between fasteners. However, even though the recommendations are followed, brittle failures such as splitting can result. For this reason, proper design and detailing of the beam to column connection is important.

Before you leave this interesting page, if you want to learn the types of connections in steel structures as well as types of joints in concrete buildings, including how to design them, read the blogs below –

Beam to Column Connections in Steel Structure| Types & Design Procedure!
What is Beam Column Joints in Reinforced Concrete Building?

Image Courtesy: Image 1, Image 3(c)

Do you have query?

Let our experts solve it for you while you rest

image
image
I need help to