Which types of connectors and fasteners to use when building a timber frame
Although you may not be an expert in building construction, you undoubtedly understand that constructing a frame out of massive pieces of wood takes more than just nails.
In order to build a durable structure, contractors and prefabricated wood structure manufacturers now use structural connectors to join wood of different shapes and sizes.
In this article, our UsiHome specialists present various types of connectors and fasteners for structural lumber to help you determine which ones to use when building a timber frame.
Timber frame: characteristics of a good joint
The performance of a timber frame joint can be affected by a variety of elements.
The mechanical strength, rigidity and ductility of the joint will affect the way the structure reacts to static and dynamic loads.
Joint characteristics such as dimensional stability and resistance to degradation provide wooden structures with more durability.
The way the joint reacts to fire is another important aspect that affects the stability of the structure in the event of a fire.
Other elements such as ease of installation, simplicity, aesthetics and cost can also help determine which joining method, connectors and fasteners to use.
Types of connectors and fasteners that can be used to build a timber frame
There are many different types of fasteners and connectors that can be used to make structural wood products and join the various components of a structure together.
Here is an overview of the main ones, which are available in several variations and formats.
The types of connectors that are traditionally used when building wooden structures or frames can be divided into two broad categories: dowel-type fasteners and shear connectors. These two categories differ in the way they distribute the load.
Dowel-type fasteners such as bolts, lag bolts, nails, screws, studs, etc. distribute the load through the depth of the wood.
On the other hand, shear connectors such as split rings, shear plates and metal connectors distribute the load across the contact surface.
The types of connectors discussed in further detail in this article fall into these two categories.
Truss connector plates
Truss connector plates are created by punching holes in thin galvanized steel sheets. These types of connectors are used to join lumber for prefabricated light-frame roof trusses.
Because the steel is galvanized, the connectors are rust resistant, meaning that they can withstand getting wet occasionally and can be used in areas that have high humidity levels, such as locations near the sea or other major bodies of water.
The sheets used to manufacture these connector plates can be 20 gauge (around 1 mm thick), 18 gauge (1.3 mm) or more rarely 16 gauge (1.6 mm), and are made of grade B (SQ255) or C (SQ275) steel in accordance with the ASTM A653/A653M standard specification. The connector plates are cut at the same time as the punching process.
The teeth, which vary in number from 1.2 to 1.6 per cm2, protrude from one side of the metal connector. They are perpendicular to the surface of the plate and measure around 8 to 10 mm in length.
These connectors are always used in pairs on opposite sides of the joint. Pressing them into the pieces of timber requires considerable mechanical force. The specific amount of force required depends on the size of the connector plates and the density of the wood in question.
These connectors are available in a wide variety of sizes and must be submitted to the Canadian Construction Materials Centre (CCMC) for evaluation.
Galvanized steel hangers
Construction contractors have access to a wide variety of hangers to create different types of joints for softwood lumber and structural composite lumber. Joist hangers and beam-to-column connections belong to this family of connectors.
Hangers are generally mass-produced and cold formed from thin galvanized steel sheets 1 mm to 2.75 mm thick (20 to 12 gauge). They also have holes drilled for nails or wood screws.
The hangers are galvanized with a G90 coating, which corresponds to 275 g of galvanizing product per square metre, enough to protect the hangers from rusting if they get wet occasionally. However, if you intend to use this type of connector to build an outdoor structure that will be exposed to the elements (a treated wood deck frame, for example), you may want to choose hangers with a thicker galvanizing coating.
The maximum lateral load transfer capacity of galvanized steel hangers should be tested according to the ASTM D1761 standard. These tests must be conducted in a controlled environment and interpreted according to the CSA O86 standard in order to obtain the factored resistance for each joint.
Because they transfer high loads to the tops and sides of beams and the tops and bases of columns, hangers are best suited for light structures. However, they can be used to join larger types of wood beams in certain circumstances.
Angles are another type of structural connector. Their 90-degree angle makes them well-suited for connecting perpendicular joists and beams.
Angles are usually made of a steel alloy that can include zinc, brass, stainless steel and other metals. Angles are measured based on the following dimensions: length of the wings (the surfaces that will be in contact with the wood), angle width (cannot be wider than the support piece), and thickness. When choosing angles, these dimensions should be aligned with the load that needs to be supported without exceeding the load the piece can take.
Angles can be installed using screws, bolts, nails, lag bolts, etc. The fasteners chosen should match the angle’s mounting holes. Interestingly, almost all models of angles have asymmetric mounting holes to prevent the wood from splitting.
UsiHome: your resource for learning more about wooden structures and joints
There are other types of connectors than can be used to join wooden structural elements, but the ones presented in this article are the most common.
If you want to find out more about the lumber industry, timber frame products and joints, check out the blog section of our website. We have plenty of interesting information you can peruse.
And if you need prefabricated wood structures of professional advice on a residential, commercial, agricultural or institutional project, contact us today!