Connection Types in Wood-Frame Buildings (2)

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4. Proprietary Connections

Proprietary connections combine the characteristics of dowel, metal connector plates and shear. They are part of the most innovative connection systems. Generally, proprietary connections are produced by a professional manufacturer or designed specifically for one building. These connection systems and similar products are more and more developed for use in larger and more complicated buildings, which are designed to take advantage of the economic, aesthetic and environmental benefits of wood. 

Customized structural framing connections, generally composed of bent or welded steel, can transfer load from the supported member (through direct bearing) to the supporting member by hanger flange bearing, fastener shear or both. They can provide a single-piece connection between two framing members.

Another proprietary connection is pre-engineered metal connector, which is usually used in all kinds of wood building. Though Common type of pre-engineered metal connectors, like metal hangers, as well as traditional fasteners (nails, bolts and rivets) are widely used and more reliable, they have inherent weakness limiting the use in large and complex buildings. So it’s necessary to develop new proprietary systems. New systems, often concealed, can make them fire-resistant when they are sufficiently below the wood surface. They can be used without impacting the strength of the wood and be designed stiffer or more flexible. It depends on their application.

In fact, proprietary products are becoming widely used now. We can see the self-tapping and self-drilling screws are more and more used in cross laminated timber and glulam structures. They are produced with different features and in many shapes and sizes, to enhance hardness for higher lateral load capacity and various other capacities for different applications. With a regular hand-held power drill, they can be driven into wood without pilot holes, which is their main advantage. In this way, the risk of mistakes are lessened and efficiency and reliability improved.

Pre-engineered connectors are usually manufactured by component manufacturers. They have specific catalogs of products that suit various situations. In spite of the ones mentioned above, categories include framing anchors, hold-down devices, straps and ties. Many components are fabricated using formed sheet metal, to increase thickness. To fully develop connection capacity, the nailing and fastening requirements must be rigorously followed, which are provided by the manufacturers.

Joinery

Traditional joinery connections are also known as carpentry connections. They are usually created by cutting notches, holes and tongues in connecting members and then get interlocked. In this kind of connection, forces are mainly transferred in compression/bearing. Metal pins or keys are needed for interlocked members, to prevent separation. When joinery connection is properly designed, there will be enough interlocking force, tightening of connections and friction, due to the self-weight and supplementary support from walls.

Joinery connections are common in single-story homes, commercial and recreational structures, but they are seldom used for modern, heavy timber buildings. On the one hand, these systems require highly developed skills, which is only possessed by experienced carpenters. On the other, such connections are labor intensive, making them uneconomical for industrial production.

Joinery connections are usually made of wood. So when exposed to moisture and drying, the change in dimensions of the wood members will be similar, but for the steel/wood connections, the change will be different between wood and steel.