What is a split ring connector?

A split ring connector is a usually steel ring that sits in pre-routed circular grooves in both timber members and, in combination with a bolt, transfers load from one member to the other. The ring takes the shear; the bolt holds the members together and stops them separating. The Dutch term is ringdeuvel.

Why use one?

A plain bolt in timber transfers very little: the timber crushes at the bolt hole and the joint goes soft. By letting a ring into both faces, the force is spread over a far greater area of timber, right around the circumference of the ring. As a result one connector carries considerably more than the same bolt on its own.

Characteristics

• Material — generally steel; aluminium versions also exist
• Fit — the grooves are cut with a dedicated connector cutter, so that the ring seats with no play. Any play means an immediate loss of stiffness
• The split with a tongue — many rings are not closed but have a gap with an overlapping tongue, so the ring can follow the movement of the timber and take up erection tolerances
• Slight taper — some rings taper a little and tighten as the bolt is pulled up

Where they are used

Split rings are used where large forces have to pass through a timber joint:

• Splices in glulam beams
• Node points in trussed rafters and lattice trusses and in timber frame structures
• Connections between timber and steel gusset plates
• Repair work on historic roof structures, strengthening existing joints

Standard

Split ring connectors fall under EN 13271, which sets out characteristic load-carrying capacities and slip moduli for timber fasteners with connectors. The design values for the joint follow from Eurocode 5.

Practical points

• Use the matching cutter. A groove cut with an ordinary router bit will never seat tightly enough
• Re-tighten. Timber shrinks as it dries. Re-tighten the bolts a few months after erection, and use spring washers by preference
• Edge and spacing distances. Keep to the specified minimum spacings and end distances, or the timber will split along the grain
• Moisture content. Assemble with timber close to the equilibrium moisture content of the finished condition

Related terms

• Dowel
• Beam
• Shrinkage crack
• Reinforcement
• Formwork

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