The bent plate is the beam that runs in the lengthwise direction of the building, rests on top of the bent posts and ties the individual timber bents together into one whole. Where the bents form the cross-frame of a barn, farmhouse or open shed, the bent plate provides the longitudinal frame: it couples the separate bents and turns them into one stable timber structure.
Function
The bent plate has two main tasks:
- Tying — it locks all the bents together lengthwise, so they cannot topple individually
- Carrying — it supports the roof structure above
The rest of the roof framing rests on or along the bent plate. The purlins and rafters carry their load down through the bent plate to the posts, which then pass the forces on to the foundation. Without a bent plate, each bent would stand on its own and the structure could “hinge” in the lengthwise direction.
Position in the structure
From bottom to top the build-up is usually:
- Bent posts — the vertical uprights
- Bent plate — the lengthwise beam on top of the posts
- Purlins — the horizontal roof beams
- Rafters or roof decking — the top layer
The bent plate is often fixed to the post head with a mortise-and-tenon joint and stiffened with braces against racking (wind load).
Application
When self-building a timber barn, lean-to or field shed, the bent plate is a key element: choose a beam size that matches the span between the posts and the roof load. Set the plate level and make tight, close-fitting joints, because the entire longitudinal stability of the structure depends on it.
Related terms
- Timber bent
- Roof structure
- Purlin
- Rafter
- Brace
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