Tie (engineering)

A hurricane tie used to fasten a rafter to a stud

A tie, structural tie, or strap, is a structural component designed to resist tension.^[1] It is the opposite of a strut or column, which is designed to resist compression. Ties may be made of any tension resisting material. In wood frame construction they are generally made of galvanized steel.^[2] Wood framing ties generally have holes allowing them to be fastened to the wood structure by nails or screws. The number and type of nails are specific to the tie and its use. The manufacturer generally specifies information as to the connection method for each of their products. Among the most common wood framing ties used is the hurricane tie or seismic tie used in the framing of wooden structures where wind uplift or seismic overturning is a concern.

Types

Hurricane tie

Hurricane ties are in place at the top of the wall as the roof trusses are being placed.

A hurricane tie is used to help make a structure (specifically wooden structures) more resistant to high winds (such as in hurricanes), resisting uplift, racking, overturning, and sliding.^[3] Each of the crucial connections in a structure, that would otherwise fail under the pressures of high winds, have a corresponding type of tie, generally made of galvanized or stainless steel, and intended to resist hurricane-force and other strong winds.

Seismic tie

Girder tiedown

Strap tie

Twist strap

Floor span connector

Angle

Z-clip

Plate

Rafter tie (and Tie-beams)

Rafter ties are designed to tie together the bottoms of opposing rafters on a roof, to resist the outward thrust where the roof meets the house ceiling and walls. This helps keep walls from spreading due to the weight of the roof and anything on it, notably wet snow. In many or most homes, the ceiling joists also serve as the rafter ties. When the walls spread, the roof ridge will sag. A sagging ridge is one clue that the home may lack adequate rafter ties. Rafter ties form the bottom chord of a simple triangular roof truss. They resist the out-thrust of a triangle that's trying to flatten under the roof's own weight or snow load. They are placed in the bottom one-third of the roof height. Rafter ties are always required unless the roof has a structural (self-supporting) ridge, or is built using engineered trusses. A lack of rafter ties is a serious structural issue in a conventionally framed roof.

The 15th century tie-beam roof at St Marys Church, Radnage, Buckinghamshire in England

A wooden beam serving this purpose is known as a tie-beam and a roof incorporating tie-beams is known as a tie-beam roof.

See also

• Framing (construction)
• Timber framing
• List of structural elements
• Tie rod

References