MECHANICAL CONNECTORS

CONNECTION• Consists of two or more members joined

with one or more mechanical fasteners.

• Connections may consist entirely of wood members but frequently involve the connection of wood to steel or other members.

• In most wood structures, connections are one of the most important components

MECHANICAL CONNECTORS• These are defined as those where fasteners

penetrate the wood. • These are constructed using two general

fastener types:Dowel Bearing

• Dowel-type fasteners are those mechanical fasteners that are most widely used for timber structures. Dowel type fasteners transmit either lateral or withdrawal loads.

• Bearing-type connections transmit lateral loads only. Bearing-type fasteners, such as shear plates and split ring connectors, transmit shear forces through bearing on the connected materials.

Bolts, coach screws and timber connectors

• Bolts, coach screws and timber connectors (split rings and shear-plates) all have higher capacities than nails and screws and are therefore better suited to applications where a large load is imposed and the space available to accommodate fasteners is limited.

• Typical applications include beam to column, beam to beam, truss, pole frame, marine structure and bridge connections as well as column, beam and truss supports.

BOLTS• Bolts are commonly used to fix large timber

members together, or timber to steel. They can also be used to attach timber to concrete or masonry.

• Care is required to make sure the anchor strength is sufficient to resist pull out loads. In addition, washers at the bolt heads must be large enough to prevent timber fibers from crushing when exposed to pull-out loads.

• Bolts function by bearing on the surface of the timber and the shearing action within the bolt itself.

HexA six sided nut.

Also referred to as a finished hex nut.

Nylon Insert LockA nut with a nylon

insertto prevent backing off.Also referred to as a

Nylock

JamA hex nut with a reduced height.

Nylon Insert Jam Lock A nylock nut with a

reduced height.

WingA nut with 'wings'

for hand tightening.

CapA nut with a domed top over the end of

the fastener.

AcornAcorn nuts are a high crown type of cap nut, used for appearance.

FlangeA nut with a built in washer like flange.

TeeA nut designed to

be driven into wood to create a threaded hole.

SquareA four sided nut.

Prevailing torque lock A non-reversible lock

nut used for high temperature applications

K-Lock or KepA nut with an attached free-spinning external

tooth lockwasher.

 

CouplingCoupling nuts are long nuts used to connect pieces of threaded rod or other male threaded fasteners.

SlottedSlotted nuts are used in conjunction with a cotter pin on drilled shank fasteners to prevent loosening.

CastleCastle nuts are similar to slotted nuts but with the slots in a rounded section above the main nut.

Table 2: Washers for Bolts

Washer Type UsesStandard cut washer  Used for screws and bolts

where the loading is lateral. Should not be used with split rings or shear plates.

 

Square plate washer Used for bolts and with split rings and shear plates. Suitable for tensile loads.

 

Round plate washer   Used for bolts and with split rings and shear plates. Suitable for tensile loads.

 

Ogee (cast iron) washer 

Used for bolts and with split rings and shear plates. Suitable for tensile loads.

 

Malleable iron washer 

Used for bolts and with split rings and shear plates. Suitable for tensile loads.

 

Bevel washer  Used where the bolt to member alignment is not perpendicular.

 

COACH SCREW• are simply large screws with hexagon heads which

can be used in situations where bolts are undesirable or cannot be used such as in blind holes i.e. holes where no access is possible to place a nut on the bolt thread.

Split Rings and Shear Plates • Split rings and shear plates are load transferring

devices which rely on bolts or lag screws to restrain the joint assembly. They are more efficient structurally than bolts or lag screws used alone because they enlarge the wood area over which a load is distributed.

• Because of their large diameter, they achieve a large bearing area without the need to remove large volumes of timber, which might otherwise weaken the members being joined.

Split-Rings • transfer load from one piece of timber to another

directly through a large diameter circular steel ring set into a groove. Two split-ring sizes are available, one having a diameter of 64 mm and the other 102 mm. The bolt through the center serves only the purpose of holding the joint together.

• The split in the ring is for the purpose of permitting free movement of the wood with the moisture content changes, which occur in service.

• Shear-Plates• are available in two diameters of 67 mm and 102 mm,

have similar load carrying capacity to split-rings and require similar installation procedures. They function by transferring load to the shear-plate and then to the bolt which carries the shear across the interface. Thus the bolt in a shear-plate joint performs the dual role of holding the joint together and transferring shear.

• METAL CONNECTOR PLATES• Metal plate can be used for support, connection and

decoration. Metal plate timber plates are used to connect beams and also give a rustic or modern look depending on the chosen materials and metal finishes.

• It support a tremendous amount of structural load, allowing heavy timber to span great distances. Often, the steel gussets are painted black and held to the timber with 3/4″ and 1″ bolts. Sometimes the steel plates are galvanized or painted in a variety of colors.