Formwork for Concrete Structures by R.L.Peurifoy and G.D- By EasyEngineering.net

82 Chapter Four
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Timber Connectors
The strength of joints between wood members used for formwork
can be increased substantially by using timber connectors. Three
types of connectors are available: split ring, two shear plates, and one
shear plate. The split ring is used with its bolt or a lag screw in single
shear. The two-shear plate connector consists of two shear plates used
back to back in the contact faces of a wood-to-wood connection with
their bolt or lag screw in single shear.
The one-shear-plate connector is used with its bolt or lag screw in
single shear with a steel strap for wood-to-metal connections. The
split ring and the two-shear plate connectors are the most common
types of connectors used with formwork.
When lag screws are used in lieu of bolts, the hole for the unthreaded
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shank should be the same diameter as the shank. The diameter of the
hole for the threaded portion of the lag screw should be approximately
70% of the shank diameter. When bolts are used, a nut is installed, with
washers placed between the outside wood member and the bolt head
and between the outside wood and the nut.
When timbers are joined with metal or other types of connectors,
the strength of the joint depends on the type and size of the connector,
the species of wood, the thickness and width of the member, the
distance of the connector from the end of the timber, the spacing of
the connectors, the direction of application of the load with respect to
the direction of the grain of the wood, the duration of the load, and
other factors.
Split-Ring Connectors
Split-ring connectors are usually restricted to situations where the
formwork is fabricated in a yard, remote from the jobsite, where a
drill press is readily available. Table 4-27 lists the design unit values
for one split ring connector and bolt installed in the side grain for
joining two members of seasoned wood in single shear. The values
are based on adequate member thicknesses, edge distances, side distances,
and spacing [1].
Tabulated nominal design values for split-ring and shear-plate
connectors are based on the assumption that the faces of the members
are brought into contact with the connector units, and allow for
seasonal variations after the wood has reached the moisture content
normal for the condition of service. When split-ring or shear-plate
connectors are installed in wood that is not seasoned to the moisture
content of the normal service condition, the connections should be
tightened by turning down the nuts periodically until moisture equilibrium
is attained.
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