laterally loaded fastener spreadsheets part 4 design values for timber connectors
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CD4 Des�gn values for t�mber connectors Timber connectors are used in conjunction with bolts to transfer
shear load between two or more members placed side by side. The
design values for timber connectors given by EC5 are unproven
for the types of connector used in the UK, and a comparison of
the design values given by EC5 and BS 5268-2:2002 indicates
that in many cases the values given by EC5 are unsafe. It is
recommended that until the EC5 rules have been reviewed, design
values for connectors should continue to be based on information
from BS 5268-2. This document gives a method for converting
the basic connector loads given in BS 5268 to design values for
use in a building which is otherwise designed to EC5.
BS 5268-2 tabulates ‘basic loads’ for one connector unit.
A basic load has to be modified by various factors to obtain a
BS 5268 permissible load value. A connector unit is defined as
one of:
• a single-sided sided toothed plate and bolt, in a steel-to
timber joint
• a double-sided toothed plate and bolt or two single-sided
toothed plates back-to-back on a single bolt, in a timber
to-timber joint
• a split ring and bolt, in a timber-to-timber joint
• a single-sided shear plate and bolt, in a steel-to-timber
joint
• two single-sided shear plates plates back-to-back on a
single bolt, in a timber-to-timber joint.
BS 5268-2 gives rules to allow for the effects on the basic load
of service class, spacing, edge and end distances, angle of load to
grain and the number of connectors in a line. These rules should
be applied to the appropriate basic load tabulated in BS 5268-2
to obtain a ‘basic design load’, Rbasic,d, for one connector unit.
Provided that the BS 5268 rules for minimum spacings and
distances are complied with and the appropriate reductions for
sub-standard dimensions are applied, it is unnecessary to consider
the corresponding rules for spacings and distances given in EC5.
The Eurocode 5 design load-carrying capacity for the
connection is then calculated as:
Rd = nkc Rbasic,d
Where n = total number of connector units
k = factor from Table CD4.1 to take account of c
the differing load duration and safety factors
used in the two codes
= BS 5268 basic load per connector unit Rbasic,d
modified for sub-standard spacing, end and
edge distance, service class, angle of load
to grain and number of connectors in a line,
according to BS 5268-2 rules
Table CD4.2 gives some indicative values of Rd for a three-
member timber-to-timber connection made with two connector
units on one bolt, to assist the designer in choosing a suitable
connector.
Table CD4.1 Recommended kc factors to convert BS 5268-2 bas�c des�gn loads for t�mber connectors used �n serv�ce classes 1 and 2 to Eurocode des�gn capac�t�es
Connector type
EC5 load durat�on Long-term Med�um-term Short-term Instantaneous
(e.g. storage) (e.g. floor �mposed) (e.g. snow) (e.g. w�nd) Toothed plates 1.35 1.35 1.51 1.69 Shear plates and split rings 1.35 1.35 1.69 2.03
Table CD4.2 Examples of short-term des�gn capac�t�es for a s�ngle 3-member C16 t�mber connect�ona
Connector type Nom�nal s�ze
(mm)
Des�gn load capac�ty under short-term load�ng �n serv�ce classes 1 and 2
(kN)
Load parallel to gra�n Load perpend�cular to gra�n
Round toothed plate 38 6.80 4.65
50 10.3 7.10
63 12.2 9.06
75 13.6 10.5
Split ring 64 26.7 18.7
102 49.8 34.7
Shear plate 67 28.9 20.2
102 40.2 28.2
Note The values shown are for a 3-member connection in C16 timber, with the central member 72mm thick and the two outer members each 44mm thick. The values are for the complete connection, i.e. for two shear planes or connector units, and are derived from BS 5268-2, factored in accordance with Table CD4.1.
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IStructE/TRADA Manual for the design of timber building structures to Eurocode 5 CDCD 4 Page 1