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for determination of the load-carrying capacity of joints with bulldog connectors,
CEN TC 124/WG 4, April1993), the second a development of this
formula based on work previously reported by the authors, and the third
was a new, simplified formula.
On average all three formulae predicted ultimate loads within 3 % of
the test values. However, only the second and third formulae correctly assessed
the effects on joint strength of timber density and member thickness.
Since some design formulae which have been proposed involve separating
the contribution of the bolt, it was decided to measure the strength of
plain bolted joints made from timber of comparable density, and with bolts
of the same two diameters that were used for the connectored joints. As
mentioned in the Introduction, it was discovered that the ultimate loads on
these bolted joints considerably exceeded the values predicted by the formulae
in EC5, so two further sets of tests were conducted using bolts
without nuts and washers, one with members of European redwood, the
other with Southern pine in order to include a timber of higher density.
Some of the bolts themselves were tested to determine their ultimate tensile
strength.
A further series of tests on toothed plates manufactured was conducted
by Lee and Lord (TRADA report E/TR/21,1961). These plates were double-sided
round toothed plates, similar to the other plates tested in 1993.
On the basis of these tests, Formula (1) gives the most consistent and
accurate results, but it must be noted that all the specimens tested had densities
of around 500 kg/m 3 and were made with thin members of similar
thickness; and, as previously noted, the formula as it stands does not adequately
allow for variations in these parameters.
1,5
j. k 18 c b, k
R � d � R
(1)
0,5 1,25 1,5
j. k 0,0014 min�k
c b, k
R � t d � R
(2)
� �
R � 0,0077 � d t � 40mm � R
(3)
j. k k c min b, k
where
R jk . is characteristic load-carrying capacity of one double-sided round
toothed plate and bolt, in N
R bk . is characteristic load-carrying capacity of the bolt per shear plane,
calculated from Eurocode 5, in N
is diameter of toothed plate, in mm
dc
t is minimum of outer member thickness and half the inner member
thickness for 3-member joints or minimum member thickness for 3member
joints, in mm
� k is characteristic density, in kg/m 3 .
All three formulae over-compensated for connector diameter according to
these test results.
Conclusions
For real bolted joints made with nuts and washers, the bolt design formulae
given in EC5 give good predictions of the yield loads but not of the absolute
ultimate loads. The predicted loads appear to be about 70 % of the
experimental values. It may be considered that design formulae for joints
made with toothed plate connectors should in a similar way predict loadcarrying
capacities which are less than the ultimate load-carrying capacity.
25-7-10 A V Page, C J Mettem
Characteristic strength of UK timber connectors
Introduction
In an official report to the meeting of CEN/TC 124 'WG4”, the members
were asked
(i) to describe a procedure for converting the allowable or working
loads for timber connectored joints used in their country to characteristic
load-carrying capacities
(ii) to compare the values obtained in this way with corresponding values
calculated from formulae proposed by E. Gehri:
0,5
1,5 � �k
�
c, k �15 c � b, k
R
where
d � �
�380 �
R N
dc is the diameter of the plate in mm
� k is the characteristic timber density in kg/m 3
R is the characteristic load-carrying capacity of the bolt in single
CIB-W18 Timber Structures – A review of meeting 1-43 4 CONNECTIONS page 4.15
bk ,
shear in N
(iii) to make proposals for obtaining characteristic values for the connectors
used in their country.