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4.16 STIFFNESS
32-7-6 A Jorissen
The stiffness of multiple bolted connections
Introduction
The slip characteristics of multiple bolted connections were analysed experimentally
and theoretically. It was found that the stiffness values obtained
by tests were considerably lower than those suggested in ENV-1-
1:1993 (Eurocode 5). This can be explained by the different hole clearances
of each bolt. An alternative equation for the stiffness of multiple bolted
connections is proposed in this paper based on about 850 short term tests
on full-scale multiple bolted connections loaded parallel to the grain and
on results obtained by a load distribution model.
Conclusions and recommendations
The research described in this paper show that the determination of the
stiffness of multiple bolted connections according to ENV-1-1:1993 (Eurocode
5) result in too high values for this connection stiffness. On the
other hand, the initial slip of the multiple bolted connections is negligible,
even if the initial slip of the individual bolts is not. Therefore it is recommended
to change the design rules for the stiffness of multiple bolted connections:
(1) the slip values should not be increased by 1 mm in order to take the
hole clearance into account.
(2) the connection 1,5 �
stiffness parameter can be calculated according to
k
kser� kbolt
with kbolt � 0,3
20
32-7-9 J Vesa, A Kevarinmäki
Creep of nailplate reinforced bolt joints
Introduction
The effect of nail plate reinforcement on timber joints has been researched
in Helsinki University of Technology since 1992. It was found that in
short duration loading the reinforcement performs well: stiffness at low
load levels is high, ultimate strength is high and the joint slip in failure is
large. The presented creep tests were started to verify the function of the
nail plate reinforced bolted joints under varying climate conditions during
long period of time.
The long-term tests started at autumn 1992. A test of 44 nail plate reinforced
bolt joints was carried out. In the test series the type of nail plates,
the loading direction of the nail plate as well as the direction between
grain and the applied force were varied. The test series consisted of three
pairs: three series were tested in a covered but unheated building (a granary)
and similar series in cyclically changed humidity and temperature conditions
with rapidly changing humidity. The duration of the tests in cyclically
changed conditions was 200 days and the tests in the natural covered
conditions are still continuing after 6.5 years loading period.
The results of the measurements between the tests series from the natural
and cyclically changed conditions were compared. The joint slip after 50
years loading of the tests pieces in the natural covered conditions was estimated
with a logarithmic function. These results were compared to the
joint slips according to EC5. Also the joint slip from other joint types of
other previous tests found from literature was compared to the nail plate
reinforced bolt joints and to joint slips according to EC5.
Conclusions
Nail plate reinforced bolt joints are very stiff compared to other joint types
that can be assembled on building site. This is emphasized in longer time
periods. The creep of nail plate reinforced bolt joints increases with the
angle between force and nail plate main axis.
The calculation methods in EC5 give too small joint slips. This applies
both to initial deformations and deformations after given time.
Joint slips after 200 days in the tests conducted under rapidly changing
humidity are generally larger than those estimated to happen in naturally
covered conditions after 50 years loading.
CIB-W18 Timber Structures – A review of meeting 1-43 4 CONNECTIONS page 4.88