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4.3 DOWEL-TYPE FASTENERS LOADED PARALLEL TO
GRAIN
12-7-2 H J Larsen
Design of bolted joints
The paper describes for the first time in CIB/W18 the Johansen theory that
forms the basis for the present design rules for laterally loaded bolted
joints. The results are compared with the design rules in Germany. The
paper also contains approximation reducing the calculations considerably.
With the spread of computers the opinion of CIB/W18 is that there is no
need for such methods.
19-7-6 L R J Whale, I Smith
The derivation of design clauses for nailed and bolted joints in Eurocode
5
Based on contracts from both the Commission of the European Communities
and the UK Department of the Environment, TRADA has study the
properties of mechanical timber joints under short-term lateral loading.
Emphasis was placed upon deriving reliable embedment characteristics for
solid timbers and sheet materials, and a broad range of timber species, and
wood-based sheet materials were included in the test programme.
Seven timbers were selected for embedment testing; UK grown Sitka
spruce and Scots pine, European redwood and whitewood, spruce-pine-fir,
keruing and greenheart. These were loaded parallel or perpendicular to the
grain in either a compressive or a tensile mode, with nails ranging from
2.65 to 6 mm in diameter and bolts from 8 mm to 20 mm in diameter.
Sheet material specimens of Finnish birch plywood, Finnish spruce
plywood, French pine plywood, Canadian Douglas fir plywood, 4.8 mm
and 8 mm tempered hardboard were also tested, with nails ranging from
2.65 mm to 4 mm in diameter. The thickness of solid wood specimens was
limited to twice the connector diameter, whilst actual board thicknesses
were used in the case of the sheet material specimens. Toleranced holes,
approximately 1.5 mm oversize, were provided in all bolted specimens.
Nailed hardwood specimens were prebored to 80 % of the nail diameter.
20-7-1 L R J Whale, I Smith, H J Larsen
Design of nailed and bolted joints. Proposals for the revision of existing
formulae in draft Eurocode 5 and the CIB Code
Based on the results of a comprehensive investigation by TRADA on
short-term properties of nailed and bolted joints (Paper 19-7-1) and the
application of that data in deriving design equations for Eurocode 5 (Paper
17-7-6) and in accordance with discussions on these papers meeting,
slight modifications are made to the design approaches which had originally
been put forward. Results from over 400 joint tests, carried out as part
of the TRADA investigation, are also presented as a testament to the accuracy
of the design equations which are proposed.
Furthermore, the results of tests on nailed plywood and tempered hardboard
specimens, which through lack of time had been precluded from the
previous analysis, are presented. These are used in an assessment of the
design approaches to board material-to-timber joints which currently exist
in the (CIB code, 1983) and the draft (Eurocode 5, 1986). As a result,
modifications are proposed which extend the range of design possibilities
for these types of joint.
The basic wood strength parameter determining the lateral load carrying
capacity of joints with nails, bolts, screws and other dowel-type fasteners
is the embedding strength f h .
The results of TRADA's recent research on these types of joint, in
(Smith, 1983) and (Whale and Smith, Paper 19-7-6) are summarised in
Figure 1, where also the values assumed in the draft (Eurocode 5, 1986)
are shown.
In the TRADA work, embedding strengths were found for plain round
nails with a diameter, d, between 2.65 and 6.0 mm loaded parallel and
perpendicular to the grain in softwoods (mean density, R an about 400-500
kg and in dense hardwoods (~mean about 700-1000 kg/m 3 ). In softwoods
no preboring was used. In hardwoods holes were prebored to 80 % of the
nail diameter.
The embedding strength was also found for bolts with a diameter between
8 and 20 mm loaded parallel and perpendicular to the grain. The
holes were approximately 1.5 mm oversized. This followed earlier work
by (Smith, 1983) in which embedding strengths were determined in European
whitewood for plain steel dowels in close-fitting holes.
For bolts, no difference was found between the softwood and dense
hardwood specimens in respect of their embedding strength density trends.
CIB-W18 Timber Structures – A review of meeting 1-43 4 CONNECTIONS page 4.17