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4.10 NAIL PLATES
14-7-1 B Norén
Design of joints with nail plates
Introduction
For some time a small Nordic group has discussed guidelines for design of
joints with nail plates in timber structures.
Their draft proposal contains these sections:
1. Definition and symbols
2. Design calculations
3. Material
4. Manufacture and control
5. Testing of plates and joints
Section 5 is principally a reference to the testing standard proposed by
NORDTEST and based on the RILEM/CIB recommendations.
The paper presented here includes only Section 1 and 2 in which is given
rules for design calculations. The outline is kept from the proposal:
2.1 Model for calculation of joints
2.2 Design against plate failure
2.3 Design against plate grip failure
2.4 Design against wood failure
2.5 Rules for specific joints
2.6 Calculation of slip
18-7-6 N I Bovim, B Norén
The strength of nail plates
Introduction
The strength of nail plates with respect to failure in the plate material have
been examined by NTI as background for a Nordic proposal This proposal
has been presented by B. Norén in Paper 14-7-1.
The present paper gives a summary of test results and proposed design
method for design against plate failure.
Today, the design against plate failure is based on:
1) strength of plate with respect to forces parallel to the joint between
connected timber members. This is called the shear strength of the
plate.
2) strength with respect to forces perpendicular to the joint. This is called
the plate strength of the plate.
The existing rules give no interaction formula for combination of "shear"
and "plate"-forces. Consider Fig. 1. The example demonstrates clearly that
existing rules do not take care of the orthotropic behaviour of nail plates.
An interaction formula based on "plate" and "shear"-components would be
still worse and in reality meaningless!
In many cases the rules are extremely unsafe (up to 200 percent for design
values given in the Norwegian approval of the tested plate). This is
the main reason for the work presented here.
Figure 1. Example of nail plate joint. Existing design rules are drawn as a
curve. Test results and common sense tell us that maximum strength is
achieved for β = 60º.
Conclusion
The presented design method gives a good prediction of the plate strength
of nail plates. The existing Nordic rules are partly unsafe and do not reflect
the orthotropic behaviour of nail plates.
CIB-W18 Timber Structures – A review of meeting 1-43 4 CONNECTIONS page 4.68