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39-7-1 P Quenneville, M Bickerdike
Effective in row capacity of multiple-fastener connections
Introduction
It is well accepted that the effective in-row capacity of multiple-fasteners
is potentially less than the sum of the capacity of each individual fastener
in the row. Since most design procedures are based on principles developed
for single fasteners failing in a ductile mode, multiple-fastener connection
resistances could not be reasonably predicted for all cases. To
overcome this shortcoming, design procedures would include modification
factors that took various geometric variables into account, trying to cover
all possible situations. In recent past, research observations have shown
that this decrease from the optimal resistance is due to the brittle failures
of the wood fibers surrounding the fasteners. Multiple-fastener connections
would fail in row-shear, group tear-out, or splitting.
A numerical model based on the load-slip behaviour of single fastener
connections was developed to study the behaviour of multiple fastener
connections failing in row-shear. Variables taken into account include single
fastener load-slip curves with varying resistances, stiffness and ultimate
slip, fastener gaps, and number of in-row fasteners. The numerical
model was developed using the finite element software ANSYS. Numerical
predictions of the connection ultimate load were compared to available
experimental results of the modeled connection configurations, showing
good agreement. The model was then used to predict the ultimate resistances
of connection configurations for various end distances and fastener
spacings. From these predictions, a design equation for row-shear
was developed.
This design equation is presented and compared to the Canadian, European
and American design provisions for the in-row connection resistance.
Conclusions
A set of design equations to predict the resistance of dowelled connections
failing in a brittle manner (row-shear, group tear-out, and net tension) for
parallel-to-grain loading is proposed. These equations are based on experimental
information along with the results from the numerical model of
Bickerdike, and prove to be an effective method of predicting the strength
of bolted timber connections loaded in the parallel-to-grain direction.
The relationship of effective number of fasteners to the number of bolts
in-the-row was used to compare the proposed set of equations to existing
design standards. The proposed design approach replicates the effective
number of fasteners for the configurations that were used to develop the
Eurocode and Canadian code.
Utilizing the minimum resistance determined from all possible failure
modes provides the flexibility to consider all possible connection scenarios
in the parallel-to-grain loading direction.
CIB-W18 Timber Structures – A review of meeting 1-43 4 CONNECTIONS page 4.65