Abstract:
The objective of this research is to understand the behavior of metal-plate-
connected (MPC) joints by examining actual MPC truss heel and tension
splice joints subjected to hurricane wind load simulations and impact loads.
A hurricane wind load simulation was applied to MPC heel joints to
determine if a large scale wind event would cause strength loss or change the
joint stiffness. An "impact" load of one second duration (as defined by the
American Forest and Paper Association (AFPA) (1991)) was also applied to
MPC heel joints and tension splice joints. Two different impact loads were
applied to MPC tension splice joints to determine if strength degradation or
stiffness change occurs due to loads with short duration and high maximum load.
Finally, MPC tension splice joints were subjected to a ramp load which linearly
increased ten times faster than the control group ramp load to determine if
shorter duration tests still produce "static" loading results. All observed properties were compared to a control group which was subjected to a static
ramp load.
Both MPC heel and tension splice joints exhibited non-linear behavior
under static ramp loads and failed with little warning because the tests were
load- controlled. Tooth withdrawal, wood shear failure, and plate failure modes
were all seen for both types of MPC joints.
Heel joints tested with the top member in tension proved to have 17%
higher average ultimate strength and 42% lower average ultimate deflection than
heel joints tested with the top member in compression. The stiffness of heel
joints increased by an average of 300% after the tension wind simulation. This
stiffness increase is possibly due to wood densification near the metal teeth.
The impact load, which increases from the dead load to double the design load
caused a stiffness increase similar to the stiffness increase produced by the
tension wind simulations. No significant strength degradation was caused by
dynamic loadings on heel joints.
The accelerated ramp load produced the same results as the static ramp
load in 1110th the time.
Joint stiffness decreased after the impact load for tension splice joints, but
increased for heel joints. Impact loads caused no decrease in strength.
Increasing the impact spike magnitude by 50% produced 360% more deflection
during the spike.
