Short-Term Duration of Load and Cyclic Performance of

The objective of this research was to evaluate the duration of load factor for metal-plate-connected (MPC) truss joints subjected to various cyclic loading conditions. Heel and tension-splice joints from a standard 30-foot span Fink truss constructed from nominal 2x4 Douglas-fir lumber were tested. A testing frame similar to that developed by Gupta and Gebremedhin (1990) was used to test the joints under several different loading conditions. A static ramp load of 780 lbs./min. was applied to ten joints (both tension-splice and heel joints) until failure was reached. This test group served as the control group for comparison with joints tested under several cyclic loading regimes, with ten joints (per joint type) in each sample group. At the end of these cyclic loadings, the joints were ramped to failure (if they survived the cyclic loading). Results were evaluated by comparing the ultimate loads and stiffnesses from the control group specimens to those from the cyclic loading groups. An evaluation of the damage resulting from the cyclic loads is also discussed. Reductions in the stiffness and strength of the joint after the cyclic loading are related to the number of cycles, and the amplitude of the cycles. The results of this research show that the current duration of load factor of 1.6 for earthquake loading used in the design of MPC joints is adequate. Signature redacted for privacy. Signature redacted for privacy