Deflection and Creep Characteristics of Trussed Rafters with Metal Plate Fasteners

Data relating midspan deflection of trussed rafters to time and upper chord load are analyzed. Empirical equations have been developed for trussed rafters fabricated with metal splice plates that express creep deflection as a function of the logarithm of time. Rate of creep is also correlated with magnitude of load. Pre-loading the trusses apparently eliminated the creep at loads below the pre-loading values and also increased the slope of the load-deflection curve. A general theory for deflection as a function of load and time is presented for trussed rafters made with metal splice plate and which have undergone no pre-load. Practical implications of the experimental deflection and creep observations are discussed with respect to deflection of trussed rafters in buildings, qualification testing for wood fasteners, and areas for research.

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