Scholarly Communications Project


Effects of Long-Term Creep on the Integrity of Modern Wood Structures

by

Jacem Tissaoui

Dissertation submitted to the Faculty of the Virginia Tech in partial fulfillment of the requirements for the degree of

Ph.D.

in

Civil Engineering

Approved

Siegfried M. Holzer, Co-Chair
Joseph R. Loferski, Co-Chair
David A. Dillard, member
Surot Thangjitham, member
Don A. Garst, member

December 10, 1996
Blacksburg, Virginia


Abstract

Short-term creep tests in tension and in compression were conducted on southern pine, Douglas-fir, yellow-poplar, and Parallam™ samples at temperatures ranging between 20 and 80°C and at 6, 9 and 12% moisture content. The principle of time-temperature su perposition was applied to form a master curve that extended for a maximum of 2 years. The horizontal shift factors followed an Arrhenius relation with activation energies ranging between 75 and 130 kJ/mole. It was not possible to superpose the complia nce curves at 70 and 80°C, this is attributed to the presence of multiple components in wood with different temperature dependence. Long-term creep tests were also conducted in tension and in compression at 20°C and 12% moisture content for over 2 years. The resulting compliance curves were fitted to the power law equation using a nonlinear fitting procedure. The results were compar ed with those of the short-term creep tests. Finite element analysis was conducted on selected wood structures to determine the effect of creep on serviceability and stability.

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