Duration of load behaviour of an aligned strand wood composite (ASC)

An aligned strand, wood composite (ASC) material was subjected to a two year duration of load (DOL) study. The experimental work was conducted in Mt. Gambier South Australia from a purpose built shed housing 42 back to back (double) vertically oriented specimen test rigs in an atmosphere not controlled for temperature and relative humidity. A total of 244 specimens were tested in two population groups, each group divided into two subgroups. One subgroup each for short term static Modulus of Rupture (MOR) and Modulus of Elasticity (MOE), and the other for long term bending strength and stiffness under stresses varying from 0.4MOR to 0.9MOR.

Creep and creep - rupture observations were taken over a two year period providing an extensive database for the evaluation of DOL properties. Monte Carlo simulations were used to give confidence in the process of assigning MOR values to the long term specimens using a statistical matched distribution technique for long term strength evaluation.

Creep and creep - rupture responses for the ASC were similar in effect but fifty percent greater in magnitude than that predicted for solid seasoned timber by AS1720.1-1988, the Australian Timber Structures Code. Creep design multipliers, and long term strength design multipliers in both working stress and limit state design formats were derived for the ASC.

A limiting strain criterion was established for the ASC and was observed to be independent of time under load and applied stress intensity. A failure strain model was presented for the ASC in a form enabling the determination of a limiting deflection for flexural (beam) members at failure.