Duration of load effect on LVL beams:Part 2. Long term load tests under constant and cyclic humidity

A research study on the long term load effects of Kerto laminated veneer lumber (LVL) was carried out at VTT in co-operation with other partners of a European project. Before the start of the long term tests, short term reference tests on Kerto LVL beams were completed (Fonselius and Ranta-Maunus 1996). The selection of load levels for the long term tests were determined based on the short term strength results. The results of long term bending experiments made by VTT are published in this report. A total of 40 LVL beams were loaded under long duration loading. Nearly structural size beams were loaded to failure under monthly increasing stepwise loading under controlled humidity conditions, including both constant (85 % RH) and cyclic humidity. The bending stress at failure when extrapolated to 6 months load duration was 67 to 75 % of the short term strength of similar beams having the same moisture content, which is equal or better than predicted by Madison curve (67 %)