Duration of load effect on curved glulam beams:Part 2. Long term load tests and analysis

This research related to the duration of load effect on curved glulam is a part of an EC-AIR project carried out at VTT in co-operation with four other EU member countries. The project includes the long term loading of 32 curved beams, as well as equivalent short term reference tests of 32 beams. The long term loading was made under both constant and cyclically varying humidity conditions. Failure is caused by tensile stress perpendicular to grain. A calculation procedure is presented to consider the effect of moisture variation as an additional loading. Both calculation and experiments reveal that a period of higher humidity can double the effective loading, depending on the duration of humid period. Experimental and calculated results are given for duration of load effect of curved glulam for two thicknesses (90 and 140 mm) under constant (85%) and cyclically changing humidity