The effect of load and relative humidity on bending creep behaviour of hornbeam in three altitudes (Case Study, Nowshahr Meshelak Branch)

For this purpose, 9 hornbeam trees at 400, 800 and 1100 meters altitude from forestry projects of Meshelak Nowshahr were selected. 324 Clear samples were cut at mature wood in diameter breast height (DBH). The prepared samples (dimensions: 2.5 × 2.5 × 41cm) in a room at temperature of 20 C and relative humidity (RH) 35, 65 and 95 % were conditioned. Afterward three weeks conditioning, at firs three points bending test for determining the maximum of bending load on 81 samples was done. 10, 20 and 30% maximum of bending load (MBL) were measured and then four points bending creep test for determining creep parameters on 243 samples at times period of 14 hours loading and 10 hours unloading in acclimatized room conditions were measured and then creep/recovery, creep modulus and relative creep were calculated.
Results indicated that, the effects of load and relative humidity on creep parameters was significant so as the maximum and the minimum relative creep were observed in 95 and 35% RH respectively and the maximum and the minimum creep modulus were observed in 35 and 95% RH respectively. The maximum and minimum relative creep in 30 and 10% MBL respectively and the maximum and minimum creep modulus in 10 and 30% MBL were observed respectively. Results indicated that the increasing of bending properties caused decreasing the creep parameters.