An estimation of critical wind speed and a calculation of mechanical properties for two Australian eucalypts

From a review of the literature it was found that the failures of trees resulted from either uprooting or stem breaking, though many factors contribute to the health and continual growth that combats failure. Most of the literature cited wind as the main reason for failure, and it was found that there was a general lack of research and knowledge on common varieties of Eucalyptus trees, such as Eucalyptus camaldulensis and Eucalyptus rubida. There were currently no published results on the E. rubida mechanical properties, while only a few publications existed on E. camaldulensis. Recent studies have shown that concern was growing about the failure of trees, especially those in close proximity to cities and urban development with potential wind speeds increasing due to global warming.<br><br>In order to investigate a means of obtaining material properties from living trees (via small core samples rather than the industry-standard method of bending tests from felled timber) the use of a relatively new instrument was investigated; the “Fractometer II”. It was found that it could potentially complement the industry standard method of testing, because the MOR for E. camaldulensis did not significantly differ between either testing methods, meaning that either method would yield valid results. E. camaldulensis and E. rubida were found to be significantly different to each other in their MOR values, thus it was recommended that Eucalypts be studied at the species level. It was found that the MOE for E. camaldulensis was 11.1 Gpa, which was similar to other studies.<br><br>Parameters such as tree shape, DBH, crown area, material properties and drag coefficient were estimated or measured for E. camaldulensis and E. rubida and these were used to predict the critical wind speed for stem breakage. The critical wind speeds were an estimation of the expected critical wind speeds for individual Eucalypt trees. Accelerometers were attached to several trees during heavy wind storms. Five sets of data from the accelerometers were used to calculate the displacement for each tree over an interval of thirty-nine seconds and then calculate the drag coefficient. From the method used to estimate drag coefficients, a high range of values were found (from 0.670 -0.915) for E. camaldulensis. The critical wind speeds ranged from 37.6 - 111 m/s for stem breakage, which was within the range expected from historical data on fallen trees in Victoria.