Gust Effect Factor for Wind Load Estimation of Tree Supporting Systems

Strong winds have caused an increasing amount of damage to fruit trees, such as uprooting and fruit drop, and various prop systems or support systems have been introduced to prevent this wind damage. When a prop system is designed against strong winds, it is essential to calculate the wind load acting on each tree in order to accurately assess the wind resistance of the prop system. In particular, the fluctuating effect is significant and cannot be ignored when the natural frequency of a tree is relatively small. In this study, vibration tests were performed to measure the natural frequencies and damping ratios of trees in order to evaluate the wind load acting on the trees. Both ambient and free vibration tests were performed, and the dynamic properties were identified and compared. It was found that the average natural frequency of trees was approximately 1.0 Hz, and therefore the dynamic effect against fluctuating wind load needs to be considered. The analysis results of the gust effect factor indicated that the wind load may be underestimated or overestimated considerably if the flexible nature of trees is neglected, or if the exact values of natural frequency and damping ratio are not available.

[1]  Emil Simiu,et al.  Wind effects on structures : fundamentals and applications to design , 1996 .

[2]  Akira Hoyano,et al.  The Effects of Windbreak Forests on the Summer Thermal Environment in a Residence , 2009 .

[3]  Kenneth E. Byrne,et al.  Wind tunnel measurements of crown streamlining and drag relationships for several hardwood species , 2005 .

[4]  Haibei Xiong,et al.  Field Testing and Investigation of the Dynamic Performance and Comfort of Timber Floors , 2011 .

[5]  G. J. Mayhead,et al.  Some drag coefficients for British forest trees derived from wind tunnel studies , 1973 .

[6]  Walter Ammann,et al.  Anchorage of mature conifers: resistive turning moment, root-soil plate geometry and root growth orientation. , 2007, Tree physiology.

[7]  Terence L. Robinson,et al.  The Evolution Towards More Competitive Apple Orchard Systems in the USA , 2008 .

[8]  Douglas A. Maguire,et al.  Natural sway frequencies and damping ratios of trees: concepts, review and synthesis of previous studies , 2004, Trees.

[9]  A. R. Ennos,et al.  The anchorage mechanics of deep rooted larch, Larix europea × L. japonica , 1996 .

[10]  J. W. Palmer,et al.  Effect of apple tree spacing and summer pruning on leaf area distribution and light interception , 1992 .

[11]  B. Gardiner,et al.  Comparison of two models for predicting the critical wind speeds required to damage coniferous trees , 2000 .

[12]  Norishige Chiba,et al.  Pseudo‐dynamics model of a cantilever beam for animating flexible leaves and branches in wind field , 2009, Comput. Animat. Virtual Worlds.

[13]  J. M. Lespinasse,et al.  APPLE TREE MANAGEMENT IN VERTICAL AXIS: APPRAISAL AFTER TEN YEARS OF EXPERIMENTS , 1986 .