Tree stability in windstorms and tree failure are important issues in urban areas where there can be risks of damage to people and property and in forests where wind damage causes economic loss. Current methods of managing trees, including pruning and assessment of mechanical strength, are mainly based on visual assessment or the experience of people such as trained arborists. Only limited data are available to assess tree strength and stability in winds, and most recent methods have used a static approach to estimate loads. Recent research on the measurement of dynamic wind loads and the effect on tree stability is giving a better understanding of how different trees cope with winds. Dynamic loads have been measured on trees with different canopy shapes and branch structures including a palm (Washingtonia robusta), a slender Italian cypress (Cupressus sempervirens) and trees with many branches and broad canopies including hoop pine (Araucaria cunninghamii) and two species of eucalypt (Eucalyptus grandis, E. teretecornus). Results indicate that sway is not a harmonic, but is very complex due to the dynamic interaction of branches. A new dynamic model of a tree is described, incorporating the dynamic structural properties of the trunk and branches. The branch mass contributes a dynamic damping, termed mass damping, which acts to reduce dangerous harmonic sway motion of the trunk and so minimizes loads and increases the mechanical stability of the tree. The results from 12 months of monitoring sway motion and wind loading forces are presented and discussed.
CFRPs offer a high strength lightweight alternative strengthening strategy to traditional methods using concrete overlays and/or steel plates in bridge engineering applications. In addition, the use of CFRPs may offer a viable retrofit/repair strategy in the case of damaged structures, where this damage may be significant. This paper reports on the performance of CFRP-based strategies for the repair and strengthening of two 40% scale continuous flat slab bridge models with significant damage arising from prior static testing to incipient collapse conditions. In addition, the performance after repair using a CFRP scheme of a RC beam-slab-column subassembly, following severe high-load cyclic testing, was also investigated. Results indicate that CFRPs offer a viable repair strategy in structural applications involving severe damage from the influence of static overload or extreme earthquakes but care needs be exercised to ensure secure adhesion where the surface under repair has locally adverse geometric features or has suffered large geometric deformation from the damage concerned.
INTRODUCTION Serviceability rather than strength is the most critical design requirement for vibration-vulnerable floor construction. Modern floor systems are being designed and constructed with longer spans owing to the need for larger column-free spaces in office and commercial retail buildings. The advances in high-strength materials and lightweight construction technologies are also altering the dynamic characteristics of floor systems. Changes in modern office layouts associated with the removal of full height partitions, heavy filing cabinets, large bookshelves and other architectural components result in a reduction of both load and damping. Hewitt
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