No abstract

Link to this article: http://journals.cambridge.org/abstract_S1359135514000268How to cite this article: Patrick Fleming, Simon Smith and Michael Ramage (2014). Measuring-up in timber: a critical perspective on mid-and highrise timber building design .

Lumen impregnation, unlike most other wood modification methods, is typically assessed by the pore-filling ratio (PFR) (i.e. the fraction of luminal porosity filled) rather than by weight percentage gain (WPG). During lumen impregnation, the impregnants act on the voids in the wood rather than on the solid mass (e.g. cell walls), but the PFR cannot be measured as conveniently as the WPG during processing. Here, it is demonstrated how the PFR can be calculated directly from the WPG if the bulk density of the untreated wood is known. The relationship between the WPG and bulk density was examined experimentally by applying a pressured impregnation on knot-free specimens from Sitka spruce with a liquid mixture of methacrylate monomers. Based on the validated model, it was possible to further study the effect of different process-related parameters, such as hydraulic pressure, on lumen impregnation. Skeletal density is another key parameter in this model, which directly reflects the amount of inaccessible pores and closed lumens, and can be independently determined by helium pycnometry. The permeability can be qualitatively evaluated by PFR as well as skeletal density. For instance, poor permeability of knotty wood, due to the large extractives content around knots, was 123Wood Sci Technol (2017) 51:1277-1290 DOI 10.1007 reflected by a lower skeletal density and inefficient lumen impregnation (low PFR). Although this model was examined on a laboratory scale, it provides guidance on the precise effect of different parameters on lumen impregnation, thereby improving the fundamental understanding of and enabling better control over the modification of wood by impregnation.

The aerodynamics involved in the galloping of lightly-iced transmission lines were studied in a series of wind tunnel experiments. A representative section of a lightly-iced conductor produced in an outdoor freezing rain simulator was used throughout. In the first set of experiments aerodynamic loads were measured on a static model at different wind speeds and angles of attack. These experiments showed that the well-established den Hartog criterion does not predict an instability at wind speeds associated with transmission line galloping. A second set of experiments examined the effects of different steady rotational motions on the aerodynamic loads. Automated controls were used to rotationally oscillate the model in a repeatable manner at various angles of attack and rotational amplitudes as well as frequencies. The drag remained consistent with quasi-steady values, while the lift was affected by the rotational motion. This rotation-induced lift was enhanced by ice surface irregularities, but further studies were needed to fully assess its importance.

No abstract