Strength of OSB Scarf Joints in Tension

The use of scarf joints to join panel products can be found in structural applications such as wood I-joists and stress-skin panels. Design specifications for plywood scarf joints have been available for decades. Corresponding information on oriented strandboard (OSB) is not yet available despite its status as a suitable alternative to plywood as a structural panel product. This project was conducted to provide such design information. Three hundred joints were fabricated and tested in tension in a dry condition. These included two nominal thicknesses of OSB (11 mm and 18 mm) from two manufacturers. The adhesive used for the joints was a resorcinol formaldehyde. The joint strengths were compared with the material strengths in tension. The results showed that optimum joint strength was reached when the scarf slope was about 1 in 7 irrespective of manufacturer and thickness. At the optimum joint slope, no loss of strength was observed compared with unjointed material. For slopes less than the optimum slope, normalized joint strength decreased slightly. As the scarf slope increased from the optimum value, normalized joint strength decreased to a value of about 0.35 for a vertical scarf (butt) joint

Load-Embedment Response of Timber to Reversed Cyclic Load

One of the most important properties governing performance of timber joints containing dowel-type fasteners is the embedment response of wood under the action of a loaded fastener. Previous investigations on load-embedment behavior of wood focused almost exclusively on monotonic loading condit ons. This paper describes a program of work to investigate the influence of wood density, fastener diameter, and loading characteristics on stiffness properties, ultimate strength, and strength degradation of load-embedment response of wood-based material when subjected to reversed cyclic loads. Mathematical functions were developed to describe both the envelope and hysteresis loops of the load-embedment response. A comparison of the model parameters reveals that initial stiffness and ultimate load increase with loading rate, wood density, and fastener diameter. Strength degradation occurs under both monotonic and cyclic loading for solid wood. The degree of strength degradation increases with any increase in loading rate, wood density, and fastener diameter, and presence of preloading history. No strength degradation occurs in plywood under either monotonic or reversed cyclic load

Managing stormwater with low impact development in highly urbanized areas

2014 is the 25th Anniverssary of the Drainage Services Department (DSD) of the HKSAR GovernmentPaper A2-2Low impact development (LID) implements small-scale hydrologic controls throughout a catchment to replicate the pre-development hydrologic regimes or in other terms control stormwater as close to the source as possible. Examples of such controls include green roofs, bioretention swales, rain gardens, porous pavements. This project evaluates the effectiveness of large-scale LID implementation in Singapore and Hong Kong. We examine the hydrologic impacts, namely peak discharge mitigation and baseflow restoration, under different land uses, rainfall conditions and LID strategies. For further comparison, we adopt an integrated distributed hydrological model for Singapore and a lumped hydraulic model for Hong Kong. Studies of both Singapore and Hong Kong suggest that LID is effective if there is substantial level of infrastructures (e.g., covering 5 to 10% of catchment area). LID is more efficient in reducing/delaying peak discharge and restoring baseflow on an average long term basis. However, its performance, particularly in peak discharge mitigation, diminishes during design storms (e.g., ARI of 5 years). In terms of modeling techniques, integrated distributed hydrologic models require extensive parameterization but can accurately simulate some important processes (e.g., increase of infiltration and restoration of baseflow) that are simplified in lumped hydraulic models. Overall, large-scale LID potentially provides more sustainable stormwater management but its success depends on factors such as design objectives, existing land uses and drainage networks. We should therefore further research to increase the feasibility of large-scale LID in highly urbanized areas such as Singapore and Hong Kong.postprin

Symmetric-Asymmetric transition in mixtures of Bose-Einstein condensates

We propose a new kind of quantum phase transition in phase separated mixtures of Bose-Einstein condensates. In this transition, the distribution of the two components changes from a symmetric to an asymmetric shape. We discuss the nature of the phase transition, the role of interface tension and the phase diagram. The symmetric to asymmetric transition is the simplest quantum phase transition that one can imagine. Careful study of this problem should provide us new insight into this burgeoning field of discovery.Comment: 6 pages, 3 eps figure