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It is difficult to describe the flow characteristics within and above urban canopies using only geometrical parameters such as plan area index (λ p ) and frontal area index (λ f ) because urban surfaces comprise buildings with random layouts, shapes, and heights. Furthermore, two types of 'randomness' are associated with the geometry of building arrays: the randomness of element heights (vertical) and that of the rotation angles of each block (horizontal). In this study, wind-tunnel experiments were conducted on seven types of urban building arrays with various roughness packing densities to measure the bulk drag coefficient (C d ) and mean wind profile; aerodynamic parameters such as roughness length (z o ) and displacement height (d) were also estimated. The results are compared with previous results from regular arrays having neither 'vertical' nor 'horizontal' randomness. In vertical random arrays, the plot of C d and z o versus λ f exhibited a monotonic increase, and z o increased by a factor of almost two for λ f = 48-70%. C d was strongly influenced by the standard deviation of the height of blocks (σ ) when λ p ≥ 17%, whereas C d was independent of σ when λ p = 7%. In the case of horizontal random arrays, the plot of the estimated C d against λ f showed a peak. The effect of both vertical and horizontal randomness of the layout on aerodynamic parameters can be explained by the structure of the vortices around the blocks; the aspect ratio of the block is an appropriate index for the estimation of such features.

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In the composite industry, natural fibres have great potential to replace synthetic fibres like carbon and glass, due to their low cost and environmentally friendly materials. Bamboo is emerging as a versatile reinforcing fibre candidate because this woody plant has a number of advantages, such as being naturally strong, biodegradable and abundantly available. In this study, a compression test with a crosshead displacement rate of 1 mm/min was conducted on square and triangular honeycomb core structures based on bamboo-epoxy composites so as to study their specific energy absorption. Both square and triangular honeycomb structures were manufactured by the slotting technique. Initially, a tensile test with the same crosshead displacement rate was conducted to study the tensile strength of unidirectional bamboo-epoxy composites with 0°, 45° and 90° fibre orientations. Bamboo-epoxy composite laminates were fabricated by applying a hand lay-up technique. The experimental data showed that the unidirectional bamboo-epoxy composite with 0° orientation offered the highest tensile strength. This indicates that the bamboo is stronger when parallel to the tensile axis. Meanwhile, the triangular honeycomb bamboo-epoxy structure offered about 10% more energy absorption than the square honeycomb structure, which indicates that the smaller cell size of honeycomb is able to absorb more energy than the bigger one.