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The UN estimate 2.5 billion new urban residents by 2050, thus further increasing global greenhouse gases (GHG) emissions and energy demand, and the environmental impacts caused by the built environment. Achieving optimal use of space and maximal efficiency in buildings is therefore fundamental for sustainable urbanisation. There is a growing belief that building taller and denser is better. However, urban environmental design often neglects life cycle GHG emissions. Here we offer a method that decouples density and tallness in urban environments and allows each to be analysed individually. We test this method on case studies of real neighbourhoods and show that taller urban environments significantly increase life cycle GHG emissions (+154%) and low-density urban environments significantly increase land use (+142%). However, increasing urban density without increasing urban height reduces life cycle GHG emissions while maximising the population capacity. These results contend the claim that building taller is the most efficient way to meet growing demand for urban space and instead show that denser urban environments do not significantly increase life cycle GHG emissions and require less land.

This paper presents the experimental and analytical studies to investigate the effect of concentrated butt-joints on the flexural properties of laminated bamboo-timber flitch beam (BTFB, or bio-flitch beam). The experimental results reveal that the concentrated butt-joints significantly reduce the flexural strength of the BTFB. They also suggest that the failure mechanism of the BTFB with or without concentrated butt-joints are completely different but less evidence shows an obvious effect of the butt-joints on the modulus of elasticity in bending. In addition, laminated bamboo lumber with concentrated butt-joints is found to be unsuitable for structural applications. The analytical predictions are in close agreement with the experimental results that demonstrate the potentials of the proposed analytical model as a forensic investigation instrument to estimate the strength reduction of the structure, if the butt-jointed laminated bamboo was, unfortunately, used in construction.

This paper presents the experimental and analytical studies to investigate the impact of concentrated laminated bamboo butt-joints on the flexural properties of vertically laminated bamboo-timber hybrid beams (VLHBs, or flitch beam). The experimental results reveal that the concentrated butt-joints significantly reduce the flexural strength of the VLHB. They also suggest that the failure mechanism of the VLHBs with or without concentrated butt-joints are completely different. In addition, laminated bamboo lumber with concentrated butt-joints was found to be unsuitable for structural applications. The analytical estimations show close agreement with the experimental results. However, due to the layout of the sample VLHB, the experimental study cannot confirm the impact of the butt-joints on the modulus of elasticity in bending.