The closely-spaced tall buildings in modern cities induce a great blockage to wind that penetrate into the cities and subsequently impede wind circulation close to the ground. High building porosity at lower heights thus becomes a new requirement for building design in congested cities. The ‘lift-up’ design, which has the main structure of the building is elevated from the ground using columns, shear walls, or a central core, or a combination of them would be a fitting solution that complies with the design guidelines without losing valuable floor area at the ground level. The void underneath including the main structure, commonly known as the ‘lift-up’ area can be used as a parking space, a sitting area, or lay access roads to nearby buildings and sites. Despite its benefits, the ‘lift...[ Read more ]

The closely-spaced tall buildings in modern cities induce a great blockage to wind that penetrate into the cities and subsequently impede wind circulation close to the ground. High building porosity at lower heights thus becomes a new requirement for building design in congested cities. The ‘lift-up’ design, which has the main structure of the building is elevated from the ground using columns, shear walls, or a central core, or a combination of them would be a fitting solution that complies with the design guidelines without losing valuable floor area at the ground level. The void underneath including the main structure, commonly known as the ‘lift-up’ area can be used as a parking space, a sitting area, or lay access roads to nearby buildings and sites. Despite its benefits, the ‘lift-up’ design has been rarely adopted for buildings because high-speed wind jets commonly found in voids underneath building threaten the safety of pedestrians. However, this conclusion was derived from the data obtained for the passage underneath building, which is not geometrically similar to the ‘lift-up’ design. It is, therefore, reasonable to assume that the lack of knowledge in pedestrian-level wind (PLW) field in the ‘lift-up’ area, and the insufficient understanding of key design parameters prevent adopting the ‘lift-up’ design for buildings. This study aims to fulfil the gap between the existing and required knowledge on designing ‘lift-up’ buildings by conducting extensive experiments and simulations and comprehensively analyzing data. There were 28 ‘lift-up’ buildings with a central core design tested in a Boundary Layer Wind Tunnel (BLWT) and Computational Fluid Dynamic (CFD) simulations. The buildings have different heights (H), and widths (W) for the main structure, and various heights (h), widths (w), depths (d), and corner shapes for the central core. The results of the analysis reveal a strong positive correlation between H and the maximum wind speed in the ‘lift-up’ area where the magnitude of the maximum wind speed slightly decreases with the increase of h. Large plan areas (w × d) of the central cores swell the area with low wind speeds but those are reduced if the central core is tall. The wind tunnel experiments indicate that the ‘lift-up’ design is more suitable for short and wide buildings compared to those adopted for tall and slender buildings. However, corner modifications can be added to the central core of tall and slender buildings in order to improve the wind conditions in the ‘lift-up’ area. The rounded corners exhibit great promise in reducing area with low wind speeds while the recessed corners are moderately effective in reducing both high and low wind speeds. The corner modifications are advantageous if the wind approaches at 0°, which is found to be the critical wind direction for evaluating PLW fields near ‘lift-up’ buildings. The 2-D and 3-D flow fields’ data obtained from the CFD simulations and the Particle Image Velocimetry (PIV) indicated that wind circulation in the lower part of the building and in the ‘lift-up’ area is significantly modified and subsequently created smaller areas of low wind speeds and larger areas with acceptable wind speeds compared to those near a similar building without the ‘lift-up’ design. The data of 28 ‘lift-up’ buildings were used to develop a second-order, nonlinear, multi-regression model that can predict the area with acceptable wind speeds considering all key design parameters of a ‘lift-up’ building. The model suggests designing the central core with its height limited by the ratio of H/h less than 30, and its aspect ratio (h/w) is limited to less than 0.6.