Effects of lift-up building design, building setback, and urban open space on pedestrian danger under the joint effect of floodwater and wind

Abstract

Urban block layouts affect both the flow patterns of floodwater and wind in urban built environments and ultimately pedestrian danger within the urban building array. Computational fluid dynamics (CFD) is used to simulate both the floodwater inundation process and the wind-blowing process within three kinds of urban block configurations under a floodwater-wind joint effect, including the lift-up building design, horizontal and vertical building setbacks, and urban open space. The obtained floodwater velocity, depth, and wind speed at the pedestrian level are adopted to quantify the level of pedestrian danger by using the instability threshold formula of a human body. A laboratory flume experiment regarding the stability/instability of a dummy that represents a pedestrian in a quasi-natural state is performed to qualitatively validate the numerical simulation results. Compared to the cuboid or triangular pillar that supports the lift-up building structure, the circular pillar yields the minimum resistance against floodwater and increases the wind speed at the pedestrian level, consequently leading to a large danger zone area. Horizontal building setbacks decrease the pedestrian danger, but vertical building setbacks intricately affect it. The existence of open space within the block decreases pedestrian danger to some extent depending on the location and area of open space. The wind plays the dominant role in triggering pedestrian instability for both the lift-up building design and the horizontal setback case. For both the lift-up building design and the open space configuration, the walking and running speeds of pedestrians decrease much more than the conventional urban block. The results of this study could be referred to by administrators and stakeholders in the design and management of urban building arrays to mitigate pedestrian risk in the content of resilient city management.