Physical vulnerability of pedestrians under the joint effect of wind and floodwater and its application in urban block flooding: Effects of urban block layout, building form and building array skyline

It has become urgent to formulate the physical vulnerability of pedestrians exposed to the compound hazard of strong wind and flooding in an urban landscape and identify the pedestrian risk characteristics within urban building arrays. In this study, the physical vulnerability of pedestrians subject to a joint effect of wind and floodwater is quantified theoretically based on a mechanical analysis in terms of floodwater velocity, depth and wind speed. Laboratory experiment regarding the instability of a dummy is performed to calibrate this vulnerability formula. The formula is adopted to quantify the pedestrian risk rating within different urban building array configurations in conjunction with computational fluid dynamics simulation, including the urban block layout, building form, and building array skyline. It is found that (i) the reverse wind reduces the area of the extreme instability risk zone of pedestrians but improves the safety zone area in comparison to the forward wind; (ii) in comparison to the determinant layout, the enclosed layout is indeed favorable to pedestrian safety; however, the staggered layout causes pedestrian safety to deteriorate; (iii) either corner modification or a change in building form leads to a large reduction in pedestrian risk; and (iv) For a parallel building skyline array, a low street aspect ratio (i.e., the ratio of building height to street width) yields an increased pedestrian risk when the aspect ratio is smaller than unity; however, a large aspect ratio produces an increased pedestrian risk when the aspect ratio exceeds unity. The protuberant skyline leads to more high-risk zones than the parallel skyline, while a concave skyline does not alter the risk distribution except for the last row of buildings. The ascending skyline configuration leads to a more complex and more uniform risk distribution pattern, while the descending skyline does not change the general risk distribution trend. These results might be referenced by engineers and managers to implement tailored measures (for example, optimizing urban array configurations) for mitigating and reducing pedestrian risk in urban regions.