Effects of building configuration and upstream buildings on pedestrian risk around ideal buildings in a floodwater-wind joint environment

Urban building affects both floodwater inundation and air flow in high-density cities, influencing the pedestrian risk within urban blocks. Previous studies have identified physical characteristics of buildings as important factors influencing either floodwater spread or the wind environment. However, the correlation between the building configuration and pedestrian risk under the combined effect of floodwater and wind is not yet fully understood. This study estimates the integrated effects of building configuration and an upstream building on the pedestrian risk around ideal buildings in a joint floodwater-wind environment. Computational fluid dynamics (CFD) simulations are performed to model the inundation depth, floodwater velocity, and wind speed at pedestrian level for single- and double-building models. The pedestrian risk in terms of the toppling instability is evaluated, and a series of laboratory flume experiments on the stability/instability of a dummy representing pedestrians in a quasi-natural state are conducted to validate the CFD simulation results. The findings show that the building configuration affects the pedestrian risk to some degree; however, the building height yields a minor effect and converging and diverging flows lead to different pedestrian risk distributions within the area of interest. Floodwater always plays a dominant role over wind in triggering pedestrian toppling, and pedestrian evacuation speeds vary depending on the circumstances. When an upstream building is added, its distance from the target building, length, and the reduced ratio relative to the reference case, as well as the interspace between its segments, influence the pedestrian risk; however, the height of the upstream building has the smallest effect on the pedestrian risk response. The study outcome can provide insights for administrators and stakeholders when implementing tailored measures against direct impacts of surging floodwater and strong wind in the context of resilient city management.