AbstractUnderstanding the flood impact dynamics on buildings is still a major challenge, especially considering the built environment. Motivated by the problem of the flood-structure interaction, this study experimentally measured loading conditions onto three-dimensional buildings to investigate flood loading mechanisms considering the shadowing effect. A total of 162 scenarios concerning different values of the initial impoundment depth (Hi), aspect ratio of the front building (α), relative longitudinal spacing (λ), and orientation of the front building (θ) were undertaken. Both flood loading mechanisms with and without considering the shadowing effect were discussed elaborately. Results showed that the existence of the front building leads to a dramatic change in flow regime upstream of the rear building, and the shadowing effect highly depends on the development of the flood flow reconstruction. In addition, the shadowing index ηF was introduced, and it was more sensitive to λ than α and θ. When the λ was less than 3.5, relative optimal values of θ were 50°, 45°, and 0° for the scenarios with α=0.5, α=1.0, and α=1.5, respectively. There was a negative dependence of the flood hazard level on the shadowing index. Besides, the modified formula of the maximum flood impact force considering the shadowing effect and fitting formulas between λ and ks were obtained. This research supports the study of flood loading mechanisms and is beneficial to the plan and design of safer building clusters.