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• The role of openings in the flood impact on a porous building is identified. • The front and back doors affect the flow field and the longitudinal impact force. • The back door controls the outflow but does not affect the longitudinal impact force. • The side window has a complex effect on the lateral exchange discharge. It becomes necessary to identify the role of openings in the impact of floods on porous buildings to better set up effective strategies for people security within buildings and implement engineering measures for building safety. In this study, a 3D numerical model is applied to identify the role of openings in the impact of a dam-break-induced flood on a porous building under different opening configurations, including different porosities of the front and back walls, various porosities of the back wall and various positions and sizes of the side window. (i) An increasing size of the front and back doors leads to a reduced maximum water level upstream of the building and a reduced area of the wake zone behind the back wall; the maximum longitudinal impact force significantly decays with the porosity in terms of a quadratic function form. (ii) A variation in the size of the back door plays a role in controlling the outflow discharge of floodwater from the building; however, it yields no clear difference in the resultant longitudinal impact force. (iii) In the short-term, the presence of the side window plays no clear role in affecting the flow field around the building; however, in the moderate timeframe, there is a clear lateral exchange: the positions of the side windows play a clear role, whereas the size of the lower side window seems to be less important; the existence of the side window greatly decreases the lateral impact force, especially for the lower sidewall. These results are of value to better understand the physical mechanism of the impact process on a porous building for implementing tailored measures for people security and structural safety. [ABSTRACT FROM AUTHOR]

• The role of openings in the flood impact on a porous building is identified. • The front and back doors affect the flow field and the longitudinal impact force. • The back door controls the outflow but does not affect the longitudinal impact force. • The side window has a complex effect on the lateral exchange discharge. It becomes necessary to identify the role of openings in the impact of floods on porous buildings to better set up effective strategies for people security within buildings and implement engineering measures for building safety. In this study, a 3D numerical model is applied to identify the role of openings in the impact of a dam-break-induced flood on a porous building under different opening configurations, including different porosities of the front and back walls, various porosities of the back wall and various positions and sizes of the side window. (i) An increasing size of the front and back doors leads to a reduced maximum water level upstream of the building and a reduced area of the wake zone behind the back wall; the maximum longitudinal impact force significantly decays with the porosity in terms of a quadratic function form. (ii) A variation in the size of the back door plays a role in controlling the outflow discharge of floodwater from the building; however, it yields no clear difference in the resultant longitudinal impact force. (iii) In the short-term, the presence of the side window plays no clear role in affecting the flow field around the building; however, in the moderate timeframe, there is a clear lateral exchange: the positions of the side windows play a clear role, whereas the size of the lower side window seems to be less important; the existence of the side window greatly decreases the lateral impact force, especially for the lower sidewall. These results are of value to better understand the physical mechanism of the impact process on a porous building for implementing tailored measures for people security and structural safety. [ABSTRACT FROM AUTHOR]