The design and calculation of overflow orifice of building roof is related to the safety of roof structure.The overflow flow calculation formulas of the square wall overflow orifice in the existing national norms are analyzed and compared.Through the analysis and deduction of different hydraulic weir flow forms,the basic calculation formulas of broad crested weir,the flow coefficient and the side shrinkage coefficient,it is concluded that the overflow orifice geometric size calculated according to the existing normative formula is smaller.Combined with the requirements of different roof drains on the water depth before the drain and the different drainage forms of building roof,it is proposed that the wall square overflow orifice belongs to the broad crested weir,and the value range of the overflow water level height of the overflow orifice and the height of the upstream wall is defined,and then a new calculation formula of the overflow flow of the roof square overflow orifice is introduced by using mathematical tools,and the rationality of the new formula is analyzed from the hydraulics and mathematical perspectives,which can be used as a reference for design colleagues.
overflowbroad crested weirflow coefficienthead of water