$$A_s = \fracM_u\phi \cdot f_y \cdot (d - a/2)$$
A professional-grade design spreadsheet typically includes the following features: Culvert worksheet.xls box culvert design calculations xls link
A standard design spreadsheet typically automates the following calculations: Box Culvert Design Spreadsheet - The Engineering Community $$A_s = \fracM_u\phi \cdot f_y \cdot (d -
“Can anyone share a link to download a free box culvert design calculations xls that includes both hydraulic sizing and reinforcement design per AASHTO LRFD 9th edition?” box culvert design calculations xls link