A box culvert must be checked for multiple limit states. The critical cases usually involve:
For a fixed-end frame, the negative moment at the top-slab end is ( M_Ed = q L^2 / 12 = 115.16 \times 3^2 / 12 = 86.37 ) kNm/m. Using a concrete cover of 50 mm, effective depth ( d = 250 - 50 - 10 = 190 ) mm. For C30/37 (( f_cd = 20 ) N/mm²) and B500C (( f_yd = 435 ) N/mm²), the required reinforcement area ( A_s ) is found via: box culvert design calculations eurocode 2021
$$d = h - c - \phi/2 = 350 - 50 - 8 = 292 \text mm$$ A box culvert must be checked for multiple limit states