> For the complete documentation index, see [llms.txt](https://docs.openbrim.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.openbrim.org/templates/box-culvert-workflow/code-check-bc/culvert-code-check-bc.md). # Culvert Code Check \[BC] The Culvert Code Check designs the culvert's reinforcement against AASHTO LRFD Section 12 and the Section 5 provisions it invokes. It extracts the forces at the barrel's design cuts, applies the reinforcement entered below, and reports a demand-to-capacity ratio for every check at every member. Members are derived from the section rather than fixed: a culvert with interior webs is checked as top slab, bottom slab, two exterior walls and one check per interior web. Each member is checked at midspan and at the face of the supporting member, for: * **Flexure** — 12.11.3 and 12.10.4.2.4a, with the resistance factors of Table 12.5.5-1 * **Shear** — 5.12.7.3, at the critical section * **Crack control** — 12.11.4 with C12.11.4-1, and 5.6.7 * **Minimum reinforcement** — 12.11.5.3 and 5.6.3.3 Fatigue is not checked: 5.5.3.1 exempts buried components with more than 3 ft of fill from a fatigue investigation. ## General **Box Culvert:** The culvert barrel to check. A selection is required. The member list, the section dimensions and the concrete strength all come from this barrel and its section. **Load Combination Table:** The table of factored combinations the demands are taken from. Strength I governs the flexure, shear and minimum reinforcement checks; Service I governs crack control. **Construction Type \[Cast-in-Place/Precast]:** Which set of resistance factors from AASHTO Table 12.5.5-1 applies. Precast box culverts are allowed higher flexural and shear factors than cast-in-place ones. **Exposure Condition Class \[Class 1/Class 2]:** The crack-control exposure class of 5.6.7. Class 1 is the ordinary case; Class 2 applies where appearance or corrosion concerns demand tighter crack widths and reduces the allowable reinforcement spacing accordingly. **Include Axial Thrust in Flexure and Crack Control \[No/Yes]:** Whether the axial thrust in the frame is combined with the moment. A closed box frame carries real thrust, and including it generally increases the flexural capacity while tightening the crack check. No checks the section in pure flexure, which is the simpler and usually more conservative reading. **Concrete Density Modification Factor:** The λ factor of 5.4.2.8, applied to the concrete tensile terms. Use 1.0 for normal-weight concrete, and the reduced values of that article for lightweight. **Design Strip Width:** The width of barrel the check is performed on. A box culvert is designed as a one-way frame per unit width, so the forces are extracted and the reinforcement is specified over this strip. Use a unit width unless there is a reason to design over a wider band. ## Reinforcement Reinforcement is entered per member and per location — midspan and end for each slab, mid-height and end for the walls — because the moment reverses between them and the bars are on opposite faces. Both exterior walls take the same reinforcement. **Reinforcement Material:** The steel used for all the bars below. Its yield strength drives every flexural and crack-control result. **Top Slab Midspan Rebar:** Bar size for the top slab at midspan, resisting the positive moment on the bottom face. **Top Slab Midspan Rebar Spacing:** Centre-to-centre spacing of those bars. Crack control limits this spacing, so it is often the input that governs rather than the bar size. **Top Slab Midspan Clear Cover:** Clear cover to those bars, measured from the concrete face. It sets the effective depth and enters the crack-control calculation directly. **Top Slab End Rebar:** Bar size for the top slab at the wall face, resisting the negative moment on the top face. **Top Slab End Rebar Spacing:** Centre-to-centre spacing of those bars. **Top Slab End Clear Cover:** Clear cover to those bars. **Bottom Slab Midspan Rebar:** Bar size for the bottom slab at midspan. **Bottom Slab Midspan Rebar Spacing:** Centre-to-centre spacing of those bars. **Bottom Slab Midspan Clear Cover:** Clear cover to those bars. The bottom slab usually needs more cover than the top, since it is cast against the bedding. **Bottom Slab End Rebar:** Bar size for the bottom slab at the wall face. **Bottom Slab End Rebar Spacing:** Centre-to-centre spacing of those bars. **Bottom Slab End Clear Cover:** Clear cover to those bars. **Wall Mid-Height Rebar (Both Walls):** Bar size at mid-height of the exterior walls, resisting the moment from lateral earth pressure and surcharge. **Wall Mid-Height Rebar Spacing:** Centre-to-centre spacing of those bars. **Wall Mid-Height Clear Cover:** Clear cover to those bars. **Wall End Rebar (Both Walls):** Bar size at the wall ends, where the wall frames into the slabs and the moment reverses. **Wall End Rebar Spacing:** Centre-to-centre spacing of those bars. **Wall End Clear Cover:** Clear cover to those bars. --- # Agent Instructions This documentation is published with GitBook. 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