> 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/openbrimfea/properties-fea/rebars-fea.md). # Rebars \[FEA] A Rebar defines a reinforcing bar size — its diameter, cross-sectional area and weight per unit length. It is a **property library** entry: it describes a bar, it does not place one. Bars are placed by section definitions and reinforcement layouts that reference this entry by name. Rebars can be imported from the built-in database (which carries standard bar designations) or defined by hand for a size the database does not cover. Rebar entries are used for **design and section analysis** — capacity checks, cracked-section properties, and reinforcement reporting. They do not create finite elements and, on their own, add nothing to the global stiffness or mass matrices. ## Properties **Diameter:** The nominal bar diameter. *Engineering influence.* Diameter drives cover and spacing checks, development and lap lengths, and the bend radii used in detailing. It also determines whether a given bar arrangement physically fits within the section — a layout that clears on paper with an understated diameter may be unbuildable. It does not by itself set the bar's contribution to capacity; that comes from the area below. Diameter and area should be **consistent** with one another. Because both are entered independently, nothing forces `A ≈ πD²/4`, and an inconsistent pair produces a section whose reported steel area does not match the bar sizes shown in the detailing. **Area:** The cross-sectional area of one bar. *Engineering influence.* This is the value that actually reaches the analysis. Flexural and axial capacity scale essentially linearly with total steel area, so an error here propagates directly into every capacity check that uses the bar. It also feeds cracked-section and section-analysis calculations, where the steel area governs the neutral-axis position and the stiffness after cracking. For standard designations, use the published nominal area rather than the geometric area computed from the nominal diameter — for deformed bars the two differ slightly and codes are written against the nominal area. Increasing the area increases capacity and, in a section analysis, moves the neutral axis toward the steel. A value of zero means the bar contributes nothing, which will show up as an unreinforced section rather than as an error. **Weight:** Weight per unit length of the bar. *Engineering influence.* This is used for **quantity reporting** — reinforcement schedules and material take-offs — not for structural behaviour. The self-weight of reinforcement is normally already inside the reinforced-concrete unit weight assigned to the concrete material, so this value does not add mass or load to the analysis. Setting it wrong affects quantities and cost, not forces. ## Verification * Cross-check diameter against area: for a standard bar, `A` should be close to `πD²/4`. A large discrepancy means one of the two was entered in the wrong unit or from the wrong row. * Compare the entry against the published table for the designation you intend to use. * Open a section that references the bar and confirm the reported total steel area equals bar area × bar count. * Check that the reinforcement is drawn at the expected size in the section view — a diameter error is usually visible immediately. * Confirm a capacity check moves in proportion when the bar count is changed, which validates that the area is being picked up. ## Common mistakes * **Inconsistent diameter and area**, most often from editing one and not the other after copying an existing entry. * **Entering the area of a bar group** rather than of a single bar, multiplying the reinforcement by the bar count. * **Mixing unit systems** — a metric bar diameter with an imperial area — which produces capacities wrong by a large factor while still looking like a plausible number. * **Defining a duplicate entry** for a bar that already exists in the database, then editing only one of the two and wondering why some sections changed and others did not. * **Expecting the Weight value to add load to the model.** It is for reporting only. --- # Agent Instructions This documentation is published with GitBook. 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