> 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/truss-bridge-workflow/load-rating-tb/girder-load-rating-tb.md).

# Girder Load Rating (LFD) \[TB]

Performs an AASHTO Load Factor Rating (LFR) for an individual girder of the truss bridge, using LFD capacities from the AASHTO Standard Specifications (flexure per Article 10.48, shear per Article 10.48.8) and rating per the Manual for Bridge Evaluation Part 6B. Positive- and negative-moment capacities are evaluated separately for a continuous girder, and the composite deck section is used for the positive-moment section modulus. The object pulls its load factors and live-load stages from a Girder Load Rating (LFD) template and reports Inventory and Operating ratings for Design (HS-20), Legal, Emergency, and Permit live loads defined on the Load Rating Combination Table (LFD).

## General

**Girder:** Pick the girder to rate. The girder's section properties and length are used for the capacity calculations, and its element name is used to extract the analysis results (moment and shear envelopes) from the staged model. The user must provide a value.

**Load Rating Template:** Pick the Girder Load Rating (LFD) template that holds the generic inputs — the LFR load factors (A1 dead, A2 inventory/operating) and the Design, Legal, Emergency, and Permit live-load stages. All global rating settings come from this template.

**Station:** The station along the girder where the rating is performed. Positive- and negative-moment demands are read at this station, so set it to the critical location for the check (typically midspan for positive moment or over a support for negative moment).

**Check For \[All/Flexure Only/Shear Only]:** Selects which limit states are rated. *All* rates both flexure and shear and reports the smaller (governing) rating factor. *Flexure Only* and *Shear Only* restrict the rating to a single effect and hide the other's cells and report section.

**PDF Name (Export):** Name used when the load-rating report is saved as a PDF. When renaming, avoid characters that interfere with parametric equations (see the [Illegal Characters](https://docs.openbrim.org/faq/general/faq-illegal-chars) page).

## Override

**Override Section \[Yes/No]:** By default the rating uses the girder's governing cross-section. Set this to *Yes* to rate a user-picked section instead — useful for a variable-section girder where the critical section differs from the default.

**Cross Section:** The section used for the capacity calculation when Override Section is *Yes*. The user must provide a value when the override is active.

**Override Span Length for Impact Factor \[No/Yes]:** The impact (dynamic load allowance) factor I = 50/(L+125) ≤ 0.30 depends on the loaded length L. By default L is the girder's own span, computed from the model. Set this to *Yes* to enter L manually.

**Span Length L:** The loaded length used in the impact formula when the impact-span override is *Yes*. Available when Override Span Length for Impact Factor is *Yes*.

**Computed Span Length L (readonly):** The span length automatically determined from the girder geometry, used for the impact factor when the override is *No*. (Read-only)

**Override Unbraced Length for LTB \[No/Yes]:** The lateral-torsional buckling (LTB) check (AASHTO Std Spec 10.48.4.1) needs the unbraced length L\_b of the compression flange (the cross-frame spacing). By default L\_b is computed from the girder's bracing. Set this to *Yes* to enter L\_b manually.

**Unbraced Length L\_b:** The compression-flange unbraced length used for the LTB check when the unbraced-length override is *Yes*. Available when Override Unbraced Length for LTB is *Yes*.

**Computed Unbraced Length L\_b (readonly):** The unbraced length automatically determined from the girder's cross-frame spacing, used for the LTB check when the override is *No*. (Read-only)


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