Floor Beam Load Rating (LFD) [TB]

Performs an AASHTO Load Factor Rating (LFR) for an individual floor beam 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. Because a floor beam frequently governs in shear rather than flexure, the object scans several stations along the member and reports the governing (worst) rating factor. Live-load effects reach the floor beam through the transverse influence-surface wheel-line distribution from the deck (not a longitudinal beam-line truck). The object pulls its load factors and live-load stages from a Floor Beam 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

Floor Beam: Pick the floor beam to rate. The floor beam's section properties and span are used for the capacity calculations, and its composite element name is used to extract the moment and shear envelopes from the analysis. The user must provide a value.

Load Rating Template: Pick the Floor Beam 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.

Rating Location [Auto (Governing)/Specific Location]: Selects how the rating station is chosen. Auto (Governing) scans several evenly-spaced stations along the floor beam and automatically rates the worst (lowest-rating) station. Specific Location rates a single user-chosen location along the member.

Location Type [Relative (0-1)/Distance From Right]: How the specific location is interpreted, always measured from the right support. Relative (0-1) is a fraction of the span (0.5 = midspan, 0 = right support). Distance From Right is a length measured from the right support along the beam. Available when Rating Location is Specific Location.

Rating Location (Relative 0-1, or Distance from right): The location at which to rate the floor beam — a 0–1 fraction or a length, depending on Location Type. Available when Rating Location is Specific Location.

Number of Force-Extraction Stations: How many evenly-spaced stations are sampled along the floor beam when scanning for the governing rating (Auto mode). The extraction always includes the two ends and the midspan, so the minimum is 3 (start / mid / end); values below 3 are clamped up to 3. Increase it for a finer scan — for example, to catch concentrated stringer reactions at interior panel points. Available when Rating Location is Auto (Governing).

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 page).

Override

Override Section [Yes/No]: By default the rating uses the floor beam's first (usual midspan) section. Set this to Yes to rate a user-picked section instead — useful for a variable-section floor beam 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. For a floor beam L is its own span (girder-to-girder), computed from the model by default. 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 floor beam's own span, automatically determined from the model geometry, used for the impact factor when the override is No. (Read-only)