Girder Load Rating (LRFR) [TB]

The girder load rating template collects the inputs that stay constant across every girder load rating station — the mapped strength and service load rating combinations, the condition and system factors, the modular ratio, construction type, span definition, and the Appendix B6 preference. Each individual girder load rating object (under the Load Rating section) points at one template, so these values do not have to be repeated at every station.

General

Strength (Load Rating Combination): The load rating combination table serves as the basis for all finite element analysis results used in the load rating equations. Pick the Load Rating Combination Table that maps the analysis result cases and their load factors for the strength limit state. The user must provide a value.

Service (Load Rating Combination): The load rating combination table serves as the basis for all finite element analysis results used in the load rating equations. Pick the Load Rating Combination Table that maps the analysis result cases and their load factors for the service limit state. The user must provide a value.

Condition Factor: Condition factor φc per AASHTO MBE Article 6A.4.2.3, based on the condition state of the member per the most recent inspection report. Typical values: 1.00 for good or satisfactory condition, 0.95 for fair condition, and 0.85 for poor condition. The value must be greater than zero for a rating factor to be computed.

System Factor: System factor φs per AASHTO MBE Article 6A.4.2.4, reflecting the level of redundancy of the superstructure system. Typical values from MBE Table 6A.4.2.4-1 range from 0.85 for non-redundant members to 1.00 for redundant multi-girder bridges. The default is 1.0, and the value must be greater than zero.

Modular Ratio Comp. Method [EsbyEc/User Input]: Selects how the modular ratio n used for the composite section properties is obtained. EsbyEc computes n as the elastic modulus of the steel divided by the elastic modulus of the deck concrete. User Input uses the value entered in Modular Ratio.

Modular Ratio: The modular ratio n used in the transformed composite section calculations when Modular Ratio Comp. Method is User Input (default 8). It must be greater than zero. Available when Modular Ratio Comp. Method is User Input.

[Yes/No] Include Haunch for Section Properties?: Depending on owner (DOT) requirements, the haunch area may or may not be included in the section property computations. Including the haunch increases the moment of inertia and section modulus and decreases the computed stresses, which is less conservative. When set to No, the haunch dimensions are still used to locate the deck relative to the girder.

Type of Construction [Shored Construction/Unshored Construction]: For steel I-girder bridges, unshored construction is most common. With Unshored Construction, permanent load applied before the concrete deck has hardened or become composite is carried by the steel section alone, while permanent load and live load applied afterwards are carried by the composite section. With Shored Construction, all permanent load is assumed to be applied after the deck has become composite; this assumption should be stated in the contract documents.

Use Deck Rebar in Plastic Mom. Calc. (Pos. Flex.) [Yes/No]: Controls whether the deck reinforcement forces (Prt and Prb) are included when computing the plastic moment for positive flexure. When set to Yes, the deck reinforcement contributes to the plastic moment capacity; when set to No, it is conservatively neglected.

Support Lines for Span Definition [All/Selection]: Specifies which support lines define the spans of the girder, which in turn determines whether the girder is treated as simple or continuous. All uses every support line associated with the girder. Selection uses only the support lines listed in Selected Support Lines.

Selected Support Lines: The Support Lines used to define the spans when Support Lines for Span Definition is Selection. Pick them from the model; only the selected support lines are used for span computation.

Appendix B6

AASHTO Appendix B6 provides an optional, simplified approach for calculating the redistribution moments from the interior-pier sections of continuous-span I-section flexural members at the service and strength limit states. It uses elastic moment envelopes and does not require an inelastic analysis; the restrictions of Article B6.2 ensure adequate ductility and robustness at the interior-pier sections.

[Yes/No] Use Appendix B6 Provisions?: When set to Yes, the girder load rating objects that use this template expose their Appendix B6 inputs (redistribution moments at supports and the adjacent-section stations). The load rating internally verifies the additional B6.2 requirements and applies the provisions only where all conditions are met, reporting the redistribution moment (ΔMrd) at each qualifying support station for the strength and service limit states.