> 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-lrfr-tb.md). # Girder Load Rating (LRFR) \[TB] Performs an AASHTO Load and Resistance Factor Rating (LRFR) per the Manual for Bridge Evaluation (MBE) Part 6A for an individual composite steel I-section girder (stringer) of the floor system at a single rating location. Flexural and shear resistances follow AASHTO LRFD Section 6 (Article 6.10). The object pulls its load rating combinations, condition and system factors, modular ratio, construction type, span definition, and Appendix B6 preference from a Girder Load Rating (LRFR) template, extracts the permanent-load (DC1, DC2, DW) and live-load effects of the girder at the rating station, and reports Inventory and Operating rating factors for the Design live load together with the Legal, Emergency, and Permit live loads defined on the Load Rating Combination Table (LRFR), at the strength and service limit states. Cover plates and section losses can be included. ## General **Girder:** Pick the Girder to rate. Its geometry, cross sections, deck, bracing, and stiffeners are used for the capacity calculations, and its elements are used to extract the analysis results at the rating station. The girder must reference a Concrete Deck, since a composite deck is required for this rating. The user must provide a value. A Frame Member can be picked here too, for example a stringer, a machinery girder or a cross girder modelled as a frame member, as long as no two of its parts (between consecutive insertion points) are 90° or more apart in direction and it does not mix vertical and non-vertical parts. It is rated as a bare steel member: set **Composite Action** to *Non-composite*, and give the rating point with Location Input Method = *Relative on Span*; each of these gives a validation issue otherwise. Its spans run between its ends and the insertion points that carry a bearing (with no bearing, the whole member is one span; at an interior insertion point whose offsets move the member along it, a rating point on the short stretch between its two sides is moved to the nearer side). The forces are read from the frame member's result line, the rated section is the member's section at the rating point (for a variable section, the section at the point, as for a girder; where two Section Data rows of a different shape cannot be interpolated, the shallower of the two is rated), its rated span is the unbraced length, and its web is rated as unstiffened (no bracing or stiffeners are read from it). **Load Rating Template:** Pick the Girder Load Rating (LRFR) template that holds the generic inputs — the strength and service load rating combinations, condition and system factors, modular ratio, construction type, span definition, and Appendix B6 preference. The user must provide a value, and the template's condition factor must be greater than zero. **Resolved Station (readonly):** The station actually used for the rating, resolved from the Location Input Method. An issue is raised if it falls outside the girder's start and end stations. (Read-only) **Panel Type \[Interior Panel/End Panel]:** Classifies the web panel at the rating station for the shear resistance. *Interior Panel* allows tension-field action for stiffened webs (AASHTO 6.10.9.3.2). *End Panel* limits the shear resistance to the shear-buckling resistance (AASHTO 6.10.9.3.3). **Location Input Method \[Station/Relative on Span/Before Section Change/After Section Change/Before Splice/After Splice]:** Selects how the rating station along the girder is defined. * *Station* — a station entered directly in Station. * *Relative on Span* — a girder span selected in Girder Span Number and a 0–1 position along it in Relative Position along Span (0-1). * *Before Section Change* / *After Section Change* — a station just before (lower station) or just after (higher station) one of the girder's section changes, stepped off by Location Offset. * *Before Splice* / *After Splice* — a station just before or just after one of the girder's field splices, stepped off by Location Offset. **Station:** The station along the bridge alignment at which the girder is rated. It must lie within the girder's start and end stations (see Girder Start Station and Girder End Station). Available when Location Input Method is *Station*. **Girder Span Number \[Girder Span 1/Girder Span 2/Girder Span 3/Girder Span 4/Girder Span 5/Girder Span 6/Girder Span 7/Girder Span 8/Girder Span 9/Girder Span 10/Girder Span 11/Girder Span 12/Girder Span 13/Girder Span 14/Girder Span 15/Girder Span 16/Girder Span 17/Girder Span 18/Girder Span 19/Girder Span 20]:** The girder span in which the rating location lies. Spans are counted in increasing station order between the span reference stations selected in Use CL of Bearings/Piers. An issue is raised if the girder has fewer spans than the number selected, or if the selected span has zero length. Available when Location Input Method is *Relative on Span*. **Relative Position along Span (0-1):** The rating location as a fraction of the selected span length, measured from the start (lower station) of the span (0 = span start, 0.5 = midspan, 1 = span end). Available when Location Input Method is *Relative on Span*. **Use CL of Bearings/Piers \[Bearings/Piers/Use the station where the Girder intersects the Pier]:** Selects the reference stations that bound each girder span. *Bearings* uses the bearing centerlines of the girder supports; *Piers* uses the support line (pier centerline) stations; *Use the station where the Girder intersects the Pier* uses the station at which the girder crosses each support. The choice only matters when the bearings are offset from the support line. Available when Location Input Method is *Relative on Span*. **Section Change No \[Section Change 1/Section Change 2/Section Change 3/Section Change 4/Section Change 5/Section Change 6/Section Change 7/Section Change 8/Section Change 9/Section Change 10/Section Change 11/Section Change 12/Section Change 13/Section Change 14/Section Change 15/Section Change 16/Section Change 17/Section Change 18/Section Change 19/Section Change 20]:** The section change used as the reference for the rating station. Section changes are the section transitions within the girder (its start and end are excluded), numbered in increasing station order. An issue is raised if the girder has no section change or fewer section changes than the number selected. Available when Location Input Method is *Before Section Change* or *After Section Change*. **Splice No \[Splice 1/Splice 2/Splice 3/Splice 4/Splice 5/Splice 6/Splice 7/Splice 8/Splice 9/Splice 10/Splice 11/Splice 12/Splice 13/Splice 14/Splice 15/Splice 16/Splice 17/Splice 18/Splice 19/Splice 20]:** The field splice used as the reference for the rating station, numbered in increasing station order. An issue is raised if the girder has no field splice or fewer splices than the number selected. Available when Location Input Method is *Before Splice* or *After Splice*. **Location Offset:** The distance along the girder from the selected section change or splice to the rating station; the direction comes from the Location Input Method. It cannot be negative, and a value of zero still steps a very small distance off the discontinuity so that the section on the chosen side is used. Available when Location Input Method is *Before Section Change*, *After Section Change*, *Before Splice*, or *After Splice*. **Straight/Curved \[Straight Bridge/Curved Bridge]:** Defines whether the girder is rated as part of a straight or a horizontally curved bridge. The default is taken from the selected girder. **PDF Name (Export):** Name used when the load rating report is saved as a PDF. When renaming the file, avoid the characters listed on the [linked](https://docs.openbrim.org/faq/general/faq-illegal-chars) page, as certain characters may interfere with parametric equations and lead to unexpected results. ## Section Dimensions **Override Section \[Yes/No]:** By default the rating uses the girder's own cross section at the rating station, taken from its section data; where the section varies linearly between two section definitions, the section at the station is rated: its outline interpolated between the two as the analysis does, its properties and plate dimensions read from that outline (an I-section, a box, a channel, a tube, an angle alike). On a parabolic or circular stretch, and for two definitions of a different shape (another number of shapes or points) that cannot be interpolated, an I-section's plate dimensions are interpolated between the two definitions along the declared variation; a box or a channel is then rated as an I-section with its webs combined, on those interpolated dimensions, and the report says so; any other shape, or a section whose plate dimensions cannot be read that way, stops with an issue there. Set this to *Yes* to rate a user-picked cross section instead. The section in use must be a rolled I-section from the section database or a plate I-section that defines the total depth, web thickness, and top and bottom flange widths and thicknesses. **Cross Section:** The cross section used for the capacity calculation when Override Section is *Yes*. The user must provide a value when the override is active. **Section Total Depth (readonly):** Total depth of the steel section used at the rating station. (Read-only) **Section Web Thickness (readonly):** Web thickness of the steel section used at the rating station. (Read-only) **Section Top Flange Width (readonly):** Top flange width of the steel section used at the rating station. (Read-only) **Section Top Flange Thickness (readonly):** Top flange thickness of the steel section used at the rating station. (Read-only) **Section Bottom Flange Width (readonly):** Bottom flange width of the steel section used at the rating station. (Read-only) **Section Bottom Flange Thickness (readonly):** Bottom flange thickness of the steel section used at the rating station. (Read-only) ## Deck Reinforcement **\[Override Deck Rebar/Use Deck Rebar] Input Data Preference:** Selects the source of the longitudinal deck reinforcement used in the composite section. *Use Deck Rebar* reads the longitudinal reinforcement (bar sizes, spacing, cover, material, and creep adjustment factor) defined on the Concrete Deck at the rating station; the deck must define its reinforcement data and rebar material. *Override Deck Rebar* uses the lumped reinforcement inputs below instead. **Lumped Top Reinforcement Area within the Effective Width:** Total area of the top layer of longitudinal deck reinforcement within the effective deck width. It must be greater than zero. Available when Input Data Preference is *Override Deck Rebar*. **Dist from the CL of top bars to deck top:** Distance from the top of the deck to the centerline of the top reinforcement layer. Available when Input Data Preference is *Override Deck Rebar*. **Lumped Bottom Reinforcement Area within the Effective Width:** Total area of the bottom layer of longitudinal deck reinforcement within the effective deck width. It must be greater than zero. Available when Input Data Preference is *Override Deck Rebar*. **Dist from the CL of bottom bars to deck bottom:** Distance from the bottom of the deck to the centerline of the bottom reinforcement layer. Available when Input Data Preference is *Override Deck Rebar*. **Deck Rebar Material:** The reinforcing steel material whose yield strength is used for the deck reinforcement. The user must provide a value when the lumped input is used. Available when Input Data Preference is *Override Deck Rebar*. **Concrete creep adjustment factor:** The deck reinforcement area is divided by this factor to account for the reduction, over time, of the force transferred from the deck steel to the rest of the cross section due to concrete creep (default 3). Available when Input Data Preference is *Override Deck Rebar*. ## Cover Plates Cover plates and side plates attached to the flanges increase the flexural capacity of the girder over part of its length. The section modulus and stresses under live load are computed with these plates included, while the actual girder plate dimensions are used for the other permanent loads. Leave a value at zero when the plate is not present. **Top Flange Cover Plate Width:** Width of the cover plate attached to the top flange. **Top Flange Cover Plate Th.:** Thickness of the cover plate attached to the top flange. **Bot. Flange Cover Plate Width:** Width of the cover plate attached to the bottom flange. **Bot. Flange Cover Plate Th.:** Thickness of the cover plate attached to the bottom flange. **Top Flange Side Plate Height:** Height of the side plate attached to the top flange. **Top Flange Side Plate Th.:** Thickness of the side plate attached to the top flange. **Bot. Flange Side Plate Height:** Height of the side plate attached to the bottom flange. **Bot. Flange Side Plate Th.:** Thickness of the side plate attached to the bottom flange. ## Section Losses Section loss inputs reduce the section or cover plate dimensions to represent corrosion or other deterioration found during inspection. Losses applied to the section dimensions affect the stresses from both permanent and live loads; losses applied only to cover plates affect the live-load stress computation. Enter each loss as a percentage of the original dimension. **Top Flange Width (%) Loss:** Percentage reduction in top flange width. **Top Flange Thickness (%) Loss:** Percentage reduction in top flange thickness. **Bottom Flange Width (%) Loss:** Percentage reduction in bottom flange width. **Bottom Flange Thickness (%) Loss:** Percentage reduction in bottom flange thickness. **Web Thickness (%) Loss:** Percentage reduction in web thickness. **Top Cover Plate Width (%) Loss:** Percentage reduction in top cover plate width. **Top Cover Plate Th. (%) Loss:** Percentage reduction in top cover plate thickness. **Bot. Cover Plate Width (%) Loss:** Percentage reduction in bottom cover plate width. **Bot. Cover Plate Th. (%) Loss:** Percentage reduction in bottom cover plate thickness. **Web Cover Plate Thickness (%) Loss:** Percentage reduction in web cover plate thickness. **Web Cover Plate Height (%) Loss:** Percentage reduction in web cover plate height. ## Overrides-Readonly **Composite Action \[Non-composite/Composite]:** Whether the girder is rated with composite action with its deck (the default) or without it. A Frame Member, which has no deck, must be rated as *Non-composite*. **Override Effective Deck Width \[Yes/No]:** Set to *Yes* to enter the effective deck width manually instead of using the value computed by the girder. This is useful when composite action is partial or the geometry is irregular. **Effective Deck Width:** The user-defined effective width of the deck acting compositely with the girder. Available when Override Effective Deck Width is *Yes*. **Computed Effective Deck Width (readonly):** The effective deck width of the girder at the rating station, as determined by the girder object. (Read-only) Available when Override Effective Deck Width is *No*. **Override Transverse Stiffener Spacing \[Yes/No]:** Set to *Yes* to enter the transverse stiffener spacing for the shear resistance manually instead of using the computed value. **Transverse Stiffener Spacing:** The user-defined transverse stiffener spacing do at the rating station. Available when Override Transverse Stiffener Spacing is *Yes*. **Computed Transverse Stiffener Spacing (readonly):** The transverse stiffener spacing determined from the model, measured along the girder between the stiffener or bracing locations on either side of the rating station (the larger adjacent panel when the rating station coincides with one). (Read-only) Available when Override Transverse Stiffener Spacing is *No*. **Override Maximum Unbraced Length \[Yes/No]:** Set to *Yes* to enter the unbraced length of the compression flange manually instead of using the computed value. **Maximum Unbraced Length:** The user-defined unbraced length Lb of the compression flange used for lateral-torsional buckling. Available when Override Maximum Unbraced Length is *Yes*. **Computed Maximum Unbraced Length (readonly):** The unbraced length determined from the model, measured along the girder between the bracing locations on either side of the rating station (the larger adjacent length when the rating station coincides with a bracing location); the girder ends bound the first and last segments. (Read-only) Available when Override Maximum Unbraced Length is *No*. **Girder Start Station (readonly):** The start station of the girder along the alignment. (Read-only) **Girder End Station (readonly):** The end station of the girder along the alignment. (Read-only) ## Appendix B6 These inputs are available only when Use Appendix B6 Provisions? is set to *Yes* on the Girder Load Rating (LRFR) template. AASHTO Appendix B6 provides an optional, simplified approach for calculating the moments redistributed from the interior-pier sections of continuous-span I-section members at the service and strength limit states; the restrictions of Article B6.2 ensure adequate ductility and robustness at the interior-pier sections. In a first run, the load rating reports the redistribution moment ΔMrd at each qualifying support; in a second run, those values are entered here for the stations adjacent to the piers. When Appendix B6 is used, a separate template per girder is recommended so the support values can be entered correctly. **Mrd at Supports List (Strength):** The redistribution moments at each support for the strength limit state, as reported by the first run, entered in a table with one row per support. A value must be entered at every bearing support, even if it is zero; no moment should be assigned to support lines added only for geometric purposes. **Mrd at Supports List (Service):** The redistribution moments at each support for the service limit state, entered the same way as the strength list. **Adj. to Interior-Pier Section Stations (Str):** For each interior pier, the station range of the sections within the unbraced lengths immediately adjacent to the interior-pier section, used for the strength limit state. The redistributed moment increases the demand at these adjacent stations while decreasing the demand at the pier. **Adj. to Interior-Pier Section Stations (Srv):** For each interior pier, the station range extending to the nearest flange transition or point of dead-load contraflexure, whichever is closest, used for the service limit state. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation by asking a question. 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