Floor Beam Load Rating (LRFR) [TB]

Performs an AASHTO Load and Resistance Factor Rating (LRFR) per the Manual for Bridge Evaluation (MBE) Part 6A for a steel I-section floor beam at a single rating location. Flexural and shear resistances follow AASHTO LRFD Section 6 (Article 6.10), for either a composite or a non-composite floor beam. The object pulls its load rating combinations, condition and system factors, modular ratio, and construction type from a Floor Beam Load Rating template, extracts the permanent-load (DC1, DC2, DW) and live-load effects of the floor beam at the rating location, 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, at the strength and service limit states. Cover plates, section losses, and an optional web opening (AISC Design Guide 2) can be included.

General

Floor Beam: Pick the Floor Beam to rate. Its geometry, cross sections, deck, and girder connections are used for the capacity calculations, and its composite element is used to extract the analysis results at the rating location. The user must provide a value.

Load Rating Template: Pick the Floor Beam Load Rating template that holds the generic inputs — the strength and service load rating combinations, condition and system factors, modular ratio, and type of construction. The user must provide a value, and the template's condition factor must be greater than zero.

Floor Beam Station (readonly): The station of the selected floor beam along the bridge alignment. (Read-only)

Resolved Distance from Right End (readonly): The rating location actually used, expressed as a distance along the floor beam measured from its right end. It is resolved from the Location Input Method and clamped to the floor beam length; an issue is raised if the requested location falls outside the floor beam. (Read-only)

Panel Type [Interior Panel/End Panel]: Classifies the web panel at the rating location 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 [Distance from Right End/Relative on Beam/Before Section Change/After Section Change]: Selects how the rating location along the floor beam is defined. All positions are measured from the right end of the floor beam.

• Distance from Right End — a length entered in Rating Loc (Dist from Right End).
• Relative on Beam — a 0–1 fraction of the floor beam length entered in Relative Position from Right End (0-1).
• Before Section Change / After Section Change — a location just before (toward the right end) or just after (away from the right end) one of the section changes defined in the floor beam's section data, stepped off by Location Offset.

Rating Loc (Dist from Right End): The distance from the right end of the floor beam to the rating location. It must be between zero and the floor beam length. Available when Location Input Method is Distance from Right End.

Relative Position from Right End (0-1): The rating location as a fraction of the floor beam length, measured from the right end (0 = right end, 0.5 = midspan, 1 = left end). It must be between 0 and 1. Available when Location Input Method is Relative on Beam.

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 location. Section changes are the interior section transitions of the floor beam (its two ends are excluded), numbered in order starting from the right end. An issue is raised if the floor beam 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.

Location Offset: The distance from the selected section change to the rating location, measured along the floor beam; 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 section change so that the section on the chosen side is used. Available when Location Input Method is Before Section Change or After Section Change.

[Simple/Continuous] Span Type: Defines whether the floor beam is treated as a simple or a continuous span. For a continuous span, the nominal flexural resistance of a compact composite section in positive flexure is limited per AASHTO Equation 6.10.7.1.2-3.

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 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 floor beam's own cross section at the rating location, taken from its section data; where the section varies between two section definitions, the plate dimensions are interpolated at the rating location. 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 location. (Read-only)

Section Web Thickness (readonly): Web thickness of the steel section used at the rating location. (Read-only)

Section Top Flange Width (readonly): Top flange width of the steel section used at the rating location. (Read-only)

Section Top Flange Thickness (readonly): Top flange thickness of the steel section used at the rating location. (Read-only)

Section Bottom Flange Width (readonly): Bottom flange width of the steel section used at the rating location. (Read-only)

Section Bottom Flange Thickness (readonly): Bottom flange thickness of the steel section used at the rating location. (Read-only)

Deck Reinforcement

The deck reinforcement inputs apply only when the floor beam acts compositely with the deck (see Composite Action under Overrides-Readonly). For a floor beam, the deck reinforcement parallel to the floor beam is the transverse deck reinforcement.

[Override Deck Rebar/Use Deck Rebar] Input Data Preference: Selects the source of the deck reinforcement used in the composite section. Use Deck Rebar reads the transverse reinforcement (bar sizes, spacing, cover, material, and creep adjustment factor) defined on the Concrete Deck at the floor beam station; the deck must define its transverse 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 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 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.

Web Opening

[Yes/No] Web Opening (AISC DG-2): Set to Yes when the floor beam web has an unreinforced rectangular opening at the rating location. The flexural and shear resistances are then reduced per AISC Design Guide 2. The design guide requires the opening depth not to exceed 70% of the member depth and the compression flange to be compact (bf/2tf ≤ 65/√Fy); an issue is raised otherwise.

Opening Depth: Depth of the web opening, ho. Available when Web Opening is Yes.

Opening Length: Length of the web opening along the floor beam, ao. Available when Web Opening is Yes.

Bottom Tee Depth: Depth of the tee below the opening, sb, measured from the bottom of the section to the bottom edge of the opening. The bottom tee depth plus the opening depth must be less than the member depth. Available when Web Opening is Yes.

Top Tee Depth (d - sb - ho): Depth of the tee above the opening, st, computed as the total depth minus the bottom tee depth and the opening depth. (Read-only) Available when Web Opening is Yes.

Opening Eccentricity from the Mid Depth: Distance e from the mid-depth of the section to the centerline of the opening, computed from the section depth, bottom tee depth, and opening depth. (Read-only) Available when Web Opening is Yes.

Elastic Section Modulus of the Unperforated Section: The smaller elastic section modulus of the steel section without the opening, used to compute the moment reduction. (Read-only) Available when Web Opening is Yes.

Bottom Tee Aspect Ratio ao/sb (readonly): Aspect ratio ν of the bottom tee, the opening length divided by the bottom tee depth. (Read-only) Available when Web Opening is Yes.

Top Tee Aspect Ratio ao/st (readonly): Aspect ratio ν of the top tee, the opening length divided by the top tee depth. (Read-only) Available when Web Opening is Yes.

Override Computed Values [Yes/No]: Set to Yes to replace the computed flexural resistance stress and tee shear coefficients with user-entered values. Available when Web Opening is Yes.

Flexural Resistance Stress F_nc: User-entered flexural resistance stress of the compression flange used with the web opening check (defaults to the yield strength of the section material). Available when Web Opening and Override Computed Values are both Yes.

Bottom Tee Shear Coefficient: User-entered shear coefficient α of the bottom tee. Available when Web Opening and Override Computed Values are both Yes.

Top Tee Shear Coefficient: User-entered shear coefficient α of the top tee. Available when Web Opening and Override Computed Values are both Yes.

Computed Bottom Tee Shear Coefficient (readonly): Shear coefficient of the bottom tee computed per AISC Design Guide 2 as α = √6 / (ν + √3) ≤ 1.0. (Read-only) Available when Web Opening is Yes and Override Computed Values is No.

Computed Top Tee Shear Coefficient (readonly): Shear coefficient of the top tee computed per AISC Design Guide 2 as α = √6 / (ν + √3) ≤ 1.0. (Read-only) Available when Web Opening is Yes and Override Computed Values is No.

Moment Reduction Factor (readonly): Ratio of the flexural capacity at the opening to that of the unperforated section, computed as 1 − ho·tw·(ho/4 + e)/S. (Read-only) Available when Web Opening is Yes.

Cover Plates

Cover plates and side plates attached to the flanges increase the flexural capacity of the floor beam at the rating location. The section modulus and stresses under live load are computed with these plates included, while the actual floor beam 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

Override Composite Action [Yes/No]: By default composite action is determined from the model (see Computed Composite Action). Set to Yes to choose it manually with Composite Action.

Composite Action [Non-composite/Composite with deck]: The composite action used when Override Composite Action is Yes. Composite with deck requires the floor beam to have a deck; an issue is raised otherwise. Available when Override Composite Action is Yes.

Computed Composite Action (readonly) [Non-composite/Composite with deck]: The composite action determined from the model: the floor beam is treated as composite when its Interior Girders Connection is set to Deck-Top Flange and it has a Concrete Deck; otherwise it is non-composite. (Read-only) Available when Override Composite Action is No.

Override Effective Deck Width [Yes/No]: Set to Yes to enter the effective deck width manually instead of using the computed value. Available when the floor beam is composite.

Effective Deck Width: The user-defined effective width of the deck acting compositely with the floor beam. Available when the floor beam is composite and Override Effective Deck Width is Yes.

Computed Effective Deck Width (readonly): The effective deck width determined automatically as half of the sum of the distances to the adjacent floor beams on either side (the tributary width of the floor beam). (Read-only) Available when the floor beam is composite and 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 location. A value greater than zero makes the web panel stiffened. Available when Override Transverse Stiffener Spacing is Yes.

Computed Transverse Stiffener Spacing (readonly): The transverse stiffener spacing determined from the model. The connections of the girders framing into the floor beam are treated as transverse stiffeners, and the spacing is the distance between the two connections on either side of the rating location (the larger adjacent panel when the rating location coincides with a connection). A value of zero means no stiffener was found and the web is treated as unstiffened. (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 of the top flange determined automatically. The stringers framing into the floor beam are taken as brace points: the value is the distance between the brace points on either side of the rating location (the floor beam ends are used where there is no stringer on a side). When the rating location falls on a stringer, the longer of the two adjacent segments is used. Without stringers it is the full length of the floor beam. Stringers brace the top flange only, so where the bottom flange is in compression (for example negative flexure on a continuous floor beam) enter the unbraced length with the override. (Read-only) Available when Override Maximum Unbraced Length is No.

Floor Beam Span (readonly): The length of the floor beam in plan, measured along the floor beam between its ends. (Read-only)