> 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/truss-load-rating-tb.md). # Truss Load Rating (LRFD) \[TB] Performs an AASHTO MBE load rating for an individual truss member. The object pulls its global settings (load rating combinations, effective length factor, condition and system factors, Rp hole reduction) from a Truss Load Rating template, then evaluates strength and service ratings for the selected truss member using section properties, connection eccentricity, and weld length. Design, legal, emergency, and permit live-load cases defined on the combination table are all reported. ## General **Truss:** Pick the truss member to rate. The member's section properties and length are used for capacity calculations, and its element name is used to extract analysis results from the staged construction model. The user must provide a value. **Load Rating Template:** Pick the Truss Load Rating template that holds the generic inputs (strength and service load rating combinations, effective length factor, condition and system factors, Rp reduction factor for holes). All global settings applied to the rating come from this template. **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 **Section Type Override \[Use Section/I-Shape/Angle/Channel/Hss-Tube/Pipe/Tee/2L-LLBB/2L-SLBB/2L-Cruciform/2L-Starred]:** Classifies the cross-section shape so the connection eccentricity (and therefore the shear lag factor U) can be derived. Leave it on *Use Section* to take the shape classification carried by the assigned section. Set an explicit shape when the assigned section is a hand-drawn shape that carries no classification of its own — otherwise the eccentricity defaults to 0 (no shear-lag reduction, U = 1). The chosen shape drives which section dimension is used as the eccentricity for tension-fracture per AASHTO LRFD 6.8.2.2. ## Shear Lag Factor Inputs used to compute the shear lag factor U for the net section in tension per AASHTO LRFD 6.8.2.2. **Truss Member - Connection Eccentricity:** The eccentricity between the connection centroid and the centroid of the connected part of the member cross-section, used as x in the shear lag factor formula U = 1 - x / L. The default is auto-computed from the truss section type (y or z section dimension depending on whether the section is a channel, tee, angle, or tube); override it when the connection detail requires a value different from that auto-computed default. Enter a positive length. **Truss Member - Max Length of the Longitudinal Welds:** The length L of the longitudinal welds at the end connection, used as the denominator in U = 1 - x / L. Enter the longer of the two weld lines when welds of unequal length are used. Enter a positive length. ## Deterioration **Section Loss - Percent of Gross Area (%):** Section loss (deterioration) taken from the bridge inspection report, entered as a percent of the gross cross-sectional area. It is section-independent, so it works for any member shape. The deteriorated gross area is Ag,loss = Ag,gross x (1 - % / 100), which then feeds the capacity checks (both yielding and buckling), conservatively reducing them. Leave it at 0 for a pristine section. Values at or above 100% are rejected (no effective section remains). ## Net Section Bolt-hole deductions for the net section of a tension member per AASHTO LRFD 6.8.3. Leave all at 0 to take the net area equal to the (deteriorated) gross area. **Bolt Holes at Critical Section (count):** Number of bolt holes removed at the critical section. The total hole area removed is (count) x (hole diameter) x (material thickness). **Bolt Hole Diameter (bolt dia + 1/8 in):** Diameter of each bolt hole used for the net-area deduction — typically the bolt diameter plus 1/8 in. Enter a positive length. **Material Thickness at Holes (0 = no deduction):** Material thickness at the bolt holes, used to compute the removed hole area. Leave it at 0 to skip the net-section deduction. The bolt-hole deduction may not exceed the available gross area (that would leave a zero or negative net section). --- # 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. 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