Truss Load Rating [TB]

The Truss Load Rating template collects inputs that stay constant across all truss member load-rating stations — the mapped strength and service load rating combinations, effective length factor, condition and system factors, and the Rp reduction factor for holes. Each individual Truss Load Rating object (under the Load Rating section) points at one template to inherit these values so they do not need to be repeated at every member.

General

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

Service (Load Rating Combination): The load rating combination table used as the basis for all finite element analysis results in the service limit state equations. Pick a Load Rating Combination Table that maps the analysis result cases and factors for service rating. Leave blank if service rating is not required; when left blank, service limit state calculations are skipped for every member that references this template.

K, Effective Length Factor (4.6.2.5): Effective length factor (K) used for compression member buckling, as specified in AASHTO LRFD Article 4.6.2.5. Typical values depend on the end-condition assumption (e.g., 1.0 for members effectively pin-pin, 0.75 for members with partial end restraint per AASHTO LRFD 4.6.2.5).

Condition Factor: Condition factor (φc) applied to nominal resistance per AASHTO MBE 6A.4.2.3. The value is based on the Bridge Management System (BMS) condition state of the element from the most recent inspection report. Typical values: 1.00 for Good/Satisfactory (BMS 1-2), 0.95 for Fair (BMS 3), and 0.85 for Poor (BMS 4).

System Factor: System factor (φs) applied to nominal resistance per AASHTO MBE 6A.4.2.4. It reflects the level of redundancy of the complete superstructure system and is typically 1.00 for conventional redundant systems, and reduced for non-redundant members such as two-girder or single-load-path trusses (e.g., 0.85 for a truss with two main members).

Rp Reduction Factor for Holes [1.0 for Holes Drilled Full Size/0.90 for Holes Punched Full Size]: Reduction factor Rp used with the net-section fracture limit state (AASHTO LRFD 6.8.2.1 / 6.13.5). Use 1.0 when the holes are drilled full size, and 0.90 when the holes are punched full size.