Section 8: Special Inspection Requirements for Internally Redundant Members and System Redundant Members

Overview

Bridges demonstrated to have Internally Redundant Members (IRM) or System Redundant Members (SRM) that would otherwise be non-redundant steel tension members (NSTM) must follow the documentation and inspection requirements of this section. Bridges not meeting all of these requirements must be inspected as NSTM elements.

Qualifying Members

Bridge members that have documented engineering analyses, and that meet the following requirements, qualify as Internally Redundant Members (IRM) or System Redundant Members (SRM):
  1. Engineering evaluations
    1. Engineering analysis demonstrating System Redundancy or Internal Redundancy must be signed and sealed by a professional engineer. Engineering evaluation must include a one-page summary outlining affected members and evaluation methods used. The completed engineering analysis and summary must be in the Bridge Attachments folder in AssetWise, under Manager Files.
    2. Engineering analysis must:
      1. Employ a method programmatically approved by TxDOT and the FHWA; and
      2. Be in accordance with at least one of the following:
        • applicable sections of the TxDOT Bridge Design Manual;
        • the AASHTO Guide Specifications for Analysis and Identification of Fracture Critical Members and System Redundant Members; or
        • the AASHTO Guide Specification for Internal Redundancy of Mechanically-Fastened Built-Up Steel Members.
      3. Follow the TxDOT Bridge Design Manual for demonstration of redundancy
  2. Initial Bridge Special Inspection
    A baseline condition of qualifying bridges must be established through an initial special inspection. The inspection techniques, method, and access for the initial special inspection must meet the requirements of a NSTM inspection and be performed within 12 months of a bridge opening to traffic. All members or components contributing to System Redundancy or Internal Redundancy of a bridge or member must be included as part of the hands-on inspection. Existing bridge members reclassified as IRM or SRM through methods programmatically approved by TxDOT and FHWA may utilize current NSTM inspections to establish baseline conditions.
  3. Condition Requirements & Inspection Frequency
    Superstructure and substructure members must have a minimum condition rating of 6 or better to qualify as IRM or SRM and be eligible for special inspections as described in this section. Members classified as SRM or IRM but do not have a condition rating of 6 or better will be inspected as NSTM members. Bridges that would otherwise qualify but have advanced corrosion, fatigue cracks, or impact damage in or along an IRM or SRM shall be inspected as a NSTM.
    Table 4-1: IRM/SRM Special Inspection Frequency
    Condition Rating
    Special Inspection Frequency
    7 or higher
    10 yrs
    6
    6 yrs
    5 or lower
    N/A
  4. Periodic Evaluation
    Qualifying bridge members must be reviewed and verified to meet all requirements for special inspection as IRM or SRM during routine inspections and special inspections. Intervals for routine inspections are as established in Section 4 of this Chapter. Verification will include confirmation that there are no defects or performance issues identified that would warrant exclusion as IRM or SRM.
    Routine Inspection Reports for bridges with IRM and SRM must include evidence of visual inspection (photos) and descriptions of qualifying members to confirm that they are still in a condition eligible for inclusion as IRM or SRM. Examples of defects that would require an IRM or SRM to be inspected as a NSTM would include defects that reduce the structural capacity or stability, impact or fire damage, and presence of repairs or retrofits without a significant history of performance.

Inspection Techniques and Inspection Interval Tolerance

Special Inspection of IRM and SRM elements are to be performed using the same techniques and access methods as that for NSTM members. The requirements and acceptable tolerances for intervals for Special Inspections of IRM and SRM is the same as that for Routine Inspections.