Wind Effects on Mast Arms

In this study, current procedures employed by the Florida Department of Transportation (FDOT) for analysis and design of mast arm structures were reviewed, and experiments were conducted to identify residual mast arm system capacity. A collection of nine mast arm configurations was selected to represent mast arm designs commonly used in Florida, as well as those most often identified as being ‘at capacity’, based on the current design and analysis procedures. Findings from review and experimental testing indicated that selected parameters—Height and Exposure Factor, K sub Z, and Drag Coefficient, C sub d (specifically those applied to segments of the mast arm shielded by signals or signs)—used for wind-load calculations may be conservative. It was concluded that height-dependent calculations of K sub Z, as opposed to the current calculation using a fixed height of 24.4 feet, could yield lower K sub Z values, and therefore lower the design wind loads on the mast arm. Furthermore, experimental wind tunnel tests conducted in this study identified that load-reducing shielding (aerodynamic shielding) of the mast arm does occur. This report proposes that the reduced wind load on the mast arm segments shielded by an attachment be implemented in design load calculations by reducing the drag coefficient on the attachment while continuing to fully load the mast arm as if unshielded. This reduced attachment drag coefficient is referred to as an incremental drag coefficient (C sub di). In addition to design load parameter modifications, hardware modifications (denoted Enclosed and Slotted) were developed and experimentally tested. Results from experimental testing of the Enclosed modification demonstrated that the addition of covers provided no load reduction compared to unmodified attachments. Results for the Slotted modification showed that a reduction in the projected area of the back plate yielded a proportional reduction in loads on the attachment. However, field implementation of area reduction (folding, rotating or mesh panels) will require full-scale testing to quantify the load reduction proportionality constant.

Language

  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Appendices; Figures; Photos; References; Tables;
  • Pagination: 83p

Subject/Index Terms

Filing Info

  • Accession Number: 01677488
  • Record Type: Publication
  • Report/Paper Numbers: Report No. 2018/127208
  • Contract Numbers: BDV31-977-59
  • Files: NTL, TRIS, ATRI, STATEDOT
  • Created Date: Aug 1 2018 8:52AM