FINITE ELEMENT BASED FATIGUE EVALUATION OF COPE HOLES IN BRIDGE GIRDERS

Welded steel bridge girders frequently utilize cope holes at web-flange transitions to permit full welding of thick flanges and to eliminate any triple point welds. These cope holes (also referred to as "rat" holes) are intended to be smooth and regular in shape. In practice, actual cope holes typically are flame cut resulting in irregular surface conditions and shapes. This irregularity in shape and surface has been the origin of a number of fatigue cracks observed in welded steel bridge girders already in service. Furthermore, the design engineer has no guidance as to which AASHTO fatigue category their details belong to because of the irregular shapes. The Kansas Department of Transportation requested a study to examine the fatigue behavior of cope holes specifically to answer the question as to which AASHTO fatigue category governs cope holes. The goal of this project is to supplement the AASHTO Bridge Design Specification by providing experimental and analytical information for designers as to how to categorize cope holes in welded steel girders. The stress field in an idealized smooth cope hole, as well as a representative actual flame cut cope hole, was determined in an actual beam. The resulting stress field, as determined with experimental stress analysis techniques, revealed a serious stress concentration located near the top of the cope hole in the web. This stress field was confirmed in a comprehensive finite element study of a section of the beam assembly using both 2-D and 3-D analysis. The results clearly show that the stress level at the critical locations on these cope holes can be as much as four times the nominal maximum bending stress in the member. Analytical studies using 3-D finite element models were conducted to ascertain how different repair options performed. The recommended repair is to remove existing flame cut material and fatigue cracks by drilling two holes and grinding to make the cope hole oval shaped. This repair improved the AASHTO category from "D" or "E" as a flame cut hole to "B" or "C" as a smooth oval hole which is a significant improvement at a reasonable cost.

Language

  • English

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: 53 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00725548
  • Record Type: Publication
  • Report/Paper Numbers: K-TRAN: KU-95-6, Final Report
  • Contract Numbers: C-696
  • Files: TRIS, ATRI, STATEDOT
  • Created Date: Sep 10 1996 12:00AM