EFFECTS OF WELDMENTS ON FATIGUE STRENGTH OF STEEL BEAMS

THE FATIGUE FRACTURES OBSERVED IN THE COVER-PLATED STEEL BEAM BRIDGES OF THE AASHO ROAD TEST AND IN OTHER SIMILAR STRUCTURES EMPHASIZE THE IMPORTANT EFFECT OF WELDING AND WELDED DETAILS ON THE LIFE EXPECTANCY OF HIGHWAY BEAM OR GIRDER BRIDGES. A REVIEW WAS MADE OF EXISTING FATIGUE DATA TO DEVELOP MATHEMATICAL RELATIONSHIPS TO DEFINE WITH STATISTICAL CONFIDENCE THE FATIGUE STRENGTH OF ROLLED AND WELDED BEAMS, ROLLED AND WELDED BEAMS WITH COVERPLATES, AND WELDED BEAMS WITH FLANGE SPLICES. STATISTICALLY VALID EXPERIMENTS WERE DEVELOPED THAT PERMITTED FORMULATION OF MATHEMATICAL RELATIONSHIPS RELATING THE FATIGUE BEHAVIOR OF BEAMS TO DESIGN DETAILS, APPLIED STRESSES, AND TYPES OF STEELS. DURING THE RESEARCH PROGRAM, 374 BEAM SPECIMENS WERE TESTED UNDER CONSTANT-AMPLITUDE CYCLIC LOADING. PILOT FATIGUE STUDIES ON VARIABLE-AMPLITUDE CYCLIC LOADING WERE ALSO CONDUCTED, USING NOTCHED BAR SPECIMENS. VALUES OF STRESS RANGE FOR SPECIFICATION PROVISIONS SHOULD BE BASED ON CONFIDENCE LIMITS. THE STUDY SHOWS THAT THE CURRENTLY USED FATIGUE PROVISIONS ARE NOT SATISFACTORY FOR A36 AND A441 STEEL ROLLED BEAMS. NEITHER ARE THEY SATISFACTORY FOR PLAIN WELDED BEAMS, COVER-PLATED BEAMS, AND FLANGE SPLICES OF A36, A441, AND A514 STEEL. STRESS RANGE ALONE ACCOUNTS FOR THE VARIATION IN CYCLE LIFE. THE FATIGUE STRENGTH OF A GIVEN WELDED DETAIL IS INDEPENDENT OF THE STRENGTH OF THE STEEL. TESTS OF ROLLED A36 AND A441 STEEL BEAMS YIELDED ABOUT THE SAME FATIGUE STRENGTH. WEB-TO-FLANGE FILLET WELDS CANNOT BE NEGLECTED AND THE BEAM CONSIDERED AS BASE METAL FOR PURPOSES OF FATIGUE DESIGN. THIS ASSUMPTION WOULD GROSSLY OVERSTATE THE FATIGUE STRENGTH OF PLAIN WELDED BEAMS. VARIATIONS IN COVER-PLATE GEOMETRY HAVE NEGLIGIBLE EFFECT ON END-WELDED COVER PLATES. COVER PLATES WIDER THAN THE FLANGE TO WHICH THEY ARE ATTACHED WILL RESULT IN A DECREASE IN FATIGUE STRENGTH UNLESS TRANSVERSE END WELDS ARE USED. THE RESULTS OF STUDIES ON PLAIN ROLLED BEAMS DID NOT CORRELATE WITH EXISTING STUDIES ON PLATE SPECIMENS. THE EMPIRICAL EXPONENTIAL MODEL RELATING STRESS RANGE TO CYCLE LIFE WAS OBSERVED TO PROVIDE THE BEST FIT TO THE TEST DATA FOR ALL BEAM SERIES. SUITABLE MATHEMATICAL DESIGN RELATIONSHIPS CAN BE DEVELOPED FOR ANY DESIRED LIFE FROM THE MATHEMATICAL MODELS RELATING STRESS RANGE TO CYCLE LIFE.

• Record URL:
  • http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rrd_18.pdf
• Supplemental Notes:
  • Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved.
• Publication Date: 1970-6

Media Info

• Media Type: Digital/other
• Pagination: 4 p.
• Serial:
  • NCHRP Research Results Digest
  • Issue Number: 18
  • Publisher: Transportation Research Board

Subject/Index Terms

• TRT Terms: Beams; Bridge construction; Bridge foundations; Bridges; Concrete tests; Construction; Fatigue (Mechanics); Fatigue tests; Fillet welds; Flanges; Flexural strength; Girder bridges; Load tests; Mathematical models; Steel; Steel plates; Stresses; Structural tests; Weldments
• Uncontrolled Terms: Fatigue life
• Subject Areas: Bridges and other structures; Construction; Geotechnology; Highways; Materials;

Filing Info

• Accession Number: 00217015
• Record Type: Publication
• Files: TRIS, TRB
• Created Date: Oct 13 1970 12:00AM