FOCUSING ON FATIGUE

Abstract

Properly designed and maintained bridges sometimes need repair for fatigue damage. Among the reasons may be that the bridge was designed before current fatigue design provisions, or initial design assumptions may have changed, or poor fabrication techniques could have resulted in weld discontinuities. Detailed repair techniques are outlined for a number fatigue related problems. Bolts are easier to use because it is difficult to get shop-quality welds in the field. Procedures for both welds and bolting are detailed. Drilling is prescribed for a number of problems and directions show how this should be done and how to place holes in the most efficient manner. Grinding and cleaning methods are given and the use of dye penetrants for testing described. Lack-of-fusion plates in backing bars are another problem, and retrofit procedures are given. The author also describes his research, with the Texas Highway of Transportation, which shows that removing diaphragms on bridges can redieve distortion stresses. More research is needed to determine the contribution of the diaphragms.