Welded Highway and Railway Bridges
1966 Edition, 1966
It is intended that these Specifications shali be suitable forthe application of shielded metal-arc welding and submerged arcwelding in the design, fabrication, field assembling and repair ofhighway and railway bridges. Other welding processes are notcovered in detail but provisions are made for their use.
These Specifications do not treat of such design considerationsas arrangement of parts, live loadings and distribution thereof andcomputation of stresses. It is expected that appropriate generalspecifications, such as the American Association of State HighwayOfficials SpeciÃications for Highway Bridges or the AmericanRailway Engineering Association Specifications for Steel RailwayBridges, will be prescribed by the Purchaser and will control inall matters that are not affected by the use of welding.
In the case of old bridges, material of questionable weldabilitymay have been used (including wrought iron or high strengthstructural silicon or nickel steeh). Accordingly, it is advisablein making important repairs to an old structure to obtain samplesof the material and make laboratory tests to determine the properwelding technique and weld values.
Work should be so detailed that the maximum amount of weldingmay be done in the flat position. Vertical and overhead welds aremore a c u l t to make but, when properly made, they have equalstrength to welds made in the flat position. Their use is,therefore, not penalized by a reduction of &e allowable unitstress but they may substantially increase the cost of thework.
In establishing suitable unit stresses for design, theSpecifications adhere as closely as practicable to publishedfindings of the Weldin? Research CounciI on the fatigue strength ofwelded joints. Fatigue failure is determined by three factors: themaximum unit stress, the range between maximum and minimum, and thenumber of applications of such cyclical variation. When the secondand third factors are both large, for a given member of a givenbridge, the maximum or fatigue failure stress is now known to bebelow the yield point found in a static test and consequently willcontrol the design. When either the second or third factor issmall, the fatip?ie failure stress is above the static yield pointand should not be invoked to control the design.
Fatigue testing has demonstrated that any sudden discontinuityof section and stress path is a factor adversely affecting thestrength of members subjected to cyclical loading. Gradual ratherthan sudden transitions of sections should be employed and, for thesame reason, groove welds are preferable to fillet welds.
Comments or inquiries on these Specifications are welcome. Theyshould be addressed to: Secretary, AWS Structural WeldingCommittee, AMERICANW ELDINGSO CIETYU, nited Engineering Center, 345East 47th Street, New York, N. Y. 10017.