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Fig. 1—A failure resulting from a slovenly job of welding. produced by a superfluous bit of weld metal which projected from an important boundary of the structure The fatigue crack centered about the stress concentration DESIGNING WELDED STRUCTURES FOR HIGH EFFICIENCY OF JOINTS HE science of structures ® is concerned with the Dart | economic distribution of elastic material to connect a © load to its reactions over a reasonable length of time. Intimately associated with this broad subject are the various methods used to join the component members of the struc- ture. While physical properties of elastic ma- terials and engineering details of their distri- bution are important factors, this article is concerned primarily with the production of ideal welded joints. Any structure built of pieces must necessarily act as a whole under its applied loads. Joint efficiencies, therefore, determine the action of the structure. As unit stresses are raised, high joint efficiencies become more and more im- portant; and as the loading cycle becomes more and more frequent, homogeneous joints become BY EVERETTE CMAPIMIZAIN Lukenweld Inc. imperative. Properly welded joints are more nearly homogeneous than any other type of connection between two pieces of material. Homogeneous joints are eminently desirable since they particularly affect the rigidity and fatigue performance of the structure. Consider the two methods of supporting a load over a span, as exemplified in the sketches in Fig. 3. The usual truss and abutment ar- rangement is essentially a three-piece struc- ture, connected by pin joints. The rigid frame bridge is a one-piece structure in which the transition from horizontal to vertical members is distinguished by the fact that this apparent joint can transmit bending moments. In the one-piece rigid frame bridge, the bending mo- PRECAUTIONS which must be observed in designing correct and efficient joints in welded steel structures were discussed at length in a paper presented at the fifty-fourth annual meeting of the American Society of Mechanical Engineers in New York, Dec. 5-7. This paper constitutes an important contribution to welding knowledge and because of its wide interest will be published in Full in MARINE REVIEW in two parts. Part |, ap- pearing herewith, deals with joint failures and causes therefor as explained by photoelastic studies ; Part Il, to appear in the next issue, will suggest corrective measures through drafting room practice and heat treatment. Two articles by the same author in the November and December MARINE REVIEW discussed similar problems as applied spe- cifically to the welding of rolled steel diesel engine structures. | The author is vice president in charge of engineering, Lukenweld Inc., division of Lukens Steel Co., Coatesville, Pa. MARINE REVIEW—January, 1934 15