THE BEHAVIOR OF RIVETED JOINTS UNDER STRESSES. 



By James E. Howard, Esq., Visitor. 



[Read at the twenty-second general meeting of the Society of Naval Architects and Marine Engineers, held in 



New York, December 10 and 11, 1914.] 



The efficiencies of riveted joints under rupturing tensile stresses constitute the 

 values on which working- loads are commonly based. Alleged factors of safety are 

 employed, fortunately not less than five on important work. One of the reasons 

 why it is fortunate that a large factor of safety is used is found in the fact that 

 a fairly good distribution of the loads is not always characteristic of riveted con- 

 struction. Furthermore, the unit values on which computations of the strength of 

 riveted joints are based, in some respects, are not fixed values as they are gener- 

 ally taken to be. 



The most important feature of the case, however, resides in the elastic be- 

 havior of the joints, one which appears to be ignored, in consequence of which 

 local strains are introduced entirely at variance with those which purport to be 

 present in well-designed engineering structures. Nominally the elastic limit of the 

 material represents a limit which should be approached with temerity. As a matter 

 of fact few, if any, riveted structures are erected which are free locally from 

 strains which do not exceed the elastic limit of the material. The structures are not 

 necessarily endangered by the presence of such overstrains. It will depend upon 

 the character of the work which they have to perform, however, whether or not 

 ultimate failure will result and the place of rupture be located by an overstrained 

 zone. 



It may be remarked, with assurance, that after a limited number of repetitions 

 of stresses, twofold or threefold, the working loads are adequate to effect rupture, 

 for working loads which are based upon the usual so-called factor of safety of five. 

 The behavior of riveted joints under stresses leads to this inference. Multiple 

 riveted, double butt-strap joints may have a degree of rigidity equal to or even in 

 excess of the solid plate for comparatively low tensile or compressive stresses, but 

 loads ranging from, say, 15,000 to 25,000 pounds per square inch commonly show 

 a material divergence in the behavior of a joint over that of the solid plate. 



When frictional resistance contributes toward the initial rigidity of the joint, 

 as it commonly does, it is uncertain whether the favorable showing of the joint in the 

 laboratory test is realized and maintained under service conditions. Vibratory effects 

 and changes in temperature seem likely to cause a creeping of the plates and dis- 

 turb the initial state of the different ply, when taken in conjunction with a constant 

 load, or more marked, it may be, in the case of alternate stresses. In riveted joints, 

 as in many other engineering examples, a careful analysis of the case is not reas- 



