This thesis deals with the procedures, equipment and results of testing large scale, tubular, axially loaded, simple K-joints to failure in fatigue. Each K-joint had a 2" diameter chord, a 18" diameter 3° branch and a 12 3/4" 9° branch. Measures were taken to ensure axial forces with little bending in both branches. This was accomplished using a specially designed load frame with capability for full adjustment of alignment. The design is presented in an appendix. Sophisticated load control was used to apply a variable force of constant peak amplitude in which the mean was zero. Various methods of crack initiation detection are discussed ranging from acoustic emissions to visual inspection. Hot spot strains were measured using rosette type strain gages with locations determined from a finite element program. Data such as strains, load versus displacement loops, and crack lengths were taken frequently throughout the test. Substantial amounts of accumulated data, which include strains and load displacement loops, are placed in the appendicies. Test results are presented in graphical form and tables using information calculated from the raw data. Complete crack progression data were kept throughout each test and presented on drawings of projections of the weld toe onto a plane, and in graphs of crack length versus cycles for the major cracks.