EXPERIMENTAL RESEARCH ON STATIC BEHAVIOR OF BIG ECCENTRIC CIRCULAR HOLLOW SECTION N-JOINTS WITH VERTICAL BRACE UNDER COMPRESSION IN SYMMETRICAL PRATT TURSS

To study the static behavior of big eccentric circular hollow section N-joints with vertical braces under compression in a symmetrical Pratt truss, four big negative eccentric specimens, four big positive eccentric specimens and one non-eccentric specimen were tested under monotonic loading. The test procedure, joint failure phenomenon, vertical jacket load-displacement curves and strain distribution curves were presented in the paper. The effect of eccentricity on ultimate capacity, stiffness and ductility of the joints was also studied. A comparison between experimental and theoretical results shows that big eccentric CHS N-joints can be regarded as rigid connection. When joint eccentricity is negative or is less than 0.25, the ultimate capacity of joints increases with the eccentricity, then it decreases when the eccentricity is between 0.25 and 1.0. As for the ultimate capacity of joints with large negative eccentricity, neither Chinese code nor Euro code yields results agreeing well with experimental results and neither is conservative. For the N-joint where the two diagonal bars are well apart, it can be treated as two Y-joints.