LOW-CYCLE FATIGUE BEHAVIOR OF SEMIRIGID TOP-AND-SEAT ANGLE CONNECTIONS

Constant amplitude reversed cyclic load tests were performed to invest igate the low-cycle fatigue behavior of a commonly used class of semi- rigid connection: the top-and-seat angle. All specimens had the same g eometrical properties. The test results show that the plastic moment c apacity and connection stiffness are sensitive to how the nut and bolt s are oriented when tightened. However, upper and lower bounds of stre ngth and stiffness can be predicted using standard yield line (plastic ) theory. The variability in strength and stiffness does not appear to affect the fatigue life. Fatigue Life predictions can be made for thi s class of connection using relationships analogous to the well-known Manson-Coffin strain-life equation for metals. Mean rotation (analogou s to mean stress) effects are also examined and are shown not to be si gnificant over the range of plastic rotations (0.003 to 0.10 radians) considered. Hysteretic energy-life and energy-rotation relations were also developed. Such relations are useful in seismic damage modeling. For the top-and-seat angle connections considered in this study, the l arge fatigue based plastic rotation capacity (approx. 3 percent) would generally significantly exceed expected demands for most structural s teel systems in a typical US earthquake, where total drift rarely exce eds 2 percent.