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.