<p>The post-tensioned energy dissipating (PTED) connection for steel frames has drawn many researchers’ attention for its good seismic performance. This particular cable is one of the key components of post-tensioned connections. However, the value of cable force can decrease due to creep in the cable and anchor systems. To evaluate seismic response by means of transient dynamic analysis, a simplified numerical model with a friction-damped, post-tensioned connection is used. The evolution patterns of the seismic response of friction-damped, post-tensioned steel frames (FDPT), along with a decrease in cable force, is systematically investigated. The interaction mechanisms between structural displacement and post-tensioning force variations were rigorously analyzed by utilizing advanced nonlinear simulations. The influence of initial PT force and friction force are revealed through parametrical analysis. Spectral decomposition techniques were employed to evaluate vibration characteristics across different excitation frequency bands. The results indicate that the intensity of seismic response generally increases with a decrease in cable force, especially for the condition in which the cable force approaches zero. The degradation of cable force caused by the creep of a cable and anchor system should be seriously considered.</p>