Effect of Inertia Force During High-Speed Reversed Cyclic Loading
During quasi-static tests of beam-column joints, cyclic displacements are applied slowly so that the actuator has enough time to perfectly execute the loading direction reversal. In contrast, during high-speed tests, an actuator has to change loading direction rapidly to exactly follow the intended displacement history. However, most actuators cannot maintain the intended loading speed and simultaneously follow a sharp peak at the reversal point. Consequently, the displacement history followed by an actuator shows a smooth transition around the peak of each cycle. Inside this transition phase, the velocity gradually decreases and a large negative acceleration exists, which induces a significant inertia force that is included in the load cell reading. If the high-speed displacement cycles are applied at the column-top, the inertia force must be accurately determined to know the correct value of storey-shear, which is the most important parameter for result interpretation. On the other hand, if the displacement cycles are applied at the beam-tips and the column-top is held stationary, the load cell reading at the column-top is free of inertia effect and gives the exact value of storey-shear. Nevertheless, the beam-tip load cell readings are influenced by inertia force. This mechanism is discussed here based on the results of a high-speed cyclic loading test of a lightly reinforced beam-column subassembly.