The Online Hybrid Test Using Mixed Control

In this chapter, an online test technique that employs mixed control of displacement and force is presented. Indeed, displacement control is not practicable when the structure is too stiff to accurately control the loading actuator's displacement. Two types of mixed control “displacement-force combined control” and “displacement-force switching control” are proposed. In displacement-force combined control, one jack is operated by displacement control and another is operated by force-control. Validity of the combined control technique was demonstrated by a series of online tests applied to a base-isolated structure subjected to horizontal and vertical ground motions simultaneously. In the displacement-force switching control, the jack is operated by displacement-control when the test specimen is flexible but switches to force-control once the specimen became stiff. Validity of the switching control technique was also checked by a series of online tests applied to the base-isolated structure subjected to vertical ground motions.