## 4 Proposed System  
### System Description  
Based on the existing inertial configurations for shake table tests, the authors conceived and developed a new inertial mass testing system. The IMS, which is located on the shake table platform, was explicitly developed to enable the shake table experiment of single cantilever-type RC columns subjected to unidirectional earthquake excitations [9], although minor modifications to the inertial system or the test sample dimensions could allow other specimens to be tested. A schematic of the proposed system is depicted in Figure 5. The IMS comprises a steel column that is pin-connected to a supporting W-beam, which is connected to the shaking platform via four high-strength poststensioning rods. The required inertial mass is incorporated into the system by using a predefined number of concrete blocks, which are connected to the steel column via high-strength poststensioning rods at a height dictated by the height of the test specimen. However, auxiliary components of the system (e.g., steel column and swiveled link) also provide a minor amount of the inertial mass. The IMS is connected to the head of the specimen through a pinned-end rigid link. The link was designed to transmit the inertial forces created on the IMS to the specimen, allowing only in-plane rotation. To monitor the lateral force transferred to the specimen, a load cell was mounted in the link close to the test specimen. Additionally, to guarantee that the concrete blocks remain connected and that the inertial forces are transferred via the rigid link while shaking, a W-beam was placed at the back of the concrete masses using various poststension rods. It is worth mentioning that one end of the stiff link was poststensioned to the W-beam attached to the IMS.  
A safety system external to the shake table system was designed to catch the IMS in the occurrence of significant displacements or specimen failure. The steel-breaced safety frame consisted of wide-flange sections for both the columns and beams and was fixed to the laboratory strong floor using high-strength rods. The two closer bays of the safety frame were braced together using a series of angle braces in a cross shape in the north-south direction (Figure 5a), whereas chevron bracing was used in the east-west direction (Figure 5b). It is important to mention that the motion on the platform is stopped when the concrete masses impact the longitudinal beams of the safety frame. A maximum drift of 63.5 cm (25 in) is allowed by the safety system in the direction of motion. In order to avoid out-of-plane motion of the IMS, a caster was connected to the web of each longitudinal beam, as shown in Figure 5b.  
Since the IMS was composed of only a steel column and concrete masses, the setting process of an RC specimen can be completed in a short time. As illustrated in Figure 6, the sequence of assembling the IMS includes the following steps: (a) attaching the supporting W-beam to the shaking platform with the clevis (Figure 6a), (b) raising the steel column and connecting it to the clevis (Figure 6b), (c) attaching the concrete blocks to the steel column and placing the steel back beam at the required height (Figure 6c), (d) setting the RC specimen by securing its footing to the shake table via high-strength poststensioning rods, (e) connecting the stiff link between the steel column and the head of the RC specimen, and (f) attaching the axial load system on the top of the RC column.  
Figure 5: Schematic of the inertial mass system (IMS) part of test setup: (**a**) 3D view; (**b**) South view.