# Shake Table Testing of Standard Cold-Formed Steel Storage Rack
## 3 Test Results
### Results of Phase Three: Shake Table Tests (Scaled Down in Time Domain)  
As the test specimen was limited to 3 meters height, the results may not be extendable for taller racks with a period longer than 0.63 s of the tested specimen. For this reason, to estimate the behaviour of taller rack frames under the same seismic actions, a similar rack configuration was subjected to the same El-Centro earthquake record, but scaled down in the time domain by a factor of 2. By using this technique, instead of changing the structure to obtain a more extended period (two times longer), the same structure was subjected to a faster earthquake. Therefore, the behaviour of a system with a given natural frequency under a squeezed time history record (e.g., faster earthquake) simulates the behaviour of a virtual structure with the longer period under a non-scaled earthquake in the time domain. Figure 12: Pallet sliding of rack specimens—Non-Scaled in the time-domain. Figure 13: Comparison of rack results—Non-Scaled in the time domain: (**a**) frame acceleration, (**b**) frame base shear, (**c**) frame lateral displacement. Figure 14 shows the structural responses for the ground motions with 40% to 220% intensities of El-Centro earthquake records with 20% increments in the scale time-domain condition. As shown, increasing the excitation intensity typically resulted in an increase in the acceleration of the system and the lateral displacement of the rack. In addition, from the test data, it was found that the front frame responses were almost identical to the back-frame results for all specimens. This indicates that the frames tended to deform as rigid bodies at each level with equal deformations at either side. As shown in Figure 15, pallets started to significantly slide on the beam after 160% intensity tests. This can be explained by the reduction in the friction coefficient between the timber pallet and the beam due to the large number of tests using the same pallets and beams, which smoothed the contact surfaces of the timber pallet with the beam flange. The tests were continued until the automatic acceleration sensor raised an alarm of reaching a high acceleration at the top level close to the table capacity during the 220% intensity test. The peak responses of the rack structure under the scaled time domain are given in Table 4.  
Figure 16 shows the displacement time history measured at the top and first level of the rack starting from 40% intensity to 220% intensity of the El-Centro earthquake. Despite the large inelastic deformations in the down-aisle direction, the racks could still provide stability without compromising their vertical load-carrying capacity. The structure's lateral displacement again showed higher inter-storey drifts at the first level, as illustrated in Figure 16. The primary reason for higher drifts at the first level is attributed to the loss of stiffness at upright and beam connections below the first level, where the plastic hinges were formed and consequently led to a soft storey response. Figure 17 indicates the failure of the specimen at the upright to beam connection, which can be attributed to the soft storey mechanism. At the end of the test with 220% intensity, local failures were visible in the uprights along the first and second level. The absolute peak acceleration of each level and the base shear for each seismic intensity are also shown in Figure 16. It is seen that the peak acceleration and base shear do not vary linearly with increasing the intensity of the earthquake. The peak acceleration recorded for specimens with a non-scaled time domain was between 0.15 and 0.7, while the corresponding peak acceleration for specimens under a scaled time domain was within a range of 0.1-0.5. In terms of peak lateral displacement, the peak displacements of specimens with a non-scaled time domain were between 15 mm and 78 mm, while for specimens with a scaled time domain the corresponding values were between 8 mm and 40 mm.