## 2 Experimental Program
### Testing Procedure
#### 2.6.2 Seismic Tests on Real-Scale Three-Storey Precast Concrete Building  
The third phase consists of seismic tests on a real-scale three-storey precast concrete building. In this case, a representative earthquake was reproduced in the laboratory, namely \"El Centro\" (an earthquake that occurred in the city of El Centro, California, USA in 1979). More specifically, the accelerogram belonging to an orientation of 220\({}^{\circ}\) was considered, because this was the most  
Figure 8: (**a** and **b**) Location of the sensors in the isolated structural walls.  
Figure 9: (**a** and **b**) Location of the sensors in the structural frames.  
unfavourable in terms on maximum horizontal accelerations. The accelerogram was obtained from the USGS (United States Geological Survey, USA) (Figure 10a).  
The accelerogram is first transformed in a diagram of horizontal displacement verus time, which is the input signal introduced to the dynamic actuator control equipment (Figure 10b). Additionally, the response spectrum of the earthquake is shown (Figure 10c).  
Figure 10c reveals that this earthquake causes the highest acceleration for structures with a natural period of 0.06 s, i.e., for structures with a natural frequency of 16.7 Hz. However, this earthquake is not only very dangerous for rigid structures, but it also provides acceleration values greater than the ground acceleration up to a period of 0.25 s, i.e., a frequency of 4 Hz.  
The earthquake was not applied directly on the building, but in a progressive way, similar to foreshocks before the main earthquake. A total of six foreshocks were applied to the building before the main earthquake. To perform it, the ordinate of the seismic signal (i.e., the diagram of horizontal displacement vs. time) was multiplied by a factor. For the first foreshock, the factor was 0.05, i.e., the shape of this earthquake is homothetic to the real \"El Centro\" earthquake but the displacements are only 5% of the main earthquake. For the rest of the foreshocks, the factors were 0.1, 0.3, 0.5, 0.7, and 0.9 respectively. Finally, the main earthquake was applied.  
The sensors used to monitor this test were load cell, accelerometers on the shake table, the intermediate slabs at the top of the walls, and displacement transducers in several positions (Figure 11).  
Figure 10: Earthquake “El Centro”. (**a**) Accelerogram; (**b**) diagram of horizontal displacement vs. time; (c) response spectrum.  
Figure 12 shows a general view of the testing. As can be observer, in addition to the self-weight of the building, a dead load of 1.50 kN/m\({}^{2}\) was included on the intermediate slab. This load was materialized using water tanks.  
Figure 11: Location of the sensors in the building.  
Figure 12: General view of the real-scale three-storey precast concrete building.  
Additionally, a one-cycle impulsive test was performed, before and after the seismic tests, in order to measure the natural frequency and the damping ratio of the building and to compare them with the excitation frequency of the earthquake. Moreover, the comparison of the natural frequency and damping ratio values, before and after the seismic event (including the main earthquakes and the foreshocks), provide useful information about the damage caused by the seismic tests.  
In this case, a displacement-time one-cycle square wave signal was applied, with an excitation frequency of 5 Hz and an amplitude of 1 mm.