# Numerical Study of the Seismic Response of an Instrumented Building with Underground Stories
## 2 Analysis Approach
### Description of the Building and Instrumentation  
The Alcazar building, illustrated in Figure 1a, is a sixteen-story RC building office located in the city of Vina del Mar, which is situated in the central coast area of Chile, where several buildings were damaged during the last Mw 8.8 Maule earthquake. The structure was built in 2008, following the 2004 Chilean Building Code, which refers to the ACI-318 provision for concrete design [35]. The building is 53.46 m tall, and the plan area is 30 m by 35 m. It also has three underground floors, destined for parking purposes, where the third basement level is 7.92 m deep underground. The first story is 3.42 m in height, and stories 2-16 are 3.24 m in height. The structural system consists of a perimeter RC moment frame in both directions, RC shear walls on the east and the west outer sides, and a central core constructed of RC shear walls.  
In summary, the gravity system comprises an RC slab supported by the core shear walls, eight rectangular columns of a perimeter frame, and four shear walls located at the perimeter. The basement structure consists of RC slabs supported by large concrete walls, which results in high stiffness of the underground structure. The foundation consists of a 120 cm thick RC foundation slab. Concrete material used for columns, beams, and  
Figure 1: The case study building. (**a**) Northwest side of view; (**b**) accelerometers’ location; (**c**) Digitexx accelerometers model D-110U installed in the building.  
walls between the 3 rd basement and 3 rd floor was specified as grade G-40 (fc\({}^{\prime}\) = 40 MPa), whereas grade G-35 (fc\({}^{\prime}\) = 35 MPa) was used between the 4 th and 16 th floors. Concrete grade G-25 (fc\({}^{\prime}\) = 25 MPa) was used for the foundation slab.  
The building was instrumented with an array of sixteen (16) force-balance Digitexx accelerometers model D-110U [36], with a sensitivity of 1.2 V/g and registered the analog acceleration with a dynamic range of 120 db between 0.01 and 50 Hz, shown in Figure 1c. The monitoring system collected the building's response to several earthquakes between 27 March 2010 and 19 April 2011. The accelerometer location is shown in Figure 1b. Four (4) sensors were installed on the third underground level, three (3) on the ground surface level, and then three (3) sensors on the third, sixth, and top floor. It is worth mentioning that the two vertical sensors 3 and 4 in the 3 rd subterranean floor were not activated. The sensors register accelerations along the two horizontal directions of the building, where one sensor measured in the EW direction and two sensors in the NS direction. This sensor distribution allowed for the monitoring of the structure's spatial motion, the capturing of torsional modes, and the partial capturing of its linear and nonlinear response features since no sensors were available on the intermediate floors (from 7 th to 16 th). The sampling rate for the sensors was 100 Hz.  
The sensors were at all times connected to a portable battery unit, which was connected to the power supply. In the case of power failure, the portable device had six-hour battery life. The portable unit was also connected to a laptop computer, which processed the data after a seismic event and sent it to a database.