# A Case Study on the Rehabilitation of a Fire-Damaged Structure
## 2 Visual Inspection of Damaged Structural Components  
The site investigation was carried out two days after the fire occurrence. The condition of all the main structural components damaged by the fire such as slabs, girders, beams, columns and walls were visually examined. Among them, severely damaged components were categorized. The location and identification number of each structural member are indicated in Figure 1. Additionally, of interest at first was whether the structural damage involved the possible explosion of batteries. However, no sign of explosion or blast was identified during the investigation. The visual inspection revealed that most of the batteries in the room were burned down, especially the Batteries #1, #4, #5 and #6. For Batteries #2 and #3, part of the battery structures still remained as  
Figure 1: Locations of structural elements and batteries in the battery room. shown in Figure 2. This condition coincides with accounts stating that the fire burned longest in the region of Batteries #4 and #5. As a result, the structural elements located above Batteries #1, #4, and #5 experienced relatively severe damage compared with those located above Batteries #2 and #3. The softit of the slabs were mostly damaged due to fire as shown in Figure 3. The concrete in the bottom cover and at mid-depth spalled, exposing the reinforcing bars. The damage was more severe in Slabs #3 and #4 than in Slabs #1 and #2. The condition of each slab can be summarized as below:  
* Slab #1: More than 50% of the concrete spalled and 60% of bottom reinforcing bars were exposed. * Slab #2: About 50% of the concrete spalled and 50% of bottom reinforcing bars were exposed. * Slab #3: More than 90% of the concrete spalled. About 90% of bottom reinforcing bars and 40% of top reinforcing bars were exposed. * Slab #4: More than 90% of the concrete spalled. About 90% of bottom reinforcing bars and 30% of top reinforcing bars were exposed. Figure 3: Damage in each span of slab on its softit, observed from the north. (**a**) Slab #1, (**b**) Slab #2, (**c**) Slab #3 and (**d**) Slab #4. Figure 2: Panoramic view of the battery room during visual inspection. Figure 4a shows the floor conditions of the HVAC (Heating, Ventilation and Air Conditioning) room, which is located right above the battery room where the fire occurred. It indicates that, in the area where the concrete has spalled, a network of cracks has developed on the top surface of the floor slab. At the time of the visual inspection, the damage to the floor slab of the battery room was not identifiable, since the debris on the floor had not been removed (see Figure 4b). Inferring from the fact that the steel structures supporting the batteries remain without excessive deformation, it is assumed that there was little or no structural damage to the floor slab. Having lost more than half of the concrete volume, all the spans from Slabs #1 to #4 are judged to have degradation in their structural capacity. The main role of the slab is to transfer the transverse load on the slab to adjacent girders and beams. This role must be restored by either replacing the damaged span of slab with new ones or by providing additional load carrying capacity to the slab. The exposed reinforcing bars might have experienced a strength reduction due to the elevated temperature during the fire. To identify the degree of the strength reduction, tests on the rebar specimens from the respective spans of slab were necessary. Although not identifiable at the time of inspection, the floor slab of the room was assumed to have retained its structural capacity and needed no retrofitting. The degree of damage in the girders and beams varied by component. At some points, the concrete covers at the bottom corner and side of girders and beams spalled and, although not dominant, the longitudinal bars and stirrups were exposed. However, neither a structural crack in vertical and diagonal nor a deflection at the center of girders and beams was identified with the naked eye.