## 4 Analysis of Heavily and Moderately Damaged Structure Materials in the Elbistan Region  
In this study, the heavily and moderately damaged structures in Elbistan surveyed by the Ministry of Environment and Urbanization were analyzed. After the Kocaii 1999 earthquake, changes in regulations and a greater inspection of buildings were instituted in the year 2000, with these factors therefore needing to be accounted for in the grouping and selection of such buildings. In this study, the structures considered for analysis were all located close to one another. Further, buildings that allowed work within them were considered. Finally, 20 buildings were selected in the region. These buildings were distinguished as being either built pre-2000 or post-2000. Later, they were divided into moderately and heavily damaged groups. They were therefore divided into four different groups. This study aimed to compare the material quality of the buildings according to their periods of construction and types of damage. To this end, in situ non-destructive tests were carried out in the buildings. Further, experimental research was conducted afterwards in the laboratory environment with samples taken from the buildings. When classifying the structures, the study codes used were the following: heavily damaged structure (H), moderately damaged structure (M), pre-2000 (O), and post-2000 (N). Some samples' cores had fragmented (Figure 6b). The samples that were obtained intact were capped and pressure tested (Figure 6c,d). In building design in Turkey, the acceptable concrete strength specified by TS 500, /1969, B160, and TS 500/1984 [39] is 14 MPa (provided by Turkish Standards). A correction factor of 0.85 for calculating the equivalent characteristic compressive strength is given by TS EN 13791/2010 [40]. In this study, although it did not seem technically appropriate to make a statistical evaluation of the samples (due to the insufficient amount of data), when considering the aggregate maximums, it can be stated with great confidence that the concrete represented by the samples was not produced according to relevant standards. These standards state that aggregate sizes and grades, standard deviations (SDs), and coefficient of variation values should be around 0.10 to 0.25, with coefficients of variability exceeding this range indicating low and very low levels of quality control standards [41; 42]. However, these standards have since been changed. New rules for concrete strength have been applied to all structures since 1975. The minimum concrete compressive strength of a structure was decreed to be C18 for first- and second-degree earthquake zones and C14 for other regions in TEC1975 [43]. These values were increased to C20 MPa in TEC2007 [44] and C25 MPa in TBEC2018 [45]. Further, after the 1997 earthquakes [46], the Turkish Ready Mixed Concrete Association stated in their evaluation meetings that the concrete class specified in the Regulation on Buildings to be Built in Disaster Areas and the Earthquake Map of Turkey would be insufficient for withstanding possible future earthquakes in terms of its strength and that the C 30 concrete class should therefore be used in buildings built in earthquake zones [39]. In this study, the concrete quality of the buildings selected for analysis was evaluated. To this end, core samples were taken from the buildings (Figure 2(a)). The effect of the core dimensions on the test results was important. According to TS 10465 [47], coring was taken from the concrete, and its suitability was evaluated. Next, the compressive strength values of the cores were compared to those of the sample codes, as shown in Figure 4. The concrete compressive strength values were around 4 MPa in the buildings with heavy and moderate damage that were built before 2000. For those built after 2000, their concrete strength values were around 14 MPa. Among the sampled buildings, the highest concrete strength was recorded for a building constructed in 2016.