## 1 Introduction
Previous Turkish Earthquake Codes (TECs) defined the minimum concrete class to be used in buildings, such as 25 MPa in the 2018 TEC and 20 MPa in the 1998 and 2007 TECs. Further, the Turkish Ready Mixed Concrete Association prepared a report that provided observations about an earthquake area. The report found that the concrete strengths of the buildings in this area ranged from 6 to 12 MPa. Additionally, many earthquake investigations carried out by researchers have provided general observations about earthquake damage. In investigations carried out in the Elazig and Malatya provinces, for instance, much of the building damage was attributed to a poor concrete mixture and concrete placement without a vibrator. Further, on 1 May 2003 in Bingol and on 8 March 2010, after the Van earthquake, researchers reported similar problems. When other recent earthquake areas were examined, it was emphasized that TS 500 standards were not generally applied [8]. Further, regarding another earthquake, it was observed that almost all buildings that were destroyed and severely damaged had concrete that did not meet the necessary standards and regulations. In particular, the concrete production for these buildings was found to have not met these standards. On construction sites, it was found that materials were produced with a low cement content using traditional methods. The researchers emphasized that such structures should have instead been built with materials that adhered to the defined requirements of various codes and qualified workmanship under strict supervision. They further suggested that, as the quality of construction materials is a fundamental factor contributing to earthquake damage, it needs to be scrutinized in more detail [9; 10]. Comprehensive examinations of traditional reinforced concrete buildings have revealed that, most of the time, the concrete strength values predicted for construction projects cannot be achieved, and values around 50% of these predictions can be attained for some buildings. The impact of using low-quality concrete can be observed in a building's structural system elements. In addition to such buildings not being able to achieve the bearing capacity aimed for in calculations, this causes a decrease in the rigidity of a building's structure, the easy deterioration of its concrete in earthquakes, and brittle fractures in its concrete due to its low shear and bond strengths. In an examination carried out in the provinces affected by the earthquake in the Marmara region, it was found that quality control tests, such as tensile and bending tests, were not often performed for the reinforced concrete steels used in construction. As a consequence of this, the insufficient mechanical properties of the reinforced concrete steel produced from scrap steel in these regions adversely affected the behavior of the carrier system elements of buildings. In the earthquakes featured in this study, the main issues were not only structural defects, design errors, and a lack of engineering services but also the earthquake accelerations that took place in Kahramanmaras and the resulting displacement demands, which were well above the level that the structures in the region were able to respond to. However, most of these structures would have been able to withstand the earthquake if the established rules and regulations were applied, even at a minimum level. This point reveals the importance of earthquake-resistant building design. Because of this, some researchers have designed reinforced concrete structures resistant to earthquakes [11; 12; 13; 14; 15; 16; 17; 18]. Further, the building stock in Turkey is currently being examined. It has been determined that the country's buildings are generally not strong enough, and, therefore, possible future earthquakes pose great risks to them; additionally, many buildings have been found to be damaged in their current form. For this reason, it is necessary to strengthen those existing structures with insufficient strength and repair those with damaged structural elements.