# Assessment of a Substandard Reinforced Concrete Frame's Beam-Column Joint Using Shake Table Testing
## 5 Results  
Accordingly, the initial frequency of the specimen was identified as \(f_{0}=2.02\) Hz. Figure 9 presents the acceleration measurements obtained from Stations 688 and 7603 for the specified specimen. The data presented in the figure suggest that station 688 experienced a malfunction during the testing process. Consequently, the sole source of acceleration data are derived from station 7603. The maximum lateral displacements observed at the top of the specimen, as measured by LVDT#1, are presented in Figure 10. The peak lateral displacement recorded was approximately 53.1 mm, corresponding to a story drift ratio of approximately 0.055 radians when subjected to a ground acceleration of 0.35 g.  
Figure 8: (**a**) The acceleration time history of the 2023 Kahramanmaras record applied in the experimental shake table tests. (**b**) Acceleration response spectra of the 2023 Kahramanmaras ground motion record corresponding to damping ratios of \(\xi\) = 2.5%, \(\xi\) = 5%, and \(\xi\) = 10%. Figure 9: Acceleration time histories recorded at selected stations during the earthquake event. (**a**) Station 688 and (**b**) Station 7603. Chord rotation serves as a critical metric in assessing the structural performance and deformation capacity of reinforced concrete (RC) elements subjected to bending stresses. Its significance lies in the evaluation of essential characteristics such as ductility, damage state, and the failure mechanisms of RC components, including beams, columns, and walls, particularly when they are exposed to seismic forces. Low-strength concrete exhibits a chord rotation capacity that is approximately 30-50% greater than that of normal-strength concrete. This enhanced capacity can be attributed to its superior ability to deform under stress. Following the completion of the tests, the calculated chord rotation value for the specimen was determined to be 0.038 radians. This measurement is noted to surpass the specified chord rotation threshold established in ASCE 41-23 [47]. A hysteretic curve illustrates the cyclic response of a structural component, such as a reinforced concrete beam or column, subjected to recurrent loading and unloading, notably in the context of seismic activity. This curve delineates the correlation between lateral force and displacement through successive loading cycles. In the case of low-strength concrete, the hysteretic curve generally reveals certain characteristics: pinching effects that arise from bond slip and cracking, a decline in strength and stiffness across loading cycles, and diminished energy dissipation when compared to elements that are well confined. Hysteresis models, which are extensively employed in the analysis of low-strength concrete structures, exhibit several significant limitations that warrant detailed examination. The constraints inherent in these hysteretic models primarily stem from the foundational assumptions incorporated within them. Typically, a multitude of models can be proposed for identical structural elements and loading scenarios, often resulting in contradictory outputs. For example, various models and their derivatives present disparate approaches to modeling the same phenomena. Moreover, even when the same modeling technique utilizes identical operators, such as R, it can yield divergent mathematical formulations. Numerous empirical hysteretic models have been introduced to capture the force-displacement characteristics of structural elements, with the Mainstone model being one of the earliest examples. Subsequent models tend to provide an algebraic representation of the force-displacement relationship, delineating elastic and plastic branches. Contemporary structural codes for low-strength concrete predominantly endorse such models within displacement-based design frameworks. However, a notable inconsistency emerges between the experimentally derived and analytically predicted ratios of hysteresis loops for low-strength concrete walls.