Browsing by Author "Kayabali, Kamil"

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A Nondestructive Testing Technique: Nail Penetration Test
(Amer Concrete inst, 2012) Selcuk, Levent; Gokce, H. Suleyman; Kayabali, Kamil; Simsek, Osman
This study presents a practical nondestructive testing (NDT) method: the nail penetration test (NPT). The major tools of the test technique are a gas nailer with 130 J (95.88 ft-lbf) power, concrete nails, and a gas nailer cell. The study covers three different limestone aggregate types. Six concrete mixtures were prepared from each aggregate type. Five nail shots were performed on each concrete mixture (or grade) and the average value was obtained. The average nail penetration depths were correlated with the compressive strength of concrete. Other NDT techniques, such as the Schmidt rebound hammer (SRH), ultrasonic pulse velocity (UPV), and Windsor probe (WP), were also applied to concrete samples. The measured compressive strength values were compared with those obtained from the empirical relationships using the data from the NPT, SRH, UPV, and WP. It was found that the reliability of the NPT to estimate the compressive strength of concrete is very high. The tool employed in the investigation covers a relatively wide range of compressive strength of concrete. This testing tool is proposed to estimate the compressive strength of in-place concrete.
A Strain Energy Framework for Evaluating Rock Mass Stability During Earthquakes
(Springer Heidelberg, 2025) Kayabali, Kamil; Habibzadeh, Farhad; Selcuk, Levent
This study examines the strain energy principle to address complex challenges in rock mechanics. Compared to conventional stress-strain assessments, the strain energy approach offers a more comprehensive perspective, representing a significant innovation in rock mechanics. The strain energy approach enhances reliability by considering energy accumulation and release alongside traditional strength analysis. Experimental studies indicate that the maximum energy stored and released during rock joint failure is comparable to earthquake energy capacities. This perspective introduces a novel approach for assessing rock mass stability during seismic events. The effectiveness of the energy-based approach is assessed using the hysteresis curves of rock joints under seismic loads. Experimental data reveal that the surface roughness of rock joints significantly influences the variation in strain energy with increasing normal stress. Moreover, evaluating the cyclic nature of earthquakes is essential for measuring strain energy, as the release of kinetic energy during an earthquake is inherently tied to its cyclic behavior. In this context, earthquake energy capacity is determined by analyzing the acceleration-time history of significant seismic events. Given that the strain energy from rock joint failure produces results comparable to earthquake energy capacities, the strain energy principle offers a more practical and realistic approach for assessing rock mass stability during earthquakes.