This paper documents a study carried out on the estimation of the bond stress-slip relationship for reinforced concrete members under axial tension loading. An analytical model is proposed that utilizes the conventional bond stress-slip theories as well as the characteristics of deformed bar and concrete cross-sectional area. An equation for the estimation of the bond stress is formulated as the function of nondimensional factors (e.g., bond stress, slip, etc.). The validity, accuracy, and efficiency of the proposed model are established by comparing the analytical results with the experimental data and the JSCE design codes, as well as the analytical models given by Ikki et al. and Shima. The analytical results presented in this paper indicate that the proposed model can effectively estimate the bond stress-slip relationship of reinforced concrete members under axial tension loading.

The accurate measurement of diverse displacements of structures is an important index for the evaluation of a structure’s safety. In this study, a comparative analysis was conducted to determine the integrated RTK-GPS/accelerometer method that can provide the most precise structure displacement measurements. For this purpose, three methods of calculating the dynamic displacements from the acceleration data were comparatively analyzed. In addition, two methods of determining dynamic, static, and quasi-static displacements by integrating the displacements measured from the RTK-GPS system and the accelerometer were also comparatively analyzed. To ensure precise comparison results, a cantilever beam was manufactured onto which diverse types of displacements were generated to evaluate the measurement accuracy by method. Linear variable differential transformer (LVDT) measurements were used as references for the evaluation to ensure accuracy. The study results showed that the most suitable method of measuring the dynamic displacement with the accelerometer was to calculate the displacement by filtering and double-integrating the acceleration data using the FIR band-pass filter. The integration method that uses frequency-based displacement extraction was most appropriate for the integrated RTK-GPS/accelerometer method of comprehensively measuring the dynamic, static, and quasi-static displacements.

This study is focused on the effect of the prestress level of fiber-reinforced polymer reinforcement on the flexural and debonding behavior of strengthened beams. A total of seven reinforced concrete beams were used in the bending test. A carbon fiber reinforced polymer plate was used as the fiber-reinforced polymer reinforcement. Test variables included various prestress levels and the use of anchorage systems. The specimens were comprised of one control beam, one bonded non-prestressed carbon fiber reinforced polymer-strengthened beam, and five bonded prestressed carbon fiber reinforced polymer-strengthened beams. The deflection-controlled three-point bending test was conducted on all beams until failure. The failure of the beam with an externally bonded carbon fiber reinforced polymer plate was attributed to the debonding of the carbon fiber reinforced polymer plate. The failure mode of beams with bonded prestressed carbon fiber reinforced polymer plates was a two-stage debonding, which was followed by the rupture of the carbon fiber reinforced polymer plates; thus, the behavior of the prestressed beams changed to the unbonded state because of the anchorage system. The cracking, yield, and debonding loads of prestressed beams increased as the prestress level of the carbon fiber reinforced polymer plate increased. However, the effect on the deflection corresponding to these loads was not significant. Also, the ultimate load was constant regardless of the prestress level, except for the case of the 70% prestressed beam, but the effect on ultimate deflection was significant. The recommended appropriate prestress level in securing the ductility of a strengthened beam was 40% or less of the tensile strength of the carbon fiber reinforced polymer plate.

In this study, nine specimens were experimentally tested to analyze the strengthening efficiency of textile-reinforced mortar (TRM) and the difference in flexural behavior between prestressed and non-prestressed TRM-strengthened reinforced concrete beam. The test results show that TRM strengthening improves the flexural strength of TRM-strengthened reinforced concrete beams with alkali-resistant-(AR-) glass textile as well as that with carbon textile. However, in the case of textile prestressing, the strengthening efficiency for flexural strength of the AR-glass textile was higher than that of the carbon textile. The flexural stiffness of AR-glass textiles increased when prestressing was introduced and the use of carbon textiles can be advantageous to reduce the decreasing ratio of flexural stiffness as the load increased. In the failure mode, textile prestressing prevents the damage of textiles effectively owing to the crack and induces the debonding of the TRM.