Experimental Research and Analysis of Influencing Factors on Hysteresis Properties of Common Steel Bars with Unbonded Sections

With the aim of investigating the factors influencing the hysteretic behavior of common steel bars with unbonded sections (CS-US), hysteresis tests of six CS-US specimens were conducted, taking unbonded length, the location of the unbonded section, steel bar diameter, steel bar strength grade, and concrete strength grade as study variables. The results show that there exist necking phenomena in steel bars and different degrees of damage to concrete in all specimens. A 3D fine model was established by Solid works and ABAQUS software and verified according to the experimental results. The results show that the simulated values are close to the experimental values. Subsequent to the validation of the model, a thorough analysis was performed to assess the energy dissipation capacity and ductility of CS-US. The findings indicate that the implementation of an unbonded section can remarkably enhance the energy dissipation capacity and ductility of CS-US. It was demonstrated that the larger the unbonded length, the greater the ductility and energy dissipation capacity of CS-US. An alteration in the bonded length at the loading end exerts minimal influence on the energy dissipation capacity and ductility of CS-US. The energy dissipation capacity and ductility of CS-US decrease with an increasing steel bar diameter or strength grade. Concrete strength grades lower than C40 have minimal impact on the energy dissipation capacity and ductility of CS-US; concrete with a strength grade higher than C40 exhibits a decrease in energy dissipation capacity and ductility initially, followed by an increase. However, the values of these parameters remain lower than those observed in concrete with a strength grade below C40. Finally, the proposed design values of the above parameters are provided as a reference for engineering applications.