Hysteresis and Seismic Analysis of Self-Reversible Buckling Braces with Polymer Tendons in Steel Frames

One of the main aims of structural seismic design is to control structural damage due to severe earthquakes. A feasible solution to control and deplete earthquake energy is to use a bracing system. When the bracing is in the process of cyclic deformation or seismic load, the plastic deformation of the compressive and tensile cycles will occur in the restrained parts of the core plates, which will create a suitable energy absorption capacity in the brace. Among them, Buckling-Restrained Brace (BRBs) are widely used due to their stable hysteresis behavior. BRB braces usually have two main parts: a core that withstands the axial force, and a lateral restraint shell to prevent the core from buckling under compressive force. In the event of a severe earthquake, the core surrenders, but still reduces structural damage by absorbing seismic energy. However, due to the fact that the stiffness after the surrender of the brace is relatively low and it is not able to return to the conditions before the surrender, the structural frame faces damage and deformation of the residue after severe earthquakes. In this regard, the buckling brace with the ability to return to the original position known as Self-Centering Buckling-Restrained Brace (SC-BRB) has recently been considered by researchers. In this type of braces, the return phase is provided by polymer tendons. Since the numerical study of SC-BRB behavior measurement has not been done so far, so the present study tries to evaluate the behavior of this type of brace and compare it with steel bending frame and braced frame. For this purpose, Abaqus software has been used.
In the present study, the results of the laboratory study of Zhou et al. (2015) in the analysis of the self-returning buckling system reinforced by SC-BRB basalt fibers have been used to validate the finite element model and the specifications of the brace to the steel frames of the case. The discussion in this study is generalized. The development of numerical model has been based on laboratory study. Then, a single-story, single-span frame in four different modes, simple bending frame, frame with simple bracing, frame with non-buckling brace, and frame with self-returning buckling brace was subjected to hysteresis and the results were compared. Then, design in ETABS software and seismic analysis in Finite element Abaqus software for 5-story structures with and without bracing against far and near Landers and Northridge earthquake faults.
Comparisons were also made between the performance of a simple bending frame, a braced frame, a buckle with a buckling brace, and a braced frame with the SC-BRB system. Finally, the seismic performance of the frame was performed with SC-BRB bracing. The general results obtained from this study are as follows: Using appropriate behavioral models of materials, very accurate answers in the analysis of non-buckling irreversible buckling by basalt polymer fibers by finite element modeling using Abaqus. A very good approximation of the results obtained from the numerical model with the research model of Zhou et al. has been able to prove the accuracy of the results of the present numerical model. The results generally indicate the very good behavior of SC-BRB braces, the use of which in the structure has significantly increased the load-bearing capacity and ductility of the structure. The application of SC-BRB bracing in the bending frame increased the lateral bearing capacity of a single-story single-span frame from 1248 kN with a 2.8-fold increase to 3576 kN. Also, the strength of the five-story structure using SC-BRB braces installed in the two modes of middle openings and side openings was 21% and 38% higher than the simple bending frame, respectively.