Unbonded Buckling-Restrained Energy-Dissipation Brace (Unbonded BRB) is an optimized energy-dissipating component derived from the traditional bonded Buckling-Restrained Brace (BRB). Its core feature lies in the unbonded layer installed between the core material and the restraining unit, which eliminates the bonding effect and friction between them, only retaining the lateral restraint of the restraining unit on the core material. This structural design endows it with multiple prominent application advantages in building seismic and vibration reduction systems:
The presence of the unbonded layer enables the core material to achieve friction-free free axial deformation under cyclic tension-compression loads, avoiding the uneven stress on the core material of traditional bonded BRBs caused by bonding force or friction. The core material can fully enter the plastic stage for energy dissipation, and its hysteresis curve is full and symmetrical, with much higher energy-dissipating efficiency than ordinary braces. Meanwhile, the restraining unit only limits the buckling deformation of the core material without participating in axial force, which greatly reduces the probability of buckling failure of the brace. In addition, the unbonded structure reduces the residual deformation coupling between the core material and the restraining unit, resulting in minimal residual deformation of the brace after an earthquake, which allows the rapid restoration of structural functions without large-scale replacement of components.
Under minor earthquakes or wind loads, the core material of Unbonded BRB remains in the elastic stage, providing sufficient stiffness to assist the structure in resisting external forces and maintaining the normal service functions of the building. Under moderate or major earthquakes, the core material quickly enters the plastic stage, absorbing a large amount of seismic energy through plastic deformation, effectively reducing the seismic response of the structure and avoiding severe damage to the main structure. This dual characteristic of "elastic lateral resistance + plastic energy dissipation" enables it to adapt to earthquake conditions of different intensities, meeting the three-level fortification objectives of "no damage under minor earthquakes, repairable under moderate earthquakes, and no collapse under major earthquakes" in building seismic design.
The cross-sectional dimensions and mechanical properties of Unbonded BRB can be flexibly customized according to the requirements of building structures. It can be conveniently adapted to both the seismic system design of new buildings and the seismic reinforcement and reconstruction of existing buildings. It is suitable for various building types such as frame structures, frame-shear wall structures, steel structure workshops, and long-span spatial structures, especially for construction projects in high-intensity earthquake zones. At the same time, its installation method is similar to that of ordinary braces, eliminating the need for large-scale modifications to the main structure. The construction is convenient, which can effectively shorten the construction period and control the reconstruction cost.
The unbonded layer is usually made of aging-resistant and corrosion-resistant polymer materials (such as polyethylene and polytetrafluoroethylene), which can effectively isolate the core material from the restraining unit and reduce the risk of corrosion of the core material. Moreover, the unbonded structure avoids the performance degradation of traditional BRBs caused by cracking and peeling of the bonded layer. During daily use, Unbonded BRB does not require frequent maintenance, only regular inspections of the integrity of the unbonded layer and the damage of the core material are needed, with simple maintenance operations and low costs. Even if local damage occurs after long-term use, it can be repaired by replacing the unbonded layer or the core material, extending the service life of the component.
Different from the traditional seismic structure mode that relies on the deformation of the main structure itself for energy dissipation, Unbonded BRB serves as an external energy-dissipating component, which can take priority to bear and consume seismic energy, greatly reducing the internal force and deformation of the main structure. This not only reduces the cross-sectional dimensions of core components such as beams, columns and shear walls, lowers the structural self-weight and project cost, but also avoids cracks or damage to the main structure due to excessive deformation, significantly improving the overall safety of the building during earthquakes and safeguarding the lives and property of personnel.