Buckling Restrained Brace: An Innovative Seismic Structural Device

Buckling restrained brace (BRB) is an innovative structural support device designed to enhance a building's resistance to lateral loads like earthquakes. The BRB exhibits ideal elastic-plastic behavior, maintaining stable performance under repeated cyclic loads. This significantly enhances the ductility and seismic capacity of structures. Compared to conventional braces, the BRB avoids compressive buckling failure, providing an economical and reliable seismic solution.

Working Principle
Features
Category
Structure
Specification

Working Principle

The BRB does not buckle under load, providing a stable lateral stiffness to effectively control the overall deformation of the structure. Under seismic action, the BRB will first enter the yielding state, dissipating seismic energy through the plastic deformation of the steel core while providing additional damping, significantly reducing the impact of the earthquake on the structure. This mechanism of 'yielding but not buckling' makes the BRB a key component in enhancing the seismic performance of structures.

Working principle of ordinary brace

Working principle of buckling restrained brace.

BRB working principle

Features

Optimized cross-section design. Cross-sectional dimensions are smaller than that of conventional steel braces, enabling efficient material utilization and reducing the structure self-weight.
Excellent ductility. The material exhibits outstanding ductility, with plastic deformation capacity meeting code requirements, and elongation after fracture ≥ 20%.
Dual functions of bracing and damping. The buckling restrained brace maintain load-bearing capacity even after compressive yielding while providing additional damping ratio under seismic action to mitigate seismic effects.
Seismic displacement control. It complies with displacement limits specified in GB 50011-2010.
Simple connection method. Buckling restrained braces can be installed via bolt connections, hinge connections, or welding, ensuring cost-effectiveness and ease of implementation.
Post-earthquake maintainability. Residual deformation rate < 0.2% after moderate and minor earthquakes, eliminating replacement needs; repairable via partial refurbishment or complete replacement post-major earthquakes.

Cross-sectional views of buckling restrained brace steel cores with different layouts.

Cross-sectional views of steel cores with different layouts

Category

BRBs are divided into circular BRBs and square BRBs by shape. Colors are not standardized and can be customized per project requirements, with common options including yellow, white, and gray.

Blue circular buckling restrained brace

A gray and two white square buckling restrained braces arranged in order.

Gray and white square buckling restrained brace

Yellow square buckling restrained brace

Structure

The BRB consists of four components: yieldable steel core, steel pipe, unbonded material, and mortar.

Yieldable steel core: The core part of the BRB, designed to resist all axial forces generated in the brace, including tension and compression.
Steel pipe: Provides lateral restraint to prevent the steel core from experiencing overall or local buckling under axial compression. It offers lateral support through bending stiffness, enhancing structural stability.
Unbonded material: Allows the steel core to move independently of the shell, avoiding the influence of shell deformation on the steel core. Ensures that the steel core can independently bear axial forces as intended in the design and perform energy dissipation.
Mortar: Laid between the steel core and the steel pipe, ensuring that the steel core can freely undergo axial deformation and reducing friction between the two. Allows the steel core to expand freely under compression, avoiding an increase in axial pressure due to friction.

BRB structure

Specifications

Material: Steel
Yield force: 500–1500 kN
Axis length: 5500–8000 mm
Product length: 3500–6000 mm
Reference product yield displacement: 4.7–8.3 mm
Exterior size: 150 mm × 150 mm, 200 mm × 200 mm

Table 1: Buckling Restrained Brace Specifications
Model	Yield Force (F)	Axis Length	Product Length	Reference Product Yield Displacement	Exterior Size (Width × Height)
Model	(kN)	(mm)	(mm)	(mm)	(mm)
BRB500-3500	500	5500	3500	4.8	150 × 150
BRB500-4000		6000	4000	5.6	150 × 150
BRB500-4500		6500	4500	6.3	150 × 150
BRB500-5000		7000	5000	6.8	150 × 150
BRB500-5500		7500	5500	7.6	150 × 150
BRB500-6000		8000	6000	8.1	150 × 150
BRB750-3500	750	5500	3500	4.7	200 × 200
BRB750-4000		6000	4000	5.5	200 × 200
BRB750-4500		6500	4500	6.2	200 × 200
BRB750-5000		7000	5000	6.9	200 × 200
BRB750-5500		7500	5500	7.6	200 × 200
BRB750-6000		8000	6000	8.1	200 × 200
BRB1000-3500	1000	5500	3500	4.7	200 × 200
BRB1000-4000		6000	4000	5.5	200 × 200
BRB1000-4500		6500	4500	6.3	200 × 200
BRB1000-5000		7000	5000	6.7	200 × 200
BRB1000-5500		7500	5500	7.4	200 × 200
BRB1000-6000		8000	6000	8.2	200 × 200
BRB1500-3500	1500	5500	3500	4.8	200 × 200
BRB1500-4000		6000	4000	5.5	200 × 200
BRB1500-4500		6500	4500	6.3	200 × 200
BRB1500-5000		7000	5000	6.7	200 × 200
BRB1500-5500		7500	5500	7.6	200 × 200
BRB1500-6000		8000	6000	8.3	200 × 200
Stiffness ratio after yield: 0.035. Recommended core material: Q235B. If other parameters are required, production can be customized according to design requirements.

Table 2: Common Core Plate Material Properties
Material Symbols	Yield Point	Tensile Strength	Yield Ratio	Elongation
Material Symbols	(N/mm²)	(N/mm²)	(%)	(%)
BLY100	100±20	200–300	≤ 60	≥ 50
BLY160	160±20	220–320	≤ 80	≥ 45
BLY225	225±20	300–400	≤ 80	≥ 40
Q235B	220±15	370–500	≤ 82	≥ 25

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