Buckling-restrained Knee Braces Research Articles

Experimental study on slender buckling-restrained knee braces with round steel bar cores

Experimental study on slender buckling-restrained knee braces with round steel bar cores

Steel rigid beam-to-column connections strengthened by buckling-restrained knee braces using round steel core bar dampers

This paper presents an innovative application of buckling-restrained knee braces (BRKBs) for spreading plasticity at the beam ends of rigid moment connections. A slender knee brace configuration consisting of a steel core bar and tube buckling restrainer is proposed. The benefit of adopting a steel bar is that it enables the downsizing of the knee brace connections between braces and beam flanges. The advantages of tube buckling restrainers include relatively simple implementation for ease of construction and reduced weight compared to mortar-filled buckling restrainers. Displacement-controlled cyclic loading tests were conducted to examine the spreading of the plasticity behaviors of rigid moment connections using the proposed BRKBs. Structural performance metrics such as hysteretic behavior, strength capacity under a given loading, and strain distributions at beam flanges were measured and analyzed in detail. Additionally, the optimal parameters for the proposed BRKBs were determined through an extensive numerical study. The results revealed that the optimal parameters of the proposed slender BRKBs significantly improve load-bearing capacity and reduce stress concentrations in the vicinity of the rigid beam-to-column connections. As a result, the plastic region on the beam is spread both inside and outside the knee brace area. Based on the research conducted thus far, it was determined that the proposed BRKB is a viable option for spreading plasticity along beams in rigid beam-to-column connections.

Seismic performance of simple steel frames with buckling-restrained knee braces & SMA to reduce residual displacement

Knee braces located in the corner regions of beams and columns have high potential to be widely used in different structures under wind and earthquake loading. Since it is possible that even such braces experience buckling, some attention has been paid to carry out research on using buckling-restrained knee braces (BRKBs). In this study, BRKBs are used in two structures with different number of stories. Due to high cost of Shape Memory Alloy, SMA, it is only utilized in the core of BRKBs rather than steel material. Nonlinear time-history analysis is conducted to evaluate the behavior of the structures under some well-known earthquake records. The results indicated that adding SMA to the BRKBs can reduce the residual deformations of the frames more than 50%.

Cyclic testing and performance evaluation of buckling-restrained knee-braced frames

This paper presents the behavior and design concept of an efficient structural steel system based on the applications of buckling-restrained knee braces (BRKBs). The advantages of a buckling-restrained knee-braced frame (BRKBF) include relatively simple connections, reparability after an earthquake, and fewer obstructions than conventional bracing systems. Various BRKBF configurations can be designed and detailed for different levels of strength, stiffness, and ductility. BRKBFs are designed so that all inelastic activities are confined to the BRKB. The key design concepts for ensuring the ductile behaviors of BRKBFs are first summarized. Cyclic tests of large-scale BRKBF sub-assemblage specimens are then carried out. The results from both experimental and analytical studies of the behavior of BRKBFs show that they can be a viable alternative to conventional structural systems.

Seismic Performance Evaluation of Long-Span Conventional Moment Frames and Buckling-Restrained Knee-Braced Truss Moment Frames

AbstractSteel moment frame (MF) is one of the most prevalent and well researched steel seismic force resisting systems worldwide. However, efficiency and feasibility of using MF diminishes for large spans. In this paper, a recently developed steel seismic force resisting system, named buckling-restrained knee-braced truss moment frame (BRKBTMF), is suggested as a better alternative system. The BRKBTMF uses buckling-restrained knee-braces with open web trusses. In this paper, a four-story prototype office building was designed using both MF and BRKBTMF systems. Performance of the prototype building with different span lengths was systematically studied. The results show that BRKBTMF uses less structural steel, yet it performs better with lower structural damage, repair costs, and probability of collapse as compared with the MF for all span lengths and under all earthquake intensities considered. Hence, it is concluded that BRKBTMF is a viable and effective alternative seismic force resisting system for lon...

Probabilistic performance assessment of gravity-designed steel frame buildings using buckling-restrained knee braces

In building design codes, buildings having less than 3 stories and a floor area less than 1000m2 are generally defined as small-scale buildings, and these are generally exempted from seismic requirements. To prevent potential loss of life and economic damage in the event of an earthquake, such buildings should be retrofitted so as to conform to current seismic design codes. In this study, a seismic retrofit scheme using buckling-restrained knee brace (BRKBs) was developed for a 2-story non-seismic gravity-designed steel frame building using the fragility contour method. To develop an effective retrofit scheme using BRKB for this building, 75 types of BRKB analytical models were used to achieve the desired performance levels and analyzed. Then, the seismic performance of the building before and after the retrofit was evaluated using the fragility contour method, and the improvement in the performance level of the probability against the structural limit state, such as component failures and structural collapse, was investigated. Based on the analytical studies, the most effective BRKB model for the retrofit scheme was proposed based on various scenarios in terms of the weight of the developed BRKB models. This study shows that the fragility contour method can be used for rapid evaluations and should be an effective tool for structural engineers to perform the seismic retrofit of buildings.

Special Issue on Performance of Timber and Hybrid Structures

Special Issue on Performance of Timber and Hybrid Structures

취약성 등고선을 이용한 비내진 2층 철골조 건축물에 대한 내진성능 평가와 보강

Based on the Korean Building Standard Law, a building less than 3-stories and in area is defined as a small-level building and, as a result, this type of building has been excluded from the requirement to comply with seismic design. In order to prevent the loss of life and property under earthquake loadings, the small-scale building should satisfy the seismic performance specified in the current code through a seismic retrofit. In this study, a seismic retrofit scheme of a Buckling-Restrained Knee Brace (BRKB) was developed for non-seismic 2-story steel buildings, including small-scale buildings, using a fragility contour method. In order to develop an effective retrofit scheme of the BRKB for the building, a total of 75 BRKB analytical models were used to achieve the desired performance levels and analyzed using the fragility contour method. The seismic performance of the retrofitted building was evaluated in terms of the weight of the developed BRKB systems. This study shows that the fragility contour method can be used for rapid evaluation and is an effective tool for structural engineers.

A Damage-Controlled Structure Using Buckling-Restrained Knee Braces

The basic concept of a damage-controlled (DC) structure is that by clearly separating the main frame from the energy absorption members, the main frame is kept within the elastic range and the seismic energy force is collectively absorbed by the members. The uniquely developed structural system embodying this concept is defined in this paper as a DC structure. Even when exposed to large earthquakes, the beam-to-column connections of the DC structure, being equipped with rotation capacity, allow seismic force to be absorbed by buckling-restrained knee braces designed to function as seismic-response-controlled members. Thus, the main frame can continue to be used by replacing only earthquake-damaged knee braces where necessary and the structural members can also be reused.In this paper, we discuss the designing process of the DC structure. First, the design flow is presented, as well as methods for designing the beam-to-column connection and buckling-restrained knee braces developed based on the results of previous tests. Next, a trial design of the DC structure is implemented based on the proposed designing methods.

Seismic Design and Dynamic Analysis of Steel Frames with Bolted Beam-to-Column Connection using Buckling-Restrained Knee Brace Dampers

Seismic Design and Dynamic Analysis of Steel Frames with Bolted Beam-to-Column Connection using Buckling-Restrained Knee Brace Dampers

PROPOSAL FOR THE STRUCTURAL DESIGN METHOD OF A SUSTAINABLE BUILDING STRUCTURE SYSTEM

A sustainable building steel structure system, which is kind of damage-controlled structure, consists of columns, beams and newly developed connections with buckling-restrained braces like knee brace. The columns and beams are connected with special long steel bars alone, facilitating demolition of the structure and able to be reused the members. Since the connections of beam-to-column are semi-rigid, the columns and beams suffer no damage. The buckling-restrained knee braces only absorb seismic energy. In the past studies, full-scale tests of the connection were carried out. Based on these results, structural models, which modeled the connection were analyzed and a mechanical model for the sustainable building structure system was established. In this paper, a structural design method is proposed on the previous experimental and analytical studies. The detail design method for the newly developed connections with buckling-restrained braces is established. A trial design is conducted where applicability of the design method is shown.

Earthquake Response of High-rise Steel Frames with Bolted Beam-to-Column Connection using Buckling-Restrained Knee Brace Dampers

Earthquake Response of High-rise Steel Frames with Bolted Beam-to-Column Connection using Buckling-Restrained Knee Brace Dampers

Design and Experimental Verification on the Performance of the Buckling-Restrained Knee Brace

Design and Experimental Verification on the Performance of the Buckling-Restrained Knee Brace

サステナブルビル構造システムの提案とその基本特性

Long service life, reuse and recycling and three primary measures for reducing environmental burden in building field. A sutainable building structure system enables the environmental burden to reduce. This structural system, which is a kind of damage-controlled structure, consists of columns, beams like knee brace. Since the connections are semi-rigid, there is no large bending moment occurring in earthquake, and the columns and beams suffer no damage. The buckling-restrained knee braces only absorb seismic energy. The columns and beams are connected with special long bolts alone, facilitating demolition of the structure and able to be reused the members. In this sudy, full-scale experiments of the connection were carried out. Based on these results, structural models, which modeled the connection, were analyzed, and the structural system was verified.

Seismic design of steel structures with buckling-restrained knee braces

Analytical models and a performance-based seismic design procedure were developed for a structure with buckling-restrained knee-braces. The hinge-connected main structural members, such as beams and columns, were designed only for gravity loads, and the knee-braces were designed to resist all the lateral seismic load. The cross-sectional size of knee-braces was estimated using the equivalent damping required to be supplied to meet a given performance objective. Parametric study was performed with design variables such as slope and yield stress of the braces. According to the time-history analysis results of a five-story structure with buckling-restrained knee-braces, the maximum displacement of the model structure turned out to correspond well with the desired target displacement after it is retrofitted by knee braces following the proposed procedure.