Critical limit states in seismic buckling‐restrained brace and connection designs

Abstract

Summary A welded end‐slot buckling‐restrained brace (WES‐BRB) has been developed at the Taiwan National Center for Research on Earthquake Engineering (NCREE). A steel frame equipped with a WES‐BRB can offer a cost‐effective solution to meet interstory drift and earthquake‐resistant design requirements for seismic steel buildings. According to the WES‐BRB and connection design procedure proposed by NCREE, there are seven key elements of a buckling‐restrained braced frame (BRBF) design that require design checking. In order to assist an engineer with the design of the WES‐BRB members and connections, an innovative cloud service named Brace on Demand has been constructed at NCREE. In this study, using 581 BRBF design examples, the effectiveness of the proposed design procedures to meet all design checks is demonstrated. It is found that the most critical limit states for an initial design are joint region buckling, gusset plate buckling, and gusset‐to‐beam and gusset‐to‐column interface strength. Accordingly, the causes of improper designs and associated strategies for improving the initial designs are discussed in this paper. Recommendations on initial selections including the BRB joint size and gusset plate thickness are given. The paper provides the detailed road map for engineers to develop the spreadsheet for BRB and connection designs. Copyright © 2014 John Wiley & Sons, Ltd.

Effect of non‐moment braced frame seismic deformations on buckling‐restrained brace end connection behavior: Theoretical analysis and subassemblage tests

“…The frame tests by Lin et al [15], Chou et al [16], and Palmer et al [17] showed that in-plane frame action force at the beam-column-gusset interface was observed. These findings [15][16][17][18][19][20][21] all highlighted the negative effect of braced frame seismic deformations on the performance of BRB connection zones. The gusset plate design considering the combined effect of brace action and frame action forces was investigated theoretically and numerically [18][19][20].…”

“…The subassemblage tests by Tremblay et al [14] showed that BRB end rotation would cause additional inplane flexural stress on BRB casing. The gusset plate design considering the combined effect of brace action and frame action forces was investigated theoretically and numerically [18][19][20]. The frame tests by Lin et al [15], Chou et al [16], and Palmer et al [17] showed that in-plane frame action force at the beam-column-gusset interface was observed.…”

Seismic retrofit of reinforced concrete frames using buckling‐restrained braces with bearing block load transfer mechanism

“…The BRB steel cores were fabricated from ASTM A572 GR50 steel plate (345 MPa nominal yield stress). The nine design limit states for the BRB and connection, including the BRB steel casing flexural buckling, gusset tension yielding or compression buckling, and gusset interface strength have been documented in the reference [11]. The restrainers in specimens WT-BS and WT-BD were fabricated from 216.3 × 4 mm and 190.7 × 4 mm circular pipes respectively.…”

“…The RC column axial load capacity was sufficient to resist axial load demands arising from structure overturning and BRBF force. Therefore, the simplified procedure using the soften strutand-tie (SST) model proposed by Hwang and Lee [30] was adopted in this study to effectively evaluate the diagonal compressive strength C d of the RC member D-regions: (11) where: ζ = cracked concrete softening coefficient; f c = concrete compressive strength; A str = effective area of the diagonal strut; K = strut-and-tie index representing the beneficial effects of the tie reinforcement on the shear strength. The discontinuity regions (D-regions) in RC members are subjected to disturbance in the flow of internal forces.…”

“…The BRB and gusset design recommendations considering the frame action effects have been documented [11,12]. Conventional braces can significantly increase the strength but also reduce the fundamental vibration period of buildings, which sometimes amplifies the seismic loading.…”